Evaluating changes in microbial population and earthworms weight during vermicomposting of cow manure containing co-trimoxazole

Background Transmission of pathogens such as fecal coliforms is regarded as a significant concern about using livestock manure in agricultural applications. Purpose The aim of this study was to evaluate the effects of vermicomposting on fecal coliforms in cow manure containing co-trimoxazole as a widely used drug for cow diseases in animal husbandry. Methods Adaptation process of earthworms was carried out in two phases for 6 weeks; then, the main process was fulfilled in 9 weeks. The final weight of cow manure per reactor was 3.5 kg. 120 g of earthworms added to each reactor (approximately 280-300 numbers in the reactor). Co-trimoxazole was also prepared with a purity of 99% from Pakdarou Co., Iran, and added to the reactors at concentrations of 10, 20, 50, and100mg/kg. Organic carbon, total Kjeldahl nitrogen (TKN), carbon-to-nitrogen (C:N) ratio, as well as phosphorus content of the reactors were measured. Fecal coliforms and parasite eggs were counted using standard laboratory methods (i.e. the Iranian Compost Standard) for 8 weeks. Results The results revealed a decrease in organic carbon, C:N ratio, and co-trimoxazole content but a rising trend in TKN and phosphorus levels. The weight of earthworms also increased at the end of the process in all reactors, except for one case. A significant reduction was observed in fecal coliforms and parasite eggs at the end of the vermicomposting. Conclusions According to the results, earthworms could be active in cow manure vermicomposting including 10-100 mg/kg concentration of co-trimoxazole antibiotic. The vermicomposting seems to be an effective method for reducing fecal coliforms and parasites in cow manure. As well, co-trimoxazole in common concentration could not have any effects on the ability of earthworms. At the end of the vermicomposting, all parameters were placed within the ICS (National) - Grade 1.