Chemical Precipitation in Wastewater Treatment

  

  1. INTRODUCTION

                Chemical precipitation in water and wastewater treatment is the change in form of materials dissolved in water into solid particles. Chemical precipitation is used to remove ionic constituents from water by the addition of counter-ions to reduce the solubility.

It is used primarily for the removal of metallic cations, but also for removal of anions such as fluoride, cyanide, and phosphate, as well as organic molecules such as the precipitation of phenols and aromatic amines by enzymes [1].and detergents and oily emulsions by barium chloride [2].

               Major precipitation processes include water softening and stabilization, heavy metal removal, and phosphate removal. Water softening involves the removal of divalent cationic species, primarily calcium and magnesium ions. Heavy metal removal is most widely practiced in the metal plating industry, where soluble salts of cadmium, chromium, copper, nickel, lead, zinc, and many others, need to be removed and possibly recovered. Phosphate removal form wastewater is used to protect receiving surface waters from eutrophication (plant growth stimulated by nutrient addition).

            Competing processes for ion removal include ion exchange, electro precipitation, and reverse osmosis. The disadvantages of these processes relative to chemical precipitation are higher capital costs and, in the case of the latter two, higher energy costs for operation. Their advantage is that all these processes are better adapted to metal recovery and recycle than chemical precipitation is. Chemical precipitation has the advantage of low capital cost and simple operation. Its major disadvantages are its operating costs from the chemical expense and the cost of disposing of the precipitated sludge that is produced [3].

           Most metals are precipitated as hydroxides, but other methods such as sulfide and carbonate precipitation are also used. In some cases, the chemical species to be removed must be oxidized or reduced to a valence that can then be precipitated directly.

Phosphate can be removed by precipitation as iron or aluminum salts, and fluorine can be removed using calcium chloride [2].

            Precipitation processes should be distinguished from coagulation and flocculation. Coagulation is the removal of finely divided non-settleable solid particles, especially colloids, by aggregation into larger particles through the destabilization of the electric double layer [4].   Flocculation is the formation of yet larger particles by the formation of bridges between coagulated particles through the adsorption of large polymer molecules and by other forces. Both coagulation and flocculation, which often occur together, result in particles that can be removed by sedimentation or filtration . Coagulation and flocculation occur subsequent to and concomitant with the precipitation processes as it is usually applied in waste treatment.

  1. PROCESS DESCRIPTION

            Precipitation is a chemical unit process in which undesirable soluble metallic ions and certain anions are removed from water or wastewater by conversion to an insoluble form. It is a commonly used treatment technique for removal of heavy metals, phosphorus, and hardness. The procedure involves alteration of the ionic equilibrium to produce insoluble precipitates that can be easily removed by sedimentation. Chemical precipitation is always followed by a solids separation operation that may include coagulation and/or sedimentation, or filtration to remove the precipitates. The process can be preceded by chemical reduction in order to change the characteristics of the metal ions to a form that can be precipitated.

  1. PROCESS TYPES

      The chemical equilibrium relationship in precipitation that affects the solubility of the component(s) can be achieved by a variety of means. One or a combination of the following processes induces the precipitation reactions in a water environment.

3.1. Hydroxide Precipitation

       Dissolved heavy metal ions can be chemically precipitated as hydroxide for removal by physical means such as sedimentation or filtration. The process uses an alkaline agent to raise the pH of the water that causes the solubility of metal ions to decrease and thus precipitate out of the solvent. The optimum pH at which metallic hydroxides are least soluble varies with the type of metal ion as shown in Fig 1. A simple form of the hydroxide precipitation reaction may be written as:

M2+ + 2(OH) = M(OH)2

     The product formed is an insoluble metal hydroxide. If the pH is below the optimum of precipitation, a soluble metal complex will form:

M2+ + OH = M(OH)+

Hydroxide precipitation is also affected by the presence of organic radicals that can form chelates and mask the typical precipitation reaction:

M2+ + OH + nR = M(R)n OH+

         Reagents commonly used to affect the hydroxide precipitation include alkaline compounds such as lime or caustic soda (sodium hydroxide). Lime in the form of quicklime or un-slaked lime, CaO, and hydrated lime, Ca(OH)2, can be used. Lime is generally made into wet suspensions or slurries before introduction into the treatment system. The precise steps involved in converting lime from the dry to the wet stage will vary according to the size of the operation and the type and form of lime used. In the smallest plants, bagged hydrated lime is often charged manually into a batch-mixing tank with the resulting “milkof-lime” (or slurry) being fed by means of a solution feeder to the treatment process.

            Where bulk hydrate lime is used, some type of dry feeder charges the lime continuously to either a batch or continuous mixer. A solution feeder transfers lime to the point of application.

             With bulk quicklime, a dry feeder is also used to charge a slaking device, where the oxides are converted to hydroxides, producing a paste or slurry. The slurry is then further diluted to milk-of-lime before being fed by gravity or pumping into the process. Dry feeders can be of the volumetric or gravimetric type. Caustic soda, in the form of 6–20% aqueous solution, is fed directly to the treatment system and does not require any dispensing and mixing equipment. The treatment chemicals may be added to a flash mixer or rapid-mix tank, or directly to the sedimentation device. Because metal hydroxides tend to be colloidal in nature, coagulation agents may also be added to facilitate settling.

3.2. Sulfide Precipitation

Both “soluble” sulfides such as hydrogen sulfide or sodium sulfide and “insoluble” sulfides such as ferrous sulfide may be used to precipitate heavy metal ions as insoluble metal sulfides. Sodium sulfide and sodium bisulfide are the two chemicals commonly used, with the choice between these two precipitation agents being strictly an economic one. Metal sulfides have lower solubilities than hydroxides in the alkaline pH range and also tend to have low solubilities at or below the neutral pH value (Fig. 1).

          The basic principle of sulfide treatment technology is similar to that of hydroxide precipitation. Sulfide is added to precipitate the metals as metal sulfides and the sludge formed is separated from solution by gravity settling or filtration. Several steps enter into the process of sulfide precipitation:

  1. Preparation of sodium sulfide. Although there is often an abundant supply of this product from by-product sources, it can also be made by reduction of sodium sulfate. The process involves an energy loss in the partial oxidation of carbon (such as that contained in coal) as

follows:

Na2SO4 4C= Na2S + 4CO2 (gas)

Sodium sulfate + carbon = metallic sulfide + carbon dioxide

  1. Precipitation of the pollutant metal (M) in the waste stream by an excess of sodium sulfide

Na2S + MSO4 = MS precipitate + Na2SO4

Sodium sulfide metallic sulfate metallic sulfide sodium sulfate

  1. Physical separation of the metal sulfide in thickeners or clarifiers, with reducing conditions

maintained by excess sulfide ion.

  1. Oxidation of excess sulfide by aeration:

Na2S + 2O2 = Na2SO4

Sodium sulfide + oxygen = sodium sulfate

Because of the toxicity of both the sulfide ion and hydrogen sulfide gas, the use of sulfide precipitation may require both pre- and posttreatment and close control of reagent additions. Pretreatment involves raising the pH of water to between 7 and 8 to reduce the formation of obnoxious hydrogen sulfide gas. The pH adjustment may be accomplished at essentially the same point as the sulfide treatment, or by addition of a solution containing both sodium sulfide and a strong base (such as caustic soda). The posttreatment consists of oxidation by aeration or chemical oxidation to remove excess sulfide, a toxic substance.

           A recently developed and patented process to eliminate the potential hazard of excess sulfide in the effluent and the formation of gaseous hydrogen sulfide uses ferrous sulfide as the sulfide source. The fresh ferrous sulfide is prepared by adding sodium sulfide to ferrous sulfate. The ferrous sulfide slurry formed is added to water to supply sufficient sulfide ions to precipitate metal sulfides, which have lower solubilities than ferrous sulfide. Typical reactions are:

FeS + Cu2+ = CuS Fe2+

Ferrous sulfide + copper ion = insoluble copper sulfide + iron ion

FeS + Ni(OH)2= Fe(OH)2 + NiS

Ferrous sulfide + nickel hydroxide = ferrous hydroxide + insoluble nickel sulfide .A detention time of 10–15 min is sufficient to allow the reaction to go to completion.

Ferrous sulfide itself is also a relatively insoluble compound. Thus, the sulfide ion concentration is limited by the solubility of ferrous sulfide, which amounts to about 0.02 mg/L, and the inherent problems associated with conventional sulfide precipitation

are minimized.

3.3. Cyanide Precipitation

Cyanide precipitation, although a method for treating cyanide in wastewater, does not destroy the cyanide molecule, which is retained in the sludge that is formed. Reports indicate that during exposure to sunlight, the cyanide complexes can break down and form free cyanide. For this reason the sludge from this treatment method must be disposed of carefully. Cyanide may be precipitated and settled out of wastewater by the addition of zinc sulfate or ferrous sulfate, which forms zinc ferrocyanide or ferro- and ferri-cyanide complexes. In the presence of iron, cyanide will form extremely stable cyanide complexes.

3.4. Carbonate Precipitation

Carbonate precipitation may be used to remove metals either by direct precipitation using a carbonate reagent such as calcium carbonate or by converting hydroxides into carbonates using carbon dioxide. The solubility of most metal carbonates is intermediate between hydroxide and sulfide solubilities; in addition, carbonates form easily filtered precipitates.

3.5. Coprecipitaion

In coprecipitaion, materials that cannot be removed from solution effectively by direct precipitation are removed by incorporating them into particles of another precipitate, which is separated by settling, filtration, or flotation.

By

Ahmed Ahmed Elserwy

Water & Environmental Consultant

Ain Shames University, Faculty of Science.

References

[1]  S. C. Atlow, Biotechnol. Bioeng. 26, 599 (1984).

[2]   B. Gomulka and E. Gomolka, Effluent Water Treat. J. (G.B.) 24, 119 (1985).

[3]  D. Biver and A. Degols, Tech. de l’ Eau (Fr.), 428/429, 31, (1982); (abstr) WRC Info., 10,83-0524 (1983).

[4]   V. K. La Ver, J. Colloid Science l9, 291–293 (1964).

Wastewater of Ceramic Industry

Introduction

          Generally the term of ceramics (ceramic products) is used for inorganic materials (with possibly some organic content), made up of nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous (e.g., a glass). Because most common ceramics are crystalline, the definition of ceramic is often restricted to inorganic crystalline materials, as opposed to the noncrystalline glasses.

      The traditional ceramic industries are sometimes referred to as the clay products or silicate industries. In recent years new products have been developed as a result of the demand for materials that withstand higher temperatures, resist greater pressure, have superior mechanical properties, possess special electrical characteristics, or can protect against corrosive chemicals.

         Ceramic industry consumes large amounts of water in molds washing and final products and in polishing of final products that generates large amount of polluted water that contains harmful chemicals with negative impact on environment.

         Pollution aspects related to the ceramic industry are mainly due to dust emission both in workplace and in ambient air. Effluents are characterized by higher concentration of suspended solids.

          Large volumes of wastewater are generated during the process. Process wastewater is generated mainly when clay materials are flushed out and suspended in flowing water during the manufacturing process and equipment cleaning. The added directly to ceramic body mixes; is subsequently evaporated into the air during the drying and firing stages.

          Different conventional physicochemical treatments have been used to treat the ceramic wastewater. Removal of pollutants produced by industrial plants is requirement for reuse of water and to obtain environmental standards. The pollutants in the Ceramic wastewater are different suspended solids, dissolved solids, chemical oxygen demand and Low Biochemical oxygen demand. This wastewater caused serious environmental problems due to their high color, large amount of suspended solids, and high chemical oxygen demand. So, they have to be removed before being discharged into the environment.

