Specific Biogas Research Articles

Evaluation of additive effecton anaerobic sewage sludge digestion

An additive based on iron oxides was applied to reduce the amount of produced sludge and to increase the production and quality of biogas. The C/N ratio was 11.0–11.3 and the pH of the sludge mixture was 7.3 before the anaerobic digestion. The determined optimal dose of the additive was 0.35 g/g of sludge dry matter over 20 days. This allowed a reduction in the sludge retention time up to 6–11 days. Consequently, maximum biogas production was reached on average 1.6 times faster, volatile solids degradation increased by 56.7%, biogas production increased by 75%, specific biogas production increased by 11.5%, and methane concentration in the biogas increased by 8.4%–18.2%. When the additive was applied, the quantity of phosphate phosphorus in the supernatant was reduced by up to 19%, and hydrogen sulfide reduction efficiency in the biogas ranged between 55% and 62%. In sludge treatment facilities, using an iron oxide-based additive could reduce the dewatering and drying costs for digested sludge by up to 35% .

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.

Mono e codigestão anaeróbia de resíduos de frutas e vegetais: Efeitos no rendimento de biogás e no biofertilizante

ABSTRACT The proper disposal of fruit and vegetable waste is essential to promote environmental sustainability, reduce the carbon footprint, improve soil quality, and contribute to the transition to a circular economy. This study examined the impact of incorporating dairy cattle wastewater (DCWW) into anaerobic co-digestion with fruit and vegetable residues and utilization of the resulting biofertilizer as a diluent in the anaerobic mono-digestion of fruit and vegetable residues (recycle). The specific biogas and methane production and the agronomic quality of the biofertilizer were evaluated in a semi-continuous trial. Two startup strategies were employed: initially, the reactors were entirely fed with inoculum (biofertilizer derived from DCWW), and fruit and vegetable residue feedstock was gradually introduced. Anaerobic co-digestion of fruit and vegetable residues with DCWW yielded the highest specific production of biogas and methane at 720 and 436 L kg-1 of volatile solids (VS), respectively. The addition of DCWW increases fruit and vegetable residue alkalinity by 249% and reduces the volatile acidity by 83.4%. Anaerobic mono-digestion of fruit and vegetable residues enhances macronutrient recovery in the biofertilizer through recycle. Logistically, directing fruit and vegetable residues to rural areas for anaerobic co-digestion with DCWW promotes agricultural biofertilizer use.

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%.

Enhancement of Fermentation Performance in the Anaerobic Co-Digestion of Chicken Manure and Corn Straw under Biogas Slurry Reflux via Air Stripping of the Digestate

Ammonium inhibition is a key limiting factor for anaerobic digestion when using chicken manure as the main substrate, especially in a digestion system with biogas slurry reflux. Air stripping is usually used as a recycled biogas slurry treatment. In this study, we carried out the anaerobic co-digestion of chicken manure and corn straw. The fermentation performance was investigated with and without air stripping at different biogas slurry reflux ratios and with an increasing organic loading rate. The results show that air stripping enhanced biogas production, system stability, and volatile solid removal efficiency via the mitigation control of ammonium inhibition. The total ammonium nitrogen in the digesters with air stripping was 20.24–46.40% lower than in those without air stripping. The highest specific biogas production and volatile solid removal efficiency values were obtained in the digesters at an organic loading rate of 3.3 g volatile solid (VS)/(L·d) and a reflux ratio of 75% with air stripping, reaching 480.43 mL/gVSadd and 63.36%, respectively. Moreover, air stripping also improved the organic loading rate and reflux ratio. Stable operation was achieved at an organic loading rate of 5.3 gVS/(L·d) and a reflux ratio of 75%, with specific biogas production of 392.35 mL/gVSadd and a volatile solid removal efficiency of 50.33%. The fermentation performance deteriorated when the organic loading rate was increased to 8.0 gVS/(L·d) at a reflux ratio of 75%, even when air stripping was conducted, indicating that a slighter lower reflux ratio (50%) could be more feasible at a higher organic loading rate (8.0 gVS/(L·d). Additionally, the methanogen community structure varied according to the use of air stripping, with a shift in the methanogenic pathway from hydrogenotrophic to acetoclastic methanogens. Overall, our findings support the adoption of air stripping for ammonium mitigation in anaerobic digestion with biogas slurry reflux.

