Abstract: A method for washing a filter is used in a seawater desalination process including a first filtration step for subjecting seawater to microfiltration or ultrafiltration, and a second filtration step for subjecting seawater after the first filtration step to a reverse osmosis treatment. The filter is a microfiltration membrane or ultrafiltration membrane used in the first filtration step. An iron compound is added to seawater in any stage in the washing method. The washing method includes a washing chemical liquid preparation step for preparing washing chemical liquid, and a sticking matter removal step for removing matter sticking to the filter by bringing the filter into contact with washing chemical liquid. In the washing chemical liquid preparation step, seawater after the first filtration step is mixed with at least hydrogen peroxide to prepare washing chemical liquid having an iron compound concentration of 1.50 mmol/L or more in terms of iron atoms.

Abstract: Provided is a method for washing a hollow fiber membrane module which comprises a hollow fiber membrane for filtering raw water containing a suspended component, said method comprising, in the following order, a first washing step for removing a suspended component that is accumulated on the hollow fiber membrane and a second washing step for carrying out an air scrubbing process in which gas is caused to pass through at least to the raw water side of the hollow fiber membrane, wherein, out of water that existed in the hollow fiber membrane module before washing, water in an amount corresponding to not less than 50 vol % of the capacity of the hollow fiber membrane module is removed in the first washing step.

Abstract: Provided is a method for washing a hollow fiber membrane module which comprises a hollow fiber membrane for filtering raw water containing a suspended component, said method comprising, in the following order, a first washing step for removing a suspended component that is accumulated on the hollow fiber membrane and a second washing step for carrying out an air scrubbing process in which gas is caused to pass through at least to the raw water side of the hollow fiber membrane, wherein, out of water that existed in the hollow fiber membrane module before washing, water in an amount corresponding to not less than 50 vol % of the capacity of the hollow fiber membrane module is removed in the first washing step.

Abstract: This method, for regenerating a member used in a device that treats seawater, involves a cleaning step for removing deposits from the member. In the cleaning step, a first chemical solution containing an acid other than hydroxydicarboxylic acid and a second chemical solution containing hydrogen peroxide, a heavy metal compound and hydroxydicarboxylic acid are used.

Abstract: A method for washing a filter is used in a seawater desalination process including a first filtration step for subjecting seawater to microfiltration or ultrafiltration, and a second filtration step for subjecting seawater after the first filtration step to a reverse osmosis treatment. The filter is a microfiltration membrane or ultrafiltration membrane used in the first filtration step. An iron compound is added to seawater in any stage in the washing method. The washing method includes a washing chemical liquid preparation step for preparing washing chemical liquid, and a sticking matter removal step for removing matter sticking to the filter by bringing the filter into contact with washing chemical liquid. In the washing chemical liquid preparation step, seawater after the first filtration step is mixed with at least hydrogen peroxide to prepare washing chemical liquid having an iron compound concentration of 1.50 mmol/L or more in terms of iron atoms.

Abstract: This method, for regenerating a member used in a device that treats seawater, involves a cleaning step for removing deposits from the member. In the cleaning step, a first chemical solution containing an acid other than hydroxydicarboxylic acid and a second chemical solution containing hydrogen peroxide, a heavy metal compound and hydroxydicarboxylic acid are used.

Abstract: A controller performs multiple regression analysis using an optimum chemical injection rate as a target variable and using one or more water quality indices of a raw water as explanatory variables and thereby derives a calculation formula for a basic chemical injection rate corresponding to the water quality indices. Next, the controller calculates the basic chemical injection rate corresponding to the water quality indices by substituting the measured values of the water quality indices of the raw water into the calculation formula. Then, the controller corrects the basic chemical injection rate based on a measured value of the water quality index of the treated water, thereby newly calculates a chemical injection rate, and outputs the newly calculated chemical injection rate as a control factor for a chemical injection pump while supplying the newly calculated chemical injection rate to calculation of the optimum chemical injection rate.

Abstract: A controller performs multiple regression analysis using an optimum chemical injection rate as a target variable and using one or more water quality indices of a raw water as explanatory variables and thereby derives a calculation formula for a basic chemical injection rate corresponding to the water quality indices. Next, the controller calculates the basic chemical injection rate corresponding to the water quality indices by substituting the measured values of the water quality indices of the raw water into the calculation formula. Then, the controller corrects the basic chemical injection rate based on a measured value of the water quality index of the treated water, thereby newly calculates a chemical injection rate, and outputs the newly calculated chemical injection rate as a control factor for a chemical injection pump while supplying the newly calculated chemical injection rate to calculation of the optimum chemical injection rate.

Abstract: Provided is a cleaning agent or cleaning method of a separation membrane which has cleaning effects equal or superior to those of conventional cleaning methods in cleaning a separation membrane used for filtration of drinking water, industrial water, river water, lake water, groundwater, reservoir water, secondary effluent, waste water, sewage water or the like; does not include a hypochlorite so that it neither generates a toxic gas nor adversely affects the human health; and needs less cleaning time owing to elimination of a rinsing step with a large amount of water. The cleaning agent or cleaning method according to the present invention is therefore safe and economical.