Recent Cryptosporidium outbreaks have highlighted concerns about filter efficiency and especially particle breakthrough. Understanding the causes of breakthrough is essential, as the parasite cannot be destroyed by conventional disinfection with chlorine. Particle breakthrough depends on many factors. This research aims to investigate the influence of temperature, humic acid (HA) level and chemical dosing on particle breakthrough in filtration. A series of temperatures were set at 5 °C, 15 °C and 25 °C; humic acid level was 5 mg L−1. Each was combined with a series of Al doses. A laser particle counter was used to assess the particle breakthrough online. Turbidity, ζ potential, and UV254 absorption were measured before and after filtration. The results showed that particle breakthrough was influenced significantly by temperature, humic acid and dosing. Particle breakthrough occurred earlier at lower temperature, while at higher temperature it was reduced at the same coagulant dose. With coagulants, even at low dose, particle breakthrough was significantly reduced. With HA 5 mg L−1, particle breakthrough was earlier and the amount was much larger than without HA even at high temperature. There was an optimal dose in filtration and it was well correlated with ζ potential.

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