Biomethane Potential Research Articles

Bioaugmented ensiling pretreatment to improve bioconversion of sweet sorghum: Effect of bio-additives on enzymatic saccharification and biomethane potential

This study proposes a novel strategy to integrate ensiling preservation with pretreatment of sweet sorghum (SS) biomass. Bio-additives, including cellulase, xylanase, liquid anaerobic digestate (LD), and rumen fluid (RF) were applied in ensiling process to improve the silage quality, sugar production by enzymatic hydrolysis, and anaerobic biomethane production of SS. Compared with others additives, LD could alter microbial community compositions and reduce the crystallinity of SS, thus improving ensiling pretreatment performance and achieving the highest reducing sugar yield of 84.73%. The methane production of LD silages was increased by 32.84% compared with the un-ensiled SS, indicating that ensiling pretreatment with LD could be an effective strategy to achieve the trans-seasonal preservation and improving the methane production of SS. Furthermore, taking techno-economic factors into account (energy net income of 96.07 USD/ton), LD additive was recommended for the bioaugmented ensiling pretreatment and downstream methane production of SS, which also contribute to recirculate the liquid digestate from biogas plant.

Biomethane Potential of Beef Cattle Slaughterhouse Waste and the Impact of Co-Digestion with Cattle Feces and Swine Slurry

Slaughterhouse waste (SW) poses significant environmental challenges due to its complex composition, but anaerobic digestion offers a way to recover valuable biogas from SW. This study investigated the anaerobic co-digestion of beef cattle slaughterhouse waste (BCSW) with either cattle feces (CF) or swine slurry (SS). The biomethane potential, maximum methane yield (Mmax), lag phase duration, and effective digestion time (Teff) for the individual substrates and the combinations were analyzed. BCSW alone exhibited Mmax of 578.5 Nml CH4/g VSadded with a lag phase of 11 days, while CF and SS alone exhibited Mmax of 397.2 and 289.8 Nml CH4/g VSadded, respectively. Co-digestion of BCSW and SS resulted in Mmax increase of 48–75.5%, with negligible effects on Teff compared to solitary SS digestion. Similarly, co-digestion of BCSW and CF increased Mmax by 6.2–40.4%, with no significant impact on Teff compared to solitary CF digestion. However, both co-digestions led to a reduction in Mmax (12.1–27%) when compared to BCSW digestion alone. Co-digestion with SS shortened the lag phase duration by 2.8–7.8 days and accelerated Teff by 5.8–8.3 days due to SS’s high concentrations of essential micronutrients like cobalt and nickel which aid digestion. This study concluded that co-digestion of BCSW with SS is an effective strategy for enhancing methane production and digestion efficiency, offering a viable approach for proper disposal of BCSW while improving biogas output.

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

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

Calculations Reconsidered: From Mass Percentages of Elements to Empirical Formula and From Empirical Formula to Theoretical Biomethane Potential

Calculations Reconsidered: From Mass Percentages of Elements to Empirical Formula and From Empirical Formula to Theoretical Biomethane Potential

Preliminary biogas production assessment on insect frass and leachates of the organic wastes fed to larvae: A Johannesburg‐based factory case study

AbstractThe biomethane potential of insect frass and leachates from waste (larvae feedstock) stockpile was evaluated. Frass was derived from a black soldier fly larvae (BSFL) operation that uses a fruit and vegetable waste diet. The two waste streams were characterized and the results of their compositional, proximate, and ultimate analysis were used in estimating methane yields from these materials. The estimated biomethane potential (BMP) of the frass ranged 149–275 L/kgVS depending on the calculation method used. This result compares well with that of empirical studies for cow manure whose BMP ranges 110–275 L/kgVS. Cow manure is the most popular biogas feedstock globally. Leachates reported an estimated BMP of 150 L/kgCOD. We conclude that it may be technically feasible to produce biogas from BSFL frass and from fruit and vegetable waste leachates. However, standard BMP experiments and semicontinuous pilot studies are still necessary before commercialization of these findings. These extra tests are executed to validate these findings and ascertain the life cycle attribute and long‐term process stability and hence determine the economics of using these potential substrates for biogas production as a strategy to implementing circularity in the fruit and vegetable industry.

