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Within the evolving regulatory landscape of the European Union concerning animal by-product (ABP) management within the circular economy framework, this study explores the concurrent objectives of safeguarding public health and environmental integrity and maximizing final product value. Anaerobic digestion (AD) emerges as a holistic solution for ABP management, addressing sanitation concerns while enhancing end-product quality. Through laboratory-scale experimentation, the AD process applied to four substrates—poultry manure, swine manure, cattle manure, and food waste—is scrutinized. Prior to AD, pasteurization at 70 °C for 60 min ensures microbial safety. Subsequently, four experimental AD cycles compare pasteurized and unpasteurized substrates. Results highlight the efficacy of pasteurization in sanitizing final products across all substrates, emphasizing its pivotal role in product safety. However, pasteurization's impact on system performance varies. While enhancing biogas yield from animal waste notably, its influence on food waste biogas production is less pronounced, indicating substrate-specific dynamics. This study offers insights into optimizing ABP management strategies, emphasizing the interplay between pasteurization, substrate characteristics, and AD performance. Such insights are crucial for advancing sustainable practices in the circular economy paradigm, balancing environmental stewardship with economic viability. [ABSTRACT FROM AUTHOR]

The adoption of new forms of energy production is one of the challenges faced by countries worldwide due to the progressive depletion of fossil fuels. In this regard, the co-digestion of organic waste in Wastewater Treatment Plants (WWTP) has gained widespread acceptance, as it not only provides an alternative for the utilization of several types of biomasses to meet energy needs but also assists in waste management and nutrient recovery. However, accepting additional substrates for co-digestion requires careful physicochemical studies, as their characteristics can influence both the stability of the process and the quality and production of biogas. In line with the above, this study implemented the case study method through descriptive analysis to evaluate the substrates accepted for anaerobic co-digestion in the Straubing WWTP in Germany (SER GmbH). As a result, it was found that floating fats (C1) and milk with inhibitors (C5) were the substrates that exhibited the highest biogas production per unit of treated mass, 90% more than distillation residues and 70% more than raw sludge. These findings underscore the importance of carefully selecting substrates for codigestion in WWTPs, highlighting the potential to harness valuable resources, as evaluated in this study, to increase efficiency in biogas production and, therefore, promote a more effective transition to sustainable energy sources in the global context. The Straubing WWTP in Germany thus becomes an example of the possibilities offered by co-digestion in sustainable energy generation and waste management. The inclusion of floating fats and milk with inhibitors as successful substrates illustrates how research and careful implementation can optimize the performance of these facilities. [ABSTRACT FROM AUTHOR]

The success of anaerobic digestion (AD) process for biogas production is contingent upon complex mix of operating factors, process conditions, and feedstock types, which could be affected by inadequate understanding of microbial, kinetic, and physicochemical processes. To address these limitations, efforts have been directed toward developing mathematical and intelligent models. Although mathematical models provide near-optimal solutions, they are time consuming, highly expensive, and demanding. Intelligent standalone models are also limited by their low predictive capability and inability to guarantee global optimal solution for the prediction of cumulative biogas yield for FFV waste. However, hyperparameter optimization of such models is essential to improve the prediction performance for cumulative biogas yield for FFV waste. Therefore, this study applies a genetic algorithm (GA) to optimize an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of cumulative biogas production. Seven (7) input variables, organic loading rate (OLR), volatile solids (VS), pH, hydraulic retention time (HRT), temperature, retention time, and reaction volume, were considered with cumulative biogas production as the output. The effect of varying clustering techniques was evaluated. The three (3) clustering techniques evaluated are fuzzy c-means and subtractive clustering and grid partitioning. The hybrid model was evaluated based on some verified statistical performance metrics. Optimal root mean squared error (RMSE), mean absolute deviation (MAD), mean absolute percentage error (MAPE), and standard deviation error (error STD) of 0.0529, 0.0326,7.6742, and 0.0474, respectively, were reported at the model testing phase for the subtractive clustering technique being the best-performing model. The results confirm the capacity of hybrid evolutionary (genetic) algorithm based on subtractive clustering technique to predict the biogas yield from FFV and serve as an effective tool for the upscaling of anaerobic digestion units as well as in techno-economic studies toward more efficient energy utilization. [ABSTRACT FROM AUTHOR]

A blend of organic municipal solid waste, slaughterhouse waste, fecal sludge, and landfill leachate was selected in different mixing ratios to formulate the best substrate mixture for biomethanation. Individual substrates were characterized, and the mixing ratio was optimized with the help of a response surface methodology tool to a value of 1:1:1:1 (with a C/N ratio of 28±0.769 and total volatile fatty acid (VFA) concentration of 2500±10.53 mg/L) to improve the overall biomethanation. The optimized blend (C/N ratio: 28.6, VFA: 2538 mg/L) was characterized for physicochemical, biological, and microbial properties and subjected to anaerobic digestion in lab-scale reactors of 1000 mL capacity with and without the addition of inoculum. The biogas yield of individual substrates and blends was ascertained separately. The observed cumulative biogas yield over 21 days from the non-inoculated substrates varied between 142±1.95 mL (24.6±0.3 ml/gVS) and 1974.5±21.72 mL (270.4±3.1 ml/gVS). In comparison, the addition of external inoculation at a 5% rate (w/w) of the substrate uplifted the minimum and maximum cumulative gas yield values to 203±9.9 mL (35.0±1.6 mL/gVS) and 3394±13.4 mL (315.3±1.2 mL/gVS), respectively. The inoculum procured from the Defence Research and Development Organisation (DRDO) was screened in advance, considering factors such as maximizing VFA production and consumption rate, biogas yield, and digestate quality. A similar outcome regarding biogas yield and digestate quality was observed for the equivalent blend. The cumulative gas yield increased from 2673±14.5 mL (373.7±2.2 mL/gVS) to 4284±111.02 mL (391.47±20.02 mL/gVS) over 21 days post-application of a similar dosage of DRDO inoculum. The 16S rRNA genomic analysis revealed that the predominant bacterial population belonged to the phylum Firmicutes, with the majority falling within the orders Clostridiales and Lactobacillales. Ultimately, the study advocates the potential of the blend mentioned above for biomethanation and concomitant enrichment of both biogas yield and digestate quality. [ABSTRACT FROM AUTHOR]

