Performance-evaluation of an integrated papyrus-bivalves mesocosms in cleansing aquaculture effluent
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The contribution of fish farming to people’s socioeconomic wellbeing is central for achieving sustainable development in developing countries. Nevertheless, intensive development of fish farming generates socioeconomic benefits at the expense of environmental gains, by addition of substantial residual feeds and metabolic wastes in the effluents that degrade the environment. Ecologically friendly wastewater treatment technologies can be used to improve the physicochemical quality of effluent before discharging into the environment. In this study, performance of integrated papyrus-bivalves constructed mesocosms to improve physicochemical quality of the effluent from pond fish farm, nutrients retention by Cyperus papyrus and bivalves, as well as survival rate of bivalves (Aspatharia spp.) were evaluated alongside performance of non-integrated papyrus and bivalves’ mesocosms. The results indicate that the removal efficiency of integrated papyrus-bivalves were; total-nitrogen (69.5%), ammoniumnitrogen (75.9%), nitrate-nitrogen (78.3%), total phosphorus (52.9%), ortho-phosphate (54.5%), and total dissolved Solids (70.5%). Similarly, the removal efficiency of papyrus mesocosms were; total nitrogen (56.9%), ammonium-nitrogen (72.8%), nitrate-nitrogen (65.2%), total phosphorus (49.9), ortho-phosphorus (49.4%), and total dissolved solids (53.4%); while bivalves mesocosms were; total nitrogen (45.5%), ammonium-nitrogen (54.0%), nitrite-nitrogen (57.7%), nitrate-nitrogen (50.9%), total-phosphorus (44.1%), orthophosphate (47.4%), and total dissolved solids (49.5%). The removal efficiencies varied significantly among the treatment mesocosms (p<0.001). Integrated papyrus-bivalves were the most efficient, followed by papyrus and bivalves mesocosms in reducing total nitrogen, ammonium-nitrogen, nitrate-nitrogen, nitrite-nitrogen, total dissolved solids. The removal of nutrients in papyrus and integrated papyrus-bivalves mesocosms were significantly higher than bivalves’ mesocosms. The amount of nitrogen and phosphorus retained by papyrus and bivalves in control mesocosms and integrated wetland were similar (p>0.05). However, within each treatment mesocosm, there was significantly more nitrogen than phosphorus retained by papyrus (p=0.020) and bivalves (p=0.049). Mortality rates of bivalves in integrated papyrusbivalves mesocosms were significantly lower than in bivalves’ mesocosms (p=0.042). Ultimately, survival rates of bivalves were significantly higher than mortality rates in bivalves mesocosms (p=0.005) and integrated papyrus-bivalves mesocosms (p=0.007). Thus, integrated papyrus-bivalves systems are feasible options for treating aquaculture effluent, since both bivalves and papyrus are separated by trophic level. Physical and biochemical removal mechanisms of pollutants are more effective in the integrated treatment systems.