Specific Methane Yield Research Articles

Investigating role of corn stover biochar supplementation on continuous pilot scale anaerobic digestion: Performance and microbial community dynamics

Biochar supplementation could facilitate microbial colonization and increase biogas and methane yield in anaerobic digestion (AD). This study investigated the impact of corn stover biochar (CSB) augmentation on the continuous pilot scale AD of rice straw. The CSB supplementation exhibited the daily average specific biogas and methane yield of 368.6 L/kg volatile solids (VS) and 230 L/kg VS, which were 35 % and 37 % higher than the control. Principle component analysis indicated that the VS reduction positively correlated with the daily average specific biogas and methane yield. Metagenomic analysis revealed that the CSB supplementation facilitated microbial colonization with the enrichment of unclassified genera from families Planococcaceae, Clostridiaceae, and Ruminococcaceae, and genus Clostridium and methanogenic archaea (Methanosarcina and Methanobacterium). The co-occurrence network revealed a notable shift in microbial interactions following the supplementation of CSB as an additive in AD. These results offer insights for enhancing the performance of the AD using CSB.

Solid-state anaerobic digestion of sweet corn waste: The effect of mixing and recirculation interval

The mixing and sludge recirculation interval is one of the key successes of the solid-state anaerobic digestion process, a promising technology for converting high-solid agro-industrial wastes to renewable energy. This study employed a pilot-scale completely stirred tank reactor to examine biogas production from sweet corn waste, including corn cobs, husks, and seeds. The reactor was operated as solid-state anaerobic digestion at an ambient temperature. The mixing and recirculating intervals were set to non-mixing and mixing for 10 minutes every 3, 6, and 12 hours. The initial total solid of the feedstock was 25%, while the hydraulic retention time was 30 days. The results showed that during the mixing and recirculation every three hours, the highest chemical oxygen demand, total solid, and volatile solid (VS) removal efficiencies were 85.42%, 62.92%, and 64.59%, respectively. The ratio between volatile fatty acid and alkalinity ranged between 0.20 and 0.30 without any sign of system failure. The highest specific methane yield of 766 L/kg VSadded was obtained in the experiment with mixing and recirculating intervals every 3 hours. It was found that the modified Gompertz model could effectively fit the methane yields with an R2 of 0.9667. The modeled methane production potential and the maximum methane production rate were 867.40 NL/kg VSadded and 132.01 NL/kg VSadded-d, respectively. Additionally, the levelized cost of the biogas produced from the solid-state anaerobic digestion of the sweet corn waste was calculated to be 0.61 USD/kg. The findings of this study can serve as a guide for the design and operation of the SS-AD system, which aims to transform various types of lignocellulosic waste into environmentally friendly energy.

Evaluation of Biochemical Methane Potential and Kinetics of Organic Waste Streams for Enhanced Biogas Production

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%.

Impact of Organic Load on Methane Yields and Kinetics during Anaerobic Digestion of Sugarcane Bagasse: Optimal Feed-to-Inoculum Ratio and Total Solids of Reactor Working Volume

The effect of increasing organic load on the specific methane yields (SMYs) and kinetics of methane production during the anaerobic digestion (AD) of sugarcane bagasse (SB) was investigated in batch experiments at 37 °C. The organic load of the batch AD system was increased based on an increase in the feed-to-inoculum (F/I) ratio (T1–T5) and increase in the Total Solids (TS)% of the working volume (T6–T10). The results show that in both the treatment sets, an increase in organic load led to a decrease in SMY. Higher organic loads in terms of F/I ratio (T4 and T5) were inhibited due to Volatile Fatty Acid (VFA) accumulation. On the other hand, higher organic loads (T8, T9 and T10) in terms of the higher TS% of the working volume was inhibited by the accumulation of NH4-N. Thus, an organic load of 50 gVS/L at an F/I ratio = 1.0 and TS = 10% (T3) was found to be the highest organic load that had no significant inhibitions among the tested treatments. The results from the kinetic studies show that the first-order kinetic model is the best fit for the SMY data, with average differences% of 2.32% and 3.13% for treatments T1–T5 and T6–T10, respectively.

