Mechanism of biochar in alleviating the inhibition of anaerobic digestion under ciprofloxacin press

Abstract

The antibiotic ciprofloxacin (CIP), detected in various aqueous environments, has broad-spectrum antimicrobial properties that can severely affect methanogenic performance in anaerobic systems. In this study, a novel strategy to alleviate the inhibition of AD performance under CIP press with the direct addition of biochar (BC) prepared from corn stover was proposed and the corresponding alleviation mechanism was investigated. When the dosage of BC was 5 and 20 g/L, the cumulative methane production in AD could reach 317.9 and 303.0 mL/g COD, and the CIP degradation efficiencies reached 94.1 % and 96.6 %, significantly higher than those of 123.0 mL/g COD and 81.2 % in the Control system. BC avoided excessive reactive oxygen species in anaerobic systems and induced severe oxidative stress response, while protecting the cell membrane and cell wall of microorganisms. Microorganisms could consume and utilize more organic extracellular polymeric substances for their growth and metabolism. When BC was involved in AD, fewer toxic intermediates were generated during CIP biodegradation, reducing acute and chronic toxicity in anaerobic systems. Microbial diversity suggested that BC could enrich functional microorganisms involved in direct interspecies electron transfer like Methanosaeta, norank_f_Bacteroidetes_vadinHA17, JGI-0000079-D21 and Syntrophomonas, thus facilitating the methanogenic process and CIP degradation. Genetic analyses showed that BC could effectively upregulate functional genes related to the conversion of butyrate-to-acetate and acetyl-to-methane under CIP stress, while functional gene abundance associated with CIP degradation enhanced partially, about encoding translocases, oxidoreductases, lyases, and ligases. Therefore, BC can be added to AD under CIP press to address its inhibited methanogenic performance.