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Anaerobic digestion plays a significant role in obtaining renewable energy through biogas production, reducing greenhouse gas emissions, helping with waste management, and bringing economic and social benefits. This work aims to examine approaches for the treatment and use of cambuci bagasse, identifying typical problems and proposing solutions concerning the application of the technique, control of operational parameters, management in dry regime conditions, optimization of efficiency, and increased productivity, using anaerobic digestion as a fundamental and central technology. The results showed the potential of electric energy and heat that could be generated by burning the biomass in a CHP system. Also, they presented the respective avoided greenhouse gas emissions in situations where biogas is applied to replace conventional heat or electricity sources. The biogas average production ratio was 102.69 m³/ton of cambuci by-product with a methane composition of around 60% in the 24th to 30th days. The experimental data obtained was subjected to calculations that indicate an electric generation of 202.98 kWh/ton of cambuci biomass and heat generation of 913.40 MJ/ton of cambuci biomass. In this theoretical scenario, for each ton of cambuci, it is possible to produce 913.4 MJ of thermal energy and 202.98 kWh of electric energy, considering the biogas burning into a CHP system. In the analysis of types of substrates regarding growth capacity, it was concluded that the substrate with a 30% dilution of the digested end was the one that showed the best growth of the cultivar's stem, obtaining a CEC of 9.1516 mol/g. [ABSTRACT FROM AUTHOR]

Considering the difficulty of digesting coffee husk (CH) and water hyacinth (WH) due to the lignin content, the present study investigated the influence of feedstock mixing ratios on the co-digestion performance of CH and WH with food waste (FW) at 38 ± 1 °C and its kinetics. Food waste was considered as co-substrate due to its ease of digestion. Batch experiments were conducted using CH/WH/FW ratios (100:0:0, 0:100:0, 35:35:30, 30:30:40, 25:25:50, 20:20:60, and 0:0:100 w/w) with total solids (TS) content of about 9.5% (w/v). The results indicated that the addition of FW significantly enhanced WH and CH digestion performance, with the maximum biogas yield of 572.60 ± 2.30 mL/gVS, best synergistic effect of 1.5, highest biodegradability of 89.22%, and a biodegradation rate of 57.82% obtained at a mix ratio of 25:25:50, which was improved by 179.71% compared to CH mono-digestion. In addition, the organic conversion efficiency of TS and volatile solids reached 69.86 and 81.48%, respectively. Conversely, CH mono-digestion yielded the lowest biogas yield of 204.71 ± 10.74 mL/g VS, highlighting its unfeasibility. The modified logistic equation showed the best fit to the experimental data. The optimum CH/WH/FW ratio of 25:25:50 demonstrated the highest biogas yield and methane content at 66.30 ± 0.76%. [ABSTRACT FROM AUTHOR]

One of the most important problems and the main obstacle of this process is the transformation of the complex structure of lignocellulose. One of the ways to break the lignocellulosic structure is to use suitable pretreatment compounds and nanoparticles with appropriate concentration. For this purpose, the synergistic effect of 6%NaOH pretreatment with different magnetite nanoparticle (MNP) concentrations was assessed for maximizing the biogas production. In this study, the optimal mixing ratio of MSW and SS codigestion was determined from our previous studies (MSW:SS 60:40). Application of the 6%NaOH pretreatment alone increased biogas and methane production by 24.6 and 35.4%, respectively, compared to the control. Also, the 6%NaOH pretreatment alone elevated cellulose by 85% while reducing lignin and hemicellulose by 64 and 33%, respectively. The greatest biogas and methane production was obtained in the reactor of 6%NaOH with an MNP concentration of 110 ppm, experiencing an 86 and 162% increase compared to the control. The greatest reduction in total solids and volatile solids was also obtained in this digestor by 76.6 and 79%, respectively, compared to the control reactor. [ABSTRACT FROM AUTHOR]

The use of agro-industrial and urban organic waste to produce energy seems to be one of the most attractive options for the future of energy supply. Anaerobic digestion is a promising process for treating organic waste and producing biogas. Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide, and hydrogen sulfide, that can be used for electrical and thermal energy generation or as fuel. However, it is still necessary to improve the technology associated with its production, adapting it to an efficient, safe, and competitive scale. Various methodologies are used to support the decision on process parameters and operating conditions to find the most effective and sustainable ones. In this study, an exergy analysis was performed to determine the exergetic efficiency and exergy destruction in the biogas process produced from the anaerobic digestion of vinasse. The analysis was performed through mass, energy, and exergy balances using literature data and computer simulation and considering the use of a continuous stirred tank reactor. The results show that the exergy destroyed in the CSTR biodigester was 1338.9 kW, accounting for 57.2% of the overall exergy destruction in the process. The heat exchanger showed the highest exergy efficiency (99.95%), with only 5.77 kW of exergy being destroyed. The authors suggest for future works that it would be interesting to perform a life cycle assessment (LCA) and exergoeconomic analysis to evaluate the environmental and economic impacts associated with biogas production from the anaerobic digestion of sugarcane vinasse. [ABSTRACT FROM AUTHOR]

The current study investigated the methane generation potential from the anaerobic bio-digestion of fruits and vegetables wastes (FVW) generated in a food supply center in Brazil. This study used the ensiling process as a pre-treatment for this lignocellulosic biomass aiming to improve the methane yield. FVW were mixed in the same proportion (0.2 g on a volatile solid basis per residue) and ensiled at room temperature (≈25 °C) for 30 and 55 days (samples Ensil-30 and Ensil-55). The ensiled and untreated waste samples were inoculated with industrial granular sludge and incubated at 37 °C (mesophilic conditions) until there was no more significant biogas generation. The experimental data were fitted to the First-order, Cone, and Modified Gompertz kinetic models. The methane yield of the ensiled samples was ≈21% higher than the methane yield of the untreated sample. Considering the ensiled samples, the methane generation was statistically the same (52.0 and 51.3 NmL/gvs for samples Ensil-30 and Ensil-55, respectively), that is, duplication of the storage period failed to increase the methane volume. Although the results indicated that the ensiling of FVW could be a viable strategy to improve the biodegradability of the lignocellulosic biomass and promote its valorization as an energy source, a preselection of the agricultural residues that will feed the biodigesters is suggested. Considering the process conditions and the residues used, the substrate characteristics were shown to carry out a key role in the bio-digestion processes and consequently in methane generation. [ABSTRACT FROM AUTHOR]

A growing paddy crop produces large quantities of parboiled rice mill wastewater (PRMWW), which contains several organic and inorganic compounds and nutrients (nitrogen and phosphate). Discharges of the rice industry's wastewater pose a substantial threat to aquatic bodies and the surrounding environment, so an eco-friendly treatment plan is necessary. Parboiling stands out among grain-processing methods due to its numerous nutritional and physical advantages. Fewer literatures have only mentioned about the severity of the organic rich liquid effluents generated after parboiling process. Generating renewable energy from anaerobic digestion (AD) is one of the most environmentally friendly technologies to address the growing energy demands. This study is intended to give a systematic and critical review of the parboiling process, solid and liquid fractions of wastes generated, and various treatment options, with special emphasis on scope of application of AD for treating PRMWW along with energy recovery. The study explains various glitches in the AD processes of PRMWW for biogas generation and also recommends co-digesting PBMWW with other carbonaceous organic substrates for improved digestibility, and to reduce the inhibitions caused by lack of alkalinity, acid accumulation, and pH imbalance. To this end, this literature review seeks to provide a broad overview of knowledge to laypeople, entrepreneurs, and researchers. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the impact of using mineral fertilizers on biogas production from vegetable waste. A mixture of wastes from a fruit and vegetable processing plant was used in the experiments, together with two commercial fertilizers, Substral and Agrecol. Experiments were conducted in 5-L anaerobic reactors operated semi-continuously at 35 °C. The application of Substral at a dose of 1 g/kg increased the production of methane and hydrogen by 40% and 78%, up to 420 LCH4/kgVS and 34 LH2/kgVS, respectively. In contrast, with Agrecol supplementation, the average yields of methane and hydrogen were 365 LCH4/kgVS and 27.7 LH2/kgVS, respectively. The beneficial effects of supplementation were due to the compositions of the mineral fertilizers, which contained nutrients and metals that stimulate the growth of microorganisms and build the structures of enzymes. The addition of mineral fertilizers changed the microbial communities of the digestates. At a family level, the main bacteria groups reported were Lactobacillaceae, Anaerolineaceae, Clostridiaceae, Synergistaceae, and Bacteroidetes vadin HA17. The predominant methanogens were Methanosarcinaceae and Methanosaetaceae. There was no clear relationship between the supplementation type and dose and the growth of individual microbial groups. However, the addition of mineral fertilizers increased the relative abundance of Lactobacillaceae and Anaerolineaceae, which are responsible for the hydrolysis and fermentation of polysaccharides into lactic acid, hydrogen, and acetic acid. [ABSTRACT FROM AUTHOR]

