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Rural African renewable fuels and fridges: cassava waste for bioethanol, with stillage mixed with manure for biogas digestion for application with dual-fuel absorption refrigeration



The growth and processing of cassava (Manihot esculenta) in Africa produces a range of waste streams which are proving problematic due to their current mismanagement. Although a range of technical solutions exists to convert these waste streams into valuable products, there has been very little progress made in applying these solutions. This review provides a broad picture of the cassava waste issue in the context of African agriculture and bioprocessing. As an outcome of the review process the authors propose a simple and scalable two-step process that biologically converts the waste streams into valuable products. The first step in the process is fermentation and distillation of the cassava waste to produce ethanol. The second step is the anaerobic digestion of the fermentation byproducts with other waste streams, including animal manure and human excrement, to produce biogas and biological fertilizers. Despite the scalability of this system, the focus of this review is the development of a conceptual system for rural smallholders to achieve multiple beneficial outcomes including treatment of multiple troublesome waste streams, production of a liquid biofuel, the provision of refrigeration through biogas powered absorption chillers, and the co-production of organic fertilizers. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd