Anaerobic Digestion Performance Research Articles

The kinetics of a two-stage completely stirred tank reactor for treating tofu wastewater by anaerobic digestion

ABSTRACT Tofu wastewater is an inevitable by-product of the bean curd production process. In this study, we used a two-stage continuous stirred tank reactor (CSTR) to treat tofu wastewater. The kinetic analysis of two CSTR reactors was conducted utilizing the material accounting model, microbial accounting model, and first-order kinetic model. The results demonstrated that the methane production coefficient of reactor 1 was 0.00573 LCH4·mg−1 greater than that of reactor 2, which is 0.00533 L CH4·mg−1. The first-order kinetic constants of reactor 1 were poorer than those of reactor 2, and their values are 0.15700 d−1 and 0.11574 d−1, respectively. The microbial yield coefficients of reactors 1 and 2 were 0.009648 and 0.060704, respectively. Under different organic loading rates, the average microbial concentrations were 25.24000 and 2.706667 mg·L−1 for reactors 1 and 2, respectively. The operational performance of the two-stage CSTR anaerobic digestion system was evaluated in order to design a novel and unique method as well as provide a new perspective for enhancing the performance of anaerobic digestion.

Enhancing effect of conductive materials and rumen microorganisms on the anaerobic digestion performance of a real traditional Chinese medicine wastewater

This work evaluated the effect of different concentrations of conductive materials and rumen microorganisms on the anaerobic digestion (AD) performance of real traditional Chinese medicine (TCM) wastewater. The experiments first determined the optimal organic concentration of 0.25 L/L for the AD system and removed suspended solids from real TCM wastewater to reduce the inhibition effect on methanogenesis. Analysis of the modified Gompertz model showed that the addition of activated carbon, biochar, cow manure, and rumen fluid at doses of 12 g/L, 12 g/L, 12 mL/L, and 125 mL/L, respectively, had the greatest effect on CH4 production, increasing the cumulative CH4 yield by 13.5 %, 10.4 %, 26.8 %, and 32.9 %. Through microbial community and metabolism pathway analyses, the conductive materials promoted direct interspecies electron transfer (DIET) between Clostridium and Methanothrix, and the acetoclastic methanogenic pathway dominated by acetyl-CoA synthase. Rumen microorganisms enhanced AD performance by promoting the growth of hydrogenotrophic methanogens and the abundance of genes dominated by formylmethanofuran dehydrogenase in the hydrogenotrophic methanogenic pathway, illustrating the relationship between microbial community and metabolism pathway. Rumen microorganisms increased CH4 production more than conductive materials in real TCM wastewater. This study helps to better understand the internal mechanisms by which different materials enhance AD performance.

Exploring interactive effects of environmental and microbial factors on food waste anaerobic digestion performance: Interpretable machine learning models

Biogas yield in anaerobic digestion (AD) involves continuous and complex biological reactions. The traditional linear models failed to quantitatively assess the interactive effects of these factors on AD performance. To further explore the internal relationship between target variables and AD performance, this study developed four machine learning models to predict biogas yield and consider the interaction among various factors. Results indicated that the highest prediction accuracy of AD performance was achieved by adding bacterial genera dataset with environmental factors. Random forest model exhibited the highest accuracy, with the testing coefficient of determination equal to 0.9879. Among two types of input features, the bacterial genera accounted for 89.9 % of the impact on biogas yield, followed by environmental factors. The results revealed Keratinibaculum and Acetomicrobium as critical bacteria. The volatile fatty acid controlled below 2000 mg/L and the improved stirring system in AD process were recommended to achieve maximum biogas yield.

Management of Tanning Waste from Leather Processing by Anaerobic Digestion Using a Dynamic Method on a Semi-Technical Scale

In the context of climate policy, measures are being taken around the world to reduce pollution. These have been intensified in the areas of transport, industry, and energy, with the goal of zero emissions. The role of the biogas plant in energy transition and as a waste treatment plant for disposal is very important. This article describes research on a dynamic anaerobic digestion (AD) process plant. The subject of this study was leather shavings, which is a problematic waste. The research presented here is intended to demonstrate the decomposition of the flesh in the process, to confirm its biogas yield, and to evaluate the biological and technical parameters of the process. High biochemical stability was achieved for each of the tests evaluated, and no specific technical requirements were demonstrated. The only technical aspect to be addressed during operation was sedimentation, which can be solved by preparing the mixture earlier or by changing the mixing method. This made it reasonable to investigate the material further in the context of an industrial project. The characteristics of protein degradation in the AD process resulted in a high methane content in the biogas, above 65%. It was also observed that the long conditioning time of biogas in the gas cushion favourably affected the proportion of methane in biogas. Analytical results confirmed 77.5% methane content, which was a very good result. This paper presents the results of a surprising effect of chromium, primarily Cr (III), on the performance of anaerobic digestion.