Comprehensive and proper management of fecal sludge (FS) is an ongoing concern in many nations. Decentralized fecal sludge treatment plants (FSTPs) are effective in this regard; however, many have experienced strong public opposition based partly on suspicion of malodor. Fecal sludge and freshly generated fecal matter (FM) samples from various FSTPs were collected, characterized, and investigated for biomethane potential. The homogenized samples were anaerobically digested for 28 days. Digestion successfully reduced total suspended solids, biochemical oxygen demand, and threshold odor number values of 97,350–97,420 mg/l, 43,230–43,260 mg/l, and 130–150 for FM, to 49,500–49,650 mg/l, 23,760–23,850 mg/l, and 3338, respectively, for FS samples. The comprehensive gas yield from Bhongir, Boduppal, and Shadnagar FS samples was 40, 55, and 31 ml, respectively. In contrast, cumulative gas generation from the FM was 26,361 ml. Digestion of FS samples also reduced concentrations of volatile solids and coliforms by 66–72% and 99%, respectively. Characterization of gas samples revealed methane and carbon dioxide concentrations as 56% and 22% for FM, and 0.4% and 61% for FS samples, respectively. Hydrogen sulfide and ammonia gas were absent in FS samples, dispelling common societal misconceptions of FSTPs being associated with malodor. [ABSTRACT FROM AUTHOR]

Co-digestion potential of the wastewater treatment sludges produced at two industries with different characteristics was investigated in anaerobic batch reactors operated at mesophilic (35±2 °C) condition. The sludge sources selected were from a food industry producing edible oil and from a textile industry producing woven fabric. Reactor performance was evaluated by the conventional parameters as well as by monitoring the biogas production during co-digestion of both industrial sludges at equal mixing proportions. Results indicated that both of these sludge sources had substantial biogas production potential with a cumulative biogas yield more than 425 mL/g-VSSfed whereas it was about 5-fold lower only for the food sludge. On the other hand, chemical oxygen demand (COD) removal reached to about 90% during co-digestion with a well recovery of pH value and alkalinity concentration for sufficient buffering at the end of incubation. Therefore, by the combination of different industrial sludges through co-digestion; higher digestion performance and improved methane yield could be achieved due to better balanced substrate and nutrients. Regarding the initial heavy metals in the supernatant phase of the mixed sludge; iron (Fe), zinc (Zn), nickel (Ni), aluminum (Al), and manganese (Mn) could be removed from 56% to 80% while no apparent removals were observed in cadmium (Cd) and lead (Pb) at the end of operation. Hence, these potential toxic pollutants in the digestate should be taken into consideration while deciding the most appropriate resource recovery and ultimate disposal methods. [ABSTRACT FROM AUTHOR]

Pretreatment is aimed at making lignin structures, which in turn causes decrystallisation and depolymerisation of cellulose. This treatment allows to increase the energy potential of substrates. A properly selected method allows for obtaining larger amounts of biogas with a high content of biomethane. The aim of the study was to analyse selected pretreatment methods (ultrasonic and hydrothermal) for biogas yield, including biomethane, and to demonstrate the effectiveness of obtaining additional electricity and heat from these methods. It was based on the literature data. On basis the study, the following information was obtained: average yield of biogas and biomethane before and after treatment, difference in yield of biogas and biomethane after treatment, and the effect of treatment on the substrate used. Moreover, an estimate was made of the effectiveness of obtaining additional electricity and heat from selected pretreatment methods compared to hard coal. Based on the analysis of the ultrasonic treatment analysis, it was shown that the best result was obtained with the ultrasound treatment of the mixture of wheat straw and cattle manure with the following parameters: frequency 24 kHz, temperature 44.30°C, time 21.23 s. This allowed a 49% increase in biogas production. The use of pretreatment would therefore allow the production of more electricity and heat capable of replacing conventional heat sources such as coal.

This article investigates the current status and distribution of the feedstock of biogas engineering in China, evaluates the temperature conditions for anaerobic co-digestion (AcoD), and assesses the biogas production potential of feedstock in AcoD, including six feedstocks, namely, maize straw (M), wheat straw (W), rice straw (R), pig manure (P), cow manure (C), and sheep manure (S). The total amount of M, W, and R was 3.89 × 108, 2.10 × 108, and 1.50 × 108 tons, respectively, and that of P, C, and S was 8.46 × 108, 1.31 × 109, and 4.95 × 108 tons, respectively. However, the spatial distributions and amount of those resources were found to be uneven in China. Heilongjiang has abundant maize straw, and Henan has abundant wheat resources. Sichuan is rich in cow manure, while Inner Mongolia is rich in sheep manure. The analysis of total biogas production (TBP) by mono-digestion and co-digestion (using two feedstocks at ratio of 1:9, 3:7, 5:5, 7:3 and 9:1) showed that co-digestion outperforms mono-digestion under 15 and 25 °C. Thus, it is necessary to study anaerobic co-digestion scheme (AcoDS), which will provide a reference for biogas engineering in different regions to promote the biogas yield based on their actual situation.

Olive oil mill waste is characterized by its high organic matter content, especially fatty acids, polyphenols, sugars, and proteins. These nutrients can be used as a source of energy for biogas production. However, olive oil mill waste can also contain heavy metals such as lead, cadmium, copper, and zinc that can be absorbed by plants. In addition, very high concentrations of heavy metals can also inhibit the anaerobic digestion process by affecting the methanogenic bacteria involved in biogas production The aim of this research is to determine the composition of solid and liquid rejections from traditional and continuous three-phase crushing systems, by analyzing samples from different oil mills in the eastern region of Morocco. We also applied the technology of anaerobic digestion of solid and liquid waste forms of oil mills, to make a link between the biogas yield and the physicochemical characteristics of these wastes. The results suggest that traditional oil mill wastewater (Discontinuous OMWW) has high organic matter, nutrients, and heavy metals content and a low concentration of phenolic compounds, which can increase its biogas production potential with a production of 10.02 Nml/ g VS, while three-phase wastewater (Continuous OMWW) has limited biogas production potential (3.83 Nml/ g VS) due to the low organic matter and nutrients content, and high concentration of phenolic compounds. Three-phase olive pomace (Continuous OMSW) has a higher biogas production (9.28 Nml/ g VS) than traditional olive pomace (Discontinuous OMSW) with 5.91 Nml/ g VS. In fact, the lower content of phenolic compounds and volatile fatty acids favors their anaerobic digestion and improves their biogas production. In conclusion, the selection of the type of waste adapted for biogas production must be based on the physicochemical and microbiological characteristics of these wastes.

