Influence of Temperature on Biogas Production Efficiency and Microbial Community in a Two-Phase Anaerobic Digestion System

Temperature-dependent transformation of microbial community: A systematic approach to analyzing functional microbes and biogas production

The stability and effectiveness of the anaerobic digestion (AD) system are significantly influenced by temperature. While majority research has focused on the composition of the microbial community in the AD process, the relationships between functional gene profile deduced from gene expression at different temperatures have received less attention. The current study investigates the AD process of potato peel waste and explores the association between biogas production and microbial gene expression at 15, 25, and 35 °C through metatranscriptomic analysis. The production of total biogas decreased with temperature at 15 °C (19.94 mL/g VS), however, it increased at 35 °C (269.50 mL/g VS). The relative abundance of Petrimonas, Clostridium, Aminobacterium, Methanobacterium, Methanothrix, and Methanosarcina were most dominant in the AD system at different temperatures. At the functional pathways level 3, α-diversity indices, including Evenness (Y = 5.85x + 8.85; R2 = 0.56), Simpson (Y = 2.20x + 2.09; R2 = 0.33), and Shannon index (Y = 1.11x + 4.64; R2 = 0.59), revealed a linear and negative correlation with biogas production. Based on KEGG level 3, several dominant functional pathways associated with Oxidative phosphorylation (ko00190) (25.09, 24.25, 24.04%), methane metabolism (ko00680) (30.58, 32.13, and 32.89%), and Carbon fixation pathways in prokaryotes (ko00720) (27.07, 26.47, and 26.29%), were identified at 15 °C, 25 °C and 35 °C. The regulation of biogas production by temperature possibly occurs through enhancement of central function pathways while decreasing the diversity of functional pathways. Therefore, the methanogenesis and associated processes received the majority of cellular resources and activities, thereby improving the effectiveness of substrate conversion to biogas. The findings of this study illustrated the crucial role of central function pathways in the effective functioning of these systems.

Long-term effect of seasonal and constant low temperatures on mesophilic biomass treating sewage in continuously stirred tank anaerobic granular reactor

A Continuously Stirred Tank Anaerobic Granular Reactor seeded with mesophilic biomass was studied for 1733 days analysing the impact of seasonal (12-23 °C) and controlled (8-15 °C) low temperatures on anaerobic treatment of sewage. Aided by intermittent dosing of 0.04% (v/v) methanol, the microbiota quickly adapted to temperature fluctuations. Chemical oxygen demand (COD) removal efficiency was high but low temperatures affected methane production. Under low-temperature stress, the Methanomythylovorans and Methanosaeta-dominated methanogenic community shifted focus to cellular repair and transport, with carbon diversion towards assimilative pathways, thereby decreasing methane yields. Specific methanogenic activity at 15 °C and 30 °C increased by five and four times, respectively, from their initial values indicating microbiota retained its mesophilic properties. Despite lower methane yield, stable and high COD removals, along with low dissolved methane and volatile fatty acids indicated that low-temperature anaerobic sewage treatment using mesophilic biomass in the long run is sustainable.

Comparison of Thermophilic-Mesophilic and Mesophilic-Thermophilic Two-Phase High-Solid Sludge Anaerobic Digestion at Different Inoculation Proportions: Digestion Performance and Microbial Diversity

