Substrate For Biogas Production Research Articles

Biogas production from water lilies, food waste, and sludge: substrate characterization and process performance

Abstract The potential of water lilies, food waste, and sludge as substrates for biogas production through anaerobic digestion was investigated. We thoroughly characterized these substrates and found that water lilies had a pH of 6.4, total solids (TS) of 18.42%, volatile solids (VS) of 81.46%, and a moisture content of 87%. Food waste exhibited a pH of 7.6, TS of 27.23%, VS of 90.6%, and a moisture content of 75%. Sludge had a pH of 6.5, TS of 6%, VS of 60%, and a moisture content of 95%. Biogas production exhibited variations among the reactors. Reactor 1 reached a cumulative production of 2,527 mL, while Reactor 4 achieved 3,404 mL, with different lag phases. Reactor 4 displayed the highest biogas yield at 262 mL/g VS. Post-digestion tests confirmed efficient digestion, with volatile fatty acids ranging from 140 to 300 mg/L acetic acid and alkalinity levels between 800 and 1,500 mg CaCO3/L. Our study estimated a significant methane content, with the potential to produce 94.32 L of methane from 1 kg of TS.

The Biochemical Methane Potential from Washing Process Wastewater in Black Soldier Fly Larvae Breeding by Inca Peanut Meal

The processing of Black Soldier Fly Larvae (BSFL) for high-quality animal feed protein is being promoted to transformation at the industry level in Thailand. This is due to the fact that the washing process of BSFL generates wastewater with high organic matter that must be treated. This research was interested in studying the potential of methane production from wastewater in the BSFL washing process that is fed by Inca meal and mixed with inoculum sludge from a swine biogas production system at different substrate and inoculum ratio of 3:1, 1:1 and 1:3 by gVS add. The system also controlled the temperature within the mesophilic condition at 35 ± 2°C. The result of this study shows that the optimum ratio which the most biochemical methane potential (BMP) was 1:1 on 45 days of fermentation period. This optimum ratio can also generate the cumulative methane gas production of 401.51 ± 24.42 NmL/gVS add with the highest methane content of 67.90%. The VS removal was 23.76% and the COD removal was 68.51%, which shows the BSFL washing process wastewater can be a substrate for biogas production and further expanded to the industry level.

Grass from Road Verges as a Substrate for Biogas Production

Maintenance of urban green infrastructure generates a large amount of biomass that can be considered a valuable feedstock for biogas production. This study aims to determine the effect of the cutting time and method of substrate preservation on the specific methane yield (SMY) of urban grass collected from road verges and median strips between roadways in wet (WF) and dry fermentation (DF) technology. The grass was collected three times in a growing season, including in spring, summer, and autumn. The biochemical methane potential (BMP) test was performed on fresh grass, grass ensiled without additives, and grass ensiled with microbiological additives. In addition, the energy potentially produced from biogas and the avoided CO2 emissions were calculated. The highest SMY (274.18 ± 22.59 NL kgVS−1) was observed for the fresh grass collected in spring and subjected to WF. At the same time, the lowest CH4 production (182.63 ± 0.48 NL kgVS−1) was found in the grass ensiled without additives, collected in summer, and digested in DF technology. A comparison of the SMY obtained from the same grass samples in the WF and DF technologies revealed that higher CH4 yields were produced in WF. The electricity and heat production were affected by the time of grass cutting, ensilage method, and AD technology. Generally, less electricity but more heat was produced in DF technology. The least electricity (469–548 kWh tDM−1) was produced from the grass cut in spring and subjected to DF, while the most electricity (621–698 kWh tDM−1) was obtained from the grass collected in autumn and subjected to WF. In the case of heat production, the situation was reversed. The least heat (1.4–1.9 GJ tDM−1) was produced by the grass collected in spring and subjected to WF, while the most heat (2.2–2.7 GJ tDM−1) was produced by the grass collected in autumn and subjected to DF. Ensilage decreased the electricity and heat production in almost all the cuttings. The total reduction in CO2 emissions may amount to 2400 kg CO2 per 1 hectare of road verges. This significant reduction demonstrates that the use of grass from roadside verges in biogas plants should be considered a feasible option. Even though urban grass should be considered a co-substrate only, it can be a valuable feedstock that may partially substitute energy crops and reduce the area needed for energy purposes. Our results reveal that biogas production from the grass waste in WF technology is a stable process. The cutting time and preservation method do not affect the AD process. In DF technology, fresh grass, especially from the late growing season used as feedstock, extends the time of biomass decomposition and, therefore, should be avoided in a real-life biogas plant.