Adaptation of a microbial consortium to pelagic Sargassum modifies its taxonomic and functional profile that improves biomethane potential.

In recent years, pelagic Sargassum has invaded the Caribbean coasts, and anaerobic digestion has been proposed as a sustainable management option. However, the complex composition of these macroalgae acts as a barrier to microbial degradation, thereby limiting methane production. Microbial adaptation is a promising strategy to improve substrate utilization and stress tolerance. This study aimed to investigate the adaptation of a microbial consortium to enhance methane production from the pelagic Sargassum. Microbial adaptation was performed in a fed-batch mode for 100days by progressive feeding of Sargassum. The evolution of the microbial community was analyzed by high-throughput sequencing of 16S rRNA amplicons. Additionally, 16S rRNA data were used to predict functional profiles using the iVikodak platform. The results showed that, after adaptation, the consortium was dominated by the bacterial phyla Bacteroidota, Firmicutes, and Atribacterota, as well as methanogens of the families Methanotrichaceae and Methanoregulaceae. The abundance of predicted genes related to different metabolic functions was affected during the adaptation stage when Sargassum concentration was increased. At the end of the adaptation stage, the abundance of the predicted genes increased again. The adapted microbial consortium demonstrated a 60% increase in both biomethane potential and biodegradability index. This work offers valuable insights into the development of treatment technologies and the effective management of pelagic Sargassum in coastal regions, emphasizing the importance of microbial adaptation in this context.

Optimizing aeration rates via bio-methane potential test for enhanced biodrying efficiency of refuse-derived fuel-3

Aeration forms a critical part of the biodrying of refuse-derived fuel-3 (RDF-3) and significantly affects the fuel’s energy potential. Understanding the organic content (OC) of RDF-3 is crucial for determining the optimal aeration strategy. In this study, we conducted a bio-methane potential (BMP) test to estimate the OC by observing the conversion of organic matter into methane (CH₄) and carbon dioxide (CO₂). The observation of BMP was conducted using anaerobic digestion approach where substrate and inoculum are important parameters considered for the success of this test. Various ratios substrate-to-inoculum (S/I) were explored to assess their impact on biogas production, our research involved testing four S/I ratios (0.25, 0.5, 1.0, and 1.5) focusing on identifying the optimal aeration strategy. Based on stoichiometric calculations, the sample’s biogas yield per gram volatile solid indicates RDF-3’s OC is 1.5%. This OC value played a role in establishing the appropriate aeration rate (AR) for the biodrying process, which was determined to be 0.6 m³/kg.day, indicating the action of effective microbial degradation processes. Ensuring the correct AR is vital for maximizing the energy potential of RDF-3. Implementing optimized aeration rates based on the BMP test in waste management practices can significantly improve RDF-3 biodrying efficiency. This approach enhances RDF quality, reduces moisture, increases calorific value, and minimizes greenhouse gas emissions, leading to more sustainable and efficient waste-to-energy conversion.

Determining biomethane potential from animal-source industry wastes by anaerobic digestion: A case study from La rioja, Spain

The animal-source food industry (ASFI) is currently facing important challenges derived from sustainability policies and market requirements. In this respect, the ecological footprint resulting from emissions, management of residues, effluents, and by-products has become a key factor not only due to the laws in force, but also from the point of view of operation efficiency and market requirements. This paper assesses the potential use of the organic wastes generated by the ASFI as a source of biofuel generation (i.e., biomethane) in the region of La Rioja (Spain). To this end, primary data were directly collected from factories and the so-produced wastes were sampled and characterized. Statistical inference from collected data leads to theoretically estimate that the region might produce up to 118.46 GWh per year, mainly provided from piggeries, which would replace 12.4 % of the natural gas used by the regional industry. Besides, this strategy also reduces the environmental footprint and the generation of added value for companies and rural localities. However, the analytics show that an excess of nitrogen content may hinder the calculated theoretical methane yields and lead to operational issues. Looking for biowaste from vegetable sources more optimal admixtures may be designed to address these concerns.