        Limits of pollutants in wastewater are depending on the type of receiving water body. The parameters that should be monitored and/or inspected are biochemical oxygen demand BOD, chemical oxygen demand COD, pH, temperature, total suspended solids TSS, and  total dissolved solids TDS,

          The problem of ceramic wastewater utilization may be solved with different treatment techniques for reuse or recycle / treated wastewater and recovery of treated water.

           Different physicochemical treatments have been used to treat the Ceramic wastewater such as coagulation with mineral coagulants and organic coagulants aids followed by sedimentation and sand filtration. The proposed system of the study under investigation is to treat the effluent for reuse or discharge into the receiving body needs the following units: screens, equalization tank, feed pump, flow regulator, mixing tank, flocculation tank and clarifier.

Effluents of Ceramic Industry                    

       Effluents of ceramic industry are characterized by:

  • Highest levels of water pollution that generated from washing of molds and final products to remove any suspended impurities on the pieces. Impurities are removed after the pouring stage and before the drying stage.
  • Spent lube oil from garage and workshops if discharged to sewer will give oily wastewater.
  • Tile polishing generates a large quantity of wastewater high in suspended solids and settable solid.
  • Industrial wastewater.

Typical effluent characteristics of the Egyptian ceramic industry are shown in the following Table 1.

Table1: Typical effluent characteristics of the Egyptian ceramic industry [1].

Parameter Average analysis (mg/liter)
pH 7.5
Total suspended solid 700
Total dissolved solid 220
Biological oxygen demand 30
Chemical oxygen demand 400
Oil and grease 25

       Effluent guidelines are applicable for direct discharges of treated effluents to surface waters for general use. Site-specific discharge levels may be established based on the availability and conditions in the use of publicly operated sewage collection and treatment systems or, if discharged directly to surface waters.

Ceramic Industry Wastewater [1].   

        Wastewater from ceramic industry generated from all industrial activities in the ceramic plants.

  1. Industrial process wastewater

       Process wastewater is mainly generated from cleaning water in preparation and casting units, and various process activities (e.g. glazing, decorating, polishing, and wet grinding). Process wastewater is characterized by turbidity and coloring, due to the very fine suspended particles of glaze and clay minerals. The potential pollutants of concern include suspended solids (e.g. clays and insoluble silicates), suspended and dissolved heavy metals (e.g. lead and zinc), sulfates, boron, and traces of organic matter.

  1. Process Wastewater Treatment

       Techniques for treating industrial process wastewater in ceramic industry include flow and load equalization with pH adjustment; sedimentation for suspended solids reduction using settling basins or clarifiers; multimedia filtration for reduction in nonsettleable suspended solids; dewatering and disposal of residuals in landfills, or if hazardous in designated hazardous waste disposal sites. Additional engineering controls may be required for advanced metals removal using membrane filtration or other physical/chemical treatment technologies.

Tables 2 present effluent guidelines for ceramic industry sector guideline values for process effluents in this sector are indicative of good international industry practice as reflected in relevant standards of countries with recognized regulatory frameworks. These levels should be achieved, without dilution, at least 95 percent of the time that the plant or unit is operating, to be calculated as a proportion of annual operating hours. Deviation from these levels in consideration of specific, local project conditions should be justified in the environmental assessment [2].

Table 2: Effluent level for ceramic tile [2].

Pollutant Units Guideline value
pH 6-9
BOD5 mg/l 50
TSS mg/l 50
Oil & Grease mg/l 10
Lead mg/l 0.2
Cadmium mg/l 0.1
Chromium (Total) mg/l 0.1
Cobalt mg/l 0.1
Copper mg/l 0.1
Nickel mg/l 0.1
Zinc mg/l 2.0
Temperature increase ºC < 3º

 

Selections of Industrial Wastewater Treatment Processes

        The Selections of industrial wastewater treatment processes or a combination of processes depends on:

  • The characteristics of industrial wastewater, these consider the form of the pollutant, i.e. suspended colloidal or dissolved, the biodegradability, and the toxicity of the organic or inorganic components.
  • The required effluent quality .consideration should also give to possible restriction such as an effluent bioassay aquatic toxicity limitation.
  • The possibility of reuse or recycle of treated effluents.
  • The costs and availability of land for any given wastewater treatment problem.

High operating costs due to the use of chemical substances and high amount of sludge and its disposal costs are shown as the important disadvantages of chemical treatment [3].

Therefore, researchers have focused on new alternative methods or alternative coagulants to reduce chemical usage by improving discharge standard with adding low cost substance.

Examples of wastewater of ceramic industry around the World

           Ceramic industry wastewaters contain high concentration of suspended & total solids and significant amount of dissolved organics resulting in high BOD or COD loads. Suspended solids can be removed from the wastewater by chemical precipitation. However, dissolved BOD/COD compounds can only be removed by biological or chemical oxidation [4].

            In a ceramic factory in Turkey, the effluent wastewater from chemical sedimentation stage was having high COD average 720 ppm. An experiment using biological activated sludge unit on a lab scale was applied to this effluent. The best results were obtained with  θc= 20h of hydraulic & θc=20 days of solids retention times (sludge age) resulting in effluent COD concentration of 40 mg/ 1 from a feed wastewater of 270 mg/1 COD content. The suspended solids content of the activated sludge effluent was approximately 52 mg/1[5].

        In Malaysia, boron is extensively used in the ceramic industry for enhancing mechanical strength of the tiles. The discharge of wastewater containing boron to the environment causes severe pollution problems. Boron is also dangerous for human consumption & causes organism’s reproductive impediments if the safe intake level is exceeded. Current methods to remove boron include ion- exchange, membrane filtration, and precipitation- coagulation, biological and chemical treatment. These methods are costly to remove boron from the wastewater and hence infeasible for industrial wastewater treatment. Adsorption- flocculation mechanism is proposed for boron removal from ceramic wastewater by using Palm Oil Mill Boiler (POMB) bottom ash and long chain polymer or flocculants. Ceramic wastewater is turbid and milky in color which contains 15 mg/ L of boron & 2000mg / L of suspended solids.

The optimum operating condition for boron adsorption on POMB bottom ash & flocculation using polymer were investigated. Adsorption isotherm of boron in bottom ash was also investigated to evaluate the adsorption capacity.  Adsorption isotherms modeling were conducted based on Langmuir & Freundlich isotherms. The results show that coarse POMB bottom ash with particle size larger than 2 mm is a suitable adsorbent where boron is removed up to 80% under the optimum conditions ( pH= 8.0, dosage = 40 g bottom  ash 300 ml wastewater, residence time= 1 h). Under the optimum operating conditions, the boron and suspended solids concentration of the treated wastewater were reduced to 3 mg /L & 5 mg /L respectively, satisfying the discharge requirements by Malaysia Department of Environment (DOE). The modeling study shows that the Adsorption isotherm of boron onto POMB bottom ash conformed to the Freundlich Osotherm. The proposed method is suitable for boron removal in ceramic wastewater especially in regions where POMB bottom ash is abundant [6].

Example in Egypt

      The objective of this work study the effect of industrial effluents on soil chemical properties when faba bean was grown on soils irrigated with the effluent of ceramic, paper & starch factories. Results showed increases in soil pH, ECe (soil salinity) and soil organic matter (OM) [7].

       Industrial liquid waste of the 10th of Ramadan city is estimated about 1700 m3/day from the dying industry, 370 m3/day from the ceramics 700 m3/day from the paper and 2000 m3/day from starch industry [43]. The objectives of this work were to assess and evaluate the effect of the direct use of industrial effluent of ceramic, paper, starch industries on some chemical properties of sandy and calcareous soils, on the amounts of chemically available of macro- micro- & biotoxic- elements and on the plant growth in these soils [7].

        Two surface soil samples having variable origins & CaCO3 content were collected from the 10th of Ramadan city (Typic Quartizipasament, El Sharkia Governorate) and from Ras Sedr researches station (Typic Torripsament, South Saini Governorate). Industrial effluents of ceramic, paper, starch factories in the 10th of Ramadan city were collected. [7].

The water treatments are tap water (control), ceramic, paper & starch industrial waste effluent. Soil mechanical analysis & the conventional chemical soil properties were determined using the standard methods [46]. Chemically available Fe, Mn, Zn, Cu, Pb, Cd, Co & Ni was spectrophotometer. All above chemical properties were determined according to Page et al (1982) [8]. The obtained results were subjected to analysis of variance with the Duncan multiple range test according to procedures outlined by steel & Torrie (1980) [43], [9].

 

By

Ahmed Ahmed Elserwy

Water & Environmental Consultant

Technical Manager Louts for Water Treatment

References

[1]    Egyptian Environmental Affairs Agency (EEAA); Egyptian Pollution Abatement Project (EPAP) Inspection Manual of Ceramic Industry, 2003.

[2]   Environmental, Health, and Safety Guidelines for Ceramic Tile and Sanitary Ware Manufacturing, international finance cooperation, World Bank group, April 2007.

[3]  Alpaslan, M.N., Dolgen, D.,and Akyarli, A., Liquid Waste Management Strategies for Coastal Areas, Water Science and Technology, 46( 8): 169-175. 2002.

[4]  Economic and Social Commission for Western Asia, “Wastewater Treatment Technologies a General Review “, United Nation, 11 September 2003.

[5]  Dincer A.R., FKargi, “Characterization and biological treatment of ceramic industry wastewater “, Bioprocess Engineering 23 (2000) 209-212 .

 [6]    Mei  Fong Shong ,Kah Peng Lee,Hui Jiun Cheing ,Iii  Izyan Syavwani Binti Ramli “Removal of boron from ceramic industry wastewater by adsorption –flocculation mechanism using palm oil mill boiler (POMB)bottom ash and polymer ” School of chemical Environmental Engineering , The university of Nottingham Malaysia Campus ,Jalan Borga, 43500,Selangor Darul  Ehsan, Malaysia,(9 may 2009).

[7]    Eid, M.A ,.Elgala, A.M ,.Hassan F.A, and Ramadan, W.F ” Effect of Industrial Effluents on soil Chemical Properties and Plant Growth” paper presented at 2nd international conference on soil of urban, industrial and mining area ,Cairo, Egypt, 2005.

[8]   Page ,A.R,R.H. Miller,and D.R.Keeney,”Methods of Soil Analysis,Part2,2nd edition “,Soil Sci.Soc.of Am.Madison,WI,(1982).

[9]   Steel, R.G,and J.H.Torrie, “Principals and procedures of statistics : A Biometrical Approach ,2nd edition ” McGraw-Hill, New York, (1980).

Disinfection of Wastewater by Ozone

  1- Introduction

          New water-treatment goals for disinfection by-products (DBP) and for microbial inactivation have increased the need for new disinfection technologies. Water and wastewater systems will need to use disinfection methods that are effective for killing pathogens without forming excessive DBP [1]. Ozone is an attractive alternative. This technology has evolved and improved in recent years, thereby increasing its potential for successful application. In August 1997, the US Environmental Protection Agency (US EPA) listed ozone as a “compliance” in the requirements of the Surface Water Treatment Rule for all three sizes of drinking water systems [2]. Many of the existing facilities using chlorination may be required to upgrade their present disinfection systems to install alternative disinfection processes.

      Ozone (O3) is a molecule that can co-exist with air or high-purity oxygen, or can dissolve in water. It is a very strong oxidizing agent and a very effective disinfectant.

Ozone is a colorless gas that has an odor most often described as the smell of air after a spring electrical thunderstorm. Some people also refer to the odor as similar to the smell of watermelons. Actually, ozone owes its name to its odor. The word ozone is derived from the Greek word ozein [3]. Ozone is an extremely unstable gas. Consequently, it must be manufactured and used onsite. It is the strongest oxidant of the common oxidizing agents. Ozone is manufactured by passing air or oxygen through two electrodes with high, alternating potential difference.

         Ozone is a very strong oxidizing agent, having an oxidation potential of 2.07 V [4].

Ozone will react with many organic and inorganic compounds in water or wastewater.

