Effect of gradual increase of salt on performance and microbial community during granulation process.

Salinity was considered to have effects on the characteristics, performance microbial communities of aerobic granular sludge. This study investigated granulation process with gradual increase of salt under different gradients. Two identical sequencing batch reactors were operated, while the influent of Ra and Rb was subjected to stepwise increments of NaCl concentrations (0-4 g/L and 0-10 g/L). The presence of filamentous bacteria may contribute to granules formed under lower salinity conditions, potentially leading to granules fragmentation. Excellent removal efficiency achieved in both reactors although there was a small accumulation of nitrite in Rb at later stages. The removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Ra were 95.31%, 93.70% and 88.66%, while the corresponding removal efficiencies in Rb were 94.19%, 89.79% and 80.74%. Salinity stimulated extracellular polymeric substances (EPS) secretion and enriched EPS producing bacteria to help maintain the integrity and stability of the aerobic granules. Heterotrophic nitrifying bacteria were responsible for NH4+-N and NO2--N oxidation of salinity systems and large number of denitrifying bacteria were detected, which ensure the high removal efficiency of TN in the systems.

Micro-polluted water source purification of root channel wetland in Jiaxing, China.

Root channel wetlands, as a new type of nature-imitating wetland system, provide a paradigm for micro-polluted water source purification; however, there is a knowledge gap on root channel wetlands' pollution removal effects and their main influencing factors after longtime operation. This study collected the turbidity, ammonia nitrogen (NH3-N), total nitrogen (TN), total phosphorus (TP), permanganate index (CODMn), dissolved oxygen (DO), and chemical oxygen demand (COD) at the inlet and outlet of Shijiuyang (SJY) wetland and Guanjinggang (GJG) wetland in Jiaxing City, China, from 2019 to 2021. The results showed that root channel wetlands had better water quality improvement effects. The SJY wetland had larger removal rates for DO, CODMn, and turbidity compared with the GJG wetland. In contrast, other water quality indexes have similar removal rates at both wetlands. The influencing factor analysis showed that water purification agent, flow, pH, and water temperature have large influences on the removal rates of pollutants for both wetlands. To address high turbidity and excessive DO, which are the primary pollutants affecting the two wetlands, implementing the diversion river before the pretreatment area and incorporating ecological floating beds in the deep purification area are recommended solutions to mitigate these issues. Compared with conventional general constructed wetlands, root channel wetlands are a more cost-effective and sustainable technology. The research is conducive to improving understanding of root channel wetland purification for micro-polluted water sources and enhancing water supply security capability in the plains water network area of the Yangtze River Delta region. PRACTITIONER POINTS: Compared with conventional general constructed wetlands, root channel wetlands are more cost-effective and sustainable technology. The SJY wetland demonstrated better removal rates for DO, CODMn, and turbidity, indicating a higher purification capacity compared to GJG wetland. Flow rate and pH are the primary factors influencing the GJG wetland, while the waterpurification agent and water temperature are the main factors affecting water quality in the SJY wetland.

Impact of untreated tannery wastewater in the evolution of multidrug-resistant bacteria in Bangladesh.

