A Life Cycle Aassessment of Sewage Sludge Treatment Options
Author
Akwo, Ngelah Sendoh
Term
10. term
Education
Publication year
2008
Pages
81
Abstract
EU’s vanddirektiv har medført store mængder spildevandsslam fra renseanlæg, hvilket skaber behov for en økonomisk og miljømæssigt forsvarlig håndtering. Dette studie anvender livscyklusvurdering (LCA) efter ISO 14040 til at sammenligne fire behandlingsmuligheder: forbrænding i cementovne, udbringning af afgasset slam på landbrugsjord, kompostering og fluidiseret leje-forbrænding. LCA vurderer input, output og potentielle miljøpåvirkninger gennem hele livscyklussen, og analysen bygger på data fra eksisterende anlæg. Resultaterne viser, at termiske processer (cementovne og fluidiserede lejer) klarer sig godt for global opvarmning og energigenvinding, men næringsstoffer går tabt. For kompostering og landbrugsudbringning er der behov for mere forskning i, hvor meget tungmetaller optages af afgrøder, og hvor meget der overføres til sigevand (leachate). Når flere påvirkningskategorier inddrages, er de termiske scenarier kun bedst for global opvarmning; de er ikke bedst for forsuring og eutrofiering. Inkluderes andre kategorier, fremstår kompostering som den mest fordelagtige løsning indtil videre. Miljøvurderinger bør derfor omfatte alle relevante påvirkningskategorier for at give et balanceret billede.
The EU water directive has led to large amounts of sewage sludge from wastewater treatment plants, creating a need for cost-effective and environmentally sound management. This study uses life cycle assessment (LCA) following ISO 14040 to compare four treatment options: incineration in cement kilns, agricultural land application of digested sludge, composting, and fluidised bed incineration. LCA evaluates inputs, outputs, and potential environmental impacts across the full life cycle, and the assessment draws on data from existing facilities. Results indicate that thermal processes (cement kilns and fluidised beds) perform well for global warming and energy recovery, but nutrients are lost. For composting and land application, more research is needed on how much heavy metal is taken up by crops and how much is transferred to leachate. When multiple impact categories are considered, thermal treatments are best only for global warming; they do not perform best for acidification and eutrophication. Including other impact categories shows composting to be the most favourable option so far. Environmental evaluations should therefore consider all relevant impact categories to provide a balanced picture.
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