Economics of using wastewater irrigation of willow in Northern Ireland

Abstract

Abstract The economics of growing short rotation willow coppice as an energy crop are marginal and highly dependent on the support for the conventional crops or enterprises they replace and on the maintenance of high yield levels. Consequently any value which can be added to the crop by giving it a dual function will greatly enhance its economic sustainability. In this context the additional use of short rotation willow coppice as a vegetation filter for wastewater (bioremediation) presents such a value added opportunity. This paper calculates the added value in terms of avoided costs for the chemical and or physical treatment of the wastewater, and the avoided costs for fertilisation of the coppice and yield improvements due to the fertilisation and irrigation effects of the application of the wastewater. In the calculated situation, the wastewater is applied to the coppice during the growing season and treatment reverts to the conventional in the dormant season. Calculations show that saved costs in the conventional treatment of wastewater are higher ( £ 5.8 – £ 14.83.5 kg N - 1 ) than the saved costs for fertiliser and higher coppice yields (equivalent to £ 0.7 kg N - 1 ). This added value that the bioremediation of wastewater confers on the energy produced from short rotation willow coppice has the potential to alter radically the economic sustainability of the crop even if, as is the likely case, not all of the avoided treatment costs will be passed on to the biomass producer.