The tannery industry produces one of the worst contaminants, and unsafe disposal in nearby waterbodies and landfills has become an imminent threat to public health, especially when the resulting multidrug-resistant bacteria and heavy metals enter community settings and animal food chains. In this study, we have collected 10 tannery wastewater (TWW) samples and 10 additional non-tannery wastewater (NTW) samples to compare the chemical oxygen demand (COD), pH, biological oxygen demand (BOD), dissolved oxygen (DO), total dissolved solids (TDS), chromium concentration, bacterial load, and antibiotic resistance profiles. While COD, pH, and chromium concentration data were previously published from our lab, this part of the study uncovers that TWW samples had a significantly higher bacterial load, compared to the non-tannery wastewater samples (5.89 × 104 and 9.38 × 103 cfu/mL, respectively), higher BOD and TDS values, and significantly lower DO values. The results showed that 53.4, 46.7, 40.0, and 40.0% of the TWW isolates were resistant to ceftriaxone, erythromycin, nalidixic acid, and azithromycin, respectively. On the other hand, 20.0, 30.0, 50.0, and 40.0% of the NTW isolates were resistant to the same antibiotics, respectively. These findings suggest that the TWW isolates were more resistant to antibiotics than the NTW isolates. Moreover, the TWW isolates exhibited higher multidrug resistance than the NTW isolates, 33.33, and 20.00%, respectively. Furthermore, spearman correlation analysis depicts that there is a negative correlation between BOD and bacterial load up to a certain level (r = - 0.7749, p = 0.0085). In addition, there is also a consistent negative correlation between COD and bacterial load (r = - 0.7112, p = 0.0252) and TDS and bacterial load (r = - 0.7621, p = 0.0104). These findings suggest that TWW could pose a significant risk to public health and the environment and highlight the importance of proper wastewater treatment in tannery industries.

Leveraging microbial synergy: Predicting the optimal consortium to enhance the performance of microbial fuel cell using Subspace-kNN.

Microbial Fuel Cells (MFCs) are a sophisticated and advanced system that uses exoelectrogenic microorganisms to generate bioenergy. Predicting performance outcomes under experimental settings is challenging due to the intricate interactions that occur in mixed-species bioelectrochemical reactors like MFCs. One of the key factors that limit the MFC's performance is the presence of a microbial consortium. Traditionally, multiple microbial consortia are implemented in MFCs to determine the best consortium. This approach is laborious, inefficient, and wasteful of time and resources. The increase in the availability of soft computational techniques has allowed for the development of alternative strategies like artificial intelligence (AI) despite the fact that a direct correlation between microbial strain, microbial consortium, and MFC performance has yet to be established. In this work, a novel generic AI model based on subspace k-Nearest Neighbour (SS-kNN) is developed to identify and forecast the best microbial consortium from the constituent microbes. The SS-kNN model is trained with thirty-five different microbial consortia sharing different effluent properties. Chemical oxygen demand (COD) reduction, voltage generation, exopolysaccharide (EPS) production, and standard deviation (SD) of voltage generation are used as input features to train the SS-kNN model. The proposed SS-kNN model offers an accuracy of 100% during training period and 85.71% when it is tested with the data obtained from existing literature. The implementation of selected consortium (as predicted by SS-kNN model) improves the COD reduction capability of MFC by 15.67% than that of its constituent microbes which is experimentally verified. In addition, to prevent the effects of climate change and mitigate water pollution, the implementation of MFC technology ensures clean and green electricity. Consequently, achieving sustainable development goals (SDG) 6, 7, and 13.

Characterizing graphene oxide waste stream and assessing its impact on anaerobic co-digestion with municipal sludge.

This study evaluated anaerobic co-digestion as a promising strategy for managing organic-contaminated waste streams generated from nanomaterial synthesis. The novel approach enabled precise quantification of organic content, efficient biomethane recovery, and a sustainable redirection of ethanol-contaminated graphene oxide (GO) dispersions. The proposed method achieved high accuracy (93-97%) in detecting organic content in ethanol-contaminated GO dispersions, significantly outperforming the conventional total chemical oxygen demand (tCOD) method, which only reached 75-77% accuracy. Additionally, co-digestion of trace ethanol content in GO dispersions with municipal sludge substantially enhanced methane production kinetics, resulting in a 17.6% increase in specific methane yield (per tCOD added) and a 284% increase in total methane production. Parallel anaerobic digestion (AD) experiments using conductive GO nanosheets (without ethanol) revealed the synergistic impact of GO nanosheets and trace ethanol content as a key mechanism driving these improvements. Furthermore, the study provided evidence of the biological reduction of GO and its magnetite-decorated counterpart, magnetic GO, as indicated by a shift in the ID/IG ratio from 1.06 to 0.77 and a G-band shift from 1606 cm⁻1-1565 cm⁻1. This reduction decreased the stability of nanosheets in the AD liquid phase, promoting their partitioning into the solid phase. This process facilitates the adsorption of the GO phase within the digestate and allows for the slow release of micronutrients when used as soil amendments.

