A method for operating a membrane separation device includes (a) setting a flow amount M(t) of permeated water and extracting the permeated water from the membrane separation device by the set flow amount M(t), and (b) temporarily stopping the extracting the permeated water, when a water level of a first water tank in which the membrane separation device is immersed, a water level of a second water tank in communication with the first tank, or a water level of a third water tank receiving overflowing water from the first water tank becomes lower than a predetermined halt water level. M(t), which is the flow amount of the permeated water during a time period t, satisfies a equation M(t)=KQ(t?1), where K is a gain (K>1), and Q(t?1) is an amount of inflow of the water-to-be-treated during a time period t?1 immediately prior to the time period t.

A desalination performance restoration agent for a cellulose acetate membrane contains: a solvent; and a modified polyvinyl alcohol mixed in the solvent. The modified polyvinyl alcohol has an acetyl group structure in at least part of polyvinyl alcohol.

A desalination performance restoration agent for a cellulose acetate membrane contains: a solvent; and a modified polyvinyl alcohol mixed in the solvent. The modified polyvinyl alcohol has an acetyl group structure in at least part of polyvinyl alcohol.

An object of the present invention is to provide a specific method for determining the fouling potential of an activated sludge solution on the basis of the characteristics of the activated sludge solution after chemical cleaning of a membrane, and to provide a suitable method for resuming operation in a rational manner after chemical cleaning of the membrane, while accurately determining the degree of recovery of the membrane filtration characteristics for the activated sludge solution. Moreover, an object of applying the present invention is to enable more effective suppression of an increase in a transmembrane pressure difference after chemical cleaning than in the prior art, leading to a reduction in the cleaning frequency of the membrane and a reduction in the used amount of cleaning chemicals and to extension of the life of the membrane.

The present invention relates to a method for operating a membrane-separation activated sludge treatment device after chemical cleaning of a membrane, the method including, after the chemical cleaning of the membrane is completed, controlling an operating condition until a normal filtration operation is resumed on the basis of characteristics of an activated sludge solution.

A reverse osmosis treatment apparatus includes a membrane unit including an osmosis membrane module. The membrane unit includes a plurality of banks connected in series, each bank including an osmosis membrane module. At least one of the banks includes a treatment water pipe valve and a concentrated water pipe valve, and a bypass pipe capable of diverting the water to be treated, which is to be supplied to the bank, around the bank and draining the water to be treated and a chemical cleaning pipe capable of supplying the reverse osmosis membrane module disposed in the bank with chemical cleaning water are connected. A reverse osmosis treatment method is for cleaning intermittently a bank having the treatment water pipe valve and the concentrated water pipe valve while continuing the reverse osmosis treatment using the remaining bank.

A reverse osmosis treatment apparatus includes a membrane unit including an osmosis membrane module. The membrane unit includes a plurality of banks connected in series, each bank including an osmosis membrane module. At least one of the banks includes a treatment water pipe valve and a concentrated water pipe valve, and a bypass pipe capable of diverting the water to be treated, which is to be supplied to the bank, around the bank and draining the water to be treated and a chemical cleaning pipe capable of supplying the reverse osmosis membrane module disposed in the bank with chemical cleaning water are connected. A reverse osmosis treatment method is for cleaning intermittently a bank having the treatment water pipe valve and the concentrated water pipe valve while continuing the reverse osmosis treatment using the remaining bank.

Provided is a cleaning agent capable of preventing a reduction in the rejection rate of an RO membrane which may occur when the membrane is cleaned, the cleaning agent including a membrane protectant that is a basic or hydrophobic amino acid, a peptide containing the amino acid as a constituent amino acid, or a derivative of the amino acid or the peptide. The cleaning agent may further include at least one agent selected from the group consisting of an alkaline agent, a combined chlorine agent, and an oxidizing agent. The amino acid is preferably arginine, lysine, or phenylalanine. Also provided are a cleaning liquid that is an aqueous solution produced by diluting the cleaning agent and a method for cleaning a reverse osmosis membrane with the cleaning liquid.

A method of producing a sugar liquid includes filtering a cellulose-derived sugar liquid through one or more separation membranes selected from the group consisting of an ultrafiltration membrane, a nanofiltration membrane and a reverse osmosis membrane and washing the separation membrane(s) after filtration with washing water containing an alkaline substance and an aromatic compound at 10? C. or more and less than 50? C.

A method of producing a sugar liquid includes filtering a cellulose-derived sugar liquid through one or more separation membranes selected from the group consisting of an ultrafiltration membrane, a nanofiltration membrane and a reverse osmosis membrane and washing the separation membrane(s) after filtration with washing water containing an alkaline substance and an aromatic compound at 10? C. or more and less than 50? C.

The present invention provides a cleaning agent for aromatic polyamide reverse osmosis membranes, the cleaning agent being composed of an aqueous solution which has a pH of 13 or more and contains a stabilized halogen, a chelating agent that contains one or more substances selected from among aliphatic carboxylic acids containing no amino group, phosphonic acid compounds containing no amino group, polyphosphoric acids, and salts thereof, and an alkaline agent. According to the present invention, an aromatic polyamide reverse osmosis membrane is cleaned with use of a cleaning liquid that is composed of an aqueous solution of this cleaning agent. A chloramine compound which is obtained by mixing a compound having a primary amino group with hypochlorous acid and/or a hypochlorite is suitable for use as the stabilized halogen.