These reactions are typically called “ozone demand” reactions. They are important in ozone disinfection system design because the reacted ozone is no longer available for disinfection. Waters or wastewaters that have high concentrations of organics or inorganics may require high ozone dosages to achieve disinfection. It is very important to conduct pilot plant studies on these wastewaters during ozone disinfection system design in order to determine the ozone reaction kinetics for the level of treatment prior to ozone disinfection.

 

  1. Reactions of Ozone with Organic Compounds

        Wastewater is composed mainly by organic compounds which are biodegradable and non-biodegradable. Several investigators developed an in-depth analysis of the reactions for ozone with various organic compounds. These reactions were described by Miller et al. [4], and are summarized below:

(a) Aromatic compounds: Phenol reacts readily with ozone in aqueous solution. Oxalic and acetic acids are relatively stable to ozonation in the absence of a catalyst such as ultraviolet light or hydrogen peroxide. Cresols and xylenols undergo oxidation with ozone at faster rates than does phenol. Pyrene, phenanthrene, and naphthalene oxidize by ring rupture.

Chlorobenzene reacts with ozone slower than does phenol.

(b) Aliphatic compounds: There is no evidence that ozone reacts with saturated aliphatic hydrocarbons under water- or wastewater-treatment conditions. There is no evidence that ozone oxidizes trihalomethanes. Ozone combined with ultraviolet radiation does oxidize chloroform to produce chloride ion, but no identified organic oxidation product. Unsaturated aliphatic or alicyclic compounds react with ozone.

(c) Pesticides: Ozonation of parathion and malathion produces paraoxon and malaoxon,respectively, as intermediates, which are more toxic than are the starting materials.

Continued ozonation degrades the oxons, but requires more ozone than the initial reaction.

Ozonation of heptachlor produces a stable product not yet identified. Aldrin and 2,4,5-T are readily oxidized by ozone, but dieldrin, chlordane, lindane, DDT, and endosulfan are only slightly affected by ozone.

(d) Humic acids: Humic materials are resistant to ozonation, requiring long ozonation times to produce small amounts of acetic, oxalic, formic, and terephthalic acids, carbon dioxide, and phenolic compounds. Ozonation of humic materials followed by immediate chlorination (within 8 min) has been shown to reduce trihalomethane formation in some cases. Ozonized organic materials generally are more biodegradable than the starting, unoxidized compounds.

 

  1. Advantages and Disadvantages

It is important to note that ozone, like other technologies, has its own set of advantages and disadvantages that show up in differing degrees from one location to the next [5].

Using ozone has the following advantages:

(a) Possesses strong oxidizing power and requires short reaction time, which enables the pathogens to be killed within a few seconds.

(b) Produces no taste or odor.

(c) Provides oxygen to the water after disinfecting.

(d) Requires no chemicals.

(e) Oxidizes iron and manganese.

(f ) Destroys and removes algae.

(g) Reacts with and removes all organic matter.

(h) Decays rapidly in water, avoiding any undesirable residual effects.

(i) Removes color, taste, and odor producing compounds.

(j) Aids coagulation by destabilization of certain types of turbidity.

Among the disadvantages of using ozone are the following:

(a) Toxic (toxicity is proportional to concentration and exposure time).

(b) Cost of ozonation is high compared with chlorination.

(c) Installation can be complicated.

(d) Ozone-destroying device is needed at the exhaust of the ozone reactor to prevent toxicity.

(e) May produce undesirable aldehydes and ketones by reacting with certain organics.

(f ) No residual effect is present in the distribution system, thus postchlorination may be required.

(g) Much less soluble in water than chlorine; thus, special mixing devices are necessary.

(h) It will not oxidize some refractory organics or will oxidize too slowly to be of practical

significance.

  1. APPLICATIONS OF OZONE

        Ozone acts both as a very strong oxidizing agent and as a very effective disinfectant.

Consequently, it has multiple uses in potable water treatment, wastewater renovation, cooling water towers, groundwater remediation, and industrial waste treatment. The

following is a snapshot description of each of its applications (5–8).

4.1. Disinfection against Pathogens

         Transfer of ozone into the water is the first step in meeting the disinfection objective, because ozone must be transferred and residual oxidants produced before effective disinfection will occur [9]. Once transferred, the residual oxidants, such as ozone, hydroxide, or peroxide must make contact with the organisms in order for the disinfection action to proceed. Design of an ozone system as primary treatment should be based

on simple criteria, including:

(a) Ozone contact concentrations,

(b) Competing ozone demands

(c) Minimum contact concentration-time (CT) to meet the required inactivation requirements, in combination with US EPA recommendations.

 

Ozone has been observed to be capable of inactivating Cryptosporidium and there is significant interest in this aspect of its application [10]. Similar findings have been reported for the control of cyanobacterial toxins (microcystins) under various bloom conditions [11]. Available data indicate that a significant increase in ozone dose (at least 1.5 mg/L) and CT may be required as compared with past practices. Therefore, these needs in addition to continuous monitoring and ensuring a low total organic carbon

(TOC) in the flow should be considered in planning.

4.2. Zebra Mussel Abatement

Zebra mussel (Dreissena polymorpha), has arrived in the United States by attaching itself to ships in the infested waters of its natural habitat. Subsequently, it was imported over by the ships to cause infestation in US waters. The growth of zebra mussels on raw water intake pipes decreases the capacity of water transmission to potable-water-treatment plants, cooling towers of power plants, and hatcheries. To restore the full water flow capacity, plant operators have resorted to mechanical means for removing the mussel infestation on intake pipes.

Ozonation seems to be the most promising among the chemical alternatives tested for controlling zebra mussel growth. An 11 MGD side stream ozonation process was designed for a fish culture plant in New England [12]. It involved the pumping of high concentration ozone in water solution (15–25 mg/L) into the intake of the raw water pipe and blending it into the intake water to attain a final ozone concentration of 0.1–0.3 mg/L, which is sufficient to control the zebra mussel infestation.

4.3. Iron and Manganese Removal

The standard oxidation–reduction potential and reaction rate of ozone is such that it can readily oxidize iron and manganese in groundwater and in water with low organic content. Groundwater systems that have iron levels above 0.1 mg/L may have iron complaints if ozonation or chlorination is added. Excessive doses of ozone will lead to the formation of permanganate, which gives water a pinkish color. This soluble form of manganese (Mn) corresponds to a theoretical stoichiometry of 2.20 mg O3/mg Mn.

3.4. Color Removal

Because humic substances are the primary cause of color in natural waters, it is useful to review the reactions of ozone with humic and fulvic acids. According to different authors, ozone doses of 1–3 mg O3/mg C lead to almost complete color removal. The ozone dosages to be applied in order to reach treatment goals for color can be very high.

It is interesting to note that when the ozone dosage is sufficient, the organic structure is modified such that the final chlorine demand can decrease. Konsowa [13]. found that ozone is efficient in the removal of color from textile dyeing wastewater. The rate of dye oxidation was determined to be a function of dye concentration, ozone concentration, ozone-air flow rate and pH. The products produced by the break down of the dye are nontoxic and can be removed by biological treatment.

4.5. Control of Taste and Odor

The National Secondary Drinking Water Regulations recommend that the threshold odors number (TON) be 3 or less in finished water. It has been shown that ozone can be effective in treating water for taste and odor problems, especially when the water is relatively free from radical scavengers.

It has also been observed that ozone, in combination with other downstream treatment processes, especially granular activated carbon (GAC) filtration, can greatly increase taste and odor treatment efficiency and reliability. Again, the causes of taste and odor compounds, as well as the source water to be treated, need to be carefully considered prior to designing a treatment system. Analysis and possibly pilot-scale experimentation may be required to determine the optimum choice of ozone and downstream treatment.

4.6. Elimination of Organic Chemicals

Ozone or advanced ozonation processes can remove many synthetic organic chemicals (SOC). This removal leads to the chemical transformation of these molecules into toxic or nontoxic by-products. Such transformation can theoretically lead to complete oxidation into carbon dioxide (CO2); however, this is rarely the case in water treatment. Any observable reduction in total organic carbon (TOC) is due to either a small degree of CO2 formation (for example, decarboxylation of amino acids) or the formation and loss of volatile compounds through stripping.

4.7. Control of Algae

Ozone, like any other oxidant, such as chlorine or chlorine dioxide, has a lethal effect on some algae or limits its growth. Ozone is also capable of inactivating certain zooplankton,e.g., mobile organisms, Notholca caudata. Such organisms must first be inactivated before they are removed by flocculation and filtration.

4.8. Aid in Coagulation and Destabilization of Turbidity

It is important to understand that the coagulating effects of ozone go beyond any direct oxidative effects on organic macro-pollutants. For this reason, one must be wary of studies claiming improved removal of organic matter when the data are based solely on color removal or ultraviolet (UV) absorption. Also, when studying the removal of DBP such as trihalomethanes, one must be careful to incorporate controls permitting the separate evaluation of ozone’s direct effects. Finally, the coagulating effects of ozone may not be observed with all waters. Whenever considering the use of ozone as a coagulant aid, the preozonation effects should be critically evaluated in pilot studies incorporating the proper controls.

 

5.Disinfection of Wastewater by Ozone

As mentioned above, transfer of ozone into the wastewater is the first step in meeting the disinfection objective. Once transferred, the residual oxidants must make contact with the microorganisms in order for the disinfection action to proceed. Therefore, similar requirements and kinetic relationships used for chlorine disinfectants can also be used for ozone disinfection.

5.1. Wastewater Treatment Prior to Ozonation

    The US EPA Water Engineering Research Laboratory and other researchers have evaluated several treatment plant effluents to determine the relationship between ozone dosage and total coliform reduction [14–18]. The most significant factor influencing the ozone dosage requirement to achieve a desired effluent total coliform concentration was the TCOD (total chemical oxygen demand) concentration of the effluent. For example, at five plants where the TCOD of the secondary effluent was less than 40 mg/L, a total coliform concentration of 1000 per 100 mL could be achieved with ozone dosages between 4 and 7 mg/L [18] .However, when Meckes et al. [18] evaluated a plant, which treated a significant amount of industrial waste (TCOD = 74 mg/L), a dosage greater than 12 mg/L was projected in order for the process to meet the 1000 total coliforms per 100 mL limit.

      Based on the results of the above researchers, it appears that there is no technical basis for excluding the use of ozone following any treatment scheme (primary, secondary, tertiary, or advanced). However, depending on the type of wastewater treated and/or the effluent disinfection requirement, the wastewater-treatment scheme may be an important economical consideration. A summary of the issues to consider when selecting the wastewater-treatment scheme prior to ozone disinfection is presented below:

      (a) Required Effluent Target

First: To meet the former US EPA standard of 200 fecal coliforms per 100 mL, tertiary treatment may not be necessary.

Second: To meet more stringent standards, such as 14 fecal coliforms per 100 mL, tertiary treatment should be considered.

Third: To meet a standard of 2.2 total coliforms per 100 mL, advanced treatment processes prior to the ozone disinfection process may be required.

        (b) Influent Coliform Concentration

First: Coliform removal is a function of transferred ozone dosage; thus, the influent coliform concentration will affect the amount of ozone dosage required to meet specific effluent criteria.

Second: Treatment processes that reduce the influent coliform concentration (such as filtration) will decrease the ozone dosage required to achieve a specific effluent standard.

        (c) Wastewater Quality Characteristics

First: The ozone demand of the wastewater significantly increases the ozone dosage requirements. A plant with a large industrial contribution may have a large ozone dosage requirement. Pilot testing to establish ozone dosage requirements in these plants is highly recommended.

Second: Incomplete nitrification and a high concentration of nitrite-nitrogen will significantly

increase the ozone demand and thus the ozone dosage requirement. The nitrite-nitrogen concentration preferably should be less than 0.15 mg/L to optimize disinfection performance.

 

By

Ahmed Ahmed Elserwy

Water & Environmental Consultant

Ain Shames University, Faculty of Science.

 

References

[1]   C. Gottschalk, J. A. Libra, and A. Saupe, Ozonation of Water and Waste Water: A Practical

Guide to Understanding Ozone and its Application, Wiley-VCH, New York, NY, 2000.

[2]  US EPA, Small System Treatment Technologies for Surface Water and Total Coliform Rules,US EPA Office of Ground Water and Drinking Water, Washington, DC, 1998.

[3]  US EPA, Design Manual—Municipal Wastewater Disinfection, US Environmental Protection Agency, EPA/625 1-86-021, Water Engineering Research Laboratory, Cincinnati,OH, 1986.

[4]   G. W. Miller, et al., An Assessment of Ozone and Chlorine Dioxide Technologies for Treatment of Municipal Water Supplies, EPA-600/2-78-147, US Environmental Protection Agency, Cincinnati, OH, 1978.

[5]   NDWC Tech brief: Ozone, Newsletter On Tap, National Drinking Water Clearinghouse (NDWC), No. 12, December, (1999).

[6]   X. Paraskeva, Y. Panagiota, Z. Graham, J. D. Nigel, Water Environment Regulation Watch, November/December, (2002).

[7] M. R. Collins, Small Systems Water Treatment Technologies: State-of-the-Art Workshop ,American Water Works Association, Denver, CO, 1998.

[8] Tri-State (2003), Ozonation Systems, Energy Technologies, Generation and Transmission Association, http://tristate.apogee.net/et/ewtwozs.asp, November, (2003).

[9]   S. Farooq, et al., Criteria of Design of Ozone Disinfection Plants, Forum on Ozone Disinfection, International Ozone Institute, 1976.

[10]   SNWA (2003), Water Quality and Water Treatment: Ozonation, Southern Nevada Water Authority, http://www.snwa.com/html/wq_treatment_ozonation.html, November.

[11]   S. J. Hoeger, D. R. Dietrich, and B. C. Hitzfeld Environmental Health Perspectives, 110,November (2002).

[12]   Bollyky Associates, Inc. Zebra Mussel Control by Ozone Treatment, http://www.bai-ozone.com/bai 11.htm, November, (2003).

[13]   A. H. Konsowa, Desalination, 158, 233–240, (2003).

[14]   E. L. Stover, et al., High Level Ozone Disinfection of Municipal Wastewater Effluents, US EPA Grant No. R8O4946, 1980.

[15]   P. W. Given and D. W. Smith, In: Municipal Wastewater Disinfection, Proceedings of Second National Symposium, Orlando, Florida, EPA-600/9-83-009, US Environmental Protection Agency, Cincinnati, OH, 1983.

[16]   H. B. Gan, et al., Forum on Ozone Disinfection, International Ozone Institute, 1976.

[17] A. D. Venosa, et al., Environment International, 4, 299–311, (1980).

[18] M. C. Meckes, et al., J. Water Pollution Control Fed., 55, 1158–1162 (1983).

Inorganic & Organic Coagulants

  • Introduction

Coagulation is an essential phenomenon in industrial wastewater treatment. Inorganic coagulants (salts of multivalent metals) are being commonly used due to its low cost and ease of use. However, their application is constrained with low flocculating efficiency and the presence of residue metal concentration in the treated water.

Organic polymeric flocculants are widely used nowadays due to its remarkable ability to flocculate efficiently with low dosage.

  • Inorganic Coagulants

Inorganic  salts  of  multivalent  metals  such  as  alum,  poly aluminum  chloride,  ferric  chloride,  ferrous  sulphate,  calcium chloride  and  magnesium  chloride  have  been  widely  used  for decades  as  coagulant.

Since the effect of coagulant is considerably influenced by the application conditions, such as water pH and stirring condition.

  • pH

Each inorganic coagulant has the optimum pH, this optimum pH range is the same to the pH range which the metallic ion composed of the coagulant stably precipitates as the hydroxide.  For example, aluminum ion stably precipitates as the hydroxide in the pH range of 5.0 to 7.5, and the optimum pH range of alum or PAC is also 5.0 to 7.5.

This fact shows that not only electrical charge neutralization but also formation of metal hydroxide floc plays the important role for the better coagulation of particles with inorganic coagulants.

  • Stirring strength and retention time

Strong stirring is required to increase the frequency which coagulants meet suspended particles to neutralize their electrical charges. Stirring also accelerates the floc formation by colliding the neutralized particles.

In the case of mixing tank for coagulation, the blade tip velocity of stirrer and the retention time are generally designed in the range of 1.5 to 3.0 m/s and 5 to 10 minutes respectively.

In case that water to be treated includes stable emulsifying particles, etc., the stirring strength and retention time should be strengthened and extended.

  • Order of chemical injection

Chemicals using for coagulation and flocculation treatment should be injected into the water in the order of inorganic coagulant, pH control agent (alkali) and polymer flocculent.

If alkali is added prior to coagulant, the charge neutralization ability of coagulant may be deteriorated because the coagulant will deposited as the metal hydroxide in water soon after the injection.

  • Organic Coagulants

The coagulation effect of organic coagulants is superior to the inorganic coagulants because of the higher ionic valences.

Some organic coagulants not only neutralize the charge of SS but also react with dissolved anionic organic compounds, such as lignin-sulfonate, anionic-surfactant, arginic acid and humic acid, and form the water insoluble salts.

Most organic coagulants are cationic low molecular weight polymers, their cationic functional groups are essentially amine-groups including primary, secondary and tertiary amine-groups, and quaternary ammonium chloride groups.

Organic coagulants show the excellent charge neutralizing abilities, however, they hardly form flocs by themselves.

Generally, the combined use of organic coagulants together with inorganic coagulants shows the better coagulation effect.

By

Ahmed Amer
Oil field services Engineer

Factors affect Dissolved Air Floatation (DAF) process performance

Flotation [1]

         Flotation may be used in lieu of the normal clarification by solids-downward-flow sedimentation basins as well as thickening the sludge in lieu of the normal sludge gravity thickening. Water containing solids is clarified and sludges are thickened because of the solids adhering to the rising bubbles of air. The breaking of the bubbles as they emerge at the surface leaves the sludge in a thickened condition.

         Figure.1 shows the flow sheet of a flotation plant. The recycled effluent is pressurized with air inside the air saturation tank. The pressurized effluent is then released into the flotation tank where minute bubbles are formed. The solids in the sludge feed then stick to the rising bubbles, thereby concentrating the sludge upon the bubbles reaching the surface and breaking. The concentrated sludge is then skimmed off as a thickened sludge.

The effluent from the flotation plant are normally recycled back to the influent of the whole treatment plant for further treatment along the influent raw wastewater. Figure 2 shows an elevational section of a flotation unit.

Dissolved Air Floatation Sludge Thickening

        In the dissolved air flotation (DAF) thickening process, air is introduced to the sludge at a pressure in excess of atmospheric pressure. When the pressure is reduced to atmospheric pressure and turbulence is created, air in excess of that required for saturation leaves the solution as fine bubbles 50 to 100 μm in diameter. These bubbles attach to the suspended solids or become enmeshed in the solids matrix. Since the average density of solids–air aggregates is less than that of water (0.6 to 0.7), they rise to the surface. Good solids flotation occurs with a solids–air aggregate specific gravity of 0.6 to 0.7. The floating solids are collected by a skimming mechanism similar to a scum skimming system.

         DAF thickening is used most efficiently for waste activated sludge.

Although other types of sludge, such as primary sludge and trickling filter

sludge, have been flotation thickened, gravity thickening of the sludge is

more economical than DAF thickening.

        The schematic of a typical DAF thickening rectangle tank is presented in Figure 3. The major components of a DAF system are the pressurization system with an air saturation tank, a recycle pump, an air compressor and pressure release valve, and a DAF tank equipped with surface skimmer and bottom solids removal mechanism. Figure 4 illustrates two models of flotation thickeners that are in use in Russia and Ukraine. There are three ways in which the pressurization system can be operated.

         In the method called total pressurization, the entire sludge flow is pumped through the pressurization tank and the air-saturated sludge is then passed through a reduction valve before entering the flotation tank. In the second method, called partial pressurization, only a part of the sludge flow is pumped through the pressurization tank. After pressurization, the pressurized and unpressurized streams are combined and mixed before they enter the flotation tank. In the third method, called the recycle pressurization, a portion of the subnatant is saturated with air in the pressurization tank and then combined and mixed with the sludge feed before it is discharged into the flotation tank.

         The major advantage of the recycle pressurization system is that it minimizes high-shear conditions, an important parameter when dealing with flocculant-type sludge. The recycle pressurization system also eliminates clogging problems with the pressurization pump, air saturation tank, and pressure release valve from the stringy material in the feed sludge. For these reasons, recycle pressurization is the most commonly used. The recycle flow can also be obtained from the secondary effluent, which has the advantage of lower suspended solids and a lower grease content than the subnatant from the DAF tank.

The flotation tank can be circular or rectangular and made of steel or concrete. Smaller tanks are usually steel and come completely assembled. For large installations requiring multiple tanks or large tanks, concrete tanks are more economical. Rectangular tanks have several advantages over circular units. In rectangular tanks, skimmers skim the entire surface and the flights can be closely spaced, allowing more efficient skimming. In a rectangular tank, bottom sludge flights are usually driven by a separate unit and hence can be operated independent of the skimmer flights.

         The main advantage of circular units is their lower cost in terms of structural concrete and mechanical equipment. However, shipping problems limit a completely assembled steel circular unit to about 9 m2 (100 ft2) or less.

Process Design Considerations [2]

Numerous factors affect DAF process performance, including the following:

  • Type and characteristics of feed sludge
  • Solids loading rate
  • Hydraulic loading rate
  • Air-to-solids ratio
  • Polymer addition

       Although sufficient data are available from operating units in more than 40 years to size DAF systems, bench- and pilot-scale testing can provide valuable information. Most manufacturers of DAF systems have designed and built bench-scale units for evaluations. These manufacturers have scale-up criteria for their equipment to predict full-scale operational parameters. Consideration should also be given to renting a pilot unit available from most manufacturers to test and evaluate the effect of such parameters as solids and hydraulic loading, recycle ratio, air-to-solids ratio, and polymer type and dosage. If sludge is not available for testing, a detailed review must be made of experience at installations where a similar type of sludge is being thickened by DAF thickeners. [3]

Type and Characteristics of Feed Sludge a variety of sludge can be thickened effectively by flotation. These include conventional WAS, extended aeration sludge, pure-oxygen activated sludge, and aerobically digested sludge.

The first step in designing a DAF system is to evaluate the characteristic of the feed sludge. Information is needed about the range of solids concentration that can be expected. If WAS is to be thickened, the mixed liquor sludge volume index (SVI) must be determined because SVI can significantly affect the DAF thickening performance. The SVI should be less than 200 if a float concentration of 4% is required with nominal polymer dosage.

Solids Loading Rate The solids loading rate is expressed as the weight of

solids per hour per unit effective flotation area. Typical solids loading rate are given in Table 1. The loading rates shown will normally result in a minimum of 4% concentration in the float. As can be seen from the table, the solids loading rate can generally be increased up to 100% with polymer addition.

Hydraulic Loading Rate The hydraulic loading rate is expressed as combined flow rates of feed sludge and recycle per unit effective flotation area (m3/m2·d or gpm/ft2). When like units are canceled, it becomes a velocity gradient to the average downward velocity of water as it flows through the flotation tank. The maximum hydraulic loading rate must always be less than the minimum rise rate of the sludge–air particles to ensure that all the particles will reach the surface before they reach the effluent end of the tank. Suggested hydraulic loading rates range from 30 to 120 m3/m2·d (0.5 to 2 gpm/ft2).

