Substrate For Anaerobic Digestion Research Articles

Methane Generation Potential of the Easily Degradable Group of Landfilled Municipal Solid Waste

Municipal solid waste (MSW) remains in sanitary landfills for many years. To maintain a circular economy, assessing the feasibility of reinserting MSW excavated from sanitary landfills into the production chain is important. This reduces environmental impacts, helping to minimize soil, water, and air pollution resulting from the decomposition of waste in landfills. In addition, it promotes economic benefits from the energy recovery of waste, such as biomass, which can generate electricity and heat, contributing to a sustainable energy matrix. The present study aimed to evaluate the easily degradable MSW group with 24 years of landfilling (ED-24) regarding its potential for methane generation. The ED group consisted of putrescible organic matter, wood, paper, cardboard, and pruning landfilled at a sanitary landfill in Southeastern Brazil. The feasibility of valuing ED-24 as a substrate for anaerobic digestion was assessed by analyzing its physical, chemical, and biochemical characterization and calculating its theoretical methane yield (TMY). The total volatile solids (TVS) and holo-cellulose contents of ED-24 were 73.45% and 61.39%, respectively, on a dry-weight basis. These values were in the range of those determined for non-landfilled lignocellulosic materials. Thus, 24 years of landfilling partially degraded the anaerobically lignocellulosic materials. The TMY of ED-24 was 233.41 mL CH4/g TVS, indicating a potential to generate methane. Despite the high lignin value, ED-24 can be valued as a substrate for anaerobic digestion.

Assessment of the Biochemical Methane Potential of Wastewater and Sludge Cake from a Poultry Slaughterhouse

Objectives : This study evaluates the potential for resource recovery through anaerobic digestion of organic waste generated in a poultry slaughterhouse, specifically focusing on poultry slaughterhouse wastewater and sludge cake obtained from in-house wastewater treatment.Methods : Basic characteristics (total solids, alkalinity, etc.), total nitrogen/ammonia nitrogen, and elemental analysis (macro and trace elements) were performed to determine the properties of the samples and calculate theoretical methane potential. Experimental methane potential was determined through BMP tests, with parameters such as lag period (λ) and maximum methane production rate (CH 4 mL/g VS/d) obtained using the modified Gompertz equation.Results and Discussion : The wastewater exhibited low organic matter concentration (1.79 g VS/kg; 3.74 g COD/L), while the sludge cake showed high total solids content (TS 170.8 g/kg) and organic matter concentration (131.5 g VS/kg; 220 g COD/L). Elemental analysis revealed that the C/N ratio was 9.17 for the sludge cake and 8.24 for the wastewater, indicating high nitrogen content. Methane production modeling using the modified Gompertz equation revealed a lag period of 7.5 days and T80 (time to produce 80% of total methane) of 21 days for wastewater, and a lag period of 2.4 days and T80 of 14 days for sludge cake.Conclusion : Wastewater and sludge cake from poultry slaughterhouses show significant potential as substrates for anaerobic digestion. However, the wastewater has low organic matter content, and the sludge cake, while high in organic matter, has low moisture and high ammonia levels. Therefore, it may be appropriate to co-digest these two substrates, or to co-digest the sludge cake with other substrates that have low nitrogen content and high water content. These findings provide fundamental data for the anaerobic digestion of slaughterhouse waste and highlight the need for further research on co-digestion and continuous processes.

Crow Search Algorithm for Modelling an Anaerobic Digestion Process: Algorithm Parameter Influence

Corn steep liquor is a waste product from the process of treating corn grain for starch extraction. It is used as a substrate in anaerobic digestion with simultaneous hydrogen and methane production in a cascade of two anaerobic bioreactors. For process research and optimisation, adequate mathematical models are required. So, the authors aim to present a high-quality model of the corn steep liquor process for the sequential production of H2 and CH4. This paper proposes a technique for identifying the best mathematical model of the process using the metaheuristics crow search algorithm (CSA). The CSA was applied for the first time to mathematical modelling of the considered two-stage anaerobic digestion process, using real experimental data. Based on the analysis of the numerical data from the model parameter identification procedures, the influence of the main CSA parameters—the flight length, fl, and the awareness probability, AP—was investigated. Applying classical statistical tests and an innovative approach, InterCriteria Analysis, recommendations about the optimal CSA parameter tuning were proposed. The best CSA algorithm performance was achieved for the AP = 0.05, fl = 3.0, followed by AP = 0.10, fl = 2.5, and AP = 0.15, fl = 3.0. The optimal tuning of the CSA parameters resulted in a 29% improvement in solution accuracy. As a result, a mathematical model of the considered two-stage anaerobic digestion process with a high degree of accuracy was developed.