Agricultural Plant Residues as Potential Co-Substrates for Biogas Production

Plant biomass can be used in many directions for bioenergy production. Biogas can be produced from a most diverse group of substrates compared to liquid or solid biofuels. The choice of substrates and technologies is crucial because it will allow getting the expected results. Not without significance is also the price and availability of substrates. Therefore, waste and residues are increasingly being used. Accordingly, the aim of the review was to analyze the potential of biogas production from agricultural plant residues and the effectiveness of using this feedstock as a co-substrate in anaerobic digestion. In this article, selected agricultural plant residues are collected, and their advantages and disadvantages as substrates for biogas production are described. Moreover, the effective technology of biogas production by anaerobic digestion on an industrial scale and calculations to obtain biogas and methane efficiency of the substrates are also included. In addition, the summarized biogas efficiency of selected plant agricultural waste under mesophilic conditions studied by many researchers is shown. On the basis of the analyzed results of this research, it can be concluded that agricultural plant residues have great potential as co-substrates for biogas production. It is important to experimentally determine both the biogas and the methane efficiency of the substrate, representing a potential raw material for the production of gaseous biofuels. The use of artificial neural networks in the prediction of biogas emission is future-proof and should facilitate the management of biogas plants. The use of waste from the cultivation and processing of plant raw materials will not only help to manage this waste rationally, but also contribute to the increase in production of renewable energy sources. Accordingly, the circular economy in terms of the management of agricultural plant residues to produce biogas will have a multi-faceted, positive impact on the environment. On the basis of this review, it can be concluded that numerous agricultural plant residues can be used as potential co-substrates for biogas production.

Aquatic Macrophyte Biomass Periodically Harvested Form Shipping Routes and Drainage Systems in a Selected Region of Poland as a Substrate for Biogas Production

One of the identified obstacles to the development of biogas plants is the limited sources of organic substrates. Hydrophytes varying in morphology, chemical composition, and origin proved to be viable alternatives. This study’s aim was to determine the feasibility of deploying biomass from the cleansing of water reservoirs for anaerobic digestion. A mass and energy balance was estimated for Warmia–Mazury Province (Poland), the so-called Thousand Lake District. The effectiveness of anaerobic digestion was determined in anaerobic batch respirometric reactors. The biomass of hydrophytes harvested from this area approximated 38,070 Mg FM/year. The biogas yield from emergent plants approximated 350 m3/MgVS, and the average CH4 content of biogas reached 55%, whereas the respective values obtained from submerged biomass reached 270 m3/MgVS and 58% CH4. The total CH4 volume achievable from the facility fed with waste biomass of this type allows producing ca. 1,654,560 m3CH4/year, which enables reaching 866 kW theoretical thermal power and 636 kWe net electrical power with the facility. The contribution of biomass from mowing in this energy effect was about 84%, whereas that of the submerged vegetation obtained by hacking the bottom was 16%.

Horse manure as resource for biogas and nanolignocellulosic fibres

Nanofibrillated cellulose (NFC) has key applications in composites, water filters and as emulsifiers. The affinity of NFC to water is a challenge, as it negatively influences its integrity. Lignin, a major component of plant biomass, is a natural hydrophobiser. Anaerobic digestion (AD) of biomass to produce biomethane allows to up-concentrate lignin in the fermentation residue containing lignocellulosic fibres. Horse manure was used as substrate for biogas production from which nanolignocellulose fibres (LCNF) were extracted. A biogas yield of 207 LN kgVS−1 with a methane concentration of 65 % was achieved. From the fermentation residue LCNFs, in yields of up to 41 %, with lignin contents between 23 and 29 wt% depending on fermentation time were obtained. Nanopapers produced from LCNFs possessed tensile strengths and moduli of 45 to 91 MPa and 7 to 8 GPa, respectively. The increased lignin content was responsible for decreased water absorption capacity of nanopapers.

