Search Results (118)

Pig slurry (PS) and wine vinasse (WV) pose environmental risks if not properly managed. Their composition makes them suitable for anaerobic co-digestion (AcoD), enhancing biomethane production and improving organic matter degradation efficiency. This research applies an innovative Design of Experiments (DoE) approach—specifically the Box–Behnken design (BBD)—to systematically optimize the AcoD process, surpassing traditional single-factor methods by efficiently evaluating the interactions. Variables such as temperature (35 °C, 52.5 °C, 70 °C), substrate ratio (25PS:75WV, 50PS:50WV, 75PS:25WV) and pH (7, 7.5, 8) were tested using a Box–Behnken design which studied the correlations between the experimental data and the model. In fact, the results showed that temperature, ratio, and their interaction significantly influenced biomethane production, being the pH the factor with the least influence on the response. Optimal conditions—pH of 8, temperature of 35 °C and a 50:50 substrate ratio—achieved a biomethane yield of 487.94 CH₄/gVS (Volatile Solids). These results demonstrate the effectiveness of the DoE methodology in maximizing biomethane production and represent a significant advancement in valorizing wastes from pig farms and wineries, promoting a circular and sustainable economy. Full article

Anaerobic digestion (AD) offers a sustainable solution by treating biodegradable waste while recovering bioenergy, enhancing the share of renewable energy. Thus, this study aims to investigate the AD for managing and valorizing residues from the potato chip industry: potato peel (PP), potato offcuts (OC), waste cooking oil (WCO), wastewater (WW), and sewage sludge (SS). In particular, the biochemical methane potential (BMP) of each residue, anaerobic co-digestion (AcoD), and greenhouse gas (GHG) emissions of an AD plant are assessed. WW, OC, and SS present a BMP of around 232–280 NmL_CH4/kg of volatile solids (VS). PP and WCO reach a BMP slightly lower than the former substrates (174–202 NmL_CH4/g_VS). AcoD results in methane yields between 150 and 250 NmL_CH4/g_VS. An up-scaled anaerobic digester is designed to manage 1.60 Mg/d of PP. A residence time of 12 days and a digester with 165 m³ is estimated, yielding 14 Nm³_CH4/Mg_VS/d. A simulated AD plant integrated with a combined heat and power unit results in a carbon footprint of 542 kg of CO₂-eq/Mg_db PP, primarily from biogenic GHG emissions. These findings highlight the potential of AD to generate renewable energy from potato industry residues while reducing fossil fuel-related GHG emissions and promoting resource circularity. Full article

This study evaluates the potential of spent coffee grounds (SCGs) as a co-substrate to improve anaerobic co-digestion (AcD) performance, with a focus on biogas yield, methane (CH₄) content, and the removal of volatile solids (VS) and total chemical oxygen demand (TCOD). Biochemical methane potential (BMP) tests were conducted in two stages. In Stage I, SCGs were blended with active sludge (AS) and the organic fraction of municipal solid waste (OFMSW) at varying ratios. The addition of 25% SCGs increased biogas production by 24.47% (AS) and 20.95% (OFMSW), while the AS50 mixture yielded the highest methane yield (0.302 Nm³/kg VS, 66.42%). However, SCG concentrations of 75% or higher reduced process stability. In Stage II, we evaluated the impact of mixing. The AS25 configuration maintained stable biogas under varying mixing conditions, showing system resilience, whereas OFMSW25 showed slight improvement. Biogas production kinetics were modeled using modified Gompertz, logistic, and first-order equations, all of which demonstrated high predictive accuracy (R² > 0.97), with the modified Gompertz model offering the best fit. Overall, SCGs show promise as a sustainable co-substrate for the improvement of methane recovery and organic matter degradation in AcD systems when applied at optimized concentrations. Full article

