Biocidal compositions

A method of treating an aqueous system to inhibit growth of one or more micro-organisms therein;

• wherein the method comprises adding (a) a phosphonium compound and (b) a polymeric ammonium compound to an aqueous system such that the weight ratio of compound (a) to compound (b) is from 0.2:1 to 20:1;
• and wherein
• the phosphonium compound (a) has formula:
• wherein each R is independently a C1-C6 alkyl group which is unsubstituted or substituted by a cyano, hydroxyl, esterified hydroxyl or aryl group;
• R1 represents a C8-C18 alkyl group which is substituted or unsubstituted;
• and
• X represents either chlorine or bromine;
• and wherein
• the polymeric ammonium compound (b) comprises the repeat unit:
• wherein each R2 is independently a C1-C2 alkyl group which is substituted or unsubstituted;
• R3 represents a C2-C18 alkyl or alkenyl group which is substituted or unsubstituted;
• and
• R4 represents a C2-C18 alkyl or alkenyl group which is substituted or unsubstituted, a diethyl ether group, an isopropanol group, a N,N-dipropylurea group or a 2-butene group.

An apparatus comprising an aqueous system which comprises (a) a phosphonium compound and (b) a polymeric ammonium compound;

• wherein the weight ratio of compound (a) to compound (b) is from 0.2:1 to 20:1;
• and wherein
• the phosphonium compound (a) has formula:
• wherein each R is independently a C1-C6 alkyl group which is unsubstituted or substituted by a cyano, hydroxyl, esterified hydroxyl or aryl group;
• R1 represents a C8-C18 alkyl group which is substituted or unsubstituted;
• and
• X represents either chlorine or bromine;
• and wherein
• the polymeric ammonium compound (b) comprises the repeat unit:
• wherein each R2 is independently a C1-C2 alkyl group which is substituted or unsubstituted;
• R3 represents a C2-C18 alkyl or alkenyl group which is substituted or unsubstituted;
• and
• R4 represents a C2-C18 alkyl or alkenyl group which is substituted or unsubstituted, a diethyl ether group, an isopropanol group, a N,N-dipropylurea group or a 2-butene group.