Bioaugmentation strategy for enhancing anaerobic digestion of high C/N ratio feedstock with methanogenic enrichment culture

Designing synthetic microbial communities for enhanced anaerobic waste treatment

Synthetic microbial communities (SynComs) are powerful tools for investigating microbial interactions and community assembly by focusing on minimal yet functionally representative members. Here, we will highlight key principles for designing SynComs, specifically emphasizing the anaerobic digestion (AD) microbiome for waste treatment and upcycling. The AD process has traditionally been used to reduce organic waste volume while producing biogas as a renewable energy source. Its microbiome features well-defined trophic layers and metabolic groups. There has been growing interest in repurposing the AD process to produce value-added products and chemical precursors, contributing to sustainable waste management and the goals of a circular economy. Optimizing the AD process requires a better understanding of microbial interactions and the influence of both biotic and abiotic parameters, where SynComs offer great promise. Focusing on AD microbiomes, we review the principles of SynComs' design, including keystone taxa and function, cross-feeding interactions, and metabolic redundancy, as well as how modeling approaches could guide SynComs design. Furthermore, we address practical considerations for working with AD SynComs and examine constructed SynComs designed for anaerobic waste digestion. Finally, we discuss the challenges associated with designing and applying SynComs to enhance our understanding of the AD process. This review aims to explore the use of synthetic communities in studying anaerobic digestion and highlights their potential for developing innovative biotechnological processes.

Decipher syntrophies and adaptive response towards enhancing conversion of propionate to methane under psychrophilic condition

Propionate is a key intermediate in anaerobic digestion (AD) under low operational temperatures, which can destabilize the process. In this study, the supplementation of syntrophic cold-tolerant consortia and trace elements significantly improved the performance of psychrophilic (20 °C) reactor, increasing methane production to 91 % of mesophilic reactor levels and reducing propionate concentrations to less than 2 % of those in untreated psychrophilic reactors. Multi-omics analyses revealed that psychrophilic conditions downregulated the methylmalonyl-CoA and aceticlastic methanogenesis pathways. Electron paramagnetic resonance analyses detected 2.6E-05mol/L reactive oxygen species as stress metabolites in the inhibited psychrophilic reactors. Conversely, supplementation with syntrophic cold-tolerant consortia and trace elements enhanced the abundance of Smithellaceae, Syntrophobacteraceae, and Methanothrix by fivefold in the bioenhanced reactors. This supplementation broadened the propionate degradation pathways from relying solely on the methylmalonyl-CoA pathway to also incorporating the dismutation pathway, while upregulating both pathways. These changes enhanced methanogenesis from propionate through improved activity of the syntrophic cold-tolerant consortia. Genome-centric metatranscriptomic analysis identified the upregulation of key antioxidant genes (sod, kat, grx), temperature regulation genes (cspA), and cryoprotective genes (pslF, pslH, cysE) within the syntrophic cold-tolerant consortia. Additionally, extracellular polymeric substance (EPS) yield per cell increased in the bioenhanced reactors by up to 1.07-fold compared to RC-P. These metabolic traits emphasize the critical roles in mitigating oxidative stress, adapting to low temperatures, and supporting efficient methanogenesis under psychrophilic conditions. These findings offer insights into the transcriptional responses and adaptive mechanisms of propionate-degrading consortia in response to psychrophilic stress.

A Mechanism of Reducing Methane Production During Sewage Sludge Composting by Adding Urea

The study of the effect of the mechanism of urea addition to sewage sludge and sawdust-composting substrates on methane production is still limited. In the present study, the systematic investigation of the effect of urea addition (0.18, 0.9 and 1.8 kg) on methane production is discussed through the dynamics of physical properties, enzymes, and the microbial community during composting. The results showed that high urea addition (1.8 kg) suppressed methane production, with a lower rate and a shorter duration of warming in the thermophilic phase, but significantly enhanced cellulase activity, urease, and peroxidase, and promoted the degradation of organic carbon, as well as the loss of nitrogen. A high addition of urea stimulated the growth and reproduction of Sinibacillus, Pseudogracilibacillus, Sporosarcina, and Oceanobacillus. The random forest model indicated that the top six independent determinants of CH4 emissions were Methanobacterium, temperature, organic matter (OM), Methanospirillum, and NH4+-N. Furthermore, structural equation modeling displayed that NH4+-N, O2, and pH were the main physicochemical properties affecting CH4 emissions. Methanobacterium, Methanosarcina, and Methanosphaera were the main archaea, and Bacillaceae were the main bacteria affecting CH4 emissions. This study provides new insights and a theoretical basis for optimizing urea addition strategies during composting.

