Thermal Hydrolysis Pretreatment Research Articles

Enhanced methane production from waste activated sludge by potassium ferrate combined with thermal hydrolysis pretreatment.

Anaerobic digestion of waste activated sludge (WAS) was one of the directions of sludge treatment, but how to effectively improve the production of methane as a resource product of anaerobic digestion of sludge still needs further research. The study examined how the combination of potassium ferrate (PF) and thermal hydrolysis (TH) pretreatment affected methane production from sludge. The results demonstrated a positive synergistic effect on methane production with PF-TH pretreatment. Specifically, by employing a 0.05 g/g TSS (total suspended solids) PF in conjunction with TH at 80 °C for 30 min, the methane yield increased from 170.66 ± 0.92 to 232.73 ± 2.21 mL/g VSS (volatile suspended solids). The co-pretreatment of PF and TH has been substantiated by mechanism studies to effectively enhance the disintegration and biodegradability of sludge. Additionally, the variation of microbial community revealed an enrichment of active microorganisms associated with anaerobic digestion after treated with PF + TH, resulting in a total abundance increase from 11.87 to 20.45% in the PF + TH group.

Optimizing cultural conditions and pretreatment for high-value single-cell protein from vegetable waste

The study aimed to produce single-cell protein (SCP) from vegetable waste through solid-state fermentation (SSF) using tomato, capsicum, eggplant, and cucumber waste. Three yeast strains, namely Candida tropicalis, Candida krusei, and Saccharomyces cerevisiae were selected to optimize cultural conditions without pretreatment of the substrate to obtain a higher yield of SCP. The study identified the best-performing yeast strains and optimized the acid and thermal hydrolysis pretreatment of vegetable waste using central composite design by response surface methodology. The substrate was pretreated with varying concentrations of sulfuric acid (2 %, 4 %, and 6 % w/v) at temperatures of 120°C, 140°C, and 160°C. The study demonstrated that SCP production could be enhanced with the acid and thermal hydrolysis of nutrient-supplemented vegetable waste by using optimized cultural conditions. Without pretreatment of vegetable waste, the yeast combination of Saccharomyces cerevisiae and Candida tropicalis achieved a maximum protein content of 10.8 mg/g of dry biomass (an increment of 63.6 % compared to control). With the same yeast strains, pretreatment of vegetable waste (with 4 % sulfuric acid at 140°C) and supplemented with a nutrient source increased SCP production to 21.9 and 31.7 mg/g (an increment of 231.8 % and 375.8 % compared to control), respectively. The study's findings suggest that SCP production from vegetable waste can be optimized through SSF and acid-thermal hydrolysis pretreatment, which could be a promising approach for efficient waste management.

Enhancing Phosphorus Release from Sewage Sludge in Anaerobic Digestion via Thermal Hydrolysis Pretreatment: Insights from Phosphorus Speciation and Molecular Biological Pathways.

This study explores the mechanisms enhancing phosphorus (P) release from sludge in anaerobic digestion (AD) with thermal hydrolysis pretreatment (THP) using sequential chemical extraction, X-ray absorption near-edge structure spectroscopy (XANES), 31P NMR, and multiomics. THP-treated sludge notably increased liquid-phase P by 53.8% over 3 days compared to sewage sludge (SS), identifying solid-phase Fe-P as the primary P source. The THP+AD also provided a higher abundance of bacteria that contributed to P release through multiple pathways (MPRPB), whereas SS+AD enriched some microbial species with single P release pathway. Moreover, species co-occurrence network analysis underlined the pivotal role of P-releasing bacteria in THP+AD, with 8 out of 16 keystones being P-releasers. Among the 63 screened genes that were related to P transformations and release, the poly beta-hydroxybutyrate (PHB) synthesis genes associated with polyphosphate bacteria-mediated P release were more abundant in THP+AD than in SS+AD. Furthermore, the upregulation of genes involved in methyl phosphonate metabolism in the THP-treated sludge enhanced the methane production potential of the AD process. These findings suggested that MPRPB were indeed the main contributors to P release, and enrichment in the THP+AD process enhanced their capability for P liberation.

