A critical comparison of the environmental impacts of different sludge management options
Rajapaksha, N. S. S.1, Clark, A.1, Le, M. S.2 and Gedara, S. A.3, 1 University of Salford, UK, 2 United Utilities PLC, UK, 3Cranfield University, UK
(free)
Sewage sludge management is an environmentally sensitive problem and systematic analyses are required to enhance understanding of the environmental consequences of the possible options. This study assessed and compared the environmental impacts of the three main sludge management options: agricultural recycling of sludge as cake, agricultural recycling of sludge as Organo Mineral Fertiliser (OMF) and incineration using standard Life Cycle Assessment (LCA) methodology, which focused on the three major environmental impact categories: global warming, eutrophication and acidification potential.
The study revealed that both agricultural recycling options contribute a reduction in environmental impacts compared to incineration since they largely replace the use of mineral fertilisers in the provision of nutritional benefits for crops. However, the calculated environmental impacts of agricultural recycling of dewatered sludge cake were lower than those for OMF recycling due to the energy consumed and emissions produced during OMF manufacture.
Given that agricultural recycling of sludge offsets the use of mineral fertilisers, the study compared sludge cake and OMF with mineral fertilisers as agricultural fertilisers. The study revealed that OMF is the most favourable agricultural fertiliser option from global warming perspective. Use of OMF to produce typical yield of Winter Wheat saves 61.47kg CO2eq/t Wheat (Grain yield) compared to conventional mineral fertilisers. Further, this study demonstrated that both OMF and sludge cake have only a minor contribution to eutrophication potential compared to conventional mineral fertilisers. Although the study only takes account of the major plant nutrient (N, P and K) supply, it still proved a useful comparison and confirmed that the use of sludge based products in agriculture gives an overall environmental benefit over conventional mineral fertilisers.
Keywords: Sludge Management; Organo Mineral Fertilisers; Recycling, Environmental Impacts, Life Cycle Assessment