This study investigated the performance of thermophilic-mesophilic (T-M) and mesophilic-thermophilic (M-T) two-phase sludge anaerobic digestion at different inoculation proportions after a change in digestion temperature. After temperature change, the pH, total ammonia nitrogen (TAN), free ammonia nitrogen (FAN), solubility chemical oxygen demand (SCOD), and total alkalinity (TA) levels of two-phase digesters were between thermophilic control digesters and mesophilic control digesters. However, the volatile fatty acid (VFA) levels of two-phase digesters were higher than those of thermophilic or mesophilic control digesters. The bacteria communities of M-T two-phase digesters were more diverse than those of T-M. After a change in digestion temperature, the bacterial community was dominated by Coprothermobacter. After a change of digestion temperature, the relative abundance (RA) of Methanobacterium, Methanosaeta, and Methanospirillum of M-T two-phase digesters was higher than that of T-M two-phase digesters. In comparison, the RA of Methanosarcina of T-M two-phase digesters was higher than that of M-T two-phase digesters. The ultimate methane yields of thermophilic control digesters were greater than those of mesophilic control digesters. Nevertheless, the ultimate methane yield levels of M-T two-phase digesters were greater than those of T-M two-phase digesters. The ultimate methane yields of all two-phase digesters presented an earlier increase and later decrease trend with the increasing inoculation proportion. Optimal methane production condition was achieved when 15% of sludge (T-M15) was inoculated under mesophilic-thermophilic conditions, which promoted 123.6% (based on mesophilic control) or 27.4% (based on thermophilic control). An optimal inoculation proportion (about 15%) balanced the number and activity of methanogens of high-solid sludge anaerobic digestion.

Effect of Temperature on Anaerobic Fermentation of Poplar Ethanol Wastewater: Performance and Microbial Communities

Temperature plays an important role in anaerobic digestion (AD), and different substrates have different optimum temperatures in AD. However, the effect of temperature on the performance of AD when cellulosic ethanol wastewater was used as a substrate was rarely reported. Therefore, the digestion characteristics of cellulosic ethanol wastewater at 25, 35, 45, and 55 °C were investigated, and the microbial communities of the sludge sample were analyzed after fermentation. The results showed that the cumulative methane production was the highest at 55 °C, 906.40 ± 50.67 mL/g VS, which was 81.06, 72.42, and 13.33% higher than that at 25, 35, and 45 °C, respectively. The content of methane was 68.13, 49.26, 70.46, and 85.84% at the terminal period of fermentation at temperatures of 25, 35, 45, and 55 °C, respectively. The testing of volatile fatty acids (VFAs) indicated that the accumulation of VFAs did not occur when the fermentation was carried out at 25, 35, and 45 °C; however, the VFA content at 55 °C was much larger than that in the three groups (25, 35, and 45 °C), and the ratio of propionic acid to acetic acid was larger than 1.4 at the late stage of fermentation, so it inhibited the fermentation. The diversity of the microbial community indicated that the floral structure and metabolic pathway of fermentation were alike at 25 and 35 °C. Firmicutes and Proteobacteria were the main flora covering the 25-55 °C-based phylum or below it. The relative abundance of Methanosaeta was the highest when fermentation temperatures were 25 and 35 °C; however, its relative abundance decreased sharply and the relative abundance of Methanosarcina increased substantially when the temperature increased from 35 to 45 °C, which indicated that Methanosarcina can exist in higher temperatures. At the same time, hydrogenotrophic methanogens such as Methanoculleus and Methanothermobacter were dominant when fermentation temperatures were 45 and 55 °C, which indicated that the metabolic pathway changed from acetoclastic methanogenesis to hydrogenotrophic methanogenesis.

Synergic role of ferrate and nitrite for triggering waste activated sludge solubilisation and acidogenic fermentation: Effectiveness evaluation and mechanism elucidation

Enhancing anaerobic treatment efficiency of waste activated sludge (WAS) toward preferable resource recovery would be an important requirement for achieving carbon-emission reduction, biosolids minimization, stabilization and security concurrently. This study demonstrated the synergic effect of potassium ferrate (PF) and nitrite on prompting WAS solubilisation and acidogenic fermentation toward harvesting volatile fatty acids (VFAs). The results indicated the PF+NaNO₂ co-pretreatment boosted 7.44 times and 1.32 times higher WAS solubilisation [peak soluble chemical oxygen demand (SCOD) of 2680 ± 52 mg/L] than that by the single nitrite- and PF-pretreatment, respectively, while about 2.77 times and 2.11 times higher VFAs production were achieved (maximum VFAs accumulation of 3536.25 ± 115.24 mg COD/L) as compared with the single pretreatment (nitrite and PF)-fermentations. Afterwards the WAS dewaterability was improved simultaneously after acidogenic fermentation. Moreover, a schematic diagram was established for illustrating mechanisms of the co-pretreatment of PF and nitrite for enhancing the VFAs generation via increasing key hydrolytic enzymes, metabolic functional genes expression, shifting microbial biotransformation pathways and elevating abundances of key microbes in acidogenic fermentation. Furthermore, the mechanistic investigations suggested that the PF addition was conducive to form a relatively conductive fermentation environment for enhancing electron transfer (ET) efficiency, which contributed to the VFAs biotransformation positively. This study provided an effective strategy for enhancing the biodegradation/bioconversion efficiency of WAS organic matters with potential profitable economic returns.

