METHOD OF PRETREATMENT FOR SEPARATION WITH REVERSE OSMOSIS MEMBRANE OF WATER TO BE TREATED

摘要

A method of pretreatment for separation with a reverse osmosis membrane is provided in which membrane filtration can be conducted at a far higher flow velocity than in conventional methods and suspended solids and organic substances can be separated/removed with higher certainty than in conventional methods to thereby mitigate the burden to be imposed on a reverse osmosis membrane in a later stage. The pretreatment method is characterized by: adding an alkali to raw water to be treated and regulating the pH thereof to 9.0 or higher to precipitate, as an insoluble substance, an ingredient dissolved in the raw water and capable of scale formation; settling and separating part of the precipitate generated by the alkali flocculation; subsequently adding a flocculant to the water while maintaining the environment having a pH of 9.0 or higher to form flocs using the remaining precipitate as flocculation nuclei; and then filtering the water through a filter medium having alkali resistance and acid resistance to remove the ingredient capable of scale formation, suspended solids, and organic substances.