Organic wastes from households, private gardens, the maintenance of urban greenery, and active nature conservation measures are often difficult to manage. This lignocellulosic biomass may be suitable for anaerobic digestion (AD). However, the mono-digestion of plant material, such as waste from active conservation measures for wetlands, results in a low methane (CH₄) yield. The aim of this study was to assess the feasibility of using common reed silage for co-digestion with plant-based biowaste from households. The specific methane yield (SMY) was determined in biochemical methane potential (BMP) tests performed on biowaste, reed silage, and combinations of reed silage with 10%, 30%, 50%, 70%, and 90% of biowaste on a fresh weight basis. The lowest SMY was observed for the mono-digestion of reed silage (160.40 ± 4.09 NL kg_VS⁻¹), while biowaste had the highest CH₄ yield (284.03 ± 7.03 NL kg_VS⁻¹). The subsequent addition of biowaste enhanced CH₄ production from 158.57 ± 7.88 NL kg_VS⁻¹ (10% of biowaste) to 233.28 ± 11.91 NL kg_VS⁻¹ (90% of biowaste). A key advantage of biogas production is its role in reducing CO₂ emissions into the atmosphere, which result from the use of conventional fuels for energy generation. The avoided CO₂ emissions generated in electricity and heat production range between 378.62 kgCO₂ t_TS⁻¹ and 676.36 kgCO₂ t_TS⁻¹ depending on the reed silage-to-biowaste ratio used for biogas production. This study reveals that reed silage is not an optimal feedstock for biogas production, and its share in co-digestion with biowaste should not exceed 10% of the total input to the biogas plant. Full article

In this study, five distinct industrial waste streams, encompassing bakery processing and kitchen waste (BP plus KW) mixture, fat, oil, and grease (FOG), ultrafiltered milk permeate (UFMP), powder whey (PW), and pulp and paper (PP) compost, underwent mesophilic biochemical methane potential (BMP) assays at F/M ratios of 1, 2, 4, and 6 g COD/g VSS. An F/M ratio of 1 g COD/g VSS showed the highest methane yield across the investigated feedstocks. In the case of UFMP and PW, an F/M ratio of 2 produced identical results to an F/M ratio of 1 despite their relatively high carbohydrate content which is easily acidified to VFAs. Increasing the F/M ratio to 2 decreased the biodegradability of both BP plus KW and FOG by 63%. Increasing the F/M ratio of the PP did not show as much of a significant impact on biodegradability compared to the other feedstocks as methane yields decreased from 135 to 92 mL CH₄/g COD, a decrease of 32%. Full article

Fallen leaves in cities are often treated as waste; therefore, they are collected, transported outside urban areas, and composted, which contributes to greenhouse gas (GHG) emissions. Instead of this conventional management approach, fallen leaves could be utilized as a feedstock in biogas production, helping to reduce GHG emissions, increase renewable energy generation, and provide fertilizer. The aim of this study was to compare the mono-digestion of fallen leaves from three tree species commonly found in parks and along streets—northern red oak (Quercus rubra L.), small-leaved lime (Tilia cordata Mill.), and Norway maple (Acer platanoides L.)—in both wet and dry anaerobic digestion (AD) systems. A biochemical methane potential (BMP) test was conducted in batch assays for each of the three substrates in both AD technologies at a temperature of 38 ± 1 °C. The highest specific methane yield (SMY) was obtained from Quercus leaves in wet AD technology, with a methane yield of 115.69 ± 4.11 NL kg_VS⁻¹. The lowest SMY (55.23 ± 3.36 NL kg_VS⁻¹) was observed during the dry AD of Tilia leaves. The type of technology had no significant impact on the SMY of Acer and Tilia leaves; however, the methane yield from Quercus leaves in wet AD was significantly higher (p < 0.05) than that from dry AD. Studies on the use of fallen leaves from Tilia cordata, Quercus rubra, and Acer platanoides as substrates in mono-digestion technology have shown their limited suitability for biogas production. Nevertheless, this feedstock may be more effectively used as a co-substrate, mainly due to the low concentrations of ammonia (NH₃) and hydrogen sulfide (H₂S) in the biogas produced from these leaves, both of which are considered inhibitors of the AD process. Full article

