How Does Clean, Clear Odorless Water Happen In Moncton
Water from the Turtle Creek Reservoir passes through the plant, removing turbidity and color, iron and manganese and is adjusted chemically so as to be less corrosive to metallic pipes.
The first stage of the process is to add lime and alum to the raw water.
During coagulation, very fine particles clump together into larger particles. These larger particles are called floc and are easier to remove from the water through filtration. Once the flocs are formed, a polymer is added to strengthen the flocs before their removal in the clarifiers and filters.
During the warmest months of the year, when the manganese and iron are at their highest, the raw water coming from the Turtle Creek Reservoir is first dosed with potassium permanganate. This chemical is used to remove iron and manganese from the water as well as to improve the taste and odor.
• Getting the Clear in Water Requires Clarification and Filtration
Next the water is then gravity fed to the clarifiers, where it flows up through four feet of media. The clarifier media at the Moncton Water Treatment Facility is made of small plastic beads, where 90-95% of the floc is removed. There are four clarifiers on operation and each clarifier needs to be cleaned every 8 hours.
As the raw water moves through the plant the remaining floc is removed by filtration through gravity mixed media filters. The mixed media filters consist of three granular materials of different size and specific density, layered in such a way to produce a filter that is coarse near the top of the bed and becomes progressively finer towards the bottom.
These filters produce water with a turbidity of less than 0.10 NTU and a color of less than 5 TCU at all times, as compared to a Canadian Drinking Water Guidelines maximum acceptable concentration (MAC) of 1.0 NTU and 15 TCU.
A total of eight filters are used and each filter can operate 3-4 days before being backwashed.
All the backwash water from washing the clarifiers and the filters is sent to the solids handling facilities, which consists of two large storage lagoons. Each lagoon has a detention time of one month. During that period, the solids in the water settle to the bottom and the clarified water eventually flows back out to Turtle Creek. The solids accumulate in the lagoon for a period of 4 to 5 years, before removal and final disposal at the sanitary landfill. • Water Goes Disinfection, Fluoridation And Corrosion Control
The clarified and filtered water now enters the clear well where the final stage of the treatment process takes place before the water is sent through the distribution system. Even with a very low turbidity of less than 0.10 NTU, the water still needs to be disinfected against water borne pathogens or infection and disease causing microorganisms. The disinfectant used at the Moncton Treatment Facility is chlorine.
Chlorine is added to the water as it flows out of the filters. Enough chlorine is being added to maintain a chlorine residual of 0.20 part per million (ppm) at the extremities distribution system, as required by the City of Moncton. Since the opening of the WTP, chlorine addition has decreased by over 50% because the cleaner treated water has a much lower chlorine demand.
Fluoride is also added to the treated water to reduce dental cavities, particularly among children. The concentration of fluoride is maintained at the Water Treatment Plant just less than 1 ppm as compared to a Canadian Drinking Water Guidelines MAC of 1.5 ppm. As part of the on going Corrosion Control Program started in 1998, a product called Aquamag is added to the water. Aquamag is a food grade ortho/polyphosphate that acts as a corrosion inhibitor in the distribution system. Also as part of corrosion control, sodium hydroxide is added to increase the naturally low pH of the water.
• Quality Control and Water Quality Checkpoints
Employees of the water departments monitor approximately 60 sites throughout the distribution systems to ensure chlorine levels meet the minimum requirement. Special attention is given to sites that have traditionally experienced low water flow or are in dead-end locations in the water network.
At these sites, water can sit for long periods and its quality can deteriorate. Flushing the waterrmains keeps the water fresh at these sites.
More than 1,500 water samples are tested every year to monitor water quality, and make corrections and adjustments where required. Thirty-one designated sites, throughout Riverview, Moncton and Dieppe, are chosen to be representative of the various zones. Samples from these sites are subjected to microbiological (bacteriological) testing in the Provincial Department of Environment and Local Government laboratory weekly. These tests monitor the presence and concentration of chlorine residual, turbidity, total coli form (bacteria), e-coli bacteria and heterotrophic plate count bacteria (HPC) in the water system.
Testing for bacteria after disinfection confirms the effectiveness of the disinfection process.
The MAC of total coli form bacteria allowed in drinking water is 10 cfu/100ml (coli form forming units) at any given site and not more than 10 per cent of the samples taken can show the presence of coli form organisms. Water utility staff follow stringent procedures in the event that bacteria are detected.
Turbidity: Turbidity levels in the reservoir at Turtle Creek are monitored regularly as the substances causing turbidity can shield bacteria from effective disinfections. Suspended matter such as clay, silt, finely divided organic and inorganic matter; soluble colored organic compounds, plankton and other microscopic organisms cause turbidity in water.
It is measured in NTUs (Nephelometric Turbidity Units), which is a measure that relates to the optical property of water that causes light to be scattered and be absorbed rather than transmitted in straight lines through the sample. The maximum acceptable concentration for water entering the distribution system is 1.0 NTU.
Control of turbidity in public drinking water supplies is important for both health and aesthetic reasons. Aesthetically, excessive turbidity detracts from the appearance of municipal water and has often been associated with unacceptable taste and odors.
The only method to reduce or eliminate turbidity is to filter the raw water. This is a primary role of the Moncton Water Treatment Plant. The finished water coming out of the water treatment plant and entering the distribution system has a turbidity of less than 0.05 NTU, 20 times less than the present maximum acceptable concentration of 1.0 NTU.
Besides improving water clarity and removing color, the filtration provides the added benefits of improved taste and odor while reducing chlorine requirements and trihalomethane formation (organic compound described below).
During 2005, turbidity levels were monitored weekly at 31 designated locations in the distribution systems. The average of over 1500 tests at the consumer’s tap was 0.2 NTU or 5 times less than the present maximum acceptable concentration. This very low turbidity indicates that high quality water is reaching the consumer’s tap in all three communities.
Organic testing of the tri-community water is undertaken quarterly each year. The concentration of Trihalomethanes (THMs), which prior to 1999 was at the MAC level, has been reduced by 75%.
For specific information on Moncton water contact: Ensor Nicholson, P.Eng. Director of Water Systems Ph: 506-859-2667 Fax: 506-853-3543 e-mail: email@example.com