Environmental Science & Engineering - www.esemag.com - September 2004
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Wastewater treatment plant upgrades for Kingston’s urban growth and development

By Dan Lalande, P. Eng.,
J. L. Richards & Associates Limited


Left: Twin flow meters and custom transition pieces in existing rectangular channel will provide the data required for flow paced chemical dosage. Right: Installation of chimney extension in grit tank.

The Kingston West Wastewater Treatment Plant (WWTP) was originally constructed as a conventional activated sludge facility. As the surrounding area developed, three treatment plants were added on the same site to achieve a total rated treatment capacity of 38,800 m³/day.

Over time, flows were directed to only plants C and D due to the condition of aging plants A and B. The challenge was to develop a program to cost-effectively optimize plants C and D to reclaim the full site capacity lost with the decommissioning of plants A and B without constructing another train.

Other project objectives included:

Increase and optimize capacity of the two largest treatment plants (C&D) in a cost-effective manner through reuse of redundant tanks while permanently decommissioning the two oldest plants (A&B).
Optimize process controls and improve operational flexibility, which would enable plant staff to further enhance the environmental performance of the plant and surpass regulatory requirements.
Implement a Septage Receiving Facility to provide a needed service to the rural residents of Kingston and three surrounding Counties, as under the Nutrient Management Act, land application of untreated septage will no longer be permitted.
Implement odour treatment measures using an environmentally friendly technology to mitigate environmental and social impacts to plant neighbours.
Construct the works while maintaining plant operations and compliance with the regulatory effluent requirements to continue to protect the environment.

Plant optimization and
designing for flexibility Installation of new flow meters, using a unique and customized design for the influent and effluent tapered transitions from a rectangular channel to a circular conduit, now enables plant staff to pro-actively control flow splitting between the two optimized plants and to flow-pace chemical dosages based on incoming flows with an immediate and automated response. Such a strategy was needed due to limited head loss being available for the new metering devices.

Historically, flow splitting and chemical dosage were adjusted based on flows measured at the outlet of the plant, with a 24 to 36 hour time delay due to the hydraulic retention time through the process. This innovative installation has resulted in an optimized use of chemicals and better process control.

The optimization program involved implementation of a fifth secondary clarifier, resulting in three different sizes of clarifiers downstream of four equally sized aeration tanks. This created an unusual challenge for splitting and redistributing flows based on surface area of each clarifier after the aeration phase of the process. New channels, including a new pre-cast inboard launder equipped with outlet ports and slide gates, were installed to provide an effective and reliable operating strategy. This feature is unique to the Kingston West Plant and required a non-conventional design strategy.

Septage receiving There are approximately 64,000 households in the City of Kingston and the three neighbouring Counties on private septic systems. Under the Nutrient Management Act, land application of untreated septage will no longer be permitted. The Septage Receiving Facility implemented as part of this project will provide a needed service and will enhance the social and environmental quality of life to the rural residents of Kingston and surrounding communities. More importantly, septage treatment is a step in the right direction in protecting groundwater resources.

The new Septage Receiving Facility is equipped with dual unloading points, surge/storage tanks, primary screening/grinding, gas detection and semi-automated control and invoicing system.

Challenges included maintaining septage receiving during construction and implementation within available space. Several redundant tanks resulting from decommissioning of the two oldest plants were reused as part of the optimization program for septage equalization and the sludge thickening process.

Odour management Odours from a Water Pollution Control Plant can have an adverse effect on surrounding properties. For example, hydrogen sulphide (H₂S) is one of the most commonly known gases. Produced from the decomposition of organic waste in anaerobic conditions, such as septage waste, H₂S has a characteristic rotten egg smell, is corrosive to some metals, and is toxic to humans, causing headaches, nausea, and eye irritation, even at low concentrations.

The Kingston West Plant’s location relative to surrounding residential and cottage properties required a proactive approach to odour treatment and mitigation. The biofiltration technology implemented as part of the upgrades mitigates potential odour impact from the septage receiving facility and the new sludge thickening process. The odour treatment system utilizes composted wood rootstock and biological processes to remove odorous compounds from the air stream. This “lowtech” system is the most cost-effective technology available, is environmentally friendly, chemical addition is not required, the spent filter material is benign and can be composted, and the energy requirements are lowest. This system will ensure that the environmental and social quality of life for the plant neighbours is not adversely affected.

Construction partnership Designing and implementing various upgrades to optimize and increase the capacity of two existing plants while maintaining operation and compliance with effluent requirements resulted in a level of complexity that is rarely encountered.

Schematic showing details of the chimney installation in grit tank to permit dewatering of forcemain due to existing valve failure.

Traditionally, design firms prepare drawings and specifications for the proposed works and the contractor is left to determine the constructability challenges and the cost to phase and stage the works while tendering the project. This has often resulted in higher tendered prices. Given the nature of the work and the level of complexity involved, the consulting engineers developed the drawings and specifications, including a detailed construction sequence, to a higher level of detail than normally seen. This detailed construction sequence, developed in consultation with plant staff and then followed by the construction team, allowed the plant to remain in operation and in compliance with its regulatory requirements during the construction phase.

Cooperation between the engineers, plant staff, and the contractor was put to the test when an old valve on a 600 mm diameter raw sewage forcemain failed to close. This valve needed to be closed and to seal fully to permit significant modifications to the on-site raw sewage pumping station while in full temporary by-pass pumping mode at a cost of $6,000 per day. The engineers developed a concept to dewater the forcemain from the discharge end by installing a “chimney” extension blindly under 1.5 m of raw sewage. The strategy was completely fleshedout and implemented by the construction team within 24 hours. Innovation and teamwork during construction by the contractor, engineers, and plant staff saved the owner significant additional by-pass pumping costs and allowed the works to proceed in a timely and safe manner.

Project benefits Infrastructure investment is costly so public dollars need to be spent wisely. The optimization program re-established the plant’s rated capacity at the lowest life cost. This will permit continued urban growth and as a result stimulate economic growth and development. More importantly, the plant’s improved performance resulting from the optimization program will ensure that the treated effluent does not adversely affect the water quality within Lake Ontario and the St-Lawrence River, vital sources of drinking water for several communities downstream. The program was completed successfully and cost-effectively, while keeping the plant in operation and in compliance with its effluent requirements. A post-construction process evaluation concluded that the actual process capacity of the optimized treatment units exceeds regulatory requirements.

Contact e-mail: dlalande@jlrichards.ca.

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