Removal of copper from cattle footbath wastewater with layered double hydroxide adsorbents as a route to antimicrobial resistance mitigation on dairy farms

Copper and zinc are routinely used in livestock antimicrobial footbaths in commercial farming. The footbath mix is a cost to farmers, and the disposal of spent footbath into slurry tanks leads to soil contamination, as well as the potential for antimicrobial metal resistance and co-selection. This study assesses the potential to mitigate a source of antimicrobial metal resistance in slurry tanks while recovering copper and zinc from spent cattle footbaths. This is the first study in literature to investigate the potential of recovering copper from cattle footbath solutions via any method. The sorbent, Ca₂Al-EDTA Layered Double Hydroxides (LDH), were used to remove Cu²⁺ from a Cu₂SO₄·5H₂0 solution at different temperatures. The maximum Cu²⁺ uptake from the Cu₂SO₄·5H₂0 solution was 568 ± 88 mg g^-1. Faster and higher equilibrium uptake was achieved by increasing the temperature of the solution. The sorbent was found to be effective in removing copper and zinc from a commercially available cattle footbath solution (filtered footbath solution Cu²⁺ uptake 283 ± 11.05 mg g^-1, Zn²⁺ uptake 60 ± 0.05 mg g^-1). Thus, this study demonstrates the opportunity for a completely novel and potentially economically beneficial method of mitigating antimicrobial resistance in agriculture and the environment, while also providing a new valuable copper and zinc waste stream for secondary metal production.