One of the key concerns of biogas plants is the disposal of comparatively large amounts of digestates in an economically and environmentally sustainable manner. This paper analyses the economic performance of anaerobic digestion of a given biogas plant based on net present value (NPV) and internal rate of return (IRR) concepts. A scenario analysis is carried out based on a linear programming model to identify feedstocks that optimize electricity production and to determine the optimal application of digestate. In addition to a default scenario, management and policy scenarios were investigated. Economic evaluations of all scenarios, except no subsidy scenario, show positive NPV. The highest NPV and IRR values are observed under reverse osmosis (RO) as a green fertilizer scenario. Our findings show that treating RO as a green fertilizer, as opposed to manure (default scenario), is not only lucrative for the plant but also lessens environmental burden of long distance transportation of concentrates. This paper also concludes that given the uncertainty of regulations concerning RO and the currently low values of digestate and heat, high investment and operating costs limit feasibility of anaerobic digestion of wastes of farm origin and other co-substrates unless subsidies are provided.

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Universal access to water, sanitation and energy services are key challenges in low income countries. The conventional model of providing water, sanitation and waste disposal as a social service is no longer viable because national authorities lack financial and human resources for operation and maintenance and for addressing the sanitation needs locally. Human excreta and wastewater represent resources that can be used to generate new income and support livelihoods through use as a source of energy. The reduction, removal and reuse of wastes must become financially feasible and economically profitable and yield high returns. This requires innovative and sustainable business models and financing instruments for their implementation. This chapter presents an overview of successful and emerging business cases for recovering energy and other useful products from wastewater and fecal sludge from low and middle income countries. The business cases are analysed for their business concepts and opportunities and challenges for scaling-up and scaling-out. Key policy implications and conclusions for supporting the business model approach in the developing world are discussed.