Effect of mowing versus abandonment of mesic grasslands in Central Europe on biomass use for biogas production: Implications for semi-natural ecosystem conservation

The economic management of lignocellulosic biomass from semi-natural grasslands is now a challenge across Europe. The abandonment of mowing these grasslands leads to the gradual degradation of these ecosystems. This study investigates how chemical and biological factors affect the suitability of biomass from abandoned grasslands for biogas production. We sampled 30 mown and 30 abandoned grassland sites in the Sudetes Mountains (Poland and Czechia). The cover contribution of short herbs was found to be significantly higher in mown grasslands (p < 0.001), while that of tall herbs was more prevalent in abandoned grasslands (p < 0.01). The specific biogas yield (SBY, NL kg−1 volatile solids) is negatively affected by an increased percentage of herbs in the biomass of mown and abandoned grasslands. This is due to the inhibitory effect of herbs on biodegradation, the increase in lignin content and the decrease in cellulose. This study highlights the importance of individual plant species in assessing grassland biomass for area biogas yield (ABY, m3 ha−1) and provides new insights into a field that has not yet been extensively investigated. In mown grasslands, ABY was most positively correlated with grass species (Arrhenatherum elatius, Trisetum flavescens and Festuca pratensis). In abandoned grasslands, the ABY was most correlated with herbaceous species (Galium aparine, Urtica dioica and Chaerophyllum aromaticum) and grasses (A. elatius and Elymus repens). Mown grasslands had significantly higher species richness (p < 0.001) compared to abandoned grasslands, but the number of species sampled did not correlate with SBY and ABY. This study contributes to the development of a sustainable bio-economy by highlighting the need for efficient use of grassland biomass. This approach helps protect semi-natural ecosystems and facilitates sustainable management of renewable resources.

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.

A novel player of methylotrophic methanogensis pathway in boosting anaerobic digestion of corn stover with effluents recycling

Effluents recycling proves to be an effective method for enhancing the performance of anaerobic digestion system for lignocellulosic-like biomass. However, a limited understanding exists regarding the regulation mechanisms of methanogens. This study aims to systematically assess the dynamic interactions between process parameters, microbial communities, and methanogenic activity throughout the AD process of corn stover with effluents recycling. The results show a significant increase in the specific biogas yields of corn stover to 369 ± 115 mL/g VS with effluents recycling, an 87 % improvement compared to the control system. Effluents recycling can recover nitrogen and selectively enrich the abundances of microorganisms such as Herbinix hemicellulosilytica, Bacteroides paurosaccharolyticus and Methanosarcina mazei, etc. Correspondingly, the strategy improves the abundance of CAZymes, enhancing the efficient depolymerization of cellulose, glucuronoarabinoxylan, xyloglucan and pectin. Methanol and methylamines originating from enhanced pectin hydrolyzation and the biogenic amine pathway boost methylotrophic methanogenesis. This study addresses knowledge gaps in producing-pathways of precursors for methylotrophic methanogenesis and elucidates the mechanism to boost methanogenesis process of lignocellulosic-like biomass with effluents recycling.

Application of Recycled Filling to Improve the Purification Performance of Confectionery Wastewater in a Vertical Anaerobic Labyrinth Flow Bioreactor

