Tetracycline in anaerobic digestion: Microbial inhibition, removal pathways, and conductive material mitigation

Tetracycline enters the environment due to its incomplete absorption in humans and animals, posing a significant ecological threat. Tetracycline can hinder the biosystems when treating tetracycline-containing wastewater/waste through anaerobic digestion. This review summarizes the role of tetracycline in inhibiting system performance and related functional microorganisms in holistic process of anaerobic digestion. Tetracycline may primarily inhibit methanogenesis by suppressing acetogenesis, with methane production reductions ranging from 10 % to complete inhibition depending on factors such as tetracycline concentration, inoculum source, substrate composition, and temperature. As a refractory pollutant, tetracycline can be removed in anaerobic digestion systems through adsorption and biodegradation, with removal efficiencies reported between 14.8 % and over 90 %. This review systematically summarizes the mechanisms of tetracycline removal pathways and evaluates the potential contributions. Co-existence of readily biodegradable substrates, extended sludge retention time, and the regulation of environmental parameters such as pH and temperature are potential strategies to enhance tetracycline removal. Moreover, the addition of conductive materials has been identified as a promising strategy to serve as tetracycline adsorbents, facilitate direct interspecies electron transfer and mediate redox reactions, and act as microbial carriers to enhance microbial activity. Finally, this review highlights that the dynamic responses and microbial survival strategies under tetracycline stress deserve further investigation. A deeper understanding of these mechanisms will offer clear theoretical guidance for upgrading technologies for tetracycline-containing wastewater/waste treatment.