The biofactories: Quantifying environmental benefits of the wastewater circular economy in Chile using life cycle assessment

The wastewater circular economy promises improved environmental impacts within the food-water-energy nexus. This requires verification as the global sanitation sectors seek to improve environmental impacts and achieve integrated water management. Life cycle assessment (LCA) has been used to compare novel technologies for wastewater treatment and recovery, but research addressing plant-wide improvements of co-product resource recovery using real data from full-scale plants is still needed, particularly in a Latin American context. In Chile, two wastewater treatment plants (WWTPs) have embraced the circular economy configuration, recovering treated effluent, biosolids, and biogas, in addition to implementing advanced nitrogen removal using different technologies. The LCA of these two WWTPs demonstrated that Plant A improved 8 out of 10 impact categories compared to the baseline conventional scenario, while Plant B improved 5 categories out of 10. The analysis of the two plants showed the influence of influent quality on environmental impacts and the trade-off that occurs between the different technologies implemented. Plant B generated larger environmental credits through increased biogas and biosolids recovery due to thermal hydrolysis pre-treatment and anaerobic digestion, combined with cogeneration of heat and power. Plant A implemented water recovery, which provided benefits on a smaller magnitude but to more impact categories. Therefore, both plants improved environmental impacts through the wastewater circular economy, but further improvements in system configurations are recommended in each.

Effect of Thermal Hydrolysis Pretreatment Time on Microbial Community Structure in Sludge Anaerobic Digestion System

To evaluate the effect of thermal hydrolysis pretreatment time on the sludge anaerobic digestion system of wastewater treatment plants (WWTPs) in Daxing district, Beijing, the structure and diversity of microbial communities in primary sludge and an activated sludge anaerobic digestion system with different thermal hydrolysis pretreatment times (15 min, 30 min, and 45 min) were analyzed using Illumina MiSeq high-throughput sequencing. The results showed that the dominant groups of digested sludge were mainly distributed in Firmicutes, Cloacimonadota, Chloroflexi, and Synergistota, with W5 being the most common genus. The sum of relative abundance of the dominant phylum was greater than 60%, and W5 accounted for 20.8%-54.5%, showing a high abundance of a few dominant species. During the anaerobic digestion of thermo-hydrolyzed sludge, the relative abundance of acetogenic methanogens decreased due to high levels of volatile fatty acids (VFAs) and ammonia nitrogen (NH4+-N) concentrations, which suggested that the hydrogenophilic methanogenic pathway was more than that of the acetogenic methanogenic pathway. Correlation analysis showed that the soluble protein and pH of thermo-hydrolyzed sludge, NH4+-N of digested sludge, and thermal hydrolysis pretreatment time were the four main environmental factors affecting microbial community structure, and NH4+-N of digested sludge had the largest negative correlation with methanogens. The thermal hydrolysis pretreatment time was negatively correlated with both the Chao index and Shannon index, so longer thermal hydrolysis pretreatment time was not conducive to microbial flora during anaerobic digestion.

Agricultural Wastes and Their By-Products for the Energy Market

The conversion of lignocellulosic agricultural waste into biofuels and other economically valuable compounds can reduce dependence on fossil fuels, reduce harmful gas emissions, support the sustainability of natural resources, including water, and minimize the amount of waste in landfills, thus reducing environmental degradation. In this paper, the conversion of agricultural wastes into biomethane, biohydrogen, biodiesel, bioethanol, biobutanol, and bio-oil is reviewed, with special emphasis on primary and secondary agricultural residues as substrates. Some novel approaches are mentioned that offer opportunities to increase the efficiency of waste valorization, e.g., hybrid systems. In addition to physical, chemical, and biological pretreatment of waste, some combined methods to mitigate the negative effects of various recalcitrant compounds on waste processing (alkali-assisted thermal pretreatment, thermal hydrolysis pretreatment, and alkali pretreatment combined with bioaugmentation) are evaluated. In addition, the production of volatile fatty acids, polyhydroxyalkanoates, biochar, hydrochar, cellulosic nanomaterials, and selected platform chemicals from lignocellulosic waste is described. Finally, the potential uses of biofuels and other recovered products are discussed.