Near infrared spectroscopy for fast characterization of animal by products feedstocks for biogas production: Calibration of a handheld device

Anaerobic digestion performance is highly influenced by the chemical composition and flow of substrates. This work evaluates the feasibility of a handheld near infrared spectrometer to predict moisture, fat, and protein content of animal by-products (ABP) mixtures further used as substrates for biogas production. The performance of a commercially handheld near infrared spectrometer (NIR) was evaluated for acquiring spectra of ABP sterilised mixtures, that were also chemically analysed. The calibration was performed by partial least square's regression technique and tested by an independent set of data. The results showed determination coefficients values ranging from 0.72 to 0.79 and root mean square errors of 2.60–4.85%. The performance of the handheld NIR spectrometer device was compared with a benchtop NIR spectrometer with a broader range of wavelength. The results suggest that NIR technology could be included as a useful estimation tool for the rapid characterization of feedstocks in biogas plants.

Influence of substrate/inoculum ratio, inoculum source and ammonia inhibition on anaerobic digestion of poultry waste

ABSTRACT Poultry wastes are rich in organic matter, allowing their use as substrates for biogas production by anaerobic digestion (AD). The major difficulty in the anaerobic digestion of this protein-rich waste is ammonia inhibition. Different results of biochemical methane potential (BMP) were obtained after the mesophilic anaerobic digestion of different avian waste in batch mode. It was shown that using two different inoculum (Liger and Saint-Brieuc) sources and different substrate-to-inoculum (S/I) ratios does not have a significant effect on the biochemical methane potential of organic laying hen droppings (OLHD); an average of 0.272 Nm3 CH4·kg−1·VS was obtained with both inocula. Otherwise, it affects the hydrolysis constant KH, and it decreases when the substrate-to-inoculum ratio increases. Furthermore, Liger is the most suitable inoculum for our substrate because it shows stability during the process even with different organic loads. Comparing the biochemical methane potential of multiple avian wastes such as organic laying hen droppings and different slaughterhouse waste highlights the importance of slaughterhouse waste in the anaerobic digestion process because of the high methane yield observed especially with the viscera (0.779 Nm3 CH4·kg−1 VS, SD = 0.027 Nm3 CH4·kg−1 VS). Moreover, methane production was affected by increasing the ammonia concentrations; when [N-NH3] > 9.8 g·N-NH3·L−1, the biochemical methane potential decreases and the lag phase increases (λ > 30 days); a total inhibition of the process was observed when ammonia concentration is above 21.8 g·L−1.

Brazilian agricultural and livestock substrates used in co‐digestion for energy purposes: Composition analysis and valuation aspects

AbstractBrazil's agriculture and livestock annually generates enormous amounts of biomass, which varies in its biochemical composition. Many studies have pointed out the benefits of using this biomass as a substrate for biogas production through anaerobic digestion (AD), mostly via the co‐digestion (co‐AD) pathway. The agriculture and livestock of southeastern Brazil – sugarcane, orange, corn, soybean, coffee, cattle, swine, and poultry – have together demonstrated their potential for producing biomass that can be used for maximizing methane production. Filter cake, vinasse, straws, bagasse, mucilage, pulp, washing water, thin stillage, and manures also have specific organic matter and nutrient content that can be evaluated from an economic perspective as co‐products of biorefineries. Some are costless but others have acquisition costs in the agricultural market. Comparing the recent biochemical compositions cited in scientific literature (technical parameter) and to know the costs (valuation parameter) is crucial for farmers and investors make decisions in large‐scale. This study conducted a bibliographical survey of biomass generated in Brazilian agroindustry as a co‐substrate for energy production. The analysis summarized two tables: 1‐ a compilation of biochemical composition of the main co‐substrates, and 2‐ the acquisition or opportunity costs, discussing innovative aspects in the context of biogas production. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Analysis of the Energy and Material Use of Manure as a Fertilizer or Substrate for Biogas Production during the Energy Crisis

The main goal of the publication was to show the differences in profit when using manure directly as fertilizer (after the storage period) or as a substrate for biogas plants with a cogeneration unit, and then using the digestate for fertilization purposes. The comparison covers the streams of costs, revenues and profits over the year between 14 October 2021 and 14 October 2022. This period was chosen due to the energy and fertilization crisis caused by the war in Ukraine. Profitability forecasts for biogas investments (including the payback period) are presented, with the reduction of greenhouse gas emissions, i.e., methane and nitrous oxide, taken into account. The performed economic, energy and ecological calculations of manure management can be used as guidelines when considering investing in biogas plants, as well as what is recently becoming a new trend: the carbon footprint of dairy production. Input substrate parameters, gaseous emissions and biogas yields were obtained from own research (manure samples were collected) and from literature data, including guidelines for international and national IPCC protocols.