In this paper, the effects of nano-zero valent iron (nZVI) on anaerobic digestion of sulphate wastewater with different SO 4 2 − /COD ratios, including the COD removal rate, methane yield, intermediate products and the change of microbial community structure, were investigated. The results showed that nZVI could effectively enhance the treatment efficiency and methane yield. Compared with the control group without nZVI, the methane yield increased from 348.6833 to 1007.05 mL CH4/gCODremoval with 4 g nZVI loading at SO 4 2 − /COD = 0.1. nZVI could make electron flow from sulphate reduction to methane production, which increased methane yield even at high sulphate concentration. The microbial community analysis showed that adding nZVI could increase the abundance of acetoclastic methanogens, which accelerated hydrolysis acidification. [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]

Olive oil mill waste is characterized by its high organic matter content, especially fatty acids, polyphenols, sugars, and proteins. These nutrients can be used as a source of energy for biogas production. However, olive oil mill waste can also contain heavy metals such as lead, cadmium, copper, and zinc that can be absorbed by plants. In addition, very high concentrations of heavy metals can also inhibit the anaerobic digestion process by affecting the methanogenic bacteria involved in biogas production The aim of this research is to determine the composition of solid and liquid rejections from traditional and continuous three-phase crushing systems, by analyzing samples from different oil mills in the eastern region of Morocco. We also applied the technology of anaerobic digestion of solid and liquid waste forms of oil mills, to make a link between the biogas yield and the physicochemical characteristics of these wastes. The results suggest that traditional oil mill wastewater (Discontinuous OMWW) has high organic matter, nutrients, and heavy metals content and a low concentration of phenolic compounds, which can increase its biogas production potential with a production of 10.02 Nml/g VS, while three-phase wastewater (Continuous OMWW) has limited biogas production potential (3.83 Nml/g VS) due to the low organic matter and nutrients content, and high concentration of phenolic compounds. Three-phase olive pomace (Continuous OMSW) has a higher biogas production (9.28 Nml/ g VS) than traditional olive pomace (Discontinuous OMSW) with 5.91 Nml/g VS. In fact, the lower content of phenolic compounds and volatile fatty acids favors their anaerobic digestion and improves their biogas production. In conclusion, the selection of the type of waste adapted for biogas production must be based on the physicochemical and microbiological characteristics of these wastes. [ABSTRACT FROM AUTHOR]

Large amounts of poultry manure (PM), corn stover (CS), and cattle manure are generated annually posing a serious environmental problem that must be addressed. Anaerobic co-digestion of poultry manure with alkali-treated corn stover is becoming more popular as a way to enhance biogas generation and organic waste management. The present study investigated the effect of four independent variables (temperature, hydraulic retention time, pH, and PM to alkali-treated corn stover ratio) on the biogas yield. Response surface methodology (RSM) and artificial neural network (ANN) have been used to optimize and predict biogas production via an anaerobic co-digestion process. The results revealed that the properly trained artificial neural network model was found to be more powerful modeling capability and accurate in prediction as compared to response surface methodology. The optimum conditions were found to be a temperature of 37 °C, a hydraulic retention time of 13 days, pH of 7, and 80% blending ratio (PM to alkali-treated corn stover). Under these conditions, the model predicted a biogas yield of 745 mL/g TS with a desirability value of 0.995. Generally, the findings of the study suggest that co-digestion of PM and alkali-treated corn stover is a promising way to increase the production of biogas by ensuring nutrient balance. [ABSTRACT FROM AUTHOR]

The upflow anaerobic hybrid (UAHB) reactor combines the advantages of a upflow anaerobic sludge blanket (UASB-type) reactor and an anaerobic filter in a single compartment. A novel configuration of the UAHB reactor, composed of two three-phase separators (3PHS), was proposed to evaluate the biogas production in the moving and fixed bed in the treatment of synthetic sewage at a temperature range of 14–21 °C and hydraulic retention time (HRT) of 12, 10 and 8 h. The bench-scale reactor was operated in three different phases with organic loading rate (VOLR) of 0.6 (0.3–0.7), 0.7 ± 0.2, and 1.1 ± 0.1 kg COD m−3 d−1, respectively, for 225 days. The average removal efficiency of chemical oxygen demand (CODt) was 78 (42–89)%, and the total biogas yield was 3090 (1704–4782) mL d−1, with 66% of the lower 3PHS (moving bed) and 34% of the upper 3PHS (fixed bed). However, no significant difference was observed between the biogas yield on the 3PHS (p-value = 0.5048), thus confirming the influence of temperature in the biogas production. The average percentage of methane was 76 (60–82)% for both beds, and the filter media increased the production by 21%. Thus, it can be concluded that the fixed bed suppressed the instability of the moving bed regarding the biogas production and contributed to the final quality of the effluent. [ABSTRACT FROM AUTHOR]

Sewage sludge, commonly used in the process of municipal wastewater treatment, is characterized by high organic load and therefore is a valuable substrate in the process of methane fermentation. However, their biodegradability may be limited by the presence of microorganisms, which show limited susceptibility to decomposition in anaerobic conditions. The aim of the conducted research was to compare the efficiency of decomposition of organic compounds in excess sludge by various methods before sending the sludge to fermentation. The paper refers to selected physical (ultrasound field, microwave radiation, low-temperature modification up to 100°C, modification with dry ice), chemical (hydrogen peroxide, Fenton's reagent, peracetic acid) and biological (enzymatic biopreparations) method of sludge disintegration garbage. Excess sludge from a mechanical--biological sewage treatment plant with the use of a highly effective method of removing biogenic substances was used as the research substrate. As a result of the use of selected physical, chemical, and biological methods of sludge disintegration, an increase in potential susceptibility to biodegradation was observed already at the stage of modification, which was confirmed by methane fermentation in the next stage and the biogas yield recorded. The highest process efficiency in terms of biogas production was recorded for sludge modified with the peracetic acid method, that is, 0.85 L/g·VSS, while the lowest increase in unit biogas production was obtained for sludge modified with dry ice 0.44 L/g·VSS. [ABSTRACT FROM AUTHOR]

