Formation and performance of partial nitrification granular sludge treating domestic sewage

Abstract

Partial nitrification granular sludge (PNGS) treating domestic sewage was successfully cultivated in a sequencing batch reactor through shortening settling time gradually based on total suspended solids in the effluent. The granulation process contained the washout of a part of flocculent sludge, the gathering of the remaining flocculent sludge, and the growth of granules. Depending on the measurement of extracellular polymer substance (EPS), including polysaccharide (PS) and protein during different periods, it was concluded that EPS was the key factor for PNGS formation and PS was the main component of EPS in the PNGS biomass. PS was mainly from the secretion of heterotrophic bacteria during endogenous respiration period. The treatment ability of PNGS was improved effectively by high ammonia concentration in a short time (18 d), and then, PNGS achieved an efficient and stable partial nitrification for domestic sewage at 20°C. The ammonia removal rate reached 0.7 kg N m−3 d−1, and the nitrite accumulation rate was maintained above 95%. The granule structure improved the partial nitrification process, mainly due to the low DO concentration in the inner layer of the granules surface and the large amount of aeration in the bulk liquid.