Performance of spirodela polyrhiza, salvinia molesta and lemna sp. In phytoremediation of fish farm wastewater
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Date
2018-04-01
Authors
Ng Yin Sim
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Abstract
Fish farm wastewater is high in dissolved nutrients and suspended solids due to accumulation of uneaten feed and fish excretions. Sedimentation reduces suspended solids but not efficient in removing dissolved nutrients while advanced treatment suffers from high cost and huge energy demand. Phytoremediation using macrophytes could solve these issues owing to low maintenance cost and significant nutrients removal. Therefore, this study intended to show the true nutrients removal capabilities of macrophytes under axenic condition and to evaluate the treatment performance of macrophytes on fish farm wastewater. In this regard, Spirodela polyrhiza, Salvinia molesta and Lemna sp. macrophytes were assessed axenically in synthetic wastewater. The ammonia removal was rapid for S. polyrhiza and Lemna sp., with 60% and 41% removal efficiency respectively within 2 days. S. polyrhiza could reduce 30% of the nitrate while Lemna sp. achieved the highest phosphate reduction, of 86% at day 12. The acquired profiles allow selection of suitable macrophytes in fish farm wastewater treatment. S. polyrhiza and Lemna sp. were chosen to treat raw fish farm wastewater via raceway pond rig (in monoculture and polyculture system). The wastewater was sourced from a local catfish farm, of ammonia, phosphate, TSS and COD levels up to 28.10 mg NH3-N/L, 5.80 mg PO43-/L, 175 mg/L and 322 mg/L respectively. The raceway pond had dimensions of 50cm x 25cm x 9 cm and the system could hold 12 L wastewater. S. polyrhiza monoculture system surpassed other systems in nitrogen and phosphorus removal where 81% ammonia was reduced to 3.90 mg NH3-N/L in 2 days whilst the nitrate, nitrite and phosphate levels were significantly lowered. It was attributed to its high uptake capabilities of various nitrogen species and phosphate. Steep decline of TSS, turbidity and COD levels (up to 75%, 88% and 71% in 2 days) were recorded. All macrophyte systems demonstrated high biomass productivity (up to 112% increment) and superiority in protein content (up to 12% increment). The effect of fed batch and periodic harvesting on treatment capacity and performance of S. polyrhiza monoculture system were also evaluated. The system with fed batch and harvesting could treat more volume of wastewater, remove higher amount of pollutants while meeting effluent limits. This study suggested that S. polyrhiza monoculture system with fed batch and optimal harvesting is feasible and effective in treating fish farm wastewater and produces useful biomass for various applications such as fish feed supplement, poultry diet, fertiliser and biofuel.