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[Display omitted] • Biogas recirculation may create multifunctional granule AD system of sewage sludge. • Biogas recirculation accelerates CH 4 recovery rate from sludge by 31–44%. • Simultaneous sludge stabilization and aggregation can be realized in this system. • This system can improve net energy profit by 78–85% for sewage sludge treatment. This study investigated the possibility of biogas recirculation-driven anaerobic granular sludge system for sewage sludge treatment, aiming to develop an energy sufficient and multifunctional anaerobic digestion (AD) system for sewage sludge with biogas upgrading, sludge stabilization and self-aggregation. Results show that biogas recirculation could enhance the CH 4 production rate by 31–44% and shorten the lag-phase duration to 0.08–0.2 day with simultaneous increment of CH 4 content (> 83% in this study). The reason is mainly associated with the stronger interspecies electron transfer under the biogas recirculation condition. In addition, 37–40% better dewaterability of the digested sludge was achieved, implying the occurrence of self-aggregation of microbial cells induced by biogas recirculation. Energy balance analysis reflects that this sewage sludge treatment system could enhance the net energy recovery by 78–85%. Moreover, almost no obvious influence was noticed on the seed granules' composition and properties. These findings suggest that the biogas recirculation-driven anaerobic granular sludge system could be a promising alternative for sewage sludge treatment, which can improve biogas quality and sludge dewaterability simultaneously towards sludge self-aggregation with no addition of other chemicals. [ABSTRACT FROM AUTHOR]

Microbe inhibition produces intermediate metabolites and toxic substances that accumulate significantly in residual sludge toxicity after continuous treatment of coal gasification wastewater with activated sludge. To address this issue, Chlorococcum humicola was cultured with sludge extract. Proteomics analysis was used to investigate the mechanism of stress response in microalgae to sludge toxicity. Upon completion of growth, microalgae treated with sludge extract produced 0.725 ± 0.036 g/L of biomass. The total organic carbon concentration and toxicity removal rates on microalgae were 75.1 ± 3.8% and 47.4 ± 2.1%, respectively. The proteomics analysis revealed that under stress conditions, microalgae altered cellular components such as the nucleus and plasma membranes, affecting the photosynthetic and respiratory processes. The logarithmic phase was characterized by a down-regulation of oxidative phosphorylation and an increase in energy synthesis regulated by the isopropyl phosphate isomerase. The results demonstrate a proteomic basis for the reduction and utilization of waste sludge, as well as provide a molecular mechanism reference for optimizing the model of cultivating microalgae using sludge. [Display omitted] • Sludge extract from hydroquinone treatment was utilized to cultivate microalgae. • The optimal cultivation ratio would increase biomass production and TOC disposal. • Oxidative phosphorylation was controlled downwards in the logarithmic phase. • Energy synthesis and biosynthesis have been adjusted under toxic stress. Synopsis Sludge extract was used to reduce sludge toxicity and increase biomass accumulation in Chlorococcum humicola. Stress altered the nucleus and plasma membranes of microalgae. [ABSTRACT FROM AUTHOR]