Biomethane production modelling from third-generation biomass

Third-generation biomass constitutes a renewable energy source that could substitute fossil fuels. This study evaluated the biomethane potential (BMP) of Ulva sp., Codium sp. and Undaria pinnatifida through anaerobic digestion. The daily production of biomethane was evaluated using different models, including Modified Gompertz, Chen and Hashimoto, First-order, Transfer and Cone models, as well as an Artificial Neural Network (ANN) model. The experimental BMP was 0.17, 0.26, and 0.32 Nm³/kg VS for Ulva sp., Codium sp., and U pinnatifida, respectively. Among the non-linear regression models, the Transfer model (R2 > 0.9915) and the First-order model (R2 > 0.9889) are the ones that best fit the experimental data. However, the ANN shows a better fit (R2 > 0.999 and RMSE<4.537) to the data compared to the non-linear regression models. Furthermore, ANN can capture the complexity of biological systems, allowing for more accurate and detailed modelling of the processes involved. The identification and optimization of the biomethane potential of macroalgae contribute to developing sustainable energy alternatives, offering a renewable energy source that could mitigate the environmental stress associated with traditional fossil fuels.

Biomethane and Green Hydrogen Production Potential from Municipal Solid Waste in Cape Coast, Ghana.

Biomethane and hydrogen are promising elements in the transition towards sustainable energy, due to their capacity to mitigate greenhouse gas emissions. In Ghana, efforts to promote sustainable waste valorization for energy production are underway; however, organic waste conversion into biomethane and hydrogen still needs to be expanded. This study aims to evaluate the potential of producing biomethane and hydrogen from the municipal solid waste in Cape Coast, and their injection into the national gas grid. The upgrading biogas obtained from anaerobic digestion of food/organic wastes was used to generate biomethane. The modified Buswell Equation and data from literature were used to estimate the amount of biomethane and hydrogen. The environmental impact was assessed using the CO2 equivalent emissions. The findings reveal that Cape Coast generated approximately 6,400 tons of food waste in 2021, with a projection to 11,000 tons by 2050. Biomethane and hydrogen quantities was estimated at 3,700,000 m³ and 784,000 kg in 2021, respectively. Their projection reaches to 6,600,000 m³ and 1,400,000 kg by 2050. Converting waste into biomethane and hydrogen is an eco-friendly method of their management and use for renewable energy in Ghana. Strategies can be integrated into Ghana national energy policies to encourage waste-to-energy projects.

Impacts of material characteristics on the anaerobic digestion kinetics and biomethane potential of American bourbon and whiskey stillage

Stillage of American whiskey (e.g., bourbon) manufacturing is an abundant byproduct that is distinguished from fuel ethanol and malt whisky stillage materials by its highly inconsistent nature due to variability in mash bill composition. The impact of stillage physicochemical characteristics on biomethane production through anaerobic digestion was assessed by characterizing American whiskey stillage samples before batch biochemical methane potential tests of whole stillage. A maximum methane yield of 419 Nml CH4/g VS was obtained under food to microbe ratio (F: M) of 0.5 and organic loading rate (OLR) of 10 g VS/L while digester instability was noted under F: M ratios exceeding 0.5 under batch production. Methane production was significantly influenced by the mash bill composition with lowest methane yields obtained with higher rye content (rye whiskey) and highest methane yields obtained with higher corn content (bourbon or corn whiskey). A multiple linear regression model including C, P, N, and Na was able to accurately describe the methane yield (R2 = 0.93). This study provides valuable insights to aid the design of anaerobic digesters generating renewable natural gas from heterogeneous American whiskey stillage.