Effects of different low temperature conditions on anaerobic digestion efficiency of pig manure and composition of archaea community

To explore the effect of low temperature on the anaerobic digestion of pig manure, the anaerobic digestion experiment was carried out under the conditions of inoculum concentration of 30% and TS of 8%. Five low-temperature gradients of 4, 8, 12, 16 and 20 °C were set to study the activities of gas production, pH, solluted chemical oxygen demand (SCOD), volatile fatty acids (VFAs), coenzymes F₄₂₀ and archaea community composition in the digestion process. The results were demonstrated: as the temperature decreased, the more unstable the gas production became, the less gas production produced, and the later the gas peak occurred. There were no significant peaks at either 4 °C or 8 °C, and the SCOD was unstable over time. From 12 °C, the SCOD increased over time, and the higher the temperature, the faster the growth trend. The pH was always greater than 7.6. 8, 12, 16, 20 °C had different degrees of VFAs accumulation at the late digestion stage. The higher the temperature, the greater the amount of volatile acid accumulation. When the VFAs of each reactor reached the maximum, the proportion of acetic acid also reached the highest. The digestion system of the five treatment groups was dominated by hydrogen-nutrient methanogenic pathway. The results could provide a further reference for the mechanism of anaerobic digestion of pig manure at low temperatures.

Effects of pH Adjustment on the Release of Carbon Source of Particulate Organic Matter (POM) in Domestic Sewage

The use of anaerobic hydrolytic fermentation to develop more available carbon sources from domestic sewage influent particulate organic matter (POM) has received increasing attention. However, the slow hydrolysis rate of POM limits the application of this technology. This study aimed to improve the carbon source release efficiency of POM by pH adjustment and to reveal the hydrolysis mechanism. Results showed that adjusting the initial pH of POM to 3, 9, and 11 enhanced carbon source release in the anaerobic hydrolysis fermentation process of POM. The pretreatment under pH value of 11 contributed to the highest yield and productivity of carbon source, reaching the soluble chemical oxygen demand (SCOD) of 2782 mg/L at the 4th day. The pH 3 pretreatment was more beneficial for phosphorus resource recovery, which contributed to the highest release concentration of PO43−-P, reaching 48.2 mg/L at the 3rd day, accounting for 90% of TP. Microbial community structure analysis indicated that pH 11 preconditioning promoted the enrichment of proteolytic bacteria (Proteocatella and Proteiniclasticum) and polysaccharide hydrolytic bacteria (Trichococcus and Acinetobacter) and inhibited the growth of acetate-consuming methanogenic archaea, which contributed to the highest carbon release of POM in domestic sewage.

Treatment of Pharma Effluent using Anaerobic Packed Bed Reactor

The treatment of pharmaceutical effluent using an appropriate technology has become so important. Anaerobic packed bed reactor is an efficient method for pharmaceutical effluent treatment because of the high organic content present in it. In this study, a heavy-polluted pharma effluent is treated using an anaerobic packed bed reactor. The performance of the anaerobic reactor was identified with respect to chemical oxygen demand (COD) removal, methane yield, and gas production. The results showed that COD was reduced from 73% to 60% for an organic loading rate (OLR) of 0.6036–1.7487 kg COD m⁻³·d⁻¹. As the OLR increases, the removal efficiency of COD decreases gradually to around 52% for an OLR of 2.34 kg COD m⁻³·d⁻¹.