Metagenomic analysis reveals metabolic mechanism of enhancing lignocellulosic anaerobic digestion mediated by CO2/O2-nanobubble water

Nanobubble water (NW) has been reported to enhance anaerobic digestion (AD), but its influence on the metabolic pathways of microorganisms remains unclear. In this study, the specific methane yields of rice straw in the CO2NW and O2NW treatments increased by 6.9% and 18.3%, respectively. The electron transport system (ETS) and coenzyme F420 activities were enhanced by the addition of NW. Metagenomic analysis showed that the abundances of most enzymes in the acidification were significantly increased by both CO2NW and O2NW. Regarding methanogenesis, CO2NW promoted the expression of genes encoding enzymes of hydrogenotrophic methanogenesis, while O2NW stimulated both the acetoclastic and hydrogenotrophic methanogenesis. With the addition of O2NW, the expressions of modules related to the tricarboxylic acid (TCA) cycle and oxidative phosphorylation were enhanced, resulting in increased ATP production. This study provided fundamental evidence of the metabolic pathways of microorganisms mediated by NW at each stage of AD.

Integrating Anaerobic Digestion With Struvite Production for Enhanced Nutrient Recovery, Pathogen Reduction, and Circularity in Manure Management

ABSTRACTIntroductionAnaerobic digestion (AD) is essential for manure management, generating biogas and nutrient‐rich digestate for organic fertilizer. However, improper digestate use can pose environmental risks. Recovering struvite, a magnesium ammonium phosphate (MAP) compound, from digestate provides a sustainable, controlled‐release fertilizer, supporting a circular economy in agriculture.Materials and MethodsThe study employed a two‐stage (liquid–solid) AD process using poultry, dairy, and swine manures, along with wasted corn silage. Digestates were sampled for physicochemical and biogas quality analyses, with feedstocks categorized into D1 and D2, and a composite (D3) formed for struvite characterization. Microbial populations were enumerated on selective media, and struvite mineral content was analysed via argon plasma emission spectrometry.ResultsThe digesters processing feedstock mixtures D1 and D2 achieved specific methane yields of 1.26 L/g CODs fed and 1.49 L/g CODs fed, with cumulative biogas production of 374 and 369 L, respectively, over four 77‐day cycles. The two‐stage AD process significantly reduced antibiotic‐resistant, Enterobacteriaceae and Enterococcus spp. Total ammoniacal nitrogen (TAN) recovery rates were high at 98%–99%, with a consistent struvite crystal mass of 0.67 g/10 mL, indicating the efficiency of this integrated process. The agronomic value of struvite was determined, indicating its potential utility as a fertilizer, and scanning electron microscopy analysis revealed diverse crystal structures, warranting further investigation into their implications for usage and storage.ConclusionThe results suggests that the two‐stage AD process efficiently transforms organic waste into high‐quality biogas, reduces antibiotic‐resistant bacteria, and facilitates nutrient recovery through struvite precipitation. This approach supports co‐digestion of multi‐substrates and promotes circular economy principles, with potassium or sodium phosphate enhancing struvite recovery for sustainable agriculture.

Comparing the effects and mechanisms of granular activated carbon and magnetite nanoparticles in dry anaerobic digestion: Focusing on microbial electron transfer and metagenomic evidence

Enhancing direct interspecies electron transfer (DIET) via granular activated carbon (GAC) and magnetite nanoparticles (MNPs) to promote methanation performance in dry anaerobic digestion (AD) systems has been extensively studied in recent years. However, the underlying mechanisms, particularly how GAC and MNPs influence DIET and extracellular polymeric substances (EPSs), remain poorly understood. In this study, the different effects and mechanisms of GAC and MNPs on dry AD fed with pig manure (PM) and corn straw were compared, with additions of 10, 20, and 50% of the volatile solid (VS) of PM. The results indicated that GAC improved the cumulative specific methane yields (CSMYs) by 18.8–20.9%, while a high dose of MNPs (50% of the VSPM) decreased the CSMY and hydrolysis rate constant by 27.0 and 75.4%, respectively. GAC provided microorganism attachment sites and functional groups for electron transfer, improving hydrolysis by enriching fermenters such as Fastidiosipila and Rikenellaceae. Nevertheless, MNPs stimulated intense dissimilatory iron reduction by Clostridium sp. in the early stage, competing with methanogens for substrates. Low and medium GAC doses (10 and 20% of the VSPM) increased the utilization of redox-active substances (e.g., humic substances and proteins) in EPS, while the high MNP dose stimulated their secretion due to microbial self-protection, impairing electron transfer. Metagenomic evidence showed that the medium GAC dose improved four methanogenic pathways and DIET mediated by microbial nanowires, while a high MNP dose impeded the final step of methanogenesis. These results provide deeper insights into the mechanisms of different conductive materials on dry AD.