Valorization of cheese-making residues in biorefineries using different combinations of dark fermentation, hydrothermal carbonization and anaerobic digestion

Dark fermentation (DF), hydrothermal carbonization (HTC) and anaerobic digestion (AD) are applied, in different combinations, to cheese whey (CW), which is the liquid effluent from the precipitation and removal of milk casein during the cheese-making process. The aim and novelty of this research is to investigate the production of various biofuels (H2-rich gas, hydrochar and biogas) in cascade, according to the waste biorefinery concept. The simplest case is the direct AD of CW. The second investigated possibility is the preliminary HTC of CW, producing hydrochar, followed by the AD of the process water from which hydrochar is separated by filtration. The third possibility is based on DF of CW, followed by the AD of the fermentate (F) from DF. The final possibility is based on DF of CW, followed by HTC of the F, and then AD of the process water. Accordingly, the physical and chemical properties of CW, F, resulting hydrochar and process water (PW), and biomethane potentials of CW, F, and process waters are studied to determine the energy and carbon balances of all variants. In brief, the first variant, direct AD of CW, is believed to be the most energy efficient method.

Enhanced anaerobic digestion of prairie biomass through alkaline-based hydroxycinnamic acid extraction

This study explores the hydroxycinnamic acid extraction from prairie biomass as a potential value-added pretreatment for enhancing the performance of anaerobic digestion. Pretreatment increased the biomethane potential of prairie biomass by 33 %; when the extraction residue was left on the biomass, the biomethane potential increased by 100 %. When the treated biomass was co-digested with manure, a 134 % and 25 % increase in methane productivity and methane content was obtained, respectively, relative to raw biomass co-digested with manure. Hydroxycinnamic acid extraction also improved anaerobic digestion performance under biochar supplementation and liquid digestate recirculation conditions. Lastly, the extraction process was optimized for hydroxycinnamic acid yield. It was found that increases in treatment temperature and time could further increase yield by 5 %. Collectively, the results show hydroxycinnamic acid extraction can be used as a highly effective pretreatment for improving the anaerobic digestion of prairie biomass.

Moderate thermal post-treatment of digestate to improve biomethane production from agricultural- and food waste

The aim of this study was to assess the feasibility of moderate thermal treatment (70 °C for one hour) of digestate in combination with post-digestion targeting residual biomethane potentials from three full-scale biogas plants digesting food waste (FW), agricultural waste (AW) and a mixture of AW and manure (AWM). Dissolved organic carbon (DOC), biomethane production, and digestate quality were investigated. For the study six laboratory-scale continuously stirred tank biogas reactors working as post-digesters, with thermally-treated and non-treated digestate were used. DOC for thermally-treated digestates increased significantly (t-test, p < 0.05); FW-digestate (110–200 %), AW-digestate (24–92 %) and for AWM-digestate (4–73 %). Indexes for corresponding DOC quality showed lower apparent organic molecular weights and decreased aromaticity (with the exception of FW-digestate). Thermal treatment of digestate improved the biomethane production during post-digestion by 21–22 % (FW-digestate) and 9 % (AW-digestate). For AMW-digestate no clear positive effect was observed, most likely due to biogas plant operational process disturbances.

Anaerobic digestion of herbal waste: a waste to energy option.

Herbal waste produced during the manufacturing of herbal products is a potential feedstock for anaerobic digestion due to high amount of organic matter that can be transformed into biogas as an energy resource. Therefore, the present study was undertaken to convert herbal waste produced during the manufacturing of common of Ayurveda products into biogas through anaerobic digestion process using batch test study under controlled mesophilic temperature conditions of 35°C with food to inoculum ratio of 0.75. The maximum biomethane potential (BMP) of 0.90 (gCH4COD/g CODfed) and sludge activity of 0.70 (gCH4-CD/gVSS) was exhibited by WS herbal waste owing to its high chemical oxygen demand (COD) of 4g/g and better solubilization potential of the organic matter showing change in volatile suspended solids (ΔVSS) of 79%. On the other hand, the waste derived from the TA herb, exhibited the least biogas yield of 0.55 (gCH4COD/g CODfed) and sludge activity of 0.40 (gCH4-CD/gVSS), albeit with higher organic matter present. This was due to the possible hindrance of waste solubilization by the presence of lignin. The waste derived from VVL and PE showed intermediate BMP and sludge activity. The methane generation rate constant (k), a key indicator of the biodegradation potential, was also evaluated. The k values showed similar trend as of BMP values ranging from 0.081 to 0.15 d-1 thus indicating the influence of presence of lignin and the change in ΔVSS. The present study proves anaerobic digestion to be an alternative treatment method to be a milestone for management of herbal wastes and can be successfully implemented on real-scale systems.

