Generating energy from waste, including anaerobic digestion
How to comply with regulations for energy recovery and advanced conversion technologies.
Overview
The UK is obliged under the revised EU Waste Framework Directive to apply the waste hierarchy. This ranks waste management options in order of environmental preference and the first priority is waste reduction.
Recovering energy from waste is only appropriate for waste that cannot be prevented, reused or recycled with less greenhouse gas emitted.
Energy recovery can be a sustainable option for waste that would otherwise go to landfill and create landfill methane emissions.
Conventional technologies
Direct combustion (incineration) of dry biomass
The heat generated by the following wastes can be used directly to warm homes and buildings or to generate electricity using a steam turbine, or both, through combined heat and power systems:
- direct combustion (incineration) of dry biomass waste such as wood waste, straw and poultry litter
- the biomass part of municipal waste
- some commercial and industrial wastes
- some construction and demolition wastes
Where waste is combusted in a combined heat and power unit, it is possible to produce both heat and power at greater efficiencies.
Combustion of waste-derived fuel
The methane produced from landfill (landfill gas) is a waste-derived fuel. It can be used in the same way as for combustion plants or it can be injected into the national gas grid. Waste derived fuel is also referred to as Solid Recovered Fuel (SRF) or Refuse Derived Fuel (RDF).
Anaerobic digestion
Anaerobic digestion (AD) is a natural process in which micro-organisms break down the organic matter found in wet biomass waste (such as sewage sludge, animal manure and slurry and waste food) in the absence of oxygen, to produce biogas (mainly a mixture of around 60% methane and 40% carbon dioxide) and digestate (a nitrogen rich fertiliser).
The biogas can be burned directly in a gas boiler to produce heat or burnt in a combined heat and power (CHP) unit to produce heat and electricity. Alternatively, the biogas can be cleaned to remove the carbon dioxide and other substances, to produce biomethane. This can be injected into the national gas grid to be used in the same way as natural gas, or used as a vehicle fuel.
The National Non-food Crops Centre (NNFCC) runs the government’s Anaerobic Digestion Portal - a gateway to information on anaerobic digestion, biogas and digestate.
Advanced conversion technologies
A number of innovative advanced, high temperature processes are beginning to emerge. These have the potential to be more efficient than conventional processes and can offer a range of different types of energy from bio-based wastes, including wood waste and municipal wastes.
The Low Carbon Innovation Co-ordination Group has recently published a Technology Innovation Needs Assessment (TINA) on Bioenergy, including wastes, which examine the potential for innovation in the bioenergy sector and the potential economic benefit they can deliver for the UK.
Read about bioenergy innovation funding opportunities, including details on an open call for EU proposals.
Gasification
Gasification is a type of advanced conversion that produces a combustible gas that is a mixture of carbon monoxide, hydrogen, carbon dioxide and methane. This gas can be used directly to generate heat and electricity. Alternatively it can be upgraded to an ultra clean gas called syngas. This can be used to manufacture either biomethane, which can be injected into the national gas grid, or transport fuels such as hydrogen, ethanol, synthetic diesel or jet fuel. The energy given off can be harnessed to generate heat and power.
Pyrolysis
Pyrolysis is a type of advanced conversion that can be used to produce either a combustible gas, oil or solid char (sometimes known as biocoal). In the future, it will be possible to upgrade pyrolysis oil to produce petrol and diesel using oil refining techniques.
The choice of technology for any project depends on the type of waste available, local circumstances and finance.
More information on the different technologies is available on the NNFCC website.
Environmental controls
All energy from waste plants must comply with regulations concerning environmental protection, animal by-products, duty of care, health and safety, waste handling and planning permission.
For more information on environmental regulations, see the Netregs website.
The Anaerobic Digestion Portal holds more regulatory information for anaerobic digestion projects.
Obstacles to energy from waste
There are a number of challenges facing energy from waste projects, even for the established technologies, and these need to be overcome for the sector to expand.
The outcome of the review of waste policies in England was published on 14 June 2011. The review looked at all aspects of waste policy and delivery in England to ensure we are taking the necessary steps towards creating a ‘zero waste’ economy, where resources are fully valued and nothing of value gets thrown away.
The review recognised the important part that energy from waste can play in helping to meet renewable energy targets, diversifying supply, and providing economic opportunities. It suggested that renewable electricity generated from waste through combustion technologies could almost treble from the current 1.2TWh to between 3.1TWh and 3.6TWh by 2020.
It outlined a number of actions, which are aimed at overcoming barriers to deployment to ensure we get the most energy out of genuinely residual waste. Actions include:
- improving communications and information on energy from waste technologies
- exploring ways to help communities benefit from hosting energy from waste infrastructure
- supporting industry in developing supply chains for waste feedstocks
- ensuring waste management legislation does not have unintended consequences on the development of energy plants
Anaerobic digestion strategy and action plan
The Anaerobic digestion strategy and action plan was also published on 14 June 2011.
The strategy sets out a vision for AD, with an estimate of potential that could reach between 3-5 TWh for heat and electricity by 2020.
The accompanying action plan is the result of the Department of Environment Food & Rural Affairs (Defra), the Department of Energy & Climate Change (DECC) and other departments working closely with industry to identify the key barriers to the development of AD and the actions that are needed to overcome them. These include:
- creation of a £10 million loan fund to develop new AD capacity in England
- improving the dissemination of information, particularly on regulatory controls
- guidance on the costs and benefits of AD, including best practice projects
- tackling specific barriers, such as the cost and complexity of connection to the gas grid
- developing skills and training for AD operators
- building markets for digestate
An update on progress on detailed actions was published in July 2012 and we will continue to work with industry to implement the agreed actions.