[N2O production in nitrogen removal by micro-expansion of granular sludge]

Controlled low dissolved oxygen (DO) in a sequencing batch reactor (SBR) was used to study the realization of micro-expansion of aerobic granular sludge, and the removal efficiency of COD and NH4+ -N as well as the production of the greenhouse gas N2O by the micro-expansion of granular sludge was investigated. The results showed that under the condition of low dissolved oxygen micro-expansion of sludge could be achieved, and the sludge volume index (SVI) was mostly in the range of 150-250 mL x g(-1). The micro-expansion of granular sludge did not have significant influence on the removal of COD and NH4+ -N. The COD removal rate increased from 89.45% to 90.99%, the NH4+ -N removal rate decreased from 77.29% to 68.29%, and the nitrification rate dropped from 38.95 x 10(-3) mg (g x min)(-1) to 33.46 x 10(-3) mg x (g x min)(-1). The micro-expansion of granular sludge had a big influence on the production of N2O, and the N2O production by the micro-expanded granular sludge was 2.42 mg x m(-3), which was 1.26 times of the N2O production of the granular sludge without micro-expansion. The N2O release rate in the micro-expanded granular sludge increased from 3.63 x 10(-3) mg x (L x min)(-1) to 4.72 x 10(-3) mg x (L x min)(-1).