Enhanced anaerobic digestion for energy recovery from brewery wastewater employing nano zero-valent iron loaded biochar prepared by residual sludge

Anaerobic digestion is an effective wastewater energization technology, but suffers from low energy conversion efficiency. In this study, a novel biochar was successfully prepared by incorporating extracellular polymeric substances (EPS) to residual sludge, and the anaerobic digestion performance could be significantly improved by employing this biochar loaded with nano zero-valent iron (NZVI@EPSBC). In comparison to the control, the cumulative methane production with 100 mg/L NZVI@EPSBC was raised by approximately 1.4-fold. The NZVI@EPSBC did not significantly change the morphology of the inoculated granular sludge, but induced the secretion of proteins and humic substances in the extracellular EPS, which are beneficial for carbon conversion and extracellular electron transport at the microscopic scale. Meanwhile, the quantitative analysis of the electron transport system also confirmed that NZVI@EPSBC could significantly improve the electron transfer efficiency in microbial respiratory chain throughout the experimental cycle, in which the highest respiratory efficiency increase of 26.51 % at 48 h. Taxonomic analysis of microbial communities showed that NZVI@EPSBC exhibited complete retention of bacteria and archaea compared to the raw sludge, while realizing an efficient cooperative pattern of syntrophic bacteria by regulating the relative abundance of specific functional bacteria, like Anaerolineaceae and Methanosaeta. Overall, the study offers a valuable strategy for achieving resourcefulness of residual sludge and EPS along with facilitating efficient energy recovery from brewery wastewater.

Feedstock-temperature interactions in anaerobic digestion with focus on psychrophilic regime

While feedstock composition and temperature are known to affect anaerobic digestion (AD) performance, their combined effect remains unexplored. By characterizing the response of AD kinetics to temperature across mesophilic and psychrophilic regimes for different agricultural residues -ranging from lignocellulose-rich crop stover to readily biodegradable potato waste–, this study aimed to study their interactive effects on AD kinetic parameters and biodegradability. Lignocellulosic material exhibited increasing biomethane potential (Bmax) with increasing temperature, while easily degradable substrates reached higher Bmax values at lower temperatures. AD rate sensitivity to temperature was lower for lignocellulose-rich feedstocks. Under mesophilic conditions, these feedstocks achieved the highest biodegradability (BD), while BD of easily degradable substrates increased with decreasing temperatures. Our findings revealed significant temperature-feedstock composition interaction effects on AD performance that holds significance for both laboratory and field-scale applications and could be used to improve the performance of psychrophilic AD in temperate-to-cold regions of developing countries.

Continuous augmentation of anaerobic digestion with electroactive microorganisms: Performance and stability

The performance and stability of a bioelectrochemical anaerobic digester (BeAD), continuously augmented with electroactive microorganisms (EAMs), were investigated. The BeAD showcased superior performance, sustaining the high COD removal efficiency and methane production rate of 76.5 % and 0.67 L/(L.d), respectively, in a stable state. Prominently, it exhibited remarkable resilience under hydraulic and organic shock loads, adeptly recuperating from disturbances up to 1000 % of its stable condition. This resilience of up to 300 % shock load was driven by increased levels of electron transport components such as quinones and riboflavins, which act as electron shuttles. However, after extreme shock exposures from 500 % to 1000 %, despite the spike in inhibitory by-products such as humic acids and ammonia, the upregulation of the mtr complex was pivotal in recovering and sustaining methane production. These insights emphasize the BeAD’s capability to bolster both performance and stability, thereby providing a potent strategy for practical application of bioelectrochemical systems.