Effect of long-term storage of cattle manure on its energy potential and biodegradability

Abstract In recent years in Russia, due to the complicated geopolitical situation in some border areas, biogas plants have been considered not only as waste utilization facilities, but also as reserve energy sources, which are safer than traditional - nuclear power plants. In this context, the development of an algorithm for the flexible operation of a biogas plant is particularly relevant, which gives rise to the need to study the stability of the system under the influence of different unfavourable factors. In this work, the influence of long-term storage of cattle manure on its energy potential and biodegradability is studied. The specific methane yield in the test variant with manure stored for 10 months before anaerobic fermentation was 1.41±0.55 ml/g oDM, which is 6.23 times lower than in the test variant with fresh manure; the methane content of manure after long-term storage is 9.66 times lower and the degree of decomposition of its organic matter is 2.72 times lower compared to similar indicators of manure processed without preliminary storage. However, the specific biogas yield from long-term stored manure is 1.66 times higher than the control, which indicates intensive formation of other gases. Thus, long-term storage has a negative impact on the energy potential of cattle manure; if it is necessary to process it in a biogas plant, it is advisable to combine it with more energy-intensive raw materials.

Elucidating Key Microbial Drivers for Methane Production during Cold Adaptation and Psychrophilic Anaerobic Digestion of Cattle Manure and Food Waste

At psychrophilic temperatures (<20 °C), anaerobic digestion produces less methane (CH4). For psychrophilic anaerobic digestion (PAD) to be successful, investigation of cold-adapted microbial consortia involved in methane production is critical. This study aimed to investigate the microbial community driving enhanced methane production from the cold-adaptation process and bioaugmentation of PAD with cold-adapted inoculum (BI). Microbial consortia in cattle manure (CM) and food waste (FW) were adapted and applied during batch PAD of CM and FW to bioaugment methane production at 15 °C. Cold adaptation and PAD with BI resulted in cumulative specific methane yields of 0.874 ± 0.231 and 0.552 ± 0.089 L CH4 g−1 volatile solids, respectively, after 14 weeks, while the absence of BI (control) led to acidification and no methane production during PAD. Following 16S rRNA V4–V5 amplicon sequencing and metagenomic analyses, Methanosarcina was revealed as a key driver of methanogenesis during cold adaptation and PAD bioaugmentation. Furthermore, based on the predictive functional and metabolic analysis of the communities, possible synergies were proposed in terms of substrate production and utilization by the dominant microbial groups. For instance, during methane production, Bacteroides and Methanobrevibacter were possibly involved in a syntrophic relationship, which promoted methanogenesis by Methanosarcina. These findings provide insight into the prospective microbial synergies that can be harnessed and/or regulated in cold-adapted inoculum for the improvement of methane production during PAD.

Different regulation strategies of anaerobic digestion by AC/CaO2 and Fe3O4/CaO2: Reactive oxygen species induction, methanogenic performance, and microbial response

This study examined the combination of activated carbon and magnetite with calcium peroxide in enhancing the anaerobic digestion (AD) performance of food waste (FW). The individual mechanisms of these two approaches were also clarified. The results indicated that AC/CaO2 achieved the highest specific methane yield of 434.4 mL/g VS, followed by Fe3O4/CaO2 (416.9 mL/g VS). Both were significantly higher than other groups (control, AC, Fe3O4, and CaO2 were 330.1, 341.4, 342.8, and 373.2 mL/g VS, respectively). Additionally, compared to Fe3O4/CaO2, AC/CaO2 further increased reactive oxygen species (ROS), thereby enhancing the hydrolytic acidification process. Simultaneously, the higher ROS levels of Fe3O4/CaO2 and AC/CaO2 promoted the formation of microbial aggregates and established a more robust enzymatic defense system and unique damage repair strategy. The research comparatively analyzed the synergistic mechanism of iron-based and carbon-based conductive materials with CaO2, providing new perspectives for optimizing the AD of FW.

Evaluating the influence of calcined eggshells and ultrasonication in the Co-digestion of avoidable and unavoidable Food Waste and OLS regression analysis of the reactor system

The technological advancements in the bio-conversion of food waste (FW) into biogas signify substantial advancements in the field of waste management. However, persistent operational challenges like rapid acidification and difficulties in maintaining the C/N ratio in mono-digestion remain, despite extensive research efforts. The present study aims to evaluate the reactor performance in co-digestion, specifically using a 1:1 ratio of unavoidable food waste (UAFW) and avoidable food waste (AFW), with the addition of calcined eggshells as an additive. Further, the study employs Ordinary Least Square (OLS) regression modeling to predict the biogas production from the co-digestion process. The experimental process involves ultrasonication pretreatment, focusing on calcined eggshells for their ability to preserve carbohydrates via Ca(OH)2, an alkaline material. The semi-continuous operation of the reactor spanned for 120 days and was divided into three phases with varying Organic Loading Rates (OLR) from 0.6 to 2.2 gVS/l/d. Characterization studies such as SEM, FTIR and TGA-DTA were performed to validate the pretreatment method and addition of egg-shells. Results indicated increased OLR led to higher Volatile Solids (VS) reduction. This was attributed to the calcined eggshells' role in adsorbing NH4+ and NO3− ions while maintaining pH levels, resulting in significantly higher biogas production. The multiple regression models used in the study yielded promising results, surpassing simple linear regression, with an adjusted R-squared value > 0.9 and p-value <0.05. The model effectively anticipated the specific methane yield, demonstrating the capability to improve energy production by co-digesting AFW and UAFW. The study presents an opportunity to divert organic waste from landfills, reduce greenhouse gas emissions, and promote sustainable waste management by using bio-waste additives, reducing reliance upon synthetic chemicals.

Effects of nanobubble water on digestate soaking hydrolysis of rice straw

This study investigated the performance of combined nanobubble water (NW) and digestate in the soaking hydrolysis process. Two types of NW (CO2NW and O2NW) with digestate were used to soak rice straw for 1, 2, 3, 5, and 7 days. During soaking process, the volatile fatty acids (VFA) concentration in the treatment with O2NW and digestate for 3 days (O2NW-3 d) reached 7179.5 mg-HAc/L. Moreover, the highest specific methane yield (SMY) obtained in this treatment could reach 336.7 NmL/gVS. Although the addition of NW did not significantly increase SMY from digestate soaking, NW could accelerate the rate of methane production and reduce digestion time of T80. The enrichment of Enterobacter in the soaking process was observed when using CO2NW and O2NW as soaking solutions which played important roles in VFA production. This study provides a new insight into environment-friendly enhanced crop straw pretreatment, combining NW and digestate soaking hydrolysis.

A robust, low-temperature, closed-loop anaerobic system for high-solid mixed farm wastes: advancing agricultural waste management solutions in Canada.

This study investigates the effectiveness of low-temperature (20 ± 1 °C) anaerobic digestion (AD) for two organic multiple farm substrate combinations: Set 1 comprising chicken manure (CM), dairy manure (DM), and waste corn silage (CS) and Set 2 comprising CM, DM, pig manure (PM), and CS. Inoculum adaptation steps were carried out using CM and CM+DM for Set 1 and Set 2, respectively. Over three consecutive operating cycles spanning 245 days with increasing organic loads, 4.3 and 2.8 g VS L-1 d-1 for Sets 1 and 2 during Cycles 1 to 5.1 and 4.6 g VS L-1 d-1for Sets 1 and 2 during Cycle 3, a closed-loop two-stage liquid-solid AD system was employed, with performance assessed via stability ratios of short-chain volatile fatty acids and alkalinity. Results demonstrate that mono-digestion of CM with adapted inoculum yielded the highest biogas production of 424 ± 4 L over 77 days, indicating superior performance by Set 1 during Phase I, whereas a similar performance was observed during Phase 2, where Sets 1 and 2 exhibited highest specific methane yields of 0.233 ± 0.028 and 0.262 ± 0.004 L g-1 VSfed, respectively, over 68 days. Analysis of heavy metal concentrations in digestates revealed a significant decrease compared to initial raw substrate concentrations, highlighting their role as nutrients for microbial growth. This study, the first of its kind, highlights the potential of low-temperature AD systems to manage diverse organic residues/byproducts and offers insights into effective performance monitoring without compromising system integrity.

