Abstract: A detergent and a method for washing applicable to selectively permeable membranes for proposed, which can attain washing of selectively permeable membranes deteriorated in its membrane performance, such as the flux, in an efficient manner within a brief time at a higher detergent effect without causing deterioration of the selectively permeable membranes and without damaging safety to human and to environment with superior handling aspect. The detergent contains a polyol having a molecular weight not higher than 400 and, if necessary, an organic solvent.

Abstract: A detergent and a method for washing applicable to selectively permeable membranes are proposed, which can attain washing of selectively permeable membranes deteriorated in its membrane performance, such as the flux, in an efficient manner within a brief time at a higher detergent effect without causing deterioration of the selectively permeable membranes and without damaging safety to human and to environment with superior handling aspect. A detergent comprising a polyol having a molecular weight not higher than 400 and, if necessary, an organic solvent is supplied to the concentrate chamber 3 of the module 1 to carry out washing of the selectively permeable membrane 2 by bringing it into contact with the selectively permeable membrane 2 and, on requirement, water or an alkaline solution is further supplied from the water tank 6 or from the alkali storage 8 to the concentrate chamber 3 of the module 1, in order to recover the membrane performance of the selectively permeable membrane 2.

Abstract: Dsiclosed is a method of treating fluoride-containing water, which comprises a reaction step where a calcium compound and/or an aluminium compound are/is added to fluoride-containing water while the pH value of the resulting suspended liquid is adjusted to fall within the range of from 6 to 8, and at least a part of the concentrated suspension to be formed in the membrane-separation step of the following stage is added to the suspended liquid and stirred and the resulting suspension is introduced into the circulation tank; a membrane-separation step where the suspension from the circulation tank is treated by membrane-separation to separate it into a permeated solution and a concentrated suspension; a circulation step where at least a part of the concentrated suspension to be taken out from the membrane-separation step is returned back to the reaction step while the remaining part thereof is circulated to the circulation tank; and a step where the permeated solution is taken out from the membrane-separation s