Sequential electro-coagulation and electro-Fenton processes for the treatment of textile wastewater.

Textile wastewater, laden with persistent dyes and non-biodegradable organics, poses a challenge for treatment in common effluent treatment plants (CETPs) using conventional methods. Pre-treatment of textile effluents is essential to ensure compatibility with CETPs. The present study employed three-dimensional (3D) aluminum and graphite electrodes for a sequential electro-coagulation and electro-Fenton (EC + EF) process. An experimental plan of 25 experiments was constructed using Taguchi method. The combination resulted in high removal efficiencies: 99.91% for color, 93.20% for chemical oxygen demand (COD), and 91.75% for total organic carbon (TOC) for the operating parameters; for EC, current density (J): 20 mA/cm2, time (t): 45 min, speed of rotation (N): 55 rpm; and for EF, current density (J): 25 mA/cm2, time (t): 50 min, iron concentration: 40 mg/L. Post-treatment, the wastewater exhibited an enhanced biodegradability index of 0.875, rendering it suitable for CETPs. There was an increase of 11% in the total energy consumption when energy spent during rotation and aeration at the time of EC and EF, respectively, were considered. This energy increases the cost and is not accounted for, in previous research. The energy consumption in kWh per g of COD removed at optimum condition for the hybrid treatment was 0.0314, which is lower than the energy consumption by other electrochemical processes employing plate electrodes. This indicates that 3D electrodes are more energy efficient than plate electrodes. PRACTITIONER POINTS: Hybrid electrochemical processes can be used as pre-treatment method for textile effluents. Three-dimensional electrodes improve removal rates with lower energy consumption. Significant color, COD, and TOC abatement were noted post-hybrid treatment of textile wastewater. Biodegradability of the textile effluent improves after the hybrid treatment.

Exploring alkali-treated corn cob for high-rate removal of NOX and SO2 from flue gas: Focus on carbon release capacity, removal performance, and comparison with conventional carbon sources.

This investigation explored the potential of utilizing alkali-treated corn cob (CC) as a solid carbon source to improve NOX and SO2 removal from flue gas. Leaching experiments unveiled a hierarchy of chemical oxygen demand release capacity: 0.03 mol/L alkali-treated CC > 0.02 mol/L > 0.01 mol/L > 0.005 mol/L > control. In NOX and SO2 removal experiments, as the inlet NOX concentration rose from 300 to 1000 mg/m3, the average NOX removal efficiency increased from 58.56 % to 80.00 %. Conversely, SO2 removal efficiency decreased from 99.96 % to 91.05 %, but swiftly rebounded to 98.56 % by day 18. The accumulation of N intermediates (NH4+, NO3-, NO2-) increased with escalating inlet NOX concentration, while the accumulation of S intermediates (SO42-, SO32-, S0) varied based on shifts in the population of functional bacteria. The elevation in inlet NOX concentration stimulated the growth of denitrifying bacteria, enhancing NOX removal efficiency. Concurrently, the population of nitrate-reducing sulfur-oxidizing bacteria and sulfate-reducing bacteria expanded, aiding in the accumulation of S0 and the removal of SO2. The comparison experiments on carbon sources confirmed the comparable NOX and SO2 removal efficiencies of alkali-treated CC and glucose, yet underscored differences in intermediates accumulation due to distinct genus structures.

Optimization of indirect wastewater characterization using led spectrophotometry: a comparative analysis of regression, scaling, and dimensionality reduction methods.