A series of batch assays have been conducted to investigate the optimal factors that can be adopted to improve the anaerobic digestion (AD) performance of Phragmites australis and increase biogas production. The assays were carried out using 125 mL microcosm reactors with a working volume of 80 mL and incubated at mesophilic conditions (37 ± 1ºC). The effect of particle size (10, 5, 2, and < 1 mm) and alkaline pre-treatment of P. australis using various concentrations of sodium hydroxide (0.5, 1, 2, and 4%) on biogas production was examined. Furthermore, the best pre-treatment incubation time (12, 24, 48, 72, 96, and 120 h) and the optimal inoculum to substrate ratio (ISR: 4:1, 2:1, 1:1, 1:2 and 1:4) were also assessed. The results revealed that the highest biogas production from P. australis was achieved at particle size < 1 mm (27.97 ± 0.07 and 16.67 ± 0.09 mL/g VS added, for pre-treated and untreated P. australis respectively); 2% and 4% NaOH concentration for pre-treatment (70.01 ± 3.75 and 76.14 ± 2.62 mL/g VS added, respectively); pre-treatment incubation time of 72, 96, and 120 h (71.18 ± 1.79, 72.46 ± 1.08, and 73.78 ± 1.87 mL/g VS added, respectively); and ISR of 1:2 for pre-treated P. australis (78.21 ± 0.36 mL/g VS added) and ISR 1:4 for untreated P. australis (28.93 ± 1.55 mL/g VS added). Determining optimal parameters in this work would guide further development of process configurations, such as continuous AD systems. [ABSTRACT FROM AUTHOR]

The current study compares the biogas production via anaerobic co-digestion of pineapple waste and cow dung to mono digestion under mesophilic condition, with the goal of modifying the substrate ratio and increasing the system stability. Five different cow dung to pineapple waste ratios (1:1, 1:2, 1:3, 2:1 and 3:1) were assessed based on volatile solid (VS) contents. The highest biogas and methane yield were obtained at a ratio of 1:3 with 179.08 mL gas/g VS and 142.89 mL CH4/g VS, respectively. When compared to mono digestion of pineapple waste, the co-digestion process improved process stability in terms of C/N ratio, total ammonia nitrogen, VS removal and pH. Biogas refinement using carbon dioxide remover was able to reach high methane percentage while lowering carbon dioxide percentage to below 3%. The kinetic study using modified Gompertz model showed that the co-digestion process had shortened lag phase, and the highest biogas production rate was observed at 12.80 mL/g VS day. This suggests that the co-digestion process could increase biogas production rate, enhance process efficiency and significantly reduce fermentation time. Co-digestion of pineapple waste with cow dung appears to be a promising approach for bioenergy recovery. [ABSTRACT FROM AUTHOR]

This study focused on determining the effect of the inoculum to substrate ratio (ISR) on biogas production efficiency from the anaerobic co-digestion of two substrates: synthetic food waste and common reeds (Phragmites australis) that were ground and pre-treated using sodium hydroxide at a concentration of 2% to increase access to their cellulose. It also studied the role of different mixing ratios of the two substrates in improving the stability of the digestion process and increasing biogas production. A series of batch tests were carried out under mesophilic conditions using three ratios of ISR: 1:4, 1:2, and 1:1, and five substrate mixing ratios (synthetic food waste: pre-treated P. australis): 25:75, 50:50, 75:25, 100:0, and 0:100. The results showed low biogas production at the ISR 1:4 (21.58±0.00–44.46±0.01 mL/g volatile solid (VS) added), and the reactors suffered from acidification at the different substrates mixing ratios, while the biogas production increased at an ISR of 1:2, where the reactors with the substrate mixing ratio of 25:75 presented the highest biogas production (82.17±0.62 mL/g VS added), and the digestion process was stable. However, the reactors with substrate mixing ratios of 50:50, 75:25, and 100:0 suffered from acidification effects at this ISR. In contrast, at ISR of 1:1, the reactors did not expose to acidification inhibition at all the substrates mixing ratios, and the highest biogas production was found at synthetic food waste: pre-treated P. australis mixing ratios of 75:25 and 100:0 (76.15±1.85 and 82.47±1.85 mL/g VS added, respectively). [ABSTRACT FROM AUTHOR]

The microbiomes play a key role in anaerobic digestion (AD) and perturbations caused by external factors like antibiotics may disturb the microbial community dynamics. This experimental investigation studied the effect of antibiotics tetracycline and spectinomycin individually and in combination at three different concentrations on the biogas, methane yield, and microbial dynamics of AD. In a limited 5 days, well-controlled, lab-scale, batch, mesophilic anaerobic digestion experiment, high concentration of spectinomycin impacted the AD process most negatively by yielding 55.13% less methane and 54.02% less biogas followed by 47.12% less methane and 38.31% less biogas in its medium concentration as compared to the control group. High concentration of combination of antibiotics least negatively impacted the biogas (12.52% decrease), and low concentration of tetracycline resulted in the least reduction of 15.17% in methane production. Flow cytometry fingerprinting has been explored as a rapid, high-throughput, objective, data-driven approach to monitor the day-to-day changes in microbial community fingerprints. Dissimilarity variations were observed from day 1 to 5 in autocorrelations data which putatively accounted for the changes in biogas production. This effective monitoring might help in improved AD operation with increased bioenergy yield and prevent the entry of antibiotics and other harmful pollutants into the food chain. [ABSTRACT FROM AUTHOR]

This is a prime time to develop and implement the "waste to energy" projects across the globe to attain a sustainable environment. Anaerobic digestion (AD) has attracted the scientific community due to its simplicity and easiness to handle, and has the potential to utilize any kind of organic waste to produce a mixture of combustible gases, i.e., biogas and digested slurry, which has further applications in agriculture, solid biofuels, and purification. The process, in turn, reduces the local waste and helps in recycling in a manner that reduces greenhouse gas (GHG) emission, conserves the resources, and establishes a circular economy in the time of undetermined future for the production of energy and safe disposal of the waste. However, the conventional processes encounter with the low biogas yield and long retention time, which discourage the developers. To enhance biogas yield and quality, the momentum of research has increased towards implementation of advanced techniques for development of efficient processes. The present article summarizes the effect of different operational parameters on AD and impact of advanced techniques for enhanced biomethane/biogas. The article further covers the life cycle assessment (LCA) and techno-economic aspect (TCA) of the AD process. This will provide the comparison of different advanced techniques in terms of biomethane/biogas yield. [ABSTRACT FROM AUTHOR]

Biochar shows great potential for enhancing anaerobic digestion (AD); however, the key factors for this remain unknown. This study evaluated the effects of pyrolysis temperature, porosity, and specific surface area (SSA) on the performance enhancement of biochar. The results showed that pyrolysis temperature played an essential role in enhancing the performance of biochar. The addition of cow manure biochar pyrolyzed at 400 °C (NFC-400) and mushroom bran biochar pyrolyzed at 550 °C (JKC-550) increased methane production by 81.30% and 77.59%, respectively, compared with that by the control. Therefore, NFC-400 showed increased gas production, while JKC-550 showed a shorter fermentation period. The SSA and porosity of biochar positively correlated with the pyrolysis temperature but not with biogas production, which indicated that their influence on AD performance enhancement by biochar was not critical. [ABSTRACT FROM AUTHOR]

