The artificial water cycle:emergy analysis of waste water treatment

摘要

The artificial water cycle can be divide into the phases of water capture from the environment potabilisation distribution waste water collection waste water treatment and discharge back into the environmentThe terminal phase of this cycle from waste water collection to discharge into the environment was assessed by emergy analysis Emergy is the quantity of solar energy needed directly or indirecdtly to provide a product or energy flow in a given process The emergy flow attributed to a process is therefore an index of the past and present environmental cost to support it Six municipalities on te western side of dthe province of Bologna were analysed Waste water collection is managed by the municipal councils and treatment of carried out in plants managed by a service company Waste water collecition was analysed by compiling a massbalance of hte sewer system serving the six municipalities including comstruction materials and sand for laying the pipelines.Emergy analysis of the water treatment plants was also carried out The results show that the great quantity of emergy repuired to treat a gram of water is largely due to input of non renewabgle fossil fuels As found in our previous analysis of the first part of the cycle treatment is likewise characterised by high expenditure of non renewable resources indicationg a correlation with energy flows.