Effect of zero-valent iron (ZVI) and biogas slurry reflux on methane production by anaerobic digestion of waste activated sludge.

This study aimed to improve anaerobic digestion (AD) efficiency through the addition of zero-valent iron (ZVI) and biogas slurry. This paper demonstrated that methane production was most effectively promoted at a biogas slurry reflux ratio of 60%. The introduction of ZVI into anaerobic systems does not enhance its bioavailability. However, both biogas slurry reflux and the combination of ZVI with biogas slurry reflux increase the relative abundance of microorganisms involved in the direct interspecific electron transfer (DIET) process. Among them, the dominant microorganisms Methanosaeta, Methanobacterium, Methanobrevibacter, and Methanolinea accounted for over 60% of the total methanogenic archaea. The Tax4Fun function prediction results indicate that biogas slurry reflux and the combination of ZVI with biogas slurry reflux can increase the content of key enzymes in the acetotrophic and hydrotrophic methanogenesis pathways, thereby strengthening these pathways. The corrosion of ZVI promotes hydrogen production, and the biogas slurry reflux provided additional alkaline and anaerobic microorganisms for the anaerobic system. Their synergistic effect promoted the growth of hydrotrophic methanogens and improved the activities of various enzymes in the hydrolysis and acidification phases, enhanced the system's buffer capacity, and prevented secondary environmental pollution. PRACTITIONER POINTS: Optimal methane production was achieved at a biogas slurry reflux ratio of 60%. Biogas slurry reflux in anaerobic digestion substantially reduced discharge. ZVI addition in combination with biogas slurry reflux facilitates the DIET process.

Evaluation of sinonasal-related quality of life of 49 patients undergoing endoscopic skull base surgery.

OBJECTIVE: This study aimed to evaluate the sinonasal-related Quality of Life (QoL) in patients undergoing endoscopic skull base surgery. METHODS: A retrospective study was performed, including patients with benign and malignant tumors at a single institution. Each patient completed the 22-Item Sino-Nasal Outcome Test (SNOT-22) and the Empty Nose Syndrome 6 Item Questionnaires (ENS6Q) to assess their perceived QoL at least 2-months after treatment. RESULTS: Forty-nine patients were enrolled in this study. The average score was 25.1 (Stander Deviation [SD] 14.99) for SNOT-22 and 6.51 (SD=5.58) for ENS6Q. Analysis of the overall results for the SNOT-22 showed that olfactory damage was the most serious syndrome. The most frequently reported high-severity sub-domains in SNOT-22 were nasal symptoms and sleep symptoms. Nasal crusting was the most severe item in ENS6Q according to the report. Nine patients (18.4%) had a score higher than 10.5 which indicates the high risk of Empty Nose Syndrome (ENS). SNOT-22 score was related to the history of radiotherapy (p< 0.05), while the ENS6Q score was not. CONCLUSIONS: The possibility of patients suffering from ENS after nasal endoscopic skull base surgery is at a low level, although the nasal cavity structure is damaged to varying degrees. Meanwhile, patients undergoing endoscopic skull base surgery were likely to suffer nasal problems and sleep disorders. Patients who had received radiotherapy have a worse QoL than those without a history of radiotherapy. LEVEL OF EVIDENCE: Level 3.

Evaluation of sinonasal-related quality of life of 49 patients undergoing endoscopic skull base surgery

Abstract Objective This study aimed to evaluate the sinonasal-related Quality of Life (QoL) in patients undergoing endoscopic skull base surgery. Methods A retrospective study was performed, including patients with benign and malignant tumors at a single institution. Each patient completed the 22-Item Sino-Nasal Outcome Test (SNOT-22) and the Empty Nose Syndrome 6 Item Questionnaires (ENS6Q) to assess their perceived QoL at least 2-months after treatment. Results Forty-nine patients were enrolled in this study. The average score was 25.1 (Stander Deviation [SD] 14.99) for SNOT-22 and 6.51 (SD = 5.58) for ENS6Q. Analysis of the overall results for the SNOT-22 showed that olfactory damage was the most serious syndrome. The most frequently reported high-severity sub-domains in SNOT-22 were nasal symptoms and sleep symptoms. Nasal crusting was the most severe item in ENS6Q according to the report. Nine patients (18.4%) had a score higher than 10.5 which indicates the high risk of Empty Nose Syndrome (ENS). SNOT-22 score was related to the history of radiotherapy (p < 0.05), while the ENS6Q score was not. Conclusions The possibility of patients suffering from ENS after nasal endoscopic skull base surgery is at a low level, although the nasal cavity structure is damaged to varying degrees. Meanwhile, patients undergoing endoscopic skull base surgery were likely to suffer nasal problems and sleep disorders. Patients who had received radiotherapy have a worse QoL than those without a history of radiotherapy. Level of evidence Level 3.