This study evaluated the biochemical methane potential (BMP) of two types of spent coffee grounds (SCG) via anaerobic co-digestion with food waste. A domestic spent coffee ground (DSCG), from coffee infusion, and an industrial spent coffee ground (ISCG), from Brazil's soluble coffee producing industry, were used as substrates. The co-substrate of food waste was obtained from a restaurant and the sludge from an upflow anaerobic sludge blanket (UASB) reactor was used as inoculum. Triplicates of anaerobic batch reactors (250 mL) were fed with SCG in the proportions of 0%, 25%, 50%, 75%, and 100% of dry weight, using a substrate/inoculum ratio of 1. The BMP tests were performed for 45 days at a mesophilic temperature (35 ± 2 °C). The highest levels of BMP were detected with 25% DSCG (0.345 Nm3CH4/kgVS), 25% ISCG (0.351 Nm3CH4/kgVS), and with 75% of DSCG (0.301 Nm3CH4/kgVS). On the other hand, 75% of ISCG presented a low percentage of BMP (0.188 Nm3CH4/kgVS), due to inhibitor compounds release as the percentage of added SCG increased. Results indicate that either domestic or industrial SCG has the potential for energy recovery via anaerobic digestion (AD). Therefore, AD is a promising alternative for SCG valorization. [ABSTRACT FROM AUTHOR]

In addition to agriculture, Brazil stands out as one of the main meat exporters. In beef production, the waste from the slaughter of a 400-kg bovine produces about 26 kg of waste. In pig farming, the waste generated in the slaughter of a 90-kg pig corresponds to 2.7 kg. Both residues are potential substrates for the production of bioenergy through anaerobic digestion and co-digestion. Likewise, the biogas plants in operation in the country annually generate 1.83 BNm3 of biogas, and the sector is expanding since the national production capacity is 42.7 Bm3/year. This biogas generated through the biological process is an energy source that stands out due to the growing demand for technologies that offer clean energy. Renewable energy sources can ensure greater diversity in the world's energy matrix, in addition to reducing greenhouse gases emissions and dependence on fossil fuels. Therefore, this review addresses the fundamentals of anaerobic digestion and co-digestion, the environmental impacts of biogas and biomethane, and Brazil's energy potential for biogas production. In addition, we discussed the biogas purification technologies, the applications of biomethane, and the current scenario and perspectives of Brazilian biogas involving government initiative policies, technical regulation, international panorama, and economic, environmental, and legislative aspects. [ABSTRACT FROM AUTHOR]

Anaerobic co-digestion is a complex process; therefore, understanding the factors related to kinetics is a prerequisite for optimizing biogas production. In this sense, this study addressed the anaerobic co-digestion of solid waste from vegetables and fruits and anaerobic sewage sludge, focusing on the kinetic modeling of biogas production and investigated synergistic effects of the concentration of total solids (TS) and substrate particle size (SPS). For that, a Factorial Design 3(2-0) was used in which the controlled variables were TS (29.2, 39.9, and 50.5 g/L) and SPS (1.68, 2.9, and 3.36 mm), with tests carried out in 2-L reactors for 200 days to quantify the biogas produced. The modified Gompertz (MG), function transfer (FT), logistic function (LF), modified first-order (FO), and Cone (CN) kinetic models were evaluated in the description of biogas production using the Akaike Information Criterion (AIC) and NRMSE, resulting in the following performance order: LF>CN>FO>MG>FT. The SPS influenced the cumulative biogas production (Mmax) and the hydrolysis constant, so that Mmax increased 221% when the SPS has been reduced from 3.36 to 1.68 mm. TS had an effect on the latency phase time and maximum biogas production rate (Rmax), so that Rmax was optimized by 40% when TS was adjusted from 50.5 to 29.2 g/L. [ABSTRACT FROM AUTHOR]

Two-stage anaerobic digestion and trace metals (TM) supplementation are promising techniques to improve biogas production. Fe2+ and Ni2+ can improve process stability since they are part of the cofactors of enzymes and microorganisms' growth. This work attempted to evaluate the effect of Fe2+ and Ni2+ addition on H2-rich biogas production from organic solid waste and the CH4-rich biogas production from the acidogenic effluents (AEs) enriched with TM. The TM concentrations that enhanced the hydrogen yield in the batch were 0.25 mg/L of Ni2+ and 334 mg/L of Fe2+. These concentrations were evaluated in a two-stage system. The substrate for the batch tests and fermentative reactor (first stage) was OSW. The AE generated in the first stage was the substrate to produce CH4-rich biogas in the second stage. In the first stage, the productivity achieved was 1823 ± 160 mL H2/L/day. However, TM supplementation decreased productivity by 65% since the VS removal increased. Megasphaera genus predominated in the first stage. Regarding the methanogenic reactor, the undiluted AE without TM caused the fast decay of the process. Nevertheless, the reactor operated stably after using AE enriched with TM as a substrate, and CH4 yields increased by 42%. The highest productivity achieved in the second stage was 1278 ± 42 mL CH4/L/day, operating with an organic loading rate of 2.8 gVS/L/day. The genera Proteiniphilum, Thermovirga, DMER64, Anaerovorax, and Syntrophomonas predominated in the second stage. In conclusion, AE enriched with TM can be used to recover the stability of anaerobic digesters, increasing methane production. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) of algal-bacterial biomass grown on wastewater has been used successfully for bio-methane production. However, challenges with AD of microalgae include inhibition due to accumulation of free ammonia (FA) and volatile fatty acids (VFAs), alkalinity depletion, and/or pH outside optimal values. In this study, algal-bacterial biomass was cultured on high-strength wastewater and then co-digested with sugarcane bagasse, an agricultural waste product that is widely available in tropical regions of the world. Biochemical methane potential (BMP) assays were set up at approximately 2% solids content with varying ratios of algal-bacterial biomass and sugarcane bagasse and varying substrate to inoculum ratios (S/I). Although methane content of biogas was similar in all digestion sets (61–67%), co-digestion sets with algae and bagasse produced higher methane yields (145 and 101 mL CH4/g VS) than algae alone (61 and 82 mL CH4/g VS) or bagasse alone (74 mL CH4/g VS). A significant correlation (r2 = 0.88, p = 0.012) was observed between algal-bacterial biomass content of the substrate and total gas production and therefore methane yield. Environmental conditions, including pH, alkalinity, total ammonia nitrogen (TAN), and VFA concentrations, were in the favorable range in all BMPs. However, co-digestion BMPs had greater initial release of COD, VFA, and TAN and greater VS reduction, indicating enhanced biodegradability of the substrates. Additional research is needed on the potential for using waste resources, such as wastewater and agricultural residuals, for biogas production in tropical regions. [ABSTRACT FROM AUTHOR]

To mitigate greenhouse gas emissions and improve energy supply security, there is an increasing effort toward the use of non-fossil energy sources. Crop residues have a great potential to be exploited as biomass for biogas production. However, due to their lignocellulosic structures they are difficult to degrade and do not reach competitive performance. A feasible option to mine these substrates is present in the forestomach of ruminants. Therefore, the aim of the present study was to use rumen microorganisms to improve anaerobic digestion (AD) of crop residues. For this purpose, hemp straw, mechanically pre-treated hemp fibers and shives, flax straw, flax shives, and aged and fresh rapeseed straw were evaluated using the rumen simulation technique. The AD of the substrates was divided into three batches. In two batches, hay was added as a control substrate. In summary, none of the analyzed substrates had an equivalent performance as the control hay, but pre-treated hemp fibers and shives had better AD parameters compared to all other alternative substrates, with the lowest pH (mean: 6.81), highest short chain fatty acid (20.0 mmol/day) and H2 production (25.6 mM) and highest degradability (25.2%). Flax straw had the second-best performance (6.81, 17.4 mmol/day, 20.6 mM and 22.2%, respectively), followed by fresh rapeseed straw, hemp straw, aged rapeseed straw and flax shives. Therefore, hemp fibers and shives demonstrated to be the most suitable substrates for AD. However, since pre-treatment can represent significant additional costs for biogas production, flax straw also demonstrated to be a good alternative. [ABSTRACT FROM AUTHOR]

