Advancements in biomass anaerobic digestion and innovative product utilization

Anaerobic digestion has been used to simultaneously realize pollution control, energy recovery, nutrient cycling, and carbon emission reduction. Among them, biomass anaerobic digestion can also contribute to bio-manufacturing, organic waste pollution in environmental protection, and national energy security in sustainable agriculture. Energy utilization can be expected to transform from conventional single energy to a multi-objective collaborative new-quality mode. Current industrial development was also characterized by technological precision, product high-endization, value diversification, and ecological low-carbonization. This study aims to systematically classify the three purposes of biomass anaerobic digestion technology: rural revitalization and food security, agricultural and rural pollution, and renewable energy conversion. A comparison was made to examine the industrial trends between the European Union and China, including standard certification, equipment manufacturing, business models, and technology breakthroughs. Furthermore, three technical links were also reviewed: the functional microbial synergistic metabolism (covering bioaugmentation of targeted functional consortia and intensification of interspecies electron transfer mechanisms), biomass feedstock pretreatment (including physical, chemical, biological, and combined technologies), and process regulation (involving feedstock solid content optimization, carbon-to-nitrogen ratio adjustment, and temperature gradient control). Four bottlenecks were identified to restrict the high-quality development of the industry: Low conversion efficiency caused by the imbalance of microbial syntrophic metabolism, long-term stability of engineering systems, great difficulty in precise regulation, and low added value of products. Four trends were also given for the new-quality utilization of biomass anaerobic digestion. 1) The "black box" of conventional anaerobic digestion was integrated with synthetic biology, multi-omics technology, and artificial intelligence. Multi-scale precise regulation was realized from microbial metabolic pathways to full engineering. 2) Anaerobic metabolic pathways were directionally regulated to apply carbon chain into high-value bio-based chemicals represented by medium- and short-chain fatty acids. The application boundary of anaerobic technology was expanded in the field of bio-manufacturing. 3) A systematic cascade high-value utilization was constructed for primary and by-products: Raw biogas was upgraded into high-end green fuels, such as liquefied biomethane (LBM) for heavy-duty transportation, shipping, and aerospace applications; Biogas residue and slurry were converted into diversified high-value products, including functional bio-fertilizers, biochar materials, and single-cell protein (SCP) feed additives. 4) Carbon emission reduction was realized for quantifiable and tradable carbon assets in the full-chain anaerobic conversion, according to China Certified Emission Reduction (CCER), thereby realizing the stable and sustainable transformation of ecological into economic value. Finally, the future directions and paths of biomass anaerobic digestion were determined using Technology Readiness Level (TRL), including organic waste treatment over the full chain at the county level. Biotechnology and information technology were integrated to realize the full-component value of biomass resources. The findings can provide important theoretical references and practical guidance for engineering and industrial formulation in the field of biomass anaerobic digestion.