Thermal hydrolysis alleviates polyethylene microplastic-induced stress in anaerobic digestion of waste activated sludge

Microplastics are known to negatively affect anaerobic digestion (AD) of waste activated sludge. However, whether thermal hydrolysis (TH) pretreatment alters the impact of microplastics on sludge AD remains unknown. Herein, the effect of TH on the impact of polyethylene (PE) microplastics in sludge AD was investigated. The results showed that the inhibition of methane production by PE at 100 particles/g total solids (TS) was reduced by 31.4% from 12.1% to 8.3% after TH at 170 °C for 30 min. Mechanism analysis indicated TH reduced the potential for reactive oxygen species production induced by PE, resulting in a 29.1 ± 5.5% reduction in cell viability loss. In addition, additive leaching increased as a result of rapid aging of PE microplastics by TH. Acetyl tri-n-butyl citrate (ATBC) release from PE with 10 and 100 particles/g TS increased 11.5-fold and 8.6-fold after TH to 68.2 ± 5.5 μg/L and 124.0 ± 5.1 μg/L, respectively. ATBC at 124.0 μg/L increased methane production by 21.4%. The released ATBC enriched SBR1031 and Euryarchaeota, which facilitate the degradation of proteins and promote methane production. This study reveals the overestimated impact of PE microplastics in sludge AD and provides new insights into the PE microplastics-induced impact in practical sludge treatment and anaerobic biological processes.

Phosphorus release and realignment in anaerobic digestion of thermal hydrolysis pretreatment sludge – Masking effects from high ammonium

Waste activated sludge (WAS) is a significant phosphorus (P) repository, and there is a growing interest in P recovery from WAS. Typically, the commercial technology for treating WAS involves thermal hydrolysis pretreatment (THP) coupled with anaerobic digestion (AD). However, there is ongoing debate regarding the transformation and distribution of P throughout this process. To address this, a long-term THP-AD process was operated in this study to comprehensively investigate P transformation and distribution. The results revealed that a substantial biodegradation of dissolved organic nitrogen (DON) raised the pH of the digestate to 8.3 during the AD process. This increased pH facilitated the dissolution of Al, leading to a reduction of 6.92 mg/L of NaOH-P. Simultaneously, sulfate reduction contributed to a decrease of 11.04 mg/L of Bipy-P in the solid. However, the reduction of Bipy-P and NaOH-P in the solid did not result in an improved P release to the supernatant. Conversely, a decrease of 23.60 mg/L P in the aqueous phase was observed after anaerobic digestion. The disappeared P was primarily precipitated with Mg and Ca, driven by the increased pH, and it contributed to the increase of HCl-P in the solid from 107.80 to 144.52 mg/L. These findings were further confirmed by results obtained from scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. This study provides valuable insights into the mechanisms of P transformation during THP-AD process that is nearly opposite from conventional AD system.

Revealing the occurrence of refractory melanoidins and inhibitions on anaerobic fermentation via thermal hydrolysis pretreatment

Thermal hydrolysis pretreatment (THP) is widely used to promote the hydrolysis of polysaccharides and proteins in waste activated sludge (WAS). However, it also generates unwanted refractory organics of melanoidins products (MPs), which should not be overlooked, especially concerning the occurrence and inhibition of hydrolases and anaerobes. In this study, the MPs occurrence by THP was investigated and inhibition mechanism on anaerobic fermentation was revealed for the first time. The results showed that SCOD in WAS significantly increased from 0.5±0.02 g/L in control to 4.1±0.02 g/L in THP at 180 °C. However, the color of MPs under a higher temperature (>120 °C) changed from colourless to dark brown. The components of MPs were mainly nitrogenous and humic acid-like refractory organics. Unwanted MPs generated above 160 °C reduced methane production by 49.1 %–89.8 %, which was due to the inhibition of protease, acidogenic bacteria, and acetoclastic methanogens. Inhibition of acetoclastic methanogens also resulted in the accumulation of VFAs. The microbial diversity clearly showed that the toxicity of MPs altered the microbial community structure, reducing the proportion of both acidogenic bacteria and acetoclastic methanogens. Therefore, the negative effect of MPs on anaerobic digestion demonstrated that THP should be re-evaluated in the production of biochemicals, which is important for achieving carbon neutrality of WWTPs in the future.

Thermal hydrolysis pretreatment of wastewater biosolids: Modelling the impact of the aerobic sludge age

This study investigates the impact of thermal hydrolysis pretreatment (THP) on the characteristics of wastewater biosolids, methane production, anaerobic biodegradability, and recycled sidestream nitrogen loads, as a function of the sludge age of the activated sludge (AS) system through a series of BioWin simulations of 3 different process configurations at sludge ages of 5, 10, 15, 20, 30, and 60 d, with and without thermal hydrolysis. BioWin's anaerobic digester and thermal hydrolysis units were calibrated by adopting and identifying various kinetic and operational parameters from the available literature and through series of full-scale plant simulations. Thermal hydrolysis improved the hydrolysis rates of the biosolids by 181%. Improvements in anaerobic biodegradability, mainly due to the conversion of endogenous products, ranged from 14% to 67% at sludge ages of 5–15 d. At sludge ages of 20–60 d, anaerobic biodegradability improved by 59% to 186% depending on the process configuration. At sludge ages of 15–60 d, methane production was relatively stable and insensitive to the biosolids composition. Despite the increase in the recycled nitrogen load by 42% to 127%, it only constituted 13% of the influent nitrogen load. Effluent ammonia concentrations remained unchanged and effluent nitrates concentrations only increased by 1.4 to 2 mg N/L, maintaining effluent standards without additional sidestream treatment.

Impact of Conditioning Agent Addition Sequence on Dewatering Performance of Advanced Anaerobic Digested Sludge

The advanced anaerobic digestion process enhances sludge resource utilization. However, thermal hydrolysis pretreatment of anaerobically digested sludge reduces dewatering efficiency due to excessive organic matter decomposition. This necessitates significant time and effort for sludge conditioning in wastewater treatment plants. Using conditioning agents can achieve high dewatering efficiency. This study investigates how the order of adding coagulants and flocculants impacts the dewatering performance of digested sludge. The results indicate that, compared to the flocculation–coagulation process with the same dosage, the coagulation–flocculation process leads to a 15–20% increase in the average particle size of digested sludge. The content of polysaccharides and proteins in S-EPS decreases by 28.8–30.8% and 10.1–11.3%, respectively. The filter cake solids content increases by 8.5%, and there is an increase in surface water channels within the flocs. This is because initially adding coagulants efficiently adsorbs small particles, forming larger aggregates that settle effectively. This promotes the breakdown of extracellular polymeric substances, releasing more bound water. Adding flocculants later bridges the aggregates, further enhancing settling and filtration performance, thereby improving sludge dewatering efficiency. These research findings contribute to a better understanding of the mechanisms of coagulant and flocculant co-conditioning for digested sludge and provide recommendations for optimizing sludge conditioning steps.

