Microbiological oxidation of hydrogen sulphide in a biofilter

The microbial oxidation of hydrogen sulphide present in an air stream was performed using a laboratory-scale biofilter packed with dry wastewater sludge (BSE, boues de station d'epuration) from an urban wastewater treatment plant. This granular and heterogeneous material contains organic and mineral components which favour colonization by bacteria. Adsorption and absorption of hydrogen sulphide taking place on such a packing (moisture content 30-40%) were determined. Results obtained with abiotic pilot units, fed with air (superficial air flow rate, 16 m/h) containing a sulphide level as high as 3260 mg/m(3), showed that chemical oxidation can occur. The presence of numerous bacteria such as Thiobacillus spp. (i.e., 10(8)-10(9) CFU/g dry weight) in biotic pilot units favoured complete oxidation to sulphate. High initial bacterial numbers and a neutral pH improved the removal efficiency of the biofilter. A high sulphide concentration (> 3000 mg/m(3)) had a negative effect on the removal efficiency. The leaching of the metals contained in the sludges was studied. Peat and BSE biofilters were compared.