Digestate: The Coproduct of Biofuel Production in a Circular Economy, and New Results for Cassava Peeling Residue Digestate

Circular economic paradigm applies residue from one process as input material for another, fostering sustainable benefits for humanity. Anaerobic digestion (AD) is an attractive technology for biogas production in a circular economy. Digestate is the residual organic matter generated as coproduct of biogas. Because digestate is nutrient rich and largely stabilized, it has varied management options. Digestate is suitable for direct use as bio-fertilizer and is a good amendment material to improve soil physical properties. However, the quality, safety, and utility of digestate are dependent upon the characteristics of feedstock, digester process, pre- and post- digestion treatments. Digestates emanating from AD of animal manure, energy crops, food processing residues, and other feedstocks have been reported in published literature. On the other hand, there is dearth of reports on digestate emanating from AD process that utilized cassava peeling residue (CPR) as sole feedstock. This chapter presents relevant information on digestates including production, feedstock, quality and safety requirements, processing and treatment technologies, regulatory aspects, applications management options, cost implications, as well as challenges and opportunities. In addition, new results of nitrogen (N), phosphorus (P), and potassium (K) compositions of liquid fraction of CPR digestate are reported.