Individual and Synergistic Effects of Metronidazole, Amoxicillin, and Ciprofloxacin on Methane Fermentation with Sewage Sludge

Abstract

AbstractMethane fermentation is widely used to dispose of sewage sludge at wastewater treatment plants (WWTPs), due to production of renewable energy in the form of biogas. Antibiotics present in wastewater may accumulate in a sewage sludge. The aim of the present study is to investigate the impact of three antibiotics from different classes in three different doses on methane production from sewage sludge. For this purpose, metronidazole (MET), amoxicillin (AMO), and ciprofloxacin (CIP) are individually added to anaerobic reactors with sewage sludge collected from municipal WWTP. The antibiotics’ highest concentration (1024 mg kg−1 of AMO; 512 mg kg−1 of MET and CIP) lowers methane production and methane content in biogas. MET exerts the most marked effect and lowers methane production to 36.8 ± 3.7 mL CH4 kg−1 volatile solids. Tested antibiotics probably inhibit methanogenic archaea, which results in volatile fatty acids (VFAs) accumulation. Addition of MET results in accumulation of many kinds of VFAs with the highest concentration of acetic acid (17.52 ± 1.85 g L−1). The addition of of AMO results in accumulation of butyric acid only (253.00 ± 15.89 g L−1). However, addition of CIP results in accumulation of mainly acetic acid (7.58 ± 0.82 g L−1) and isovaleric acid (2.01 ± 0.41 g L−1). Next, synergistic effect of these antibiotics in a low concentration of 16 mg kg−1 of AMO, 8 mg kg−1 of MET, and 2 mg kg−1 of CIP is measured in semi‐continuous conditions and causes inbibition of methane production and accumulation of VFAs.