In order to improve the biogas production from sweet sorghum bagasse (SSB) pretreated with alkaline hydrogen peroxide and reveal the influence of zeolite dosage and TE on the anaerobic digestion performance, as well as the synergistic effect of zeolite dosage and TE, three dosages of zeolite and trace elements (TE) were used as additives for batched biogas production from pretreated sweet sorghum bagasse slurry (PSSBS). The results showed that the maximum methane production of 274.5 mL/g volatile solid (VS) from the group of PSSBS + 5 g/L zeolite + 1 mL TE could be obtained and 58.4% higher than that of untreated sweet sorghum bagasse. Modified Gompertz model estimation demonstrated that the PSSBS + 5 g/L zeolite + 1 mL TE group caused the highest methane production rate to improve by up to 41.6% from SSB and by at least 39.9% from PSSBS. Moreover, with the zeolite and TE addition, activities of cellulase and dehydrogenase of the digestate analysis indicated a positive influence on biogas production and the high alkalinity maintained the stability of the system. This work will provide experimental reference for biogas production from sweet sorghum bagasse. [ABSTRACT FROM AUTHOR]

Co-digestion implementation in wastewater treatment plants enhances biogas yield, so this research investigated the optimal ratio of biodegradable waste and sewage sludge. The increase in biogas production was investigated through batch tests using basic BMP equipment, while synergistic effects were evaluated by chemical oxygen demand (COD) balance. Analyses were performed in four volume basis ratios (3/1, 1/1, 1/3, 1/0) of primary sludge and food waste with added low food waste: 3.375%, 4.675%, and 5.35%, respectively. The best proportion was found to be 1/3 with the maximum biogas production (618.7 mL/g VS added) and the organic removal of 52.8% COD elimination. The highest enhancement rate was observed among co-digs 3/1 and 1/1 (105.72 mL/g VS). A positive correlation between biogas yield and COD removal is noticed while microbial flux required an optimal pH, value of 8 significantly decreased daily production rate. COD reductions further supported the synergistic impact; specifically, an additional 7.1%, 12.8%, and 17% of COD were converted into biogas during the co-digestions 1, 2, and 3, respectively. Three mathematical models were applied to estimate the kinetic parameters and check the accuracy of the experiment. The first-order model with a hydrolysis rate of 0.23–0.27 indicated rapidly biodegradable co-/substrates, modified Gompertz confirmed immediate commencement of co-digs through zero lag phase, while the Cone model had the best fit of over 99% for all trials. Finally, the study points out that the COD method based on linear dependence can be used for developing relatively accurate model for biogas potential estimation in anaerobic digestors. [ABSTRACT FROM AUTHOR]

Cassava pulp (CP) is a starchy lignocellulose waste with starch granules entrapped within the cell wall. The enriched hydrolytic and acidogenic bacterial consortium (EHA) was established to break down the lignocellulosic structure and free starch granules during CP conversion into volatile fatty acids (VFAs). Consecutive batch subcultures were used to acclimatize the anaerobic lignocellulolytic microbial consortium for the anaerobic digestion of CP. Hydrolytic and acidogenic microorganisms in the anaerobic lignocellulolytic microbial consortium were then enriched by inhibiting methanogenic activity until a stable consortium, namely EHA4, was obtained. The performance of EHA4 in CP utilization was investigated based on different operating conditions, including CP concentration, inoculum-to-substrate ratio, and pH adjustment. The alpha diversity revealed that the acclimatization and enrichment decreased the consortium's species richness, creating a solid community specializing in CP hydrolysis and acidification. EHA4 consortium used 100% of CP added within 4 days while producing high-yield VFAs dominated by butyrate and acetate. Clostridium was the dominant bacteria related to hydrolysis and acidification of CP found in EHA4 (41% relative abundance). The performance of EHA4 to degrade higher CP concentration showed a decrease in CP removal due to total VFAs inhibition while maintaining the pH recovered the CP utilization up to 4%. EHA4 is a potential microbial consortium for starchy lignocellulosic CP hydrolysis and acidification as the inoculum starter in biogas production in the future. [ABSTRACT FROM AUTHOR]

This study investigated the use of mineral fertilizers for the improvement of biogas production from vegetable wastes. Five fertilizers of various chemical compositions were selected, and two blends of vegetable wastes were composed for the experiments. The results demonstrated the highest improvement in biogas production using the mineral fertilizer SUBSTRAL dedicated to conifers, which was characterized by a diverse chemical composition and the lack of sulfur. The addition of this fertilizer in a dose of 1 g/kg increased methane and hydrogen yields by up to 49% compared to the control. The maximum methane production of 336 NmL/gVS was achieved after supplementation of the mixture containing corn, green peas, and green bean wastes, whereas the highest hydrogen yield of 49 NmL/gVS was reported in the experiments with the blend containing carrot, cauliflower, and broccoli. A simplified cost analysis showed that the use of 1 kg of mineral fertilizer to supplement the anaerobic digestion of vegetable waste for biogas production can generate additional revenues of up to 2399 €. [ABSTRACT FROM AUTHOR]

The dynamic model of the biogas project was created with changing parameter values over time and compared to the static model of the same project based on constant values of the same parameters. For the dynamic model, the same methods were used to evaluate the biogas project as for the static model to calculate substrate mix volumes, costs, farm production volumes, number of biogas plant equipment, driers, and other numerical characteristics of the farm. Project risks were evaluated by the sensitivity analysis and Monte Carlo simulation. The study was conducted for four scenarios regarding the substrate mix structure and the possibility of selling electricity on the market. In the scenarios, the scale of the project was determined by the size and structure of agricultural and biogas production. The results have shown that when only wastes are used as substrates, net present values (NPVs) of the project are equal to 29.45 and 56.50 M RUB in dependence on the possibility to sell electricity on the market. At the same time, when the substrate mix is diversified, the project NPVs are equal to 89.17 and 186.68 M RUB depending on the ability to sell all the produced electricity to the common power grid. The results of the sensitivity analysis defined that the values of elasticity coefficients are less than 3.14%. Results of the Monte Carlo simulation have shown a probability distribution of positive NPVs for each scenario. This study was conducted to make recommendations for business and municipalities. [ABSTRACT FROM AUTHOR]

Diverse feedstocks utilized in anaerobic digestion (AD) pose challenges to enzymatic disintegration because of their nature and complex physical structures and thereby limiting biogas generation. To overcome this, the AD process is often combined with pretreatment techniques, which facilitate the breaking of organic feedstock into smaller molecules and eventually result in enhanced biogas production. Among several techniques, ultrasound-assisted pretreatment of AD feedstock remains promising because it is simple to implement, requires no chemicals, and combines physical (or cavitation) and biological phenomena for degrading AD feed. This review is primarily centered on the applications of ultrasound pretreatment for disintegrating various feedstocks and increasing biogas production during AD. Biogas generation is described in relation to the ultrasound-assisted disintegration of dairy industry waste, hybrid food and municipal wastes, olive mill wastewater, rice straw, tannery wastewater, meat processing sludge, hybrid industrial waste municipal sewage sludge, and lignocellulosic biomass. The disintegration schemes of feedstocks under ultrasound are proposed. COD is solubilized, and suspended solids (SS) are reduced upon ultrasonication. The impact of ultrasonic treatment on biogas production might be amplified if paired with alkali. Furthermore, the techno-economic commercial scopes of ultrasound pretreatment-based biogas production are discussed, and recommendations for future studies are suggested. [ABSTRACT FROM AUTHOR]

