Cement-based biocide coatings for controlling algal growth in water distribution canals

The germicidal effectiveness of various additives when blended within a microstructure of a cement based system was studied. The relationship between the chemical and physical characteristics of concrete surfaces and their ability to have an enhanced resistance to algal growth was documented through a novel set of laboratory and field testing. The main potential areas of application for these new cement composite systems involve the lining of canal surfaces where fixed-surface biocides are desirable to control biofouling. Different biocide formulations containing class F fly ash, silica fume, Zn oxide, copper slag, ammonium chloride, sodium bromide, and cetyl-methyl-ammonium bromide were evaluated for the mitigation of algal growth on concrete surfaces. Mortar coupons treated with these formulations were tested under laboratory and field conditions. These new cement composite systems were compared with proprietary products that are commercially available and applied using a latex paint. Laboratory scale screening experiments showed that various concentrations of zinc oxide significantly inhibited algal growth even after nine months. It was observed that 20% zinc oxide in concrete produced optimal algal inhibition compared to other additives. Copper slag, ammonium chloride, sodium bromide, and fly ash, when added singly, also showed algal inhibition capabilities. Addition of zinc oxide and ammonium chloride (10% each) in mortar mix was as effective as expensive proprietary chemicals in reducing algal growth on concrete surfaces under laboratory and field conditions.