Biofilm formation in dairy wastewater system irrigation pipes can reduce treatment capacity, increasing maintenance and cleaning costs. Understanding the effect of different components in the wastewater on growth and yield of bacteria present could help prevent excessive build-up of biofilms. This study investigated, in aerobic and anaerobic conditions, the effect of calcium, sodium and magnesium concentrations on growth rates, yields and saturation constants of four known biofilm forming bacteria associated with the blockage of an irrigation system. The ions tested (Ca2+, Mg2+, Na+) varied growth rates with biofilm growth in the presence of calcium being significantly slower (P < 0.05) than planktonic growth in sodium. Along with the slower growth, the addition of Ca2+ (up to 0.1 M) increased biofilm formation while addition over 0.5 M prevented biofilm formation. Knowing the nutritional requirements of the bacteria and the effects of the ions will be useful in predicting the growth, development and strategies in controlling biofilm formation in dairy wastewater.

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