A comprehensive review on the production and enhancement techniques of gaseous biofuels and their applications in IC engines with special reference to the associated performance and emission characteristics

The increasing global demand for energy, coupled with environmental concerns associated with fossil fuels, has led to the exploration of alternative fuel sources. Gaseous biofuels, derived from organic matter, have gained attention due to their renewable nature and clean combustion characteristics. The paper extensively explores production pathways for gaseous biofuels, including biogas, syngas, and hydrogen, providing insightful discussions on various sources and processes. The energy content, physical, and chemical properties of gaseous biofuels have been analysed, highlighting their potential as viable alternatives to conventional fuels. Distinctive properties of biogas, producer gas, and hydrogen that impact combustion characteristics and engine efficiency in IC engines are underscored. Furthermore, the review systematically reviews enhancement techniques for gaseous biofuels, encompassing strategies to augment quality, purity, and combustion efficiency. Various methods, ranging from substrate pretreatment for biogas to membrane separation for hydrogen, illustrate effective means of enhancing fuel performance. Rigorous examination of performance parameters such as brake thermal efficiency, specific fuel consumption and emissions characteristics such as NOx, CO, CO2, HC of gaseous biofuels in dual-fuel mode emphasizes efficiency and environmental impact, offering valuable insights into their feasibility as engine fuels. The findings of this review will serve as a valuable resource for researchers, engineers, and policymakers involved in alternative fuels and sustainable transportation, while also highlighting the need for further research and development to fully unlock the potential of gaseous biofuels in IC engines.

Agronomic and phytotoxicity test with biosolids from anaerobic CO-DIGESTION with temperature and micro-organism phase separation, based on sewage sludge, vinasse and poultry manure

This study deals with energy and agronomic valorisation by anaerobic co-digestion with temperature and microorganism phase separation of sewage sludge, vinasse and poultry manure, with the aim of achieving an integral waste management, obtaining bioenergy and biofertilizer that returns nutrients to the soil in a natural way. The yields obtained were 40 mL H2/gVS and 391 mLCH4/gVS. The resulting effluent showed more than 98 % removal of E. coli and Total Coliforms, as well as total removal of Salmonella. The results obtained in the phytotoxicity tests showed that all the proportions studied had phytostimulant and phytonutrient properties, with 20 % having the highest germination index (GI) with mean values of 145.30 %. Finally, the agronomic trial carried out with strawberry crops (Fragaria sp.) showed that the addition of this biosolid has fertilising properties and can be used as an agronomic amendment, with an increase of 145 % in fresh weight and 102.5 % in dry weight, and fruit production doubled with respect to the control. The ANOVA statistical study corroborated that there were significant differences in crop growth when applying different proportions of biofertilizer in the fertilizer. Therefore, these results show that this technology is promising and would contribute environmentally, socially and economically to the transfer towards a circular economy model.

From laboratory- to industrial-scale plants: Future of anaerobic digestion of olive mill solid wastes

In this review, the main properties of olive mill solid waste, the primary by-product of olive oil production, and its feasibility as a feedstock for anaerobic digesters operating at laboratory-, pilot- and industrial-scales are discussed in detail. Nutrient addition and thermal pretreatments were found to have the potential to address the challenges arising from the high carbon-to-nitrogen ratio, the low pH, and the high concentration of phenolic compounds. Furthermore, anaerobic co-digestion with different organic feedstocks has been identified as one of the most promising options to solve the aforementioned problems and the seasonality nature of olive waste, while improving the efficiency of anaerobic treatment plants that operate throughout the whole year. The insights generated from this study show co-digestion with wastes from animal farming to be the most environmentally and economically sustainable method for improving anaerobic digestion processes with olive mill solid waste.

