Management of milking wastewater as a significant control point of microbial pollution in the environment

Milking wastewater (MW) is an under-recognised reservoir of antibiotic resistant bacteria (ARB) and antimicrobial resistance genes (ARGs). The aim of the study is to evaluate MW as a point source pollutant for the presence of ARB and ARGs, to develop a treatment plant, and to address current legislation.

Milking wastewater was analysed for the total number of bacteria, Enterococcus spp., Staphylococcus spp., Enterobacterales, and Clostridium perfringens. Microbial identification by MALDI-TOF MS was followed by antimicrobial susceptibility testing and detection of ARGs. Wastewater samples were also tested for the antimicrobials presence using immunochromatographic tests. An on-site two-chamber MW treatment plant was designed with consideration of its cost-effectiveness and profitability. The system incorporated filtration through a mixture of fine sand and 10% kaolin, or a fine sand filter bed, yielding hydraulic conductivity coefficients of 5.13 × 10-6 m/s and 5.36 × 10-5 m/s, respectively. The treated effluent was considered suitable for activities not requiring tap water quality.

Escherichia coli and Enterococcus spp. were identified as ARB. PCR confirmed the presence of ARGs conferring resistance to β-lactams (cphA, bla_GES1-9,11, bla_TEM1,2) and chloramphenicol (cfr). Milkling wastewater samples also tested positive for chloramphenicol.

To mitigate environmental contamination, regulations should be established for the release of bioactive substances, with penalties imposed for non-compliance with recommended safety measures.