Studies on the Evaluation of Biocenosis in Sewage Oxidation Ponds for Fish Culture  

Sreenivasa V. , Prabhdevi L. , Mitiku Tesso
Department of Biology, Ambo University, PO Box No. 19, Ambo, Ethiopia
Author    Correspondence author
International Journal of Aquaculture, 2014, Vol. 4, No. 25   doi: 10.5376/ija.2014.04.0025
Received: 20 Sep., 2014    Accepted: 11 Oct., 2014    Published: 10 Dec., 2014
© 2014 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Sreenivasa et al., 2014, Studies on the Evaluation of Biocenosis in Sewage Oxidation Ponds for Fish Culture, International Journal of Aquaculture, Vol.4, No.25: 1-7 (doi: 10.5376/ija.2014.04.0025)


Studies were conducted to assess the impact of Biocenosis on water quality parameters like temperature, pH, conductivity, total alkalinity, chloride, dissolved oxygen and carbon dioxide in the sewage oxidation ponds at Ambo University campus, Ethiopia. The phytoplankton of 10 genera belonging to Chlorophyceae, Bacillariophyceae, Euglenoideae and Cyanophyceae as well as zooplankton such as rotifers, ostracods and copepods were observed. The major benthic fauna recorded were seven genera of insects and a single genus of oligochaete and nematode respectively. Three dominant bacterial genera namely Enterobacter sp, E-coli and Pseudomonas sp. were isolated from the water. In McConkey agar medium the mean density of the bacterial population was found to be 27 x103, 29 x103 and 6 x103 in the three ponds respectively. Whereas, in the Pseudomonas agar they were found to be 79x103, 74x103 and 107x103 respectively in ponds 1, 2 and 3. However, in the nutrient agar, the bacterial colonies were moderate in numbers and the mean values were 22 x103, 37 x103 and 17x103 in pond 1, 2 and 3 respectively. The results on the physico-chemical parameters indicated that the alkaline pHand high dissolved oxygen in the second and third oxidation ponds were within the permissible level for fish culture. Further, the results on the phytoplankton also revealed the high photosynthetic activity which enhances oxygen content and production of live food organisms.

Biocenosis; Enterobacter sp.; E. coli; Pseudomonas sp.