Use of additives to improve collective biogas plant performances: A comprehensive review

Nowadays, anaerobic digestion (AD) is being increasingly encouraged to increase the production of biogas and thus of biomethane. Due to the high diversity among feedstocks used, the variability of operating parameters and the size of collective biogas plants, different incidents and limitations may occur (e.g., inhibitions, foaming, complex rheology). To improve performance and overcome these limitations, several additives can be used. This literature review aims to summarize the effects of the addition of various additives in co-digestion continuous or semi-continuous reactors to fit as much as possible with collective biogas plant challenges. The addition of (i) microbial strains or consortia, (ii) enzymes and (iii) inorganic additives (trace elements, carbon-based materials) in digester is analyzed and discussed. Several challenges associated with the use of additives for AD process at collective biogas plant scale requiring further research work are highlighted: elucidation of mechanisms, dosage and combination of additives, environmental assessment, economic feasibility, etc.

Combined Biological and Chemical/Physicochemical Pretreatment Methods of Lignocellulosic Biomass for Bioethanol and Biomethane Energy Production—A Review

Lignocellulosic biomass is a low-cost and environmentally-friendly resource that can be used to produce biofuels such as bioethanol and biogas, which are the leading candidates for the partial substitution of fossil fuels. However, the main challenge of using lignocellulosic materials for biofuel production is the low accessibility to cellulose for hydrolysis of enzymes and microorganisms, which can be overcome by pretreatment. Biological and chemical pretreatments have their own disadvantages, which could be reduced by combining the two methods. In this article, we review biological–chemical combined pretreatment strategies for biogas and bioethanol production. The synergy of fungal/enzyme–NaOH pretreatment is the only biological–chemical combination studied for biogas production and has proven to be effective. The use of enzyme, which is relatively expensive, has the advantage of hydrolysis efficiency compared to fungi. Nonetheless, there is vast scope for research and development of other chemical–biological combinations for biogas production. With respect to ethanol production, fungal–organosolv combination is widely studied and can achieve a maximum of 82% theoretical yield. Order of pretreatment is also important, as fungi may reduce the accessibility of cellulose made available by prior chemical strategies and suppress lignin degradation. The biofuel yield of similarly pretreated biomass can vary depending on the downstream process. Therefore, new strategies, such as bioaugmentation and genetically engineered strains, could help to further intensify biofuel yields.

Methanosarcina thermophila bioaugmentation and its synergy with biochar growth support particles versus polypropylene microplastics in thermophilic food waste anaerobic digestion

Both biochar supplementation as well as bioaugmentation have been shown in literature to improve the methane yield of anaerobic digestion. In this study, the combination of both are evaluated by growing Methanosarcina thermophila on biochar support particles prior to augmentation of thermophilic food waste anaerobic digestion. Biochar stand alone, bioaugmentation solely, a combination of both added separately or grown together, and utilizing polypropylene (PP) microplastics as growth support instead were all tested when starting up a thermophilic process from mesophilic inoculum. Methanosarcina thermophila and biochar supplementation displayed synergy, with 5% M. thermophila on 1 g/L biochar presenting a 32% increase in specific methane yield over the control. Double the bioaugmentation dosage/concentration was also trialled with a thermophilic inoculum, and 10% M. thermophila grown on 2 g/L biochar displayed the best results with a 20% increase specific methane yield from its control standard.

Propionate-cultured sludge bioaugmentation to enhance methane production and micropollutant degradation in landfill leachate treatment

This research investigates the use of propionate-cultured sludge to enhance methane (CH₄) production and micropollutant biodegradation in biochemical methane potential (BMP) experiment treating landfill leachate. The experiments were carried out using non-acclimatized and acclimatized seed sludge with variable food to microorganism ratios of 1:1 and 1:2. Under the propionate-cultured sludge bioaugmentation, the concentrations of propionate-cultured sludge were varied between 10, 20, and 30 % (v/v). The acclimatized seed sludge exhibited high microbial abundance and diversity which promoted the CH₄ production and micropollutant biodegradation. The modified Gompertz model indicated that the optimal condition was the acclimatized seed sludge with 30% (v/v) propionate-cultured sludge, achieving the lag time (λ), maximum CH₄ production rate (R_max), and maximum CH₄ potential yield (P_max) of 0.57 day, 17.35 NmL/h, and 140.58 NmL/g COD. The research novelty lies in the use of propionate-cultured sludge bioaugmentation in landfill leachate treatment to enhance CH₄ production and micropollutant biodegradation.