Experimental Analysis for Determining Potential of Wastewater Sludge Mixed with Degraded Biomass as Substrates for Biogas Production

In the context of increased energy demands and finding solutions for energetic autonomy, the use of waste base materials has increased in recent years in all areas of research. In this context, waste waters, sludge or slurry, biodegradable materials, second generation effluents, and their byproducts are some of the key substrates of interest to obtain biogas through AD (anaerobe digestion). The goal is to utilize these materials as a base for the generation of renewable energy and thereby make it the main source of energy for households or industries. This paper aims to characterize, from a physical and chemical point of view, wastewater from Timis county as a base substrate material in the co-fermentation process with cereal residual biomass. We aimed to determine the energetic potential of the wastewater and perform preliminary testing at a small and pilot-sized experimental installation for biogas production with Timis wastewater as the main energy carrier. The novelty of the paper stems from the use of a patented pilot installation as our experimental approach, as well as the use of a different comparative scale co-fermentation process for biogas production. The conclusions will be traced relative to the obtained results, and preliminary solutions will be proposed for further avenues on this topic.

Augmentation in polyhydroxybutyrate and biogas production from waste activated sludge through mild sonication induced thermo-fenton disintegration

In this study, an innovative approach was developed to enhance the hydrolysis through phase-separated pretreatment by removing exopolymeric substances via mild sonication followed by thermo-Fenton disintegration. The exopolymeric substances fragmentation was enhanced at the sonic specific energy input of 2.58 kJ/kg total solids. After exopolymeric substance removal, the disintegration of biomass by thermo-Fenton yield the solubilization of 29.8 % at Fe2+:H2O2 dosage and temperature of 0.009:0.036 g/g suspended solids and 80 °C as compared to thermo-Fenton alone disintegration. The polyhydroxybutyrate content of 93.1 % was accumulated by Bacillus aryabhattai at the optimum time of 42 h, while providing 70 % (v/v) pre-treated supernatant as a carbon source under nutrient-limiting condition. Moreover, the biogas generation of 0.187 L/g chemical oxygen demand was achieved using settled pretreated sludge. The pretreated sludge sample thus served as a carbon source for polyhydroxybutyrate producers as well as substrate for biogas production.

The novel oligopeptide utilizing species Anaeropeptidivorans aminofermentans M3/9T, its role in anaerobic digestion and occurrence as deduced from large-scale fragment recruitment analyses.

Research on biogas-producing microbial communities aims at elucidation of correlations and dependencies between the anaerobic digestion (AD) process and the corresponding microbiome composition in order to optimize the performance of the process and the biogas output. Previously, Lachnospiraceae species were frequently detected in mesophilic to moderately thermophilic biogas reactors. To analyze adaptive genome features of a representative Lachnospiraceae strain, Anaeropeptidivorans aminofermentans M3/9T was isolated from a mesophilic laboratory-scale biogas plant and its genome was sequenced and analyzed in detail. Strain M3/9T possesses a number of genes encoding enzymes for degradation of proteins, oligo- and dipeptides. Moreover, genes encoding enzymes participating in fermentation of amino acids released from peptide hydrolysis were also identified. Based on further findings obtained from metabolic pathway reconstruction, M3/9T was predicted to participate in acidogenesis within the AD process. To understand the genomic diversity between the biogas isolate M3/9T and closely related Anaerotignum type strains, genome sequence comparisons were performed. M3/9T harbors 1,693 strain-specific genes among others encoding different peptidases, a phosphotransferase system (PTS) for sugar uptake, but also proteins involved in extracellular solute binding and import, sporulation and flagellar biosynthesis. In order to determine the occurrence of M3/9T in other environments, large-scale fragment recruitments with the M3/9T genome as a template and publicly available metagenomes representing different environments was performed. The strain was detected in the intestine of mammals, being most abundant in goat feces, occasionally used as a substrate for biogas production.

