Industrial Water Reuse at Gold Bar
The city of Edmonton, provincial capital of Alberta, is experiencing an economic boom in part due to the large oil sands projects in northern Alberta. Growth to over one million people in the greater Edmonton area, coupled with increased industrial and commercial business, has resulted in more demand for clean water.
Alberta Environment, which oversees water allocation from the North Saskatchewan River, the city’s main source of water, is seeking to balance water allocation with responsible watershed protection.
One company needing access to more water was Petro-Canada, which was planning a major upgrade to its refinery located east of the Gold Bar plant in Strathcona County. New federal regulations required the refinery to reduce sulphur levels in gasoline and diesel. For this purpose and to allow the refinery to process bitumen and bitumen-based feedstocks, the refinery requires additional water to produce hydrogen and steam.
Faced with water shortages, the company explored the option of drawing water from the North Saskatchewan River, but this proved expensive. Instead the company and the city agreed to develop a project that would allow Petro-Canada to use treated effluent from the Gold Bar Wastewater Treatment Plant.
Currently, the city’s Gold Bar Wastewater Treatment Plant treats wastewater from about 700,000 people and has the capacity to treat 310 million litres of wastewater per day. For the past few years, the city has also explored options to treat its wastewater effluent to a level suitable for industrial, commercial and municipal reuse.
Working with the city, the Associated Engineering team explored what treatment options were able to produce a high quality effluent suitable for Petro-Canada’s use. The team determined that membrane filter technology was the most suitable option.
Following Associated Engineering’s completion of a feasibility study and conceptual design, the city engaged the firm as prime consultant for the detailed design, construction management and commissioning of the membrane facility. UMA Engineering was subconsultant for instrumentation, controls and construction inspection; Magna IV for electrical engineering.
The arrangement called for the city to design, build and operate the membrane facility with funding provided by Petro-Canada. In addition, Petro-Canada would design and build a 5.5-kilometre pipeline to carry the treated effluent from the Gold Bar Plant to their refinery.
The initial phase of the project required a plant that would produce 5 million litres per day of treated wastewater to be commissioned by the end of 2005, with an additional 10 million litres per day to be on stream by 2007.
Which type of membrane and where to locate it?
Membrane filters are a relatively new technology for water and wastewater treatment. Current membrane technology incorporates direct treatment of primary effluent through membrane bioreactors as well as treatment of secondary effluent to a high final quality. Membrane bioreactor processes combine biological treatment, secondary clarification and filtration into one process step. This is advantageous where space is limited, as in this case.
The sheer size of the facility posed challenges — this would be the largest water reuse facility to employ membrane technology in Canada. In addition, the water reuse facility was to be added into an operating wastewater treatment plant, a plant that was undergoing construction of other upgrades at the same time.
Once the team identified the most suitable membrane system, they determined the most suitable configuration. There were four possible locations: (1) within the existing bioreactors, (2) within existing secondary clarifiers, (3) within a separate tertiary facility using post secondary submerged filtration (vacuum), or (4) within a separate tertiary facility using post secondary filtration (pressure). The team evaluated these options from economic and non-economic aspects. The main economic factors included the location, operating requirements and capital and life cycle costs.
The team recommended housing the membrane facilities in a heated building due to the risk of the membranes freezing when they are removed from the tanks for servicing. The building enclosure would also enable any odour to be controlled and minimize noise from the large number of pumps.
While scum and foam are sometimes seen as significant problems in certain membrane processes, the team found that their occurrence would depend on the location of the membrane processes relative to the other plant processes.
Taking these and other factors into consideration, the engineering team determined that options 1 and 2 were too costly. They narrowed their choice to options 3 and 4 where the membranes would be located downstream of the existing bioreactors and clarifiers. Membrane equipment vendors were then invited to submit proposals which enabled the team to recommend option 3, submerged membranes, as the system to be constructed. This option added the least complexity to the operating processes of the plant.
The $14 million facility was completed on budget and on schedule in December 2005 with an initial production of 5 million litres per day. In addition to supplying Petro-Canada, the plant supplies recycled water to a nearby park and ski hill.
Name of project: Gold Bar Wastewater Treatment Plant Industrial Water Reuse Facility
Award-winning firm: Associated Engineering, Edmonton – prime consultant, project management, process and mechanical design (Steven Croxford, P.Eng., Patrick Given, P.Eng., Richard Watson, P.Eng.)
Owner: City of Edmonton
Project partner: Petro-Canada
Instrumentation, controls and construction inspection: UMA Engineering
Electrical engineering: Magna IV
Architecture: D.E. Schaefer