Today’s failures in solid waste management is a situation that jeopardizes our environment in huge ways: landfills are the third largest anthropogenic source of methane gas (which can have a global warming potential 25 times more than that of carbon dioxide), and plastic waste has formed what has been regarded as the eight continent which consists of floating plastic masses in the oceans that have greatly endangered marine life.
Many solid waste management problems originate from urban areas where most of the world’s population reside, and where the pressures to get waste out of sight by any means possible is great. The approach to solid waste management, in particular, that of municipal solid waste (MSW), has been the same in its most fundamental regards for the past few decades with a slow pace in innovation.
For example, waste trucks still collect and transport waste, source-sorting of waste from residents is still largely at the mercy of the discretion of households, and landfilling is still largely used across the world even in developed countries. One reason for this may be that the solid waste management sector is less lucrative than the fossil fuel industry, and so it does not attract enough research and development, competitiveness or penalties from regulators to improve the trajectory of the sector fast enough.
What is the future of municipal solid waste management, especially for developing countries? Is there a way to sustainably process MSW faster than we generate it? Could the cost of the MSW management be reduced to a point to encourage the growth of the markets of value-added products from waste products such as biogas, compost, recycled materials? This paper explores the solutions to this multifaceted issue in waste management by narrowing down the culprit responsible for the failure of waste management systems to the largest fraction of municipal solid waste: the organic fraction.
Handling the organic fraction of municipal solid waste (OFMSW), which could vary from 28% in high income countries to 64% in low income countries, poses well known challenges such as having a zero potential to either be recycled or reused, and being responsible for waste managers opting for the more economical landfilling process if OFMSW is not separated at the source of waste generation.
Therefore, a waste manager’s capacity to separate and handle the OFMSW in a cost-effective manner might as well be his weakest link in implementing any integrated solid waste management (ISWM) system. Then, there is the need to achieve environmental sustainability and win over community participation to sort their waste at the source since for some countries, particularly those of the OECD, household waste makes up over 80% of MSW.
As a feasible starting point for conceiving a product that can fulfil the requirements stated above, solid-state anaerobic digestion (SS-AD) technology offers almost all the right answers: it converts organic waste to a fuel (biogas) and compost by a biological process which has the least environmental impact compared to other thermochemical conversion processes, and it does so with a minimal use of heat and water resources.
However, some reputed and commercially successful SS-AD systems in operation today are operating in a centralized manner, and they are sited in Europe where energy prices are high enough to cause a shift to the use of more affordable renewable energy. For urban areas in other parts of the world, especially for those in developing countries with scarce land resources and inadequate road infrastructure, centralized plants may prove commercially unsustainable because of the added transportation costs and unavailability of land to site an SS-AD plant. Therefore, the missing keys to implementing this solution could lie in using a decentralized operation of an SS-AD plant.
This would call for some level of innovation in the SS-AD system’s design to achieve compactness and scalability in its operation. These possibilities are what this paper explores and makes recommendations on. This study’s deductions were based on a review of several SS-AD systems with reputed commercial success or a potential for it. These included the Valorga, Dranco, Kompogas, Biopercolat and the Anaerobic Phased System. The solutions proposed in this study were considered most useful for densely populated cities in developing countries with inadequate or dilapidated solid waste management infrastructure.
These findings are described in the article entitled Decentralized anaerobic digestion systems for increased utilization of biogas from municipal solid waste, recently published in the journal Renewable and Sustainable Energy Reviews. This work was conducted by Chukwunonso Chinedu Anyaoku and Saeid Baroutian from the University of Auckland.