Performance of an anaerobic biofilm reactor through the application of different operational conditions

Inadequate management of Municipal Solid Waste (MSW) and the energy crisis due to dependence on fossil fuels (carbon and hydrocarbons) are growing problems in Latin American countries such as Mexico. These problems are caused by various factors, including the lack of infrastructure and the limited development of technologies focused on addressing these areas. In Mexico, between 37.55 and 43.84 million tons of MSW are generated annually, while 5,896 PJ of fossil fuels are produced in the same period, contributing strongly to environmental pollution due to inadequate management and procurement-use processes respectively. In order to mitigate these problems, it is necessary to propose dual-purpose strategies, such as anaerobic digestion, that can help in the treatment of the organic fraction of MSW (OFMSW) and at the same time producing biogas as a renewable energy source. For these reasons, the aim of this work was to evaluate the performance of an anaerobic biofilm reactor through increases in the Organic Loading Rate (OLR) using the liquid fraction of the OFMSW as a substrate for biogas production. An anaerobic biofilm reactor called the Anaerobic Hybrid Reactor (AHR) was used to carry out this stud. The performance of the AHR in four stages applying different OLR values from 5 to 21 gCOD/L.d was analyzed. Anaerobic biofilm formation, pH, %COD and %solids removal, alkalinity, biogas production, and methane yield were evaluated. After 119 days of reactor operation, 93.45% colonization of the inverse fluidized bed, 85% total and soluble COD and removals greater than 80% for TS and VS, alkalinity less than 0.3, around 20 L of biogas per day with methane yields of 0.31 LCH4 at STP/gCODrem were obtained. The use of high OLR allows a larger volume of OFMSW liquid fraction to be treated producing a greater quantity of biogas with an excellent methane yield, thus demonstrating the high efficiency of the AHR.

ЭНЕРГЕТИЧЕСКИЙ ПОТЕНЦИАЛ И БИОДЕГРАДАЦИЯ ПОДСЫРНОЙ СЫВОРОТКИ ПРИ ЕЕ ПЕРЕРАБОТКЕ В БИОГАЗ

Utilization of cheese whey is an actual problem of the dairy industry all over the world. The production of food and feed based on it is low-profit and not acceptable for every enterprise. About half of the nutrients in milk pass into whey, so it can become a valuable energy resource - used, for example, as a substrate for biogas production. However, some researchers note that when processed in a biogas plant, a high content of acidic whey can slow down or completely block the process of biogas synthesis due to the low pH value. In our experiment, monofermentation of acidic cheese whey was carried out, and no such negative phenomena were observed. This may be due to the features of the inoculum used in the experiment. The substrate showed high productivity: the specific yield of biogas was 723.65±18.60 ml/g dm, the specific yield of methane was 379.12±11.55 ml/g dm. Thus, about 17.69 m3 of methane can be produced from 1 ton of acid cheese whey, the combustion of which generates 72.33 kW of electrical energy and 74.09 kW of thermal energy. The sale of this amount of electricity to the grid will make it possible to receive 643.73 rubles. Utilization of cheese whey for a biogas station is beneficial: this substrate has a high energy potential, and the price for its disposal is quite high. From an environmental point of view, an important indicator is the degree of biodegradation of the waste. In the reactor of a laboratory biogas plant, the degree of degradation of acid cheese whey, excluding inorganic carbon dissolved in the liquid fraction, was 41.42%.

Biogas production from food waste from a prototype biogas digester

Food waste from a school feeding nutrition program, if not correctly disposed, has a high level of pollution. Food waste can be utilised as a substrate for biogas production. The aim of the research was to construct a low-cost biogas digester for Bongumusa FET School in Mpumalanga province in South Africa and to assess its performance when fed with available food waste. A prototype biogas digester was designed, constructed and fed with food waste namely: vegetable peels, mealie meal, samp, rice, pilchards and fruit peels. The food waste was crushed and mixed with water before it was fed into the biogas digester. Cow dung was used as inoculum for the food waste. The temperature of slurry, the pH and biogas production were measured during a retention time of thirty days. It was observed that the initial pH dropped at the start of the experiment and this was attributed to the volatile fatty acid formation in acidogenesis and acetogenesis. The pH began to rise gradually as the volatile fatty acids were consumed by the methanogens to methane and carbon dioxide. From the results, it was observed that food waste is a good source of biogas for the school. In addition, the food waste was found to be an attractive method for environmental protection and energy saving for Bongumusa FET School. The biogas from the food waste can be used to replace imported Liquid Petroleum Gas (LPG) that is used in the school for heating purposes.

