A novel biological treatment process for removing hydrogen sulfide from anaerobic biogas using a bio-scrubber has been developed. The treatment process is composed of a gas/liquid contact tower and an aeration tank. The biogas from an anaerobic wastewater treatment process is introduced into a multiple-bubble-tray contact tower (bio-scrubber) and scrubbed with activated sludge liquor from an aeration tank. The sludge liquor containing sulfides is then returned to the aeration tank, where the sulfide is oxidized to sulfate by sulfur-oxidizing bacteria such as Thiobacillus. The contact tower is designed to be air tight in order to prevent air from mixing into the biogas used as a fuel. A simulation model was developed to calculate effluent gas concentrations from the contact tower, incorporating input parameters such as influent hydrogen sulfide concentrations, gas flow rates, and gas/liquid ratios. Using the simulation model, design criteria were calculated and a full-scale plant for treating biogas from a UASB process for potato processing wastewater was constructed. The data shows that the hydrogen sulfide in the biogas was effectively reduced from 2,000 ppm to less than 20 ppm.

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Granule floatation may occur at higher organic loadings, resulting in a loss of active granules and a decrease in the treatment capacity of UASB reactors. Granular sludge sampled from full-scale UASB reactors was studied to investigate the mechanism of granule floatation. It was found that granules float due to the buoyant force created by the gas bubbles entrapped in the hollow spaces of granules. Two hypotheses on the mechanisms of hollowing were presented, and in order to prevent granule floatation, the protocol, i.e., grinding of floating granules by a mechanical device and dosing of Fe into the reactors, was proposed. The protocol was evaluated in a series of lab-scale experiments and proven to be effective and practical for use in full-scale UASB reactors.

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