New insights of anaerobic performance, antibiotic resistance gene removal, microbial community structure: applying graphite-based materials in wet anaerobic digestion

The addition of carbonaceous materials into anaerobic digestion (AD) has gained widespread attention due to their significant effects on anaerobic performance and antibiotic resistance gene (ARG) removal. This study selected graphite, graphene, and graphene oxide (GO) as additives to investigate variations in AD performance, ARG removal, microbial community diversity and structure in wet AD systems. The results indicated that the addition of graphite-based materials in wet AD systems could increase degradation of solid organic matters by 0.91%-3.41% and utilization of soluble organic fractions by 10.43%-13.67%, but could not stimulate methane production. After the addition of graphite and graphene, ARG removal rates were effectively increased to 90.85% and 94.22%, respectively. However, the total ARG removal rate was reduced to 77.46% with the addition of GO. In addition, the microbial diversity in the wet AD process was enhanced with the addition of GO only, graphite and graphene led to a reduction in it. As for bacterial community, graphite and graphene increased the abundance of Thermotogae from 43.43% to 57.42% and 58.74%, while GO increased the abundance of Firmicute from 49.90% to 56.27%. For the archaeal community, the proportion of hydrogenotrophic methanogens was improved when adding each graphite-based material; however, only GO increased Methanosaeta that was acetoclastic methanogens. Finally, methanogens were found as the ARG host, and ARGs that belong to the same subtype might exist in the same host bacteria.

Bioaugmentation with a propionate-degrading methanogenic culture to improve methane production from chicken manure

Volatile fatty acid (VFA) accumulation caused by high ammonia concentrations is often encountered during the anaerobic digestion (AD) of ammonia-rich substrates. In this study, propionate-degrading methanogenic cultures were introduced to augment the semi-continuous AD of chicken manure under high ammonia levels. Introduction of a methanogenic culture enhanced the methane yield in the bioaugmented digester by 17-26% when the organic loading rate (OLR) was 2-4 g L^-1d^-1 compared to that in the control. When the OLR was further increased from 4.0 L^-1d^-1 to 5.0 g L^-1d^-1, and bioaugmentation ceased, methane yield improved by 15-18% under a high total ammonia nitrogen level of 5.0-8.4 g NH₄⁺-N/L. Moreover, bioaugmentation reconstructed the methanogenic community in the digester, promoting the dominance of hydrogenotrophic Methanobacterium and slightly increasing the abundance of aceticlastic Methanothrix and the syntrophic propionate-oxidizing bacteria Syntrophobacter, which were the key contributors to the improved AD under high ammonia concentrations.

Bioaugmentation improves batch psychrophilic anaerobic co-digestion of cattle manure and corn straw

Low temperatures result in poor anaerobic digestion (AD). To investigate whether bioaugmentation can improve anaerobic co-digestion of cattle manure and corn straw at 20 °C, five different doses of methanogenic propionate-degrading culture (4%, 8%, 12%, 14%, and 16%) were added to batch AD systems to compare bioaugmentation performance. The results showed that the methane production of all the bioaugmented digesters was enhanced compared to the control, increasing 2.80-4.20-fold with digestion times (T₈₀) shorter by 11-22 d. The recommended dose for biogas production was 14%, and the recommended dose for the highest bioaugmentation efficiency of microbes was 4%. These improvements were due to the addition of methanogenic propionate-degrading culture, which alleviated volatile fatty acids (VFA) accumulation, especially that of acetate and propionate. Metagenomic sequencing analysis indicated that the increased proportion of propionate-oxidizing bacteria, syntrophic butyrate-oxidizing bacteria, and acetoclastic methanogens in bioaugmentation reactors may be responsible for better AD performance.

Tracking microbial community shifts during recovery process in overloaded anaerobic digesters under biological and non-biological supplementation strategies

Anaerobic digestion encounters operational instability due to fluctuations in organic loading. Propionic acid (HPr) is frequently accumulated due to its unfavorable reaction thermodynamics. Here, 'specific' bioaugmentation using HPr enrichment cultures (three different injection regimes of quantity and frequency) was compared with 'non-specific' bioaugmentation using anaerobic sludge, and with non-biological supplementation of magnetite or coenzyme M. The specific bioaugmentation treatments showed superior recovery responses during continuous feeding after a peak overload. A 'one-shot' bioaugmentation with enrichment showed the best remediation, with ~25% recovery time and >10% CH₄ conversion efficiency compared to the control. Consecutive bioaugmentation showed evidence of increased stability of the introduced community. Families Synergistaceae, Syntrophobacteraceae, and Kosmotogaceae were likely responsible for HPr-oxidation, in potential syntrophy with Methanoculleus and Methanobacterium. The different supplementation strategies can be considered to reduce the effect of start-up or overload in anaerobic digesters based on the availability of supplementation resources.

