Canadian Municipal Water News & Review - Fall 2012 - (Page 11)
SaskWater’s New Water Treatment Plant for Gravelbourg Delivers Improved Water
BY S A SK WAT E R S TA F F
commercial Crown water utility, recently completed a new water treatment plant for the Town of
Gravelbourg in southern Saskatchewan. Of the nine options evaluated, this new plant, one of the ﬁrst of its kind in the province, is the only one that would meet the Saskatchewan Ministry of Environment’s (MOE) new regulations.
Gravelbourg has what one might say is very challenging water. The raw water source, Thomson Lake, is extremely difﬁcult to treat as the water quality parameters ﬂuctuate widely throughout the year. The water is particularly difﬁcult to treat in the winter months when ice cover reduces the amount of dissolved oxygen in the water and manganese levels are elevated. When the soluble manganese reacts with disinfectant, colour and turbidity problems occur. During most of the year, potassium permanganate is injected at the raw water pump station to oxidize the soluble manganese. On occasion during the winter months, manganese removal is difﬁcult to achieve by potassium permanganate injection alone and an additional oxidant, chlorine is used. This in turn creates additional problems with the trihalomethane (THM) levels. The original treatment plant was a conventional surface water plant with coagulation, ﬂocculation, sedimentation, ﬁ ltration and disinfection with chlorine (gas) and was incapable of meeting the new THM regulations that the MOE had introduced, or addressing the problematic aesthetic water quality issues associated with the Thomson Lake water. As a result, in February 2009, SaskWater completed an evaluation of nine possible options for treating water with the common goal of achieving a safe, sustainable and reliable solution for Gravelbourg that would meet all regulatory requirements. Of these, the only option that met the THM regulations and addressed other aesthetic issues was an ultra ﬁ ltration (UF) membrane system followed by a nano ﬁ ltration membrane (NF) system.
The existing multi-media ﬁ ltration system was not sufﬁcient to prepare the water for the NF system. The Silt Density Index (SDI) which measures fouling capacity of water by percentage drop in the ﬂow rate/minute was 6 percent and less than 3 percent was required. To solve this issue, the new plant has retained the existing contact chamber ﬂocculator and clariﬁer as pretreatment and converted the existing two ﬁ lters to transfer chambers for the new UF/NF membrane system. A UF membrane system was then installed to more effectively take out the colloidal and bio-foulants, and to bring SDI below three.
Then, a NF membrane system with smaller pores or openings was installed to remove the dissolved minerals (i.e., TDS, hardness, sodium, sulphate, manganese, calcium and iron). Once the water leaves the NF membranes, sodium hypochlorite is added as a disinfectant. The removal of the organics by the membrane systems greatly reduces the potential for disinfection by-products (THMs). “The combined treatment process has resulted in a ﬁ nal drinking water of very high quality,” said Jeff Mander, Director of District Operations with SaskWater. The community is very pleased with the new and improved water.
FALL | AUTOMNE 2012 |
Table of Contents for the Digital Edition of Canadian Municipal Water News & Review - Fall 2012
PRESIDENT’S MESSAGE/ MESSAGE DU PRÉSIDENT
DRINKING WATER SAFETY PLANS
WINDSOR LAKE WATER TREATMENT PLANT
SASKWATER’S NEW WATER TREATMENT PLANT
RISK MANAGEMENT IN ENGINEERING DESIGN
MANAGING MUNICIPAL WASTEWATER IN SASKATCHEWAN
PRODUCTS & SERVICES MARKETPLACE
INDEX OF ADVERTISERS/ INDEX DES A NNONCEURS
Canadian Municipal Water News & Review - Fall 2012