Study of extracellular polymeric substances in the biofilms of a suspended biofilter for nitric oxide removal

The extraction and quantitative analysis of extracellular polymeric substances (EPS) have been frequently reported in studies of activated sludge. However, little is currently known about the EPS in the biofilms of biofilter systems. This study investigates the EPS in biofilms of Chelatococcus daeguensis TAD1 established in a suspended biofilter for nitric oxide (NO) removal under thermophilic conditions. Polysaccharide was the main EPS component under all experimental operation conditions of the aerobic biofilter, although the EPS contents and components varied under different operating conditions. As the concentration of the inlet NO varied from 200 to 2000 mg/m3, the EPS and protein contents generally increased. At the highest inlet concentration (2000 mg/m3), the EPS and protein contents reached 0.118 and 0.055 mg/g, respectively (representing increases of 7.3 and 35 %, respectively, over the inlet concentration of 200 mg/m3). In contrast, the polysaccharide content was quite stable against inlet NO concentration. Decreasing the empty bed residence time increased the EPS and polysaccharide contents, but exerted little effect on the protein content. Varying the pH of the circulating fluid from 4 to 8 changed the EPS and its components in complex ways. We also found a strong correlation between the total EPS content and the NO removal efficiency. Therefore, it is possible to take EPS into consideration for biofilter control.