Thermally enhanced solid-liquid separation process in food waste biorefinery: modelling the anaerobic digestion of solid residues.

The biochemical valorization potential of food waste (FW) could be exploited by extracting decreasing added-value bio-based products and converting the final residues into energy. In this context, multi-purpose and versatile schemes integrating thermal and biochemical conversion processes will play a key role. An upstream thermal pretreatment + solid-liquid separation unit was here proposed to optimize the conversion of the liquid fraction of FW into valuable chemicals through semi-continuous fermentation process, and the conversion of the residual solid fraction into biomethane through anaerobic digestion. The solid residues obtained after thermal pretreatment presented a higher soluble COD fraction, which resulted in higher methane production with respect to the raw residues (0.33 vs. 0.29 Nm3CH4 kg-1VSfed) and higher risk of acidification and failure of methanogenesis when operating at lower HRT (20d). On the contrary, at HRT = 40 d, the pretreatment did not affect the methane conversion rates and both tests evidenced similar methane productions of 0.33 Nm3CH4 kg-1VSfed. In the reactor fed with pretreated residue, the association of hydrogenotrophic methanogens with syntrophic bacteria prevented the acidification of the system. Modelling proved the eligibility of the FW solid residues as substrates for anaerobic digestion, given their small inert fractions that ranged between 0% and 30% of the total COD content.

NUTRIENT CHARACTERIZATION, BIOGAS AND ELECTRICITY GENERATION POTENTIALS OF ROOT AND TUBER WASTES

Rapid population growth and increasing food demand have led to a significant rise in organic waste generation, which has had a negative impact on the environment. However, these wastes can be utilized as substrates for anaerobic digestion (AD) biogas production, providing a sustainable and environmentally friendly waste management solution. The aim of this study was to evaluate the nutrient composition, biogas potential, and electricity generation capacity of root and tuber waste as a feedstock for biogas production. Waste samples were collected from various restaurants in Malumfashi. The nutrient composition of the waste samples was analyzed using standardized AOAC methods, and the biogas potential was estimated using the Baserga model equations. The results revealed that the waste samples had a total solid content of 94.70%, a volatile solid content of 87.60%, a crude protein content of 0.10%, a nitrogen-free extract of 5.1%, a crude fiber content of 5.04%, a crude fat content of 7.1%, and an ash content of 5.3%. The estimated biogas yield from complete degradation of fresh organic matter from roots and tubers was 501m3/ton, with a methane content of 52%. Based on the calorific value of biogas and the efficiency of electrical conversion, the estimated electrical potential was determined to be 1072 kWh/ton. The study recommends the utilization of root and tuber waste as a valuable resource for biogas generation and renewable energy production. Additionally, further research should be conducted to determine the specific biogas production outputs of root and tuber wastes.

Evaluation of batch mesophilic anaerobic digestion of waste Euro banknotes for methane Production: Preliminary studies and kinetic approach

The European Central Bank is striving to find environmentally friendly alternative methods of waste disposal. In 2020, it decided to end the disposal of Waste Euro Banknotes (W€B) in landfills and planned to use them for recycling and/or energy recovery. Despite being recognized as an effective tool in a circular economy model, there are no reported studies on the use of W€B as a substrate in anaerobic digestion (AD). Thus, the aim of this research was to assess the viability of W€B to be converted into high-value-added energy products (mainly methane) through AD. W€B (€10 and €20 denominations) provided by the Bank of Spain were used. Biochemical methane potential (BMP) tests of pre-treated (grinded) and untreated W€B were assessed at mesophilic temperature. The ultimate methane yield was considerably higher for pre-treated W€B (334 ± 23 NmL CH4 g VS-1added) than for untreated W€B (297 ± 14 NmL CH4 g VS-1added). The Logistic or Sigmoidal kinetic model adequately fit the experimental data and allowed for obtaining the kinetic parameters of each case studied. In this sense, an increase of 22.4 % in the maximum methane production rate (Rmax) was observed for the pre-treated W€B (52.5 ± 0.9 mL CH4 (g VS·d)-1 compared to the untreated W€B (16.2 ± 1.8 mL CH4 (g VS·d)-1). According to the obtained results, AD may be a good alternative for the energetic valorization and recycling of W€B.

