Demand-oriented biogas production and biogas storage in digestate by flexibly feeding a full-scale biogas plant

Effect of phase-separation and thin-slurry recirculation on flexible biogas production from maize silage and bedding straw

This study investigates a two-stage anaerobic digestion (AD) process to enhance methane production from lignocellulosic biomass, in this case bedding straw, co-fed with maize silage. The system combines phase separation and double thin-slurry recirculation under mesophilic conditions. The first hydrolysis-acidogenesis stage produced over 10 g L-1 short-chain carboxylic acids (SCCA) at an organic loading rate of 1.3-3.0 g (L d)-1 when fed with a content of 50 wt% straw. The subsequent methanogenesis stage achieved a maximum methane yield of 260 mL CH4 gCOD-1, with 50 % variation in methane production within 24 h. Thin-slurry recirculation was shown to improve the methane content by 20 %. Cell activity and quick recovery of gas production was proven after fasting periods of several weeks. The approach demonstrates the potential for flexible, efficient processing of bedding straw in AD without further treatment beyond cutting.

Improving the shock resistance of anaerobic digestion under demand-oriented biogas production mode by using converter steel slag powder

Introducing flexible biogas production (FB) can result in instantaneous high-shock loads for anaerobic digestion system, posing risks to the system's stable operation. Steel slag, a typical metallurgical solid waste, has been demonstrated to enhance the buffering capacity of digestion systems, thereby increasing methane production and achieving 'waste treatment using waste'. However, its efficacy under high-shock loads in FB is uncertain. Pulse feeding experiments simulating FB were conducted to analyse the system's impact resistance with steel slag addition and investigate its enhancement mechanisms. The addition of steel slag improved the methane production rate under various shock conditions, with a particularly notable enhancement under concentration shock. This scenario also saw a significant increase in the generation of soluble chemical oxygen demand and its utilization by microorganisms. This can be attributed to the enrichment of hydrolytic bacterial phyla (Firmicutes) and genera (Gelria), with functional gene analysis revealing an increase in genes associated with Fe(III) reduction and CO2-to-methane pathways. The study results indicate that the role of steel slag as an alkaline, iron-rich material enhances system alkalinity, reduces inhibition from H2 partial pressure and boosts hydrogenotrophic methanogen activity, making it suitable as an exogenous enhancer for demand-oriented anaerobic digestion.

Nitrogen-doped activated carbon-based steel slag composite material as an accelerant for enhancing the resilience of flexible biogas production process against shock loads: Performance, mechanism and modified ADM1 modeling

Anaerobic digestion for flexible biogas production can lead to digestion inhibition under high shock loads. While steel slag addition has shown promise in enhancing system buffering, its limitations necessitate innovation. This study synthesized the nitrogen-doped activated carbon composite from steel slag to mitigate intermediate product accumulation during flexible biogas production. Material characterization preceded experiments introducing the composite into anaerobic digestion systems, evaluating its impact on methane production efficiency under hydraulic and concentration sudden shocks. Mechanistic insights were derived from microbial community and metagenomic analyses, facilitating the construction of the modified Anaerobic Digestion Model No. 1 (ADM1) to quantitatively assess the material's effects. Results indicate superior resistance to concentration shocks with substantial increment of methane production rate up to 33.45% compared with control group, which is mediated by direct interspecies electron transfer, though diminishing with increasing shock intensity. This study contributes theoretical foundations for stable flexible biogas production and offers an effective predictive tool for conductor material reinforcement processes.

Evaluating the sustainability of demand oriented biogas supply programs under different flexible hierarchies: A suggested approach based on the triple bottom line principle

In this paper, a decision-making approach based on the triple bottom line concept is presented for evaluating the sustainability of demand-oriented biogas supply (DOBS) programs with regard to their environmental, economic, and social impacts. For the assessment, an indicator system was developed, whose main parameters were quantified by integrating emergy analysis, economic benefit assessment, and a proposed social risk accounting method. The Charnes-Cooper-Wei-Huang (CCWH) model with constrained cone was adopted to calculate the comprehensive sustainability via the synthesis of the economic, environmental, and social indicators, in which eight scenarios were set according to the flexibility hierarchy of biogas supplied for load demand, biogas production mode, and feeding substrates. The evaluation results show that the DOBS scenario of supplying for real-time varying power demand by using straw and livestock manure has the highest sustainability score in our case study. Based on the results, corresponding managerial implications are proposed.