Organic waste has the potential to produce methane gas as a substitute for petrol-based fuels, while reducing landfilling and possible environmental pollution. Generally, anaerobic digestion (AD) is used only in wastewater treatment plants as a tertiary stage of sewage sludge treatment, generating a fraction of the energy that such process plants require. In this study, four different wastes—food waste (FW), dairy industry waste (DIW), brewery waste (BW), and cardboard waste (CBW)—were tested for biogas production. The biochemical methane potential (BMP) of each sample was evaluated using an automatic methane potential system (AMPTS). Operating parameters such as pH, temperature, total solids, and volatile solids were measured. Experiments on the anaerobic digestion of the samples were monitored under mesophilic conditions (temperature 37 °C, retention time 30 days). Specific methane yields (SMYs), as well as the theoretical methane potential (BMPth), were used to calculate the biodegradability of the substrates, obtaining the highest biodegradability for BW at 95.1% and producing 462.3 ± 1.25 NmL CH₄/g volatile solids (VS), followed by FW at an inoculum-to-substrate ratio (ISR) of 2 at 84% generating 391.3 NmLCH₄/g VS. The BMP test of the dairy industry waste at an inoculum-to-substrate ratio of 1 was heavily inhibited by bacteria overloading of the easily degradable organic matter, obtaining a total methane production of 106.3 NmL CH₄/g VS and a biodegradability index of 24.8%. The kinetic modeling study demonstrated that the best-fitting model was the modified Gompertz model, presenting the highest coefficient of determination (R²) values, the lowest root means square error (RMSE) values for five of the substrates, and the best specific biogas yield estimation with a percentage difference ranging from 0.3 to 3.6%. Full article

Biodegradable organic waste offers significant opportunities for resource recovery within the frame of the circular economy. In this work, the effects of carbon-encapsulated iron nanoparticles and ozone pre-treatments in the mesophilic methanogenic stage of a temperature-phased an-aerobic digestion have been studied using biochemical methanogenic potential (BMP) tests and modeling simulation. To do that, digestates from a pre-treated thermophilic acidogenic reactor that co-digested sludge and wine vinasse were used. The addition of nanoparticles favored the removal of particulate matter, which increased by 9% and 6% in terms of total solids and volatile solids, respectively. When combined with ozone pre-treatment, these increases were 27% and 24%, respectively, demonstrating enhanced AD efficiency. The dose of iron nanoparticles encapsulated in carbon did not result in a statistically significant increase in methane production when sludge and vinasse were used as feedstock. The combination of nanoparticles with the ozone pre-treatment significantly improved the methanogenic phase of the second stage, increasing the methane production yield by 22% and reducing the lag phase from 10 days to 3 days, according to the modified Gompertz model. Full article

This study explores the potential of biochar derived from microwave-assisted catalytic pyrolysis of solid digestate as an additive to enhance the stability and performance of the anaerobic digestion process. The focus was placed on the effects of biochar dosage, pyrolysis temperature, and pyrolysis catalyst on methane production. Biochemical methane potential (BMP) tests using synthetic food waste as the substrate revealed a dosage-dependent relationship with specific methane yield (SMY). At a low biochar dosage of 0.1 g/g total solids (TS), improvement in methane (CH₄) production was marginal, whereas a high dosage of 0.6 g/g TS increased CH₄ content by at least 10% and improved yield by 35–52%. ANOVA analysis indicated that biochar dosage level significantly influenced CH₄ yield, while pyrolysis temperature (400 °C vs. 500 °C) and catalyst (20 wt% K₃PO₄ vs. 10 wt% K₃PO₄/10 wt% clinoptilolite) did not lead to significant differences in CH₄ yield between the treatments. Correlation analysis results suggested that biochar’s most impactful properties on methane yield would be dosage-adjusted specific surface area (or total surface area per unit volume of substrate) and aromaticity index. The findings underscore the potential of solid-digestate-derived biochar as a beneficial additive for anaerobic digestion and hence the sustainability of food waste management system. Full article

