Formation and quantification of soluble microbial products and N _2O production by ammonia-oxidizing bacteria (AOB)-enriched activated sludge

摘要

Ammonia-oxidizing bacteria (AOB) play an importance role in nitrogen conversion in biological wastewater treatment systems. AOB produce soluble microbial products (SMPs) and nitrous oxides (N _2O), respectively, as aqueous and gaseous products at a trace level in their metabolism and decay processes. In this work both experimental and modeling approaches were used to explore the formation of SMP and N _2O by an AOB-enriched activated sludge in batch tests and a sequencing batch reactor. The results demonstrated that the N _2O emission was related closely with the dissolved oxygen concentration and could be stimulated under oxygen-limited conditions. The denitrification by the AOB with nitrite as their terminal electron acceptor was the main source for the N _2O production. The SMPs released by the AOB were composed mainly of biomass-associated products (BAPs), which resulted from the hydrolysis of extracellular polymeric substances. Under stable operating conditions, the average gaseous N _2O concentration in the sequencing batch reactor was about 0.36ppm, accounting for 0.44% of the total ammonium oxidation. The SMP concentration in the reactor was of about 20mg/L, in which BAP accounted for more than 65% of SMP. These results might provide useful and valuable information about the nitritation process, which plays an important role in biological wastewater treatment systems.