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IntroductionPetawawa's Wastewater Treatment Facility was upgraded in 1998. In keeping with the Town's 'dynamic by nature' outlook, Town officials chose to upgrade the facility to a full secondary treatment process. This newly upgraded plant would include primary treatment, secondary treatment, Sequencing Batch Reactivator (SBR) technology, UV disinfection, sludge thickening process, as well as a full biosolids utilization program. The new facility using cutting edge technology that is completely biological, meaning that no chemicals are used in the treatment process, therefore no chemicals or chemical by-products are passed on to the receiving stream, which in this case is the Ottawa River. The disinfection process uses Ultraviolet light, which again is a completely environmentally friendly technology. The facility serves the Town, which includes both CFB Petawawa Town sites, encompassing a population of over 15,000. The plant is rated at 8730 cubic meters/day, with a peak day flow of 17460 cubic meters/day. Presently, the facility is operating at approximately 5400 cubic meters/day, which gives the Town ample capacity to handle its projected growth and community requirements, with no foreseeable upgrades required until the year 2018. The Town of Petawawa has contracted the services of the Ontario Clean Water Agency (OCWA) to maintain and operate both the Wastewater Facilities as well the Water Treatment Facilities. OCWA may be reached at: Town of Petawawa Waste Water Treatment Facility << Back to top HistoryA brief history of the Petawawa WPCP(Water Pollution Control Plant) is summarized below: The original WPCP was constructed in 1960 by the Department of National Defense (DND) to service CFB Petawawa. The plant was a primary wastewater treatment plant with an average design flow of 7,700 cubic metres per day. The plant was re- rated to 4,500 cubic metres per day when phosphorous removal facilities were added. In 1970, an agreement was made between the Ontario Water Resources Commission (now the MOE) and DND to accept Village of Petawawa sewage at the plant. The Village's sanitary sewage system was constructed in 1974-75 as an extension to those properties belonging to the CFB. Components added to the system included a major trunk sewer, two sub area pumping stations and various gravity collector sewers. In 1978, at the request of the Village, the MOE (now Ontario Clean Water Agency) agreed to operate the plant and sanitary collection system. From 1981 to 1986, various plant modifications and improvements were made to the existing primary treatment plant. This included enhanced gas mixing and collection, upgrades to influent screening, grit removal, a new chlorine contact chamber, upgraded chemical dosing facilities for phosphorous removal, new sludge pumping equipment and improvements to existing buildings. DND contributed 75% to the cost of the project. In 1988, the Government of Canada announced its intention to close some military bases across Canada and transfer personnel from London, Ontario to CFB Petawawa. The MOE advised the Village of Petawawa in 1988 that sewage flows were exceeding the plant capacity and that unless steps were taken to alleviate the flows, no further development should take place in Petawawa. In 1989, the Village of Petawawa retained JL Richards & Associates Limited to assess the plant capacity and, if feasible, to request approval to the MOE to re-rate the plant capacity from 4,500 cubic metres per day to 5,600 cubic metres per day. In January 1989 an application to re-rate the plant was submitted to the MOE In November of 1989, the DND proposed that the Village assume of ownership of the plant and that DND would share in the cost of upgrading and expanding the plant. In 1990, the Village of Petawawa retained Janota Patrick Engineering Consultants to provide engineering services for upgrading of the Village Waterworks. In 1991, the Village requested Janota Patrick to extend its services to include the upgrading of the Village's sewage works including expansion of the Water Pollution Control Plant. To assist with the transfer of the water pollution control plant from DND to the Village, Janota Patrick carried out a study which reported on the following:
A plant scale pilot project was undertaken in February 1991 for a period of 30 days to determine the plant's treatment performance at twice the normal flow. This was done by taking half of the plant out of operation. In June 1991, approval was given by the MOE to re-rate the existing plant to 5,610 m3/day. This approval was given subject to the Village providing the MOE with a written commitment to proceed with the enlargement of the existing plant, including secondary treatment. In August 1991, Council of the Village of Petawawa passed a resolution authorizing Janota Patrick Engineering Consultants along with JL Richards & Associates Limited to proceed with a Class Environmental Assessment Study to expand and upgrade the WPCP. This Class EA was initiated to expand hydraulic and organic loading capacity of the plant through the addition of secondary treatment and to address odour complaints through improvements to sludge handling facilities. In October 1995 the EAR for the Class EA