Treatment of Wet Fish Sludge with Vermicomposting
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Aquaculture, the cultured production of fish, is growing at a rapid pace worldwide. The industry is generating approximately 140,000 cubic meter wastewater per year. For this industry to flourish, viable methods for treating the resulting waste stream must be identified. The various methods were tried by many researchers like sand filtration method, recirculating aquaculture system, intermittent filtration methods. The most of the industries use sand filtration methods for treating aquaculture wastewater and the problems associated: the reduction in hydraulic conductivity, accumulation of solid due to which anaerobic conditions developed. This study investigated possible treatment technologies for wastewater and sludge produced from Blue Ridge Aquaculture (BRA), an indoor, recirculating aquaculture facility where tilapias (Oreochromis) are raised. Research focused on the use of vermicomposting in conjunction with sand bed filtration to filter aquaculture waste and treat the resulting solids. Two experiments were conducted: a feedstock acceptability test and a filter bed test.
The feedstock acceptability test evaluated the suitability of the fish sludge (mixed with cardboard) as a feedstock for the worms involved in the vermicomposting process. The results showed that as the percentage of fish sludge in the feed increased from 0 to 50%, there was a corresponding increase in the growth rate of E.fetida biomass.
The filter bed test appraised the feasibility and effectiveness of incorporating vermicomposting in sand filter beds to directly treat aquaculture wastewater. Popular in early wastewater treatment systems, sand filtration has seen a resurgence in recent years. To test the potential for even more effective filtration, sixteen sand filter beds were established--twelve that included worms and four that did not. Wastewater (1.5 % total solids) from BRA was applied to the sand beds at loading rates of 400 to 1000 grams of volatile solids/m2/week. Filter beds containing worms exhibited no ponding over the 70-day experimental period. However, all units without worms failed (exhibited ponding) by the 24th day of operation.
Removal efficiencies obtained from the filter bed study for total solids (TS), volatile solids (VS), total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus (TP), sulfate, chlorides, and ammonia-N were greater in filter beds with worms than beds without worms. The worms were crucial to maintaining porosity in the filter beds, hence keeping the filters functioning over time. Worm filter beds removed approximately 100% of the TS, VS, TSS and Ammonia-N, 90% of the TP, 50% of the chlorides, 80% of the sulfate and 70% of the COD. Maximum hydraulic conductivity of 35 cm/day was achieved at the maximum application rate. All the worm filter beds therefore had greater hydraulic conductivity than filter beds without worms. The potential impact is to treat the wastewater effectively, to increase the flow of water, and may be to maintain the aerobic conditions on the worm filterbeds.
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