Effects of Stepwise Temperature Shifts in Anaerobic Digestion for Treating Municipal Wastewater Sludge: A Genomic Study

In wastewater treatment plants (WWTP), anaerobic digester (AD) units are commonly operated under mesophilic and thermophilic conditions. In some cases, during the dry season, maintaining a stable temperature in the digester requires additional power to operate a conditioning system. Without proper conditioning systems, methanogens are vulnerable to temperature shifts. This study investigated the effects of temperature shifts on CH₄ gas production and microbial diversity during anaerobic digestion of anaerobic sewage sludge using a metagenomic approach. The research was conducted in lab-scale AD under stepwise upshifted temperature from 42 to 48 °C. The results showed that significant methanogen population reduction during the temperature shift affected the CH₄ production. With 70 days of incubation each, CH₄ production decreased from 4.55 L·g⁻¹-chemical oxygen demand (COD) at 42 °C with methanogen/total population (M·TP⁻¹) ratio of 0.041 to 1.52 L·g⁻¹ COD (M·TP⁻¹ ratio 0.027) and then to 0.94 L·g⁻¹ COD ( M·TP⁻¹ ratio 0.026) after the temperature was shifted to 45 °C and 48 °C, respectively. Methanosaeta was the most prevalent methanogen during the thermal change. This finding suggests that the Methanosaeta genus was a thermotolerant archaea. Anaerobaculum, Fervidobacterium, and Tepidanaerobacter were bacterial genera and grew well in shifted-up temperatures, implying heat-resistant characteristics.

Augmentation characteristics and microbial community dynamics of low temperature resistant composite strains LTF-27

Biogas production in the cold regions of China is hindered by low temperatures, which led to slow lignocellulose biotransformation. Cold-adapted lignocellulose degrading microbial complex community LTF-27 was used to investigate the influence of hydrolysis on biogas production. After 5 days of hydrolysis at 15 ± 1 °C, the hydrolysis conversion rate of the corn straw went up to 22.64%, and the concentration of acetic acid increased to 2596.56 mg/L. The methane production rates of total solids (TS) inoculated by LTF-27 reached 204.72 mL/g, which was higher than the biogas (161.34 mL/g), and the control group (CK) inoculated with cultural solution (121.19 mL/g), the methane production rate of volatile solids (VS) increased by 26.88% and 68.92%, respectively. Parabacteroides, Lysinibacillus, and Citrobacter were the main organisms that were responsible for hydrolysis. While numerous other bacteria genera in the gas-producing phase, Macellibacteroides were the most commonly occurring one. Methanosarcina and Methanobacteriaceae contributed 86.25% and 11.80% of the total Archaea abundance during this phase. This study proves the psychrotrophic LTF-27's applicability in hydrolysis and biomass gas production in low temperatures.

Multiscale engineering of microbial cell factories: A step forward towards sustainable natural products industry

Microbial cell factories (bacteria and fungi) are the leading producers of beneficial natural products such as lycopene, carotene, herbal medicine, and biodiesel etc. These microorganisms are considered efficient due to their effective bioprocessing strategy (monoculture- and consortial-based approach) under distinct processing conditions. Meanwhile, the advancement in genetic and process optimization techniques leads to enhanced biosynthesis of natural products that are known functional ingredients with numerous applications in the food, cosmetic and medical industries. Natural consortia and monoculture thrive in nature in a small proportion, such as wastewater, food products, and soils. In similitude to natural consortia, it is possible to engineer artificial microbial consortia and program their behaviours via synthetic biology tools. Therefore, this review summarizes the optimization of genetic and physicochemical parameters of the microbial system for improved production of natural products. Also, this review presents a brief history of natural consortium and describes the functional properties of monocultures. This review focuses on synthetic biology tools that enable new approaches to design synthetic consortia; and highlights the syntropic interactions that determine the performance and stability of synthetic consortia. In particular, the effect of processing conditions and advanced genetic techniques to improve the productibility of both monoculture and consortial based systems have been greatly emphasized. In this context, possible strategies are also discussed to give an insight into microbial engineering for improved production of natural products in the future. In summary, it is concluded that the coupling of genomic modifications with optimum physicochemical factors would be promising for producing a robust microbial cell factory that shall contribute to the increased production of natural products.

