Potential of small biogas plants to produce energy and compost

We have a renewable energy source which is largely untapped in Ireland.  Anaerobic Digestion (AD) is a great story to tell.  It takes slurry and surplus agri waste as well as certain types of waste currently sent to landfill and turns it into renewable energy. It also produces an organic fertiliser. The technology is proven and widely used across Europe.  Here are some questions and answers about AD and its potential use in Ireland.

Visitors at  the AFBI (Agri-Food and Biosciences Institute) anaerobic slurry digester at Hillsborough, Co Down

Visitors at the AFBI (Agri-Food and Biosciences Institute) anaerobic slurry digester at Hillsborough, Co Down

What is AD?

AD is a natural biological process in which micro-organisms break down organic matter, in the absence of oxygen, to form biogas (a mixture of methane and carbon dioxide) and digestate (a compost like organic fertiliser).

Organic materials such as food waste, sewage sludge, farm animal wastes/slurry, energy crops, aquaculture and seafood processing waste can all be digested.  The waste is typically decontaminated to remove any plastic, packaging, glass, etc. and then blended into slurry which is pasteurised before being digested.  During the digestion process bacteria convert the organic matter to biogas which is used in a combined heat and power (CHP) engine to produce electricity and heat.  The electricity generated is exported to the grid and the heat is captured and used in the process.  Any excess heat can be sold to external users or if there is a requirement for heat it can be used on site.  The material left over from the process is separated into a fibrous dry solid, which can be used as a soil conditioner and fertiliser, and a liquid which can be used as a liquid fertiliser.

What are the Benefits of AD?

AD has an important role to play in the fight against climate change and can help Ireland meet its international commitments to reduce greenhouse gas emissions.  By diverting organic waste from landfill, AD can be used to reduce the uncontrolled emissions of methane that are produced as waste breaks down in landfill.  The EU’s Landfill Directive is set to increasingly prohibit the disposal of organic waste to landfill.   AD can provide an alternative treatment for this material.

Energy sourced from AD will contribute towards Ireland’s 2020 renewable energy targets and diversify the national fuel mix, which reduces the country’s reliance on fossil fuels.  The digestate can be used to replace imported chemical fertilisers which are made using fossil fuels as well as peat extracted from our bogs.

AD has the potential to deliver additional environmental benefits including the improvement of air quality through odour reduction and reduced emissions of ammonia and nitrogen oxides.   It also has water quality benefits as the process destroys pathogenic and faecal micro-organisms and reduces organic pollution associated with landfill.

What is the current status of AD development in Ireland?

In Ireland the current numbers of AD plants are modest for on-farm, community projects, sewage treatment plants and industrial plants.  Most of the plants are relatively small.  While a number of renewable energy developers and waste management companies have been seeking to exploit AD opportunities for some time there is still nowhere near the number we might expect.

What is preventing the development of more AD plants?

In 2013 there were over 10,000 AD plants in operation on mainland Europe. In Germany alone there were over 6,800 AD plants. The UK has 147 plants in operation. So, why are there so few AD plants in Ireland?

In May 2010 a new bioenergy support price structure (REFIT III) was introduced. However, the payments for electricity under the REFIT III scheme are significantly below those of other European countries.

In addition to increased electricity prices, AD plants in other European countries receive capital grants and support payments for the heat produced in the AD process.  Ten other European counties including the UK all provide legislative mechanisms and financial support for the injection of biogas into the gas network.  This allows the biogas to be used in the most efficient way, e.g. to feed power stations or even to fuel vehicles.  However, there is currently no such legislation in Ireland.

Given the notably lower electricity tariffs available in Ireland, AD developers are forced to rely on income derived from gate fees (the waste producer pays the AD plant to take the waste).  In order to secure project finance, AD developers require long term contracts with credit worthy counterparties for the supply of waste.  A combination of the economic downturn (and its dramatic effect on waste volumes) and indecision on the governmental waste policy have made long term contracts with waste producers difficult to secure.

The high cost and the lengthy planning and licencing process can also act as a barrier to AD development.  The requirement to deal with several Government departments and agencies means the planning and licencing process is overly complex and inefficient.

 What is the future for AD in Ireland?

The European example has taught us that AD is a viable industry, but only if substantial and adequate returns are achievable for investors. Our REFIT must be at least in line with, if not higher than those being offered by our European counterparts. The increase in the REFIT will require no start-up cost, yet will reap immeasurable benefits in relation to employment, security of energy supply, exchequer returns, greenhouse emissions, EU environmental targets, budget spending and energy efficiency.

It is predicted that by 2020, wind energy alone will provide up to 30% of Ireland’s electricity requirements.  Couple this with the 12% of Ireland’s electricity requirements that just 1,000 380kW plants would produce if developed over the next ten years and Ireland should meet its 2020 EU requirements for renewable energy. It would also create employment and ensure security of energy supply without any need for additional capital Government investment.

See www.seai.ie for more information on AD.  The AD Europe 2014 conference takes place in the City North Hotel, Gormanstown, Co Meath from 20th -21st Feb 2014. See www.adeurope2014.eu. It is organised by the Composting & Anaerobic Digestion Association of Ireland (www.cre.ie) in cooperation with the European Compost Network ECN.

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