Air-to-Solids Ratio The air-to-solids ratio is perhaps the single most important factor affecting DAF performance. It is defined as the weight ratio of air to the solids in the feed stream. The ratio for a particular application is a function of the characteristics of the sludge, principally the SVI, the air dissolving efficiency of the pressurization system, and distribution of the air–solids mixture into the flotation tank. For domestic wastewater sludge, reported values of air-to-solids ratios range from 0.01 to 0.4, with most systems operating at a value under 0.06.

Polymer Addition Chemical conditioning with polymer has a marked effect on DAF thickener performance. The particles in a given sludge may not be amenable to the flotation process because their small size will not allow proper air bubble attachment. The surface properties of the particles may also have to be altered before effective flotation can occur. Sludge particles can be surrounded by electrically charged layers that disperse the particles in the liquid phase. Polymers can neutralize the charge, causing the particles to coagulate so that the air bubbles can attach to them for effective flotation.

Bench- or pilot-scale testing is the most effective method to determine the optimal amount of polymer required and the point of addition (in the feed stream or the recycle stream) for a particular installation. Typical polymer dosages range from 2 to 5 g polymer per kilogram of dry solids (4 to

10 lb/ton).

In the lower ranges of solids and hydraulic loading rates, polymer addition typically is not necessary. Polymer conditioning usually affects solids capture to a greater extent than float solids concentration. With polymer addition, float solids can be increased by about 0.5%; however, the solids capture efficiency can be increased from about 90% to better than 95%.

By

Ahmed Ahmed Elserwy

Water & Environmental Consultant

Technical Manager Louts for Water Treatment

References

[1]      Physical–chemical treatment of water and wastewater / Arcadio Pacquiao Sincero, Sr.,Gregoria Alivio Sincero, IWA publishing ,2003.

[2]   Wastewater sludge processing / Izrail S. Turovskiy, P. K. Mathai, John Wiley & Sons, Inc., Hoboken, New Jersey,2006.

[3]   Gulas, V., Benefi eld, L., and Randall, C. (1978), Factors Affecting the Design of Dissolved

Air Flotation Systems, Journal of the Water Pollution Control Federation, Vol. 50, p. 1835.

[4]   (1979), Process Design Manual for Sludge Treatment and Disposal, EPA 625/1-79/011

Advanced Oxidation Processes Basics and Applications

Introduction

               Anthropogenic activities include rapidly growing industrialization, a series of new constructions, many fold increases in transportation, aerospace movements, developmental and enhancement in technologies, that is, nuclear power, pharmaceutical, pesticides, herbicides, agriculture, and so on. These are all the most desirable activities for human development and welfare, but they also lead to the generation and release of objectionable materials into the environment. Thus, they pollute the whole environment, making our life on this beautiful earth quite miserable. The situation, if not controlled in a timely manner, would become a malignant problem for the survival of mankind on the earth. Many rivers are being polluted by effluent water from industries and domestic sectors. This creates a problem for the aquatic life by turning water into a resource of no use. So, it is of utmost necessity to solve this problem of water pollution.

            The most important challenge in the twenty-first century is to combat against the ever-increasing environmental pollution. To have a neat, clean, healthy, and green environment, there is an urgent need to search for such an approach, which may be applicable at room temperature, safe to handle, economic, and eco-friendly. And above all, the main requirement of the treatment is that it should not be harmful to the environment in any manner.

              Although conventional oxidation technologies are available for the oxidation of pollutants or disinfection of pathogenic contaminants using a variety of oxidants such as chlorine, peracetic acid, permanganate, hydrogen peroxide (H2O2), and ozone, there is another group of chemical oxidative processes called advanced oxidation processes (AOPs) or advanced oxidation technologies (AOTs). The concept of AOPs was originally established by Glaze et al. (1987) [1]. It is defined as “oxidation processes, which generate highly reactive radicals (especially hydroxyl radicals) in sufficient quantity to affect the water treatment.” These processes are capable of degrading almost all organic contaminants.

                It is clear from standard redox potential data that hydroxyl radical is the strongest known oxidant (2.80 V), second to fluorine (3.03 V).

          Therefore, the complete mineralization of most of the organic matters is possible, when the hydroxyl radicals are the main oxidizing species in the solution. This is one of the major advantages of AOPs, since other chemical oxidation processes mostly lead to partial oxidation of the target compounds, and thus, the generation of new hazardous compounds is possible. The other advantage of AOPs is the generation of negligible amounts of residues and their applicability; in case of very low concentrations of pollutants.

      The term advanced oxidation processes (AOP), describes a series of processes which are used for the chemical treatment of organic and inorganic pollutants in wastewaters. AOPs are based on the generation of reactive oxygen species (ROS) such as hydroxyl radicals. Generating hydroxyl radicals is possible via various ways such as photocatalytic, electrochemical, sonochemical. Typical AOPs are H2O2/hv, ozone/hv, ozone/ H2O2/hv, TiO2/hv, (photo-)Fenton systems and electrochemical processes.

Advanced Oxidation Processes (AOPs) are efficient methods to remove organic contamination not degradable by means of biological processes. AOPs are a set of processes involving the production of very reactive oxygen species able to destroy a wide range of organic compounds. AOPs are driven by external energy sources such as electric power, ultraviolet radiation (UV) or solar light, so these processes are often more expensive than conventional biological wastewater treatment. Moreover, AOPs can be applied for the disinfection of water, air and for remediation of contaminated soils.

 

Various AOPs

             Although a number of techniques are available under AOPs (more than 10), the main groups of AOPs are four. These are (i) Fenton and photo-Fenton, (ii) ozonolysis, (iii) photocatalysis, and (iv) sonolysis-based processes. These oxidation processes can produce in situ reactive free radicals, mainly hydroxyl radicals. A hydroxyl radical is a nonselective oxidant, which can oxidize a wide range of organic molecules.

            A hydroxyl radical has some interesting characteristics, which make it quite important in AOPs. These are:

  1. It is short-lived
  2. It can be easily produced
  3. It is a powerful oxidant
  4. It is electrophilic in behavior
  5. It is ubiquitous in nature
  6. It is highly reactive
  7. It is nonselective

The reactivity of hydroxyl radical (2.06) is next to that of fluorine (2.23), followed by that of atomic oxygen (1.78), H2O2 (1.31), and then permanganate (1.24). It is the high redox potential of hydroxyl radical that makes it a powerful oxidant. Thus, hydroxyl radicals have emerged not only as an effective but also as an economic and eco-friendly species.

        Hydroxyl radicals can react in water by four different routes: (i) addition,(ii) hydrogen abstraction, (iii) electron transfer, and (iv) radical interaction.

         The treatment of wastewaters can be carried out using these hydroxyl radicals.

             The contaminants are degraded to smaller or less harmful fragments and, in the majority of cases, complete mineralization of the pollutants has been achieved. Even persistent organic pollutants (POPs) can be degraded to the desirable extent using AOPs involving hydroxyl radicals as an active oxidizing agent.

              Degradation and detoxification of formalin wastewaters by AOPs has been observed by Kajitvichyanukul et al. (2006) [2]. A comparison of different AOPs for phenol degradation was made by Esplugas et al. (2002). Priya et al. (2008) achieved complete photodegradation of phenol in a reasonable time, that is, less than 5 h, when the concentration of phenol was ≤100 ppm. A comparison of various AOPs has also been given by Saritha et al. (2007) for the degradation of 4-chloro-2-nitro-phenol. The decolorization and mineralization of acid orange-6 azo dye were observed by Hsing et al. (2007) using AOPs. [3,4,5,6]

             Kawaguchi (1992) reported the photo oxidation of phenol in aqueous solution in the presence of H2O2. The photo degradation of phenol resulted in the stoichiometric conversion of phenol with practically complete mineralization.

 

AOP mechanism

Advanced oxidation involves several steps schematized in the figure below (Figure 1) and explained as follows:

  1. Formation of strong oxidants (e.g. hydroxyl radicals).
  2. Reaction of these oxidants with organic compounds in the water producing biodegradable intermediates.
  3. Reaction of biodegradable intermediates with oxidants referred to as mineralization (i.e. production of water, carbon dioxide and inorganic salts).

    By

    Ahmed Ahmed Elserwy

    Water & Environmental Consultant

    Technical Manager Louts for Water Treatment

References

[1]  Glaze, W.H., J.W. Kang, and D. Chapin. 1987. The chemistry of water treatment processes involving ozone, hydrogen peroxide and ultraviolet radiation. Ozone Sci. Eng. 9: 335–352.

[2]  Kajitvichyanukul, P., M.C. Lu, C.-H. Liao, W. Wirojanagud, and T. Koottatep. 2006. Degradation and detoxification of formalin waste water by advanced oxidation processes. J. Hazard. Mater. 135: 337–343.

[3]  Esplugas, S., J. Gimenez, S. Contreras, E. Pascual, and M. Rodreguez. 2002. Comparison of different advanced oxidation processes for phenol degredation Water Res. 36: 1034–1042.

[4] Priya, S.S., M. Premalatha, and N. Anantharaman. 2008. Solar photocatalytic treatment of phenolic waste water – Potential, challenges and opportunities. ARPN J. Eng. Appl. Sci. 3(6): 36–41.

[5]  Saritha, P., C. Aparna, V. Himabindu, and Y. Anjaneyulu. 2007. Comparison of various advanced oxidation processes for the degradation of 4-chloro-2-nitrophenol. J.Hazard. Mater. 149: 609–614.

[6]  Hsing, H.J., P.C. Chiang, E.E. Chan, and M.-Y. Chen. 2007. The decolorization and investigation of acid orange 6 dye in aqueous solution by advanced oxidation processes: A comparative study. J. Hazard. Mater. 141: 8–16.

[7]Mazille, Félicien. “Advanced Oxidation Processes | SSWM. Sustainable Sanitation and Water Management”. Archived from the original on May 28, 2012. Retrieved 13 June 2012.

[8]  Comninellis C., Kapalka A., Malato S., Parsons S.A., Poulios I. and Mantzavinos D. (2008) Advanced oxidation processes for water  treatment: advances and trends for R&D, J. Chem.  Technol. Biotechnol., 83,769-776.

Selected Nanomaterials applications in waste water treatment

Selected Nanomaterials applications in waste water treatment

Ahmed Hasham (M.Sc. Env. Chemistry) /  Ahmedhasham83@outlook.com

Introduction:

Water pollution is the most difficult environmental challenges facing society. Therefore, the release of pollutants from sewage or industrial wastewater in the must be considered as a threat to the environment. Characterizing the physical, chemical and biological aspects of raw water and treated water is crucial to ensure that they are safe for disposal in the aquatic or desert environment.

Water pollution:

Leaching of pollutants into groundwater from sewage or industrial water cause serious health problems, which may be used by humans for drinking and other purposes in some areas. It is worth mentioning that a man cannot live more than three days without water.

Heavy metals are likely to be the most common water problem consumers face. Heavy metals (such as arsenic, zinc, iron, manganese, aluminum, cadmium, lead, etc.) cause many health problems if found in drinking water at concentrations higher than permitted.

Nanotechnology history:

Nanotechnology first appeared millions of years ago as molecules began to arrange in complex shapes and structures that launched life on Earth. At the nanoscale, substances have different physical, chemical and biological properties than their normal size characteristics.

Nanomaterials

Nanomaterials may be defined as materials smaller than 100 nm in at least one dimension. At this scale, materials regularly have novel size-dependent properties different from their large scale.

Nano-materials has the ability to clean up huge polluted locations, saving time, excluding the need for removal of pollutants, and hence decreasing pollutant concentration to the minimum levels. Advances in nanoscale science suggest that many of the current problems on water quality could be solved or avoided by using nanomaterials such as non-adsorbent, nanocatalyst, bioactive nanoparticles, nanostructured catalytic membranes, nano-powder, nanotubes, magnetic nanoparticles, nanosensors. Nanomaterials are the main players that promise many profits through their nanoenabled applications in multiple fields. Nanomaterials has been used in many environmental applications such as the treatment of contaminated water for drinking, agriculture and more recent application than through conventional means. The explosive development in nanotechnology research has presented new strategies in environmental remediation.