Overview on agricultural potentials of biogas slurry (BGS): applications, challenges, and solutions

The residual slurry obtained from the anaerobic digestion (AD) of biogas feed substrates such as livestock dung is known as BGS. BGS is a rich source of nutrients and bioactive compounds having an important role in establishing diverse microbial communities, accelerating nutrient use efficiency, and promoting overall soil and plant health management. However, challenges such as lower C/N transformation rates, ammonia volatilization, high pH, and bulkiness limit their extensive applications. Here we review the strategies of BGS valorization through microbial and organomineral amendments. Such cohesive approaches can serve dual purposes viz. green organic inputs for sustainable agriculture practices and value addition of biomass waste. The literature survey has been conducted to identify the knowledge gaps and critically analyze the latest technological interventions to upgrade the BGS for potential applications in agriculture fields. The major points are as follows: (1) Bio/nanotechnology-inspired approaches could serve as a constructive platform for integrating BGS with other organic materials to exploit microbial diversity dynamics through multi-substrate interactions. (2) Advancements in next-generation sequencing (NGS) pave an ideal pathway to study the complex microflora and translate the potential information into bioprospecting of BGS to ameliorate existing bio-fertilizer formulations. (3) Nanoparticles (NPs) have the potential to establish a link between syntrophic bacteria and methanogens through direct interspecies electron transfer and thereby contribute towards improved efficiency of AD. (4) Developments in techniques of nutrient recovery from the BGS facilities' negative GHGs emissions and energy-efficient models for nitrogen removal. (5) Possibilities of formulating low-cost substrates for mass-multiplication of beneficial microbes, bioprospecting of such microbes to produce bioactive compounds of anti-phytopathogenic activities, and developing BGS-inspired biofertilizer formulations integrating NPs, microbial inoculants, and deoiled seed cakes have been examined.

Effect of Hydraulic Retention Time on the Performance of a Compact Moving Bed Biofilm Reactor for Effluent Polishing of Treated Sewage

Treated effluent from a wastewater treatment plant can be further reused as a water resource for a water supply treatment plant. In this case, the treated sewage gathered in the study of the Class V National Water Quality Standard (NWQS) of Malaysia would be treated for use as a water resource for a water treatment plant. In a moving bed biofilm reactor (MBBR) with a 500-L working volume, organic pollutants, undesirable nutrients, and bacteria were removed without disinfectant. At 24-h hydraulic retention time (HRT), the maximum removal efficiency of 5-day biological oxygen demand, ammonia–nitrogen (NH3-N), and total phosphorus were 71%, 48%, and 12%, respectively. The biofilm thickness, which was captured using scanning electron microscopy, increased from 102.6 μm (24-h HRT) to 297.1 μm (2-h HRT). A metagenomic analysis using 16S rRNA showed an abundance of anaerobic bacteria, especially from the Proteobacteria phylum, which made up almost 53% of the total microbes. MBBR operated at 24-h HRT could improve effluent quality, as its characteristics fell into Class IIA of the NWQS of Malaysia, with the exception of the NH3-N content, which indicated that the effluent needed conventional treatment prior to being reused as potable water.

Start-up phase optimization of two-phase anaerobic digestion of food waste: Effects of organic loading rate and hydraulic retention time

The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the dynamics of acidogenic and methanogenic processes in two-phase anaerobic digestion (TPAD) of food waste (FW) were investigated to determine the start-up operational conditions. Seven arrangements of TPAD systems under mesophilic conditions were evaluated, each containing one acidogenic reactor and one methanogenic reactor. The work analyzed two HRTs (2 and 3 days) and four OLRs (2, 3, 4 and 5 kgVS.m^-3.d^-1). The 2D5KG system obtained VS and COD removal of 68% and 72%; SMP of 273 L_methane.kg.VS^-1. The 3D4KG system obtained VS and COD removal of 70 and 66%; SMP of 252 L_methane.kg.VS^-1. Valeric acid predominated in the acidogenic reactor in both HRT and OLR evaluated, followed by butyric acid. In the methanogenic reactor, the main methane production route was the butyric acid conversion into acetic acid and finally methane. Higher OLR benefits the methane production. The microbiological profile indicated the pathway of methanogenesis by acetoclastic methanogenesis. The canonical correlation analysis allowed to verify that the groups are independent and, therefore, the variables analyzed in the acidogenic reactor have an influence on the methanogenic reactor.

