A Life Cycle Aassessment of Sewage Sludge Treatment Options

Student thesis: Master Thesis and HD Thesis

  • Ngelah Sendoh Akwo
The enactment of the EU water directive resulted in the production of huge amounts of sewage sludge from waste water treatment plants; consequently it becomes necessary that this excess sludge be managed in an economically and environmentally acceptable way. This study is focused on the use of Life cycle assessment to compare different options for the treatment of sewage sludge so as to determine which method is more environmentally friendly. Four treatment options are analysed and they include cement kiln incineration, agricultural land application of digested sludge, composting and finally fluidised bed incineration. The Life Cycle Assessment tool used for evaluating the environmental performance of these treatment options is based on the ISO14040 series which defines LCA as the compilation and f evaluation of the inputs, outputs and potential environmental impacts of a system throughout its life cycle; from the production of raw materials t the disposal of the waste generated. This study uses data from existing sewage sludge treatment and thermal treatment facilities. According to the results of the study, As far as composting and agricultural application of sewage sludge is concerned, much research needs to be carried out to establish the exact amount of heavy metals that is effectively take up by plants and crops as well as the amount transferred to another phase like leachate. (Hospido et al 2005). Also, though thermal processes such as incineration in cement kilns and fluidised bed incineration prove to be promising technologies vis-à-vis global warming and energy recovery, more efforts are still needed to improve the valuable, viable products as nutrients are lost during the process. Moreover, these conclusions are base only on one impact category and since it is the subject of current debates and research, it is not surprising that most researchers use only this impact category to make their conclusions. It is worth noting that an evaluation of the environmental impacts of sewage sludge treatment should be based on an analysis of the effect of the treatment options on the different impact categories so as to be able to get a clear picture of the consequences of using these technologies. As indicated by the study, the thermal treatment scenarios show the best results only for the impact category of global warming. This is however not true for the other two impact categories Acidification and Eutrophication. An inclusion of other impact categories shows composting to be the bets scenario so far (see appendix); it is thus necessary when analysing the effects of sludge treatment systems to analyse the effects on all impact categories
Publication date2008
Number of pages81
Publishing institutionAalborg University
ID: 14465522