Investigating potential auxiliary anaerobic digestion activity of phage under polyvinyl chloride microplastic stress

Polyvinyl chloride (PVC) microplastics present in sewage were trapped in sludge, thereby hindering anaerobic digestion performance of waste active sludge (WAS). Phages regulate virocell metabolism by encoding auxiliary metabolic genes (AMGs) related to energy acquisition and material degradation, supporting hosts survive in harsh environments and play a crucial role in biogeochemical cycles. This study investigated the potential effects of phages on the recovery of WAS anaerobic digestion under PVC stress. We observed a significant alteration in the phage community induced by PVC microplastics. Phages encoded AMGs related to anaerobic digestion and cell growth probably alleviate PVC microplastics inhibition on WAS anaerobic digestion, and 54.2 % of hydrolysis-related GHs and 40.8 % of acidification-related AMGs were actively transcribed in the PVC-exposed group. Additionally, the degradation of chitin and peptidoglycan during hydrolysis and the conversion of glucose to pyruvate during acidification were more susceptible to phages. Prediction of phage-host relationship indicated that the phyla Pseudomonadota were predominantly targeted hosts by hydrolysis-related and acidification-related phages, and PVC toxicity had minimal impact on phage-host interaction. Our findings highlight the importance of phages in anaerobic digestion and provide a novel strategy for using phages in the functional recovery of microplastic-exposed sludge.

Revealing synergistic mechanisms of biochar-assisted microbial electrolysis cells in enhancing the anaerobic digestion performance of waste activated sludge: Extracellular polymeric substances characterization, enzyme activity assay, and multi-omics analysis

Although biochar (BC)-assisted microbial electrolysis cells (MEC) has been shown to improve anaerobic digestion (AD) performance of waste activated sludge (WAS), the underlying mechanisms remain unclear. This study conducted an in-depth investigation into the mechanism based on analyses of extracellular polymeric substances (EPS) characteristics, enzyme activities and multi-omics. The results showed that compared with the control group, methane production improved by 16.73 %, 21.32 %, and 29.37 % in the BC, MEC, and BC-assisted MEC (BC-MEC) groups, respectively. The reconfiguration of the protein secondary structure increased the hydrophobicity of the EPS, thereby promoting microbial aggregation. In addition, partial least-squares path modeling (PLS-PM) and mantel test based on the enzyme activity and multi-omics analyses revealed that the promotional effect of MEC on the hydrolysis of WAS was superior to that of BC, while BC was more advantageous in promoting electron transfer and biofilm formation regulated by quorum sensing. The synergistic effects of BC and MEC were exemplified in the BC-MEC group. g_norank_Aminicenantales responsible for the hydrolysis of WAS was enriched (29.6 %), and the activities of hydrolytic enzymes including α-glucosidases and proteases were increased by 29.1 % and 43.6 %, respectively. Further, the expressions of genes related to acyl homoserine lactones (AHLs) and diffusible signal factor (DSF) in quorum sensing systems, as well as the genes related to hydrogenase involved in electron transfer (mbhJKL, hyfB-JR, hypA-F, and hoxFHUY), were up-regulated in the BC-MEC group. This facilitated electron transfer and microbial communication, consequently enhancing methane production. This research significantly advances the understanding of the mechanism by which BC-assisted MEC enhances AD performance and provides valuable insights into strategies for improving energy recovery from WAS.

Anaerobic digestion performance and kinetics of biomass pretreated with various fungal strains utilizing exponential and sigmoidal equation models

Corn silage was pretreated with white rot fungi to optimize the methane generation capacity of biomass and the effect of the most important pretreatment parameters on the anaerobic digestion performance of material was determined by employing mathematical modelling. Pretreatment with selective fungi led to optimal increment in methane production from 0.301 m3kgVS−1 from corn silage to 0.465 m3kgVS−1 from the 10-day modified material, whereas non-selective fungi had negative effect. A reverse L-shape curve observed for the corn silage indicated an uninterrupted methane production and was not modified when the substrate was pretreated with Dichomitus squalens, Irpex lacteus and Trametes versicolor. Exponential models fitted L-curves better than sigmoidal equations with Cone model providing the most accurate predictions regardless of the selective or non-selective feature of the fungal strain used for the pretreatment of corn silage. Increasing pretreatment time led to a differentiation of the methane yield and adjustment of the curve shape to a stepped outline adequately modelled by Cone and transference models. Contrary to three-parameter sigmoidal models a fourth shape variable included in Richards equation was crucial, allowing for a flexible inflection point that enabled an accurate replication of an S-shape curve obtained for methane production from the hybrid substrate.

