Biological nitrogen and phosphorus removal in an anaerobic/anoxic sequencing batch reactor with separated biofilm nitrification

Abstract

An Anaerobic/Anoxic Sequencing Batch Reactor (A/A SBR) with separated batch biofilm nitrification was tested for nutrient removal against a five step Anaerobic-anoxic/Oxic SBR (A/O SBR). Piggery wastewater, particularly challenging for its low COD/N ratio, was used as feed. After feeding, the A/A SBR ran under anaerobic conditions for organic carbon sequestering and phosphorus removal. A settling phase was allowed to separate an ammonia-rich supernatant to be nitrified in a external biofilm reactor. The nitrified effluent returned to the A/A SBR where nitrates were removed, being used as final electron acceptors for luxury P-uptake and organic carbon oxidation. A/A SBR showed very good N and P removal capacities with excellent sludge settling properties. On the other hand, organic carbon removal efficiency with nitrate was lower than with oxygen. Batch biofilm nitrification was very effective, with very high nitrification rates. Presence of poly-P bacteria in the A/A SBR sludge was assessed through microscopic observation and from the high cellular poly-phosphate content.