Effect of thermal hydrolysis pretreatment on the occurrence of N-acyl homoserine lactone during anaerobic digestion of waste activated sludge.

This study sought to investigate the relationship between N-acyl homoserine lactones (AHLs) and methanogenic microorganisms, focusing on endogenous AHLs in the anaerobic digestion (AD) process. By analyzing waste activated sludge (WAS) samples, we examine the changes in microbial communities and the AHLs-methanogens connection. The Mantel test and Spearman correlation analysis were conducted to gain novel insights into the AD process. Our findings demonstrate that thermal hydrolysis pretreatment (THP) modifies AHL concentrations during AD, thereby enhancing methanogenic bacteria activity and regulating social interactions among microorganisms. In the Eth group (AD of THP samples labeled Eth), Methanobacterium and Methanosarcina accounted for over 80% of the methanogenic bacteria, with correlation coefficients greater than 0.5 between these bacterial taxa and N-hexyl-l-homoserine lactone (C6-HSL) and N-enanthyl-l-homoserine lactone (C7-HSL).

Characteristics of digested sludge-derived biochar for promoting methane production during anaerobic digestion of waste activated sludge.

This study investigated a novel method for enhancing methane production during anaerobic digestion of waste activated sludge with digested sludge-derived biochar (DSBC). Using response surface methodology, the following process conditions for DSBC synthesis were optimized: heating rate = 13.23 °C/min, pyrolysis temperature = 516 °C, and heating time = 192 min. DSBC significantly enhanced the methane production by 48 % and improved key coenzyme activity that accelerated the bioconversion of organic matter while promoting the decomposition and transformation of volatile fatty acids. Consequently, the lag period of methane production was shortened to 4.89 days, while the average proportion of methane greatly increased to 73.22%. Thus, DSBC could facilitate efficient methanogenesis in the anaerobic system by promoting electron transfer between syntrophic partners through the charge-discharge cycle of surface oxygen-containing functional groups. The study provides a reference for the resource utilization of anaerobic sludge residues and efficient anaerobic methanogenesis from sludge.

Investigating the synergic role of asynchronous dosed protease and lysozyme for facilitating excess sludge solubilization and acidogenic fermentation.

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.

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.

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

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.

Novel nitrogen-doped biochar supported magnetite promotes anaerobic digestion: Material characterization and metagenomic analysis.

Although different conductive materials have been applied to anaerobic digestion, there has not been a material that can really combine their merits and make up their shortcoming from each other. In this study, a novel nitrogen-doped biochar supported magnetite (Fe3O4@N-BC) was synthesized. Various material characterizations confirmed that nitrogen atoms were successful doped into the biochar and magnetite precipitated on its surface. 5 g/L Fe3O4@N-BC achieved the highest promotion of cumulative CH4 production by 1.75 times compared with the blank group. Further metagenomic analysis revealed that Fe3O4@N-BC could increase the gene abundances of pilA, MmcA, Fpo, Rnf and HdrEd in bacteria Clotridium, Pseudomonas and Syntrophomonas and archaea Methanosarcina. Redundancy analysis showed that it was electrical conductivity and electron exchange capacity that were the key physicochemical characteristics for Fe3O4@N-BC to facilitating direct interspecies electron transfer. This study provides a reference for future conductive material synthesis and its application for anaerobic digestion.

Metagenomic analysis reveals the size effect of magnetite on anaerobic digestion of waste activated sludge after thermal hydrolysis pretreatment.

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 F420 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.

Impact of divalent cations on lysozyme-induced solubilisation of waste-activated sludge: Perspectives of extracellular polymeric substances and surface electronegativity.

