Greywater reuse inside buildings is a possible way to preserve water resources and face up to water scarcity. This study is focused on a technical-economic analysis of greywater treatment by a direct nanofiltration (NF) process or by a submerged membrane bioreactor (SMBR) for on-site recycling. The aim of this paper is to analyse the cost of recycled water for two different configurations (50 and 500 inhabitants) in order to demonstrate the relevance of the implementation of membrane processes for greywater recycling, depending on the production capacity of the equipment and the price of drinking water. The first step was to define a method to access the description of the cost of producing recycled water. The direct costs were defined as a sum of fixed costs due to equipment, maintenance and depreciation, and variable costs generated by chemical products and electricity consumptions. They were estimated from an experimental approach and from data found in literature, enabling operating conditions for greywater recycling to be determined. The cost of treated water by a SMBR unit with a processing capacity of 500 persons is close to 4.40 € m−3, while the cost is 4.81 € m−3 with a NF process running in the same conditions. These costs are similar to the price of drinking water in some European countries.

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