Abstract: A method and apparatus for removing soluble silica efficiently from accompanied water, produced from wells containing calcium ion, soluble silica, and sulfate ion, and not clogging a reverse osmosis membrane in the reverse osmosis membrane treatment process after that, includes adding a magnesium salt to mix with the accompanied water under alkaline conditions to produce insoluble silica and calcium sulfate. A microfiltration (MF) membrane treatment process includes treating a first reaction solution obtained in said magnesium salt adding process, with a microfiltration membrane to separate insolubilized silica and calcium sulfate by filtration. An acid adding process includes adding an acid to and mixing with filtrate obtained in the MF membrane treatment process to render a pH value of the filtrate on the range from 5 to 9 and a negative Langeliar saturation index.

Abstract: A method and apparatus for removing soluble silica efficiently from accompanied water, produced from wells containing calcium ion, soluble silica, and sulfate ion, and not clogging a reverse osmosis membrane in the reverse osmosis membrane treatment process after that, includes adding a magnesium salt to mix with the accompanied water under alkaline conditions to produce insoluble silica and calcium sulfate. A microfiltration (MF) membrane treatment process includes treating a first reaction solution obtained in said magnesium salt adding process, with a microfiltration membrane to separate insolubilized silica and calcium sulfate by filtration. An acid adding process includes adding an acid to and mixing with filtrate obtained in the MF membrane treatment process to render a pH value of the filtrate on the range from 5 to 9 and a negative Langeliar saturation index.

Abstract: It is to provide a process for manufacturing potable water from a liquid to be treated, such as seawater by using forward osmosis membrane, wherein the solution after the separation of water from dilute draw solution diluted by the migration of water from the liquid to be treated, is stably regenerated and reutilized and an apparatus therefor, and the process and apparatus are a process for manufacturing potable water which comprises, a forward osmosis step wherein a liquid of which solvent is water is allowed to contact with a draw solution produced by dissolving a prescribed amount of a volatile material in water through a semi-permeable membrane, and water in said liquid is allowed to migrate to said draw solution through said semi-permeable membrane, a distillation step wherein a dilute draw solution having been diluted with water which was produced in said step is adjusted to a prescribed temperature, and then is delivered to a distillation column where gas comprising the volatile material and water vapo