Covanta and the waste hierarchy: A case study

Covanta works with local authorities and communities to provide tailored solutions to meet their waste disposal needs and complement local recycling efforts by generating energy from waste that cannot be sensibly recycled.

Dublin Waste to Energy Ltd

Covanta is the lead partner in the Dublin Waste to Energy Combined Heat and Power (CHP) project to turn up to 600,000 tonnes of waste, left over after maximum recycling and composting have taken place, into enough energy to generate electricity for up to 50,000 homes and district heating for up to a further 60,000 homes.

The Dublin Waste to Energy project will use highly efficient incineration to complement householder separation of waste at source and local authority recycling and composting efforts enabling the region to meet its ambitious target of 59% recycling and reduction of landfill to 16%. In fact, the Dublin Waste to Energy plant can be classified as recovery of resources (rather than disposal) in line with the revised 1975 EU Waste Framework Directive as the plant will provide efficiencies of over 65% through the provision of electricity alone and even greater efficiencies once district heating has been added.

For each tonne of waste processed at the Dublin facility, the need to import one barrel of oil or to mine one quarter tonne of coal will be avoided, thus reducing reliance on fossil fuels in the future. The facility could also prevent up to 600,000 tonnes of carbon dioxide from entering the atmosphere each year helping to reduce waste climate change impacts.

As part of an integrated waste management plan, Covanta will work with the four Dublin local authorities to introduce measures to encourage waste prevention, recycling, composting and increased environmental awareness within the region.

• Combined Heat and Power (CHP)
  
  Combined Heat and Power (CHP) technology captures “waste” heat from power generation and can be used to provide hot water and district heating schemes for homes, businesses and industrial processes. Compared to the average 38% efficiency provided by old fashioned power stations, CHP can provide up to 80%efficiencies as well as lower cost heat and electricity while making a significant contribution to UK sustainable energy goals.
  
   
• Householder separation of waste at source
  
  The separation of waste by householders into different fractions at source allows optimum recycling, composting and recovery of energy from waste to take place, reducing the volume of waste sent to landfill. For example, Dublin operates a “Three Bin System” whereby waste is sorted into residual, dry recyclable and organic waste.
  
   
• Recovery – the fourth 'R'
  
  After Reduce, Reuse, Recycle, the recovery of energy from residual waste is preferable to landfill disposal. Using waste as a fuel, EfW technology recovers energy from residual waste to generate clean renewable energy.
  
  The revised 1975 Waste Framework Directive was formally adopted by the EU Council on the 21 October 2008, introducing a number of significant changes to waste management rules in the EU. In particular, the Directive has reclassified ‘energy efficient’ municipal solid waste incinerators (also known as energy from waste, or EFW, plants) as waste ‘recovery’, rather than ‘disposal’, operations. The energy efficiency rate required of such plants will be 60% for existing EFW plants and 65% for new plants.
  
   
• Composting
  
  Composting uses natural biological processes to breakdown organic material to form compost. It can be carried out on a variety of scales ranging from residential compost heaps through to large centralized sites using In Vessel Composting (IVC) or Anaerobic Digestion (AD).
  
   
• In-Vessel Composting
  
  In-Vessel Composting is a process to treat biodegradeable waste in enclosed systems (for example a drum, silo, concrete lined trench or similar) under closely controlled environmental conditions. The system usually has a mechanism to turn/mix the waste and ensure adequate aeration under controlled temperature and moisture conditions.
  
  By source separating Bio Municipal Waste into garden and kitchen wastes, biodegradeable waste can be reduced in weight by up to 50% and converted into a nutrient rich soil conditioner. Householders must, however, ensure that Bio waste is not contaminated with foreign bodies ( e.g. glass, plastic, packaging)if the compost product is to find market applications.
  
   
• Anaerobic Digestion
  
  Anaerobic Digestion is a biological treatment process that breaks down biodegradable/ organic waste, using little or no oxygen, into compost. The biogas that is produced during this process can be used to generate electricity and heat, which can be fed back into the process. In the UK, however, AD has until recently been limited to small on farm digesters with little off-site heat or energy provision.
  
  When treating municipal waste, AD can be used to process specific source separate waste streams such as separately collected food waste, complementing recycling and the recovery of energy from residual waste.
  
   
• How can EfW help to combat climate change?
  
  According to the IPCC approximately 63% of global warming is attributable to carbon dioxide (CO2) emissions, with the majority of CO2 emissions coming from the burning of fossil fuels for energy generation and transportation. Methane ranks second to CO2 in its global warming contribution at 18%. Methane is 20 times more potent than CO2. Landfills are one of the largest sources of methane emissions, which are generated when waste is buried and then decomposes. For this reason the EU has issued a directive to limit the landfilling of biodegradable municipal solid waste to 35% of the quantity generated in 1995.
  
  EfW is a net reducer of greenhouse gas emissions because it eliminates methane from landfills and offsets the need to burn fossil fuel in power plants.
  
   
• Integrated waste management
  
  Covanta works with local authorities to provide tailored waste management and energy solutions to local needs. Covanta constantly seeks innovative approaches to ensure that our solutions utilize the most advanced technology while delivering the most competitive cost and guaranteeing to meet landfill diversion targets.