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

Pretreatment is aimed at making lignin structures, which in turn causes decrystallisation and depolymerisation of cellulose. This treatment allows to increase the energy potential of substrates. A properly selected method allows for obtaining larger amounts of biogas with a high content of biomethane. The aim of the study was to analyse selected pretreatment methods (ultrasonic and hydrothermal) for biogas yield, including biomethane, and to demonstrate the effectiveness of obtaining additional electricity and heat from these methods. It was based on the literature data. On basis the study, the following information was obtained: average yield of biogas and biomethane before and after treatment, difference in yield of biogas and biomethane after treatment, and the effect of treatment on the substrate used. Moreover, an estimate was made of the effectiveness of obtaining additional electricity and heat from selected pretreatment methods compared to hard coal. Based on the analysis of the ultrasonic treatment analysis, it was shown that the best result was obtained with the ultrasound treatment of the mixture of wheat straw and cattle manure with the following parameters: frequency 24 kHz, temperature 44.30°C, time 21.23 s. This allowed a 49% increase in biogas production. The use of pretreatment would therefore allow the production of more electricity and heat capable of replacing conventional heat sources such as coal. [ABSTRACT FROM AUTHOR]

Harvest residues of sunflower, maize, oilseed rape and soybeans make up more than 50% of the total biomass yield and can also be used to obtain bioenergy. As a source of bioenergy, preference is given to harvesting residues that contain more cellulose and oil, such as soybean straw. Soybean breeding aims to create varieties with higher biomass and increased oil yield per hectare, as well as to create varieties that would be more suitable for industrial processing for the production of technical oils. In this study, the productive parameters of soybeans were investigated in two years, 2021 and 2022. The average yields of soybeans varied from 2.8 t ha-1 (2022) to 2.9 t ha-1 (2022). The total soybean biomass yield was 4.8 t ha-1, while the biogas yield was 384.5 m3 ha-1. The year had a significant impact on soybean production. The more favourable year for production was 2021, with significantly higher yields of grain, biomass and biogas, compared to 2022.

Biogas upgrading is essential in order to increase the calorific value and improve the quality of raw biogas. This present study aims at investigating the optimum performance of a near atmospheric pressure water scrubbing (NAPWS) system for biogas upgrading while using both the adsorption and absorption techniques. This was achieved through a two-stage process: namely, the Taguchi approach followed by the response surface methodology (RSM). The Taguchi orthogonal array design consisted of 27 runs where the raw biogas pressure (10 - 30 kPa), liquid flow rates (2.6 - 4.2 l/ min.) and variations of the steel wool height (0 - 45.72 cm) in the adsorption column were experimentally studied with respect to the methane (CH4) yield and removal efficiency of hydrogen sulfide (H2S) and carbon dioxide (CO2). From the experiments, the removal efficiency of hydrogen sulfide was greater than 87% with the average bio-methane content of 77.67%. During the second-stage, the analysis of variance (ANOVA) and the RSM were undertaken for optimization of the process parameters. The optimum bio-methane concentration of 84.71 (%v/v) CH4 and 13.31 (%v/v) CO2 was attained at gas pressure of 14kPa, liquid flow rate of 4.2 l/min., and steel wool height at 22.86cm obtained through numerical optimization. These results revealed that the utilization of the Taguchi and the RSM yielded to the best optimal system performance with the liquid flow rate as the most significant factor

This study investigated the mesophilic and thermophilic anaerobic fermentation of rape straw with biochar addition. The effects of biochar on the biogas yield, degradation of lignocellulose, bacterial community, and crystallinity were explored. The results showed that the biogas yield and methane content increased as the biochar concentration was increased. The biochar concentration of 5.0% resulted in a high biogas yield in mesophilic and thermophilic anaerobic digestion at 142.2 mL/g and 193.5 mL/g, respectively, which were 40.5% and 21.0% improvements compared with the control. The corresponding methane contents were 59.4% and 57.0%, respectively. For the lignocellulose degradation, the cellulose content in the mesophilic AD decreased from 54.0% in the pretreated rape straw to between 18.7% and 25.0%. The microbial community results showed that as the biochar concentration was increased, the relative abundance of Firmicutes initially increased before it decreased. Among the microbial community results, the relative abundances of Firmicutes and Bacteroides in the biogas residue of the mesophilic anaerobic digestion were the highest in the biogas residue with the 5.0% biochar concentration sample in the mesophilic AD, at 27.06% and 39.20%, respectively. This result revealed the mechanism of biochar to improve the biogas production of rape straw in anaerobic fermentation.

Abstract The harmless disposal and recycling treatment technology of livestock manure has received increasing attention in recent years. In this study, Fe2(SO4)3 was added during anaerobic digestion (AD) of pig manure (PM) to investigate the effects of different doses of Fe2(SO4)3 on biogas yield and heavy metal passivation. The results showed that the highest biogas yield was observed after adding a moderate dose of Fe2(SO4)3 (3%, based on the total solids), while the elevated result was inhibited as the Fe2(SO4)3 dosage increased. The analysis of solid digestate (solid matter remaining after AD) revealed that AD effectively passivated Cu, Zn, and As, which can be further improved with the addition of Fe2(SO4)3. However, the passivated Cd performance during this process was negligible. Furthermore, seed germination index (GI) trial results indicated that Fe2(SO4)3-assisted AD reduced the toxicity of end products to plants. To summarize, AD assisted by the addition of an appropriate amount of Fe2(SO4)3 is feasible to treat PM, and the addition of Fe2(SO4)3 at 3% was the most economic and environmental-friendly. This work could provide useful methods for the control of heavy metal pollution in the soil. Article highlights Adding 3% dose of Fe2(SO4)3 could increase methane yield by 66.76%. Fe2(SO4)3-assisted AD passivated HMs and reduced their bioavailability. The 3% Fe2(SO4)3-assisted AD significantly reduced the toxicity of end products to plants.