Effects of Seasonal Temperature Variation on Slurry Temperature and Biogas Composition of a Commercial Fixed-Dome Anaerobic Digester Used in Bangladesh

Biogas is produced in Bangladesh mostly through fixed-dome anaerobic digesters, which usually operate without any temperature controller. An experiment was conducted to monitor the seasonal temperature variation inside a fixed-dome type digester and its effect on biogas composition. A commercial-scale digester with a working volume of 350 m3 was used for this study. Three k-type thermocouple sensors were used to monitor the ambient, biogas, and slurry temperatures in real-time. The results showed that the average ambient temperature in the autumn, late autumn, and winter was 29.05, 22.90, and 17.64 °C, respectively. The average slurry temperature in the autumn (30.38 °C) was higher than in the late autumn (29.36 °C) and in the winter (25.76 °C). The highest and lowest slurry temperatures were found to be 31.11 and 24.47 °C, respectively, which indicated that the digester worked within a wide temperature range, establishing both psychrophilic and mesophilic operational conditions. Higher methane concentrations were observed in the autumn than in the late autumn and winter. The CO2 and H2S concentrations were higher in the winter than those of in the autumn and late autumn. The electricity generation in the winter was 47.85% and 45.15% lower than in the autumn and late autumn, respectively.

Harnessing energy from the waste produced in Bangladesh: evaluating potential technologies

With the increasing trend of the urban population in Bangladesh, waste generation is also increasing. With 70% organic solid waste, the urban areas generate 23,688 tonnes of waste per day. This rapid enhancement in waste production has an adverse effect onlandfill resources and the day-to-day lifestyle. In this regard adopting waste to energy techniques can be considered good idea to overcome the current waste management problem. This WtE conversion technique solves the landfill resources problem and produces electricity and heat to be supplied. This study aims to investigate the current status of MSW management in Bangladesh and identify the major problems. Here, five fundamental methods such as pyrolysis, incineration, anaerobic digestion (AD), gasification, hydrothermal carbonization (HTC) are reviewed critically and discussed the feasibilities in Bangladesh to generate power. The analysis is done considering different types of parameters like moisture content, calorific value, and residence time. These analyses pertaining to MSW management may be fruitful for encouraging researchers and authorities to improve further.

High-Solid Anaerobic Digestion: Reviewing Strategies for Increasing Reactor Performance

High-solid and solid-state anaerobic digestion are technologies capable of achieving high reactor productivity. The high organic load admissible for this type of configuration makes these technologies an ideal ally in the conversion of waste into bioenergy. However, there are still several factors associated with these technologies that result in low performance. The economic model based on a linear approach is unsustainable, and changes leading to the development of a low-carbon model with a high degree of circularity are necessary. Digestion technology may represent a key driver leading these changes but it is undeniable that the profitability of these plants needs to be increased. In the present review, the digestion process under high-solid-content configurations is analyzed and the different strategies for increasing reactor productivity that have been studied in recent years are described. Percolating reactor configurations and the use of low-cost adsorbents, nanoparticles and micro-aeration seem the most suitable approaches to increase volumetric production and reduce initial capital investment costs.

Novel insights of impacts of solid content on high solid anaerobic digestion of cow manure: Kinetics and microbial community dynamics

High solid anaerobic digestion has become the mainstream technology for sustainable on-farm treatment of solid wastes but has not been optimized with respect to increasing solid content in cow manure (CM). In the present study, CM was batch digested at total solid (TS) of 5%, 10%, 15% and 20% and microbial communities were investigated. The process remained stable up to 15% TS. The biomethane production rate at TS of 10% and 15% was reported to be 352.2 mL g^-1 VS and 318.6 mL g^-1 VS, reaching up to 83% and 75% of TS 5% biomethane, respectively. Kinetics results disclosed that the biodegradable organics could be utilized at increasing solid content with decreasing hydrolysis rate. The abundances of hydrogenotrophic and methylotrophic methanogens increased significantly with increasing solid content. This study is of great importance for understanding and application of high solid anaerobic digestion of cow manure.