Some of these applications using the nanomaterials properties that relate to their high specific surface area, such as fast dissolution, high reactivity, and strong sorption. Others take advantage of their discontinuous properties, such as superparamagnetic, localized surface plasmon resonance (SPR), and quantum confinement effect. Most applications discussed in this article are still in the stage of research and development.

Titanium dioxide nanoparticles

 Titanium dioxide nanoparticles, also called ultrafine titanium dioxide, are particles of titanium dioxide (TiO2) with diameters less than 100 nm. Ultrafine TiO2 is used in sunscreens due to its ability to block UV radiation while remaining transparent on the skin, and its photocatalytic sterilizing properties also make it useful for many applications.

Nano particles of TiO2 are found different in their surface-to-volume ratio, their properties change so that they acquire catalytic ability. Activated by the ultraviolet (UV) component in sunlight, they break down toxins or enhance other relevant reactions. Titanium oxide photocatalysts have been broadly studied for solar energy conversion and environmental applications in the past several decades, because of their high chemical stability, good photoactivity, relatively low cost, and nontoxicity.

Photocatalytic oxidation process:

In the photocatalytic oxidation process, organic pollutants are cracked in the presence of semiconductor photocatalysts, an energetic light source, or an oxidant such as oxygen or air. Only photons with energies greater than the band gap energy (ΔE) can result in the excitation of valence band (VB) electrons that then promote possible reactions.

Recently, advanced oxidation processes (AOPs) using (TiO2) have been used successfully to toxic pollutants removal from industrial wastewater.

TiO2 features as photocatalytic agent:

  1. High photochemical reactivity.
  2. High photocatalytic activity.
  3. Low cost.
  4. Stability in aquatic systems.
  5. Low environmental toxicity.

 Mechanism of dye degradation upon irradiation

Photocatalytic oxidation is an AOP for elimination of trace pollutants and microbial pathogens. It is a valuable pretreatment for hazardous and non biodegradable pollutants to enhance their biodegradability. Photocatalysis can also be used as a polishing step to treat recalcitrant organic compounds. The major barrier for its wide application is slow kinetics, due to limited light fluence and photocatalytic activity. Current research focuses on increasing photocatalytic reaction kinetics and photoactivity range.

Gold nanoparticles

The modification of the Au surface with appropriate chemical species can improve separation and preconcentration efficiency, analytical selectivity; make the Gold nanoparticles (AuNPs), is consider the one of the wide selections of core resources available, coupled with tunable surface properties in the form of inorganics or inorganic–organic amalgams, have been described as an excellent platform for a broad range of analytical methods.

Advantage of Gold nanoparticles (AuNPs):

  1. High surface-to-volume ratio.
  2. Easy surface modification.
  3. Simple synthesis methods.

The AuNPs have been applied successfully used in:

  1. Removal of peptides.
  2. Removal of proteins.
  3. Removal of heavy metal ions.
  4. Removal of polycyclic aromatic hydrocarbons (PAHs).

Zerovalent iron nanoparticles

 Elemental iron has been used as an ideal candidate for remediation, for the following reasons:

  1. Low-cost,
  2. Extremely easy to prepare and apply to a variety of systems.
  3. No toxicity induced by its usage.

The idea of using metals such as iron as remediation is depend on reduction–oxidation reactions, in which a neutral electron donor (a metal) chemically reduces an electron acceptor (a pollutant). Nanoscale iron particles have surface areas greater than larger-sized powders, which leads to enhanced reactivity for the redox process.

Iron nanoparticles applications such as:

  1. Decomposition of halogenated hydrocarbons to benign hydrocarbons.
  2. Remediation of heavy metals.
  3. Solvents dechlorination

A significant loss of reactivity can occur before the particles are able to reach the target contaminant. In addition, zerovalent iron nanoparticles tend to flocculate when added to water, resulting in a reduction in the effective surface area of the metal.

Therefore, the effectiveness of a remediation depends on the accessibility of the contaminants to the nanoparticles, and the maximum efficiency of remediation will be achieved only if the metal nanoparticles can effectively migrate without oxidation to the contaminant or the water– contaminant interface.

 To overcome such difficulties, a regularly used strategy is to integrate iron nanoparticles within support materials, such as polymers, porous carbon, and polyelectrolytes.

Finally, Nanotechnology for water and wastewater management is depending on the matchless properties of nanomaterials and their conjunction with current treatment technologies present great chances to revolutionize water and wastewater treatment. Nanotechnology has shown huge possibility in water treatment technologies. The recent development of nanotechnology has raised the possibility of environmental decontamination through several nanomaterials cut the process and tools.

Another nanomaterials application in water treatment field may be discussed in another article.

للاطلاع على أكبر مكتبة مجانية في مجال علوم وهندسة المياه يرجى زيارة المنتدى من الرابط التالي

watertechexperts.com/vb/forum.php

للاطلاع على مزيد من المقالات باللغة الانجليزية يرجى زيارة مدونتنا باللغة الانجليزية من الرابط التالي

www.water-tech-market.com/blog

لارسال أي استفسارات أو أسئلة أو طلبات يرجى الانضمام لجروب المنتدى على الفيس بوك من الرابط التالي

www.facebook.com/groups/waterexperts

References

Abhijith, K.S., and Thakur, M.S. Analytical Methods, 2012, 4, 4250–4256.

Cao, G.Z. Nanostructures and Nanomaterials, Synthesis, Properties and Application, Imperial College Press,

London, 329, 2004.

Chae, H.K., Perez, D.Y.S., Kim, J., Go, Y., Eddaoudi, M., Matzger, A.J., O’Keeffe, M., and Yaghi, O.M. A route

to high surface area, porosity and inclusion of large molecules in crystals. Nature, 2004, 427, 523–525.

Chen, L., Lou, T., Yu, C., and Kang, Q. N-1-(2-mercaptoethyl)thymine modification of gold nanoparticles: A highly selective and sensitive colorimetric chemosensor for Hg

. Analyst, 2011, 136, 4770–4773.

Chun, C.L., Penn, R.L., and Arnold, W.A. Environmental Science and Technology 2006, 40, 3299–3304.

Cloete, T.E., Kwaadsteniet, M.D., Botes, M., and Lopez-Romero, J.M., Nanotechnology in Water Treatment Applications. Caister Academic Press, Wymondham, UK, 2010.

Elimelech, M., and Phillip, W.A. The future of seawater desalination: Energy, technology, and the environment. Science, 2011, 333, 712.Eshel, K. British Medical Journal, 2007, 334, 610–616.

Furukawa, H., Cordova, K.E., O’Keeffe, M., and Yaghi, O.M. The chemistry and applications of metal-organic frameworks. Science, 2013, 341, 1230–1234.

Guzman, K.A.D., Taylor, M.R., and Banfield, J.F. Environmental Science and Technology, 2006, 40, 1401–1407.

Hang, Y., Qin, Y., and Shen, J. Separation and microcolumn preconcentration of traces of rare earth elements on nanoscale TiO2 and their determination in geological samples by ICP-AES, Journal of SeparationScience, 2003, 26, 957–960.

Harada, M. Minamata disease: Methylmercury poisoning in Japan caused by environmental pollution. Critical Reviews in Toxicology, 1995, 25, 1–24.

Hidaka, H., Jou, H., Nohara, K., and Zhao, J. Photocatalytic degradation of the hydrophobic pesticidePermethrin in fluoro surfactant/TiO2 aqueous dispersions. Chemosphere, 1992, 25, 1589–1597

بعض تطبيقات تقنية النانوتكنولوجي في معالجة مياه الصرف

بعض تطبيقات تقنية النانوتكنولوجي في معالجة مياه الصرف

بقلم/ أحمد محمد هشام

ماجستير كيمياء تحليلية

Ahmedhasham83@outlook.com

مقدمة

يعد تلوث المياه أصعب التحديات البيئية التي تواجه المجتمع. لذلك ، يجب اعتبار الملوثات من مياه الصرف الصحي أو مياه الصرف الصناعية تهديدًا للبيئة. ولذلك يعتبر تميّز الجوانب الفيزيائية والكيميائية والبيولوجية للمياه الخام والمياه المعالجة أهمية حاسمة لضمان أنها آمنة للتخلص منها في البيئة المائية أو الصحراوية.

ويتسبب وصول الملوثات للمياه الجوفية من مياه المجاري أو المياه الصناعية في مشاكل صحية خطيرة ، لأن المياه الجوفية يمكن أن يستخدمها البشر لأغراض الشرب ولأغراض أخرى في بعض المناطق. ومن المرجح أن تكون المعادن الثقيلة هي المشكلة المائية الأكثر شيوعًا التي يواجهها المستهلكون. تسبب المعادن الثقيلة (مثل الزرنيخ والزنك والحديد والمنجنيز والألمنيوم والكادميوم والرصاص وما إلى ذلك) العديد من المشاكل الصحية إذا وجدت في مياه الشرب بتركيزات أعلى من المسموح به.

تقنية النانو

ظهرت تقنية النانو لأول مرة منذ ملايين السنين حيث بدأت الجزيئات بالترتيب في أشكال وهياكل معقدة أطلقت الحياة على الأرض. ومن الجدير بالذكر أن المواد في المقياس النانوي لها خصائص فيزيائية وكيميائية وبيولوجية مختلفة عن خصائص الحجم الطبيعي.ويمكن تعريف المواد النانوية كمواد أصغر من 100 نانومتر في بعد واحد على الأقل. في هذا المقياس ، تحتوي المواد بشكل منتظم على خصائص جديدة تعتمد على الحجم تختلف عن نطاقها الكبير.

خواص المواد النانومترية:

استخدام تقنية النانو في  معالجة المواقع الملوثة أثبت جدارة ، وتوفير الوقت وتقليل تركيز الملوثات إلى الحد الأدنى من المستويات المسموحة. تشير التطورات في العلوم النانوية إلى أن العديد من المشاكل الحالية المتعلقة بجودة المياه يمكن حلها أو تجنبها باستخدام مواد متناهية الصغر ، مثل المواد الممتزات النانوية ، أو الجسيمات النانوية النشطة بيولوجيًا ، أو الأغشية الحفزية النانومترية ، أو مساحيق النانو ، أو الأنابيب النانوية ، أو الجسيمات النانوية المغناطيسية ، أو أجهزة الاستشعار النانوية. المواد النانوية هي الجهات الرئيسية التي تعد بالكثير من المزايا من خلال تطبيقاتها النانوية في مجالات متعددة. وقد استخدمت المواد النانوية في العديد من التطبيقات البيئية مثل معالجة المياه الملوثة للشرب والزراعة والتطبيقات الحديثة أكثر من الوسائل التقليدية. وقد قدم التطور المتسارع في بحوث تكنولوجيا النانو استراتيجيات جديدة في مجال المعالجة البيئية.

بعض هذه التطبيقات تستخدم خصائص المواد النانوية التي ترتبط بمساحة سطحها العالية ، ومثل الذوبان السريع ، التفاعل العالي ، والامتصاص القوي. ويستفيد آخرون من خصائصهم المتقطعة ، مثل رنين البلازمون السطحي الموضعي(SPR) ، والتأثير الكمي. معظم التطبيقات التي نوقشت في هذه المقالة لا تزال في مرحلة البحث والتطوير.