This study explores the potential of food waste-recycling wastewater (FRW) for biogas production, emphasizing oil–water separation before anaerobic digestion. Three FRW samples were analyzed: non-treated (FRW), water–oil separated (FRW_sep), and mixed with domestic sewage (FRW_mix). Physicochemical characterization showed a 26% reduction in crude lipid content after oil–water separation. The biochemical methane potential (BMP) tests revealed similar methane yields for FRW_sep and FRW_mix compared to non-treated FRW. Microbial analysis identified Firmicutes and Methanoculleus as active populations. Energy balance suggests that combining biodiesel and biogas production can enhance net energy recovery. This research indicates that oil–water separation in FRW treatment can optimize anaerobic digestion, contributing to sustainable waste management and renewable energy generation. Full article

In this study, the optimum mixing ratio of food waste (FW) and livestock manure (LM) was investigated to improve the methane yield efficiency and prohibit the inhibition factors (organic loading rate and NH₄⁺) from inhibiting the anaerobic co-digestion of FW and LM under mesophilic and thermophilic conditions. The research involved the following: (I) the analysis of the characteristics of FW and LM, (II) the evaluation of the potential and toxicity of the anaerobic digestion of I have confirmed that there is no problem. FW and LM using the biochemical methane potential (BMP) and anaerobic toxicity assay (ATA) tests, (III) the evaluation of the anaerobic co-digestion of FW and LM using the BMP test, and (IV) the evaluation of the optimum mixing ratio using mathematical modeling. The characteristics of FW and LM were analyzed to evaluate the theoretical methane potential and inhibition factor. The BMP test was carried out to evaluate the concentration of the biodegradable organic matter, biogas production rate, and methane yield. The ATA test was carried out to evaluate the impact of the inhibition concentration. Ultimately, mathematical models, such as a first-order reaction and a modified Gompertz model, were implemented to evaluate the optimum mixing ratio for the anaerobic co-digestion of FW and LM. FW had a higher concentration of degradable organic matter than LM. The initial operational parameters of the anaerobic digestion were determined to be appropriate at an organic matter concentration of less than 2.5 g/L and a TN concentration of 2,000 mg/L. In conclusion, as a result of evaluation through mathematical models, it was determined that anaerobic microorganisms were more sensitive to inhibitory factors under the thermophilic condition than under the mesophilic condition, and the optimum mixing ratio of FW to LM was 5:1 (vol:vol) based on kinetic results (k: 0.080; B_u: 0.23 L CH₄/g VS_added; P: 100.84 mL; R_m: 10.23 mL/day; λ: 1.44 days). Full article

In this study, the impact of bioplastic design on anaerobic digestion for biogas production was investigated. This research aims to facilitate the integration of bioplastics into a circular economy, which is why our study proposes considering not only aspects related to their degradation in the formulation but also ensuring efficient behavior in anaerobic digestion plants. Thermoplastic starch (TPS) samples, derived from different starch sources and formulated with varying concentrations of calcium carbonate and thicknesses, were subjected to anaerobic digestion tests. Three key parameters were explored: the influence of filler concentration, the effect of sample thickness, and the role of starch origin. Biogas production and kinetics were assessed using biochemical methane potential (BMP) tests. The results reveal that calcium carbonate concentration negatively influenced the methane production rate, reaching 30 NmL/gVS/day for the filler-free sample, highlighting the importance of understanding filler effects on anaerobic digestion. Additionally, thicker samples exhibited slower biogas production, with a rate of 25 NmL/gVS/day compared to 30 NmL/gVS/day for the thinnest sample, emphasizing the relevance of sample thickness in influencing digestion kinetics. The starch origin did not yield significant differences in biogas production, providing valuable insights into the feasibility of using diverse starch sources in bioplastic formulations. This study enhances our understanding of bioplastic behavior during anaerobic digestion, offering essential insights for optimizing waste management strategies and advancing circular economy practices. Full article

