Effect of salinity towards phytoremediation of synthetic fish farm wastewater by lemna minor

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Date
2019-06
Authors
Kethis A/L Selvabala
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Abstract
Phytoremediation has the potential for treatment and reuse of wastewater in intensive aquaculture systems. This technique serves the purpose of reducing the pollution caused by fish farming which will preserve the surface and ground water quality. In this study, the response of duckweed Lemna minor (L.minor) to salinity was evaluated by monitoring nutrient removal efficiency, water quality and the biochemical composition of the macrophytes after phytoremediation. The synthetic fish farm wastewater was supplemented with certain concentrations of NaCl such as 2.2 ppt, 5.0 ppt, 7.5 ppt, 10.0 ppt and 12.5 ppt. Growth decreased with increasing concentrations of NaCl. The lower concentrations of NaCl (2.2 ppt, 5.0 ppt and 7.5 ppt) saw the macrophytes growing healthily while the higher concentrations (10.0 ppt and 12.5 ppt) still showed positive growth eventhough there was growth reduction. Nitrate uptake by L.minor was relatively low under all salinity levels due to the uptake preference of ammonia by the macrophytes. Ammonia and phosphate uptake was rapid for all concentrations of NaCl but the macrophytes at lower salinities had greater removal efficiencies than at higher salinities. In terms of the chemical oxygen demand, the lower concentrations of NaCl exhibited far better removal efficiencies than at higher salinities. The carbohydrate content of the macrophytes at the end of the experiment increased with increasing salinity whereas there was decreasing protein content with increasing salinity levels. Overall, the results presented in this study confirm that L.minor is sensitive to salinity but also has the ability for adaptation because it continued to grow in spite of exposure to NaCl.
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