Control of N2O-emissions from Sidestream Treatment

Sidestream treatment usually represents a well controlled process optimised for saving energy and external carbon. Considering high ammonia concentrations of sludge dewatering liquors an additional control target appears significant – gaseous N2O emissions that can amount to several percent of the incoming nitrogen load. Due to the high global warming potential, N2O emission limitation seems to be essential for sustainable application of such systems. The aim of the study was to analyse the impact of common control parameters on these emissions in order to suggest a control strategy. A pilot plant and a full scale deammonification system (DEMON) have been monitored for N2O under different operation conditions. It was shown that nitrite is the main driver for production of N2O emissions. Dissolved oxygen and pH did not have significant impacts on the formation of N2O off-gas. Hence, controlling nitrite formation will also control N2O production. Intermittent aeration control based on the pH-signal seems to be an appropriate solution.