This study investigated the effect of enzymatic and hydrothermal pretreatment approaches on the solubilization of organic matter, structure, and biogas yield from microalgal biomass. The soluble chemical oxygen demand (sCOD) concentration increased by 1.21–3.30- and 5.54–6.60-fold compared to control by enzymatic and hydrothermal pretreatments respectively. The hydrothermal pretreatment affected the structural changes in the microalgal biomass markedly; nonetheless, increased enzymatic concentration also had a definite effect on it as determined by qualitative approaches like scanning electron microscopy and Fourier transform infrared spectroscopy. Also, the hydrothermal pretreatment (100 °C for 30 min) resulted in the highest biogas production potential (P) of 765.37 mLg−1 VS at a maximum biogas production rate (Rm) of 22.66 mLg−1 day−1 with a very short lag phase (λ) of 0.07 days. The biogas production of pretreated microalgal biomass particularly at higher enzyme dose (20%, 24 h) and higher hydrothermal pretreatment temperature (120 °C, 30 min) showed a significant but weak correlation (R = 0.53) with sCOD, thus demonstrating that the less organic matter was used up for the biogas production. The modified Gompertz model explained the anaerobic digestion of microalgal biomass more accurately and had a better fit to the experimental data comparatively because of the low root mean square error (3.259–16.728), residual sum of squares (78.887–177.025), and Akaike's Information Criterion (38.605–62.853). [ABSTRACT FROM AUTHOR]

[Display omitted] • AP-CQDs as accelerants is used firstly in the AcoD systems. • Adding 0.36 wt.% AP-CQDs obtains the optimal cumulative CH 4 yield (339.64 mL/g VS). • The digestate with AP-CQDs shows considerable stability and fertility (46.65 g/kg). • AP-CQDs have abundant functional groups and excellent EEC (0.70 μmol e-/g AP-CQDs). • The underlying mechanism of AP-CQDs accelerants in the AcoD system is illustrated. Carbon materials have been widely used in anaerobic digestion (AD), but the role of zero-dimensional carbon quantum dots (CQDs) in anaerobic co-digestion (AcoD) has not yet been reported. In this work, the effect of aloe peel-derived CQDs (AP-CQDs) on the AcoD system of aloe peel and dairy manure was investigated. The addition of AP-CQDs accelerants increased the cumulative CH 4 yield from 201.14 to 266.92–339.64 mL/g VS and increased total chemical oxygen demand removal efficiency from 34.72 % to 48.77–57.87 %. The use of a digestate with 0.36 wt.% of AP-CQDs resulted in a thermogravimetric mass loss of 47.15 % and a promising total nutrient content of 46.65 g/kg. The excellent electron exchange capacity of AP-CQDs may facilitate direct interspecies electron transfer during the AD process. Moreover, the use of AP-CQDs can enrich methanogenic microorganisms (Methanosarcina and Methanobacterium). These findings provide a viable strategy for improving methane production and create awareness regarding the dual use of biomass waste. [ABSTRACT FROM AUTHOR]

The paper presents research on the impact of adding various forms of sorghum to sewage sludge on the anaerobic digestion process. The use of liquid sewage sludge alone in biogas plants at wastewater treatment plants is inefficient due to the low total solid (dry matter) content of this substrate. The tests revealed that the production of methane in biogas is low and amounted to 17.9% (105.4 Nm3∙Mg−1, VS—volatile solid). Therefore, other substrates should be blended with sewage sludge to increase the total solid of the batch. Sorghum silage, sorghum pomace, and sorghum juice were added to the sewage sludge in various proportions during the research. As a result, the improvement of the biogas process, the stabilization of the biogas production curve, as well as the increase in methane yield were observed. The most biogas and methane were obtained from a mixture of sorghum juice (5%) and sewage sludge (664.8 Nm3∙Mg−1 VS and 53.9%, respectively). Biogas production from other substrates based on sorghum and sewage sludge ranged from 457.4 to 588.8 Nm3∙Mg−1 VS. For a mixture of juice (7%) and sewage sludge, the batch was acidified, and biogas production was only 281.5 Nm3∙Mg−1 VS. Studies have shown that intelligent blending of an alternative raw material (compared to traditional maize silage) with sewage sludge allows for similar biogas yields while maintaining a stable anaerobic digestion process. [ABSTRACT FROM AUTHOR]

To overcome the anthropogenic impacts resulting from the constant growth of the world population, industries like wastewater treatment plants and food processing must be adapted to follow this tendency and suppress the associated challenges and needs arising from this global situation. In the context of the circular economy, optimising the biogas produced in the anaerobic digesters during sludge stabilisation is fundamental to ensure the energy self-sufficiency of wastewater treatment plants. The anaerobic co-digestion of two or more substrates is a viable option to overcome the drawbacks of mono-digestion and to improve methane production. Considering the economic viability of the anaerobic digestion system, it is of major importance to address the potential of the spare capacity existing in the anaerobic reactors by incorporating readily biodegradable wastes.This review compiles the works published between 2015 and 2023 regarding the anaerobic co-digestion of municipal sewage sludge with fruit and vegetable wastes, presenting a critical analysis of the gaps and future perspectives on this topic. The results demonstrated the effectiveness of co-digestion to correct imbalances from mono-digestion, and in some works, mono-digestion of fruit and vegetable wastes obtained higher biogas yields than the mono-digestion of municipal sewage sludge. For instance, the increment in biogas production varied from around 4 up to 500% when comparing mono-digestion with co-digestion trials. In two studies, the biogas production from fruit and vegetable wastes was 13 and 94% higher than in the trials with only municipal sewage sludge. Multi-stage systems enhanced anaerobic digestion due to the improvement in the early stages of the process, namely the hydrolysis which is usually the limiting phase. A significant number of the experimental trials (9 out of 20 studies) were performed in batch reactors due to easy operation and maintenance, revealing the gap of studies with other types of reactors like the continuous stirred tank reactor, which is the most used in wastewater treatment plants. The reduced number of articles within this scope (20) demonstrates that there is still potential to improve the knowledge and fill in the existing gaps, aiming to increase the energetic self-sufficiency of wastewater treatment plants.

The study aims to examine biogas-aerating recirculation on biomethanation in a farm-scale digester with water hyacinth substrate. The experiment was conducted with the difference in biogas-aerating times and frequencies. Methane yield considerably improved by 27.44–52.12%, 50.19–62.30% and 63.11−71.46% for aerating biogas from 15 to 60 minutes at once, twice and four-time d−1, respectively. Maximum biogas yields were estimated for biogas-aerating at once, twice, and four daily repetitions at 47.8, 78.0, and 145 minutes. Biogas-aerating 30 minutes at twice d−1 and 15–60 minutes at four-time d−1 displayed great potential for biogas production augmentation.

Globally, the production of municipal solid waste is rising annually because of consumerism and the urbanization process. In the past few years, different researchers have explored strategies for generating biogas from various organic wastes. In this study, kitchen waste and municipal solid waste were characterized by several physical-chemical parameters. Ten of these substrates were mono-digested for biogas production in batch reactors where cabbage showed a 96.36 ± 1.73% volatile solid and biogas yield of 800 ± 8.8 mL within 10 days, while cooked rice had an 83.00 ± 1.49% volatile solid, and a biogas yield of 2821 ± 31.03 mL within 28 days. The CN ratio for cabbage and cooked rice waste was 13.9 and 30.9 respectively, whereas their pH values were 6.2 and 7.2. Based on the characterization and biogas yields attained, cooked rice waste could be mono-digested for biogas production and no published work showed a high yield as the current study while the other substrates require co-digestion to improve the biogas yield.