Stearate from Steel Wire Drawing Processes as a Resource

STAR (Stearato dai processi di Trafilatura del filo di Acciaio come Risorsa) project, funded by the Italian Ministry of the Environment, has the ambition of redesigning the use and life cycle of waste stearates from the steel wire drawing industry, promoting the circular life of such materials. Waste stearate is having a strong impact on the economic and environmental sustainability of the steel wire production processes, adding up to the increasing pressure that industry has been facing in the last years: the pandemic crisis, the raw material price increase, the commercial restrictions related to the Ukraine and other regional conflicts.The short-term goal of the project is to develop a technology to be applied on a local scale and the long-term one is expanding it internationally. The benefits are both environmental, due to the reduction of waste and related impact on the environment, and economic, due to stearate valorization.First, stearate waste from wire drawing process were characterized in order to valorize them in the production of new materials or as an energy source.Samples of stearate waste were provided by wire drawing industries and the analyses showed that the humidity content was always low (0.1 – 5 %), while the volatile solids (VS) content varied from 2 to 70%, covering a very wide range and thus indicating a variable organic matter content. The mean higher heating value was 26 MJ/kg and the Chemical Oxygen Demand (COD) 500 mg O2/g and correlated well with VS. pH was strongly basic (&gt;11).Anaerobic digestion can surely have an important role in valorization, as it allows to recover energy and to produce a stabilized digestate for which a further use can be studied, according to its properties. Preliminary BMP tests (BMP = Biomethane Potential) determined a biomethane production in the range 500-900 L/kgVS, much higher than the production from animal waste (around 400 L/kgVS). The toxicity of the digestate was assessed by Microtox® assay and was negligible. This finding supports the hypothesis that recalcitrant compounds, which do not undergo degradation in anaerobic conditions, are not toxic.

Anaerobic Co-Digestion of Cattle Manure with Ruminal Waste to Increase Biogas Production

Cattle manure (CM) is mostly used as an inoculum in order to start-up of agricultural biogas plants or as a co-substrate in the anaerobic digestion of lignocellulosic content. Rumen fluid microbiota is also considered to be effective in lignocellulose digestion. It is known that microorganisms in the ruminal waste facilitate the hydrolysis of lignocellulosic structures. However, there are few studies on the inoculum effect of rumen microorganisms on bioreactor performances when rumen content is used as co-substrate and inoculum together with cattle manure, and it is not clear how rumen waste can be used in various anaerobic digestion systems. In this study, biogas production efficiencies obtained from lignocellulosic content in mono and cosubstrate (1:1 and 1:2 Volatile Solids) bioreactors formed by using ruminal waste (RW) and CM microbial communities were investigated. In order to determine the biogas production efficiencies, biomethane potential (BMP) experiments that simulate anaerobic digestion process conditions in a laboratory environment were applied. Treatment with 50% application of RW cosubstrate, 65.51% biogas and 70.64% methane production efficiency increases were achieved compared to monosubstrate CM bioreactor.

