Annacis Island Wastewater Treatment Plant Secondary Treatment Upgrade

ABR Consultants, Burnaby, B.C., a joint venture of Associated Engineering (B.C.) Ltd., Brown and Caldwell Consultants Canada Ltd. and Reid Crowther and Partners Ltd.

Category: Water Resources

Serving approximately one million people in the Greater Vancouver area of British Columbia, the upgraded Annacis Island Wastewater Treatment Plant in Delta is the largest facility of its kind in the world.

The plant has been discharging primary effluent into the Fraser River since the 1970s. The river is the world’s largest salmon fishery and a major habitat for marine and bird life. While its receiving waters have an amazing ability to assimilate wastewater discharges, the daily discharge of millions of litres of primary effluent was contributing to a diminishing water quality.

To protect the river the British Columbia government directed the Greater Vancouver Regional District (GVRD) to upgrade the Annacis plant to provide secondary treatment to the effluent. While primary treatment involved screens to remove large debris such as plastics and wood, sedimentation and disinfection, the secondary treatment uses biological treatment processes to remove a greater portion (about 95%) of the solids and oxygen-consuming matter from the wastewater.

The GRVD engaged ABR Consultants to complete the planning and detailed design of the facilities, oversee construction, train operators, assist in commissioning the facilities and manage the overall project.

The upgraded plant can treat 480 million litres of wastewater per day, and is capable of being expanded to twice that capacity. The size of the plant and absence of any existing secondary treatment components combined to make the upgrade a very large and complex project. It also incorporates many innovative processes.

Trickling filter/solids contact

The B.C. Ministry of Environment, Lands and Parks established stringent criteria for the Annacis plant. Whereas in other jurisdictions effluent criteria are based on monthly averages, the Annacis plant has to meet daily maximum effluent criteria. Therefore it must perform optimally every day, which is a challenge for a plant that handles industrial wastewater and combined sewer flows in addition to domestic wastewater.

After systematically evaluating 17 alternative processes, the team recommended the trickling filter/solids contact (TF/SC) process. This process ranked highest in terms of costs, reliability, flexibility, and ease of operation and maintenance. It also performs optimally under stress conditions such as fluctuating flows and “shock” loads.

The trickling filter/solids contact process consists of four 52-metre diameter trickling filters (concrete tanks containing plastic filter cross-flow media), followed by four 6,000 m3 solids contact (aeration) tanks. Biological film growing on the filter media removes most of the soluble carbonaceous biochemical oxygen demand (BOD) in the wastewater. Excess biofilm is sloughed off the media and flows to the solids contact tanks where the biomass in a biological suspension (mixed liquor) removes remaining soluble BOD. Finally, the mixed liquor flows to 12 secondary clarifiers which separate the biomass from the treated effluent. The treated effluent is discharged to the river, while the biomass returns to the solids contact tanks to continue its work.

Other features of the design include the world’s largest vertical turbine, solids-handling pumps to lift wastewater from the primary treatment area to the trickling filters, and an ingenious method for removing nuisances common in trickling filters: snails. The designers developed a simple solution consisting of steeply sloped floors in the contact tank, and aerated snail-removal chambers.

Secondary treatment substantially increases the amount of biosolids, or sludge, that the plant produces. Removing debris from the biosolids is essential for the material to be an aesthetically acceptable and marketable product. As a result, one of North America’s first installed sludge screens was incorporated into the process to remove debris.

The team considered several methods for producing high-grade biosolids but ultimately devised a new process: extended (multi-tank), thermophilic (high temperature) digestion. The advantage is that the sludge travels in a continuous flow through tanks in series, ensuring that pathogens do not break through to the effluent biosolids as a result of short-circuiting through a single tank.

Energy savings, seismic design

To conserve energy, methane gas produced from the sludge digestion is used to generate power and heat for the plant. The biogas fuels four 850 kW cogeneration engines, providing about 50 per cent of the plant power demand and ensuring emergency power. Waste heat from the clean-burning cogeneration engines is also recovered for space and process heating.

Since many businesses surround the plant and thousands of commuters travel on the Alex Fraser Bridge overhead, controlling odours was crucial for the plant to gain public acceptance. Using caustic soda scrubbers and natural biofilters the designers managed to reduce odours to non-detectable levels at the fenceline.

The plant, which incorporates 20 circular tanks of 40 metres diameter and larger, as well as many smaller tanks, is founded on sandy soils in an area susceptible to seismic liquefaction. To reduce the seismic risk the team developed a design incorporating innovative hinged joints to structurally tie the large tanks and building foundations together. If liquefaction should occur, the raft serves to minimize differential settlement, while permitting flexural movement.

Plant operators can monitor and control the operations through a fully integrated process control and information management system. The plant-wide system communicates with more than 5,000 pieces of equipment, including more than 4,000 instruments, 700 motors, 12 programmable logic controllers, 50 electrical distribution system power monitors, 50 feeder protection relay and ground alarm detectors and more than 100 variable frequency drives.

After seven years of planning, design and construction, secondary treatment at the Annacis Island plant began in October 1998. The project met all critical milestones and costs were $90 million below the original $530 million budget. Since start-up, effluent has consistently met stringent provincial discharge criteria, preserving the Fraser River’s resources for generations to come.

Project name: Annacis Island Wastewater Treatment Plant, Secondary Treatment Upgrade

Award winner: ABR Consultants (prime consultant). Project team leaders: Steve Krugel, P.Eng. (project manager), Dave Winter, P.Eng. (construction manager), Kim Fries, P.Eng. (process design)

Client/owner: Greater Vancouver Regional District. Don Littleford, P.Eng., Lloyd Slesak, P.Eng., Les Pickard, P.Eng., Miroslav Zelezny, P.Eng.

Other consultants: Dayton & Knight (influent pumping station), Fransen Engineering (69 kV substation), Kilborn Engineering Pacific (influent pumping station), Klohn-Crippen Consultants (geotechnical), Metro Testing Laboratories (materials testing), Seaconsult Marine Research (oceanography), Toby Russell Buckwell & Partners (architects)

Photographer: Bob Clarke, Colin Jewall (aerial)