The novel application of polyoxometalates for achieving sludge deep dewatering using low-temperature thermal hydrolysis pretreatment

Traditional thermal hydrolysis pretreatment (THP) for sludge deep dewatering is energy-intensive and poses the risk of generating bio-toxic substances that affect downstream wastewater treatment processes. To address these challenges, this study introduces the novel application of polyoxometalates (POMs) in THP to achieve sludge deep dewatering at lower temperatures. Specifically, under the optimal conditions with a POMs dosage of 1.0 mM/g VSS and a THP temperature of 140 °C, a reduction of 30.36%, 88.31%, and 55.04% in WC, SRF, and CST, respectively, was achieved compared to 20-RS-THP. Further analysis revealed that both the acidity and the biological effect of POMs played the dominant role in enhancing sludge dewatering. Spectroscopic techniques and molecular simulations revealed changes in protein structure during THP induced the POMs-proteins interaction. Results revealed that at lower THP temperatures (<80 °C), POMs induced protonation of functional groups in amino acid residues, strengthening electrostatic interactions. As temperatures increased (80–140 °C), more binding sites in hydrophilic amino acid residues became available for hydrogen bonding with POMs. This interaction led to structural changes in proteins, facilitating water liberation and the formation of sludge colloidal aggregates with improved drainage channels. However, at higher temperatures (140–180 °C), the exposure of hydrophobic sites, the loss of hydrophilic amino acids, and the occurrence of the Maillard reaction in proteins partially offset POMs' binding effects. Moreover, the development of magnetized POMs-based materials may offer sustainability and economic benefits for POMs-based sludge treatment and disposal technologies.

Review of Melanoidins as By-Product from Thermal Hydrolysis of Sludge: Properties, Hazards, and Removal

Melanoidins, as macromolecular heterogeneous organic polymers, are produced from the Maillard reaction between amino and carbonyl groups during the thermal hydrolysis pretreatment (THP) of sludge. The brown color and recalcitrance of melanoidins pose a serious threat to wastewater treatment systems, such as invalidating UV disinfection and decreasing the efficiency of anaerobic digestion; thus, they have gradually received much concern in recent years. However, currently the study on THP-origin melanoidins is limited by a lack of reliable extraction and quantification methods. This paper presents a comprehensive review of the physical, chemical, and biological properties of melanoidins from different sources to fill the research gap on THP-origin melanoidins. The adverse effects of melanoidins on the management of wastewater and sludge are discussed, and for the first time, special attention is paid to the potential environmental hazards of THP-origin melanoidins to natural ecosystems. The removal technologies of melanoidins are summarized and compared as well. Finally, the suggested areas that future studies should focus on are provided. This review is dedicated to providing guidance on melanoidin research and management for the better development of the THP industry.

Process modelling and techno-economic analysis of anaerobic digestion of sewage sludge integrated with wet oxidation using a gravity pressure vessel and thermal hydrolysis

Anaerobic digestion (AD) of sewage sludge is used to biodegrade sewage sludge into biomethane and digestate. With the addition of thermal processes such as thermal hydrolysis (TH) and wet oxidation (WO), AD biodegradability generally improves. Implementation of additional treatment is challenging due to the limitation in the mass and energy balances. Hence, tools such as process simulation can be utilized to predict the input and output around the process. In addition, an economic analysis needs to be conducted to check the economic feasibility. The techno-economic analysis (TEA), an integrated method to evaluate a process scheme through simulation and subsequent economic analysis, is effective in providing a systematic understanding of economic implications and the feasibility of a process by identifying the bottlenecks and uncertainties that have a significant impact on the technology. TEA of AD, especially incorporating the TH or WO using gravity pressure vessel (GPV) technology, is limited in the literature. A comprehensive TEA of the AD and the pre- and post-treatment schemes can be utilized to determine the most feasible pathway for sludge treatment for implementation in the wastewater industry. In this study, TEA for four different scenarios of AD was conducted using Aspen Plus and economic analysis tools: (1) without any pre- or post-treatment, (2) with TH pre-treatment, (3) with 100 % WO post-treatment, and (4) with 20 % partial wet oxidation (PWO) and acid hydrolysis pre- or post-treatment. A simulation model (GPVM) was developed using Aspen Plus to mimic the GPV reactor. The study outcomes showed that Scenario 3 with 100 % WO post-treatment was the most suitable for processing parameters and sludge treatment cost. The sensitivity analysis concluded that operating cost and plant capacity are the dominant factors that impact the plant feasibility significantly.

