EPS and SMP as Stability Indicators During the Biofiltration of Diffuse Methane Emissions

Biofiltration of an air stream polluted with diffuse CH4 concentrations of 0.19 % (v v−1) was carried out. These emissions can be encountered at different industrial facilities such as wastewater treatment plants and landfills. The effect of ammonium supplied in the nutrient solution was studied in a range from 0 to 1 g N-NH4 + L−1, taking account its effect on CH4 removal efficiency (RE), CO2 production, ammonium conversion and the occurrence of exopolymeric substances. Additional batch assays were performed in order to evaluate the most suitable pH and temperature ranges for the biomass used as inoculum. A conventional biofilter was operated along 225 days achieving maximum CH4 elimination capacities of up to 11.2 g CH4 m-3 h−1, corresponding to REs of 62 %, using 0.52 g N L−1 of ammonia as nitrogen source in the nutrient solution and operating at an empty bed residence time of 4.4 min. CO2 production values confirmed that most of this elimination was biological and not absorption into the liquid phase. The occurrence of instability periods resulted in a clear increase of the soluble microbial products (SMPs) contained in the liquid phase, especially in the protein fraction, which could be used as a monitoring tool to follow the stress conditions of the biofilter. Results indicate interesting links between the performance of the biofilter and the presence of extracellular polysaccharide and protein concentration in the liquid phase, with increasing concentrations detected when the process was not stable.