Four years after it opened, the Capital Regional District’s sewage-treatment plant at McLoughlin Point will get its first major cleanout this spring.
The CRD said it will take 21 days to scrub the massive “backwash” tank, which receives the dirty water and debris for the secondary stage of the sewage-treatment process.
That means for three weeks, the region’s collected sewage will only get primary treatment — screening and some filtration — before it’s pumped into Juan de Fuca Strait via a two-kilometre outfall pipeline.
The three-week bypass is expected to take place in March and April, pending approvals from Environment Canada and the Department of Fisheries and Oceans, said CRD spokesman Andy Orr.
Orr said it’s the first time the secondary and tertiary treatment processes will be bypassed since the $775-million plant went online in January 2021.
“We have had other bypasses at McLoughlin for other maintenance work, but this is the first bypass of the full secondary portion of the system, and the bypass of longest duration ever,” said Orr.
He said this type of cleanout of the backwash tank will happen every three to five years.
The work is expected to produce odours over the scheduled 21-day period. Orr said the CRD will try to minimize the smell from the plant, adding the work is being planned “before summer, when odours are of more concern.”
The effluent being pumped into the ocean won’t be raw sewage, according to the CRD.
Before the plant was built, the region’s sewage was only screened and de-gritted before flowing into the ocean.
Orr said primary treatment during the bypass will involve solids removal through high-rate clarifiers — a sedimentation tank that separates suspended solids from water — before the effluent is discharged into the ocean.
McLoughlin Point is designed to treat 108 million litres of sewage a day, the equivalent of 43 Olympic-sized swimming pools.
Before the sewage reaches the plant, screening to six millimetres removes a lot of the plastics, small stones, paper, cloth and other debris.
Once sewage arrives at McLoughlin Point, it flows into a series of deep vertical tanks for primary treatment, where solids are removed.
The secondary stage is a biological process.
After the primary effluent is screened down to two millimetres, sewage flows into massive tank reactors, where micro-organisms are delivered in pellets that consume organic compounds in the waste quickly, and reproduce to form cells that turn into residual biological solids.
An extra layer of screening comes in the form of massive sand bags, four and a half metres deep, that act as a filter. Air is pumped through to help the living organisms survive and do their work.
From there, the effluent makes its way into tertiary treatment tanks, where wastewater is strained through large discs that filter wastewater to a micron level and remove many of the pharmaceuticals, hormones and micro plastics, although they don’t eliminate them all.
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