Anaerobic wastewater treatment is, in many cases, a justified alternative to typical activated sludge processes, from a technological, economic, and ecological point of view. The optimisation of fermentation reactors is primarily concerned with increasing the biodegradation of organic compounds and biogas production, as well as improving efficiency in the removal of nitrogen and phosphorus compounds. The aim of the research was to determine the impact of using low-cost recycled filling on the efficiency of treating real confectionery wastewater in a vertical anaerobic labyrinth flow bioreactor. The experiments focused on selecting the organic loading rate that would allow for the effective biodegradation and removal of pollutants, as well as the efficient production of biomethane. It was found that the tested reactor can operate efficiently at a maximum organic loading rate (OLR) of 7.0–8.0 g of chemical oxygen demand (COD)/L·d. In this OLR range, high efficiency was guaranteed for both wastewater treatment and biogas production. However, increasing the OLR value to 8.0 g COD/L·d had a significant negative effect on the methane (CH4) content in the biogas. The most efficient variants achieved a biodegradation efficiency of around 90% of the organic compounds, a CH4 content of over 70% in the biogas, and a biogas yield of over 400 L/kg of COD removed. A significant influence of the applied OLR on the ratio of free organic acids (FOS) to total alkaline capacity (TAC) and pH was observed, as well as a strong correlation of these indicators with the specific biogas yield and CH4 content. The application of a solution based on the use of a hybrid system of anaerobic granulated sludge and an anaerobic filter resulted in an efficient treatment process and an almost complete elimination of suspensions from the wastewater.

Magnetic iron oxide nanoparticle enhanced microwave pretreatment for anaerobic digestion of meat industry sludge

Our study investigates the effects of iron oxide (Fe3O4) nanoparticles combined microwave pretreatment on the anaerobic digestibility and soluble chemical oxygen demand (SCOD) of meat industry sludge. One of our main objectives was to see whether the different microwave-based pretreatment procedures can enhance biogas production by improving the biological availability of organic compounds. Results demonstrated that combining microwave irradiation with magnetic iron oxide nanoparticles considerably increased SCOD (enhancement ratio was above 1.5), the rate of specific biogas production, and the total cumulative specific biogas volume (more than a threefold increment), while having no negative effect on the biomethane content. Furthermore, the assessment of the sludge samples’ dielectric properties (dielectric constant and loss factor measured at the frequency of 500 MHz) showed a strong correlation with SCOD changes (r = 0.9942, R2 = 0.99), offering a novel method to evaluate pretreatment efficiency.

Optimizing Biogas Production and Digestive Stability through Waste Co-Digestion

This study aimed to enhance the nutrient balance of municipal solid waste (MSW), characterized by a high carbon-to-nitrogen (C/N) ratio, which is a critical factor in the anaerobic digestion process. The investigation involved the addition of MSW, which is rich in carbon content, to food waste (FW) with high nitrogen content. The goal was to determine an optimal co-substrate mixing ratio of MSW and FW for anaerobic co-digestion at mesophilic temperatures, aiming to improve process stability and performance to achieve higher biogas yield. The co-digestion experiments encompassed five mixing ratios of MSW and FW with C/N ratios of 20, 25, 30, 35, and 40 under mesophilic conditions in a laboratory. The results indicated that the highest specific biogas yield, reaching 827 L/kg VS, was attained when the co-substrate feedstock had a balanced C/N ratio of 20, surpassing the 520 L/kg vs. obtained from MSW digestion alone. As the proportion of MSW increased in the co-substrate mixing feedstock, the biogas production rate decreased. Additionally, the study explored the optimal substrate-to-inoculum (S/I) ratio, focusing on the co-substrate feedstock with a C/N ratio of 20. Four S/I ratios (0.5, 1.0, 1.5, and 2.0) were examined, revealing that the highest specific biogas yield, at 642 L/kg VS, occurred at an S/I ratio of 0.5. An accumulation in volatile fatty acids (VFAs) was observed at higher S/I ratios, attributed to the lower abundance of inoculum microorganisms in the anaerobic digestion process. Overall, the findings suggested that the optimum C/N ratio for co-digestion of MSW and FW falls within the range of 20–25/1, while the preferred S/I ratio is 0.5.