Anaerobic digestion (AD) is a promising biowaste valorization technology for sustainable energy, circular economy, local energy community growth, and supporting local authorities’ environmental goals. This paper presents a systematic review meta-analysis methodology for biomethane estimation, using over 600 values of volatile solids (VS) content and biochemical methane potential (BMP) of six different waste streams, collected from 240 scientific studies. The waste streams include cow manure (CM), sheep/goat manure (SGM), wheat straw (WS), household waste (HW), organic fraction of municipal solid waste (OFMSW), and sewage sludge (SS). The statistical analysis showed a mean VS content of 11.9% (CM), 37.3% (SGM), 83.1% (WS), 20.8% (HW), 19.4% (OFMSW), and 10.6% (SS), with BMP values of 204.6, 184.1, 305.1, 361.7, 308.3, and 273.1 L CH₄/kg VS, respectively. The case study of Kozani, Greece, demonstrated the methodology’s applicability, revealing a potential annual CH₄ production of 15,429,102 m³ (corresponding to 551 TJ of energy), with SGM, WS, and CM as key substrates. Kozani, aiming for climate neutrality by 2030, currently employs conventional waste management, like composting, while many local business residual streams remain unused. The proposed model facilitates the design and implementation of AD units for a sustainable, climate-neutral future. Full article

The use of agricultural residues in biogas plants is becoming increasingly important, as they represent an efficient and sustainable substrate alternative. Pelletizing straw can have positive effects on transportation, handling, and biogas production. In this study, different grain straw pellets from mobile and stationary pelleting plants in Germany as well as the corresponding untreated straw were characterized and investigated for their suitability for anaerobic digestion (AD). Therefore, tests on the biochemical methane potential (BMP) and the chemical–physical characterization of unpelletized straw and straw pellets were carried out. The characterization of the pellets and the straw revealed a high average total solid content of 91.8% for the industrially produced straw pellets and of 90.8% for the straw. The particle size distribution within the tested pellet samples varied greatly depending on the pelleting process and the pre-treatment of the straw. In addition, a high C/N ratio of 91:1 on average was determined for the straw pellets, whereas the average higher heating value (HHV) content of the pellets was 17.58 MJ kg⁻¹. In the BMP tests, the methane production yields ranged from 260–319 normal liter (NL) CH₄ kg⁻¹ volatile solids (VS) for the straw pellets and between 262 and 289 NL CH₄ kg⁻¹ VS for the unpelletized straw. Overall, pelleting increases the methane yield on average from 274 to 286 NL CH₄ kg⁻¹ VS, which corresponds to an increase in methane yield of 4.3%. Based on the results, the feasibility of using straw pellets for AD could be confirmed, which can facilitate the possibility of increased biogas production from agricultural residues such as straw pellets and thus make the substrate supply more sustainable. Full article

The study aimed to evaluate and compare the co-digestion of swine wastewater (SW) and other co-substrates: grass residue (GR), food waste (FW), and poultry litter (PL). The comparisons were performed using the biochemical methane potential (BMP) test. The maximum accumulated methane (CH₄) production was submitted to a joint analysis of variance. Tukey’s test (α = 0.05) was used to compare the results of the treatments, and Dunnett’s test (α = 0.05) was used to compare the ratios (100:0, 75:25, 50:50, 25:75, and 0:100) (based on volatile solids—VS). In addition, both the synergistic effect and kinetic adjustment of some models were evaluated. The results indicated that the co-digestion of all substrates (GR, FW, and PL) with SW improved the methane production yield in comparison with mono-digestion (GR, FW, and PL). A positive synergistic effect was observed for the FW:SW (25:75 and 75:25). According to both Tukey’s and Dunnett’s tests (α = 0.05), the FW:SW ratio of 25:75 did not show statistical difference compared with the mono-digestion (SW), which exhibited the largest CH₄ production. Among the models evaluated, the modified Gompertz function presented the best fit. For the co-digestion treatments, the ratio of FW:SW of 25:75 exhibited the most promising potential for integrated management, demonstrating the best synergistic effect among the substrates. In this context, methane production from co-digestion equalled that of mono-digestion, while enabling integrated residue management. Full article