Use of UASB reactors for brackish aquaculture sludge digestion under different conditions

Treatment and disposal of high volume of salty waste production in recirculating aquaculture systems (RASs) is a major challenge and the sludge is often a source of environmental pollution and salinization of receiving soils and water bodies. Anaerobic digestion is an efficient mean for the treatment of wastes of different origins and might serve a useful tool for the reduction of salty aquaculture discharge load. Use of an upflow anaerobic sludge blanket (UASB) reactor for digestion of brackish aquaculture sludge from RASs under different C:N ratios, temperatures, and hydraulic retention times demonstrated high removal efficiencies of over 92% as volatile solids (VS), 98% as chemical oxygen demand and 81% as total suspended solids in all reactors. Methane production topped 7.1 mL/gVS d and was limited by low C:N ratio but was not influenced by temperature fluctuations. The treated liquid effluent from all reactors was of sufficient quality for reuse in the RAS, leading to significant water recycling and saving rates. UASB may be an attractive solution for brackish sludge management in RASs.

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► UASB reduced >90% solids of saline aquaculture sludge @ 6 d HRT under ambient conditions.
► Low biogas production was observed most likely because of low C:N (∼15) ratio.
► Sludge removal & water reuse uncouple dependency between aquaculture &water bodies.