Fuzzy Mamdani Model (FMM), Artificial Neural Network (ANN), and Response Surface Methodology (RSM) models were adopted to model and optimise biogas production on assorted substrates of poultry wastes (PW) and cow dung in a modular biodigester system. The gas produced at retention time of 42 days was within the range of 50 to 52 ml/day. The temperature range was between the range of 20 and 40 °C, while the pH values were stable at optimal range of 8.0. The statistical analysis of the experimental result obtained from methane yield, using different computational technique, reveals that fuzzy Mamdani model reflect zero (0) values for average absolute deviation (AAD), mean average error (MAE), standard error of prediction (SEP), and root-mean-square error (RMSE) and average coefficient of determination (R2) of one (1.0). ANN result obtain showed AAD value of 0.00011991, MAE value of 0.000061538, SEP value of 0.0000044369, and RMSE value of 0.00022188 and R2 value of 1.0, and RSM result reveals absolute AAD of 0.0030, MAE of 0.0015, SEP of 0.00011092, RMSE of 0.0055, and R2 of 0.9998. It can be concluded from the result of the analysis that RSM gave a good prediction of the model while ANN and FMM models produced slightly better results. The result obtained from the FMM model seems marginally better and superior in terms of forecasting of biogas and methane production rate with satisfactory outcome. [ABSTRACT FROM AUTHOR]

In this study, predominant bacterial and archaeal populations and their roles during anaerobic mono-digestion of food waste (FW) and co-digestion of FW with straw pellets (SP) at thermophilic temperature (53 ± 1 °C) were assessed by Next Generation Sequencing (NGS) analysis at organic loading rates (OLRs) of 3.0 and 7.0 gVS/L/d. Depending on the seed; results revealed that Firmicutes, Bacteroidetes, and Proteobacteria were, respectively the most prevalent bacterial phyla at both OLRs investigated. On the other hand, Euryarchaeota was dominated by methanogens playing crucial role in biogas production and correlated mainly with the activities of Methanobacteria and Methanomicrobia at class level. Acetoclastic Methanosaetae was the predominant genus at OLR = 3.0 gVS/L/d; however, shared the same predominance with hydrogenotrophic methanogens Methanospirillium at the highest OLR. Although no clear effect in response to straw addition at OLR of 3.0 gVS/L/d could be seen in terms of methanogenic archaea at genus level, hydrogenotrophic methanogens revealed some shift from Methanobacterium to Methanospirillium at higher OLR. Nevertheless, no prominent microbial shift in the presence of wheat straw at increased OLR was likely due to adapted inoculation at start-up which was also demonstrated by relatively stable biogas yields during co-digestion. [ABSTRACT FROM AUTHOR]

Biogas upgrading is essential in order to increase the calorific value and improve the quality of raw biogas. This present study aims at investigating the optimum performance of a near atmospheric pressure water scrubbing (NAPWS) system for biogas upgrading while using both the adsorption and absorption techniques. This was achieved through a two-stage process: namely, the Taguchi approach followed by the response surface methodology (RSM). The Taguchi orthogonal array design consisted of 27 runs where the raw biogas pressure (10 - 30 kPa), liquid flow rates (2.6 - 4.2 l/ min.) and variations of the steel wool height (0 - 45.72 cm) in the adsorption column were experimentally studied with respect to the methane (CH4) yield and removal efficiency of hydrogen sulfide (H2S) and carbon dioxide (CO2). From the experiments, the removal efficiency of hydrogen sulfide was greater than 87% with the average bio-methane content of 77.67%. During the second-stage, the analysis of variance (ANOVA) and the RSM were undertaken for optimization of the process parameters. The optimum bio-methane concentration of 84.71 (%v/v) CH4 and 13.31 (%v/v) CO2 was attained at gas pressure of 14kPa, liquid flow rate of 4.2 l/min., and steel wool height at 22.86cm obtained through numerical optimization. These results revealed that the utilization of the Taguchi and the RSM yielded to the best optimal system performance with the liquid flow rate as the most significant factor. [ABSTRACT FROM AUTHOR]

A statistical-based regression approach and machine learning (ML) algorithms (response surface methodology (RSM), feed-forward backpropagation artificial neural network (ANN) and multi-layer adaptive neuro-fuzzy inference system (ANFIS)) were explored for the optimization and prediction of biogas resulting from the anaerobic digestion (AD) of pretreated Ulva Intestinalis Linnaeus (UIL). ANFIS model was found to better predict and model the process of biogas production from the AD of pretreated UIL owing to low mean square error (MSE) and RMSE values (0.8841 and 0.9402-US, 0.9628 and 0.9812-O 3 , 0.1387 and 0.3724-MW and 0.3018 and 1.1410-Fe 3 O 4) and highest values of R2 (0.9998-US, 0.9996-O 3 , 0.9996-MW and 0.9995-Fe 3 O 4). Optimum conditions for biogas yield as a result of the various pretreatment processes based on the ANFIS model were US-15 power/time, time-40 min and the biogas yield-181.0 mL.gVS−1, O 3 -15.0 mg/min, time-40.0 min and biogas yield of 164.0 mL.gVS−1, MW-2.3 power/time, time-40.0 min and biogas yield-81.7 mL.gVS−1 and Fe 3 O 4 -20.0 mg L−1, time-40.0 min and biogas yield-154 mL.gVS−1. The results obtained show that the ML and statistical-based models were effective in approximating the biogas yield with high precision and low error and could be beneficial for the biogas production scale-up process. [Display omitted] • RSM, ANN and ANFIS models were explored for biogas production. • The biogas yield was predicted based on the low MSE and RMSE values and high R2 values. • The ANFIS model best modelled the pretreatment of UIL for obtaining biogas yield. • A prediction model with high precision and low error could be effective for the biogas production scale-up. [ABSTRACT FROM AUTHOR]

