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[Display omitted] • Fe(VI) drove numerous carbon release of 140.65 mgC/gVSS by EPS and cell disruption. • Alkaline condition and advanced oxidation majorly contributed to carbon migration. • Carbon recovery of 63.68 mgC/gVSS was achievable in short-term biotransformation. • Remarkable carbon source usability (high C/N) and nutrient recovery were achieved. • Fe(VI) treatment provided considerable economic benefit and GHG-emission reduction. The short-chain fatty acids produced from waste activated sludge were deemed as the preferred carbon sources, however the specific carbon migration and recovery patterns have been rarely reported. This study demonstrated that Fe(VI) was capable of driving interphase carbon release and biotransformation towards carbon recovery in short-term anaerobic fermentation (48 h). Interestingly, the Fe(VI)-derived alkaline condition played the foremost and continuous driving force in interphase carbon migration with the proportions of 50.53–70.52 %, while the advanced oxidization provided the second most contributions of 25.46–45.82 % in short-acting role. Correspondingly, numerous extracellular and intracellular carbon sources of 136.66 mg C/g VSS were released in 4-h Fe(VI) treatment by structural protein molecule loosening, which were mainly composed of proteins (tryptophan and tyrosine), polysaccharides and humic acids. Meanwhile, 48.73 % of the dissolved carbon sources were bio-transformed for improving sludge acidification, contributing to the overall carbon recovery of 63.68 mg C/g VSS. The effective carbon source extraction was implemented by solid–liquid separation. The high C/N in fermentative liquid was achievable, suggesting considerable bio-availability of the recovered carbon sources. This indeed created economic benefits and carbon-emission reduction depending on alternative carbon source utilization and residual sludge solid reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbide slag greatly facilitated sludge hydrolysis rate to 14.73% in 4-h treatment. • Contribution distribution of carbide compositions to fermentation was quantified. • Alkaline hydrolysis dominantly drove EPS and cell disruption by protein loosening. • Numerous SCFAs of 2219.70 mg/L were produced with improved acidification. • Carbide slag treatment enhanced economic income and GHG-emission reduction. The anaerobic fermentation has been regarded as promising technology for short-chain fatty acids (SCFAs) recovery from excess sludge. Despite that various treatment approaches have been developed, the sustainable waste utilization of carbide slag in enhancing anaerobic fermentation has rarely been reported. It demonstrated that the carbide slag-derived alkaline condition dominantly contributed to triggering extracellular polymeric substance disruption and microbial cell lysis by protein molecule deconstruction. Considerable sludge hydrolysis was facilitated owing to extracellular and intracellular organic matter release, solubilizing 14.73 % of total solid organic matters in 4-h treatment. Correspondingly, massive SCFAs of 2219.70 mg COD/L (mainly acetate) were produced through 8-day anaerobic fermentation, with the improved acidification and the inhibited methanogenesis. Approximately 83.03–96.21 % of the recoverable SCFAs were extracted after sludge conditioning and solid–liquid separation, providing remarkable economic benefit of 196.23 CNY/ton VSS and carbon-emission reduction of 0.069–0.347 ton CO 2 /ton VSS. The findings proposed an innovative and sustainable carbide slag-driven anaerobic fermentation strategy for SCFAs recovery and waste stabilization, with low heavy metal residual and negligible environmental risks in "two wastes into one resource" pattern. [ABSTRACT FROM AUTHOR]

In decades, anaerobic fermentation with short-chain fatty acids (SCFAs) recovery from excess sludge have attained rising attention. However, rigid particulate organic matter (POMs) structure with slow hydrolysis limited anaerobic fermentation performance of excess sludge. Remarkable sludge hydrolysis performance was supposed to be achievable by the synchronous EPS repture and microbial cell lysis. This study clarified the improvement of overall anaerobic fermentation performance by combination treatment of lysozyme (Lyso) catalysis and metal regulation (MR). The Lyso + MR treatment triggered EPS rupture by protein structure deflocculation while catalyzing microbial cell lysis, which promoted massive extracellular and intracellular POMs hydrolysis. As a result, a significant amount of SCOD (5646.67 mg/L) was produced. Such endogenous organic matters hydrolysis led to considerable SCFAs accumulation (3651.14 mg COD/L) through 48-h anaerobic fermentation at 1.75 g/g SS cation-exchange resin and Lyso dosage of 10% (w/w), which was 5.945 times higher than that in the control. Additionally, it suggested that most of the recovered SCFAs remained in fermentative liquid after chemical conditioning and mechanical dewatering towards solid-liquid separation, which provided considerable economic benefit of 363.6–1059.1 CNY/ton SS. [Display omitted] • Extracellular and intracellular POMs were hydrolyzed by Lyso + MR treatment. • Lyso catalysis and MR treatment greatly promoted cell lysis and EPS rupture. • Considerable SCFAs of 3651 mg COD/L was produced by Lyso + MR assistant fermentation. • Satisfactory sludge dewaterability was achievable by chemical conditioning. • Engineering implications were expounded with economic benefits by SCFAs recovery. