Comparative Life Cycle Assessment Study of Pretreatment Alternatives for RO

Abstract:
Water scarcity is an increasing problem, which not only arid regions in the world have to face. Throughout the world a definite trend to intensified usage of reverse osmosis desalination as a means to overcome current or the threat of future water scarcity can be observed. Desalination being on the one hand a very promising technology making fresh water available has on the other hand a not negligible environmental load due to its high associated energy consumption and intensive usage of chemicals in all process steps. Due to the fouling sensitivity of reverse osmosis membrane elements, high quality feed water is required to ensure long-term stable operation. In the past, most reverse osmosis plants used conventional pretreatment consisting of e.g. coagualtion and dual media filtration. With declining raw water quality and decreasing membrane costs, in more and more projects the use of membrane pretreatment prior to the reverse osmosis stage has been considered as an alternative to conventional pretreatment. Several authors have compared conventional and membrane based pretreatment mostly regarding the economic benefit. However, eventual environmental benefits of membrane pretreatment due to reduced usage of chemicals, increased membrane life time, reduced pressure losses and higher fluxes have not been in the focus of research activities so far. This work evaluates conventional and membrane based pretreatment and their influence on the entire RO process regarding the overall environmental impact using life cycle analysis applying a commercial software tool. Standardized evaluation methods such as the ecoindicator 97, EI99 and 2002+ methods are used to achieve objective results. Data implemented comes from extensive literature study of various membrane and conventional pretreatment studies. Environmental scores are calculated individually for each process alternatives and compared regarding their overall environmental impact. A sensitivity study is conducted to account for uncertainties regarding energy consumption for water production by RO.

Keywords:
Reverse Osmosis, Desalination, Ultrafiltation Pretreatment, Life-Cycle Assessment

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