Wardsville’s Napier-Reid Extended Aeration Treatment Plant

The effluent from the Wardsville sewage collection system flows to an Extended Aeration Treatment Plant. This plant is composed of the following major components:


Aeration Basin

The effluent enters a large concrete basin that has air diffusers at the bottom to continually supply air to the tank. Present in the tank are microorganisms that use the air to live on while they consume the contaminants in the sewage. The level of contaminants in the sewage is measured by the BOD. The influent sewage BOD is around 140 mg/l. When the discharge leaves the plant, it is typically less than 10 mg/l.


As the sewage leaves the aeration basin, it goes into a clarifier, where the solids and microorganisms settle out. A chemical called alum is added to aid in the settling of the solids and to help remove phosphates.


The filter is a final polishing step, required to get the phosphates down to a very low level. The influent sewage phosphates of 5 mg/l are typically reduced to less than 1 mg/l in the plant discharge. Reduction in phosphates is important because excess phosphate in the river causes algae growth.

Post Aeration Tank

After leaving the filter the effluent is aerated again to ensure that there is sufficient oxygen to support marine life once it is discharged to the river.

UV Chamber

Just before being discharged, the effluent passes through a bank of Ultraviolet (UV) lights that kill any remaining bacteria, including E-coli. The effluent is then piped out to the Thames River.

Municipality of Southwest Middlesex.






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