Quorum-sensing molecules regulate biochar-assisted anaerobic digestion system for methane production: Single-stage vs. two-stage digestion

Promoting methane production performance from waste activated sludge is of great significance for energy self-sufficiency operation of wastewater treatment plants. This study evaluated the methane production enhancement strategies of biochar and quorum-sensing molecules like N-acylated homoserine lactone (AHL) in single-stage and two-stage anaerobic digestion systems. The methane yield increased to 134.9 mL/g volatile suspended solids in single-stage digestion system, which was 41.7 % higher than that of control group, while it in two-stage digestion system was not only lower than that obtained in single-stage digestion system but also less than that observed in groups adding AHL either at the beginning or on the third day of experiment period. The mechanism studies indicated that the single-stage digestion strategy promoted solubilization, hydrolysis, acetogenesis, and methanogenesis stages and improved the conversion and utilization of organic matters with the enhanced syntrophic metabolisms between microorganisms. In addition, the electron transfer activity between microorganisms was promoted, with an increase ratio of 54.7 %, meanwhile, the syntrophic relationships between methanogens such as Methanosarcina and electroactive bacteria such as norank_f__Bacteroidetes_vadinHA17 were promoted. As a result, both acetotrophic and hydrogenotrophic methanogenesis pathways were improved. This study provided some novel approaches for promoting anaerobic digestion performance while using biochar as the additive.

Comparing the effects and mechanisms of granular activated carbon and magnetite nanoparticles in dry anaerobic digestion: Focusing on microbial electron transfer and metagenomic evidence

Enhancing direct interspecies electron transfer (DIET) via granular activated carbon (GAC) and magnetite nanoparticles (MNPs) to promote methanation performance in dry anaerobic digestion (AD) systems has been extensively studied in recent years. However, the underlying mechanisms, particularly how GAC and MNPs influence DIET and extracellular polymeric substances (EPSs), remain poorly understood. In this study, the different effects and mechanisms of GAC and MNPs on dry AD fed with pig manure (PM) and corn straw were compared, with additions of 10, 20, and 50% of the volatile solid (VS) of PM. The results indicated that GAC improved the cumulative specific methane yields (CSMYs) by 18.8–20.9%, while a high dose of MNPs (50% of the VSPM) decreased the CSMY and hydrolysis rate constant by 27.0 and 75.4%, respectively. GAC provided microorganism attachment sites and functional groups for electron transfer, improving hydrolysis by enriching fermenters such as Fastidiosipila and Rikenellaceae. Nevertheless, MNPs stimulated intense dissimilatory iron reduction by Clostridium sp. in the early stage, competing with methanogens for substrates. Low and medium GAC doses (10 and 20% of the VSPM) increased the utilization of redox-active substances (e.g., humic substances and proteins) in EPS, while the high MNP dose stimulated their secretion due to microbial self-protection, impairing electron transfer. Metagenomic evidence showed that the medium GAC dose improved four methanogenic pathways and DIET mediated by microbial nanowires, while a high MNP dose impeded the final step of methanogenesis. These results provide deeper insights into the mechanisms of different conductive materials on dry AD.

Deciphering the microbial interactions and metabolic shifts at different COD/sulfate ratios in electro-assisted anaerobic digestion

This research aims to investigate the influence of sulfate on the performance of microbial electrolysis cell-assisted anaerobic digester (MEC-AD) across varying sulfate conditions, including no sulfate and reduced COD/sulfate ratios from 20 to 1. The principal results indicate a gradual decline in methane yield in the MEC-AD from 78.7 ± 2.3 % under no sulfate conditions to 56.2 ± 2.0 % at a COD/sulfate ratio of 1, contrasting with a more substantial decrease in the control reactor (69.9 ± 3.6 % to 32.8 ± 1.5 %). The MEC-AD reactor exhibits heightened resilience to sulfide toxicity, showcasing higher specific methanogenic activities. Key findings suggest that the MEC-AD reactor maintains lower free sulfide concentrations, attributed to its higher pH and potential anodic sulfide oxidation. Additionally, the study reveals the promotion of syntrophic partnerships in the MEC-AD reactor, particularly between sulfate-reducing bacteria (SRB) such as Desulfovibrio, Desulfomicrobium, and Desulfobulbus, and other microbial groups, including hydrogenotrophic methanogens and electroactive bacteria. The integration of these mechanisms highlights the MEC-AD reactor's ability to effectively mitigate sulfate-induced challenges and enhance overall anaerobic digestion performance. This study presents a significant step forward in the development of resilient anaerobic digestion systems capable of efficiently handling sulfate stress.

