The Greater Vancouver Regional District (GVRD) serves the Greater Vancouver, British Columbia area,
delivering water to eighteen lower mainland municipalities, which in turn deliver water to
approximately 2.1 million people. Water is collected from three mountainous watersheds: Capilano,
Coquitlam, and Seymour. The GVRD adopted its Drinking Water Management Plan (DWMP) in
August 2005 and its strategy is to use a risk management multi-barrier approach from source to tap.
The Coquitlam watershed is closed to the public, industry, and agriculture to minimize potential
contamination of the source water. The Coquitlam source is currently using ozone for primary
disinfection and chlorine for secondary disinfection. The GVRD plans to install ultraviolet (UV) disinfection for
Cryptosporidium control downstream of the ozone treatment for Giardia and viruses. While the
Coquitlam source water turbidity is low and filtration can be avoided in accordance with the
Guidelines for Canadian Water Quality, there may be infrequent but likely events of high source
water turbidity. This study was undertaken to demonstrate the degree to which an elevated turbidity
event would diminish the effectiveness of the disinfection system. Specifically, the question asked
was whether elevated turbidity at the Coquitlam source could directly impair the effectiveness of
either the UV disinfection of Cryptosporidium or the ozone disinfection of Giardia and viruses. A
second concern was whether elevated turbidity might minimize the advantage gained when UV is
applied downstream of ozone.
In this study, bulk water samples and concentrated suspended material were collected and used to
quantify and characterize the microbiological and physical characteristics of Coquitlam source
water. Further efforts were directed toward re-suspending subsamples of the collected
concentrated material into reactor volumes of the bulk water, and evaluating the efficacy of ozone
and UV at disinfecting natural or seeded microorganisms across a range of turbidities
experimentally prepared from native Coquitlam particles. Specifically, the study examined the
disinfection by ozone and UV of seeded coliphage MS2, Cryptosporidium oocysts and Giardia
cysts. Finally, the study investigated the effect of ozone on UV absorbance to determine whether the
oxidant would continue to improve the UV treatability of Coquitlam water under high turbidity
conditions, to the degree it has been shown to do so at the lower turbidity levels generally present. Includes 17 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 390 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 19 |
| Published : | 11/01/2007 |