Sewage water pollution is one of the major problems faced by most cities in the developing countries creating a number of health issues as well as environmental pollution. In the developed countries domestic sewage is treated by centralized sewage treatment plants in urban areas. Whereas, constructed wet lands are widely used in developing countries in which natural, microbial, biological, physical and chemical processes are involved. This system is particularly suited for tropical and subtropical countries where high temperature and high intensity of light promotes the efficiency of the removal of waste components in the water (Mara et al., 1992). In this system the algal diversity increases from pond to pond along the series. The presence of the microorganisms is essential in the biological wastewater treatment systems where the organic matter is degraded by a variety of microorganisms such as bacteria, algae, protozoa and rotifers. The growth of algae helps in the removal of pathogens and faecal coliforms in synergy with photo-oxidation (Curtis, 1994). Twenty-five species of bacteria including coliforms are used as water quality indicators for drinking and bathing purpose (Klein and Casida, 1967) Aeromonas sp, Enterobacter sp, Escherichia sp, Flavobacteriumsp, and Pseudomonas sp. were identified with the fish culture systems in Ghana (Ampofo and Clerk, 2003).
During the course of sewage purification a characteristic succession of biocenosis is observed in the stabilization ponds. The microscopic flora and fauna; bacteria, protozoa and algae in the ponds are important in waste decomposition (Goulden, 1976; Task Force on Natural Systems, 1990). Sewage induces fluctuations on physico-chemical characteristics of the water and influence the phytoplankton dynamics (Liao and Lean, 1978; Wetzel, 1983; Figueredo and Giani, 2001). Anneville et al. (2004) reported that the sedimentation, grazing pressure, light, CO2 and nutrient concentration act as forces responsible for the species composition of phytoplankton. Munawar (1972 a & b) emphasized that the euglenoids are the best indicators of organic pollution.The most common bacterial pathogens in sewage are Escherichia coli, Salmonella sp, Shigella sp, and
Campylobacter sp.(Gerba, 1983; El-Motaium et al., 2000). There is an inverse relationship between flagellates and ciliateswithin activated sludge. A large population of flagellates in the ponds indicate an overload of sludge while the presence ofciliates shows that the treatment system is functioning properly. The invertebrate fauna which depends on the plankton as food in sewage treatment ponds attract wildlife. More number of invertebrate species in sewage ponds is associated with high algal productivity (Wallace and Merritt, 1980; Richardson, 1984). In certain systems abundance of invertebrates has also been attributed to paucity of insect predators (Brightman and Fox, 1976; Williams, 1985; Dodson, 1987). However, the sewage water drained into rivers without treatment in many developing countries leads to spreading of diseases, increase in biological oxygen demand and eutrophication (Dicicco, 1979; Sahset et al., 2006) resulting in unsuitable habitat for the inhabitants (Reynolds, 1997; Calijuri et al., 2002).
Aquatic macrophytes grown on sewage ponds act as bio-filters, removes pollutants like nitrogen, phosphorus, pesticides, phenols and heavy metals, thereby improving the quality of the water. The presence of water plants like Eichhornia crassipes, Alternantheraphyloxiroides, Pistia stratiotes etc. can bring changes in the nutrient dynamics significantly by hampering algal photosynthesis resulting in reduced dissolved oxygen. However, this condition favors the release of nitrogen and phosphorous from sediments which may further aid the rapid growth of macrophytes (Gutierrez et al., 2001; Masifwa et al., 2001; Scheer et al., 2003).
Aquaculture in waste water is one possible means of water renovation, environmental protection and food production, which has been practiced in some countries for a long time (Allen and Hepher, 1976; Gaigher, 1983). Pillay (1973) also emphasized the use of domestic waste water for highly profitable fish culture. The yield of fish from the sewage effluent fed ponds was reported to be higher than culturing in freshwater (Sharma, 1983; Solamalai et al., 2003). A wide variety of fish have been cultured in sewage treated ponds including carps, tilapia (Oreochromis spp.), milkfish (Chanos chanos), catfish (Pangasius spp.) and barbs (Puntius gonionotus). Okoye et al. (1986) reported that the stocking of common carp (Cyprinus carpio) and tilapia (Sarotherodon galilaeus) in sewage fed ponds resulted good production in New Bussa, Nigeria. Edwards (1990) reviewed the practice of fish culture in sewerage ponds where the aquatic macrophytes serve as food for herbivorous fishes. Considering the above findings the present study was undertaken to evaluate the physico-chemical parameters and the biocenosis of water in the sewage treatment ponds at Ambo university campus for fish culture.
1 Materials and Methods
There are seven sewage treatment ponds present in the Ambo University campus from which three oxidation ponds were selected for the present study. The ponds are constructed with stone pavement on the sides and interconnected by filter gates. One of the oxidation pond’s surface was covered by the water hyacinth, Eichhornia crassipes.
Water samples from the oxidation ponds were collected on three consecutive weeks for determination of physico-chemical parameters such as temperature, pH, conductivity, alkalinity, chloride, dissolved oxygen, and carbon dioxide. The surface temperature, pH and conductivity were measured using digital probes at the site. Dissolved oxygen, carbon dioxide, alkalinity and chloride contents were estimated in the laboratory by following standard methods (Strickland and Parsons, 1972; APHA, 1998). Plankton samples were collected using a plankton net made of No.20 bolting silk. The samples were fixed in Lugol’s Iodine for identification and enumeration of phytoplankton and zooplankton (Edmondson, 1959). The benthic macrofauna were collected, identified and counted. Total heterotrophic bacteria and certain pathogenic bacteria were enumerated using different selective media, isolated and identified by following the method described in FDA BAM (1998).
2 Results and Discussion
2.1 Physico-chemical parameters
Temperature is one of the most important ecological factors which control behavioral characteristics of organisms, solubility of gases and minerals in water. The water temperature in the ponds varied from 18 to 22° C (Table 1). The average temperature in the oxidation ponds 1, 2 and 3 were 18.33° C and 20.5° C and 21.83° C respectively. The reduction in temperature in the first pond may be related to excessive growth of plants which prevent the light penetration into the water column. Whereas, the other pond surfaces were free from macrophytes so that light rays can reach the bottom and increase the water temperature. Aquatic organisms are sensitive to changes in pH hence it is necessary to control or monitor its level in the biological treatment of sewage (Jeffrey et al., 1998). The pH values in all the three ponds varied between 6 and 8. The observed values are within the permissible limits for the culture of freshwater fish (Boyd, 1998; Dutta et al., 2010). This variation may be due to the oxidative processes with the aid of photosynthetic plankton in the water. The dissolved oxygen was found to be very low or below detectable level in pond 1 where the water surface is covered with Eichhornia plants.The plant cover prevents the dissolution of atmospheric oxygen and hence aerobic decomposition of organic matter results in depletion of oxygen in the water. In pond 2 and 3, the average values were 5.66 mg/l and 5.61 mg/l respectively. The slightly higher dissolved oxygen (DO) 5.7 mg/l was recorded in the oxidation pond 2 which could be due to photosynthetic activity of the large population of phytoplankton as stated by Nandini (1999). The photosynthetic activity in such ponds may be intensified by the availability of light and increased temperature (Meijun Chen et al.,2011). The amount of carbon dioxide varied from 0.9 mg/l to 4.4 mg/l in sewage ponds. The highest CO2 level was noticed in the oxidation pond 1. There was a gradual decline in CO2 from pond 1 to 3. In the absence of DO in pond 1, the decomposition of organic matter through anaerobic process results in the accumulation of CO2. Whereas, in the other ponds which are exposed to sunlight the carbon dioxide evolved during decomposition are used up by phytoplankton for photosynthesis during the day time as mentioned by Sreenivasan (1980).