A wide range of techniques are currently used to improve the performance of the anaerobic digestion (AD) process, including co-digestion, inoculation, and addition of various accelerants. In the current study, ruminant intestinal waste inoculum effect on AD of cow manure was investigated. It was hypothesized that methanogens present in intestinal waste will enhance anaerobic digestion, which will result in increased biogas production. Five different cow manure/intestinal waste ratios (1:0, 9:1, 7:3, 1:1, 0:1) on wet weight basis were introduced in AD systems at mesophilic environment (37 °C) to find the best combination of cow manure and intestinal waste. Among tested cow manure/intestinal waste ratios, 9:1, 7:3, and 1:1 demonstrated a good synergistic effect and yielded higher cumulative biogas yields than cow manure and ruminant intestinal waste alone. The cow manure/intestinal waste (9:1) had the maximum cumulative biogas yield (239 ± 5.0 mL/g VS), chemical oxygen demand (COD) removal rate (40 ± 0.56%), volatile solid (VS) removal rate (27 ± 1%), and total solid (TS) removal rate (24 ± 0.52%). In the current study, nutrients' status (nitrogen, N; phosphorus, P; and potassium, K) of digestate was determined while most of the previous studies are only on biogas production. A 9:1 ratio of cow manure to intestinal waste was found to be the best with a cumulative NPK of 4.53%. The inoculation technique using intestinal waste can be an effective means of increasing the efficiency of biodegradable waste. [ABSTRACT FROM AUTHOR]

Inconsistent digestion of palm oil mill effluent (POME) causes difficulties for regulatory compliance plus inadequate biogas generation. In this study, Moringa Oleifera filtrate was co-digested with POME in a pilot-scale integrated anaerobic–aerobic bioreactor (IAAB) having three processes/compartments: anaerobic, aerobic and sedimentation. A 35-day monitoring was carried out for the mono- and co-digestion processes at an organic loading rate (OLR) of 30.0 g COD/L.day. Addition of M. oleifera filtrate at 500 mg/L was capable of removing 95–96%, 99–100% and 93–96% chemical oxygen demand, biochemical oxygen demand (BOD) and total suspended solid, respectively with overall improvement up to 6% in final POME quality and 72% for methane yield. The final discharge remained stable consistently and complied with the set limit (BOD ≤ 20 mg/L) despite high OLR was employed. The ability of the IAAB to hold high concentration of mixed liquor volatile suspended solids (56,000–67,000 mg/L), coupled with high carbon (C) and nitrogen (N) sources as food to microorganisms (F/M), and the ability of the dimeric cationic protein in the shelled M. oleifera to coagulate POME solids had successfully provided appropriate F/M and C/N ratios for co-digestion. The formation of large and dense flocs aided by M. oleifera extract allowed sludge to settle down easily as reflected by the average sludge volume index (SVI) of 34 (i.e., less than the preferred SVI of 100). The IAAB system exhibited good stability and pH adjustment was unnecessary. Long-term IAAB performance data is required to demonstrate its doable implementation on a large scale. [ABSTRACT FROM AUTHOR]

Extrusion, a physical pretreatment, is normally used for the pretreatment of lignocellulosic materials to improve biogas production. Wheat straw (WS) and its solid digestate (digested wheat straw, WSD) were selected to evaluate the effect of extrusion on lignocellulose structure and biogas production from WS and WSD. The WS and WSD were extruded and then were used for biogas production at (37 ± 1) °C in a batch model. The results showed that the cellulose, hemicellulose, and lignin contents of WS and WSD were 28%, 25%, and 14% and 30%, 25%, and 22%, respectively, while the cumulative biogas yields of WS and WSD were 179 and 57 mL/g TSadded (total solid, TS). After extrusion treatment, the cumulative biogas yields of WS and WSD were increased by 23% and 152%, respectively, while the cumulative methane yields of WS and WSD were increased by 27% and 192%, respectively, compared to the unextruded biomass. The results of scanning electron microscope and specific surface area (SSA) indicated that the lignocellulose structure in WSD suffered greater destruction and the increase in the SSA in WSD was 51-percentage points compared to WS pretreated by extrusion. Therefore, it is technically feasible to use extrusion treatment as a pretreatment for the reuse of digested wheat straw for biogas production. [ABSTRACT FROM AUTHOR]

In Mexico, productive activities related to poultry farming and the sugarcane industry generate large amounts of three byproducts, sewage sludge, chicken litter, and sugarcane wastes, which have high concentrations of organic matter and lignocellulosic material. Therefore, the objective of the present study was to evaluate the effect of acid pretreatment with different doses of acetic acid (2%, 3%, and 4% v/v) and exposure times of 30, 60, and 90 min on the solubilization of organic matter and biogas production in the anaerobic codigestion of a mixture of agroindustrial wastes. The biodegradability and biogas production were evaluated by anaerobic digestion for 30 days. Finally, for 90 days of semi-continuous operation, the increase in applied organic load of 1 KgVS/(m3.d) was considered with Δ1 KgVS/(m3.d) every 30 days until reaching 3 KgVS/(m3.d). Acid pretreatment with a dose of 4% acetic acid and an exposure time of 90 min improved the solubility and hydrolysis, considering the limiting stage of the anaerobic process, reducing the hydraulic retention time from 19 to 11 d to reach –Δ 38% VS, and increasing biogas yields (Ybio = 609 ± 11.7 to 1857.2 ± 7.5 Lbio/gVSrem) and methane yields (YCH4 = 426.9 ± 8.19 to 1392.9 ± 5.65 LCH4/gVSrem). [ABSTRACT FROM AUTHOR]

Water hyacinth is a non-edible plant having a severe impact on aquatic ecosystems through native vegetation displacement and lower dissolved oxygen concentration. High cellulose and low lignin content make water hyacinth a potential source for biofuel production. Water hyacinth was subjected to acid pretreatment using organic acids (citric acid (CA) and oxalic acid (OA)) and mineral acid (hydrochloric acid (HA)) to enhance enzymatic saccharification, and ethanol and biogas production. Under optimized pretreatment condition, the reducing sugars released from enzymatic saccharifications of CA-, OA-, and HA-pretreated samples increased by 2.56-, 1.71-, and 1.62-fold, respectively, than untreated sample. Maximum ethanol yield (8.97 g/L) was observed for OA-pretreated (1.68-fold increase) than untreated water hyacinth, whereas CA-pretreated sample produced the highest biogas yield (3421.5 mL) after anaerobic digestion for 45 days. The increase in the yield of ethanol and biogas for OA and CA is attributed to the changes in the hemicellulose and lignin structure. The change in the structural morphology was observed through FTIR characterization of untreated and treated water hyacinth. In addition, the effect of post-washing after pretreatment on fermentation efficiency was evaluated and the result suggested that CA residues had no negative effect on ethanol production. Pretreatment of water hyacinth using organic acids could benefit the biorefineries through the biofuel production and reduction of wastewater generated from this process. [ABSTRACT FROM AUTHOR]

The digestion of community solid waste has great development prospects and economic benefits in the context of waste segregation. However, a large amount of biogas slurry is produced in the anaerobic digestion process and needs to be treated. In this study, the digestion performance and optimal recirculation batch in the digestion of community solid waste were investigated when multiple batches of recirculated slurry were mixed with inoculated sludge in the optimal ratio (a sludge volume percentage of 50%) as the inoculum. The results showed that the biogas yield and methane yield per unit load increased gradually with the number of recirculation batches and reached their maximum values in the seventh batch, which were 80.63% (1382.2 mL/g volatile solids) and 51.0% (812.4 mL/g volatile solids) more than the respective initial values. After four cycles of cultivation, the accumulation of volatile fatty acids (VFAs) was significantly alleviated, and the total VFA concentration in the seventh batch was reduced by 49.7% in comparison with the initial value. The digestion process produced methane mainly via hydrogenotrophic methanogenesis and syntrophic acetic acid-oxidizing methanogenesis. The genera Methanobacterium and Methanomassiliicoccus were closely associated with the biogas production performance. These results are helpful to increase the utilization rate of biogas slurry, improve the performance of multiple-batch digestion of community solid waste, and provide relevant biological evidence. [ABSTRACT FROM AUTHOR]