Phase Separation in Anaerobic Digestion: A Potential for Easier Process Combination?

The flexibilization of bioenergy production has the potential to counteract partly other fluctuating renewable energy sources (such as wind and solar power). As a weather-independent energy source, anaerobic digestion (AD) can offer on-demand energy supply through biogas production. Separation of the stages in anaerobic digestion represents a promising strategy for the flexibilization of the fermentative part of biogas production. Segregation in two reactor systems facilitates monitoring and control of the provision of educts to the second methanogenic stage, thus controlling biogas production. Two-stage operation has proven to reach similar or even higher methane yields and biogas purities than single-stage operation in many different fields of application. It furthermore allows methanation of green hydrogen and an easier combination of material and energy use of many biogenic raw and residual biomass sources. A lot of research has been conducted in recent years regarding the process phase separation in multi-stage AD operation, which includes more than two stages. Reliable monitoring tools, coupled with effluent recirculation, bioaugmentation and simulation have the potential to overcome the current drawbacks of a sophisticated and unstable operation. This review aims to summarize recent developments, new perspectives for coupling processes for energy and material use and a system integration of AD for power-to-gas applications. Thereby, cell physiological and engineering aspects as well as the basic economic feasibility are discussed. As conclusion, monitoring and control concepts as well as suitable separation technologies and finally the data basis for techno-economic and ecologic assessments have to be improved.

Optimization of lactate production from co-fermentation of swine manure with apple waste and dynamics of microbial communities

Co-anaerobic fermentation (co-AF) of swine manure (SM) and apple waste (AW) has been proved to be beneficial for lactic acid (LA) production. In order to further improve the LA production, three important parameters, namely AW in feedstock, temperature, volatile solids (VS) of feedstock, were evaluated using Box-Behnken design and response surface methodology. The quadratic regression model was developed and interactive effects was found between the three parameters. Results showed that the maximum concentration, 31.18 g LA/L (with LA yield of 0.62 g/g VS), was obtained under optimum conditions of 60.4% AW in feedstock, 34.7 ℃, and 5.0% VS. At the optimum conditions, the solubilization of organic matter was enhanced compared with mono-fermentation of SM. Microbial community structure of the reactor diverged greatly with fermentation time. Clostridium and Lactobacillus were dominant bacteria in the fermentation process, resulting in a remarkably LA accumulation.

Recycling anaerobic digestate enhances the co-digestion potential of agro-industrial residues: influence of different digestates as sources of microbial inoculum

Anaerobic codigestion (AcD) of agroindustrial residues was investigated. Granular sludge from bench-scale bioreactors digesting different manure were acclimated and recycled as microbial seed sludge to demonstrate inoculum-type influence on digestion performance. The biomethane potential (BMP) assay was operated for 30 days at 40 ± 2 °C in batch-type laboratory-scale reactors (100 mL). In inoculum amended reactors, codigestion showed significant, yet distinctive, biomethanation than monodigestion with a 5-fold increase (p < 0.05) in average biogas (248.3 ± 5.30 mL gVS-1) and CH4 yield (207.5 ± 4.15 mL gVS-1). The pH, soluble chemical oxygen demand (sCOD) and volatile fatty acids (VFAs) concentrations were within limits for stable AcD process with elevated total solids (TS) and volatile solids (VS) removal efficiencies. This study reinforces advancements in the recycling of digestate in biodigesters and suggests the appropriate selection of inoculum, preferably cow manure, to essentially boost methane production from these wastes.

High-solid digestion from cellulosic ethanol stillage with activated sludge of simultaneous propionate degradation and methanogenesis

High solid anaerobic digestion (HSAD) was an emerging bioconversion technology which had the advantages of small digester, less digestate and low heating energy. A one-stage anaerobic system in CSTR by inoculating activated sludge of simultaneous propionate degradation and methanogenesis was proposed to improve the high-solid digestion performance and to stabilize the reaction process. Semi-continuous mode was successfully used to perform HSAD from cellulosic ethanol whole stillage at an initial substrate loading of 15.4% (w/w) dry matter content with different OLRs from 1.5 to 5.0 gVS·L^-1 d^-1 at an HRT of 30 days. The average methane yield during whole digestion reached 349.9 mL⋅gVS^-1 with a total VS removal rate of 61.3%. The acclimation mechanism of multifunctional activated sludge was also explored by analyzing the functional property, physiological activity and microbial community structure. The results indicated the feasibility and efficiency of multifunctional activated sludge in a semi-continuous high-solid stirred tank reactor system.

