Phosphorus Removal and Greenhouse Gas N2O Emission in a Lime-Induced Aerobic Sludge Granule Process

Abstract

Aerobic sludge granulation was achieved in an activated sludge process continuously fed with lime (Ca2+ 100 mg l−1 influent) every other day. Eighteen days after lime addition, activated sludge granules with the size of 0.5-2.2 mm were formed, which occupied 10-25% of total sludge volume. Sludge volume index (SVI) was reduced to an average of 50 ml g−1, which increased average sludge concentration to 3.6-5.0 gVSSl−1, 1.6-2.1 times of that of control. Greenhouse gas N2O emission was also significantly reduced: N2O concentration from the lime-addition reactor was 5-15 ppmv, 47-61% of that of control. Effluent PO4-P concentration was generally lower than 1 mgl−1 when average influent PO4-P concentration was 6.07-6.37 mgl−1. Total phosphorus (TP) and total nitrogen (TN) removal efficiencies were around 89.6% and 14.5-16.1%, over 3.5 and 1 times higher than those of control, respectively. COD removal rate in the lime-addition reactor was 2.05-2.48 kgCODm−3 d−1, higher than 1.34-1.61kgCOD m−3 d−1 in the control.