Search

Anaerobic digestion (AD) is a promising technique for waste management, which can achieve sludge stabilization and energy recovery. This study successfully prepared Fe 3 O 4 @ceramsite from WAS and applied it as an additive in sludge digestion, aiming to improve the conversion of organics to biomethane efficiency. Results showed that after adding the Fe 3 O 4 @ceramsite, the methane production was enhanced by 34.7% compared with the control group (88.0 ± 0.1 mL/g VS). Further mechanisms investigation revealed that Fe 3 O 4 @ceramsite enhanced digesta stability by strong buffering capacity, improved sludge conductivity, and promoted Fe (III) reduction. Moreover, Fe 3 O 4 @ceramsite has a larger surface area and better porous structure, which also facilitated AD performance. Microbial community analysis showed that some functional anaerobes related to AD such as Spirochaeta and Smithella were enriched with Fe 3 O 4 @ceramsite treatment. Potential syntrophic metabolisms between syntrophic bacteria (Syntrophomonas , associated with DIET) and methanogens were also detected in the Fe 3 O 4 @ceramsite treatment AD system. • Fe 3 O 4 @ceramsite promoted methane production from WAS digestion. • Fe 3 O 4 @ceramsite enhanced digesta stability and sludge organics dissolution. • Larger surface area and better pore structure of Fe 3 O 4 @ceramsite facilitated AD performance. • Some functional anaerobes related to AD were enriched. [ABSTRACT FROM AUTHOR]

Methane recovery from waste activated sludge (WAS) through anaerobic digestion is generally restricted by the poor degradability of WAS. Herein, a novel sludge pretreatment technology by using the calcium hypochlorite (Ca(ClO) 2) in enhancing the methane production from WAS anaerobic digestion was reported. The solubilization of WAS was significantly increased after 10–240 mg Ca(ClO) 2 /g VS (VS: volatile solids) pretreatment for 48 h, under which the solubilization was 1.7–3.4 folds (i.e., 0.17–0.34 mg SCOD/mg VS; SCOD: soluble chemical oxygen demand) higher than that without Ca(ClO) 2 pretreatment (i.e., 0.1 mg SCOD/mg VS). Correspondingly, the methane production was increased from 250.0 ± 5.3 mL/g VS to 385.1 ± 3.3 mL/g VS with the doses of Ca(ClO) 2 increasing from 10 mg/g VS to 240 mg/g VS, resulted in an increasing methane production of 3.6%–59.7% than that without Ca(ClO) 2 pretreatment. The microbial community composition results exhibited that the populations of key acidogens (e.g., Longilinea sp.) and methanogens (e.g., Methanosaeta sp.) were both reduced significantly. Moreover, Ca(ClO) 2 decreased the cells viability, leading to a 76.2% reduction of living cells fraction. Accordingly, it was further confirmed that high dosage of Ca(ClO) 2 could inhibit three microbial-related processes relevant to methane production, i.e., acidification, hydrolysis and methanogenesis. [Display omitted] • Ca(ClO) 2 pretreatment enhanced methane production from WAS digestion. • Methane yield is positively related to pretreatment level of Ca(ClO) 2. • High dosage of Ca(ClO) 2 decreased the abundance of acidogens and methanogens. • High dosage of Ca(ClO) 2 inhibited hydrolysis, acidification, and methanogenesis. [ABSTRACT FROM AUTHOR]

Wastes recycling and reutilization technique could simultaneously fulfill waste control and energy recovery sustainably, which has attracted increasing attention. This work proposed a novel waste reuse technology utilizing ceramsite and amended Fe 2 O 3 -ceramsite made from waste activated sludge (WAS) as additives to promote the yield of methane from WAS anaerobic digestion (AD). Experimental results demonstrated that compared to the control (85.05 ± 0.2 mL CH 4 /g-VS), the cumulative methane yield was effectively enhanced by 14% and 40% when ceramsite and Fe 2 O 3 -ceramsite were added. Further investigation revealed that ceramsite, especially the Fe 2 O 3 -ceramsite, enriched the populations of key anaerobes involved in hydrolysis, acidification, and methanogenesis. Meanwhile, potential syntrophic metabolisms between syntrophic bacteria and methanogens were confirmed in the Fe 2 O 3 -ceramsite AD system. Mechanisms studies exhibited that ceramsite and Fe 2 O 3 -ceramsite reinforced intermediate processes for methane production. The favorable pore structure, enhanced Fe (III) reduction capacity and conductivity also contributed a lot to the AD process. [Display omitted] • Amended Fe 2 O 3 -ceramsite was more favorable to enhance WAS anaerobic digestion. • Ceramsite enriched functional microbes and constructed potential syntrophic metabolisms. • Intermediate processes for methane production were all enhanced by ceramsite. • Better pore structure and enhanced conductivity facilitated the methane production. [ABSTRACT FROM AUTHOR]

Clarithromycin retained in waste activated sludge (WAS) inevitably enters the anaerobic digestion system. So far, the complex impacts and fate of clarithromycin in continuous operated WAS anaerobic digestion system are still unclear. In this study, two semi-continuous long-term reactors were set up to investigate the effect of clarithromycin on biogas production and antibiotic resistance genes (ARGs) during WAS anaerobic digestion, and a batch test was carried out to explore the potential metabolic mechanism. Experimental results showed that clarithromycin at lower concentrations (i.e., 0.1 and 1.0 mg/L) did not affect biogas production, whereas the decrease in biogas production was observed when the concentration of clarithromycin was further increased to 10 mg/L. Correspondingly, the relative abundance of functional bacteria in WAS anaerobic digestion (i.e., Anaerolineaceae and Microtrichales) was reduced with long-term clarithromycin exposure. The investigation of ARGs suggested that the effect of methylation belonging to the target site modification played a critical role for the anaerobic microorganisms in the expression of antibiotic resistance, and ermF , played dominated ARGs, presented the most remarkable proliferation. In comparison, the role of efflux pump was weakened with a significant decrease of two detected efflux genes. During WAS anaerobic digestion, clarithromycin could be partially degraded into metabolites with lower antimicrobial activity including oleandomycin and 5-O-desosaminyl-6-O-methylerythronolide and other metabolites without antimicrobial activity. • Clarithromycin inhibited biogas production from WAS anaerobic digestion. • Most methylase ARGs in digested sludge were increased after clarithromycin exposure. • Clarithromycin was partially degraded after anaerobic digestion. • Oleandomycin (m/z 671 and m/z 590) were the main metabolites of clarithromycin. [ABSTRACT FROM AUTHOR]