Review on anaerobic digestion of rice straw for biogas production

India is an agrarian country producing a large amount of rice straw as an agricultural residue. These residues are burnt openly leading to severe environmental pollution and health hazards. Among several options available, anaerobic digestion of rice straw into biomethane gas and digestate is a promising technology. The current paper reviews the characteristics, principles of rice straw and the process variables (temperature, volatile fatty acids, and pH, carbon to nitrogen ratio, metal elements and organic loading rate) that affect the performance of the rice straw digestion and process strategies which may alleviate the barriers and may improve the biomethane yield. Co-digestion of rice straw with nitrogen-rich substrates is proven to be an effective way to balance the carbon to nitrogen ratio, in turn, leads to nutrient balance and enhance the biomethane yields of anaerobic co-digestion system. Moreover, pretreatment is another effective strategy; physical, chemical and biological pretreatments are reviewed in the article which improved the performance of digester. The utilisation of rice straw along with other co-substrates and appropriate pretreatment may be a recommended sustainable solution for preventing environmental and health hazards.

The application status, development and future trend of nano-iron materials in anaerobic digestion system

Growing environment problem and emphasis of environmental protection motivate intense research efforts in exploring technology to improve treatment efficiency on refractory organic pollutants. Hence, finding a method to make up for the deficiency of anaerobic digestion (AD) is very attractive and challenging tasks. The recent spark in the interest for the usage of some nanomaterials as an additive to strengthen AD system. The adoption of iron compounds can influence the performance and stability in AD system. However, different iron species and compounds can influence AD system in significantly different ways, both positive and negative. Therefore, strengthening mechanism, treatment efficiency, microbial community changes in Nanoscale Zero Valent Iron (nZVI) and Fe₃O₄ nanoparticles (Fe₃O₄ NPs) added AD systems were summarized by this review. The strengthening effects of nZVI and Fe₃O₄ NPs in different pollutants treatment system were analyzed. Previous study on the effects of nZVI and Fe₃O₄ NPs addition on AD have reported the concentration of nZVI and Fe₃O₄ NPs, and the types and biodegradability of pollutants might be the key factors that determine the direction and extent of effect in AD system. This review provides a summary on the nZVI and Fe₃O₄ NPs added AD system to establish experiment systems and conduct follow-up experiments in future study.

Strategies for recovery of imbalanced full-scale biogas reactor feeding with palm oil mill effluent

Background

Full-scale biogas production from palm oil mill effluent (POME) was inhibited by low pH and highly volatile fatty acid (VFA) accumulation. Three strategies were investigated for recovering the anaerobic digestion (AD) imbalance on biogas production, namely the dilution method (tap water vs. biogas effluent), pH adjustment method (NaOH, NaHCO₃, Ca(OH)₂, oil palm ash), and bioaugmentation (active methane-producing sludge) method. The highly economical and feasible method was selected and validated in a full-scale application.

Results

The inhibited sludge from a full-scale biogas reactor could be recovered within 30–36 days by employing various strategies. Dilution of the inhibited sludge with biogas effluent at a ratio of 8:2, pH adjustment with 0.14% w/v NaOH, and 8.0% w/v oil palm ash were considered to be more economically feasible than other strategies tested (dilution with tap water, or pH adjustment with 0.50% w/v Ca(OH)₂, or 1.25% NaHCO₃ and bioaugmentation) with a recovery time of 30–36 days. The recovered biogas reactor exhibited a 35–83% higher methane yield than self-recovery, with a significantly increased hydrolysis constant (k_H) and specific methanogenic activity (SMA). The population of Clostridium sp., Bacillus sp., and Methanosarcina sp. increased in the recovered sludge. The imbalanced full-scale hybrid cover lagoon reactor was recovered within 15 days by dilution with biogas effluent at a ratio of 8:2 and a better result than the lab-scale test (36 days).

Conclusion

Dilution of the inhibited sludge with biogas effluent could recover the imbalance of the full-scale POME-biogas reactor with economically feasible and high biogas production performance.

