Anaerobic digestion in the elimination of antibiotics and antibiotic-resistant genes from the environment – A comprehensive review

Antibiotics are considered emerging contaminants that may cause substantial detrimental effects on the environment. The severe threat is the development of antibiotic resistance due to its frequent consumption. This review presents the feasibility of anaerobic digestion (AD) in eliminating antibiotics and antibiotic-resistant genes (ARGs) from the environment. This review concludes that anaerobic membrane bioreactor (AnMBR) is the most productive technology for antibiotics (sulfamethoxazole, sulfadiazine, trimethoprim, clarithromycin, erythromycin, ciprofloxacin, ofloxacin, cefalexin, cephradine) and ARGs removal (sul1, sul2, tetO, tetW, ermF, ermB, blaNDM-1, blaCTX-M-15, blaoxa-48, blaoxa-1). Inhibition to AD in terms of biogas or methane production upon antibiotics exposure has been observed for sulfamethoxazole (>25 mg/l), tetracycline (>1 mg/l), ofloxacin (>10 mg/l), ciprofloxacin (>80 mg/l), sulfamerazine (>90 mg/l), tylosin (>130 mg/l) and ceftiofur (>10 mg/l). This review also fortifies that microorganisms belonging to phylum Proteobacteria, Firmicutes, Chloroflexi, Bacteroidetes, Thermotogae, Euryarchaeota, Elusmicrobia, Chlorobi, Spirochaetes, Synergistetes, and Actinobacteria are important for stable performance of AD in terms of antibiotics removal and bioenergy production. However, the effects of antibiotics (individual and combined) on bioenergy production and microbial compositions have not been extensively investigated for AnMBR. Thus, further research must focus on these research gaps. In addition, AnMBR can be integrated with microbial fuel cells (MFCs) to enhance antibiotics and ARGs removal and mitigate membrane fouling issues while simultaneously producing bioelectricity and chemicals. Hence, future studies must examine their combined performance for antibiotic wastewater treatment. Additionally, mesophilic and thermophilic anaerobic digesters are exceptional in eliminating major ARGs (tetracyclines, sulfonamides, macrolides, fluoroquinolones, trimethoprim, beta-lactamase, aminoglycosides, florfenicol) from both biosolids (sludge) and manure. Nevertheless, forthcoming research must investigate their combined performance especially by using activated carbon and nano zero-valent iron (NZVI) in eliminating ARGs and enhancing bioenergy production.