Rainwater harvesting can provide an alternative water source, which may demand little treatment, depending on the end use. Some starches have been used in water treatment as coagulant/flocculant/filtration aid, and might be applied as primary coagulant. Here, we show direct filtration with hydraulic rapid mixing, using 2–6 mg L−1 cationic corn starch as primary coagulant, considerably improves roof-harvested rainwater quality, achieving removal efficiencies of up to 71.7% of apparent colour, 78% of turbidity, 1.1 log-unit of total coliform, and 1.6 log-unit of Escherichia coli, meeting guidelines for turbidity, even for potable purposes. Cationic corn starch has proved to be a suitable primary coagulant when filtration is performed in a single-layer sand filter (coefficient of uniformity: 1.8, effective particle size: 0.52 mm), at hydraulic loading rate of 450 m day−1. However, a disinfection unit is required to meet an absence of faecal coliform.
- corn starch
- direct filtration
- full-scale rainwater treatment
- rainwater harvesting
- First received 13 March 2015.
- Accepted in revised form 19 June 2015.
- © IWA Publishing 2015