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Effects and Mechanism of Pre-ozonation on Sand Filtration Performance

Diatoms were shown to be responsible for clogging the sand filtration tanks in the waterworks of Beijing treating reservoir source water. The effect of pre-ozonation on the performance of the sand filter was investigated using a continuous-flow (200 L h−1) pilot experimental system. At the optimum ozone dose of 1.0 mg L−1, the filter run time was prolonged 2.7–2.8-fold, the number of 2–5 μm diameter particles decreased from 353–829 ml−1 to 53–269 ml−1 and the turbidity in the filtrate decreased from >0.2 NTU to < 0.1 NTU. Laboratory tests showed that ozone was able to break the cells of the diatoms, including Fragilaria sp., Diatoma sp. and Navicula sp., into smaller particles, and the optimum ozone dose was also 1.0 mg L−1. Decomposition of algae is likely to be the main reason for the significantly improved performance of filtration.