Integrated Composting and Anaerobic Digestion for Zoo Waste Management: A Review

India is home to more than 150 zoological parks that play a vital role in biodiversity conservation, education, and tourism. However, these facilities generate considerable quantities of biodegradable waste daily, including animal manure, bedding litter, uneaten feed, and garden residues. Traditional disposal methods such as open dumping, incineration, or basic composting lead to foul odors, greenhouse gas emissions, and potential pathogen spread. In the Indian context, where climatic conditions and organic waste composition vary widely, integrated anaerobic digestion (AD) and composting systems have emerged as a sustainable and economically feasible strategy for zoo waste management. Anaerobic digestion produces renewable biogas energy, while composting of the digestate ensures safe stabilization and nutrient recycling. This review consolidates recent developments in India (2018–2025) related to integrated AD–composting technologies, focusing on the composition of zoo waste, process optimization, and environmental and economic outcomes. Case studies from the National Zoological Park (New Delhi), Mysuru Zoo (Karnataka), Nehru Zoological Park (Hyderabad) and Nandankanan Zoo (Bhubaneswar) demonstrate the feasibility of these systems. The review emphasizes that integrated waste-to-energy and composting models can reduce waste volume by up to 80%, achieve near-zero landfill disposal, and contribute to India’s national missions such as Swachh Bharat Abhiyan and Waste to Wealth Programme. Challenges related to technology adoption, operational expertise, and policy implementation are also discussed, along with recommendations for future research and inter-institutional collaboration. Overall, the integration of anaerobic digestion and composting provides a sustainable, circular solution for managing zoo waste in India, aligning environmental stewardship with clean energy generation and nutrient recovery.