Evaluating Biogas Production of Polylactic acid with the addition of Conductive Materials

Objectives:The demand for polylactic acid (PLA) is increasing as an alternative to conventional petroleum-based plastics due to its eco-friendly characteristics. PLA can be processed through anaerobic digestion (AD) along with other organic wastes to promote efficient and controlled biodegradation. This study aimed to evaluate the feasibility of biogas production through AD of PLA and to enhance efficiency through the addition of conductive materials.Methods:Two sets of biochemical methane potential (BMP) tests were conducted. The first BMP test involved substrate/inoculum ratios (SIRs) of 0.6, 0.8, 1.0, 1.2, 1.4, and 1.6 (g COD PLA/g COD seed sludge). Conductive materials powdered activated carbon (PAC), carbon nanotube (CNT), and Magnetite were individually added to reactors at a concentration of 3 g/L in the second test.Results and Discussion:The study revealed an increasing trend in methane production and methane yield with higher levels of PLA input. However, a decline in methane yield was observed when PLA was injected at levels surpassing 35g COD/L. This phenomenon can be attributed to a prolonged Lag phase, indicating a longer adaptation period for microorganisms, consequently resulting in a reduction of the conversion rate from 1g COD substrate to methane. The introduction of conductive material led to elevated cumulative methane production and methane yield in comparison to the control group. Notably, Magnetite exhibited the highest increase rate among the tested materials. Additionally, the addition of PAC demonstrated favorable results in terms of methane production rate at 99.4mL/L/Day and a Lag phase of 5.7 days. Conclusion:Experiments were conducted to evaluate the effects of PLA biogas production and the injection of PAC, CNT, and Magnetite at various substrate/inoculum ratios. When PLA was used as a substrate for anaerobic digestion, its feasibility was confirmed. However, it exhibited lower efficiency compared to other substrates. Therefore, the addition of a conductive material was found to increase the biogas production efficiency.

Biogas production potential of aquatic weeds as the next-generation feedstock for bioenergy production: a review.

Aquatic weeds have exceptionally high reproduction rates, are rich in cellulose and hemicellulose, and contain a negligible amount of lignin, making them an ideal crop for the next generation of biofuels. Previously reported studies proposed that water hyacinth, water lettuce, common duckweeds, and water spinach can be managed or utilized using different advanced techniques; from them, anaerobic digestion is one of the feasible and cost-effective techniques to manage these biowastes. The present study was carried out to investigate the potential of utilizing four common aquatic weed species (water hyacinth, water lettuce, common duckweeds, and water spinach) as substrates for anaerobic digestion in order to produce biogas for use in biofuels. The high reproduction rates and high cellulose and hemicellulose content, coupled with low lignin content, of these aquatic weeds make them ideal candidates for this purpose. The study evaluated the feasibility of using anaerobic digestion as a management technique for these aquatic weeds, which are often considered invasive and difficult to control. The results from various studies indicate that these aquatic weeds are productive feedstock options for anaerobic digestion, yielding a high biogas output. Among the aquatic weeds studied, water hyacinth, water lettuce, and common duckweeds exhibit higher methane production compared to water spinach. The study provides an overview of the characteristics and management strategies of these aquatic weeds in relation to biogas production, with possible future developments in the field.

Impacts of organic solvent toxicity on resource recovery from Scenedesmus obliquus biomass after lipid extraction

