The effect of inoculation and the type of carrier material used on the biofiltration of methyl sulphides

Abstract

Low elimination capacities (less than 10 gm⁻³day⁻¹) were observed for the odorant dimethyl sulphide (Me₂S) when either wood bark or compost was used as the carrier material in a laboratory-scale biofilter. Enrichment experiments were set up by incubation of garden soil samples during 4 weeks with 100 ppm (v/v) headspace concentrations of both Me₂S and dimethyl disulphide (Me₂S₂). After transfer to a mineral medium, Me₂S- and Me₂S₂-degrading enrichment cultures were obtained for all five soil samples tested, both compounds being converted stoichiometrically to sulphuric acid. Upon inoculation of the laboratory-scale biofilter with one of these enrichment cultures (± 120 g cell dry weight m⁻³ reactor), the elimination capacity for Me₂S increased in a 3-week period to 35 gm⁻³ day⁻¹ and 680 gm⁻³ day⁻¹ when wood bark and compost were used as the respective carrier materials. Both inoculated biofilters were able to degrade Me₂S₂, however the elimination capacities obtained for Me₂S₂ were lower (e.g. 24 g m⁻³ day⁻¹ for the wood bark filter) compared to those for Me₂S. For both inoculated biofilters, a gradual decrease of the elimination capacity for the methyl sulphides was observed as a result of acidification of the carrier material, suggesting that pH regulation is necessary if long-term biofiltration experiments are to be performed.