Possibilities of Utilising Biomass Collected from Road Verges to Produce Biogas and Biodiesel

Grass collected as part of roadside maintenance is conventionally subjected to composting, which has the disadvantage of generating significant CO2 emissions. Thus, it is crucial to find an alternative method for the utilisation of grass waste. The aim of this study was to determine the specific biogas yield (SBY) from the anaerobic mono-digestion of grass from road verges and to assess the content of Fatty Acid Methyl Esters (FAMEs) in grass in relation to the time of cutting and the preservation method of the studied material. The biochemical biogas potential (BBP) test and the FAMEs content were performed on fresh and ensiled grass collected in spring, summer, and autumn. The highest biogas production was obtained from fresh grass cut in spring (715.05 ± 26.43 NL kgVS−1), while the minimum SBY was observed for fresh grass cut in summer (540.19 ± 24.32 NL kgVS−1). The methane (CH4) content in the biogas ranged between 55.0 ± 2.0% and 60.0 ± 1.0%. The contents of ammonia (NH3) and hydrogen sulphide (H2S) in biogas remained below the threshold values for these inhibitors. The highest level of total FAMEs was determined in fresh grass cut in autumn (98.08 ± 19.25 mg gDM−1), while the lowest level was detected in fresh grass cut in spring (56.37 ± 7.03 mg gDM−1). C16:0 and C18:0, which are ideal for biofuel production, were present in the largest amount (66.87 ± 15.56 mg gDM−1) in fresh grass cut in autumn. The ensiling process significantly impacted the content of total FAMEs in spring grass, leading to a reduction in total saturated fatty acids (SFAs) and an increase in total unsaturated fatty acids (USFAs). We conclude that grass biomass collected during the maintenance of road verges is a valuable feedstock for the production of both liquid and gaseous biofuels; however, generating energy from biogas appears to be more efficient than producing biodiesel.

NUTRIENT CHARACTERIZATION, BIOGAS AND ELECTRICITY GENERATION POTENTIALS OF ROOT AND TUBER WASTES

Rapid population growth and increasing food demand have led to a significant rise in organic waste generation, which has had a negative impact on the environment. However, these wastes can be utilized as substrates for anaerobic digestion (AD) biogas production, providing a sustainable and environmentally friendly waste management solution. The aim of this study was to evaluate the nutrient composition, biogas potential, and electricity generation capacity of root and tuber waste as a feedstock for biogas production. Waste samples were collected from various restaurants in Malumfashi. The nutrient composition of the waste samples was analyzed using standardized AOAC methods, and the biogas potential was estimated using the Baserga model equations. The results revealed that the waste samples had a total solid content of 94.70%, a volatile solid content of 87.60%, a crude protein content of 0.10%, a nitrogen-free extract of 5.1%, a crude fiber content of 5.04%, a crude fat content of 7.1%, and an ash content of 5.3%. The estimated biogas yield from complete degradation of fresh organic matter from roots and tubers was 501m3/ton, with a methane content of 52%. Based on the calorific value of biogas and the efficiency of electrical conversion, the estimated electrical potential was determined to be 1072 kWh/ton. The study recommends the utilization of root and tuber waste as a valuable resource for biogas generation and renewable energy production. Additionally, further research should be conducted to determine the specific biogas production outputs of root and tuber wastes.

Optimizing anaerobic digestion from chicken droppings: impact of inoculation with IL and IL-KT01 inoculums on specific biogas production

Optimizing anaerobic digestion from chicken droppings: impact of inoculation with IL and IL-KT01 inoculums on specific biogas production

Real-world assessment of a decentralized food waste anaerobic digestion system: A test-bedding case study application

Addressing the global challenge of food waste, this research delves into the assessment of an on-site food waste treatment solution through a full-scale decentralized anaerobic digester (AD) system, specifically deployed at a Singapore hawker centre. Demonstrating efficiency in Singapore's tropical climate (29 °C) without external heating, the 10.8 m³ digester exhibited resilience over 234 days, navigating through real-world fluctuations in average organic loading rates ranging from 0.07 ± 0.02 to 0.81 ± 0.38 kgVS/(m3d). The normalized specific biogas production averaged 0.70 ± 0.48 m3/kgVS, accompanied by a methane concentration of 56.9 ± 2.9%. During peak performance, with an organic loading rate of 1.1 kgVS/(m3d), the system achieved an impressive volumetric biogas production rate of 1.18 m3biogas/m3reactor, equivalent to 1.1 m3/kgVS of specific biogas production per day. The energy assessment revealed consumption rates of 0.57–0.97 m3/kWh, positioning it comparably with commercialized biogas technologies in China and Taiwan. In the realm of microbiome composition, the prevalence of hydrogenotrophic methanogens, including Methanomicrobia, Thermoplasmata, and Nanoarchaeia, is notable. These methanogens showcase a remarkable tolerance to acetate, surpassing common aceticlastic methanogens by 11 times, thereby playing a pivotal role in enhancing the stability of the AD system over extended periods. On the economic front, the present AD system yielded losses ranging from SG$552,434 to SG$742,919, primarily due to a low payback period and substantial investment costs. Profitability becomes a possibility if there are significant reductions in capital costs and operator salaries. The challenges encountered during the operation of this decentralized system, along with the corresponding mitigation measures, are thoroughly discussed. Positioned as a promising test-bedding model, this application underscores its technical feasibility potential for sustainable food waste management through AD technology in Singapore. It stands as a replicable prototype, contributing to closing the food waste loop and advancing the bioeconomy.

