Over the years, research development has gradually shifted towards the accomplishment of the Sustainable Development Goals (SDGs) and circular economy-oriented research. This had been achieved by the incorporation of a few key enablers and strategies into studies, such as environmental protection, product-life cycle, waste hierarchy, waste reduction, sustainable consumption, and so on. Anaerobic Digestion (AD) and composting are seen as one of the key drivers of the envisioned circular economy, as they recover valuable resources such as energy, clean water, and nutrients from the by-products of companies, communities, and agro-industrial sectors.

AD and composting are both natural biological processes that can serve as long-term waste management and recycling solutions by providing renewable energy and organic fertilizer while fulfilling the nutrient requirements and reducing greenhouse gas emissions. New technology and enhanced processes in anaerobic digestion and composting can create the ideal scenario in which continuous flow of resources can be a viable long-term waste management solution. Green engineering techniques can be utilized in AD and composting since they are economically feasible while also reducing pollutants and health and environmental threats.

This Special Issue aims to contribute to waste management by sharing and understanding current knowledge on anaerobic digestion and composting research and development. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Feedstock formulation, process reaction, and safety
• Production of new microbes and biocatalysts
• Design, operation, and stability of anaerobic digestion-composting
• Optimization of integrated anaerobic digestion-composting
• Controlled digested and compost leachate processing
• Phytotoxicity and toxicity assessment of the products
• Vermicomposting and larvae-based bioprocessing