LED spectrophotometry is a robust technique for the indirect characterization of wastewater pollutant load through correlation modeling. To tackle this issue, a dataset with 1300 samples was collected, from both raw and treated wastewater from 45 wastewater treatment plants in Spain and Chile collected over 4 years. The type of regressor, scaling, and dimensionality reduction technique and nature of the data play crucial roles in the performance of the processing pipeline. Eighty-four pipelines were tested through exhaustive experimentation resulting from the combination of 7 regression techniques, 3 scaling methods, and 4 possible dimensional reductions. Those combinations were tested on the prediction of chemical oxygen demand (COD) and total suspended solids (TSS). Each pipeline underwent a tenfold cross-validation on 15 sub-datasets derived from the original dataset, accounting for variations in plants and wastewater types. The results point to the normalization of the data followed by a conversion through the PCA to finally apply a Random Forest Regressor as the combination which stood out These results highlight the importance of modeling strategies in wastewater management using techniques such as LED spectrophotometry.

Comparative study on the effects of anionic, cationic, and nonionic polyacrylamide surface modified magnetic micro-particles (MMP) for anaerobic digestion treatment of vegetable waste water (VWW).

Anaerobic digestion provides a solution for the treatment of vegetable waste water (VWW), but there are currently limited targeted treatment methods available. Building upon previous studies, this research investigated the effects of polyacrylamide-modified magnetic micro-particles (MMP) on anaerobic digestion (AD) of VWW. Three variations of these particles were created by grafting anionic, cationic, and non-ionic polyacrylamide (PAM) onto the MMPs' surfaces, resulting in aPAM-MMP, cPAM-MMP, and nPAM-MMP, respectively. In AD experiments, the addition of aPAM-MMP notably enhanced the degradation of chemical oxygen demand (COD) in VWW. COD decreased to 1290 mg/L in the reactor with aPAM-MMP by day 12 and remained low, while the other reactors had COD concentrations of 4137.5, 5510, and 3010 mg/L on the same day, decreasing thereafter. This modification also improved the production and utilization of hydrogen gas and volatile fatty acids (VFAs), along with the conversion of methane. When tested for bioaffinity using fluorescent GFP-E.coli bacteria, the aPAM-MMP, cPAM-MMP, and nPAM-MMP demonstrated increases in fluorescence intensity by 51.66%, 36.13%, and 37.02%, respectively, compared to unmodified MMP when attached with GFP-E.coli. Further analyses of microbial community revealed that the reactor with aPAM-MMP had the highest microbial richness and enriched bacteria capable of organic matter degradation, such as Bacteroidota, Synergistota, Chloroflexi, Halobacterota phyla, and Parabacteroides, Muribaculaceae, and Azotobacter genera. In conclusion, our experiment verifies that APAM-MMP promotes anaerobic treatment of VWW and provides a novel reference point for enhancing VWW degradation.

Hyperspectral Imaging Technique to Characterize Digestate and Visualize Physical Impurities in Anaerobically Digested Biowaste.

Methods used to monitor anaerobic digestion (AD) indicators are commonly based on wet chemical analyses, which consume time and materials. In addition, physical disturbances, such as floating granules (FGs), must be monitored manually. In this study, we present an eco-friendly, high-throughput methodology that uses near-infrared hyperspectral imaging (NIR-HSI) to build a machine-learning model for characterizing the chemical composition of the digestate and a target detection algorithm for identifying FGs. A total of 732 digestate samples were used to develop and validate a model for calculating total nitrogen (TN), total organic carbon (TOC), total ammonia nitrogen (TAN), and chemical oxygen demand (COD), which are the chemical indicators of responses to disturbances in the AD process. Among these parameters, good model performance was obtained using the dried digestates data set, where the coefficient of determination (R2test) and the root-mean-square error (RMSEtest) were 0.82 and 1090 mg/L for TOC, and 0.86 and 690 mg/L for TN, respectively. Furthermore, the unique spectral features of the FGs in reactors with a lipid-rich substrate meant that they could also be identified by the HSI system. Based on these findings, developing NIR-HSI solutions to monitor the digestate properties in AD plants has great potential for industrial application.