Residual biomass obtained after microalgae lipid extraction is rich in carbon and nutrients and has great potential for use as a substrate in anaerobic digestion, microalgae cultivation, and plant cultivation. However, residues from organic solvents can make it unfeasible to use the biomass in these applications. In this work, ethyl acetate (EA) and hexane-ethanol mixture (HE) were used to evaluate the yield and quality of lipids extracted from the microalga Scenedesmus obliquus BR003. Also, the toxicity of these solvents to anaerobic digestion, microalgae cultivation, and seed germination was evaluated at concentrations similar to those found in the residual biomass after lipid extraction. Lipid yields were 83.1% and 55.4% for HE and EA, respectively, where EA extracted mostly neutral lipids. In the HE mixture, hexane showed no significant effect in toxicity assays due to its low solubility in the aqueous fraction. However, ethanol in this mixture migrates to the aqueous phase, and the effective concentrations at 50% (EC50) were 3.78, 26.97, and 4.97 g L−1 for methanogenic archaea, S. obliquus, and lettuce seeds, respectively. The EA showed EC50 values of 18.74, 18.02, and 5.85 g L−1 for methanogenic archaea, S. obliquus, and lettuce seeds, respectively. The EA was less toxic to anaerobic microorganisms and lettuce seeds when compared to ethanol, which was less toxic to S. obliquus, making EA an environmentally friendly solvent for industrial use. Our study provides novel information on the criteria of solvent selection when aiming at resource recovery from residual microalgae biomass after lipid extraction.

Inhibition insights of hydrothermal liquid digestate in anaerobic digestion: Impact on organics conversion and inhibitor degradation

Hydrothermal liquid digestate has been widely accepted as a substrate in anaerobic digestion (AD) for energy recovery. However, the potential negative impacts of hydrothermal liquid digestate on AD remain unclear. In this study, the organic biodegradability of hydrothermal liquid digestate produced from hydrothermal treatment (HTT) at different temperatures was analyzed, and the formation and degradation process of potential inhibitory substances were discussed. Results demonstrated that the AD lag phase of hydrothermal liquid digestate increased from 3 days at raw liquid digestate to 5–21 days. When the HTT temperature reached 220 °C, the methane yield decreased by 48%, and more than 71% of the organics in the hydrothermal liquid digestate were not utilized by AD. Biorefractory substances, such as fulvic and humic acids, accumulate in the hydrothermal liquid digestate. Potential inhibitory substances from Maillard reactions mainly affect the methanogenesis of AD. Most inhibitory substances were degraded within 7–22 days, with the degradation rate following the order of pyrroles > pyrazines > ketones > imidazoles > indoles. The AD community structure and methane conversion were partially re-established after most inhibitory substances were degraded. This study provides valuable information on eliminating the potential negative effects of hydrothermal liquid digestate on AD.

A Review on Start-Up Phase Optimization of Kitchen Waste Anaerobic Digestion

Kitchen waste has been confirmed as an appropriate substrate for anaerobic digestion, although means of alleviating the difficulties and time-consuming nature of the start-up phase need to be further explored. Based on the mechanism of anaerobic digestion, we discuss the factors influencing the anaerobic start-up phase of kitchen waste. By controlling the temperature, pH, organic loading rate, inoculation ratio and other parameters, the high activity of methane-producing archaea and other bacteria can be intensified, thereby increasing the biogas yield. Furthermore, we introduce the methods of substrate pretreatment, operating condition optimization and conductive material addition. Finally, we put forward future perspectives and research gaps related to accelerating the start-up phase of anaerobic bioreactors utilized for kitchen waste biodegradation.

Anaerobic Digestion of Microalga Chlorella protothecoides and Metagenomic Analysis of Reddish-Colored Digestate

Microalga Chlorella protothecoides materials were assessed as substrates for anaerobic digestion (AD) aiming at the simultaneous production of biogas/methane and pigments: whole autotrophic (AA) and heterotrophic algae (H); extracted heterotrophic microalgae from lipid production (HExt); and pretreated heterotrophic microalgae through enzymatic (HPEnz), autoclave (HPA), and ultrasound (HPU) processes. AA was more suitable for AD than H, as it was more efficiently converted into methane (279 vs. 180 L CH4/kg VSin). In comparison, the pretreatment of heterotrophic microalgae had a positive effect on AD, with registered methane yield increases from 263 to 290 L CH4/kg VSin (HPU, HPA, HExt). Reddish pigmentation developed in H and HPU units due to the presence of purple non-sulfur bacteria (PNSB). This phenomenon and the changes in microbiota structure during AD were confirmed by metagenomic analysis. At the end of the process, the relative abundance of Clostridiales and Bacillales increased, enhancing the hydrolysis of compounds in acetate. Consistently, Methanosaeta became the comparatively dominant methanogen, meaning that methane was produced through the acetoclastic methanogenesis pathway. The obtained results indicate for AD biorefinery feasibility—regarding the simultaneous production of biogas/methane—a digestate flow and pigments (bacteriochlorophyll a and carotenoids).

