Combined electrical-alkali pretreatment to increase the anaerobic hydrolysis rate of waste activated sludge during anaerobic digestion

Objectives : Various pre-treatment methods have been applied to waste activated sludge(WAS) to improve the efficiency of anaerobic digestion(AD) by enhancing hydrolysis. The objective of this study was to find out the relationship between increased solubilization and AD efficiency in response to the application of different pretreatment methods(Acid+Heat and Alkali+Heat) to WAS.Methods : Acid+Heat(pH 2+130℃) and Alkali+Heat(pH 10+130℃) pretreatment processes were performed by adding HCl and KOH, respectively. A biochemical methane potential(BMP) test was subsequently conducted to determine the AD efficiency of pretreated WAS. Finally, the physicochemical characteristics in the effluent of AD of WAS, done by excitation-emission matrix(EEM) and size exclusion chromatography(SEC), were analyzed to investigate the degree of changed intermediates during microbial degradation of organic compounds.Results : Both Acid+Heat and Alkali+Heat pretreatments resulted in similar solubilization of WAS, reaching 34.1 and 36.3%, respectively. Meanwhile, it was found that the CH4 yield obtained from the Alkali+Heat pretreated sample was lower than the sample of Acid+Heat. The results of EEM analysis showed that the Alkali+Heat pretreated WAS had a higher portion of less biodegradable organic compounds with high- molecular weight in the soluble sample than that of the Alkali+Heat pretreated sample.Conclusion : This study was conducted to clarify the relationship by comparing the hydrolysis rate and AD efficiency according to the application of Acid+Heat and Alkali+Heat pretreatment. It was found that the amount of methane generated could vary depending on the properties of the dissolved substances in response to different pretreatment approaches.

The electrochemical (EC) combined with hypochlorite (ClO–) pretreatment has been proven to be effective in improving disintegration of waste-activated sludge (WAS) and enhancing anaerobic digestion recently. The ClO– dosage had a significant impact on the performance of WAS solubilization and biogas production in terms of the disintegration degree (DDCOD), release of proteins (PNs) and polysaccharides (PSs), soluble nitrogen and phosphate, and subsequent anaerobic digestion. The results showed that a higher ClO– dosage was favorable to WAS solubilization and EC–ClO– pretreatment was able to rupture the floc structure and break cells apart. According to batch anaerobic digestion tests, the optimum ClO– dosage for EC–ClO– pretreatment was 0.6% (v/v), with up to 61.1% higher methane production compared to the unpretreated sludge after mesophilic anaerobic digestion for 40 days. Model-based analysis suggested that EC–ClO– pretreatment could enhance the hydrolysis process as well as methane potential. Moreover...

Mechanistic insights into the roles of ferric chloride on methane production in anaerobic digestion of waste activated sludge

ABSTRACTThe microalgae Chlorella sorokiniana are used as co-substrate for waste activated sludge (WAS) anaerobic digestion. The specific objective of this research was to evaluate the feasibility of improving methane production from anaerobic digestion of WAS in co-digestion with this microalga, based on an optimized mixture percentage. Thus, the anaerobic co-digestion of both substrates aims to overcome the drawbacks of the anaerobic digestion of single WAS, simultaneously improving its management. Different co-digestion mixtures (0% WAS-100% microalgae; 25% WAS-75% microalgae; 50% WAS-50% microalgae; 75% WAS-25% microalgae; 100% WAS-0% microalgae) were studied. The highest methane yield (442 mL CH4/g VS) was obtained for the mixture with 75% WAS and 25% microalgae. This value was 22% and 39% higher than that obtained in the anaerobic digestion of the sole substrates WAS and microalgae, respectively, as well as 16% and 25% higher than those obtained for the co-digestion mixtures with 25% WAS and 75% microalgae and 50% WAS and 50% microalgae, respectively. The kinetic constant of the process increased 42%, 42% and 12%, respectively, for the mixtures with 25%, 50% and 75% of WAS compared to the substrate without WAS. Anaerobic digestion of WAS, together with C. sorokiniana, has been clearly improved by ensuring its viability, suitability and efficiency.

Enhanced hydrolysis/acidogenesis and potential mechanism in thermal-alkali-biofilm synergistic pretreatment of high-solid and low-organic-content sludge

Use of lyophilized and acclimated digestate dominated by Methanobrevibacter as a start-up inoculum in anaerobic digester led to higher methane production in biochemical methane potential assays

Novel anaerobic digestion of waste activated sludge via isoelectric-point pretreatment: Ultra-short solids retention time and high methane yield

Occurrence, effect, and fate of residual microplastics in anaerobic digestion of waste activated sludge: A state-of-the-art review

How does synthetic musks affect methane production from the anaerobic digestion of waste activated sludge?

Enhancement of waste activated sludge hydrolysate digestion efficiency via promotion of direct interspecies electron transfer.

Anaerobic digestion has been widely applied for waste activated sludge (WAS) treatment. However, methane production from anaerobic digestion of WAS is usually limited by the slow hydrolysis rate and/or poor biochemical methane potential of WAS. This work systematically studied the effects of three different types of zero valent iron (i.e., iron powder, clean scrap and rusty scrap) on methane production from WAS in anaerobic digestion, by using both experimental and mathematical approaches. The results demonstrated that both the clean and the rusty iron scrap were more effective than the iron powder for improving methane production from WAS. Model-based analysis showed that ZVI addition significantly enhanced methane production from WAS through improving the biochemical methane potential of WAS rather than its hydrolysis rate. Economic analysis indicated that the ZVI-based technology for enhancing methane production from WAS is economically attractive, particularly considering that iron scrap can be freely acquired from industrial waste. Based on these results, the ZVI-based anaerobic digestion process of this work could be easily integrated with the conventional chemical phosphorus removal process in wastewater treatment plant to form a cost-effective and environment-friendly approach, enabling maximum resource recovery/reuse while achieving enhanced methane production in wastewater treatment system.

Enhanced methane production from anaerobic digestion of waste activated sludge through preliminary pretreatment using calcium hypochlorite

A majority of microplastics (MPs) in wastewater treatment plants are aggregated in waste activated sludge (WAS) and potentially threaten the subsequent anaerobic digestion. Meanwhile, many physical and chemical techniques have been used as pretreatment methods to improve the anaerobic digestion of WAS. However, the effects of frequently used pretreatments on the MPs during WAS anaerobic digestion remain poorly characterized. Here, the impacts of physical (ultrasonic and thermal methods) and chemical pretreatments (alkaline and Fenton methods) on the anaerobic digestion performance of WAS containing polystyrene microplastics (PS-MPs) were investigated. Thermal and chemical pretreatments showed obvious improvements in sludge disintegration, the methane yields of which were increased by 17.5–20.4%. The concentrations of sodium dodecyl sulfate leached from PS-MPs in chemically pretreated groups were 1.7–2.6 times higher than those of the physical pretreatments in spite of the high efficiency of digestion. In addition, the generation of reactive oxygen species among four pretreated groups showed no significant difference (p > 0.05) and a slight increase compared with that of the control. As for the long-term effects of pretreatments on microbial communities, the thermally pretreated digester exhibited the highest proportion of methanogens (phyla Halobacterota and Euryarchaeota) among the four pretreatments, accounting for 13.2%. From the perspectives of the performance of anaerobic digestion and the toxic alteration of MPs, thermal pretreatment is more recommended to improve the anaerobic digestion of WAS containing PS-MPs.

Enhanced hydrolysis of waste activated sludge for methane production via anaerobic digestion under N2-nanobubble water addition.

The impact and fate of clarithromycin in anaerobic digestion of waste activated sludge for biogas production