Biological treatment of H2S using pellet activated carbon as a carrier of microorganisms in a biofilter

Biological treatment is an emerging technology for treating off-gases from wastewater treatment plants. The most commonly reported odourous compound in off-gases is hydrogen sulfide (H2S), which has a very low odor threshold. This study aims to evaluate the feasibility of using a biological activated carbon as a novel packing material, to achieve a performance-enhanced biofiltration processes in treating H2S through an optimum balance and combination of the adsorption capacity with the biodegradation of H2S by the bacteria immobilized on the material. The biofilm was mostly developed through culturing the bacteria in the presence of carbon pellets in mineral media. Scanning electron microscopy (SEM) was used to identify the biofilm development on carbon surface. Two identical laboratory scale biofilters, one was operated with biological activated carbon (BAC) and another with virgin carbon without bacteria immobilization. Various concentrations of H2S (up to 125 ppmv) were used to determine the optimum column performance. A rapid startup (a few days) was observed for H2S removal in the biofilter. At a volumetric loading of 1600 m3 m−3 h−1 (at 87 ppmv H2S inlet concentration), elimination capacity of the BAC (181 gH2S m−3 h−1) at removal efficiency (RE) of 94% was achieved. If the inlet concentration was kept at below 30 ppmv, high H2S removal (over 99%) was achieved at a gas retention time (GRT) as low as 2 s, a value, which is shorter than most previously reported for biofilter operations. The bacteria population in the acidic biofilter demonstrated capacity for removal of H2S in a broad pH range (pH 1–7). There are experimental evidences showing that the spent BAC could be re-used as packing material in a biofilter based on BAC. Overall, the results indicated that an unprecedented performance could be achieved by using BAC as the supporting media for H2S biofiltration.