AWWA WQTC60707

Slow sand filtration is a sustainable technology for drinking water treatment in smallcommunities. The process, however, is sensitive to high raw water turbidity levels thatcan lead to premature clogging of the filter and frequent cleaning requirements, resultingin increased risk of pathogen breakthrough. Multistage filtration, consisting of roughingfiltration followed by slow sand filtration, can overcome these treatment limitations andprovide a robust treatment alternative for surface water sources of variable water quality.Testing was conducted on two different pilot multistage filtration systems and fed withwater from the Grand River, a municipally and agriculturally impacted river in SouthernOntario. One system featured pre-ozonation and post-granular activated carbon (GAC)stages, while the other featured a second stage of slow sand filtration for increasedrobustness.Removal of turbidity and coliform bacteria under elevated influent turbidities, low watertemperature, and increased hydraulic loading rates were investigated. In addition, theslow sand filters in each pilot system were challenged with high concentrations ofinactivated Cryptosporidium parvum oocysts.Both pilot multistage filtration systems achieved effluent turbidities of less than 0.5 NTUdespite temperatures below 5°C, influent turbidities in excess of 20 NTU, and hydraulicloading rates as high as 0.8 m/h. Removal of total coliforms was complete in pilotsystem 1 with ozonation. Pilot system 2 reduced total coliforms to 2 MPN/100 mL in80% of the measurements, despite influent levels as high as 2400 MPN/100 mL,temperatures less than 5°C, and hydraulic loadings as high as 0.6 m/h. The averageremoval of Cryptosporidium oocysts was greater than 2 logs in each challenge test, withhydraulic loading rates ranging from 0.4 to 0.8 m/h.This research assists in determining the potential of multistage filtrationtechnology as a safe and sustainable drinking water treatment alternative for smallcommunities, which are dependent on surface water sources of variable water quality,both in North America and developing countries. Includes 13 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

22

File Size:

1 file , 2.5 MB