Simulation and Optimisation of Integrated Anaerobic-Aerobic Bioreactor (IAAB) for the Treatment of Palm Oil Mill Effluent

This study highlights an innovative piece of hybrid technology, whereby the combination of anaerobic and aerobic processes into a single reactor, namely, the integrated anaerobic–aerobic bioreactor (IAAB) can surpass the limits of conventional methods treating palm oil mill effluent (POME). Optimisation of IAAB using SuperPro Designer V9 simulator for maximum biogas yield while addressing its economic and environmental trade-offs was conducted for the first time. Parameters such as hydraulic retention time (HRT) and organic loading rate (OLR) were optimised in the anaerobic compartment from 10 days and 6.2 g COD/L day to 9 days and 6.9 g COD/L day, respectively. Furthermore, sludge recycle ratio was optimised from 20% to 50% in the aerobic compartment. The optimisation was successful where the biogas yield increased from 0.24 to 0.29 L CH4/g CODremoved with excellent Chemical Oxygen Demand (COD), and Biological Oxygen Demand (BOD) removal efficiencies up to 99% with 5.8% lower net expenditure. This simulation results were comparable against the pre-commercialized IAAB with 11.4% increase in methane yield after optimisation. Economic analysis had proven the optimised process to be feasible, resulting in return on investment (ROI), payback time, and internal rate of return (IRR) of 24.5%, 4.1 years, and 17.9%, respectively.

Development of a Mathematical Model and Validation for Methane Production Using Cow Dung as Substrate in the Underground Biogas Digester

South Africa is highly dependent on conventional fuels from non-renewable energy sources such as coal and fossil fuels. The methane from biogas is a renewable energy source for generating electricity using a combined heat and power plant. Therefore, the aim of the study is to develop and validate a mathematical model for predicting methane production in an underground biogas digester. The developed model was able to predict the production of methane gas as separate entity differing from other models. A total of 286 datasets were used as a trained dataset for the model development, and 144 datasets served as test data for the validation of the model, making a total of 430 measured datasets of all the predictors. The determination coefficient (R2) and the p-value of the predicted and calculated methane yield were 0.962 and 0.920, respectively. The high R2 in the present study confirms a good correlation between the model and experimental value. Hence, the model is of significance because it is applicable in predicting the performance of methane production of systems of the same design used in different locations, thereby arriving at the same constant values. From the study, the ambient weather factors (ambient temperature, relative humidity, and global horizontal irradiance) affected the methane production. Additionally, the indoor parameters (pH, gas temperature, slurry bottom and slurry top temperature) impacted on the yield of the methane production because the scaling factors associated with these quantities are non-zero real numbers. Hence, the scope of the study did not consider the volume of the biogas digester as an input parameter to the response.

Strategies to boost anaerobic digestion performance of cow manure: Laboratory achievements and their full-scale application potential

Cow manure represents a surplus manure waste in agricultural food sectors, which requires proper disposal. Anaerobic digestion, in this regard, has raised global interest owing to its apparent environmental benefits, including simultaneous waste diminishment and renewable energy generation. However, dedicated intensifications are necessary to promote the degradation of recalcitrant lignocellulosic components of cow manure. Hence, this manuscript presents a review of how to exploit cow manure in anaerobic digestion through different incentives extensively at lab-scale and full-scale. These strategies comprise 1) co-digestion; 2) pretreatment; 3) introduction of additives (trace metals, carbon-based materials, low-cost composites, nanomaterials, and microbial cultures); 4) innovative systems (bio-electrochemical fields and laser irradiation). Results imply that co-digestion and pretreatment approaches gain the predominance on promoting the digestion performance of cow manure. Particularly, for the co-digestion scenario, the selection of lignin-poor co-substrate is highlighted to produce maximum synergy and pronounced removal of lignocellulosic compounds of cow manure. Mechanical, thermal, and biological (composting) pretreatments generate mild improvement at laboratory-scale and are proved applicable in full-scale facilities. It is noteworthy that the introduction of additives (Fe-based nanomaterials, carbon-based materials, and composites) is acquiring more attention and shows promising full-scale application potential. Finally, bio-electrochemical fields stand out in laboratory trials and may serve as future reactor modules in agricultural anaerobic digestion installations treating cow manure.