A new strategy to recover from volatile fatty acid inhibition in anaerobic digestion by photosynthetic bacteria

The accumulation of volatile fatty acids (VFAs) can decrease reactor pH and inhibit methane-producing process. For the first time, photosynthetic bacteria (PSB) were used to recover from VFAs inhibition (pH 6.0) of an anaerobic digestion system. After adding PSB for 12 days with and without light condition, the methane content recovered from 33.3% to 60.5% and from 32.1% to 59.3%, respectively; the pH increased to 7.1 and 6.8, respectively, the system alkalinity rapidly increased to 2238 and 1921 mg/L, respectively; the sCOD decreased from 5600 to 995 mg/L and from 5575 to 2025 mg/L, respectively; and the contents of formic acid, acetic acid, propionic acid and total VFA were greatly reduced. Microbial analysis found that PSB bioaugmentation could maintain microbial diversity of the system. PSB bioaugmentation could effectively relieve acids accumulation and stimulate methane production especially under light condition. It is also found that light could accelerate recovery with or without bioaugmentation.

Effect of bioaugmentation on digestate metal concentrations in anaerobic digestion of sewage sludge

This study examined the influence of bioaugmentation on metal concentrations (aluminum, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel and zinc) in anaerobically digested sewage sludge. To improve the digestion efficiency, bioaugmentation with a mixture of wild-living Archaea and Bacteria (MAB) from Yellowstone National Park, USA, was used. The total concentration of all metals was higher in the digestate than in the feedstock. During anaerobic digestion, the percent increase in the concentration of most of metals was slightly higher in the bioaugmented runs than in the un-augmented runs, but these differences were not statistically significant. However, the percent increase in cadmium and cobalt concentration was significantly higher in the bioaugmented runs than in the un-augmented runs. At MAB doses of 9 and 13% v/v, cadmium concentration in the digestate was 211 and 308% higher than in the feedstock, respectively, and cobalt concentration was 138 and 165%, respectively. Bioaugmentation increased over 4 times the percentage of Pseudomonas sp. in the biomass that are able to efficiently accumulate metals by both extracellular adsorption and intracellular uptake. Biogas production was not affected by the increased metal concentrations. In conclusion, bioaugmentation increased the concentration of metals in dry sludge, which means that it could potentially have negative effects on the environment.

Bioaugmentation to enhance anaerobic digestion of food waste: Dosage, frequency and economic analysis

This study investigated whether bioaugmentation can improve the anaerobic digestion (AD) performance of food waste (FW), as well as the effects of addition dosage and frequency on the bioaugmentation's performance and economic feasibility. The findings demonstrated that all the bioaugmented digesters, regardless of dosage and frequency, performed more effectively in biogas production than the non-bioaugmentation control. Furthermore, relatively higher dosages or frequencies increased AD performance. Introducing 0.25 g L^-1 d^-1 of bioaugmentation seed every three days increased OLR and volumetric biogas production 8-fold and 12-fold, respectively, compared to the non-bioaugmentation control. Whole-genome sequencing analysis showed that bioaugmentation enhanced the population of the acetoclastic Methanothrix (belong to the order Methanosarcinales). Moreover, high abundance of Methanothrix (exceeding 80%) contributed to a better AD performance. Economic analysis of an up-scale biogas plant suggested that an appropriate bioaugmentation process increased income, thus increasing the profit to 3696 CNY d^-1 if treated at 21 t FW.

Acclimation of Acid-Tolerant Methanogenic Culture for Bioaugmentation: Strategy Comparison and Microbiome Succession

To enrich an acid-tolerant methanogenic culture used as bioaugmented seed under acidic conditions, we operated four semicontinuous digesters under various conditions of pH decline for producing methane at pH 5.0. 16S rRNA amplification was performed to unravel the association between declining pH and microbiome succession. The findings demonstrated that a gradual decrease of pH, at a step size of 0.5, and a prolonged run time at each pH could achieve a suitable microbial culture, in which acetoclastic Methanothrix and hydrogenotrophic Methanolinea represented the dominant methanogens. In contrast, a sharp decline in pH could result in heavy loss of the acetoclastic methanogen Methanothrix, leading to a cessation of methane production. Hydrogenotrophic methanogens exhibited high acid tolerance, and Methanospirillum could thrive despite a sudden low-pH shock. Although Methanolinea required a longer time to enrich, it played a substantial role in methane production under an acidic environment.