Peering into a Simplified Digestor for Households: Performance, Cost and Carbon-Neutral Niche

In this study, a black-shading cylindrical water tank made of high-density polyethylene was locally manufactured as a household digestor for treating cow manure in Bangladesh. Effluent slurry instead of water was reused for manure dilution under manure-to-slurry ratios of 1:2 and 1:1, to assess this small prototype’s production efficiency and feasibility. The specific biogas production at both ratios matched well, by 0.12 m3/kg VS and 0.14 m3/kg VS, respectively, while the former slurry dilution operation outperformed in daily and accumulative biogas production by 16% and 57%, correspondingly, referring to 0.49 Nm3/d on average and 8.55 Nm3 in total, potentially meeting a 2 h household cooking energy requirement. From a nationwide viewpoint, slurry dilution was proven to be a great initiative to conserve water amounting to 50,286,751 m3 for 114,810 households of 6 person-equivalents annually, while cutting chemical costs by USD 32,720,684/yr and trimming annual greenhouse gas emission by 1.8 million tons of CO2e. This study revealed that a small prototype digestor could be an alternative energy source for cost-effective and eco-friendly household applications.

ЭНЕРГЕТИЧЕСКИЙ ПОТЕНЦИАЛ И ОСОБЕННОСТИ БИОДЕГРАДАЦИИ ЗЕРНОВОЙ ПЫЛИ ПРИ ЕЕ ПЕРЕРАБОТКЕ В БИОГАЗ

The composition of the dust that is generated during the collection, transportation, processing and storage of grain is different and complex. The amount of grain dust can reach 26% by weight of the raw material. Due to the ability to ignite spontaneously, it is classified as a hazard class 3, and if it enters the human body, it can cause harm to health, therefore, grain processing enterprises take measures to reduce the concentration of grain dust in the air. On the other hand, the dust generated during grain processing is, due to its chemical composition, a valua- ble raw material, the loss of which is undesirable. The world literature describes such methods for processing aspiration grain dust as hydrolysis and the preparation of nutrient media for microorganisms, briquetting and combustion, use in composting, as well as conversion into biogas. The purpose of this work is to study the features of processing aspiration grain dusts of various agricultural crops into biogas and determine their energy potential and biodegradability. As a result of our laboratory studies, it was established that the specific biogas and methane yield from soybean grain dust was 186.37±58.89 – 230.30±21.90 and 95.54±36.95 – 122.17±15.39 ml/g VS respectively; from barley grain dust – 165.06±9.37 – 191.41±5.65 and 86.45±6.37 – 100.18±6.65 ml/g VS respectively. The concentration of methane in biogas in different variants ranged from 46.75±7.14 to 52.75±1.60%. When recycling 1 ton of these grain dusts at a biogas station, you can get from 278.70 to 382.25 kW of electrical energy and from 285.50 to 391.57 kW of thermal energy. The degree of decomposition of organic matter of substrates in our study is generally low – from 5.61±0.08 to 5.91±0.37%. Thus, it has been established that the grain dusts studied in this work can be considered as a promising cosubstrats for existing or planned biogas stations. The recommended processing time is no more than 35 days.

