 |
| Erection of the tank during plant upgrade. |
|
| Erection of the tank during plant upgrade. |
The Dunnville, Ontario Water Pollution Control Plant underwent a substantial plant upgrade in 2001, including earthwork, a new digester building, mechanical, electrical and instrumentation projects. One of the key issues in the selection of the digester tank was future design capacity. Designers wanted a tank that could be expanded at a later date for increased flows without incurring the cost of building a new aerobic digester. Low life cycle cost was another important criteria used to select the glass fused to steel coating. This coating is not like any field applied coating. The factory coating is permanent, which will drastically reduce any yearly maintenance recoating costs. This brought about the selection of the bolted glass fused to steel Aquastore tank manufactured by Engineered Storage Products Company.
The existing tank and foundation were designed to support the addition of another 2 rings of steel or 157 cubic metres of treatment and an aluminum dome roof. Tank dimensions are 15.3 m x 5.87 m high, containing 1,083 cubic metres. The tank and foundation are also designed to support the loads from an aluminum geodesic dome, if odour from the digester tank becomes an issue. If the tank ever needs to be expanded and/or a geodesic dome added, this work can be done at a fraction of the cost of building any new kind of treatment tank.
Because of the inertness of the final coating, this style of tank can be used for treatment such as anaerobic digesters, trickling filters and leachate storage. Borosilicate glass compositions are ground, blended with minerals and clays, then mixed with water to form a sprayable slurry. This formulation is fused to the steel sheets at 1600 degrees F to produce the tank coating. The molten glass reacts with the steel surface to form an inert system that is chemically and physically bonded to the steel. The sheet edges are flame sprayed with a protective stainless steel alloy. Glass is then added to double coat regular sheet edges with barrier coatings, so that the steel panels are encapsulated in glass. This tank will never need re-painting through its life cycle.
In the photograph, one can see the building jacks, which are tied to a common driveshaft and drive. The tank is built completely from the ground; as a ring of steel is assembled, the tank is raised until completed. The foundation ring of steel is embedded in the concrete and tied to the rebar. To ensure liquid tightness, bentonite seal strips are attached to the interior of the steel and embedded in the concrete.
The whole project took several months to complete, but once the foundation was poured, the tank was built in less than one week. This aerobic digester was designed with a jet manifold aeration system to meet the oxygen demands of 577 kg/day. To accommodate the required piping, the tank shell had a number of penetrations, which were all field located and flanged connected. A factory supplied cathodic protection system was engineered and installed to electrically protect any submerged metallic components inside the tank vessel.
The project was engineered and managed by American Water Services (formerly Azurix North America) and the General Contractor was Hira Ltd., from St. Thomas. Work also consisted of a new aerobic digester vessel supplied and erected by Greatario Engineered Storage Systems.
See our home page on how to order your subscription. We regret we can only accept orders from Canada and the United States.