Abstract

Removal of phosphate and nitrate from the effluent of a fish farm with a recirculation system was tested in a sequencing moving bed biofilm bioreactor (SMBBR) over a 160-day period. This bioprocess made use of a stock tank (ST) that allowed the same volume of anaerobic water to be reused from one batch to another. Water from the ST contained an excess of a carbon source (acetate), which made it possible to alternate between anaerobic (1.5 h) and aerobic/anoxic (4 h) conditions to achieve enhanced biological phosphorus removal (EBPR). The developed biomass (2,072 mg total solids m-2 d-1 and 892 mg total volatile solids m-2 d-1 ) removed 7.5 mg of PO4-P per litre and 8.5 mg of NO3-N per litre from an influent containing 10 mg of PO4-P per litre and 21 mg NO3-N per litre. The dynamic variation of phosphate and chemical oxygen demand (COD) in the influent showed that the biomass was sensitive to the CODavailable/Pinfluent ratio. A ratio of 10 to 15 mg of COD per milligram of P seemed to favour phosphorus accumulating organisms (PAOs). Differences between the nitrate, phosphate, and oxygen reduction kinetics suggested that the denitrification could be attributed to organisms other than PAOs. The SMBBR-ST showed potential for EBPR and for denitrification as well. However, the economic feasibility of implementing such a process in a full-scale operation remains to be demonstrated.

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