Effect of micelles-forming surfactant on performance of anaerobic digestion of synthetic municipal wastewater

Effect of micelles-forming surfactant on performance of anaerobic digestion of synthetic municipal wastewater

Interaction of poly dimethyl diallyl ammonium chloride with sludge components: Anaerobic digestion performance and adaptive changes of anaerobic microbes

The wide utilization of poly dimethyl diallyl ammonium chloride (polyDADMAC) in industrial conditions leads to its accumulation in waste activated sludge (WAS), thereby affecting subsequent WAS treatment processes. This work investigated the interaction between polyDADMAC and WAS components from the perspective of anaerobic digestion (AD) performance and anaerobes adaptability variation. The results showed that polyDADMAC decreased the content of biodegradable organic substrates (i.e., soluble protein and carbohydrate) by binding with the functional groups and then settling to the solid phase, thus impeding the subsequent utilization. Higher concentrations of polyDADMAC prompted an initial protective response of excreting organic substrates into extracellular environment, but its toxicity to archaea was irreversible. Consequently, polyDADMAC inhibited the processes of AD and induced a 30 % reduction in methane production with 0.05 g polyDADMAC/g total suspended solid (TSS) addition. Changes in microbial community structure indicated that archaea involved in methane production (e.g., Anaerolineaceae sp. and Methanosaeta sp.) were inhibited when exposed to polyDADMAC. However, several adaptive bacteria with the ability of utilizing complex organics and participating in nitrogen cycle (e.g., Aminicenantales sp. and Ellin6067 sp.) were enriched with the above dosage. Specifically, the decreased abundance of genes relevant to methane metabolism pathway (i.e., mer and cdh) and increased abundance of genes involved in metabolism of cofactors and vitamins (e.g., nad and thi) indicated the toxicity of polyDADMAC and the irritant response of microflora. Moreover, polyDADMAC underwent degradation in AD system, resulting in a 12 % reduction in 15 days, accompanied by an increase in the -NO2 functional group. In general, this study provided a thorough understanding of the interaction between polyDADMAC and WAS components, raising concerns regarding the elimination of endogenous pollutants during AD.

Influence of Fe2O3 Nanoparticles Synthesized by using Nd: Yag laser (532) nm on the Anaerobic digester performance

Influence of Fe2O3 Nanoparticles Synthesized by using Nd: Yag laser (532) nm on the Anaerobic digester performance

Influence of Fe2O3 Nanoparticles Synthesized by using Nd: Yag laser (1064) nm on the Anaerobic digester performance

Influence of Fe2O3 Nanoparticles Synthesized by using Nd: Yag laser (1064) nm on the Anaerobic digester performance

Insight into response mechanism of short-chain fatty acids to refined microbial transformation order of dissolved organic matter ranked by molecular weight during dry anaerobic digestion

Dynamic transformation of dissolved organic matter (DOM) contributes to short-chain fatty acids (SCFAs) production during anaerobic digestion. However, the impact of refined transformation of DOM ranked by molecular weight (MW) on SCFAs has never been investigated. Results indicated that DOM conversion order was 3500–7000 Da>(MW>14000 Da) > 7000–4000 Da during hydrolysis stage, while it was independent of their MW in acidogenesis phase and followed a low to high MW order during methanogenesis stage. Proteins-like DOMs with different MW were closely related to SCFAs. Eight groups of microorganisms (e.g., Bacillus and Caldicoprobacter) responsible for the conversion of proteins-like DOMs to SCFAs. The possible routes linking environmental properties to microorganisms-proteins-like DOMs-SCFAs connections were constructed. Microbial activity modifications by regulating moisture, pH, NO3−-N and NH4+-N can expedite the conversion of proteins-like DOMs to SCFAs. The study emphasizes the importance of MW-classification-based biotransformation of organic waste, offering a potential strategy to enhance anaerobic digestion performance.

Enhancing the High-Solid Anaerobic Digestion of Horticultural Waste by Adding Surfactants.

The influence of adding surfactants on the performance of high-solid anaerobic digestion of horticultural waste was extensively investigated in batch systems. Adding Tween series and polyethylene glycol series non-ionic surfactants had positive effects on biogas production, resulting in 370.1 mL/g VS and 256.6 mL/g VS with Tween 60 and polyethylene glycol 300 at a surfactant-to-grass mass ratio of 0.20, while the biogas production of anaerobic digestion without surfactants was 107.54 mL/g VS. The optimal and economically feasible choice was adding Tween 20 at a ratio of 0.08 g/g grass in high-solid anaerobic digestion. A kinetics model reliably represented the relationship between surfactant concentration and biogas production. The mechanism of surfactants working on lignocellulose was investigated. The improvement in high-solid anaerobic digestion by adding surfactants was attributed to the interaction between lignocelluloses and surfactants and the extraction of biodegradable fractions from the porous structure. An economic analysis showed that adding Tween 20 was likely to make a profit and be more feasible than adding Tween 60 and polyethylene glycol 300. This study confirms the enhancement in biogas production from horticultural waste by adding non-ionic surfactants.

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.