Removal of antibiotics from water and waste milk by ozonation: kinetics, byproducts, and antimicrobial activity

Abstract

The use of antibiotics in the dairy farming for curing and growth promotion results in the production of massive quantities of non-recyclable wastewater by the conventional purification techniques. Additionally, waste milk is produced during the drug withholding periods, which is not suitable for human or animal consumption and cause huge economic loss as well as present serious environmental waste. This study was designed to investigate the decomposition of various antibiotic compounds in un-buffered aqueous solutions and milk samples by ozonation process. Commonly administered broad-spectrum antibiotics such as amoxicillin, doxycycline, ciprofloxacin, and sulphadiazine were selected as model examples in the current investigation. Gradual exposure of these antibiotics to increasing ozone gas concentration induced increasing removal percentages of the antibiotics in spiked water and milk samples. The removal reached 95% across all the tested treated antibiotics with ozone dose as low as 75 mg L^-1. It was noted that the removal of antibiotics in milk samples is more efficient with faster rate constants. This was attributed to the self-buffering characteristic of milk that maintains the neutral pH, keeping the amine groups un-protonated and more reactive towards the electrophilic attack by the molecular ozone. ¹H NMR as well as HPLC experiments support the near complete removal of antibiotics and indicated the break down to simpler and more soluble fragments of acidic nature. Bacterial growth experiments, conducted with E. coli, and milk ageing experiments provided clear evidences that the resulting decomposition byproducts lack both toxicity effect and antimicrobial activity. This study provides a viable route to remove hazardous materials, which contribute to a growing issue of antibiotic resistance of pathogenic bacteria.

Keywords: Antibiotics; Antimicrobial activity; Decomposition; Milk samples; Ozonation treatment.