Carbon flow, energy metabolic intensity and metagenomic characteristics of a Fe (III)-enhanced anerobic digestion system during treating swine wastewater

Deep treatment and bioenergy recovery of swine wastewater (SW) are beneficial for constructing a low-carbon footprint and resource-recycling society. In this study, Fe (III) addition from 0 to 600 mg/L significantly increased the methane (CH4) content of the recovered biogas from 61.4 ± 2.0 to 89.3 ± 2.0 % during SW treatment in an anaerobic membrane digestion system. The specific methane yields (SMY) also increased significantly from 0.20 ± 0.05 to 0.29 ± 0.02 L/g COD. Fe (III) and its bio-transformed products which participated in establishing direct interspecific electron transfer (DIET), upregulated the abundance of e-pili and Nicotinamide adenine dinucleotide (NADH), enriched electroactive bacteria. The increase in cellular adenosine triphosphate (cATP) from 6583 to 14,518 ng/gVSS and electron transport system (ETS) from 1468 to 1968 mg/(g·h) promoted the intensity of energy flow and electron flow during anaerobic digestion of SW. Moreover, Fe (III) promoted the hydrolysis and acidification of organic matters, and strengthened the acetoacetic methanogenesis pathway. This study established an approach for harvesting high quality bioenergy from SW and revealed the effects and mechanisms from the view of carbon flow, energy metabolic intensity and metagenomics.

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

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

Synergistic effects of low temperature and alkali on the anaerobic digestion of corn stover

Combined with the climatic conditions in cold areas, the effect of the NaOH-pretreatment at low temperature on the methane yield of corn stover was studied by anaerobic digestion at batch mode. For the alkali/freezing pretreatment, the sample reached a maximum specific methane yield of 280.48 ± 21.75 mL/g VS at the conditions of freezing time of 15 days and 2.0 % NaOH. Lower temperature-alkali pretreatment had an obvious effect on the structure of samples, with significant changes in the contents of elemental C, N, cellulose, and lignin, as well as an increase in crystallinity. In addition, a higher energy conversion efficiency (77.9 %) was obtained for the sample pretreated by alkaline/freezing. The results showed that the methane yield after pretreatment followed by alkali/freezing treatment > water/freezing treatment > freezing treatment. Therefore, alkali/freezing pretreatment is an effective method to improve the performance of the anaerobic digestion of corn stover. This study could provide a pathway for developing a low-temperature pretreatment by combining with the climate characteristics of cold areas.

Multi-criteria-based decision-making assessment for anaerobic digestion of ammonia-rich distillery wastewater: Effect of pyrochar and temperature

Energy-efficient wastewater treatment units are imperative to achieve carbon neutrality and a circular economy at the industrial scale. In the present study, pyrochar loading and digestion temperature were tested to assess their impact on the performance of an anaerobic digester running on distillery wastewater. The digestion temperature (37 °C and 55 °C) and pyrochar loading (7.5 – 30 g/L.feed) were selected as two primary design factors. Experiments were designed using Taguchi’s design of experiments and specific methane yield, total ammonia nitrogen, pH and buffering capacity were selected as experimental outputs for multi-criteria assessment. The results from the confirmation test indicated that the addition of pyrochar (7.5 g/Lfeed) improved the methane yield (276 ± 15 L/kg VS) significantly compared to the control (167 ± 15 L/kg VS) at 37 °C. The detailed post-digestion analysis showed that the adsorption of ammonia on pyrochar may be the primary reason for enhanced digester performance.

Anaerobic Digestion of Cuttings from Grassland in Protected Landscape Areas

Orchard meadows are biodiversity hotspots, as the understory often consists of species-rich lowland hay meadows. Due to the low energy density of the grass, it is not suitable as feed, but the energetic utilisation of cuttings from orchard meadows for biogas production could facilitate the protection of these semi-natural grasslands. Here, lowland hay meadows and extensively used orchards were investigated to assess their potential for anaerobic digestion in biogas plants. Aboveground biomass was harvested weekly from three lowland hay meadows differing in conservation statuses and analysed for cell wall components (aNDF, ADF, and ADL), nutritional values (XF, XL, XP), and methane formation potential by anaerobic digestion. Further, orchard meadows were harvested twice during summer and analysed in the same way. Specific methane yield decreased linearly with cutting dates from 0.325 m3 kg−1(oDM) to 0.237 m3 kg−1(oDM). The cumulated area-related methane yields of the orchards ranged from 818 m3 ha−1 to 1036 m3 ha−1. Specific methane yields were linearly correlated with XL, aNDF, ADF, and ADL.

