Use of a field-scale biofilter for the degradation of the organophosphate insecticide coumaphos in cattle dip wastes

Abstract

Insecticide wastes generated from livestock dipping operations are well suited for biodegradation processes since these wastes are concentrated, contained, and have no other significant toxic components. A field-scale biofilter capable of treating 15 000-litre batches of dip waste containing the acaricide coumaphos was used to reduce the coumaphos concentration in two successive 11 000-litre batch trials from 2000 mg litre -1 to 10 mg litre -1 in approximately 14 days at 25-29°C. Removal of coumaphos from the biofilter effluent is a function of both physical filtration and biodegradation by the biofilter. However, stoichiometric increases in chloride levels in the effluent as coumaphos concentrations decreased confirmed that coumaphos was being degraded by the biofilter rather than just being filtered out. In subsequent 5500-litre batch experiments, the addition of a vitamin supplement to the biofilter-treated dip resulted in a further decrease in coumaphos concentration to approximately 1 mg litre -1 . Results from incubations of two representative Texas soils with biofilter-treated dip spiked with [benzo-U- 14 C] coumaphos revealed that 32-36% of the spiked [ 14 C] coumaphos was mineralized in the soils after 110 days at 30°C.