Oxidation ponds for municipal wastewater treatment

By:Dr. Mohamed Elsofy Zain Elabedien Ezz Eldien

Microbiology Lab Manger – Reference Lab of Waste Water (RLWW) Holding Company for Water and Wastewater (HCWW)

Introduction:

Oxidation ponds are known as stabilization ponds which provide greater advantages in treatment over mechanically based units. Ponds can be described as self-sufficient treatment units, because the efficacy of treatment is contingent upon the maintenance of the overall microbial communities of bacteria, viruses, fungi, protozoa, and the proper balance of organics such as (light, dissolved oxygen, nutrients, algal presence and temperature) (Amengual-Morro et al., 2012). Ponds are self-sufficient; there is a reduction of operator responsibilities to manage treatment, reduction in labor costs, and increase in the potential fiscal returns from the tangible products generated by the treatment unit (Hosetti and Frost 1998).

Subject:

Ponds can be used for the purpose of ‘polishing,’ or providing additional treatment to what has been found within conventional treatment methods (Veeresh et al.,2010). Ponds simplify the treatment process by reducing the need for multiple treatment units. So oxidation ponds are a treatment processes that can be used in regions where treating of wastewater using conventional treatment methods are expensive. Indeed, oxidation ponds are commonly used in many regions around the world, specifically in places with year-round mild to warm climates.

Types of oxidation ponds:

There are four major types of oxidation ponds: aerobic (high-rate), anaerobic, facultative, and maturation ponds.

1- Aerobic (high-rate) ponds:

Aerobic ponds are known as high-rate algal ponds that maintain dissolved oxygen throughout a depth of 30–45 cm because of algal photosynthetic activity. Photosynthetic activity supplies oxygen during the day, while at night the wind creates aeration due to the shallow depth of the pond (Davis and Cornwell, 2008).

Aerobic ponds are well known for having high biochemical oxygen demand (BOD) removal potential and are ideal for areas where the cost of land is not expensive. Other characteristics of these ponds include a detention time of 2–6 days and a BOD removal efficiency reach to 95 %.

2- Anaerobic ponds:

Anaerobic ponds operate without the presence of dissolved oxygen, the major products are carbon dioxide and methane (Quiroga, 2011), Typically, these ponds are designed to have a depth of 2–5 m, with a detention time between 1 and 1.5 days, an optimum pH less than 6.2, temperatures greater than 15ºC (Kayombo et al., 2010).

Anaerobic ponds can remove 60 % BOD. However, this efficiency is climate dependent, the driving force behind treatment is sedimentation where Helminthes settle to the bottom of the pond, and bacteria and viruses are removed by attaching to settling solids within the pond or die with the loss of available food or by the presence of predators. In practice, anaerobic ponds are usually incorporated alongside facultative ponds (Martinez et al., 2014).

3- Facultative ponds:

A facultative pond is a treatment unit with anaerobic and aerobic conditions. A typical pond is divided into an aerobic surface region consisting of bacteria and algae. Anaerobic bottom region, consisting of anaerobic bacteria, and a region in between anaerobic and aerobic conditions, where bacteria can thrive in both conditions, if used in series, effluent from a previously treated source enters the pond. Facultative ponds treat BOD, typically within a range of 100–400 kg BOD/ha/day, by removing BOD by 95 %. Because facultative ponds employ algae as decomposers, the treatment time can range between 2 and 3 weeks, which are attributed to the photosynthetic processes that occur within the unit. A facultative pond on average has a depth of 1–2 m.

4-Maturation ponds:

Similar to facultative ponds, maturation ponds use algae as a primary driving force in the treatment. Nevertheless, while facultative ponds typically treat BOD, maturation ponds remove fecal coliform, pathogens, and nutrients (Cinara, 2004). In comparison with the other pond types, the characteristics of the maturation pond include a depth range between 1 and 1.15 m, which makes it shallower than all of the ponds besides the aerobic.

Arrangement of ponds:

There are two arrangements for a multiple pond system; series and/ or parallel. In the series arrangement, wastewater is treated in the initial and subsequent ponds and then polished in the final pond; while wastewater flow is evenly divided in the parallel pond arrangement each multiple pond arrangement has its benefits and therefore an operator can change the pond arrangement depending on the situation. For example, ponds operating in parallel prevent interruption of treatment during the cooler months of the year. This is when a pond can experience low biological activity. Low biological activity can create anaerobic conditions within a pond. In addition, the application of ponds in parallel can reduce problems related to periodic low dissolved oxygen concentrations, particularly in the morning hours, On the other hand, ponds in series are ideal during the summer months and also during periods of low biological loading, Nevertheless, the choice of applying multiple ponds can be beneficial for treatment as compared to a single pond arrangement.

Design factors:

Understanding design factors is important in controlling pollutants such as BOD5. There are many factors that affect the efficiency of BOD5 removal in waste stabilization ponds. These factors include raw wastewater strength, food-to-microorganism ratio (F/M), organic loading rates, pH, and hydraulic detention time (HRT).

We will explain in detail these factors in the next issue.

 

References:

Amengual-Morro C, Moya Niell G, Martinez-Taberner A (2012) Phytoplankton as bioindicator for waste stabilization ponds. J Environ Manag 95:S71–S76.

Hosetti B, Frost S (1998) A review of the control of biological waste treatment in stabilization ponds. Crit Rev Environ Sci Techno l28:193–218.

Veeresh M, Veeresh AV, Huddar BD, Hosetti BB (2010) Dynamics of industrial waste stabilization pond treatment process. Environ Monit Assess 169:55–65.

Quiroga FJ (2011) Waste stabilization ponds for waste water treatment, anaerobic pond.

Kayombo S, Mbwette TSA, Katima JHY, Ladegaard N, Jorgensen SE (2010) Waste stabilization ponds and constructed wetland design manual. UNEP International Environmental Technology Center..

Martinez FC, Cansino AT, Garcia MAA, Kalashnikov V, Rojas RL (2014) Mathematical analysis for the optimization of a design in a facultative pond: indicator organism and organic matter. Math Probl Eng 1–12.

Cinara Columbia (2004). Waste stabilization ponds for wastewater treatment: FAQ sheet on waste stabilization ponds.

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.