Microalgal-bacterial sludge enhances dimethyl phthalate (DMP) biodegradation beyond adsorption: Metabolic pathways, microbial responses, and adaptive mechanisms.

Abstract

Phthalate acid esters (PAEs), as typical environmental endocrine disruptors, pose severe threats to ecosystems and human health due to their persistence in aquatic environments, while conventional wastewater treatment processes exhibit low removal efficiency and risk secondary pollution. This study constructed microalgal-bacterial sludge (MABS) to systematically investigate its removal efficiency and the degradation mechanisms of dimethyl phthalate (DMP). The results demonstrate that, compared to conventional activated sludge (AS), DMP MABS exhibited greater tolerance to DMP and higher DMP removal efficiency, reaching 96.9%, with biodegradation rather than adsorption becoming the dominant removal route, improved settling performance (SVI decreased to 51.19 mL/g), increased biomass, and stimulated secretion of extracellular polymeric substances (EPS, up to 40.00 mg/g VSS) to form a protective barrier against toxicity. Microbial analysis revealed that Pseudomonadota dominated the microbial community and was strongly associated with metabolic functions, while MAG-based metagenomic binning identified Burkholderiales as the largest order-level contributor to DMP-related functional genes. Integrating EPS characterization with metagenomic evidence, we further hypothesize an EPS-mediated microalgal-bacterial interaction model in which LB-EPS enriches DMP at the aggregate interface, TB-EPS stabilizes oxic-anoxic microzones, and microalgal-derived oxygen and carbon sources, signaling, chemotaxis, biofilm formation, and vitamin-associated functions collectively support bacterial DMP catabolism. Qualitatively assigned intermediates together with metagenomic annotations proposing a putative DMP biodegradation pathway involve de-esterification to monomethyl phthalate and phthalic acid (lip, gnl, and pgl, etc.), followed by aerobic dioxygenase-catalyzed or anaerobic decarboxylation to protocatechuic acid (pht3, pht4, and pht5, etc.) or benzoic acid (benA-xylX and benB-xylY), ultimately entering the tricarboxylic acid cycle (pcaG, pcaF, ligK, and galD, etc.). This technology integrates high-efficiency degradation, energy conservation, and resource recovery potential, providing theoretical and technical foundations for wastewater treatment plants to address emerging pollutants.