Author

Zhihong Liu

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Aug 2026

Hydrothermal versus photo-aged polyethylene microplastics: Aging mode-dependent oxidative stress and enzyme inhibition in waste activated sludge fermentation.

The aging of microplastics (MPs) inevitably occurs during sludge treatment, leading to the leaching of dissolved organic matter (DOM) and associated chemical additives. However, the impact and mechanism of aged leachate on anaerobic fermentation of waste activated sludge (WAS), particularly its ecological risks and implications for sludge resource recovery, remain poorly understood. This study investigated the effects of leachates prepared from photochemically (PC) and hydrothermally (HT) aged polyethylene (PE) MPs at an initial PE-MPs concentration of 5 g/L on short-chain fatty acids (SCFAs) production during WAS anaerobic fermentation. The results showed that PC and HT leachates reduced SCFAs production by 21% and 30.6%, respectively, and shifted the product composition from acetate-dominant to a mixed-acid profile. Biochemical analyses revealed that the aged leachates induced oxidative stress and inhibited protease and α-glucosidase activities, resulting in only 2.3%-6.0% protein degradation and a 23.1%-23.8% decrease in carbohydrate hydrolysis efficiency. Microbial community analysis further demonstrated that both PC and HT leachates reduced microbial diversity and the abundance of key hydrolytic genera, thereby compromising the functions of acid-producing and nitrogen-cycling bacteria. Analysis of leachate composition indicated that HT leachates released more oxygen-containing depolymerization products and additives, leading to stronger inhibition of microbial activity and hydrolysis processes. ECOSAR predictions suggested that several phenolic antioxidants and phthalate plasticizers may pose relatively high aquatic hazards. Their presence may partly contribute to the stronger biological inhibition observed in the aged-leachate treatments. These findings provide critical insights into the toxicity mechanisms of aged MP leachates in sludge fermentation systems.

Jie Wu, Jiating Hao, Yanwei Xue et al. · Journal of Hazardous Materia... · 0 citations

Jul 2026

Deciphering the synergistic mechanism of quorum sensing and sulfate-reducing bacteria for directed acetate conversion during sludge fermentation.

The restricted bioconversion of C3-C5 short-chain fatty acids (SCFAs) to acetate due to thermodynamic limitations is the main bottleneck during sludge fermentation. To alleviate this constraint, this study developed an optimized approach by integrating quorum sensing regulation with incomplete-oxidation sulfate-reducing bacteria (io-SRB) to improve the selective conversion of carbon towards acetate. The results revealed that the addition of 5 μM C8-HSL combined with io-SRB led to the highest SCFAs and acetate production at 141.9 mg COD/g VSS and 87.2 mg COD/g VSS at 5 d, which was 37% and 37% higher than the group without C8-HSL addition, while increase the C8-HSL dosage had no significant promotion of SCFAs production. C8-HSL effectively accelerated the efficient utilization of soluble carbohydrates and proteins during sludge fermentation, and functional group analysis further confirmed its promotional effect on the biotransformation of macromolecular organic matter throughout the fermentation process. Functional microbes, i.e., hydrolytic bacteria, acid-producing bacteria, and io-SRB (e.g., Desulfobulbus and Desulfovibrio), were enriched in the 5 μM C8-HSL system. The molecular ecological network and Mantel analysis revealed cooperative interactions among these functional microorganisms. Moreover, the synergistic effects of exogenous C8-HSL with io-SRB enhanced the expression of key functional genes involved in glycolysis, amino-acid metabolism, and acetate synthesis pathways. These findings may improve the understanding of the biological transformation mechanisms of sludge organic matter, and provide useful theoretical support for the efficient production of value-added products from sludge fermentation.

Yimin Jing, Shuli Liu, Qianxue Li et al. · Bioresource Technology · 0 citations