Biocidal control in aqueous membrane separation systems

A process for controlling biofouling in an aqueous membrane separation system comprising water and one or more protected membranes, which process comprises:

• I) contacting, upstream of the protected membrane(s), feed water and a biocidal amount of a bromine-containing biocide to form treated water;
• II) measuring a bromine residual in the treated water at a monitoring location which is downstream of the contacting in I) and upstream of the protected membrane(s);
• and
• III) contacting the treated water and a reducing amount of one or more reducing agents near or downstream of the monitoring location and upstream of the protected membrane(s);
• wherein the reducing agent is capable of reducing biocidal bromine to bromide ions;
• and
• wherein the bromine-containing biocide comprises:
• A) one or more 1,3-dibromo-5,5-dialkylhydantoins;
• B) one or more N,N′-bromochloro-5,5-dialkylhydantoins;
• C) one or more alkali metal hypobromites and/or one or more alkaline earth metal hypobromites, formed in water from (i) one or more bromide sources and (ii) one or more hypochlorite salts and/or hypochlorous acid;
• D) a bromine-based biocide formed in water from (i) one or more bromide sources, (ii) an oxidant, (iii) at least one inorganic base, and (iv) sulfamic acid and/or a metal salt of sulfamic acid;
• E) a bromine-based biocide formed in water from (i) bromine chloride or bromine chloride and bromine, with or without conjoint use of chlorine, and (ii) overbased alkali metal salt of sulfamic acid and/or sulfamic acid, alkali metal base, and water, wherein (i) and (ii) are in relative proportions such that there is an atom ratio of nitrogen to active bromine greater than 0.93, and wherein the bromine-based biocide has a pH of greater than 7;
• F) a bromine-based biocide formed in water by ozonation of one or more bromide sources;
• or
• G) a bromine-based biocide formed in water electrolytically from one or more bromide sources.