Volatile methyl siloxanes (VMS) are biogas pollutants generated from the metabolism of polydimethylsiloxanes (PDMS) in anaerobic digestion processes. In the past, VMS were considered an issue only for biogas produced in landfills. However, the widespread presence of VMS in different types of biogas has been demonstrated in recent years as a consequence of the intensive use of PDMS in the formulation of personal care products, industrial lubricants, glues, paints, and detergents. Burning biogas (or biomethane) laden with VMS leads the formation of silicate (SiO2) deposits, resulting in abrasion and severe lubrication issues, which finally produce irreversible damage to energy production devices. The present work provides a comprehensive review of the VMS concentrations recently reported in several types of biogas, as well as the physical–chemical technologies available on a commercial scale for the removal of VMS. Alternative biological processes for VMS removal are also described, including the most recent advances in microbial degradation mechanisms, bioreactor configurations, and operation modes. Critical research niches and challenges towards the consolidation of biotechnologies as efficient and cost-effective VMS treatment systems are identified and critically discussed. [ABSTRACT FROM AUTHOR]

Although drawing inspiration from live animals to develop processes, technologies, or materials is not a new approach, there is rising interest toward biomimicry for implementing new ideas. This review presents the mechanisms and strategies of mechanical pretreatment developed by animals to enhance the digestion of their food. There is ample data in the literature describing animal digestive systems; however, very few compilations encompass all clades with a main focus on mechanical pretreatment. The objective is to improve, through a bioinspired approach, the design of anaerobic digestion processes that are comparable but less efficient than animal digestion. To assess the variety and diversity of strategies that animals have developed during their evolution to adapt and optimize this pretreatment step, the following items were identified, classified, and related: (i) types of mechanical pretreatments, (ii) organs used, (iii) body location of mechanical pretreatment organs, and (iv) substrates, according to their accessibility. Animals are found to have converged toward several solutions to mechanically process their food. The type of organ is associated with the phylogeny while the type of pretreatment is rather associated with the type of food protection. Grinding is the most commonly used pretreatment, covering the widest range of substrates and ensured by the largest number of organs. Finally, animal pretreatment strategies and industrial grinders are compared and discussed in order to identify potential technological improvements. [ABSTRACT FROM AUTHOR]

JUNCAO, as energy grass, was used in mesophilic anaerobic digestion (MAD) to produce methane, which has a huge market potential in biomass energy. This study was conducted to evaluate the characteristics of MAD of Arundo donax cv. Lvzhou No.1 (Lvzhou No.1) and Pennisetum giganteum z.x.lin (P. giganteum) (the growth cycle of 5 months), and explore the relationship between microbial community structure and its function during MAD process. The results showed that cumulative biogas production and cumulative methane content Lvzhou No. 1 (370.37 mL/g VS and 280.08 mL/g VS) with richer nutrition were higher than those of P. giganteum (313.04 mL/g VS and 233.78 mL/g VS) within 30 days of MAD. And the maximum methane concentration could increase to 78% and 75%, respectively. The volatile fatty acid (VFA) of Lvzhou No. 1 and P. giganteums showed a trend of increasing at first then decreasing, and reached the production peak on the first day (1372.40 mg/L) and second day (1061.18 mg/L), respectively. Hemicellulose of both was preferentially degraded with the highest degradation rate (48.27~77.45%). At last, the microbial community analysis suggested that the dominant bacteria in the MAD system at the phylum level belonged to Firmicutes, Bacteroidetes, and Euryarchaeota. Among them, unidentified_Clostridiales and Ruminofilibacter exhibited dominance in the production of acidic substances in this system, and methanogenic function was mainly associated with Methanosaeta. In conclusion, this study would provide new evidence for MAD of JUNCAO as new energy resources, which would pave the way for large-scale MAD of energy plants in the future. [ABSTRACT FROM AUTHOR]

A simulation method (SM), linear programming method (LPM), project evaluation methods (PEMs), and whole farm modeling (WFM) were applied to analyze the investment appeal of a biogas project on a Russian farm. The biogas project was evaluated for constant input parameters. The project efficiency evaluation procedure was elaborated to evaluate and maximize biogas investment project efficiency. The procedure to evaluate the project efficiency includes defining the optimal state of the farm for the situations "with project" and "without project." The main elements for optimization are the equipment for anaerobic digestion, substrate blend structure, fertilizing plan, cost plan, and farm production structure. The optimization was fulfilled by simulation modeling (SM) and LPM. The situations "with project" and "without project" were compared by using PEMs, the main indicators of project efficiency: net present value (NPV), internal rate of return (IRR), payback period (PBP), and profitability index (PI). The optimal substrate blend structure was defined by the direct search method (DSM) to select the probe providing the highest NPV afterward. The procedure to maximize biogas project efficiency was applied to justify the benefits of biogas production on the farm under corresponding conditions and to work out the recommendations for businesses and municipalities. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an efficient and eco-friendly process for the biodegradation of various organic biomass which could potentially produce biomethane and results in no waste accumulation. The palm oil industry concurrently produces three types of possible organic pollutants namely palm oil mill effluent (POME), palm empty fruit bunch fiber (PEFF) and oil palm decanter cake (OPDC). Therefore, this work aimed to study the anaerobic mono- and co-digestion of the substrates from palm industry. Results revealed that the co-digestion of PEFF + POME + OPDC resulted in highest cumulative methane yield of 0.40 L CH4/(g VS added); 0.28 L CH4/(g VS added) from PEFF + POME and 0.27 L CH4/(g VS added) from POME + OPDC. The methane content in biogas and volatile solid (VS) reduction from all the mono- and co-digestion experiments were found to be in the range of 69–71.5% and 40–75%, respectively. These results suggest that the co-digestion of these substrates is superior in biogas yield than mono-digestion. Further, the kinetic parameters were evaluated using the modified Gompertz model equation to determine the lag phase of the process and the maximum biogas generation rate from all the reactors, R2 in all the cases was found to be > 0.95. Next-generation sequencing analysis illustrated wide variety of dominant bacterial species belonging to phylum Firmicutes, Bacteroidetes, Proteobacteria and Chloroflexi. Hydrogenotrophic methanogenesis and acetoclastic methanogenesis were the prevailing methane-generating pathway involved that can be confirmed by the abundance of genus Methanospirillum and Methanothrix, Methanosarcina. [ABSTRACT FROM AUTHOR]

Considered a high-volume waste, soybean molasses is the main byproduct of soybean protein concentrate production and is viscous liquid with high concentrations of soluble carbohydrates, proteins, and lipids. The main goal of this study was to evaluate the potential use of soybean molasses as organic matter for biological degradation in a modified anaerobic–aerobic baffled reactor (AABR) for biogas generation. The AABR was designed with four chambers with useful volume of 5 L, spatially separated, being the first three chambers anaerobic, and the fourth chamber aerobic. The reactor was fed with diluted soybean molasses for six operational conditions (0.43 at 3.86 kgCOD/m3 day). The experimental results showed that the anaerobic system efficiency, in terms of CODTotal removal, was particularly good with values between 73 and 95%. Regarding the entire system, the mean value of percentage CODTotal removal was around 88 and 98% which led to the final effluent concentration between 34 and 764 mgO2/L. The results show that AABR has great potential for biological degradation of soybean molasses and production of biogas estimated up to 180,000 m3/year with high concentrations of methane (86%). [ABSTRACT FROM AUTHOR]

The waste by the pruning Opuntia ficus-indica (OFI) cactus crop is considered a substrate for generating biogas. However, the physicochemical composition and the lignocellulosic fibers, difficulty the anaerobic digestion (AD) process, which generates biogas with a low yield of CH4. The present study implemented the application of combined pretreatments techniques: the mechanical (wet grinding), chemical (alkaline), thermal (modified basic hydrolysis), and organic load control in the OFI waste to control the parameters that influence AD are particle size, pH, residue solubility, and organic load control to evaluate the increase of the biogas. An orthogonal Taguchi L8 design experimental was employed to test the biochemical potential methane (BMP) assay. The better combination of pretreatments was mechanical level 1 (M1 = 0.5–0.8 mm), chemical level 2 (pH2 = 8.5), thermal level 1 (T1 = 30 °C), and concentration level 2 (C1 = 30 gCODL−1) resulted in the most significant increase of CH4 in the biogas with a production of 755.31 NmLCH4. The results show that the combined pretreatments in the OFI waste increased by 160% the methane production with a yield of 201.04 NmLCH4gVS−1 higher than the waste OFI without pretreatment (21.77 NmLCH4gVS−1). The equivalent energy potential of the waste was 5.96 GJton−1 and 33.98 GJ ha−1 yr−1 OFI waste. The combined pretreatments in the OFI waste improve the quality of the biogas and solve the environmental problem that is the inadequate management of the waste. [ABSTRACT FROM AUTHOR]

