Novel resources recovery from anaerobic digestates: Current trends and future perspectives

Abstract

Anaerobic digestion (AD) is a well-known process with potential applications in the energy sector and waste management. The generation of digestate material during the AD process is considered a waste material. Although agriculture is a significant end-user of digestate, the surplus nutrient content, agricultural crop requirements, escalating transport costs, regulatory demands, and market acceptance constitute significant hurdles for utilizing digestate in agriculture alone. Many new innovative technologies are being developed as alternative approaches for digestate management and related options. Anaerobic digestate incorporates versatile characteristics including essential plant nutrients, enzymes, extracellular polysaccharides and trace elements. These properties give the AD digestate much application potential when combined with the appropriate treatments and valorization process. Microbial bioconversion, fermentation, hydrothermal carbonization, pyrolysis, Vacuum thermal stripping, Nijhuis Ammonium Recovery, Electrodialysis, Trans Membrane Chemi Sorption, Osmotic membrane bioreactor, chemical precipitation, Catalytic decomposition are the important processes commonly used to valorize the AD digestate. The AD digestate can be used as an organic amendment in agriculture, a substrate for algae cultivation, nitrogen and phosphorus extraction, energy production, synthesis of hydrochar and pyrochar for pollutants adsorption, energy storage and conversion, synthesis of various carbon and doped metal nanoparticles for photocatalytic activity and production of high-value chemicals. Among the multiple avenues open to applied research, some are entirely new. Hence, this review aims to incorporate recent research trends in AD digestate valorization, and subsequently generate knowledge on the preparation of novel products applicable to various sectors.

Graphical abstract

KEYWORDS:

• Biofuels
• digestate valorization
• high-value chemicals
• hydrochar
• nanomaterials
• nutrient recovery
• pyrochar

Acknowledgments

The authors wish to thank the Australian Government for providing financial support through Endeavour Research Fellowship program and The University of Newcastle, Australia and Tamil Nadu Agricultural University, India for providing necessary support and facilities to perform this work.