Table 1 Physico-chemical parameters of the water

The condutivity in all the three ponds varied from 1134 to 1423
µS/cm. The maximum conductivity was observed in the oxidation pond 2 and minimum in pond 1. In general the values declined in the third week associated with the variation in the ionic composition of the water. Ions that determine the conductivity are hydrogen, hydroxyl ions and nutrients such as phosphate and nitrate (Dusan et al., 1994). The main process that reduces conductivity in wastewater treatment is nutrient removal (Aguado et al., 2006; Maurer and Gujer, 1995) through biofiltration by the plants. The plants in the pond 1 utilize the nutrients, phosphates and nitrate, along with many elements required for their growth in large amount than the phytoplankton and the bacteria.
The amount of chloride in pond 3 was greater (163.07 mg/l) than the other oxidation ponds. In the first oxidation pond the chloride was comparatively less and it was reduced at the end of the observation. Earlier studies have indicated that the chloride values tend to fluctuate between 49 -315 ppm (Solamalai et al., 2003) in the treatment ponds. Hence the observed level of chloride was within the permissible limit for the culture of fish. The alkalinity of the water in the ponds varied from 200 mg/l – 300 mg/l however, in pond 3 the variation was negligible. According to Solamalai et al. (2003) in the domestic sewage the alkalinity values vary from 180 - 300 ppm and it depends on various climate, composition, and treatment conditions. The high alkalinity values indicates the rate of biogeochemical process, anaerobic mineralization of organic matter and photosynthesis that is happening in the water in the epilimnion, as well as the NH4 and NO3 assimilation (Carmouze, 1986; Ahamad et al., 2011). According to Alikunhi (1957) water with alkalinity greater than 100 mg/l is productive and the observed alkalinity values in the ponds were within limit prescribed for fresh water fish culture in sewage treatment ponds.
2.2 Zooplankton
In the present study four groups of zooplankton such as, copepoda, rotifera, ostracoda and cladocera were observed (Table 2).

Table 2 Zooplankton in the treatment ponds

The copepods and their larval stages constituted a predominant group in oxidation pond 1 and 3.
Ahamad et al. (2011) reported that rotifers, cladocerans, copepods and ostracods constitute the major zooplankton population in the sewage fed fish ponds and contributed significantly to secondary production of the ponds. In oxidation pond 1, the copepods and their naupli were numerically dominant along with the rotifers, Brachionus rubens and B. plicatilis. The rotifera represented by four genera were more abundant in oxidation ponds 2 and 3. In pond 2 the rotifers especially Asplanchna sp. followed by B. rubens, B. plicatilis and B. calyciflorus dominated and the number of copepods and Daphnia were moderate. In pond 3, the number of the ostracod, Eucypris pigra and the rotifer Asplanchna sp. were very high followed by copepoda, naupli and cladocera. In general, the number and species of zooplankton were higher in pond 2 and 3 than pond 1. However, the rotifers were minimum in pond 1 than 2 and 3 (Table 2). Earlier studies revealed that a few genera of rotifers and Ostracoda are capable of withstanding anaerobic conditions for at least short period (Kownacki, 1977; Pennak, 1989). The present study also indicated higher population density of crustacean genera in the pond 3 where oxygen level was more than the other ponds. The present results are in conformity with the statement of Cauchie et al. (2000) that the planktonic community in the stabilization ponds was composed of the branchiopods and the cyclopoid copepods.
2.3 Phytoplankton
Phytoplankton population in the sewage oxidation ponds belonged to the division Chlorophyceae, Cyanophyceae, Bacillariophyceae and Euglenophyceae (Table 3). The members of theBacillariophyceae represented with more number of genus (4) than the other groups. The greater abundance of phytoplankton was noticed in the oxidation pond 2. In pond 1 the number of species and their numerical density was comparatively lower and only Pondorina, Coelastrum and Staroneis were found in small numbers. However, Euglena and Phacus occurred throughout the study period. In general the phytoplankton population was minimum in this pond due to the complete masking of sunlight by the Eichhornia plants. In pond 3 the number of Euglena and Phacus was very high along with the diatoms, Cyclotella, Fragilaria and Navicula.

