Char fuel production in developing countries – A review of urban biowaste carbonization

Urban households in low- and middle-income countries (LAMICs) face the challenge of finding affordable, reliable and sustainable cooking fuel supplies. Most city residents use wood-based charcoal derived from mostly informal supply chains, which are linked to unsustainable forest logging, low efficiency production methods and long transportation routes, all factors that contribute to environmental degradation. At the same time, the provision of adequate and equitable solid waste management (SWM) services remains a major urban challenge, with municipal solid waste mainly consisting of organics. Sales of briquettes made from carbonized biowaste can potentially foster waste collection and enhance cost-recovery of SWM systems, while contributing to a sustainable energy supply. This article provides essential information for understanding the potential for and limitations of char production from urban solid biowaste to tackle both SWM and cooking fuel challenges simultaneously. It reviews the current state of charcoal consumption, provides an overview of the SWM situation and explores the potential of converting biowaste streams into char in LAMICs. Existing carbonization technologies are presented and their advantages and disadvantages examined by means of a weighted assessment matrix (Pugh method) using technical, financial and environmental/health criteria. For financially viable carbonization the feedstock should be continuously available at no cost and have physical and chemical properties suitable for pyrolysis: dry, unmixed and homogeneous. Thus, separated waste obtained near the source of generation is important. The existing bulk of mixed, wet household and market wastes, however, require carbonization technologies that are associated with high capital investment. Overall, it has been shown that low-tech retorts have the highest suitability for biowaste carbonization in LAMICs. Further research is required to improve energy efficiency, reduce air pollution, guarantee safe operation and assess financial viability. Beyond the technical aspects, policy measures to support sustainable char production from biowaste are necessary to nurture government support.