John Wiley & Sons, Ltd.

Understanding the impacts of allocation approaches during process‐based life cycle assessment of water treatment chemicals

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Chemicals are an important component of advanced water treatment operations not only in terms of economics, but also from an environmental standpoint. Tools such as life cycle assessment (LCA) are useful for estimating the environmental impacts of water treatment operations. At the same time, LCA analysts must manage several fundamental and as yet unresolved methodological challenges, one of which is the question of how best to ‘allocate’ environmental burdens in multi‐functional processes. Using water treatment chemicals as a case study example, this paper aims to quantify the variability in greenhouse gas emissions estimates stemming from methodological choices made in respect of allocation during LCA. The chemicals investigated and reported here are those most important to coagulation and disinfection processes, and the outcomes are illustrated on the basis of treating 1000 megalitres of non‐coagulated and non‐disinfected water. Recent process and economic data for the production of these chemicals is used and methodological alternatives for solving the multifunctionality problem, including system expansion and mass, exergy and economic allocation, are applied to data from chlor‐alkali plants. In addition, Monte Carlo simulation is included to provide a comprehensive picture of the robustness of economic allocation results to changes in the market price of these industrial commodities. For disinfection, results demonstrate that chlorine gas has a lower global warming potential (GWP) than sodium hypochlorite irrespective of the technique used to solve allocation issues. For coagulation, when mass or economic allocation is used to solve the multifunctionality problem in the chlor‐alkali facility, ferric chloride was found to have a higher GWP than aluminium sulphate and a slightly lower burden where system expansion or exergy allocation are applied instead. Monte Carlo results demonstrate that when economic allocation is used, GWP results were relatively robust and resilient to the changes in commodity prices encountered during the study period, with standard deviations <6% for all chlor‐alkali‐produced chemicals reported here. Overall outcomes from the study demonstrate the potential variability in LCA results according to the allocation approach taken and emphasise the need for a consensus approach to water sector LCAs. Integr Environ Assess Manag © 2013 SETAC

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