Developing a biogas centralised circular bioeconomy using agricultural residues - Challenges and opportunities

Recent advances in co-digestion conjugates for anaerobic digestion of food waste

Anaerobic digestion (AD) is a biological process that breaks down organic waste materials, such as food waste (FW) that produces biogas and digestate. The biogas can be utilized as biofuel, and digestate could be applied as fertilizer. However, AD of FW alone has limitations on optimal degradation, digester stability and biogas yield. Co-digestion of FW along with other organic wastes such as animal manure, agricultural residue, sewage sludge and industrial organic waste, has shown substantial improvement in degradation process with increased biogas yield. The inadequacies in FW for optimum AD, like low carbon-to-nitrogen ratio (C/N ratio), lack of trace elements and irregular particle sizes, can be nullified by adding appropriate co-digestion conjugates. This review aims to describe the characteristic inadequacies of FW and examines the effect on mesophilic co-digestion of FW with animal manure, waste sludge and agricultural wastes for biogas production optimization. A critical review on the impact of pretreatment and co-digestion to enrich the methane (CH4) content in biogas has been performed. The review also examines the microbial community shift due to co-digestion, which is critical for the stability of an anaerobic digester. Finally, it discusses the prospects and challenges for the widespread application of the co-digestion technique as an effective organic waste management practice.

Farm biogas project considering carbon trading indicates promising economic results-a case study

The application of the farm biogas project is a perfect measure to deal with the increasingly nervous global climate problem and energy crisis and can support the accomplishment of urgently needed carbon peaking and carbon neutrality effectively. But the poor economic benefits hinder its better development. Thus, this paper aims to enhance the economics of farm biogas projects and explore a win-win model for economic and environmental benefits by studying the economic impact of participation in carbon trading on three types of farm biogas projects. First, economic analysis of farm biogas projects based on life cycle cost is carried out using case analysis. Second, the greenhouse gas emission reductions are calculated and benefits from carbon trading are considered. Then, the economic robustness was tested. Specifically, the economics of all three types of farm biogas projects is improved after carbon trading. The ecological farm biogas project has the best economic performance, with a net present value of $551,689.11, internal rate of return of 49%, and payback period of 2.39 years. In addition, the emission reductions of 5045.79 t CO₂e, 7420.28 t CO₂e, and 148.41 t CO₂e are very significant. Based on these, suggestions for developing farm biogas projects and introducing biogas projects to carbon trading are put forward for the reference of governments and investors when making investments and reforms. According to the result, participation of farm biogas projects in carbon trading can effectively enhance economic benefits and accelerate the achievement of the greenhouse gas emission reduction target which is of great significance to the urgent goal of global green and low-carbon transformation.