Search

Improving the anaerobic fermentation (AF) efficiency of excess sludge (ES) is essential for attaining biosolid minimization, stabilization, resource recovery, and carbon-emission reduction. Along these lines, here, the synergistic mechanism of protease and lysozyme for enhancing hydrolysis and AF efficiency with better recovery of volatile fatty acids (VFAs) was thoroughly investigated. Single lysozyme was capable of reducing the zeta potential and fractal dimension when dosed into the ES-AF system, which was beneficial for increasing the contact probability between proteases and extracellular proteins. Moreover, the weight-averaged molecular weight of the loosely-bound extracellular polymeric substance (LB-EPS) reduced from 1867 to 1490 in the protease-AF group, which facilitated the penetration of EPS by the lysozyme. The soluble DNA and extracellular DNA (eDNA) of the enzyme cocktail pretreated group increased by 23.24 % and 77.09 %, and the cell viability decreased after 6-hour hydrolysis, demonstrating a better hydrolysis efficiency. Remarkably, the asynchronous dosed enzyme cocktail pretreatment was proven a better strategy to enhance both the solubilization and hydrolysis processes since the synergistic effect of these two enzymes can exclude the mutual interference. As a result, the VFAs were increased by 1.26 times higher than the blank group. The underlying mechanism of an environmental-friendly and effective strategy was examined to promote ES hydrolysis and acidogenic fermentation, which was beneficial for the recovery of VFAs and carbon-emission reduction., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

The accumulation of poly aluminum chloride (PAC) in dewatered waste activated sludge (WAS) can cause severe Al pollution and significantly reduce the production of volatile fatty acids (VFAs) from anaerobic fermentation. Herein, the combination of lysozyme and sodium citrate pretreatment was applied to stabilize the aluminum and enhance the VFAs production via anaerobic fermentation. The complexation and stabilization of aluminum by the citrate was efficient, which is conducive to relieving the inhibition of aluminum on lysozymes and other extracellular hydrolases. Compared with the control group, the lysozyme, protease and α-glucosidase activities were obtained at 1.86, 1.72, and 1.15 times, respectively, following the pretreatment. 129.71 mg/g volatile suspended solids (VSS) of soluble proteins and 26.3 mg/g VSS of polysaccharides were obtained within 4 h, together with the degradation of 124 % more proteins and 75 % more polysaccharides within three days. This provided a sufficient number of substrates for VFA production. 588.4 mg COD/g VSS of total VFAs were obtained after the six-day anaerobic fermentation from Al-rich WAS following the combination of lysozyme and sodium citrate pretreatment, which was 7.3 times higher than that of the control group. This study presents a novel approach for enhancing VFA production in anaerobic fermentation as well as reducing risk of Al hazards from Al-rich WAS., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Although magnetite has been widely investigated in anaerobic digestion (AD), its role in the practical AD of waste-activated sludge (WAS) after thermal hydrolysis pretreatment (THP) and its size effect remain unclear. In this study, magnetite with four different particle sizes was added during the AD of WAS after THP. With the reduction of magnetite particle size, cumulative methane production was increased, while the optimal dosage of magnetite decreased, with 0.1 μm magnetite at an optimal dosage of 2 g/L achieving the highest cumulative methane production increase of 111.97 % compared with the blank group (without magnetite). Smaller magnetite particles increased α-glucosidase and protease activities, coenzyme F 420 concentration, and electron-transport system activity (20.30 %, 173.02 %, 60.39 % and 158.08 % higher respectively than the blank group). The size of magnetite also influenced the establishment of direct interspecies electron transfer (DIET) during AD. Based on the analysis of the pilA gene abundance, magnetite with a large particle size could promote the formation of e-pili in syntrophic electroactive bacteria (Clostridium, Syntrophomonas, and Pseudomonas) and methanogens (Methanospirillum), thereby completing electron transfer. However, small-sized magnetite particles stimulated DIET by enhancing the secretion of conductive proteins in extracellular polymeric substances and membrane-bound enzymes (Fpo) in Methanosarcina., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this study., (Copyright © 2022 Elsevier B.V. All rights reserved.)