CBCL, Consulting Engineers Tatamagouche Water Treatment Plant

The new water treatment plant at Tatamagouche, a village of 800 people on the northern shores of Nova Scotia, uses an innovative combination of treatment processes to produce extremely high quality potable water. Owned by the county of Colchester, the plant is believed to be the first municipal water treatment plant to combine both ultrafiltration and nanofiltration technologies.

The quality of raw water in the French River that supplies the plant is highly variable. It has extreme levels of particulate and dissolved contaminants that make conventional treatment approaches very challenging.

With the help of CBCL Consulting Engineers and Dalhousie University, the municipality investigated many different advanced treatment solutions for the new plant.

Among the advanced processes tested were microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF). The three systems have membranes with progressively smaller pore sizes. The smaller the pore size, the better the water quality produced.

The tests revealed that while the NF process achieved excellent quality water, it could not handle the loading of contaminants without clogging or fouling prematurely. The UF system was effective at removing particulate material, but did not remove much dissolved organic material.

During the analysis, an “A-ha” moment came when it became obvious that the UF process could effectively function as a pretreatment system, protecting the NF system while removing virtually all particulate material. The NF system would remove dissolved organic material to ensure that disinfection by-products (potentially cancer causing) are kept very low. What one system can’t remove, the other can, making the new process an effective teaming of well proven technologies.

Challenges remained, however. Five vendors submitted bids for the project, but few had experience with both types of systems, which meant there were compatibility issues. The selected manufacturer, GE, is a large company with many treatment lines, but they had never supplied the ultrafiltration and nanofiltration systems together for a municipal system. It meant the control system logic for each process had to be reworked so that the systems could effectively communicate via the plant’s new computer control system. The task required extensive liaison between CBCL staff and GE.

Complex Treatment Path

Raw water from the French River follows a complex path through the new treatment system, which can process 400 litres per minute. From an infiltration gallery under the riverbed, the water is pumped through a pre-treatment strainer and conveyed to two ZBOX-18 UF membrane skids oper ated in parallel. The raw water fills three membrane tanks each containing six ZeeWeed 1000 UF modules, which have a nominal pore size of 0.02 microns. After processing through the UF systems, the water enters the NF treatment units. It passes through two cartridge filters and into two GE Osmonics PRO-100NF skids installed in parallel. Each skid contains a total of six pressure vessels and each pressure vessel contains four spiral wound NF membrane modules. Following the NF units the permeate (treated water) is disinfected and pumped to the community’s water storage reservoir, and the concentrate (waste stream) is combined with the UF reject and discharged to the environment. The system is designed to provide full redundancy to ensure the plant can provide water to the community at peak rates even when a UF and NF treatment train is off line.

Reduced Chemicals

The combination of the two processes ensures that the treated water far exceeds current regulatory requirements without the use of chemical coagulants.

The current regulatory limit for THM’s (trihalomethanes), the most prevalent of the disinfection by-products, is 100 g/L. THM levels of 200-300 g/L common previously have been reduced to 10-15 g/L in the new plant. Turbidity levels in the French River often peak to over 100 NTU (nephelometric turbidity units) yet the plant reliably produces treated water with turbidity readings of 0.01 NTU or less.

As a result, the plant requires 80% less chlorine than the plant it replaced and has a lower environmental footprint. It addresses many of the challenges of operating a smaller municipal water treatment facility, and has a lower life cycle cost. The project met the budget and a six-month construction schedule, starting up in January 2008.

Project name: Tatamagouche Water Treatment Plant, N.S.

Award-winning firm: (prime consultant) CBCL, Consulting Engineers, Halifax, N.S. (Andrew Gates, P. Eng., Kevin Bezanson, P. Eng., Michael Chaulk, P. Eng., Dwayne Doucette, P. Eng., Randy O’Connor, P. Eng., Matthew Rodgers, P. Eng.)

Owner: County of Colchester

Other key players: Maritime Testing (geotechnical); L & R Construction (general contractor); GE Water (equipment)