Quantification and Controlling Spread of Antibiotics and Resistant Strains in Wastewater and Sludge

Abstract

A wide range of organic compounds used in agriculture, industry, livestock, poultry, aquaculture, consumer goods, and pharmaceutical products are released into the environment. Many of these contaminants are classified as emerging contaminants (ECs) because they are not regulated and monitored in the environment. Due to their persistent and recalcitrant characteristics, they are of serious concern. The untreated wastewater when used for irrigation results in the transfer of these antibiotics to the crops and other environmental matrices. Unfortunately, conventional treatment technologies are unable to remove these compounds from the wastewater. In the study conducted in Rawalpindi/Islamabad, Pakistan, the presence and quantification of selected antibiotics in wastewater were investigated. The untreated wastewater, often used for irrigation, raises concerns about the transfer of antibiotics to crops and the environment. Despite conventional treatment technologies, these compounds persist, prompting the exploration of effective, environmentally friendly removal techniques. High-performance liquid chromatography coupled with a diode array detector (HPLC-DAD) based method was optimized for the simultaneous detection of fluoroquinolones, penicillin, tetracyclines, and sulfonamides in wastewater. The method's validation adhered to International Council for Harmonisation (ICH) guidelines. Ciprofloxacin dominated with the highest concentration at 332.154 μg mL–1, followed by ofloxacin, ampicillin, levofloxacin, and sulfamethoxazole. The study's second objective aimed at removing antibiotics from wastewater using solventless adsorbents, polydimethylsiloxane (PDMS), and polyethylene (PE). Batch experiments over two weeks, maintaining pH 7 and 25°C, revealed PDMS's outstanding removal efficiency (99.71% for ofloxacin) and notable rates for oxytetracycline, ciprofloxacin, and sulfamethoxazole. PE also demonstrated significant removal efficiencies. Isotherm modeling confirmed Langmuir as the governing mechanism for ofloxacin and sulfamethoxazole on both PDMS and PE. Freundlich was suitable for oxytetracycline and ciprofloxacin on PE. PE, for all antibiotics, exhibited Langmuir as the main governing mechanism with R2 > 0.9. Kinetic modeling showed pseudo-first order for ciprofloxacin on PE and pseudo-second order for

xxi

other antibiotics with high R2

values. Regeneration studies indicated PDMS and PE's potential effectiveness across multiple cycles. PDMS maintained removal efficiencies ≥74%, while PE showed 93% for oxytetracycline and reduced efficiency for sulfamethoxazole in the fourth cycle. In the third objective, sludge from Islamabad's wastewater treatment plant was collected and whole genome sequencing revealed a high abundance of antibiotic-resistance genes (ARGs). Co-composting with rice husk reduced ARGs by up to 85%. In-silico studies targeted the smeE gene encoding an efflux pump. SN50 emerged as a promising chemical, identified through molecular docking, druggability analysis, and further validation. The detailed study addressed interconnected solutions for antibiotic reduction and removal, ARG reduction in sludge for potential compost use, and combating antibiotic resistance transfer through in-silico efflux pump inhibition. The findings emphasized the urgency of addressing antibiotic contamination in wastewater, with the study's multifaceted approach providing valuable insights and potential strategies for mitigating environmental and public health risks associated with antibiotic residues and ARGs.