was placed on public record for a 30 day review period. In 1996, detailed design of the WPCP expansion was undertaken by Janota Patrick & Associates Limited. And JL Richards & Associates Limited. Construction of the facilities was carried out in 1997/98 and the expanded plant was commissioned in 1998. Environmental ComplianceGeneralIn Ontario, sewage systems are approved either under the Ontario Water Resources Act (OWRA) or under the Environmental Protection Act (EPA). In general, a sewage system which discharges treated effluent to a surface water requires approval under Section 53 of the OWRA (formerly Section 24). The Ministry of the Environment's (MOE's) legislative authority to manage the quality of Ontario's water resources is provided under the Act and includes specifying sewage treatment works effluent requirements which are typically presented in the form of a Certificate of Approval (a legal instrument). The purpose of issuing a Certificate of Approval (C of A) for sewage treatment system is to ensure adequate protection of Ontario's surface waters. Effluent limits are incorporated into the Certificate of Approval to ensure minimal impact to the receiving stream. Effluent QualityThe Petawawa WPCP is operated under C of A # 1276-5YFSZH, issued on June 24, 2006. Conditions placed in this C of A address a number of issues associated with the operation and maintenance of the Petawawa WPCP and also specify effluent "requirements" and "objectives" along with sampling requirements. Table 1 presents a summary of the effluent requirements and objectives specified in the C of A. Table 1: Certificate of Approval Effluent Requirements/Objectives
The effluent "requirements" represent the concentrations which indicate noncompliance. The effluent "objectives"are intended as target concentrations which should be set as goals to be achieved under most operating conditions. Noncompliance with the C of A occurs if:
Also set out in the C of A are the minimum requirements for determining effluent quality. These sampling requirements are presented in the next table.
<< Back to top Plant CapacityThe incoming flows to a Water Pollution Control Plant fluctuate throughout any given day. Higher "base" flows occur in the morning, noon and night when domestic water usage is high, while lower base flows occur in between these peak periods. Groundwater infiltration and direct inflows (I/I) into the collection system (i.e. extraneous flows) also contribute to the overall sewage flow received by a treatment plant. The average day flow represents the total quantity of sewage received by the Water Pollution Control Plant over the course of a year divided by the number of days in a year. The peak day flow represents the highest volume of sewage received over a given 24 hour day period. The Petawawa WPCP has been designed to accommodate an average day flow of 8,730 cubic metres per day (2:1 peaking factor). These flows are based on a 20 year design period which takes into account population growth within the community as well as CFB Petawawa requirements. Sewage flows also tend to fluctuate over the course a year (i.e. seasonal variations). For example, flows during the spring thaw are usually much higher than during other time periods of the year due to higher infiltration and direct inflows into the collection system. The magnitude of these flows largely depends on the condition of the collection system, surrounding soils, groundwater table and direct connections ( e.g. roof drains, weeping tiles, etc.). A maximum day design flow usually accounts for very high 1/1 flows which typically occur during the spring thaw. The maximum day flow allows for very high I/I rates occurring concurrent with the maximum 24 hour domestic flows. This flow is intended to represent "worst case" conditions and the design of hydraulic devices and controls in a plant is usually based on maximum day flows. However, the treatment process is not normally designed to handle such high flows and must be by-passed. Based on the Operating Certificate of Approval (C of A), the Petawawa WPCP is "approved" to treat sewage at an average daily flow of 8,730 cubic metres per day and a peak daily flow of 17,460 cubic metres per day . The plant is not permitted to accept flows in excess of 17,460 cubic metres per day, and any flows larger should be by-passed. << Back to top  Primary Wastewater TreatmentThe objective of primary wastewater treatment is to remove the readily settleable and floatable solids from the raw wastewater stream. Primary treatment at the Petawawa WPCP includes chemical addition, screening, grit removal, preaeration, scum removal (skimming) and sedimentation (or primary clarification). The purpose of these processes are outlined below: Chemical AdditionTo improve settling performance in sedimentation tanks by increasing floc formation. Also used to precipitate and remove phosphorous and to control odors. ScreeningTo remove larger solids which could interfere with other components of the wastewater treatment system. Grit RemovalTo remove discrete granular particles such as sand, cinders, rocks and other substances which could interfere with other components of the wastewater treatment system. Pre-aerationTo provide a more uniform distribution of suspended