Bioconversion of cow manure through vermicomposting: effects of tylosin concentration on the weight of worms and manure quality

This study investigated batch-fed vermicomposting of cow manure, with a specific focus on assessing the effects of tylosin on the weight of earthworms and the overall quality of the resulting manure. Five reactors, including three concentrations of tylosin (50, 100, and 150 mg/kg) and two control reactors, were employed. Residual tylosin concentrations were measured using high-performance liquid chromatography (HPLC). Quality parameters such as pH, temperature, volatile solids (VS), organic carbon content (OCC), electrical conductivity (EC), ash content, C/N ratio, total Kjeldahl nitrogen (TKN), and microbial content were evaluated. The toxicity and maturity of vermicompost were assessed by determining the germination index (GI). The study also monitored variations in the earthworm's weight. The results demonstrated a decreasing trend in VS, OCC, C/N, and fecal coliforms, along with increased pH, EC, ash content, and TKN during the vermicomposting process. Furthermore, investigations revealed significant reductions in the reactors with tylosin concentrations of 50, 100, and 150 mg/kg, resulting in the removal of 98%, 90.48%, and 89.38% of the initial tylosin, respectively. This result confirms the faster removal of tylosin in reactors with lower concentrations. Degradation of tylosin also conforms to first-order kinetics. The findings showed a significant influence of tylosin on the weight of Eisenia fetida earthworms and the lowest antibiotic concentration led to the highest weight gain. Finally, the high percentage of germination index (90-100%) showed that the quality and maturity of vermicompost is by national and international standards.