Effect of C/N and Sludge Concentration on the pH-Regulated Nitrosation System

Abstract

pH is one of the most important means of control for the realization and stability of the nitrosation system. To study the change rule of pH values of the nitrosation system and the influence of pollution removal and transformation at different pH under the conditions of different C/N (0, 1, 2, 3,4) and sludge concentrations (sludge amount:water content was 1:6, 1:3, 1:1), batch tests were conducted with tapered bottles using sodium acetate as the carbon source and inoculated with mature nitrosation sludge. The results showed that the higher the C/N, the higher the pH increment and the denitrification efficiency at the same sludge concentration. At the same C/N, a higher sludge concentration corresponded to a smaller pH increment but a higher denitrification efficiency. The removal and transformation of carbon and nitrogen was highly correlated with pH changes in the reaction system, and the denitrification and nitrosation reactions were in sequence. Throughout the operational period of the system, as pH increased, the specific organic matter removal rate was 7-16 times as much as when pH decreased. However, as pH decreased, the specific ammonia oxidation rate (SAOR) was 1-20 times that of when pH increased. When pH was less than 6.1, the system lost its ability to oxidize ammonia-nitrogen. The highest removal efficiency of carbon and nitrogen in the system was achieved when C/N was 4. Ammonia transformation 80% COD removal at the three sludge concentrations took 480, 350, and 300 min, respectively. Under different conditions, the proportion of nitrosation in the system remained above 50% and the concentration of NO3--N remained below 5 mg·L-1, which indicated that the system was dominated by nitrosation.