The Start-Up of Continuous Biohydrogen Production from Cheese Whey: Comparison of Inoculum Pretreatment Methods and Reactors with Moving and Fixed Polyurethane Carriers

This article presents the results of the start-up of continuous production of biohydrogen from cheese whey (CW) in an anaerobic filter (AF) and anaerobic fluidized bed (AFB) with a polyurethane carrier. Heat and acid pretreatments were used for the inactivation of hydrogen-scavengers in the inoculum (mesophilic and thermophilic anaerobic sludge). Acid pretreatment was effective for thermophilic anaerobic sludge to suppress methanogenic activity, and heat treatment was effective for mesophilic anaerobic sludge. Maximum specific yields of hydrogen, namely 178 mL/g chemical oxygen demand (COD) and 149 mL/g COD for AFB and AF, respectively, were obtained at the hydraulic retention time (HRT) of 4.5 days and organic load rate (OLR) of 6.61 kg COD/(m3 day). At the same time, the maximum hydrogen production rates of 1.28 and 1.9 NL/(L day) for AF and AFB, respectively, were obtained at the HRT of 2.02 days and OLR of 14.88 kg COD/(m3 day). At the phylum level, the dominant taxa were Firmicutes (65% in AF and 60% in AFB), and at the genus level, Lactobacillus (40% in AF and 43% in AFB) and Bifidobacterium (24% in AF and 30% in AFB).

Optimization of Reactor Temperature for Continuous Anaerobic Digestion of Cow Manure: Bangladesh Perspective

Converting organic waste into energy through anaerobic digestion is gaining popularity day by day. The reactor temperature is considered as one of the most vital factors for the digestion process. An experiment was conducted in the Biogas Laboratory of Green Energy Knowledge Hub at Bangladesh Agricultural University (BAU) to examine the influence of temperature on anaerobic digestion of cow-dung. Laboratory-scale continuous stirred tank reactors with a working volume of 15 L were operated for a 30-day retention time. The reactors were set at 20 °C, 25 °C, 30 °C, 35 °C, 40 °C and 45 °C, respectively to determine the effect of temperature on anaerobic digestion performance. Different parameters like total solids, volatile solids, pH, volatile fatty acids, ammonia nitrogen, total nitrogen, biogas production rate and methane concentration were examined. Among all the reactors, the reactor at 40 °C temperature produced maximum biogas (312.43 L/kg VS) and methane yields (209.70 L/kg VS), followed by the reactors at 35 °C and 30 °C, respectively. Statistical analysis of the obtained experimental results using Minitab® showed that the optimum process performance in terms of methane yield and volatile solid degradation is achieved at a reactor temperature of 35.82 °C.

Long-Term Storage and Use of Artificially Immobilized Anaerobic Sludge as a Powerful Biocatalyst for Conversion of Various Wastes Including Those Containing Xenobiotics to Biogas

The aim of this paper is to demonstrate the possibilities of anaerobic sludge cells immobilized into poly(vinyl alcohol) cryogel for the methanogenic conversion of various lignocellulosic waste and other media containing antibiotics (ampicillin, kanamycin, benzylpenicillin) or pesticides (chlorpyrifos or methiocarb and its derivatives). It was established that the immobilized cells of the anaerobic consortium can be stored frozen for at least three years while preserving a high level of metabolic activity. The cells after the long-term storage in an immobilized and frozen state were applied for the methanogenesis of a wide number of wastes, and an increase in both methane yield and methane portion in the produced biogas as compared to the conventionally used suspended anaerobic sludge cells, was ensured. It was shown that the “additional” introduction of bacterial Clostridium acetobutylicum, Pseudomonas sp., Enterococcus faecalis cells (also immobilized using same support) improves characteristics of methanogenesis catalyzed by immobilized anaerobic sludge.