The Impact of Exogenous Aerobic Bacteria on Sustainable Methane Production Associated with Municipal Solid Waste Biodegradation: Revealed by High-Throughput Sequencing

In this work, the impact of exogenous aerobic bacteria mixture (EABM) on municipal solid waste (MSW) is well evaluated in the following aspects: biogas production, leachate analysis, organic waste degradation, EABM population, and the composition of microbial communities. The study was designed and performed as follows: the control bioreactor (R1) was filled up with MSW and the culture medium of EABM and the experimental bioreactor (R2) was filled up with MSW and EABM. The data suggests that the composition of microbial communities (bacterial and methanogenic) in R1 and R2 were similar at day 0, while the addition of EABM in R2 led to a differential abundance of Bacillus cereus, Bacillus subtilis, Staphylococcus saprophyticus, Staphlyoccus xylosus, and Pantoea agglomerans in two bioreactors. The population of exogenous aerobic bacteria in R2 greatly increased during hydrolysis and acidogenesis stages, and subsequently increased the degradation of volatile solid (VS), protein, lipid, and lignin by 59.25%, 25.68%, 60.47%, and 197.62%, respectively, compared to R1. The duration of hydrolysis and acidogenesis in R2 was 33.33% shorter than that in R1. At the end of the study, the accumulative methane yield in R2 (494.4 L) was almost three times more than that in R1 (187.4 L). In addition, the abundance of acetoclasic methanogens increased at acetogenesis and methanogenesis stages in both bioreactors, which indicates that acetoclasic methanogens (especially Methanoseata) could contribute to methane production. This study demonstrates that EABM can accelerate organic waste degradation to promote MSW biodegradation and methane production. Moreover, the operational parameters helped EABM to generate 20.85% more in accumulative methane yield. With a better understanding of how EABM affects MSW and the composition of bacterial community, this study offers a potential practical approach to MSW disposal and cleaner energy generation worldwide.

Biogas production from palm oil mill effluent and empty fruit bunches by coupled liquid and solid-state anaerobic digestion

Biogas production of palm oil mill effluent (POME) and empty fruit bunches (EFB) was performed by coupled liquid (L-AD) and solid-state (SS-AD) anaerobic digestion processes. POME was fed to L-AD digester, while mixed of effluent from L-AD and EFB was fed to SS-AD digester. The maximum overall methane production of 60.9 m³-CH₄·ton^-1 waste was obtained at an optimal hydraulic retention time of 30 days and an organic loading rate of 1.66 gVS·L^-1-reactor·d^-1 for L-AD and 6.03 gVS·L^-1-reactor·d^-1 for SS-AD with L-AD effluent recycling rate of 16.7 mL·L^-1-reactor·d^-1. The bacterial community in the L-AD reactor was different from the SS-AD reactor, while the archaeal community was similar in both reactors. Synergistaceae, Caldicoprobacteraceae and Lachnospiraceae were increased in the SS-AD reactor. Coupling L-AD and SS-AD is able to increase energy production by 29% and 71% compared to the L-AD and SS-AD alone, respectively, with no outsource SS-AD inoculum required.

Effect of bioaugmentation on the microbial community and mono-digestion performance of Pennisetum hybrid

In this study, bioaugmentation with methanogenic propionate-utilizing enrichment was investigated as a method to improve the mono-digestion performance of Pennisetum hybrid in a semi-continuous mode. The effect of bioaugmentation on the microbial community was analyzed as well. The results demonstrate that the steady-state organic loading rate (OLR) of the bioaugmented reactor increased to 4.0 g VS/(L·d) with a volumetric biogas production of 1.95 ± 0.17 m³/(m³·d). In contrast, the non-bioaugmented reactor failed at an OLR of 2.0 g VS/(L·d) accompanied with the accumulation of volatile fatty acids (VFAs). The results of whole genome pyrosequencing analysis suggest that the decrease in relative abundance of syntrophic butyrate and propionate oxidizers, such as Syntrophomonas, Syntrophobacter, and Syntrophorhabdus, reduced the conversion efficiency of butyrate and propionate which leads to the accumulation of butyrate and propionate, influencing the performance of the mono-digestion reactor. Conversely, in the bioaugmented reactor, the higher density of protein- and amino acid-utilizing bacteria, such as Proteiniphilum, Thermovirga, and Lutaonella, as well as the syntrophic association of Syntrophomonas spp. coupled with the methanogens Methanosarcina and Methanocella has a positive effect on system stability and performance.