Biofilters are popular for the removal of odours from gaseous emissions in wastewater treatment plants because of their low capital costs and low energy requirements. In an aerobic environment, the microbes in biofilter oxidize odorous gases like hydrogen sulphide (H2S) and ammonia (NH3) to non-odorous sulphate and nitrate. This paper describes a pilot plant biofilter setup at a local waste water treatment plant (WWTP) which has been in continuous operation for more than 150 days, removes both H2S and NH3 at an average removal efficiency of 91.96% and 100%, respectively. Unlike a conventional biofilter, the pH of this biofilter was not adjusted by addition of chemicals or buffers and the H2SO4 produced from the biological conversion of H2S is periodically washed down and allowed to accumulate in a concentrated form at the base of the biofilter. NH3 entering at the base is removed, not by biological oxidation, but by the chemical reaction of ammonium with sulphate to form ammonium sulphate. The ammonium sulphate produced in biofilter is washed down and the volume of leachate produced is less than 0.2mL of leachate/L of reactor/day. Estimated cost savings of converting the current chemical scrubber used at the WWTP to a similar biofilter described in this study is included with this paper.
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