ReviewWaste biorefineries: Enabling circular economies in developing countries
Graphical abstract
Introduction
Today, the world is facing many serious challenges, including ever-growing human population and the consequent security for food, energy, and water (Amulya et al., 2016). In addition, the greenhouse gas (GHG) emissions and various other pollutants are posing a serious threat to mankind due to anthropogenic climate change (Ouda et al., 2016). As a result, the gap between environmental sustainability and economic growth is increasing (Nizami et al., 2017). Therefore, the need for sustainable technologies, mandates, and policies to mitigate climatic change and provide a constant supply of energy and feed has become critical for enabling circular economies in the developing countries (Guerrero et al., 2013, Sadef et al., 2016a).
The sustainable disposal of waste is still in infancy in most of the developing countries due to limited allocated budgets, infrastructure and maintenance facilities (Tozlu et al., 2016, Tan et al., 2015, Nizami et al., 2016a). The high generation rates of organic waste and its disposal to open dumpsites or non-sanitary landfills are resulting in adverse environmental, economic and social problems (Sharholy et al., 2008, Nizami et al., 2016b). The actual collection of waste from most cities in developing countries like India, Pakistan and Bangladesh is only around 60%, while the remaining waste lies in the empty plots, street sides, along with the road, railway lines, drains, and low-lying areas (Hoornweg and Bhada-Tata, 2012, Sadef et al., 2016a). In poor regions, the unplanned growth of new cities is making the situation even worse (Miandad et al., 2016a, Miandad et al., 2017). The municipalities dealing with municipal waste are unable to upgrade the facilities to international standards, as in most cases the waste management is the city’s largest budgetary item (Brunner and Rechberger, 2015). The solid waste management costs will increase from current annual US $205.4 billion to around US $375.5 billion by 2025 worldwide (Hoornweg and Bhada-Tata, 2012).
The efficient treatment of waste is critical not only from a sanitation point of view but also due to associated economic and environmental benefits (Rathi, 2006). Similarly, the fuels if produced from feedstocks that are cultivated on a good agriculture land are blamed for high prices of food and animal feed in some parts of the world (Sims et al., 2010). Therefore, the strategic deployment of biofuels is required from such non-food feedstocks that reduce the land use impacts and GHG emissions in comparison to conventional fuels (Singh et al., 2010, Ouda et al., 2015). The biorefinery technologies such as pyrolysis, fermentation, gasification, anaerobic digestion (AD), incineration, refuse derived fuel (RDF) and plasma arc gasification have emerged as promising methods to produce fuels from non-food feedstocks such as cereal straw, sugarcane bagasse, perennial grasses, corn stover, agricultural and forest biomass waste, and municipal and industrial organic waste (Naik et al., 2010, Miandad et al., 2016b). However, each biorefinery technology can produce a specific fuel depending on the type and availability of feedstock (Sanaei et al., 2012, Mohan et al., 2016a). Therefore, if such technologies could be combined under an integrated waste biorefinery concept, mixed and multiple feedstocks could be treated to produce various products in the form of food, feed, fuel, power, and heat along with value-added chemicals (Posada et al., 2013).
In most of the developing countries, the concept of waste biorefineries is very relevant and imperative due to the environmental and economic overburden caused by the current waste disposal practices and for fulfilling the increasing energy demands along with the creation of new businesses, job markets and improvements in the public health and local environment (Ismail and Nizami, 2016). It is estimated that around US $410 billion can be generated only from the world market of municipal waste recycling. However, only a quarter of this waste is recovered or recycled for the beneficial purposes (Guerrero et al., 2013, Hossain et al., 2014).
This study aims to examine the potential of waste biorefineries in developing countries as a solution to their current waste disposal issues and as facilities to produce fuels, power, heat, value-added materials and chemicals in order to enable circular economies. In addition, the challenges and barriers, including the technical and regional issues in route to successful implementation of biorefinery concept in developing countries are also presented. Furthermore, a detailed technical, economic and environmental analysis of waste biorefineries is included using life cycle assessment (LCA). The study concludes with recommendations in order to address the relevant challenges in most of the developing countries.
Section snippets
Waste generation and energy demands
Substantial growth in population and urbanization along with raised livings standards in most of the developing countries have elevated the energy demands together with increased municipal waste generation (Fig. 1a-d). In 2013, the world population was around 7.2 billion that is estimated to reach up to 9.6 billion by 2050 and will mainly concentrate in the developing world with more than half only in African countries (UN-DESA, 2012). Similarly, the urban areas of the world currently
Integrated waste biorefineries
The biorefineries mentioned in the second section are primarily based on single conversion process to produce distinctive fuels and chemicals. However, integrated biorefineries use additional biobased or multiple feedstocks for the production of various biofuels, power, and chemical materials. Typically, all of the electricity or a fraction of the power generated by a refinery can be used for its operation, and the rest of the energy or products will be considered for the commercial enterprise.
Conclusions
Waste biorefineries in developing countries are a way forward not only to achieve sustainable waste management but also generate significant economic and environmental benefits. The economic benefits include recovery of energy and value-added products, land savings, new opportunities and businesses development and landfill cost savings. Whereas, the environmental benefits are in the form of reduced GHG emissions from the current disposal practices and savings of natural resources of land, soil
Acknowledgement
Dr. Abdul-Sattar Nizami and Dr. Mohammad Rehan acknowledge the Center of Excellence in Environmental Studies (CEES), King Abdulaziz University (KAU), Jeddah, Saudi Arabia and Ministry of Education, Saudi Arabia for financial support under Grant No. 2/S/1435 and 2/S/1438. Authors are also thankful to Deanship of Scientific Research (DSR) at KAU, Saudi Arabia for their financial and technical support to CEES.
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