Decentralised system for demand-oriented collection of food waste - Assessment of biomethane potential, pathogen development and microbial community structure

Enormous amounts of food waste (FW) are produced worldwide, requiring efficient disposal strategies, both economically and ecologically. Anaerobic digestion to produce biomethane is among the most promising strategies, but requires proper solutions for storage and delivery of the waste material. Here, a decentralized system for demand-oriented FW storage and its practical usability was assessed. FW was stored under batch and fed-batch strategies at 5 °C, 20 °C and 30 °C for 28 days. The results showed that FW can be stored without cooling since bacterially produced lactic acid rapidly stabilized the material and inactivated pathogens. While FW storage worked well under all storage conditions and strategies, 16S analysis revealed a distinct microbiota, which was highly characteristic for each storage temperature. Moreover, FW storage had no negative impact on methane yield and stored FW contained readily degradable substances for demand-oriented biogas production.

Promoting biomethane production from propionate with Fe2O3@carbon nanotubes composites

Using a batch anaerobic system constructed with 60 mL serum bottles, potential of a composite material with Fe₂O₃ nanoparticles decorated on carbon nanotubes (CNTs) to enhance biomethane production was investigated. The composites (Fe₂O₃@CNTs) with well dispersed Fe₂O₃ nanoparticles (4.5 nm) were fabricated by a facile thermal decomposition method in a muffle furnace under nitrogen atmosphere. Compared with Fe₂O₃, Fe₂O₃@CNTs showed a large specific surface area and good electrical conductivity. Supplementation of Fe₂O₃@CNTs to the propionate-degrading enrichments enhanced the methane production rate, which was 10.4-fold higher than that in the control experiment without material addition. The addition of Fe₂O₃@CNTs also not only showed a clearly electrochemical response to flavin and cytochrome C, but also reduced the electron transfer resistance when compared to the control. Comparative analysis showed that Fe₂O₃ in Fe₂O₃@CNTs played a key role in initiating electrochemical response and triggering rapid methane production, while CNTs functioned as rapid electron conduits to facilitate electron transfer from iron-reducing bacteria (e.g., Acinetobacter, Syntrophomonas, and Geobacter) to methanogens (e.g. Methanosarcina).

Estimation of Biogas Generated in Two Landfills in South-Central Ecuador

The landfill is a final disposal technique to confine municipal solid waste (MSW), where organic matter is degraded generating leachate and biogas composed of methane gases (CH4), carbon dioxide (CO2) and other gases that contribute to global warming. The objective of the current research was to estimate the amount of biogas generated through the LandGEM 3.03 mathematical model to determine the amount of electrical energy generated and the number of homes that would be supplied with electrical energy from 2021 to 2144. As a result of the application, it was estimated that in the Pichacay landfill, the highest point of biogas generation in 2053 would be 76,982,177 (m3/year) that would generate 81,226,339.36 (kWh/year), and would supply 5083 homes with electricity. Similarly, in the Las Iguanas landfill, the highest point would be 693,975,228 (m3/year) of biogas that produces 73,223,5296.7 (kWh/year) and would supply electricity to 45,825 homes. Of the performed gas analyses in the Pichacay landfill in 2020, an average of 51.49% CH4, 40.35% CO2, 1.75% O2 and 17.8% H2S was presented, while in the Las Iguanas landfill, for 2020 and 2021, we obtained an average of 51.88/CH4, 36.62% CO2, 1.01% O2 and 187.58 ppm H2S. Finally, the biogas generated by being harnessed minimizes the impacts related to global warming and climate change and would contribute electricity to the nearby communities.

Anaerobic digestion beyond biogas

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, "Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions.