Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


Civil, Structural & Environmental Engineering

First Advisor

Dr. Jerry D. Murphy.


In 1990 the transport sector accounted for 9,5% of all Irish emissions. By 2010 it is predicted that transport emissions will have increased by 179%, accounting for 18.8% of all emissions. It is predicted that transport emissions will therefore be around 14,000 kt in 2010. This equates to around €370 million pa in carbon taxes if and when the taxation regime is introduced. This €370 million may be used to facilitate a biofuel industry (for example, by reducing excise duty on biofuels).

The proposed carbon tax along with the EU Biofuels Directive aims to encourage the use of renewable transport fuels. Ethanol and biogas are two possible alternatives to petrol and diesel. The added incentive to utilising these two fuels is that they can be derived from type 1 biomass (commercial, domestic, agricultural, and some industrial wastes). Utilising these wastes to produce fuel will therefore reduce the volume of waste going to landfill.

Biogas when cleaned to 97% CH4 (methane) may be used as a transport fuel. Various models were investigated to establish the optimal biogas system for Ireland. The models analysed different sizes and different feedstocks. The feedstocks investigated were pig slurry and the organic fraction of municipal solid waste (OFMSW). The models indicate that biogas production from OFMSW only is more beneficial economically and environmentally than co-digestion of OFMSW and pig slurry. Economies of scale are significant.

Ethanol has been known as a fuel for many decades. It can be used in a blend with petrol (up to 10% ethanol) in all spark ignition engines manufactured since the 1970’s without any noticeable decrease in vehicle performance. A number of scenarios were investigated utilising biomass type 1 (biomass residues and wastes), in this case paper, and biomass type 2 (energy crops), in this case sugar beet. The models indicate that ethanol produced from waste paper has an economic and environmental advantage over ethanol produced from sugar beet. Economies of scale are significant.

In comparing biogas and ethanol in terms of economics, biogas is a preferred option due to the gate fee obtained (€150 /1 of OFMSW is used in the model). In the model utilising OFMSW as the feedstock, a profit of €0.43 / m^ of cleaned biogas is obtained before the sale of cleaned biogas is allowed for. If no gate fee is charged for OFMSW, ethanol produced from waste paper is a cheaper option at a required sale price of €0.69 /L. These compare favourably with petrol and diesel. Environmentally, both biogas and ethanol exhibit their own distinct advantages. Biogas is beneficial in terms of achieving sustainability and meeting the Kyoto Protocol. This is largely due to the redeployment of OFMSW from landfill. Biogas does not aid greatly in achieving the targets of the Biofuels Directive. Ethanol on the other hand offers the best solution in terms of meeting the Biofuel Directive targets.

The practicable potential for biofuels from biogas and ethanol is established. Combining the cleaned biogas and ethanol potential as discussed above, approximately 5.1% of petrol and diesel could be replaced with biogas and ethanol at an initial capital cost of around €622 million.


Karl McCarthyB. Eng. MIEI.

A Thesis Submitted to HETAC in Candidature for the Degree of Master of Engineering July 2004.

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