Biogas Dynamics and Microbial Composition Employing Different Inocula and Substrates in Continuous Stirred-Tank Reactors

The current investigation delved into the utilization of cattle and municipal sanitary inocula for anaerobic digestion of poultry wastes, addressing a crucial and pragmatic challenge in waste management. The emphasis on poultry waste is pertinent due to its well-documented impediments in anaerobic digestion, attributed to heightened levels of ammonia and volatile fatty acids (VFAs). The strategic selection of cattle and municipal sanitary inocula suggests an approach aimed at bolstering the anaerobic digestion process. In this study, we evaluated the use of cattle and municipal sanitary inocula for the anaerobic digestion of various poultry wastes, which is often challenged by high levels of ammonia and volatile fatty acids (VFAs). The substrates tested included belt waste (Poultry A), poultry litter plus feed residues (Poultry B), tray hatchery ©, and stillage. These substrates were processed in two continuous stirred tank reactors (CSTRs), R-1 (with antibiotic monensin) and R-2 (without monensin). Initially, both reactors operated with the same hydraulic retention time (HRT), using a substrate ratio of stillage: belt: tray hatchery (S:B:T) of 70:15:15. On the 41st day, the HRT was adjusted to 20 days, and the substrate ratio was changed to S:A:T 70:40:40. The specific methane yield for R-1 started at 10.768 L g−1 COD, but decreased to 2.65 L g−1 COD by the end of the experiment. For R-2, the specific methane yield varied between 0.45 L g−1 COD and 0.243 L g−1 COD. Microbial composition in the reactors changed over time. In R-1, bacteroides were consistently dominant, while firmicutes were less abundant compared to R-2. Proteobacteria were initially low in abundance, but spirochetes were found in both reactors throughout the experiment. The study concluded that Poultry B substrates, due to their rich nutrient and trace element composition, are suitable for biogas plants. Municipal sanitary inocula also showed promise due to their resilience in high ammonia concentrations. Further research into biofilm interactions is recommended to better understand microbial responses to high ammonia concentrations, which can lead to propionate production in anaerobic digestion (AD).

Semi-Continuous Testing: The Effect of Mechanical Pre-treatment on Degradation of Complex Organic Matter

This study investigates the impact of pre-treatment intensity on biogas production in anaerobic digestion processes using three different substrates: BPWSB, TWSB, and PWSB. The experimental design includes semicontinuous tests with various pre-treatment levels (PTLs) to analyze specific methane yields and process stability indicators. Reactor performance comparisons reveal differences in methane production profiles among substrates, with GWSB generally outperforming BPWSB and PWSB. Additionally, PTL4 consistently yields higher specific methane yields than PTL3 and PTL2 across all substrates due to its greater surface area. The specific methane yields for BPWSB, TWSB, and PWSB are comparable but not identical. The highest specific methane yield was produced by BPWSB for PTL2 (M=225.6, SD=57.7), while the lowest was produced by GWSB (M=181.2, SD=51.9). The results suggest that the specific methane yields for BPWSB, TWSB, and PWSB are similar but not identical. Again, BPWSB PTL3 (M=255, SD=63.5) differed significantly from the others, whereas GWSB had the lowest specific methane yield (M=211.7, SD=56.6). Likewise, BPWSB PTL4 outperformed the other substrates (M=290.3, SD=69.3), while GWSB PTL4 had the least (M=218.3, SD=69.4). Intensive pre-treatment shows no detrimental effects on system stability, with reduced foaming tendency observed at higher pre-treatment intensities. These results indicate that carefully choosing pre-treatment methods can boost methane yields while addressing operational difficulties, emphasizing the significance of pre-treatment in sustainable waste management and renewable energy generation. Future studies could investigate further pre-treatment methods and their long-term impacts on biogas output and system stability, offering more comprehensive insights into process refinement.