Aerobic Granular Sludge as a Substrate in Anaerobic Digestion—Current Status and Perspectives

Even though many wastewater treatment systems have been applied so far, there is still a need to develop methods, the implementation of which are technologically and economically justified. The aerobic granular sludge (AGS) method, which has been developed for several years, may represent an alternative to traditional technologies. One of the barriers to AGS deployment is the limited knowledge on the determinants and efficiency of the anaerobic digestion (AD) of AGS, as little research has been devoted to it. Therefore, the aim of the present paper is to summarize the current state of knowledge on the subject, including a review of technological conditions, process performance, and AGS parameters that can impact AD, and currently used pre-treatment methods. The anaerobic stabilization performance of AGS is compared against conventional activated sludge (CAS). The paper also identifies avenues for further research and practical implementations to further optimize the process and to determine whether AD is viable in full-scale plants.

Improved production of biogas via microbial digestion of pressmud using CuO/Cu2O based nanocatalyst prepared from pressmud and sugarcane bagasse waste

Biogas production through anaerobic digestions of organic wastes using microbes is a potential alternative to maintain the long term sustainability of the environment and also to full-fill the energy demands and waste management issues. In this context, pressmud can be a vital substrate which is generated from sugarcane industries and found to be broadly available. In this work, biogas improvement has been investigated in presence of CuO/Cu2O based nanocatalyst wherein pressmud is employed as a substrate in anaerobic digestion. Herein, CuO/Cu2O based nanocatalyst has been prepared using the aqueous extract prepared from the combination of PM and SCB which is employed as a reducing agent. The physicochemical properties of CuO/Cu2O nanocatalyst have been probed through different techniques and it is noticed that using 1.0 % CuO/Cu2O based nanocatalyst employed in AD process, cumulative biogas 224.7 mL CH4 /g VS could be recorded after 42 days.

Activated Carbon Facilitates Anaerobic Digestion of Furfural Wastewater: Effect of Direct Interspecies Electron Transfer

Anaerobic digestion of furfural wastewater suffers from toxicity to microbes, which reduces its performance. The toxic effects may be eliminated by a sustainable way of conductive material supplementation. In this study, the effect on anaerobic digestion of furfural (0.5–4 g/L) was investigated by adding 0–40 g/L granular activated carbon (GAC) in batch tests. The innovation of this current study is to explore the potential direct interspecies electron transfer (DIET) for the first time in furfural degradation as the sole substrate in anaerobic digestion. The results demonstrated that when furfural was the sole substrate, in the presence of GAC, the peak methane production rate was increased by 46.0%, while the specific methane yield was improved by 24.7%, compared with the control. Additionally, the electroactive Geobacter sulfurreducens abundance in biofilms attached to the surface of GAC was 19.0 folds higher than that in the control. The abundances of the related genes of methane metabolism and furfural degradation in biofilms were 1.1 and 5.8 folds higher than the control by metagenomic analysis, respectively. These lines of evidence suggested that the pathway of furfural metabolism to methane among Moorella species, G. sulfurreducens, and Methanothrix species based on DIET was likely established.

Availability and Co-Substrate Potential of Typha latifolia for Biogas Production in Funtua, Katsina State, Nigeria

In order to reduce global warming through fossil fuel utilization, biogas production from biodegradable biomass seems a sustainable alternative. This study evaluated the availability and co-substrate potential of T. latifolia for biogas production in Funtua, Katsina State Nigeria. A purposive sampling technique was used in selecting the wards that were used for this study. A 1204 metres transect was used for 32 quadrats; 19 of these were laid on the 953m contiguous land area at intervals of 50m; 9 quadrats covered 450m, 5 quadrats were on 250m, 3 on 153m, and 2 on 100m. The remaining 13 transects were laid on the 251m un-contiguous patches. Coordinates of various potentials sites were recorded using Global positioning system. There were an average of 27 T. latifolia stands per m2. A total of 32,388 of T. latifolia stands were recorded in the study area; Dukke ward (23,968), Makera (8,205) and Maska 216. T. latifolia is available in lqrge quantities, and a potential co substrate in anaerobic digestion for biogas production in Funtua. It is recommended that the study should be replicated in time later to establish a trend of the T. latifolia species in terms of population.

