Formation and quantification of soluble microbial products and N2O production by ammonia-oxidizing bacteria (AOB)-enriched activated sludge

Abstract

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 (N2O), 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 N2O by an AOB-enriched activated sludge in batch tests and a sequencing batch reactor. The results demonstrated that the N2O 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 N2O 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 N2O 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.