Greenhouse gases from membrane bioreactors: a pilot plant case study

In this study the N2O emitted from the aerobic and anoxic tank of a Sequential Batch (SB) Membrane Bioreactor (MBR) pilot plant has been investigated. The SB-MBR pilot plant was fed with a mixture of synthetic and real wastewater. The influence of salinity on N2O concentration was analyzed by gradually increasing the salinity by addition of salt to concentrations ranging from 0 to 10 gNaCl L-1. The results demonstrated that the N2O concentration of the gaseous samples was strongly influenced by the salinity in the range of 0.25 ppm to 3.4 ppm salinity. This result was explained by lower autotrophic kinetics due to the biomass lysis. Dissolved oxygen concentration and salinity were found to be the key factors affecting N2O concentration in the gaseous samples withdrawn from the anoxic tank. Despite the fact that the N2O concentration in the anoxic tank was higher than in the aerobic one, it was found that the aerobic tank emitted around 15 times more N2O than the anoxic one