Table 3 Phytoplankton in the sewage pond

The green algae constituted an important group among the phytoplankton in the treatment ponds. Graham and Wilcox (2000) stated that green algae seemed to be favored by high level of nutrients, their structural and physiological adaptations such as small size, deformed shapes, and formation of mucilaginous colonies which reduce loss due to sedimentation and/or grazing by zooplankton.
The genus Pandorina was dominant among the Chlorophytes in pond 2 while the genus Euglena was high in ponds 2 & 3. This observation is in conformity with those of Silva (1998) and Pereira et al. (2001). Cyanobacteria have been reported to dominate in some maturation and stabilization ponds during high temperature periods (Pereira et al., 2001). In the present study the genus Oscillatoria was found in the oxidation ponds 2 and 3. Athayde et al. (2000) stated that the micro-algae are an important part of wastewater treatment as suppliers of oxygen in the water to augment the rate of biochemical oxidation of the organic matter. In the present study the occurrence of many species of phytoplankton indicates the existence of aerobic conditions which is essential for the fish culture.
2.4 Benthic fauna
A number of organisms were collected from the bottom sediment and on the delicate branches of the roots of the Eichhornia plant. These macro-organisms include mainly aquatic and terrestrial insects, their larval stages, oligochaetes and nematodes (Table 4). The nematode, Rhabditis sp. was recorded from the first pond only. The Tubifex sp. was more common and abundant in pond 1 and 2. The larvae of Chironomus and mosquitoes were found to be higher in pond 2. The Hemipteran bugs were found densely in ponds 1 and 3. The snipe fly larvae was more common in pond 2. In the oxidation pond 1, the larva of caddis fly and dragon fly were more in numbers when compared to other ponds. The abundance of species in oxidation ponds might be due to their high level of tolerance to organic pollution and low oxygen tension in the water (Moyo, 1997). The larvae of Chironomus and Tubifex were more on the root tips than the other invertebrate species. According to Wallace and Merritt (1980) some species of benthos were found in high number when algal productivity was maximum.The present findings are in conformity with the studies of Olive and Dambach (1973), Brightman and Fox (1976) and Kondratieff et al. (1984) that benthic invertebrates were concentrated in areas in the streams and wetlands receiving organic waste. Dehghani et al. (2007) also observed that sewage maturation ponds are appropriate for the growth and development of aquatic insects especially species of Diptera and Hemiptera.

Table 4 Benthic faunal assemblage in oxidation ponds

2.5 Total bacterial population
The population density of bacteria in the water of the sewage pond cultured on various media are presented in Table 5. The highest population was noticed in water samples cultured with Pseudomonas agar in the ponds. The highest mean density was 79 x103, 74x103 and 107x103 respectively in ponds 1, 2 and 3. In the McConkey agar medium the bacterial counts were low and the mean value being 27 x103, 29 x103 and 6 x103 in ponds 1, 2 and 3 respectively. In the nutrient agar the bacterial colonies were moderate in number and the mean values were 22 x103, 37 x103 and 17x103 in pond 1, 2 and 3 respectively. There was a decline in the bacterial population in pond 3. The present results are in conformity with the results of Rajasekaran (2008). The results indicated the presence of E.coli, Enterobacter sp. and Pseudomonas sp. in the ponds. According to Mara et al. (1992) the reduction in pathogens and faecal coli forms in oxidation ponds are influenced by algal activity or exposure to ultraviolet radiation.

Table 5 Bacterial number (CFU/ml) in oxidation ponds

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