A pilot-scale study on the partial nitritation-anammox process for treatment of anaerobic sludge digester effluent

Abstract

The treatment of the sludge digester effluent taken from a full-scale municipal wastewater treatment plant (WWTP), in Istanbul, Turkey using a pilot-scale partial nitritation (PN)/anammox (A) reactor was examined and maximum nitrogen removal rate (NRR) of 0.65 kg N/m3/d was achieved in this study. The PN, which was carried out in a continuously stirred tank reactor, successfully converted 56.4±4.8% of NH4+-N to NO2–-N. The effluent NO3–-N concentration kept below 1 mg/L with 0.4–0.8 mg/L of dissolved oxygen (DO) and pH of 7.2±0.1 at 25±3.3°C. Partially nitrified sludge digester effluent was further treated in a continuously stirred tank (CSTAn) anammox reactor, where high ammonium removal efficiency (ARE) achieved with a NO2–-N:NH4+-N and NO3–-N:NH4+-N ratios of 1.28±0.06:1 and 0.29±0.07:1, respectively. The results show that ARE up to 94±0.05% and total nitrogen removal of 75.6±12.6% were achieved. This study also illustrated that in CSTAn reactor, better NRR achieved when pH and DO were 7.72±0.04; 0.02±0.02 mg/L, respectively. However, the NRR was tending to rise below 10 mg/L of NO2–-N. The biomass concentration in the CSTAn reactor was 1075±330 g VSS/L with the SAA 0.38±0.06 kgN/kgVSS/d in the whole study. The anammox activity increased exponentially and correlated with the observed growth in volatile suspended solids.