Monitoring biofilter clogging: biochemical characteristics of the biomass

The low temperature of the snowmelt water in the spring seems to affect the biofiltration of wastewaters; biofilters clog rapidly during the critical period of March and April. This study presents the results of biochemical tests carried out in wash-water (biomass) of a Biodrof®-type biofilter. These tests deal with the measurement of hydrolase, dehydrogenase (DHA) and total polysaccharides (TP). The wash-water analyses showed ratios of 41% total polysaccharides over VSS (w/w) during the cold period, corresponding to influent temperatures of 7.5–13.5°C. During the warmer period (15.0–18.0°C), this ratio is 26%. Observations of the biomass show an abundance of fixed ciliated protozoans during the cold period, being replaced by a bacterial and fungal biofilm during the warmer period. Moreover, during the cold period, the biomass contains less extra-cellular enzyme like β-glucosidase type, but the ratio of active biomass measured using the dehydrogenase glucose (DHA) is the same for all temperature ranges measured here. This implies that weak hydrolytic activity, coupled with accumulation of a biofilm and inert particles of the influent encourages a rapid clogging of the biofilter. The loads in CODt and SS as well as the filtration rates have but little effect on the premature clogging of the biofilter under spring conditions.