Review and Bibliometric Analysis of Biogas Power Plants in Indonesia

The demand for energy is increasing due to population growth, technological advancements, and a growing need for sustainable energy sources. Indonesia, which faces an energy deficit, is exploring alternatives to fossil fuels. Biogas, produced through the anaerobic fermentation of organic matter, offers a clean and sustainable energy option while addressing waste disposal issues. Therefore, this literature review examines various aspects of a biogas power plant, including a feasibility study that encompasses technical and economic analyses, generator design, trials, implementation, and post-implementation evaluation. In this review, we gathered scientific papers from Google Scholar using the keywords "pembangkit listrik biogas" between 2019 and 2022, with a focus on recent content. Patents and citations were excluded from the Google Scholar searches to ensure article relevance. Out of a total of 40 articles, 30 were rejected because they did not originate from scientific journals. The collected articles are categorized based on the materials used for biogas generation in power plants. This systematic approach yielded 10 relevant articles. Consequently, the literature reveals that various raw materials, such as palm oil mill waste (POME), livestock manure, and organic waste, hold the potential for biogas production. The results emphasize the economic feasibility of specific biogas projects, the environmental challenges they pose, and the positive impact they have on community well-being

Life cycle assessment of sludge anaerobic digestion combined with land application treatment route: Greenhouse gas emission and reduction potential

Sewage sludge treatment and disposal is essential for water environment protection and pollution management. Coupling anaerobic digestion with land application offers a promising solution to recycle energy and resources to reduce greenhouse gas(GHG) emissions. However, the comprehensive assessment of the anaerobic digestion treatment route on GHG emissions and reduction potential is lacking. This study used life cycle assessment(LCA) to evaluate the GHG emissions based on two cases. The GHG emissions resulting from the digested sludge land application was considered, and the reduction potentials resulting from biogas utilization and substituting chemical fertilizers were also analyzed. The results showed the net GHG emissions of the two cases were 178.92 and − 26.33 kg CO2-eq/tDS, respectively. When excluding the reduction, the GHG emissions of the two cases were 519.32 and 352.97 kg CO2-eq/tDS, respectively, where the dewatering, digested sludge drying, and land application were the main contributors. The GHG emissions associated with the digested sludge land application accounted for 28% and 45% of the total GHG emissions in two cases, respectively. The GHG emission reduction could be achieved by sludge substitution for chemical fertilizer, which could offset 65.5% and 107.5% of the total GHG emissions in two cases, respectively. While the biogas utilization could only offset less than 10% of the total GHG emissions of both cases. Likewise, improving organic content or specific biogas yield rates could only offset up to 26.2% and 40.3% of the total GHG emissions. These findings provide understanding into evaluating GHG emissions of the sludge anaerobic digestion treatment route.

Impact of Thermo-Mechanical Pretreatment of Sargassum muticum on Anaerobic Co-Digestion with Wheat Straw

Sargassum muticum (SM) is an invasive macroalgal species seasonally occurring in large quantities. While generally suitable for anaerobic digestion, recent studies resulted in low specific methane yields (SMYs), presumably due to salt, polyphenol, and high fiber contents of this marine biomass. In this study, the specific biogas yield (SBY) and SMY of SM alone as well as in co-digestion with wheat straw (WS) were investigated in batch tests at process temperatures of 44 ± 1.4 °C with a retention time of approx. 40 d. The pretreatment variants of SM were examined with regard to desalination and disintegration to potentially improve digestibility and to enhance the overall performance in anaerobic digestion. A sole mechanical treatment (pressing) and a thermo-mechanical treatment (heating and pressing) were tested. Batch assays showed that pressing increased the SMY by 15.1% whereas heating and pressing decreased the SMY by 15.7% compared to the untreated variant (87.64 ± 8.72 mL/gVS). Both anaerobic digestion experiments generally showed that co-digestion with WS can be recommended for SM, but the observed SBY and SMY were still similar to those of other studies in which SM was not pretreated. The mechanical pretreatment of SM, however, offers the potential to enhance the SMY in the anaerobic digestion of SM with WS, but further research is necessary to identify the optimum upgrading approaches since the overall SMY of SM is relatively low compared to other substrates that are commonly used in anaerobic digestion. In addition to anaerobic digestion, SM as an already available biomass could also be of interest for further utilization approaches such as fiber production.