Cow dung is generally used as the feedstock material for the anaerobic digestion to produce biogas. A selection of alternate biomass material is needed to reduce the consumption or to eliminate the use of cow dung. Recently, cottonseed hull has been considered as the primary substrate to produce biogas. In this paper, the effect of biogas production on anaerobic co-digestion of CD with pre-treated CSH using sulfuric acid, hydrochloric acid, hydrogen per oxide, and acetic acid is investigated. The concentration of each acid has been varied as 1%, 2%, and 3%. In addition, the two alkaline, namely, sodium hydroxide and calcium hydroxide, are used at different concentrations of 4%, 6%, and 8%. The biogas yield obtained from the mono-digestion of pre-treated CSH and the co-digestion of CD with chemically treated CSH at the ratio of 75:25 (CD: CSH) using the experimental results are compared. The enhancement of biogas production from the batch reactors at mesophilic temperature where the cow dung is mono- and co-digested with acid-treated and alkaline-treated cotton seed hull are observed and compared. The maximum biogas yield is achieved for the treated CSH at the concentration of 6% NaOH that offers 13-fold improvement over untreated CSH during mono-digestion. Whereas in co-digestion, it achieved a 6-fold improvement over untreated CSH with the ratio of 75:25 at the concentration of 6% Ca(OH)2. [ABSTRACT FROM AUTHOR]

This study evaluated the ability of the bacterium Azospirillum brasilense to establish a synergic association with the microalgae Chlorella sp. and Scenedesmus sp. co-cultured in suspension and supplied with biogas (75% CH4–25% CO2). The results demonstrated that under the stressful composition of biogas, signal molecule production, such as indole-3-acetic acid (IAA) and tryptophan (Trp) production by the bacterium and microalgae, respectively, allowed the maintenance of their affinity and mutualistic association. Chlorella sp. and Scenedesmus sp. co-cultured in suspension with the bacterium showed higher CO2 fixation rates, 0.29 ± 0.05 and 0.31 ± 0.06 g·L−1·day−1, respectively, than cultured alone, 0.17 ± 0.04 and 0.22 ± 0.03 g·L−1·day−1. Similarly, biomass production of Chlorella sp. (1.4 ± 0.4 g·L−1) and Scenedesmus sp. (1.6 ± 0.5 g·L−1) and their cell composition—mainly carbohydrates and proteins—also enhanced in both microalgae interacting with the bacterium. Overall, these results indicate that, co-cultured in suspension, this consortium microalga–A. brasilense did not change its mutualistic interaction during the specific conditions of CO2 capture from biogas. [ABSTRACT FROM AUTHOR]

Experiments in series horizontal anaerobic reactors with fixed bed (HARFB) were conducted to evaluate the co-digestion of crude glycerol (CG) from biodiesel production and domestic sewage (DS) concerning the start-up strategy and best organic loading rate (OLR) to improve biogas production as well as to analyze the dynamic changes in the anaerobic microbial consortium during their operation. This approach can be used to increase the buffering capacity of anaerobic reactors as well as dilute toxic compounds. The reactor configuration applied at the present research is a novelty about CG and DS co-digestion and biogas production. The highest hydrogen generation was 10.3 mol H2 (m3 day−1) in reactor R1, and the highest methane yield was 312.0 and 283.9 L CH4 (m3 day−1) in R2 and R3, respectively. These values, obtained with mixed culture, agree with previous co-digestion research. The three-stage system showed high efficiency in removing crude glycerol and chemical oxygen demand (COD), with consumptions of 99.9%, both. The strategy of co-digestion is positive to avoid substrate inhibition. In addition, there was a change in the relative abundance of microorganisms among R1, R2, and R3 and a considerable decrease in the diversity index in the fermentation reactor (R1). The results have shown the potential of applying HARFB reactors for energy recovery and alternative waste disposal. [ABSTRACT FROM AUTHOR]

The purpose of this research is to evaluate the biogas potential of agriculture in the typical Russian region. The design of this study was completed using the main kinds of agricultural production of the Tambov region as the feedstocks for biogas production. Average amounts of the feedstocks were calculated on the base of data for the period 2009–2018. The quantities and revenues of electricity, heat, and biofertilizers from biogas produced from various substrates were estimated and mapped for each of the twenty-three municipal districts of the region. Results revealed an average total monetary biogas potential of 88.52 × 109 RUB for the Tambov region per year, where 75.43% are provided by electricity and heat energy and the remaining 24.57%—by biofertilizers, therefore, biogas potential of the Tambov region is comparable with biogas potential of a European country. Such feedstocks as sunflower silage, cereal grain, and cereal straw were defined as the most attractive substrates in the region. At the same time, the most of feedstocks being the main farmers' commodity production are debatable to be used as substrates; as for Russian farmers, biogas production is a new and not well-known technology. Nevertheless, the developed calculation method can now be applied by local authorities of the Tambov region and other regions of the Russian Federation as the base to develop the biogas sector in the most promising areas by supporting farmers and business structures and attracting investments in biogas technology. [ABSTRACT FROM AUTHOR]

In this paper, the regions where Cynara cardunculus L. is cultivated in Turkey are revealed, with data obtained from several locations in Turkey. Furthermore, the installation of active biogas plants in these regions has been identified, and the utilization of Cynara cardunculus L. residues as a biomass source, particularly in Izmir biogas plants, has been investigated. To begin, the amount of Cynara cardunculus L. cultivated in the world and Turkey has been determined. According to the Food and Agriculture Organization of the United Nations (FAO)'s recent data for 2019, approximately 1.6 million tons of Cynara cardunculus L. were produced globally, with Turkey accounting for nearly 2.5% of this quantity. The data from the Biomass Energy Potential Map for Turkey (BEPA) was reviewed, and it was calculated that approximately 40 thousand tons of Cynara cardunculus L. are produced in Turkey each year. Furthermore, the agricultural production of this crop in Turkey generates roughly 225 thousand tons of residues. In comparison to other regions, the Izmir region generates 32.5% of Turkey's Cynara cardunculus L. residues. However, no research on the evaluation of this residue potential and the utilization of Cynara cardunculus L. residues in biogas production has been conducted to date. As a result, it was aimed at the residual potential of Cynara cardunculus L. in various regions of Turkey, as well as its potential utilization as a biomass resource for biogas plants in these areas. It has been calculated that 1.65% of the Izmir population could supply its energy demands by utilizing the energy equivalent of the Izmir region's wastes. [ABSTRACT FROM AUTHOR]

This study investigated the effects of carbon-based conductive material (granular activated carbon (GAC), graphene, and petroleum coke) supplementation on anaerobic digestion (AD) of food waste (FW). GAC and graphene have been used in anaerobic digestion applications previously. Even though petroleum coke has a very similar elemental characterization with biochar, to the best of our knowledge, it was never investigated as a supplement to improve AD. All of the materials were found to improve the biogas production and methane yields in AD of FW. Supplementation of GAC (1 g/L), petroleum coke (0.25 g/L), and graphene (0.05 g/L) enhanced biogas production by 31.3 ± 4.4%, 51.7 ± 1.2%, and 41.9 ± 3.8%, and methane yields by 26.3 ± 1.1%, 31.2 ± 0.6%, and 26.1 ± 1.6% on average, respectively. The highest methane yield was determined as 484.9 ± 38.5 mL CH4/g VS in reactors supplemented with petroleum coke (0.25 g/L), which is higher than reported in relevant studies. This unique finding suggests that petroleum coke, which is a waste by-product from oil refineries, can be used to enhance AD similar to other commercial carbon-based additives. After confirming with further research, this observation may open a new avenue for oil refineries in terms of managing petroleum coke as one of the important by-products of this sector. [ABSTRACT FROM AUTHOR]

