Effects of periods of starvation and fluctuating hydrogen sulfide concentration on biofilter dynamics and performance

The paper describes the results of a systematic study of the transient behavior of biofilters treating reduced sulfur pulping odors and VOCs. They were exposed to variations in contaminant loading and periods of starvation. Three bench-scale biofilters with different filter media were used. Filter media materials used were the mixtures of compost/perlite (4:1), hog fuel/perlite (4:1), and compost/hog fuel/perlite (2:2:1). Hydrogen sulfide, the main malodorous gas produced from kraft pulping processes, was used as the test contaminant. The starvation period comprised of two stages: the ‘no-contaminant-loading phase' when only humidified air was passing through the biofilters, and the ‘idle phase' when no air was passing through the biofilters. The response of each biofilter to variations in contaminant mass loading was studied by abruptly changing the concentration and/or flow rate of the inlet waste air stream. Contaminant concentration was continuously measured until a new steady state, for each stage, was achieved. Concentration spikes were applied to study the effects of shock loading on the biofilter removal rates. Biofilters responded effectively to H₂S concentration variations and shock loading by rapidly recovering to the original removal rates within 2–8 h. The re-acclimation times to reach full capacity were very short ranging between 15 and 120 h. Extended periods of starvation resulted in longer re-acclimation periods, so does the idle phase as compared to no-contaminant-loading phase.