Investigating upflow anaerobic sludge blanket process to treat forward osmosis effluents of concentrated municipal wastewater under psychrophilic temperature.

This work investigated the stability of the Upflow Anaerobic Sludge Blanket (UASB) reactor under psychrophilic temperatures with varying feed streams, simulating typical and concentrated sewage. In Phase I, treating municipal wastewater, chemical oxygen demand (COD) removal dropped from 77 ± 6 % to 41 ± 2 % as hydraulic retention time decreased from 24 to 12 h and organic loading rate (OLR) increased from 0.6 to 1.3 gCOD/(L∙d). In Phase II, at a similar OLR (≈1.2 gCOD/(L∙d)), the UASB treated organic-rich effluents (from 1.0 to 2.1 ± 0.1 gCOD/L) resulting from the pre-treatment of the forward osmosis (FO) process. The UASB performance improved significantly, achieving 87 ± 3 % COD removal and 63 ± 4 % methane recovery, with microbial analysis confirming methanogen growth. The COD mass balance showed up to 30 % more electrical energy recovery from sewage compared to conventional wastewater treatment plants (WWTPs), indicating that the FO-UASB combination is a promising approach to achieve energy-neutral operation in WWTPs.

Combining radio frequency heating and alkaline treatment for enhancement of sludge disintegration and volatile fatty acids production from anaerobic fermentation.

Sludge pretreatment plays a crucial role in solubilizing particulate matters to release organic matter for subsequent anaerobic fermentation (AF). This study innovatively combines radio frequency (RF) heating and alkaline treatment, and finds that the combined pretreatment achieved a sludge disintegration rate of 35.11 %, which is 15.19 % and 8.48 % higher than single RF or alkaline pretreatment. The dissociated ions from the alkali are conducive to RF action on sludge. Furthermore, the combined pretreatment significantly benefits the subsequent AF experiments, resulting in a 9-fold increase in volatile fatty acids production. Considering cost-effectiveness, the optimal operating condition is a 10-minute RF treatment at pH 10 with a total cost of 4.35 × 10-3 dollars per kg soluble chemical oxygen demand (SCOD) increased. These findings provide a foundational basis for the development of a novel technology for sludge pretreatment.

Integrated process of Tetrasphaera-dominated in-situ waste activated sludge fermentation, biological phosphorus removal and endogenous denitrification in single reactor for treatment of wastewater with limited carbon sources.

An integrated process of sludge in-situ fermentation, biological phosphorus removal and endogenous denitrification (ISFPR-ED) was developed to treat low ratio of chemical oxygen demand to nitrogen (COD/N) wastewater and waste activated sludge (WAS) in a single reactor. Nutrient removal and WAS reduction were achieved due to Tetrasphaera-dominated sludge fermentation provided organic carbon in extending the anaerobic duration. The WAS reduction efficiency, effluent orthophosphate (PO43--P) and total inorganic nitrogen reached 28.1 %, less than 0.4 and 7.2 mg/L, respectively. While organic carbon was reduced by 67 %. Tetrasphaera, conventional polyphosphate accumulating organisms (PAOs) stored glycogen, amino acids, and PHA for nutrient removal. Excess energy from fermentation enhanced anaerobic PO43--P uptake by Tetrasphaera. Tetrasphaera was the dominant PO43--P removal and fermentation bacteria, working synergistically with conventional PAOs and fermenting microorganisms. This integrated process improves nutrient removal efficiency and reduces operating costs for carbon addition and WAS disposal in wastewater treatment.

Full-scale study on high-rate low-temperature anaerobic digestion of agro-food wastewater: process performances and microbial community.

