The Municipality of Port Hope constructed a 11,300 cubic meter per day sewage treatment plant (STP) to replace the existing plant which had deteriorated and did not have adequate capacity for wet weather flow. The new STP was commissioned on April 1, 2010 and had a grand opening on April 23, 2010.
Flow to the new plant will be directed to a new headworks facility consisting of mechanically cleaned screens and vortex grit removal. The two mechanically cleaned filter screens have 6 mm openings to remove large debris and rags in order to protect downstream equipment. Sand and grit is removed in two parallel vortex grit removal systems. Collected screenings and grit are automatically washed and compacted to reduce odours and volume.
The new headworks is also equipped with a new automated septage and hauled sewage receiving station. The station incorporated a flowmeter and billing system for cost recovery. All hauled waste is directed to an equalization tank to minimize loading fluctuations in the treatment facility.
Following preliminary treatment, flow is directed to three parallel aeration tanks which provide almost 24 hours of retention time to remove organics and ammonia through biological treatment. The aeration tanks are equipped with energy efficient fine bubble diffusers and incorporate a small unaerated zone to enhance settling characteristics and reduce overall energy costs in the treatment process.
Biological solids in the aeration tank effluent are settled in three parallel rectangular settling tanks, known as secondary clarifiers, which provide approximately 8 hours retention time. The majority of these settled solids are returned to the aeration tank to enhance the treatment efficiency and a small portion is wasted to aerobic digesters for stabilization.
Treated effluent from the secondary clarifiers is disinfected in two parallel chlorine contact tanks. Prior to discharge, chlorine is removed through dechlorination to produce an effluent which is non-toxic to aquatic life. Under normal conditions, final effluent is discharged by gravity through a diffused outfall extending approximately 235 m offshore into Lake Ontario. The protect the treatment facility from flooding under extreme peak flow or high lake level conditions, an automated effluent pumping station is provided to elevate the treated effluent prior to discharge.
Excess biosolids from the secondary clarifiers are directed to a two-stage aerobic digestion process for stabilization. Overall, the biosolids are stabilized for more than 45 days to ensure compliance with all Ministry of Environment Guidelines. The stabilized biosolids are dewatered in a centrifuge to reduce the volume by approximately 90% and produce a moist soil-like produce which is suitable for beneficial re-use on agricultural land. A large covered cake storage building is provided on-site to store biosolids during the winter months when beneficial re-use sites are not available.