Halophytes as Feedstock for Biogas Production: Composition Analysis and Biomethane Potential of Salicornia spp. Plant Material from Hydroponic and Seawater Irrigation Systems

The halophyte plant species Salicornia europaea and Salicornia ramosissima were investigated for their potential to serve as a substrate for biogas production. Salicornia europaea was cultivated in hydroponic systems under varying salt concentrations (0, 10, 20, and 30 g/L NaCl), while S. ramosissima was grown in greenhouse farming with aquaculture effluent irrigation. The biomethane potential of the two halophyte feedstocks was determined through batch experiments, and correlations to the plant biochemical composition were investigated. Ash and mineral content of S. europaea was correlated to the increasing salt concentration used for plant cultivation in hydroponic systems. No indication of inhibition of the anaerobic digestion process was detected for sodium concentrations of up to 2400 mg/L in the anaerobic batch-test assays. The highest biomethane yield of S. europaea of 250 mL CH4/gVS was obtained when grown under 20 g/L NaCl and up to 300 mL CH4/gVS for S. ramosissima. By concentrating the dry matter content, the biomethane yield per ton of feedstock could be increased from 24 m3 CH4/t of the fresh halophyte plant to 74 m3 CH4/t by fractionation into a pulp fraction and to 149 m3 CH4/t by drying of the plant at room temperature for 1 week.

Microbial Pretreatment of Chicken Feather and Its Co-digestion With Rice Husk and Green Grocery Waste for Enhanced Biogas Production.

To utilize wastes and residues sustainably and excellently, there is a need to fend for efficient methods and resources for biogas production. Use of poultry waste for biogas production represents one of the most important routes toward reaching global renewable energy targets. The current study involves microbial pretreatment of chicken feather waste, followed by its co-digestion with rice husk and green grocery waste in batch and continuous reactors, respectively. Microbial pretreatment of chicken feathers by keratinase secreting Pseudomonas aeruginosa was an effective and eco-friendly approach to make its recalcitrant structure available as a raw substrate for biogas production. The current study also addressed the enhancement and stability of anaerobic digestion by co-digestion. Results demonstrated that biogas production was increased by microbial pretreatment of chicken feathers and that the percentage increase in biogas yield was 1.1% in microbialy pretreated feathers compared to mono-digestion (non-pretreated feathers) in batch fermentation. The highest yield of biogas was obtained in a batch reactor having co-digestion of pretreated rice husk and microbial pretreated chicken feathers. The co-digestion of chicken feathers hydrolysate with green grocery waste in continuous fermentation mode has also enhanced the biogas yield as compared to average of mono-digestion (chicken feather hydrolysate and green grocery waste) and, therefore, improve the efficiency of the overall process.

Review on potential of using agricultural, municipal solid and industrial wastes as substrates for biogas production in Nigeria

Review on potential of using agricultural, municipal solid and industrial wastes as substrates for biogas production in Nigeria

Simultaneous carbon dioxide reduction and methane generation in biogas for rural household use via anaerobic digestion of wetland grass with cow dung

In the present study, wetland grass (common reed) and cow manure were used as substrates for biogas production during 45-days hydraulic retention reaction. The fermenter has a total volume of 200 L and a working volume of 150 L. Following biogas generation, methane enhancement processes were combined with a chemical process. The solvents including H2O, NaOH, and Ca(OH)2 were taken in two consecutive columns for 3 h, and variation of components was measured after every 15 min. The results showed 2,254 L of biogas as 343.08 ml CH4g-1VSremoved of yields, with concomitant removal of H2S by H2O, NaOH, and Ca(OH)2 absorbers. The total removal of H2S using H2O, NaOH, and Ca(OH)2 was observed to be were 55.56, 98.89, and 98.75 %, respectively. A total enhancement of methane production using NaOH and Ca(OH)2 was observed to be 88.04 and 85.9%, respectively. As a result, H2S and CO2 emissions are significantly decreased, while low-cost chemical treatments improve bio-methane generation. This study also highlights the environmental implications of co-digesting wetland grass with cow dung, and the findings indicated that the strategy is highly effective in increasing biogas production and methane contents.