Enhanced acidogenic fermentation from Al-rich waste activated sludge by combining lysozyme and sodium citrate pretreatment: Perspectives of Al stabilization and enzyme activity

Investigating enhancement of protease and lysozyme combination pretreatment on hydrolysis of sludge organics under humic acid inhibition

This study investigated the impact of humic acid (HA) on enzymatic pretreatment efficiency, focusing on sludge properties and HA molecular structure. The results showed that enzymatic pretreatment alleviates HA inhibition, improving hydrolysis efficiency. In the presence of HA, soluble proteins and polysaccharides in the enzyme-cocktail group reached 27.7 mg/L and 23.9 mg/L, 1.4 and 1.3 times higher than the blank group, respectively. The enzyme-cocktail group also had the highest soluble DNA concentration (19.4 mg/L) and the lowest viable cell proportion (69.3 %), indicating effective cell lysis. Enzyme-cocktail pretreatment reduced electrostatic repulsion, enhancing the mobility of extracellular organics. Enzyme interactions with HA released internal hydrolases and decreased amide groups on the HA surface, increasing the availability of biodegradable substrates. Overall, enzymatic pretreatment proves effective in mitigating HA-induced inhibition, thereby improving sludge biodegradation and enhancing carbon recovery in anaerobic fermentation.

Effect of lysozyme combined with hydrothermal pretreatment on excess sludge and anaerobic digestion

Anaerobic digestion (AD) is widely employed for sludge stabilization and waste reduction. However, the slow hydrolysis process hinders methane production and leads to prolonged sludge issues. In this study, an efficient and eco-friendly lysozyme pre-treatment method was utilized to address these challenges. By optimizing lysozyme dosage, hydrolysis and cell lysis were maximized. Furthermore, lysozyme combined with hydrothermal pretreatment enhanced overall efficiency. Results indicate that: (1) When lysozyme dosage reached 90 mg/g TS after 240 min of pretreatment, SCOD, soluble polysaccharides, and protein content reached their maxima at 855.00, 44.09, and 204.86 mg/L, respectively. This represented an increase of 85.87%, 365.58%, and 259.21% compared to the untreated sludge. Three-dimensional fluorescence spectroscopy revealed the highest fluorescence intensity in the IV region (soluble microbial product), promoting microbial metabolic activity. (2) Lysozyme combined with hydrothermal pretreatment significantly increased SCOD, soluble proteins, and polysaccharide release from sludge, reducing SCOD release time. Orthogonal experiments identified Group 3 as the most effective for SCOD and soluble polysaccharide release, while Group 9 released the most soluble proteins. The significance order of factors influencing SCOD, soluble proteins, and polysaccharide release is hydrothermal temperature > hydrothermal time > enzymatic digestion time.(3) The lysozyme-assisted hydrothermal pretreatment group exhibited the fastest release and the highest SCOD concentration of 8,135.00 mg/L during anaerobic digestion. Maximum SCOD consumption and cumulative gas production increased by 95.89% and 130.58%, respectively, compared to the control group, allowing gas production to conclude 3 days earlier.

Lysozyme coupling protease pretreatment to relieve the humic acid inhibition on excess sludge anaerobic fermentation

The asynchronous dosed protease and lysozyme combination pretreatment was proved to be effective in enhancing the anaerobic fermentation of waste activated sludge (WAS). However, humic acid (HA) in the sludge could interact with hydrolase and restrain the hydrolysis efficiency, thus inhibiting short-chain fatty acids (SCFAs) production. This study investigated the effectiveness and mechanism of enzymatic pretreatment against HA. Results showed that the enzyme cocktail method increased the extracellular bioavailable contents by 34 %, which raised SCFAs production by 89.69 % (1269.65 mg COD /L). The balanced ratio of hydrolysis and fermentation communities suggested that the small molecular organics generated by the hydrolysis community could be sufficiently utilized by fermentation communities. The metabolism of amino acids and glucose was facilitated, and the activities of key enzymes were enhanced. These results clarified the effect of asynchronous enzyme cocktail pretreatment against HA inhibition and contributed to SCFAs production, which offered fresh perspectives on carbon recovery.

