Improvement of nitrification in winter using dewatering water

Abstract

The reject water from the bioreactor of a domestic sewage treatment plant consists of supernatants of the anaerobic digestion tank and sludge thickener and dewatering water, which account for about 1–3% of the wastewater influent flow rate. Among these, dewatering water is very beneficial as it makes nitrification bacteria the dominant micro-organisms due to their higher nitrogen concentration and alkalinity, and their lower suspended solid, compared to those of the digester supernatant. This study was designed to improve the efficiency of nitrification in winter. Toward this end, the number of nitrifying micro-organisms was increased using dewatering water in the nitrification tank, and then they were introduced into the aeration tank to investigate the nitrification trends before and after the introduction. A comparative experiment was conducted at 12.5°C with an aeration tank having a capacity of 20 m3/d. The results showed average NH4+–N concentrations of the treated water of 8.5 and 18.4 mg/L in the pilot plant and the sewage treatment plant, respectively, and average NO3−–N concentrations of the treated water were 24.3 and 6.0 mg/L, respectively, which revealed nitrification improvement with the injection of dewatering water. The results of the microbiological analysis showed 3.27% total nitrification bacteria in the aeration tank of the pilot plant and 1.28% in that of the wastewater treatment plant, which indicate that the winter nitrification improved in the pilot plant.