Enhancing anaerobic digestion of dewatered sewage sludge through thermal hydrolysis pretreatment: Performance evaluation and microbial community analysis

This study explored the effectiveness of thermal hydrolysis (TH) in conditioning dewatered sewage sludge (DSS) for enhanced anaerobic digestion (AD). The TH pretreatment employed in this study (30 min at 170°C and 6 bar) significantly improved the bioavailability of DSS. The degree of solubilization varied with the physicochemical characteristics of DSS collected over three seasons: 16.8–24.8% on a volatile solids (VS) basis and 9.4–33.7% on a chemical oxygen demand (COD) basis. Correspondingly, the dissolved fraction of VS in DSS increased by 2.1–3.4-fold, and the soluble fraction of COD rose by 1.4–2.9-fold. The duplicate anaerobic reactors treating the TH-pretreated DSS did not achieve steady-state operation at the intended design organic loading rate (OLR) of 3.8 g VS/L·d, but showed stable performance at an OLR of 3.4 g VS/L·d with significantly higher methane yield (0.26–0.29 L/g VS fed) and VS removal (35–38%) than those reported for untreated DSS and comparable to TH-pretreated DSS. The reactors' microbial community structures changed dynamically as the OLR varied, with shifts in dominance between acetoclastic and hydrogenotrophic methanogens. The results highlight the promising potential of TH-AD process for efficiently treating DSS while emphasizing the importance of optimizing OLR for stable operation.

The Biofactory: Quantifying Life Cycle Sustainability Impacts of the Wastewater Circular Economy in Chile

The wastewater circular economy (WW-CE) represents a solution to improving sanitation coverage and management worldwide. However, the transition to circular wastewater treatment plants (WWTPs) requires facilitation to enhance decision-makers’ understanding of the integral sustainability impacts of the WW-CE. This research implemented a Life Cycle Sustainability Assessment (LCSA), combining Life Cycle Assessment, Social Life Cycle Assessment and Life Cycle Costing with a Multi-criteria Decision Making (MCDM) model to quantify the environmental, social, and economic impacts of different WWTPs technologies. Two real WWTPs (Plant A and Plant B) in Chile have embraced alternative WW-CE configurations, adopting the title Biofactories, and are considered as case studies in this investigation. A comparative LCSA considered the service of a 1,000,000-population equivalent, under three scenarios: wastewater discharge without treatment, conventional WWTPs, and biofactory WW-CE configurations. The results demonstrate that the transition to WW-CEs improved integral sustainability, and decreased integrated environmental, social, and economic impacts by 30% in Plant A, demonstrating better performance in terms environmental and social impacts. However, a 58% decrease in integral sustainability impacts for Plant B was achieved via the economic advantage of the thermal hydrolysis pre-treatment of sludge. The urgent need to adopt sustainable decision-making models to improve sanitation coverage and sustainability performance of the sanitation industry across the globe is discussed. The WW-CE in Chile presents an opportunity for this to be achieved.

Anaerobic digestion of an invasive aquatic plant Ludwigia grandiflora by thermal hydrolysis pretreatment: Correlations between methane kinetics and substrate composition