جسيمات ثاني أكسيد التيتانيوم النانوية

جسيمات ثاني أكسيد التيتانيوم النانوية ، التي تسمى أيضًا ثاني أكسيد التيتانيوم المتناهية الصغر ، هي جسيمات ثاني أكسيد التيتانيوم  وبأقطار أقل من 100 نانومتر. وتستخدم جسيمات ثاني أكسيد التيتانيوم متناهية الصغر في واقيات الشمس بسبب قدرته على منع الأشعة فوق البنفسجية مع الحفاظ على شفافية البشرة ، كما أن خصائص التعقيم الضوئي لها تجعلها مفيدة للعديد من التطبيقات.

تم العثور على جزيئات نانو TiO2 مختلفة في نسبة سطح إلى حجم ، تتغير خصائصها بحيث اكتساب القدرة التحفيزية. تنشط بواسطة عنصر الأشعة فوق البنفسجية في ضوء الشمس ، فإنها تكسر السموم أو تعزيز ردود الفعل الأخرى ذات الصلة. تمت دراسة عوامل التحفيز الضوئي لأكسيد التيتانيوم على نطاق واسع من أجل تحويل الطاقة الشمسية والتطبيقات البيئية في العقود الماضية ، وذلك بسبب ثباتها الكيميائي العالي ، ونشاطها الضوئي الجيد ، وتكلفتها المنخفضة نسبياً ، وعدم السمية.

في عملية أكسدة التحفيز الضوئي ، يتم تكسير الملوثات العضوية في وجود محفزات ضوئية لأشباه الموصلات ، أو مصدر ضوء نشيط ، أو أكسدة مثل الأكسجين أو الهواء. فقط الفوتونات ذات الطاقات الأكبر من طاقة الإستثارة ΔE  يمكن أن تؤدي إلى إثارة إلكترونات نطاق التكافؤ التي تحفز لاحقًا للتفاعلات المحتملة.

 

التحفيز الضوئي

في الآونة الأخيرة ، استخدمت عمليات الأكسدة المتقدمة  (AOPs) باستخدام (TiO2) بنجاح لإزالة الملوثات السامة من مياه الصرف الصناعي. يحتوي TiO2 على ميزات فريدة تجعله حفاز ضوئي مميزللأسباب التالية :

  1. تفاعلية ضوئية عالية.
  2. النشاط التحفيزي العالي.
  3. منخفض التكلفة.
  4. الاستقرار في النظم المائية.
  5. سمية بيئية منخفضة.

آلية ازالة  الأصباغ عند استخدام التحفيز الضوئي كما يلي:

أكسدة التحفيز الضوئي (AOP) للقضاء على الملوثات والجراثيم المسببة للأمراض هي عبارة عن معالجة مسبقة للملوثات الخطرة وغير القابلة للتحلل البيولوجي لتحسين قدرتها على التحلل البيولوجي. يمكن أيضًا استخدام التحفيز الضوئي كخطوة تمهيدية لمعالجة المركبات العضوية. الحاجز الرئيسي لتطبيقه على نطاق واسع هو الحركية البطيئة ، وذلك بسبب محدودية انسيابية الضوء والنشاط التحفيزي.

جسيمات الذهب النانوية

يمكن أن يؤدي تعديل سطح جزيئات الذهب مع الأنواع الكيميائية المناسبة إلى تحسين كفاءة الفصل ، والانتقائية التحليلية ؛مما جعل الجسيمات  الذهب النانوية (AuNPs) ، تعتبر واحدة من الاختيارات الواسعة للموارد الأساسية المتاحة ، مقترنة بخصائص سطح قابلة للانضغاط في شكل غير عضوي أو ملغمات “عضوية-غير عضوية “، وقد وصفت بأنها ممتازة لمجموعة واسعة من التطبيقات البيئية وذلك بسبب:

  1. ارتفاع نسبة السطح / الحجم.
  2. سهولة تطوير السطح.
  3. طرق تحضير بسيطة.

تم استخدام جسيمات  الذهب النانوية بنجاح في:

  1. إزالة الببتيدات.
  2. إزالة البروتينات.
  3. إزالة أيونات المعادن الثقيلة.
  4. إزالة الهيدروكربونات العطرية متعددة الحلقات

 

جسيمات الحديد النانوية صفرية التكافؤ

تم استخدام الحديد العنصري في تقنيات معالجة مختلفة للأسباب التالية:

  1. منخفضة التكلفة،
  2. سهلة التحضير والتطبيق.
  3. لاتوجد سمية للأنظمة المائية.

تعتمد فكرة استخدام المعادن مثل الحديد كتقنية معالجة على تفاعلات الأكسدة  والأختزال، حيث يقوم مانح الإلكترون المحايد (المعدن) بتقليل مستقبِل الإلكترون (أحد الملوثات) كيميائياً. تحتوي جسيمات الحديد النانوية على مساحات سطحية أكبر من المساحيق الأكبر حجمًا ، مما يؤدي إلى تعزيز التفاعل لعملية إزالة الأكسدة.

تم فحص جسيمات الحديد النانوية على نطاق واسع للعديد من التطبيقات مثل:

  1. تحلل الهيدروكربونات المهلجنة للهيدروكربونات الحميدة.
  2. علاج المعادن الثقيلة.
  3. إزالة الكلور المذيبات

يمكن أن يحدث فقد كبير في التفاعل قبل أن تتمكن الجزيئات من الوصول إلى الملوث المستهدف. بالإضافة إلى ذلك ، تميل الجسيمات النانوية للحديد صفرية التكافؤ إلى التلبد عند إضافتها إلى الماء ، مما يؤدي إلى انخفاض في المساحة السطحية الفعالة للمعادن.ولذلك ، تعتمد فعالية المعالجة على إمكانية الوصول إلى الملوثات إلى الجسيمات النانوية ، ولن تتحقق أقصى كفاءة للعلاج إلا إذا كانت الجسيمات النانوية المعدنية يمكن أن تنتقل بفعالية دون أكسدة إلى المادة الملوثة أو السطح الملوث بالماء. وللتغلب على هذه الصعوبات ، تتمثل الإستراتيجية المستخدمة في دمج جسيمات الحديد النانوية مع مواد مثل البوليمرات ، والكربون المسامي ، والبولي إلكتروليت.

 

وأخيرًا ، تعتمد تقنية النانو المستخدمة في معالجة المياه والصرف الصحي على الخواص الفريدة للمواد النانوية ، كما أن تقاربها مع تقنيات المعالجة الحالية تقدم فرصًا كبيرة لإحداث ثورة في معالجة المياه ومعالجة مياه الصرف الصحي. أظهرت تقنية النانو إمكانية هائلة في تقنيات معالجة المياه. وقد أدى التطور الأخير في تكنولوجيا النانو إلى زيادة إمكانية التطهير البيئي من خلال العديد من المواد النانوية.

ويمكن مناقشة تطبيق آخر من المواد النانوية في مجال معالجة المياه في مقال أخرى.

 

 

References

Abhijith, K.S., and Thakur, M.S. Analytical Methods, 2012, 4, 4250–4256.

Cao, G.Z. Nanostructures and Nanomaterials, Synthesis, Properties and Application, Imperial College Press,

London, 329, 2004.

Chae, H.K., Perez, D.Y.S., Kim, J., Go, Y., Eddaoudi, M., Matzger, A.J., O’Keeffe, M., and Yaghi, O.M. A route

to high surface area, porosity and inclusion of large molecules in crystals. Nature, 2004, 427, 523–525.

Chen, L., Lou, T., Yu, C., and Kang, Q. N-1-(2-mercaptoethyl)thymine modification of gold nanoparticles: A highly selective and sensitive colorimetric chemosensor for Hg

. Analyst, 2011, 136, 4770–4773.

Chun, C.L., Penn, R.L., and Arnold, W.A. Environmental Science and Technology 2006, 40, 3299–3304.

Cloete, T.E., Kwaadsteniet, M.D., Botes, M., and Lopez-Romero, J.M., Nanotechnology in Water Treatment Applications. Caister Academic Press, Wymondham, UK, 2010.

Elimelech, M., and Phillip, W.A. The future of seawater desalination: Energy, technology, and the environment. Science, 2011, 333, 712.Eshel, K. British Medical Journal, 2007, 334, 610–616.

Furukawa, H., Cordova, K.E., O’Keeffe, M., and Yaghi, O.M. The chemistry and applications of metal-organic frameworks. Science, 2013, 341, 1230–1234.

Guzman, K.A.D., Taylor, M.R., and Banfield, J.F. Environmental Science and Technology, 2006, 40, 1401–1407.

Hang, Y., Qin, Y., and Shen, J. Separation and microcolumn preconcentration of traces of rare earth elements on nanoscale TiO2 and their determination in geological samples by ICP-AES, Journal of SeparationScience, 2003, 26, 957–960.

Harada, M. Minamata disease: Methylmercury poisoning in Japan caused by environmental pollution. Critical Reviews in Toxicology, 1995, 25, 1–24.

Hidaka, H., Jou, H., Nohara, K., and Zhao, J. Photocatalytic degradation of the hydrophobic pesticidePermethrin in fluoro surfactant/TiO2 aqueous dispersions. Chemosphere, 1992, 25, 1589–1597

ACTIVATED CARBON PRODUCTION & APPLICATIONS

ACTIVATED CARBON PRODUCTION & APPLICATIONS

What is activated Carbon?

Activated carbon is a form of carbon that has been treated to make it extremely porous and thus to have a very large surface area available for adsorption and chemical reactions. It is usually derived from charcoal (also called active carbon, activated charcoal, or activated coal).1

Importance of activated carbon:

Activated carbons are considered to be the most successful adsorbent materials due to:

  • High adsorption capacity for pollutants, e.g. dyes, heavy metals, pharmaceuticals, phenols.
  • They possess large surface area.
  • They possess different surface functional groups, which include carboxyl, carbonyl, phenol, quinone, lactone and other groups bound to the edges of the graphite-like layers.

So that, they are considered as good adsorbents both in liquid and gas phases.2

The most widely used carbonaceous resources for the manufacturing of activated carbons are coal, wood and coconut shell. These types of origins are quite expensive and often imported, in many countries; later making it necessary, for developing countries, to find a cheap and available source for the preparation of activated carbon.3

Surface area of activated carbon:

It is treated physically or chemically to generate microfissures that hugely rise its adsorptive surface area. The great surface area (between 500 and 1500 m2/g) and electrical charge successfully adsorb a wide range of polar combinations, particularly phenols and their derivatives.4

Examples of Activate Carbon Applications:

  • Drinking water purification
  • Wastewater treatment.
  • Glycerin manufacturing.
  • Dye removal
  • Decolorize wine.
  • Odor control systems.5

Deodorizing carbons are valuable in removing mercaptan off-odors, but may also remove desired flavor compounds. Activated carbon may also give the treated wine an atypical odor.6

Additionally, activated carbon has an oxidizing assets. Although this can be valuable, trials using small wine samples are vital to avoiding undesirable, unexpected effects.7

Alternative sources:

To reduce the production cost of activated carbons, some green by products are lately suggested like:8

  1. Olive-waste cakes 9
  2. Cattle-manue compost.10
  3. Bamboo materials.11
  4. Apple pulp.12
  5. Potato peel. 13
  6. Banana peel.14

Environmental pollution:

Environmental pollution can be defined as the contamination of the physical and biological components of the earth/atmosphere system to such a normal level of environmental processes are badly affected. The presence of contaminants into the environment lead to harm to humans or other living organisms.

Environmental pollution is categorized in three main groups:

  • Air pollution.
  • Water pollution.
  • Soil pollution.8

lignocellulosic bio-mass

Biomass derived from plants, called lignocellulosic bio-mass, is the richest and bio-renewable bio-mass on earth. The major components of woody plants, as well as grasses and agricultural residues are:

three structural polymers:

  • Lignin (10–25%),
  • Hemicellulose (20–30%)
  • Cellulose (40– 50%).

non-structural components such as:

  • proteins,
  • chlorophylls,
  • ash,
  • waxes,
  • tannins (in the case of wood)
  • and pectin (in most of fibers). 8

Specifically, lignocellulosic wastes are a low cost natural carbon source for the production of various materials including activated carbon.

