Removal of Hydrogen Sulfide from Biogas Using a Bubbling Tank Fed with Aerated Wastewater

The work develops a simple bubbling tank scrubber that is fed with aerating wastewater for the removal of hydrogen sulfide (H2S) in biogas. A 2,000 L plastic tank, in which fixed liquid levels 0.80 and 1.0 m and volumes of 1.1 and 1.4 m(3) was kept, was used for the scrubbing tests. A polyvinyl chloride (PVC) pipe with holes of 1 mm diameter was used to sparge the biogas into the tank liquid. Results indicate that with an influent liquid of pH 7.5-7.7, a flow rate of 23-25 L influent biogas flow rates of 0.050-0.200 m(3) min(-1), and a H2S concentration of 907 +/- 212 ppm, the pH of the effluent liquid stabilized at 6.6-6.9. With gas/liquid rate ratio of 2-8 m(3) m(-3) liquid and volumetric gassing intensities of 0.04-0.20 m(3) m(-3) liquid min(-1), average H2S removals of 86-71% were obtained. Absorption of CO2 in the tested digester gas into the scrubbing liquid caused a decrease in the pH, thus decreasing the H2S removal efficiency. Increasing pH of the scrubbing liquid to 8.0 improved the H2S removal efficiency to as high as 99%.