MICROBIOLOGICAL OXIDATION OF HYDROGEN-SULFIDE IN A BIOFILTER

The microbial oxidation of hydrogen sulphide present in an air stream was performed using a laboratory-scale biofilter packed with dry waste water sludge (BSE, boues de station d'epuration) from an urban wastewa ter 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 w ith 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 c hemical oxidation can occur. The presence of numerous bacteria such as Thiobacillus spp. (i.e., 10(8)-10(9) CFU/g dry weight) in biotic pilo t units favoured complete oxidation to sulphate. High initial bacteria l numbers and a neutral pH improved the removal efficiency of the biof ilter. A high sulphide concentration (> 3000 mg/m(3)) had a negative e ffect on the removal efficiency. The leaching of the metals contained in the sludges was studied. Peat and BSE biofilters were compared.