Anaerobic Co-Digestion of Fish Sludge Originating from a Recirculating Aquaculture System

Anaerobic co-digestion (AcoD) of fish sludge (FS) with food waste (FW), and fruit and vegetable waste (FVW) for biogas and methane production was optimised in small-scale bioreactors, and batch and semi-continuous pilot-scale digesters, under mesophilic (37 ℃) conditions. An experimental mixture design was first applied to small-scale biomethane potential (BMP) tests, to determine the optimal mixture proportions of the AcoD of FS, FW, and FVW that maximise the specific methane yield (SMY in NmLCH4 gVS−1). The optimal mixture proportion was 67%FS:18%FW:19%FVW (w/w), producing 401 mLCH4 gVS−1, which was 8 times higher than the SMY when FS was mono-digested (48 mLCH4 gVS−1). The SMY achieved in batch pilot-scale digesters were 70–82% of methane yields obtained in BMP tests under the same operating conditions, with stable biogas production and no apparent inhibition during the batch run. Semi-continuous operation of the pilot-scale digester was undertaken with organic loading rates (OLRs) of 1, 2, and 3 gVSL-1d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$gVS{L}^{-1}{d}^{-1}$$\\end{document}, provided intermittently. However, the digester did not achieve stable biogas production at all of the evaluated OLRs, due to the intermittent feeding and accumulation of volatile fatty acids (VFAs): Improved process stability was achieved at an OLR of 2 gVSL-1d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$gVS{L}^{-1}{d}^{-1}$$\\end{document}, compared to OLRs of 1 and 3 gVSL-1d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$gVS{L}^{-1}{d}^{-1}$$\\end{document}. Optimisation of the AcoD process resulted in attractive biomethane yields from FS with FW and FVW co-feeds, indicating that producing biogas from co-digestion of FS with relevant substrates is a valuable managing tool for FS, while simultaneously providing renewable energy. The work provides novel data that elucidated optimal proportions in which to combine FS, FW and FVW to obtain optimal biogas production, and provided important new information relevant for the scale up and continuous operation of an AD process for treating FS.Graphical

Co-hydrothermal carbonization as a potential method of utilising digested sludge and screenings from wastewater treatment plants towards energy application

Anaerobic digestion is one of the most recommended methods for utilising sewage sludge produced by wastewater treatment plants. However, the increasing amount of micropollutants in digested sludge can significantly limit its future utilisation. Recent studies suggests that the hydrothermal carbonization process can be used as a complementary method for sludge management, due to the improved quality of solid products - hydrochar. Moreover, this allows for the possibility of reusing liquid by-products in the anaerobic digestion process for biogas production. However, hydrochar generated from hydrothermal carbonization has a higher concentration of heavy metals and low energy value, which limits its use in agriculture and energy sectors. This study highlights a partial resolution to this problem, by mixing digested sludge with screenings in the co-hydrothermal carbonization process. The findings of this study show improvements in the properties of hydrochar including total solids measured according to ISO, inorganic fractions determined by inductively coupled plasma optical emission spectrometry and higher calorific values measured by the calorimetric bomb. Biomethane potential tests were conducted on liquid by-products. The results showed an average increase in biomethane potential from liquids obtained from co-hydrothermal carbonization compared to liquids from hydrothermal carbonization of digested sludge without screenings in series 1, 2 and 3 - up to 60 %, 40 % and 26 % for three different sludges with initial total solids content of 2.6 %, 12.5 % and 21.5 % w/w.

The Influence of Polyphenolic Compounds on Anaerobic Digestion of Pepper Processing Waste during Biogas and Biomethane Production

Pepper processing waste has the potential to be used as a substrate in the process of anaerobic digestion, but because of its high polyphenol content, certain limitations are expected. During the determination of the biodegradability of pepper samples, a biogas potential of 687 L/kg DM was observed, as well as a biomethane potential of 401 L/kg DM. While both the testing of biodegradability and the process in the pilot scale progressed, it was observed that total polyphenol content in both cases decreased. Also, as far as individual polyphenols during the process in the pilot scale are concerned, it can be observed that at the end of the process no procyanidin A2, epicatechin, myricetin, and quercetin were detected. The observed concentration of the ferulic acid on the last day of the process was 0.09 µg/g. Finally, it can be concluded that the presence of polyphenols did not significantly affect the biogas potential of pepper waste. Due to its relatively stable biogas production, as far as biogas production on the pilot scale is concerned, it can be concluded that pepper processing waste has the potential to be used as a substrate for biogas production.