Method of membrane separation

摘要

Clogging of membrane by slime adhesion is efficiently prevented and stable treatment can be carried out for a long period of time at a low cost by a small amount of chemicals without membrane deterioration and trihalomethane formation, even if applied to the water having a large number of viable cell counts and a harsh water quality by supplying water to be treated to a membrane separation apparatus 4, adding intermittently to the water to be treated a combined chlorine agent containing sulfamic compound, and repeating a non-addition feeding period in which water to be treated is supplied for 6-120 hours without addition of the combined chlorine agent, and an intermittent addition feeding period in which water to be treated is supplied for 0.5-40 hours under the addition of a combined chlorine agent at a biofilm exfoliating concentration in an early stage of biofilm formation during the non-addition feeding period.

主权项

1. A method of membrane separation, comprising the successive steps of:
supplying a water to be treated to a membrane separation apparatus having a membrane for a non-addition period in which a combined chlorine treating agent is not added and supplying a water to be treated to the membrane separation apparatus for an intermittent addition feeding period in which a combined chlorine treating agent is added, wherein the combined chlorine treating agent is an aqueous agent containing an alkali metal hydroxide, a sulfamic acid compound, and a chlorine-based oxidizing agent, a viable cell count, log CFU/mL, of the water to be treated is 3 or more, the non-addition feeding period is for 6-120 hours and the intermittent addition feeding period commences during the formation of a biofilm on the membrane and is for 0.5-40 hours, the concentration of the combined chlorine treating agent in the water to be treated in the intermittent addition feeding period is 0.5-20 mg/L as total chlorine for exfoliating the biofilm formed on the membrane while the biofilm is in a non-adhesive condition, and the combined chlorine treating agent is added during the intermittent addition feeding period at an additive amount R in which R, represented by the following formula (4) is 3 or more,
R=(Intermittent addition feeding period in hours×(1000×Intermittent addition concentration in mg-Cl/L)2.5)/((Non-addition feeding period in hours)3.0×10log CFU/mL)  (4).