Ludwigia grandiflora, an emerging aquatic weed, has become a global waterway invader, causing various environmental issues. Anaerobic digestion (AD) of lignocellulosic biomass is a cost-effective treatment method. To enhance methane yield, pretreatment is required to break the rigid lignocellulose structure, which hampers the biodegradability of the biomass. Therefore, in this study, we examined the impact of thermal hydrolysis (TH) pretreatment on L. grandiflora through batch AD tests at temperatures ranging from 150 to 210 °C, with durations of 10 and 30 mins. At 180 °C for 30 mins (severity factor of 3.8), methane yield increased significantly by 142.7 % compared to the untreated condition. Significant methane production differences were observed at temperatures equal to or above 165 °C. Longer retention times, such as 30 mins, were crucial for enhancing methane yield. Additionally, the Modified Gompertz model was a good fit for the AD process, with R2 values ranging from 0.996 to 0.935 and lag phase reduction from 0.273 (untreated) to 0.102-0.000 days for the pretreated conditions. Methane yield and production rates increased from 88.85 mL g-VS−1 and 15.01 mL g-VS−1 day−1 (untreated) to 110.48-206.41 mL g-VS−1 and 30.76-71.33 mL g-VS−1 day−1, respectively. Pearson correlation revealed a positive correlation between cellulose and methane yield enhancement, while lignin, crystallinity index, and pH showed negative correlations. Despite these negative correlations, their impact on the AD process was limited. Overall, changes in lignocellulosic structure and increased cellulose content were the main factors enhancing methane production. Additionally, the study recommends a new cost-effective reactor design for TH pretreatment.

Characterization of melanoidins in thermal hydrolysis sludge and effects on dewatering performance

Thermal hydrolysis pretreatment (THP) of sludge can form the refractory brown melanoidins due to the occurrence of the Maillard reaction, which adversely involves the subsequent sludge anaerobic digestion (AD) process. However, details of the generation pattern of melanoidins and how they affect the sludge dewaterability remain largely unknown. This work aims to determine an approach to characterize and quantify the melanoidins created by THP of sludge. On this basis, the effect of melanoidins on sludge dewatering performance was revealed by adding synthetic melanoidins to the mixed sludge. Experimental results showed that three-dimensional fluorescence-region integration (3DEEM-FRI) could effectively distinguish melanoidins from other organic substances and achieve semi-quantitative characterization in sludge. The melanoidins significantly deteriorated the sludge dewaterability, and the lowest solids content of the filter cake (TS) was only 17.78% at the addition of 480 mg (g TS)-1, which was a drop of about 20% compared to the control group. The mechanism investigations indicated that the internal structure of sludge becoming particularly complicated and the opportunities for molecules to collide with each other enlarged because of the contribution of melanoidins, resulting in the increment of the sludge apparent viscosity and consistency coefficient (k), a decline of the flow behavior index (n) and a weakening of flowability. Melanoidins could capture massive water molecules and carry negative charges with the decrease of sludge particle size and zeta potential value, which enhanced the electrostatic repulsion between sludge particles and abated the flocculation ability, thus further aggravating the sludge dewatering performance.

Impact of thermal hydrolysis time on volatile fatty acids production from sludge fermentation: Insights into dissolved organic matter transformation and microbial succession

While thermal hydrolysis pretreatment (THP) represents a promising technology for enhancing the production of volatile fatty acids (VFAs), the specific impact mechanisms of the THP duration on the acidogenic fermentation process have yet to be fully understood. This study addresses this gap by investigating the influence of various THP times on biochemical processes, microbial components, and genetic mechanisms during the fermentation process. The results indicate that extending the THP duration from 10 to 30 min is advantageous for achieving higher VFAs production and an increased proportion of acetic acid (2876.5 and 28.9% versus 4523.8 mg COD L−1 and 44.6%). Mechanism investigations revealed that longer THP durations are particularly effective in enhancing hydrolysis and solubilization. Notably, The PN and PS concentrations at THP time of 30 min was 68.6% and 83.6% higher than that at THP time of 10 min at 2nd d. Additionally, extended THP durations led to the enrichment of VFAs-producing and hydrolysis functional microorganisms (e.g., Comamonas, Fonticella, Bacillus and Romboutsia), along with the specialized functional genes (e.g., accA, accC, accD and bccA), which are crucial for elevated VFAs production. Collectively, this study provides comprehensive insights into the impact mechanisms of varying THP durations on VFAs production and offers valuable contributions to the field of sludge management and resource recovery research.

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).