IMPACT OF OPERATING CONDITIONS ON THE TREATMENT OF ATAD OFFGASES WITH BIOFILTERS

The results of pilot scale testing that was performed to evaluate the use of biofilters for treatment of ATAD offgases under controlled conditions are presented in this paper. The biofilter temperature, source of post-humidification water, bed pH and pollutant loading were varied to assess their impact on the removal of a mixture of reduced sulphur compounds (RSC's) and NH3. Sampling events consisted of hourly measurements of the RSC and NH3 in the biofilter influent and effluent over a 24 hour, which was the interval between feeding of the ATAD. The leachate from the biofilter was also characterized with respect to pH, NH4+, SO42-, NO3- and NO2- concentrations to allow for mass balances on sulfur and nitrogen and to identify the removal mechanisms that were active in the biofilter.Temperature was observed to have a substantial impact on nitrification in the biofilter but had little impact on the removal of RSC's. The source of post-humidification water (potable vs. plant) did not appear to influence the performance of the biofilter. Increasing the leachate pH in the biofilter did not appear to affect either the rate of nitrification or the rate of oxidation of reduced sulfur compounds. The elimination capacity of RSC's did not appear to be exceeded over the range of loadings examined in this study. The loadings of NH3 appeared to be higher than the biofilters elimination capacity for this substance.