The lignin is considered to be the main sponsor for activated carbons production, properties such as the mean pore size versus the specific porous volume are achieved by all originator’s components whatever is its weight input.

Activated Carbons Production:

The production of activated carbons from lignocellulosic materials is a two stage process:

  1. Carbonization at low temperatures (700–800 K), in the absence of oxygen, to eliminate volatile materials.
  2. Subsequent activation at higher temperatures (1100–1300 K) to increase the porosity and the surface area of the solid.8

Activation Process:

The process of activation can be carried out through different ways:

  • Chemical activation using chemicals such as (KOH, H3PO4, ZnCl2.
  • Physical / Thermal activation using CO, air or water vapor.
  • Previous two methods combined.8

Advantage of physical activation:

  • Low-cost process with a lower environmental impact.15

Advantage of chemical activation:

  • Porosity improvement (adsorption capacity) of the final material.15

Diagram for activated carbon production:

 

Source: http://www.acarbons.com/activated-carbon-manufacture-steam-activation/

Source : https://pubs.rsc.org/en/content/articlehtml/2016/gc/c6gc03206k

Source: https://rbpaonline.com/activated-carbon-process-flow-chart/high-surface-area-oxygenenriched-activated-carbon-synthesized/

Pre-treatment process of biomass should follow the following criteria: 8

  1. Low energy and resource consumption.
  2. Low water and chemical consumption.
  3. Low operation risk and safe to operate.
  4. Cost effective
  5. Eco-friendly.

Optimized manufacturing processes allow the production of materials with surface areas ranging up to 3000 m2g-1 and pore volumes of up to 1.8 cm3g-1, bringing about an immense diversity of applications.16

The challenge is to develop adsorbents which are not only cost effective and environmentally friendly, but also have high efficiency, selectivity and regeneration δ rate and cycles. 8

Factors affecting activated carbon properties:

The preparation conditions of carbonaceous materials affect the physicochemical properties of the produced material such as:

  • Surface area.
  • Pore size distribution.

Another critical factor is physicochemical properties of the origin itself; depending on:

  • Weather conditions.
  • Harvesting methods.
  • The season that it is collected.
  • Initial moisture and oxygen content.
  • Derived components fraction of cellulose, hemicellulose and lignin.8

By/ Ahmed Hasham

        M.Sc. Env. Analytical Chemistry

      Ahmedhasha83@outlook.com

        ORCID: 0000-0002-0202-6664

 

References

  • Pierson, H. O. (2012).Handbook of carbon, graphite, diamonds and fullerenes: processing, properties and applications. William Andrew.
  • Pan, B., Pan, B., Zhang, W., Lv, L., Zhang, Q., & Zheng, S. (2009). Development of polymeric and polymer-based hybrid adsorbents for pollutants removal from waters.Chemical Engineering Journal151(1-3), 19-29.
  • Emrich, W. (2013).Handbook of charcoal making: The traditional and industrial methods (Vol. 7). Springer Science & Business Media.
  • Kalderis, D., Bethanis, S., Paraskeva, P., & Diamadopoulos, E. (2008). Production of activated carbon from bagasse and rice husk by a single-stage chemical activation method at low retention times.Bioresource technology99(15), 6809-6816.
  • Hiltzik, Laurence, Edward Tolles, and David Walker. “Coated activated carbon for contaminant removal from a fluid stream.” U.S. Patent Application 10/929,845, filed February 17, 2005.
  • Bhatnagar, A., Hogland, W., Marques, M., & Sillanpää, M. (2013). An overview of the modification methods of activated carbon for its water treatment applications.Chemical Engineering Journal219, 499-511.
  • Olivares-Marín, M., Del Prete, V., Garcia-Moruno, E., Fernández-González, C., Macías-García, A., & Gómez-Serrano, V. (2009). The development of an activated carbon from cherry stones and its use in the removal of ochratoxin A from red wine.Food Control20(3), 298-303.
  • Crini, G., & Lichtfouse, E. Green Adsorbents for Pollutant Removal.
  • Baccar, R., Bouzid, J., Feki, M., & Montiel, A. (2009). Preparation of activated carbon from Tunisian olive-waste cakes and its application for adsorption of heavy metal ions.Journal of Hazardous Materials,162(2-3), 1522-1529.
  • Kosheleva, R., Mitropoulos, A. C., & Kyzas, G. Z. (2018). Activated Carbon from Food Waste. InGreen Adsorbents for Pollutant Removal (pp. 159-182). Springer, Cham.
  • Hameed, B. H., Din, A. M., & Ahmad, A. L. (2007). Adsorption of methylene blue onto bamboo-based activated carbon: kinetics and equilibrium studies.Journal of hazardous materials141(3), 819-825.
  • Srinivasakannan, C., & Bakar, M. Z. A. (2004). Production of activated carbon from rubber wood sawdust.Biomass and Bioenergy27(1), 89-96.
  • Moreno-Piraján, J. C., & Giraldo, L. (2011). Activated carbon obtained by pyrolysis of potato peel for the removal of heavy metal copper (II) from aqueous solutions.Journal of Analytical and Applied Pyrolysis90(1), 42-47.
  • Mopoung, S. (2008). Surface image of charcoal and activated charcoal from banana peel.Journal of Microscopy Society of Thailand22, 15-19.
  • Maciá-Agulló, J. A., Moore, B. C., Cazorla-Amorós, D., & Linares-Solano, A. (2004). Activation of coal tar pitch carbon fibres: Physical activation vs. chemical activation.Carbon,42(7), 1367-1370.
  • Leimkuehler, E. P. (2010).Production, characterization, and applications of activated carbon (Doctoral dissertation, University of Missouri–Columbia).

Heavy metals removal using modified leaves biomass

Heavy metals removal using modified leaves biomass

By: Ahmed Hasham

M.Sc. Env. Analytical Chemistry

Introduction:

Continuous industrial development has resulted in raised levels of toxic heavy metals. This has been entangled, almost everywhere, in most industrial applications involving leakage and redistribution of heavy metals, such as metallurgy, iron and steel, electroplating, leather working etc. Wastewater produced from these industrial activities affect the environment, the human health and ecosystem.1

The heavy metals, such as Hg, Cr, Pb, Zn, Cu, Ni, Cd, As, Co, Sn, etc. must be removed from water to avoid the harmful effect on the environment and human health.

Many methods have been applied for removing metal ions from aqueous solution generally depending on physical, chemical, and biological technologies.2

Most of these are ineffective or excessively expensive when the metal concentrations are less than 100 mg/L.

For example, some of these treatment methods will be very costly, especially when treating large amounts of wastewater, so it is became necessary to found an cheap, effective and eco- friendly method to remove heavy metals from water.4

Researches on biosorption focus on the biosorbents, the biosorption mechanism, and large-scale experiments. Although many biological materials can bind heavy metals, only those with sufficiently high metal-binding capacity and selectivity for heavy metals are suitable for use in a full-scale biosorption process. 5

 Raw leaves as Biosorbents:

Leaf adsorbents are among the most studied biosorbents for the removal of metal ions, because leaves are considered as adsorbents because it is:

  • Available,
  • Cheap
  • Eco- friendly materials
  • The high sorption capacity.6

 But, it has been often ignored because it has:

  • Low mechanical strength.

So that it must be modified to be avoid this advantage.7

What is the mechanism of metal removal using leaves?

The leaves containing functional groups such as carboxyl, amine, amide, methyl groups and hydroxyl groups which considered the major groups responsible for the biosorption process.8

The pH of the aqueous solution has been considered the most important parameter controlling the metal adsorption by adsorbents. The pH can affect the form and the quantity of metal ions in water and the form and quantity of an adsorbent’s surface sites. In general, the removal of metal cations due to the well-known competition between H ions and metal ions in the solution.9

Modified Leaf Biomass as Heavy Metal Biosorbents:

 Methods of surface modification:

 The main goal of surface modification is to improve the biosorption efficiency. The greatest valuable and widely studied surface modification of leaf biomass is the chemical modification. 10

Advantage of surface chemical modification:

  • Low cost
  • Procedure is very easy.
  • It is a one-step process in the most of the cases.

 

  • Classification of surface modification and its aims 6

 The use of each modification method aims to a specific effect like to improve the chemical surface heterogeneity, increase the number and spreading of the functional groups available for mandatory with the metal and/or alter the surface morphology; thus the useful pretreatment method should be chosen according to the targeted metal ion.11

Maximum adsorbent capacity an increased with the increase in temperature this is due to the increase in the number of available active sites on the adsorbent.12

معالجة
leafs, water, adsorption

 The most important factor affected the adsorption performance is the particle size of the biomass powder.

 Two different approaches during the developing of the raw biomass was followed:

  • To control the particle size of the biomass in a specific range by sieving. The most commonly range was between 250 and 500 μm. 13
  • The second one is to collect and use the powder of less than a specific maximum in size value. Different maximum particle sizes were reported, such as 500,180, 100, or even 80 μm.6

Regeneration of biosorbents

The reusability of biosorbents offer an economic benefit and is preferred for the practical and profitable usefulness in wastewater treatment processes. Numerous studies have been done for regeneration and reuse of modified leaf biomass after metal adsorption.8

 Desorption studies also help to control the biosorption mechanisms such as ion exchange, complexation and physisorption. The most common eluents used are diluted HCl, NaOH, HNO, and EDTA solutions, usually in concentration up to0.1 mol/L.6

The contact of biosorbents in acidic conditions due to strong desorption agents such as HCl, can affect the biomass rigidity due to biomass degradation and decrease of binding sites number.6,8

References:

 Sun, J., Ji, Y., Cai, F., & Li, J. (2012). Heavy Metal Removal Through Biosorptive Pathways. In Advances in Water Treatment and Pollution Prevention (pp. 95-145). Springer, Dordrecht. ‏

Barakat, M. A. (2011). New trends in removing heavy metals from industrial wastewater. Arabian journal of chemistry, 4(4), 361-377.‏

Fu, F., & Wang, Q. (2011). Removal of heavy metal ions from wastewaters: a review. Journal of environmental management, 92(3), 407-418.‏

Garg, V. K., Gupta, R., Kumar, R., & Gupta, R. K. (2004). Adsorption of chromium from aqueous solution on treated sawdust. Bioresource technology, 92(1), 79-81.‏

Volesky, B. (1990). Removal and recovery of heavy metals by biosorption. Biosorption of heavy metals, 7-43.‏

Kyzas, G. Z., & Kostoglou, M. (2014). Green adsorbents for wastewaters: a critical review. Materials, 7(1), 333-364.‏

Crini, G., & Lichtfouse, E. (Eds.). (2018). Green Adsorbents for Pollutant Removal: Innovative materials (Vol. 19). Springer.‏

Ngah, W. W., & Hanafiah, M. A. K. M. (2008). Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: a review. Bioresource technology, 99(10), 3935-3948.‏

Larous, S., Meniai, A. H., & Lehocine, M. B. (2005). Experimental study of the removal of copper from aqueous solutions by adsorption using sawdust. Desalination, 185(1-3), 483-490.‏

Bai, R. S., & Abraham, T. E. (2002). Studies on enhancement of Cr (VI) biosorption by chemically modified biomass of Rhizopus nigricans. Water Research, 36(5), 1224-1236.‏

Wang, J., & Chen, C. (2009). Biosorbents for heavy metals removal and their future. Biotechnology advances, 27(2), 195-226.‏

Babel, S., & Kurniawan, T. A. (2003). Low-cost adsorbents for heavy metals uptake from contaminated water: a review. Journal of hazardous materials, 97(1-3), 219-243.‏

Volesky, B. (1990). Removal and recovery of heavy metals by biosorption. Biosorption of heavy metals, 7-43.‏