Co-digestion of sewage sludge with food waste is a beneficial pathway for sewage plants to enhance their biogas yield. This paper employs hybrid programming with system dynamics simulation to optimize such a co-digestion system from the perspective of demand-oriented biogas supply chain, thus to improve the efficiency of the biogas utilization. The optimum operational parameters of the co-digestion system are derived from the simulation model. It is demonstrated that the demand-oriented biogas supply mechanism can be effectively driven under market-oriented incentive policy. For better compensation of the external cost to assist the operations of the co-digestion supply chain, it is suggested that the substrate collection and transportation subsidy should be combined with the renewables portfolio standard to be implemented as the optimum incentives. The limitations of the study are discussed to lay the foundation for future improvements.

This paper explores the feasibility of flexible biogas production by co-digestion of food waste and sewage sludge based on experiments and mathematical modeling. First, laboratory-scale experiments were carried out in variable operating conditions in terms of organic loading rate and feeding frequency to the digester. It is demonstrated that biogas production can achieve rapid responses to arbitrary feedings through co-digestion, and the stability of the anaerobic digestion process is not affected by the overloading of substrates. Compared with the conventional continuous mode, the required biogas storage capacity in flexible feeding mode can be significantly reduced. The optimum employed feeding organic loading rate (OLR) is identified, and how to adjust the feeding scheme for flexible biogas production is also discussed. Finally, a simplified prediction model for flexible biogas production is proposed and verified by experimental data, which could be conveniently used for demand-oriented control. It is expected that this research could give some theoretical basis for the enhancement of biogas utilization efficiency, thus expanding the applications of bio-energy.

Biogas can be regarded as a dispatchable renewable source when changing into the demand-oriented operation mode (DO), thus could be used for complementing with solar and wind power in distributed energy system (DES) as a substitute for chemical energy storage. However, if the DO is implemented in regional DES, uncertainties are emerged caused by the complex interest interaction between the seller and the buyer groups formed by the biogas plant and the DES’s dispatching center, thus making the development trend of DO unknown. In this context, this study explored the diffusion law of DO in regional DES by establishing a mathematical model based on an evolutionary game between the two major stakeholders, during which the evolutionarily stable strategy (ESS) was deduced for understanding their strategy selections, and then the dynamic diffusion trend was simulated by the system dynamics via a case example. Finally, the sensitivity analysis of parameters is carried out and the optimal policy instruments are proposed according to the main influencing factors. The study revealed that when the DES can realize monetized returns from socio-environmental benefits, the adoption of DO becomes more feasible. Importantly, the revenue generated from electricity sales, by the dispatching center when they do not utilize biogas, emerged as the most critical parameter influencing the ultimate outcomes. The limitations of this research and modeling are discussed to lay a foundation for further improvement.

Biogas can be used for complementary load-balancing with renewable intermittent power, thus maintaining overall energy output stability. However, biogas load balancing is typically used in small-scale distributed energy systems, constrained by factors such as technology and land requirements, making it challenging to scale up. Therefore, this study proposes a closed-loop ecological cycle system, where biogas provides load leveling support for large-scale intermittent power sources in desertified regions dominated by animal husbandry. The biogas slurry and residue produced are used for land restoration and subsequent cultivation of high-quality economic crops, with the resulting straw used for the next round of biogas production. This study conducts an economic assessment of the aforementioned system and analyzes a case study of a load-balancing biogas project in Northwest China. Accounting results indicating that the system's net present value is 0.108 million yuan/m3, internal rate of return is 0.60%, and payback period is 22 years. Additionally, sensitivity backward deduction analysis identified the reasonable value ranges for key system parameters. According to the results, we offer management recommendations to promote the proposed system, supporting innovative biomass energy utilization and enhancing renewable energy stability.Implications: This research introduces a novel closed-loop ecological cycle system that integrates large-scale peak-shaving biogas with renewable energy sources, offering a sustainable solution for enhancing energy stability and environmental sustainability in desertified areas. The study's economic evaluation reveals the critical role of ecological restoration costs in the overall viability of such systems, indicating the necessity for policy support to make them economically attractive. Our findings suggest that targeted subsidies, based on the quantified ecological benefits, are essential for incentivizing the adoption of this model. By providing specific conditions under which the system is economically feasible, this work informs policymakers on how to design effective incentive structures, thereby promoting the wider application of biogas and contributing to the goals of sustainable development and climate resilience. The research underscores the importance of integrating economic and ecological considerations to achieve long-term sustainability, making it a valuable reference for future energy policies and practices.

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 CO ₂ -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 H ₂ partial pressure and boosts hydrogenotrophic methanogen activity, making it suitable as an exogenous enhancer for demand-oriented anaerobic digestion.