The fast-growing global population has led to a substantial increase in food production, which generates large volumes of wastewater during the process. Despite most industrial wastewater being discharged at lower ambient temperatures (<20 °C), majority of the high-rate anaerobic reactors are operated at mesophilic temperatures (>30 °C). High-rate low-temperature anaerobic digestion (LtAD) has proven successful in treating industrial wastewater both at laboratory and pilot scales, boasting efficient organic removal and biogas production. In this study, we demonstrated the feasibility of two full-scale high-rate LtAD bioreactors treating meat processing and dairy wastewater, and the microbial communities in both reactors were examined. Both reactors exhibited rapid start-up, achieving considerable chemical oxygen demand (COD) removal efficiencies (total COD removal >80%) and generating high-quality biogas (CH4% in biogas >75%). Long-term operations (6-12 months) underscored the robustness of LtAD bioreactors even during winter periods (average temperature <12 °C), as evidenced by sustained high COD removal rates (total COD removal >80%). The stable performance was underpinned by a resilient microbial community comprising active acetoclastic methanogens, hydrolytic, and fermentative bacteria. These findings underscore the feasibility of high-rate low-temperature anaerobic wastewater treatment, offering promising solutions to the zero-emission wastewater treatment challenge.

Calcium oxide enhances the anaerobic co-digestion of excess sludge and plant waste: performance and mechanism.

The study investigates the effect of the oxidant calcium oxide (CaO) on the codigestion of excess sludge (ES) and plant waste (PW) under mesophilic anaerobic conditions to enhance methane production. The findings indicate that CaO significantly elevated methane yield in the codigestion system, with an optimum CaO addition of 6% resulting in a maximum methane production of 461 mL/g volatile solids, which is approximately 1.3 times that of the control group. Mechanistic exploration revealed that CaO facilitated the disintegration of organic matter, enhanced the release of soluble chemical oxygen demand, and increased the concentrations of soluble proteins and polysaccharides within the codigestion substrate. The presence of CaO was conducive to the generation and biological transformation of volatile fatty acids, with a notable accumulation of acetic acid, a smaller carboxylic acid within the VFAs. The proportion of acetate in the CaO-amended group increased to 32.6-36.9%. Enzymatic analysis disclosed that CaO enhanced the activity of hydrolytic and acidogenic enzymes associated with the ES and PW codigestion process but suppressed the activity of coenzyme F420. Moreover, CaO augmented the nutrient load in the fermentation liquid. The study provides an alternative scheme for the efficient resource utilization of ES and PW.

Wastewater treatment process using immobilized microalgae.

Microalgae biomass products are gaining popularity due to their diverse applications in various sectors. However, the costs associated with media ingredients and cell harvesting pose challenges to the scale-up of microalgae cultivation. This study evaluated the growth and nutrient removal efficiency (RE) of immobilized microalgae Tetradesmus obliquus in sodium alginate beads cultivated in swine manure-based wastewater compared to free cells. The main findings of this research include (i) immobilized cells outperformed free cells, showing approximately 2.3 times higher biomass production, especially at 10% effluent concentration; (ii) enhanced organic carbon removal was observed, with a significant 62% reduction in chemical oxygen demand (383.46-144.84 mg L-1) within 48 h for immobilized cells compared to 6% in free culture; (iii) both immobilized and free cells exhibited efficient removal of total nitrogen and total phosphorus, with high REs exceeding 99% for phosphorus. In addition, microscopic analysis confirmed successful cell dispersion within the alginate beads, ensuring efficient light and substrate transfer. Overall, the results highlight the potential of immobilization techniques and alternative media, such as biodigested swine manure, to enhance microalgal growth and nutrient RE, offering promising prospects for sustainable wastewater treatment processes.

Integrating enhanced biological phosphorus removal in adsorption-stage to treat real domestic sewage.

Wastewater treatment innovation toward resource recovery facilities raises concerns about the adsorption and bio-degradation (A-B) process. This study integrated enhanced biological phosphorus removal (EBPR) into the A-stage for real domestic sewage treatment using the short sludge retention time (S-SRT) approach. The S-SRT approach resulted in outstanding phosphorus (over 90 %) and COD removal (approximately 88 %), increased sludge yield and organic matter content, and a 1.68-fold increase in energy recovery efficiency by sludge anaerobic digestion. The inhibition of nitrification relieved competition for carbon sources between denitrification and phosphorus removal, allowing for the enrichment of phosphorus-accumulating organisms (PAOs) such as Tetrasphaera and Halomonas, leading to enhanced phosphorus removal activities. Biological adsorption also plays a significant role in achieving steady phosphorus removal performance. This study demonstrates the potential of the S-SRT approach as an effective strategy for simultaneous carbon and phosphorus capture in the A-stage, contributing to energy and nutrient recovery from sewage.

Lab-scale evaluation of Microalgal-Bacterial granular sludge as a sustainable alternative for brewery wastewater treatment.

Microalgal-bacterial granular sludge (MBGS) could offer a sustainable alternative to traditional aerobic methods in brewery wastewater (BWW) treatment. This study compared MBGS with conventional activated sludge (AS) in treating real BWW and highlighted its advantages and challenges. MBGS achieved comparable chemical oxygen demand removal efficiency (93%) compared to AS (89%). Additionally, MBGS exhibited higher phosphate removal capabilities than AS. Extra nitrogen was added to influent to balance C/N ratio of BWW. MBGS was robust in handling C/N ratio fluctuations with an 82% total nitrogen removal efficiency. Metagenomic analysis further indicated that most of the genes involved in carbon, nitrogen and phosphorus metabolism were up-regulated in MBGS compared to AS. Despite changes in the microbial community and settling ability due to high starch and sugar content in BWW, MBGS demonstrated high efficiency and sustainability. Further research should optimize MBGS operation strategies to fully realize its potential for sustainable BWW treatment.

Enhancing methane production in anaerobic digestion of waste activated sludge by combined thermal hydrolysis and photocatalysis pretreatment.

Thermal hydrolysis (TH) is promising for sludge pretreatment, but the refractory substances generated at high temperatures inhibit anaerobic digestion. In this study, a novel combined TH and photocatalytic pretreatment method was proposed to improve the anaerobic digestion performance of waste activated sludge. The results showed that the combined pretreatment (170 °C, 0.5 g/L TiO2) increased methane yield by 66 % from 111 ± 5 m L/g VS to 185 ± 5 m L/g VS. After TH pretreatment, photocatalysis further promoted sludge solubilization by destroying extracellular polymeric substances, resulting in an increase in released soluble organic matter from 292 ± 16 mg/L to 4,091 ± 85 mg/L. In addition, photocatalysis improved the biodegradability of sludge by reducing the melanoidin and humic acid contents by 26 % and 20 %, respectively. The proposed novel pretreatment method effectively overcomes the bottleneck of TH technology and provides an alternative pretreatment technology for improving sludge resource recovery.

Enhancement of methane production from anaerobic co-digestion of food waste and dewatered sludge by thermal, ultrasonic and alkaline technologies integrated with protease pretreatment.

Pretreatments to improve the efficiency of anaerobic digestion (AD) have gained more attention. The efficiency and mechanism of neutral protease (NP) integrated with other methods remain unclear. This study investigated the efficacy of thermal, alkaline and ultrasonic technologies integrated with NP as the pre-treatments for AD of food waste and dewatered sludge. Results showed the thermal method integrated with NP (TH-NP) was the most effective, achieving a 104.2% improvement in methane production. In this case, TH-NP increased soluble chemical oxygen demand and protein concentrations by 8.6% and 39.8%, respectively. Microbial community analysis indicated that TH-NP promoted the symbiosis between Woesearchaeales and hydrogenotrophic methanogenesis. Furthermore, the PICRUSt2 analysis revealed that TH-NP increased the activities of most enzymes in the acetate and propionate metabolic pathways. In summary, TH-NP is more effective in increasing the AD efficiency compared to other combined pretreatments. This study provides theoretical support for protease-induced pretreatment technology.