The aim of this series is to provide a literature review on the current status of Energy from Waste (EfW). Due to the length it will be split into three parts. Part 1: Introduction to the topic, a brief history, classifications and policy influences. Part 2: Proven capability, scalability and efficiency. Part 3: Alternative technologies, barriers and gaps in current understanding.
So here goes!
Energy security and climate change are primary issues of the 21st century. Moreover, waste management has been a challenge throughout history. Waste can be defined as a substance or object which the holder discards, intends to discard or is required to discard . Energy from waste (EfW) combines both the processing of waste and generation of energy in the form of electricity and/or heat. Numerous authors refer to EfW as a renewable source of energy –, Fodor and Klemes  noted that this classification varied depending on the legislation of individual countries. The EU considers EfW to be a renewable source of energy , .
Although the main objective of combustion is to treat the waste through volume reduction and destruction of harmful substances, it can also recovery energy, mineral and chemical content . Ludwig  recognised that the process ‘killed two birds with one stone’ by reducing the burden of waste in addition to generating energy. This has been later highlighted by Nemet  and Fodor , with the additional points of reducing the volume of waste to land fill and decreasing the combustion of fossil fuels.
There are a chain of processes involved in waste management and EfW is one part of that chain . EfW includes a range of thermal process of which combustion is one. Waste combustion is the oxidation of combustible materials contained within waste . Previously designated ‘incineration’ this term has been incorporated into the new term ‘waste to energy’ (WtE) or ‘energy-from-waste’ (EfW) . The objective of this series of articles is to review the current knowledge surrounding EfW and to identify areas which require additional research.
2. Brief History
The first functional MSW incinerator was constructed in 1874 in Nottingham . Since its infancy the combustion sector has evolved rapidly . In the last decade there has been both social and legislative power pushing for better methods of handling waste . Reducing the amount of waste to landfill has been a particular focus, largely due to its methane contributions to climate change . The trend to reduce emissions  and reduce waste to landfill meant a growth in waste recovery technologies including combustion . Meacher stated “As a nation, we have to minimise the amount of waste that we produce and get as much value as possible out of what is left” . The aim shifted towards not just combustion but combustion with energy generation to gain ‘added value’ from the waste .
Waste has become a resource opportunity rather than a disposal problem . Incineration with energy recovery (heat and electricity) showed a 20% growth from 2004-2008 and has continued to grow since . Modern technology combines processes to allow a reduced number of key pieces of machinery thereby increasing the efficiency of the process . The current aims are to improve capital and operational costs whilst producing energy and staying within increasingly strict environmental limits . It is thought that the industry will continue to grow in the future . With the main drivers being energy security, climate change mitigation and the desire to increase resource efficiency , .
EfW includes a variety of processes, Adu-Gyamfi et al  produced a simple schematic explaining their categorisation (Figure 1). The focus of this article is on conventional incineration, found under the thermal category of EfW, combustion technology includes rotary kiln, moving gate and fluidised bed combustion. Although the advanced thermal processes are not classified as combustion, their end products are usually subsequently combusted .
Substances will burn with sufficient amounts of oxygen at the right ignition temperature , in some cases a thermal chain reaction will occur resulting in self-sustaining combustion requiring no additional auxiliary fuels . The flue gases are a by-product, which also happen to contain energy in the form of heat, which can then be turned into electricity . In addition the process produces bottom ash and metal, which can in some cases be used as aggregate in construction .
4. Policy influences
EfW is influenced by both waste and energy policy and legislation. Many authors recognise the importance of the Waste framework Directive 2008/98/EC , , , . The current operating conditions are regulated through this directive . It puts EfW higher in the waste hierarchy than its previous directive (2006/12/EC), allowing high efficiency installations to benefit from recovery status rather than disposal status. This attracts investors towards EfW, deterring land filling activities , . Despite these benefits Grosso et al  noted some flaws in its calculation of energy recovery efficiency (particularly the R1 formula), highlighting its bias towards larger installations in colder countries.
The EU landfill Directive includes an annual escalator for landfill tax and requires member states to divert biodegradable waste from landfills, thereby encouraging other recovery technologies (e.g. EfW) , . The UK government is also committed to producing at least 15% of its energy from a renewables mix by 2020 under the EU Renewable Energy Directive (RED) 2009/28/EC . The UK has outlined EfW as an important contributor to energy security in both its Renewable Energy Strategy and the UK’s Biomass Strategy . Incentives such as the Renewable Obligations Certificates or ROCs (2002) and the Renewable Heat Incentive (RHI) (2011) may also have a role to play in the future . Although so far EfW has struggled to benefit from these incentives .
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