Warning the environmental risks of emerging contaminants on low-carbon sludge anaerobic digestion treatment

Emerging contaminants (ECs) in waste-activated sludge (WAS) pose significant risks to ecosystems and human health. Anaerobic digestion (AD), a microbial-driven waste management technology, is particularly vulnerable to interference from ECs. This review comprehensively explores the effects of various ECs, including pharmaceuticals, personal care products, endocrine-disrupting chemicals, perfluoroalkyl and polyfluoroalkyl substances, and microplastics, on AD processes and their underlying mechanisms. ECs typically inhibit sludge digestion by disrupting extracellular polymeric substance structures, altering enzyme activity, and affecting microbial communities and metabolic functions. However, at low concentrations, some microorganisms can adapt and restore methane production. Addressing the synergistic and antagonistic interactions of multiple ECs, which complicate treatment outcomes, is critical. Additionally, ECs alter the removal of resistance genes during AD by reshaping microbial host structures, enhancing horizontal gene transfer, and activating reaction pathways, increasing ecological risks. AD also demonstrates limited efficiency in degrading ECs, reducing the quality of digestate as biofertilizer and potentially impacting human health via the food chain. To improve AD efficiency in the presence of ECs, strategies such as source control, pretreatment, and novel green technologies are proposed. This review provides key insights into optimizing AD performance and resilience for EC-laden organic waste, emphasizing integrated and adaptive approaches to meet evolving challenges.