Lysozyme hydrolysis can accelerate waste-activated sludge (WAS) solubilisation, which can significantly shorten the process and promote the efficiency of anaerobic digestion. This study investigated the impact of divalent cations on lysozyme-induced solubilisation of WAS. The performance of lysozyme pretreatment was dramatically inhibited by Mg2+ and Ca2+. Compared to the control group, the amount of net SCOD, protein, and polysaccharides released to the supernatant were reduced by 36.6%, 44.7%, and 35.8%, respectively, in the presence of divalent cations. The extracellular polymeric substance (EPS) matrix became tightly bound, resulting in fewer proteins and polysaccharides being extracted from loosely-bound EPS (LB-EPS) with divalent cations, which was detrimental to the solubilisation of WAS. Divalent cations decreased the surface electronegativity of sludge particles and prolonged the adsorption of lysozymes by sludge flocs. More than 16.6% of total lysozymes remained in the liquid phase of WAS after 240 min Mg2+ and Ca2+ strengthened the binding among proteins and polysaccharides and promoted the intermolecular cross-linking of polysaccharides. The EPS matrix formed a dense spatial reticular structure that blocked the transfer of lysozymes from the EPS matrix to the pellet. As a result, the lysozymes accumulated in LB-EPS rather than hydrolysing the microorganism's cell wall. This study provides a new perspective on the restriction of WAS pretreatment with lysozymes and optimises the method of lysozyme-induced solubilisation of WAS.

Impact of magnesium ions on lysozyme-triggered disintegration and solubilization of waste activated sludge.

Lysozyme can efficiently accelerate solubilization and hydrolysis of waste activated sludge (WAS) for anerobic digestion. However, the effect of lysozyme was easily to be inhibited by metal ions in WAS. The impact of magnesium ions (Mg2+) on lysozyme catalyze WAS disintegration was investigated in this study. The effect of lysozyme on WAS hydrolysis could be hindered by Mg2+. Relatively high concentrations (>50 mg/L) of Mg2+ in sludge significantly reduced the release of soluble polysaccharides and proteins from WAS, while sulfate ions or chloride ions caused no such effect. Proteins were difficult to be extracted from extracellular polymeric substances (EPS) of WAS in the presence of Mg2+ (>10 mg/L) due to the divalent cation bridging (DCB) behavior, while the extraction of polysaccharides was not significantly affected. The polysaccharides and proteins in the inner EPS layer were transferred to the outer layer during the lysozyme treatment, and total quantities of both components maintained constantly. At least 23.1% lysozymes were trapped in the liquid phase of 100 mg Mg2+/L in the first hour. Mg2+ could significantly affect the transfer of lysozyme from liquid phase to the inner layer of sludge. Mg2+ neutralized the negative surface charge of the sludge particles, which hindered the absorption of positively charged lysozyme molecules by sludge flocs from the liquid phase. The proteins of TB-EPS had higher ratios of α-helixes and tighter structures than those in LB-EPS, which could impede the lysozyme transfer to the cell wall.

Insights into carbon recovery from excess sludge through enzyme-catalyzing hydrolysis strategy: Environmental benefits and carbon-emission reduction.

This study introduced the excellent improvement of enzyme cocktail (lysozyme and protease) on hydrolysis efficiency and the role of reducing carbon emission as an alternative carbon source. The best dosing method after optimization was to add four parts of lysozyme at 0 h and one part of protease at 1 h. The extracellular proteins and polysaccharides increased by 118% and 64% respectively under the optimal dosing mode. Enzyme cocktails reduced more organic matters and extended the distribution of sludge particles in the small particle size part. The enzymatic-treated sludge could reduce 21.09 kg CO2/t VSS if utilized to replace methanol for denitrification carbon source. Enzyme cocktails did better in enhancing both solubilization and hydrolysis than single enzymes under the optimal method. This study will provide a more integrated and comprehensive system for enzymatic pretreatment and new insight into the enzymatic pretreatment enhancing hydrolysis and reducing carbon emission.

New insight into enhanced short-chain fatty acids production from waste activated sludge through pretreatment of cation exchange resin coupled NaCl addition.

In this study, a novel pretreatment of cation exchange resin (CER) coupled NaCl addition was proposed to enhance waste activated sludge (WAS) hydrolysis and promote short-chain fatty acids (SCFAs) production in the anaerobic fermentation process. At the optimal pretreatment condition of 3 g/g SS CER and 15 g/L NaCl, considerable SCOD (i.e. 5107 mg/L, 35.4% of TCOD) was released after 2-day coupled treatment, which provided sufficient organic substance for the subsequent SCFAs production. The sludge hydrolysis mechanism was illustrated, i.e. CER triggered extracellular polymeric substances (EPS) disruption and NaCl induced microbial cells lysis. The synergistic interaction between CER and NaCl pretreatment was investigated and application potential of fermentative liquid was evaluated after the coupled pretreatment-enhanced anaerobic fermentation. In the presence of abundant biodegradable substrates in the fermentative liquid, 4742 mg COD/L (i.e. 388 mg COD/g VSS) of SCFAs production was achieved within 6-day anaerobic fermentation, mainly composed of acetic and propionic acids (70.4% of total SCFAs).