and floating solids to sedimentation facilities and to a lesser extent to provide grease separation, odour control, and increase BOD removal rates. Scum RemovalTo remove grease and other floatable materials from the wastewater. Typically carried out in sedimentation tanks. SedimentationTo remove flocculent particles and hence remove a portion of the BOD and SS from the wastewater. This is typically accomplished in sedimentation tanks or clarifiers which allow settleable materials to accumulate at the bottom of the tank and supernatant to overflow into a collection system. Solids thicken at the bottom and are drawn off for further treatment and disposal. Supernatant is conveyed to further treatment processes and/or discharged to a receiving water body. << Back to top  Secondary Wastewater TreatmentThe objective of Secondary wastewater treatment is to remove the non-settleable solids from the wastewater stream. Secondary wastewater treatment is accomplished at the Petawawa WPCP by utilizing a Sequencing Batch Reactor (SBR) activated sludge process, which incorporates Biological Nutrient Removal (BNR). This treatment method incorporates a proprietary system referred to as ICEAS@ (Intermittent Cycle Extended Aeration System). Traditional Activated SludgeThe traditional activated sludge process combines biological and physical treatment methods with the objectives of coagulating and removing the nonsettleable solids and stabilizing the organic matter contained in the raw sewage. In general, organic matter (typically measured as Biochemical Oxygen Demand and referred to as substrate or food), and nutrients in the raw sewage are utilized by microorganisms (e.g. bacteria) to grow and reproduce into a settleable cellular mass. The activated sludge process involves the removal of organic matter using suspended biological growth under aerobic conditions (accomplished in a reactor). The term "activated" refers to the microbial mass formed by the process, which serves to stabilize ( or consume) the waste. Note:The removal of organic matter from the waste stream is important since organic matter exerts oxygen demand which would deplete the natural oxygen content of a receiving water. The biological portion of the process involves the introduction of organic matter (raw sewage) into a reactor which contains microorganisms. This biological slurry is referred to as "mixed liquor". The microbes (e.g.. bacteria) convert the colloidal (i.e. very small) and dissolved organic matter into various gases and cell tissue as described by the following chemical reaction: << Back to top  Anaerobic Sludge DigestionAnaerobic sludge digestion is a process typically employed at many wastewater treatment plants to treat (or stabilize), the various primary and secondary sludges produced. Anaerobic sludge digestion also reduces odours and bacteria levels, decreases the amount of solids present in the sludge (and hence hauling costs), and produces energy in the form of methane and carbon dioxide gases which can be utilized as an energy source at the facility. As the name implies, stabilization of sludges occurs in the absence of oxygen. Digestion occurs in three stages. In the first stage, complex solid organics, cellulose, proteins, lignins and lipids are broken down by extracellular enzymes into soluble organic fatty acids, alcohols, carbon dioxide and ammonia. In the second stage, the products of the first stage are converted into various organic acids and alcohols by acid forming microorganisms. In the third stage, two forms of methane-forming bacteria convert hydrogen and carbon dioxide to methane and acetate to methane and carbon dioxide. The rate limiting stage (i.e. the stage which is the slowest) controls the process. This is usually stage three since the methane forming bacteria reproduce very slowly. These methane bacteria are also very sensitive to environmental factors such as pH, alkalinity, temperature and toxins and, therefore, the control of these factors is very important to control the digestion process. Anaerobic sludge digestion can involve a conventional standard-rate single stage process; a high rate continuous-flow stirred process or; a two-stage process. The two stage process (utilized at the Petawawa WPCP) incorporates a first stage (primary) digesters and a second stage (secondary) digesters. Digestion occurs in the primary digester vessel. Raw sludges are sent to the primary digester where they are mixed and heated usually through circulation lines and by gas mixing equipment. Digested sludge is then transferred to the secondary digesters. The secondary digester serves four purposes: as a storage vessel for digested solids, as a standby primary tank, as a source for seed, and, as a quiescent basin for supernatant withdrawal. Sludge from the primary digester is conveyed by gravity to the secondary digester where it settles and stratifies into gas, scum, supernatant and digested sludge layers. Gas is withdrawn from the top of the digesters and can be used as an energy source (or alternatively wasted), and supernatant is decanted to minimize sludge haulage costs. Digested sludge and scum can be transferred to a storage facility or directly to hauling trucks. << Back to top |
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