Facilitating effects of the synergy with zero-valent iron and peroxysulfate on the sludge anaerobic fermentation system: Combined biological enzyme, microbial community and fermentation mechanism assessment

This study evaluated a synergetic waste activated sludge treatment strategy with environmentally friendly zero-valent iron nanoparticles (Fe0) and peroxysulfate. To verify the feasibility of the synergistic treatment, Fe0, peroxysulfate, and the mixture of peroxysulfate and Fe0 (synergy treatment) were added to different sludge fermentation systems. The study demonstrated that the synergy treatment fermentation system displayed remarkable hydrolysis performance with 435.50 mg COD/L of protein and 197.67 mg COD/L of polysaccharide, which increased 1.13-2.85 times (protein) and 1.12-1.49 times (polysaccharide) for other three fermentation system. Additionally, the synergy treatment fermentation system (754.52 mg COD/L) exhibited a well acidification performance which was 1.35-41.73 times for other systems (18.08-557.27 mg COD/L). The synergy treatment fermentation system had a facilitating effect on the activity of protease, dehydrogenase, and alkaline phosphatase, which guaranteed the transformation of organic matter. Results also indicated that Comamonas, Soehngenia, Pseudomonas, and Fusibacter were enriched in synergy treatment, which was beneficial to produce SCFAs. The activation of Fe0 on peroxysulfate promoting electron transfer, improving the active groups, and increasing the enrichment of functional microorganisms showed the advanced nature of synergy treatment. These results proved the feasibility of synergy treatment with Fe0 and peroxysulfate to enhance waste activated sludge anaerobic fermentation.

Synergistic promotion of sludge reduction by surfactant-producing and lysozyme-producing bacteria: Optimization and effect of Na. BIORESOURCE TECHNOLOGY 2024;393:130065. [PMID: 37984671 DOI: 10.1016/j.biortech.2023.130065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

To improve the efficiency of aerobic digestion, this investigation utilized the synergistic effect of lysozyme-producing strain YH14 and surfactant-producing strain ZXY4 to promote sludge hydrolysis, and added NaCl to enhance this promoting effect. The best performance in promoting sludge hydrolysis was achieved when the inoculum of functional bacteria was 12 % (inoculum ratio of strain YH14: strain ZXY4 = 1:3) and the dosage of NaCl was 5 g L-1, which caused an increase of 19.25 % in the SS removal rate and 2588.21 mg L-1 in the SCOD release, as compared with the control. Fluorescence region integral analysis shows that the synergy of two functional bacteria and NaCl can enhance the biodegradability of sludge. Protein secondary structure analysis shows that strain ZXY4 and Na+ cause the EPS structure to loosen, increasing the chances of lysozyme lysis of bacteria. Nucleotide metabolism, metabolism of other amino acids and membrane transport enhanced in a co-processing system.

Enantioselective effects of chiral prothioconazole and its metabolites: Oxidative stress in HepG2 cells and lysozyme activity

Chiral pesticides may exhibit enantioselectivity in terms of bioconcentration, environmental fate, and reproductive toxicity. Here, chiral prothioconazole and its metabolites were selected to thoroughly investigate their enantioselective toxicity and mechanisms at the molecular and cellular levels. Multispectral techniques revealed that the interaction between chiral PTC/PTCD and lysozyme resulted in the formation of a complex, leading to a change in the conformation of lysozyme. Meanwhile, the effect of different conformations of PTC/PTCD on the conformation of lysozyme differed, and its metabolites were able to exert a greater effect on lysozyme compared to prothioconazole. Moreover, the S-configuration of PTCD interacted most strongly with lysozyme. This conclusion was further verified by DFT calculations and molecular docking as well. Furthermore, the oxidative stress indicators within HepG2 cells were also affected by chiral prothioconazole and its metabolites. Specifically, S-PTCD induced more substantial perturbation of the normal oxidative stress processes in HepG2 cells, and the magnitude of the perturbation varied significantly among different configurations (P > 0.05). Overall, chiral prothioconazole and its metabolites exhibit enantioselective effects on lysozyme conformation and oxidative stress processes in HepG2 cells. This work provides a scientific basis for a more comprehensive risk assessment of the environmental behaviors and effects caused by chiral pesticides, as well as for the screening of highly efficient and less biotoxic enantiomeric monomers.

Revealing the mechanism of novel nitrogen-doped biochar supported magnetite (NBM) enhancing anaerobic digestion of waste-activated sludge by sludge characteristics

Anaerobic digestion (AD) is a promising technology in waste treatment and energy recovery. However, it suffers from long retention time and low biogas yield. In this study, novel nitrogen-doped biochar supported magnetite (NBM) was synthesized and applied to enhance the AD of waste-activated sludge. Results showed that NBM increased cumulative methane production and SCOD removal efficiency by up to 1.75 times and 15% respectively at 5 g/L compared with the blank. NBM enhanced both hydrolysis and methanogenesis process during AD and the activities of α-glucosidase, protease, coenzyme F₄₂₀ and electron transport system were increased by 19%, 163%, 104% and 160% respectively at 5 g/L NBM compared with the blank. NBM also facilitated the secretion of conductive protein in extracellular polymeric substances as well as the formation of conductive pili, leading to 3.18-7.59 times higher sludge electrical conductivity. Microbial community analysis revealed that bacteria Clostridia and archaea Methanosarcina and Methanosaeta were enriched by the addition of NBM, and direct interspecies electron transfer might be promoted between them. This study provides a practical reference for future material synthesis and its application.