Biochemical methane potential of Opuntia ficus-indica (L.) Mill. cladodes in co-digestion with cow manure

In recent years, Opuntia ficus-indica (L.) Mill. (OF) has emerged as a species that has a growing role in the area of agro-energy for their use as substrate in anaerobic digestion for the production of biogas and methane. In order to improve Biochemical Methane Potential (BMP), the objective of this study was to evaluate the influence of different feedstock ratios of cladodes in co-digestion with cow manure (CM) (OF:CM, 0:100 to 95:5) to determine the best co-digestion condition that improves BMP. Two co-digestion systems had BMP statistically significantly higher than the mono-digestion system, with improvements in the range of 80–92%. No statistical differences were found among the tested co-digestion treatments. These results demonstrate that the co-digestion of and CM biomass enhanced methane production through anaerobic digestion, with important implications for bioenergy production.

The Effect of Kitchen Detergent on the Anaerobic Degradation of Recovered Food Waste Solid from Food Waste Disposers

In Republic of Korea, waste disposer-treated food waste can be recovered from the waste disposer wastewater before it is discharged into the sewer system. The solid phase in the waste disposer-treated food waste can be subjected to anaerobic digestion. However, it contains kitchen detergent that can inhibit the anaerobic digestion process. The objectives of this study were to evaluate the degradation and phase distribution of kitchen detergent and the effect of the detergent on the anaerobic degradation of the solid phase in the waste disposer-treated food waste. 47-58% (w/w) of detergent existed in the recovered solid phase. According to biochemical methane potential tests, 70% (w/w) of the detergent had been anaerobically degraded and 4-5% and 26-30% (w/w) of the liquid and solid phases remained, respectively. In the range of 0-300 mg/L of kitchen detergent, the maximum methane generation rate slowed as the concentration increased and the maximum methane production was statistically the same. When the detergent concentration was 450 mg/L, the maximum methane production of the recovered food waste decreased by 22.8% (v/v). These indicate that the inhibition on the methane potential would not happen due to degradation of the detergent for an estimated probable concentration of 101.4 mg/L. When considering the expected detergent concentration in the disposer wastewater, the recovered food waste can be used as an anaerobic digestion substrate without inhibiting methane recovery.

Generation of biofuel from anaerobic digestion of Scenedesmus obliquus grown in energetic‐laden industrial wastewater: Understanding microalgae strains, co‐digestants, and digestate toxicity

AbstractMicroalgae as a substrate for anaerobic digestion (AD) offer promising outcomes over other conventional feedstocks. In this work, the generation of biofuel in the form of biogas via AD using wastewater‐grown microalgae was investigated. In particular, batch screening of different microalga strains and co‐substrates, culminated into the evaluation of biomethane potential (BMP) from AD of Scenedesmus obliquus grown in energetic‐laden wastewater through benchtop‐scale semi‐continuous reactor. Effectiveness of AD was evaluated for biogas yield, volatile solids (VS) removal, and kinetics for various microalga strains as potential substrate candidates. High carbon content co‐digestants were also investigated including return activated sludge and waste office pulped paper. At semi‐continuous scale, the specific BMPs associated with of 15, 20, and 30 days hydraulic residence times (HRT) were determined as 67.0, 86.6, and 86.3 ml CH4/g VS (added) with average methane content of 70%. In addition, toxicological assessments showed that AD effluent was benign towards renew growth of biomass, thus showing the potential for nutrients recover.

Energy Production From Biomass, Case Study: Cow Farm

Recently the use of biomass for biogas production is very limited in Albania. According to data acquired from the study, the highest share in the entire structure of urban solid waste is that of organic waste 41-61.2%. A large part of these wastes is bio digestible and can used for production or utilized as potential substrate in anaerobic digestion to produce biogas, a renewable source of energy and environment friendly too. Live stocks waste and especially cow manure farms are concerned in this study because there are a high number 11813 of them are spread all over Albania. In addition, the amount of cow manure exceeds 37,693.92 ton/year. In this case study is presented a cow farm located near Tirana, the capital city of Albania with 200 cow heads which in the future will become 700 cow heads. The total amount of cow manure produced in this farm is 1825 ton/year, a considerable quantity of manure available for biogas production. This paper presents the type of digester, calculation of the biogas production yield, the obtained energy, the payback period of the initial investment and the net present value of this farm batcher digestor.