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na+-regulation drove sludge disintegration and solid–liquid interface variation. • Numerous carbon release (20.43%) was achieved from EPS disruption and cell lysis. • 70.83% of released carbon source was transformed into SCFAs in 4-day fermentation. • Overall carbon recovery rate of 12.51 % was achievable from WAS by Na+-regulation. • Considerable carbon source availability with high C/N provided practical benefits. Short-chain fatty acids (SCFAs) produced from anaerobic fermentation of waste activated sludge (WAS) have been regarded as the preferred carbon source, however the carbon migration pattern has rarely been reported. This work elucidated that the Na+ assistant anaerobic fermentation could facilitate carbon source release and bio-transformation towards carbon recovery from WAS. Obvious disintegration of sludge flocs and property variation of solid–liquid interface were triggered with Na+-regulation, leading to extracellular polymeric substance disruption and microbial cell apoptosis by protein structure loosening and osmotic pressure stress. Thereby, extracellular and intracellular carbon source (e.g. proteins, carbohydrates) were simultaneously solubilized, contributing to considerable carbon migration from sludge solid into liquid phase (up to 20.43 %). Meanwhile, 61.30 % of the released carbon source was bio-transformed with the improved sludge acidification in 4-day Na+ assistant anaerobic fermentation. Substantial SCFAs of 61.39 mg C/g VSS was produced, which was mainly composed by acetate and propionate (69.07 %). As such, the overall carbon recovery rate of 12.51 % was achievable. The carbon source bio-availability in fermentative liquid indeed created economic benefits and carbon-emission reduction depending on alternative carbon source utilization and residual carbon source reduction in fermented sludge disposal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective Na+ stress improved protease activity and promoted DOMs biodegradation. • Na+ stress induced bacteria screening with reduced species richness and diversity. • Selective Na+ stress facilitated "SCFAs-producing" microbial community formation. • Salt-tolerant acidogens were enriched and vulnerable methanogens were inhibited. • Na+ stress is prime inducement to modify microbial community for SCFAs accumulation. The short-chain fatty acids (SCFAs) production was facilitated in Na+ assistant anaerobic fermentation of waste activated sludge, whereas the relevant micro-ecosystem characteristics were unclear. This work explored the microbial community and hydrolases shifts under Na+ stress. It demonstrated that the selective Na+ stress increased protease activities to 126–160% while inhibiting α-glucosidase activities to 83.1–91.3%. Correspondingly, the biodegradation rates of protein and glucose were improved from 25.6% and 45.8% to 39.0% and 55.2%, respectively. Furthermore, the microbial species richness and biodiversity gradually decreased, attributing to Na+-induced cell lysis. Selective Na+ stress was the prime inducement for microbial community evolution and promoted "SCFAs-producing" bacterial community formation by "bacteria-screening" roles. Overall, the hydrolytic bacteria and acidogens became dominant bacteria, which were resistive to Na+ stress, while the SCFAs consumers were restrained as they are salinity-sensitive. Such microbial community shift modified functional metabolisms for enhancing anaerobic fermentation performance. The pathways for metabolism and genetic information processing were improved, positively relating to the facilitated catabolism of fermentation substrates. Consequently, the mechanism of maximized SCFAs accumulation by selective Na+ stress was proposed, i.e. microbial modification of fermentation ecosystem for facilitating sludge hydrolysis and acidification with impeded methanogenesis. [ABSTRACT FROM AUTHOR]

Short-chain fatty acids (SCFAs) recovery through anaerobic fermentation is a promising pathway to achieve economic benefits and carbon-emission reduction in waste activated sludge management. Although numerous pretreatment approaches have been investigated, alkaline hydrolase blend (AHB) incubation at initial pH 10.0 condition for enhancing anaerobic fermentation has rarely been reported. In this study, the sludge flocs were disintegrated into electronegative particle fragments with extracellular polymeric substance disruption and microbial cell lysis, owing to the synergistic effect of alkali-triggered sludge solubilization and AHB-catalyzed hydrolysis. Substantial sludge hydrolysis and biodegradable organic matter release were thereby induced. After pH 10 + AHB pretreatment for 2 h, numerous SCOD release of 5109 mg/L was achievable, which was approximately 12.4, 2.02, and 1.19 times higher than those in control, pH 10 and pH 10+alkaline protease pretreatments, respectively. Meanwhile, the AHB boosted hydrolysis and biodegradation of dissolved organic matters, promoting a low molecular weight shift in molecular weight distribution. The dissolved organic matter compositions tended to low molecular weight organic matters, accelerating the overall anaerobic fermentation process. Correspondingly, considerable SCFAs of 528.9 mg COD/g VSS was produced through a short-term anaerobic fermentation (3 days), which was 5.6, 1.7 and 1.1 times higher than the maximum SCFAs production by control, pH 10 and pH 12–10+alkaline protease pretreatments, respectively. The produced SCFAs were mostly composed of acetate (58.7%), which could be recovered as biodegradable carbon source. By adopting the AHB-based strategy, economic benefits of 392.4–580.6 CNY/ton sludge SS and carbon-emission reduction of 0.207–0.521 ton CO 2 /ton sludge SS were achievable. Apparently, the AHB-based strategy is a cost-effective and carbon-beneficial technology for sludge management. [Display omitted] • pH 10 + AHB pretreatment induced remarkable sludge hydrolysis (SCOD/TCOD = 32.5%). • AHB facilitated DOMs hydrolysis and biodegradation with low molecular weight shift. • Alkali-triggered sludge solubilization and AHB-catalyzed hydrolysis was proposed. • SCFAs of 349.9 mg COD/g SS was produced by a short-term anaerobic fermentation. • Carbon recovery with economic and carbon-emission reduction benefits were assessed. [ABSTRACT FROM AUTHOR]