Excessive amounts of pelagic Sargassum arriving at Mexican coastlines result in the deterioration of soil and water quality and the endangerment of endemic aquatic species, so far proper management strategies for this biomass are not being developed. Anaerobic digestion is a well-established technology for energy recovery of organic residues. However, the conversion of Sargassum is unsatisfactory as it was confirmed in this study with only 21% of theoretical methane yield. To make this conversion strategy more favourable, pretreatment is recommended. The present work compares the effectiveness of steam explosion and extrusion to increase digestibility of Sargassum. Both methods were found to improve the bioconversion of the macroalgae by nearly 80%. The solubilization of organic matter with a yield of 145 ± 3.8 mg of chemical oxygen demand (COD) per g of dry biomass (TS) obtained by steam explosion was significantly higher than that of extrusion giving rise to 64.2 ± 7.1 mg COD g−1TS. In contrast, the methane yield evaluated in batch assays for both treatments was significantly the same with 114 ± 4 mLN CH4 per gram of volatile solids (VS) for the conversion of steam-exploded substrate and 108 ± 6 mLN CH4 g−1VS when extrusion as pretreatment method was applied. In summary, extrusion may be the preferred technology to tackle this kind of biomass as removal of salt is intrinsically tied to dewatering stream. [ABSTRACT FROM AUTHOR]

The purpose of this research is to experimentally evaluate the anaerobic co-digestion in the city of Guaranda of slaughterhouse residues (RM) with straw residues from agriculture, such as amaranth residues (AM), quinoa residues (QU) and residues of wheat (TR), to reduce slaughterhouse discharges and prevent contamination of the city. The study was carried out on a laboratory scale in 311-ml biodigesters under mesophilic conditions of 37 °C. In addition, sewage sludge was used as inoculum with two relationships between substrate and inoculum (SIR 1:1 and SIR 1:2). The design was completed using three relationships between substrate (RM) and co-substrate (AM, QU and TR): 25:75, 50:50 and 75:25. Anaerobic co-digestion resulted in methane yields of 407 ml CH4/g VS, with a methane content in the biogas of 77% for the mixture of RM and QU (RM-QU (25:75)). The increase in inoculum in the mixtures composed of RM and QU increased the biodegradability between 17 and 22%. However, in the mixtures of slaughterhouse waste and amaranth (RM-AM (25:75)), a further increase in inoculum reduced biodegradability by 5%. The results revealed that there is a greater synergy between the RM and QU as the percentage of QU in the mixture is increased. This meant that the co-digestion of the RM with the QU accelerates the biodegradability of the mixture, increasing the production of biogas. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effects of compaction on the anaerobic biodegradability of straw. In the study, compaction tests were carried out at different applied pressures, i.e., 0 (CK), 277 (T1), 555 (T2), and 1109 Pa (T3), respectively. The results showed that the maximum gain in biogas production was 298.35 mL·g−1 TS for the T2 reactor, significantly higher than CK (228.51 mL·g−1 TS) and T3 (249.14 mL·g−1 TS) reactors. The concentration of COD and TVFA of the T3 reactor was the highest throughout the anaerobic digestion (AD) process, the same thing for DHA, with maximum values of 39.12 g/L, 11.62 g/L, and 31.97 ug TPF/(h mL), respectively. However, the effect of compaction on the physical and chemical indicators of digestive fluid was not significant during the batch-type AD process. The factor analysis results suggested that the major factors affecting biogas production were influenced by the compaction and varied based on the different stages of digestion. Scanning electron microscopy (SEM) showed that the straw surface was damaged as the compaction increases. The degradation of TS in the AD did correlate to biogas yield, the best performance of TS loss rate was T2 (44.79%), and the lowest was CK (37.64%). This research concluded that compaction on gas production via changing the environment during the bath AD process and proper compaction could positively affect biogas yield, while excessive compaction will inhibit gas production. The impacts of compaction on the physicochemical indexes of the liquid digestate, structural and compositional changes of solid digestate, and biogas yield [ABSTRACT FROM AUTHOR]

This study estimates agricultural residue biomass available for biogas generation in smallholder farming systems in the rural Vakinankaratra region of Madagascar, during 2017–2018. Estimations of biomass were done using a combination of agricultural household surveys, literature models, and publicly available data. Manure from four types of farm animals and 17 residue types from ten crops were assessed. In the studied period, gross biomass produced from animal manure and crop residue were 19.4 ± 7.41 and 7.3 ± 1.08 tonnes fresh weight per year per agricultural household, respectively, of which up to 54% and 83% are estimated as recoverable for the production of bioenergy in the studied area, respectively. Estimations indicate that available animal manure and crop residue have the potential to generate 291 ± 92 and 745 ± 122 Nm3 of methane per year per agricultural household respectively, equivalent to 10.5 ± 3.34 and 26.8 ± 4.28 GJ of heat energy from manure and residues, respectively. Theoretically, the average estimated energy potential can result in the complete substitution of domestic fuels in agricultural households. Approximately 0.12 tonnes of nitrogen per household per year can be recovered from the estimated digestate (using all residue types) after energy recovery, which can be employed for crop fertilization. The recovered nitrogen corresponds to 0.26 tonnes urea fertilizer per household per year. The investigation shows that anaerobic digestion based on crop residue and manure has the potential to meet a significant portion of energy needs of smallholder farmers in the Vakinankaratra region of Madagascar and can make an important contribution to providing fertilizer for on-farm use. [ABSTRACT FROM AUTHOR]

Rice straw is an abundant lignocellulosic biomass used to produce biogas. However, its resistant structure hinders biogas production. In this study, three pretreatments, microwave, ammoniation, and microwave-assisted ammoniation (MAA), were evaluated for their use in improving biogas production from rice straw. After an 18-day digestion, methane production by rice straw pretreated with MAA was 281.56 mL/g (volatile solids of substrate), which was 25.43%, 7.96%, and 18.18% more than that produced following the control, microwave, and ammoniation pretreatments, respectively. These increases were mainly attributed to the change in the resistant structure of rice straw following the MAA pretreatment and a more stable anaerobic digestion system. The degradation rate for the volatile solids of the rice straw pretreated with MAA during anaerobic digestion was 71.20%, which was 4.71%, and 4.86% higher than the rates observed using microwave and ammoniation pretreatments, respectively. In addition, the MAA method had a T90 fermentation cycle of 6 days, which was 33.3%, 25.0%, and 33.3% shorter than those for the control, microwave, and ammoniation methods, respectively. This technology shows the potential to enhance biogas production from the anaerobic digestion of rice straw. [ABSTRACT FROM AUTHOR]

Grass clippings have a good biomethane potential and, if acquired from roadside verges, nature management or natural grasslands do not compete for arable land, avoiding the food versus fuel debate. However, before the grass is processed in a wet anaerobic digester, a pretreatment step is advisable to minimize the problems associated with its fibrous nature. In this study, the effects of a semi-industrial extrusion pretreatment on fresh and ensiled grass were investigated through an energetic and economic assessment. Extrusion improved the mixing properties of the grass feedstock and reduced the formation of a floating layer even at a solid concentration of 10% (w/v). This pretreatment also enhanced the biomethane potential of ensiled grass and fresh grass by, respectively, 18 and 11% on a fresh matter basis, while shredding reduced this value by 14% when compared to fresh grass. This was attributed to changes in the volatile solids (VS) content of the treated samples, as all conditions resulted in similar biomethane yields when calculated per ton of VS, ranging from 325.5 to 337.6 Nm3 CH4/ton VS. However, ensiling resulted in a longer lag phase during biogas production attributed to the leaching of readily available sugars from the ruptured plant cells; nevertheless, this is not expected to be significant in a buffered industrial system. The revenue resulting from the extrusion treatment, between €6 and €17 per tonne of FM, compensated the cost of this additional step, indicating that extrusion would be a techno-economically sound process for the anaerobic digestion of grass. [ABSTRACT FROM AUTHOR]