DEVELOPMENT OF A 2-SLUDGE, 3-STAGE SYSTEM FOR NITROGEN AND PHOSPHORUS REMOVAL FROM HIGH-STRENGTH WASTEWATER USING GRANULAR SLUDGE AND BIOFILMS

A novel 2-sludge 3-stage process using a combination of granular sludge and biofilms was developed to achieve biological removal of nitrogen and phosphorus from high-strength industrial wastewater. The system consists of a granular sequencing batch reactor (SBR) working under alternating anaerobic/anoxic/aerobic conditions and an aerobic biofilm SBR. The wastewater is first fed to the granular SBR, where easily biodegradable carbon is taken up primarily by polyphosphate accumulating organisms. The supernatant resulting from a quick settling of the granular sludge is then fed to the biofilm SBR for nitrification, which produces oxidised nitrogen that is returned to the granular reactor for simultaneous nitrate and phosphorus removal. While maximising the utilization of organic substrate and reducing operational costs, as do other 2-sludge processes previously reported in literature, the proposed system solves the bottleneck problem of traditional two-sludge systems, namely high effluent ammonia concentration, due to its high volume exchanged ratios. An ammonia oxidation rate of 32mgN/L.h was achieved in the biofilm SBR, which produced nitrite as the final product. To avoid P-uptake inhibition by nitrite, the nitrite-containing stream was continuously fed to the granular reactor in the anoxic phase. The system currently achieves a nitrogen and phosphorus removal efficiency of 85% and 50%, respectively. The effluent is suitable for land application or for discharge to domestic wastewater treatment plants.