Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece Valorisation of solid waste as key opportunity for green city development in the growing urban areas of the developing world Yohannis Fetene a , Taffere Addis b, ⁎ , Abebe Beyene c , Helmut Kloos d a Ethiopian Environment and Forest Research Institute, Jimma Research Center, P.O. Box 1187, Jimma, Ethiopia b Ethiopian Institute of Water Resources, Addis Ababa University, P.O. Box 150461, Addis Ababa, Ethiopia c Department of Environmental Health Science and Technology, Jimma University, P.O. Box 378, Jimma, Ethiopia d Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA ARTICLE INFO Keywords: Biochar Composting Energy recovery Pyrolysis Waste management Ethiopia ABSTRACT Lack of integrated solid waste management practice in fast-growing cities of developing countries is posing a threat to sustainable and green cities development. The fast growing Jimma City in Ethiopia requires up-to-date waste quantification and characterization data for the planning and implementation of sound waste management options such as composting and energy recovery that could create new jobs and promote private sector in- volvement. Therefore, we quantified, characterized and evaluated energy potential and nutrient value of household solid waste from Jimma City. Total daily waste generated from the city’s households was estimated to be 85.8 tons, with an average per capita generation rate of 0.56 ± 0.17 kg/day. The biodegradable organic waste comprises 76% by weight and had optimum moisture content and carbon to nitrogen ratio for composting. The energy content of combustible household waste was estimated to be 17.5 MJ/kg for gross heating value and 9.54 MJ/kg for the net heating value that surpasses the lower limit for thermal treatment process to be eco- nomically viable. Waste-to-energy conversion of combustible waste of cities could reduce annually about 25,303 metric tons of carbon dioxide equivalent greenhouse gas emissions. Char briquettes produced through pyrolysis of solid waste could be a potential substitute for firewood to prevent deforestation and indoor air pollution. In conclusion, composting and pyrolysis are sound waste management options for green cities development in developing countries while minimizing public health risks and cost of treatment and disposal. 1. Introduction Solid waste has to be seen as a resource in the Sustainable Development Goals era for building green cities [1,2]. For example, landfill mitigation and diversion, energy recovery from waste, recycling and other types of sound municipal solid waste (MSW) management practices may reduce current global greenhouse gas emissions by 10–15% [3]. Urban waste in developing countries mostly ends up in unregulated dumping sites within or outside cities and a large propor- tion is burned in open fields [4,5]. Therefore, greening the MSW sector in developing countries requires a shift from business as usual practices to ecologically sound, socially acceptable, and economically viable approaches that seek direct and indirect economic benefits [1]. Despite progress in solid waste management, practices during the last decade, fundamental institutional, financial, social, and environ- mental problems remain prominent challenges in cities of developing countries that demand appropriate measures [6]. Appropriate waste management planning and implementation can be undertaken by the quantity and composition of waste, which depends on the consumption pattern, recycling and reuse at the point of generation, and socio- economic and culture of cities [2,7]. For instance, whereas low and middle-income cities generate mostly biodegradable organic waste, the waste in high-income cities is more diversified, with larger shares of plastic [3]. But waste quantity and composition data are lacking in most developing countries, including Ethiopia, where Jimma City is a case in point. Solid waste management practices in developing countries focus largely on waste collection and disposal in landfills. Few attempts have been made to adopt proactive integrated waste management practices that involve waste reduction at the source, reuse, recycling and re- source recovery [5,6,8]. As a result, many cities in developing countries are facing environmental and health risks while losing economic op- portunities from waste management sector. From a sustainable devel- opment perspective, the focus should be on the reduction of waste, https://doi.org/10.1016/j.jece.2018.11.023 Received 3 August 2018; Received in revised form 18 October 2018; Accepted 11 November 2018 ⁎ Corresponding author. E-mail address: taffere.addis@aau.edu.et (T. Addis). Journal of Environmental Chemical Engineering 6 (2018) 7144–7151 Available online 12 November 2018 2213-3437/ © 2018 Elsevier Ltd. All rights reserved. T