[Display omitted] • pH 11 is the most suitable pH value for the thermal alkaline process (TAP). • Biogas yield of PS after TAP at pH 11 could increase up to 81%. • Biogas yield of WAS after TAP at pH 11 increased up to 72%. • Net electricity generation of WAS after TAP at pH 11 improved up to 43%. • The results are transferable along the 7 WWTPs, and a model WWTP investigated. Because of the naturally limited anaerobic degradability and limited biogas yield of raw sludge (RS), this study aims to increase the biogas production of primary sludge (PS) and waste activated sludge (WAS) by the integration of thermal alkaline process (TAP). PH 11 is confirmed to be the most suitable pH value for the TAP of both sludges. Moreover, with the pretreatment at pH 11 and 160 °C (6 bar) for 30 min, the investigated PSs and WASs achieved an increased biogas production of up to 81 % and 72 %, respectively. The improved net electricity production of WASs after TAP varied between 15–43 % compared to conventional WAS digestion. However, the TAP of PS at pH 11 enhanced the biogas production by 1–81 %, which did not constantly contribute to an improved net electricity production. [ABSTRACT FROM AUTHOR]

Abstract Semi‐natural lowland and mountain mesic meadows are grasslands rich in species, and their conservation status depends on treatments such as mowing or grazing livestock. In many countries, the condition of grasslands is deteriorating because of their inappropriate use or abandonment. This study aimed to determine the effects of the species composition of plant communities and functional plant groups on the methane yield from biomass harvested from mesic grasslands in the Sudetes Mountains. Biogas potential analysis was performed based on biomass samples collected from Poland and the Czech Republic. The biogas potential was determined in 40 day‐long batch anaerobic digestion tests. The average methane yield obtained from the biomass was 246 ± 16 NL CH4 kg−1 VS, whereas the methane yield per hectare was 870 ± 203 m3 CH4 ha−1. Plant communities comprising different dominant species had no effect on the methane yield but affected the methane yield per hectare. Additionally, the species composition of grasslands with a higher percentage of forbs had lower biomass yield, resulting in lower methane yields per hectare. The continuity of the low‐intensity management of mountain grassland, which can be provided by the utilization of their biomass for bioenergy production, sustains high biodiversity and ensures appropriate meadow conservation.

Biogas yield in anaerobic digestion (AD) involves continuous and complex biological reactions. The traditional linear models failed to quantitatively assess the interactive effects of these factors on AD performance. To further explore the internal relationship between target variables and AD performance, this study developed four machine learning models to predict biogas yield and consider the interaction among various factors. Results indicated that the highest prediction accuracy of AD performance was achieved by adding bacterial genera dataset with environmental factors. Random forest model exhibited the highest accuracy, with the testing coefficient of determination equal to 0.9879. Among two types of input features, the bacterial genera accounted for 89.9 % of the impact on biogas yield, followed by environmental factors. The results revealed Keratinibaculum and Acetomicrobium as critical bacteria. The volatile fatty acid controlled below 2000 mg/L and the improved stirring system in AD process were recommended to achieve maximum biogas yield., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Poultry wastes (PW) and palm oil mill effluents (POME) are thought to be promising starting materials for biogas production. In the present study, the optimization of biomethanization process from co-digested (PW) and POME was investigated. To assist digestion, samples were sun-dried, ground, and mixed with water to form slurry. The central composite design was used in the experimental design, while the desirability function was applied in the process optimization of the co-digestion process. The interactive effects of temperature, pH, and hydraulic retention time were equally studied. The results showed a high co-efficient of determination (R2) value of 0.9920. Also, the predicted and experimental values obtained were 4377.71 ml and 4379.01 respectively, while the optimum conditions obtained were 45 °C, 8.00 and 15 days for temperature, pH, and hydraulic retention time, respectively. This finding shows that the proposed technique is effective and robust in predicting biomethane generation from co-digested POME and PW.

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

Biogas is one of the renewable energy resources produced from the anaerobic fermentation of biomass. About 60% of Pakistan population live in rural areas that demand energy source for domestic and commercial use. Therefore, biogas plants can be used as one of the renewable energy sources in Pakistan. This paper described the development and performance evaluation of small size household portable biogas plant. The lightweight double-ply polypropylene material is used to fabricate the biogas plant, which is durable and easily portable. The volume of the digester was 2.15 m3, and the gasholder volume was 0.84 m3. The performance of the developed plant and biogas production is verified by three different treatments of feeding materials, i.e., buffalo dung (BD), buffalo dung plus sheep waste (BD + SW), and buffalo dung plus chicken droppings (BD + CD). The maximum biogas productions for treatments BD, BD + CD and BD + SW were recorded 0.59 m3/kg-VS, 0.61 m3/kg-VS, and 0.79 m3/kg-VS, respectively. The AMPTS was also conducted to compare total methane production. The nutrient analysis performed for both substrate and slurry showed improved nutrient quantity in the slurry. The cost estimation cleared that fixed biogas plants have 1.27 times more costly than that of portable biogas plants. The developed biogas plant is favorable for its light in weight and low cost, and it can produce enough methane gas to fulfill the domestic requirements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermally pretreated harvest residues and manure were anaerobically co-digested. • Four machine learning methods were tested for biogas and methane yield prediction. • Recursive Feature Elimination was the optimal feature selection approach. • R2 for biogas and methane yield prediction was up to 0.820 and 0.823, respectively. • An ensemble machine learning produced stable accuracy regardless of input datasets. This study aimed to clarify the statistical accuracy assessment approaches used in recent biogas prediction studies using state-of-the-art ensemble machine learning approach according to 10-fold cross-validation in 100 repetitions. Three thermally pretreated harvest residue types (maize stover, sunflower stalk and soybean straw) and manure were anaerobically co-digested, measuring biogas and methane yield alongside eight thermal preprocessing and biomass covariates. These were the inputs to an ensemble machine learning approach for biogas and methane yield prediction, employing three feature selection approaches. The Support Vector Machine prediction with the Recursive Feature Elimination resulted in the highest prediction accuracy, achieving the coefficient of determination of 0.820 and 0.823 for biogas and methane yield prediction, respectively. This study demonstrated an extreme dependency of prediction accuracy to input dataset properties, which could only be mitigated with ensemble machine learning and strongly suggested that the split-sample approach, often used in previous studies, should be avoided. [ABSTRACT FROM AUTHOR]

The highly toxic species common ragwort (Jacobaea vulgaris Gaertn.) prefers to migrate into protected dry grassland biotopes and limits the use of the resulting biomass as animal feed. There is an urgent need for a safe alternative use of the contaminated biomass apart from landfill disposal. We investigated the optional utilization of biomethanization of fresh and ensiled common ragwort biomasses and evaluated their energetic potentials by estimation models based on biochemical characteristics and by standardized batch experiments. The fresh and ensiled substrates yielded 174 LN∙kg−1 oDM methane and 185 LN∙kg−1 oDM, respectively. Ensiling reduced the toxic pyrrolizidine alkaloid content by 76.6%; a subsequent wet fermentation for an additional reduction is recommended. In comparison with other biomasses from landscape cultivation, ragwort biomass can be ensiled readily but has a limited energy potential if harvested at its peak flowering stage. Considering these properties and limitations, the energetic utilization is a promising option for a sustainable handling of Senecio-contaminated biomasses in landscape conservation practice and represents a safe alternative for reducing pyrrolizidine alkaloid entry into the agri-food sector. [ABSTRACT FROM AUTHOR]

A shift from a linear economy to a circular economy of resource consumption is vital for diverting the value from lost resources to resource-efficient products towards developing a sustainable system. Household digesters provide one opportunity to create a biogas-based circular economy. Because household digesters are typically fed a wide and variable range of substrates, it is important to determine the ideal mixing ratios for them. In this study, an anaerobic digester startup process was analyzed and an assessment of anaerobic co-digestion of food waste with different livestock manures was carried out at ambient temperatures. Food waste (FW), cow manure (CM), poultry litter (PL) and goat manure (GM) were co-digested at mixing ratios (FW:PL:CM) of 2:1:1, 2:2:1, 1:1:2, 1:1:1 (wt/wt) and FW:PL:GM at mixing ratios of 2:1:1 and 1:1:2, at an organic loading rate of 1 g volatile solid (VS)/L/day, and 8% total solids. A maximum methane yield was obtained from co-digestion of FW:PL:GM at a mixing ratio of 2:1:1 in autumn-to-winter conditions, 21–10 °C, while the mixing ratio of FW:PL:CM at 2:2:1, showed negligible methane production under the same temperature condition. This study suggests that co-digestion of food waste and poultry litter with goat manure yields more biogas than other substrate combinations. Therefore, selecting suitable co-substrates with an optimized mixing ratio can promote several key indicators of a biogas-based circular economy towards achieving sustainable development goals 2, 3, 5, 6, 7, 9, 13 and 15. [ABSTRACT FROM AUTHOR]

BACKGROUND The accumulative municipal solid waste (MSW) production calls for emerging efficient technology for its handling. Anaerobic digestion (AD) of MSW provides effective waste volatilization. The high C/N ratio of MSW and increasing organic loading rates (OLRs) are central AD restrictions that affect the AD process performance, inhibition due to aggregation of volatile fatty acids (VFAs), and rapid fall in pH. RESULTS: This study examines the consequence of OLRs on AD of MSW with a high C/N ratio of 406 in food waste (FW) to have a balanced C/N ratio of 30. Three batch scale digesters investigate under mesophilic conditions (35 °C) with OLRs of 10, 15, and 20 gVS L−1 to assess the digester performance and stability in biogas yield, methane yield, and volatile solids (VS) reduction. The cumulative biogas and methane yield are observed to be 1336 and 776 mL gVS−1, respectively, with a VS reduction rate of 78%, at 10 gVS L−1. VFA/alkalinity ratio ranges from 0.02 to 0.01 at OLR of 10 and 15 gVS L−1, which designates a higher buffering capability of the digester. While VFA/alkalinity ratio of 0.48 observes at OLR of 20 gVS L−1. A rapid deprivation in digester performance and stability finds at ORL of 15 and 20 gVS L−1. The cumulative biogas yield and methane yield decrease with the increase in OLR from 10 to 20 gVS L−1. CONCLUSION: This study provided sufficient information for better AD processes and operational circumstances that are an optimum and effective method to convert organic matter to biogas fuel. © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The circular economy offers a new product-waste-product model, in this case obtaining biofuels from rye biomass. The circular economy introduces a new product design, which will enable its functionality for a longer period of use. Secale cereale L. is an economically important crop for food, feed and bioenergy. The objective of this study was to estimate productivity of rye genotypes and the possibility of obtaining biogas from rye biomass during two growing seasons, 2019-2020. The aim of this study was to examine the influence of year and genotype on rye productivity parameters, biogas, methane yield, methane proportion, and the possibility of using rye as an alternative fuel in Serbia. The influence of the year and genotypes on the parameters of rye productivity, biogas and methane yield, methane content and the possibility of using rye as an alternative fuel in Serbia was investigated. Genotype and year × genotype interaction had a statistically significant effect on biogas yield, methane yield and methane content in the studied rye genotypes. Genotype G1 had the mean of green biomass yield (25.73 t ha-1) significantly higher compared to genotype G2 (23.75 t ha-1) in both years of experiment. Green biomass yield (24.11 t ha-1) was better in 2019 compared to 2020. Biogas yield varied from 260.57 m3 ha-1 (genotype G1) to 214.58 m3 ha-1 (genotype G2). Biogas yield were better in 2019 (237.85 m3 ha-1) compared to 2020 (237.30 m3 ha-1). A positive statistically highly significant correlation was attained between the green biomass yield and the length of the spikes (0.82**), green biomass yield and biogas yield (0.93**), green biomass yield and methane content (0.90**). [ABSTRACT FROM AUTHOR]

Semi‐natural lowland and mountain mesic meadows are grasslands rich in species, and their conservation status depends on treatments such as mowing or grazing livestock. In many countries, the condition of grasslands is deteriorating because of their inappropriate use or abandonment. This study aimed to determine the effects of the species composition of plant communities and functional plant groups on the methane yield from biomass harvested from mesic grasslands in the Sudetes Mountains. Biogas potential analysis was performed based on biomass samples collected from Poland and the Czech Republic. The biogas potential was determined in 40 day‐long batch anaerobic digestion tests. The average methane yield obtained from the biomass was 246 ± 16 NL CH4 kg−1 VS, whereas the methane yield per hectare was 870 ± 203 m3 CH4 ha−1. Plant communities comprising different dominant species had no effect on the methane yield but affected the methane yield per hectare. Additionally, the species composition of grasslands with a higher percentage of forbs had lower biomass yield, resulting in lower methane yields per hectare. The continuity of the low‐intensity management of mountain grassland, which can be provided by the utilization of their biomass for bioenergy production, sustains high biodiversity and ensures appropriate meadow conservation. [ABSTRACT FROM AUTHOR]