PEI·Video

After you flush: Take a tour of P.E.I.'s largest municipal sewage plant

The smell inside the Charlottetown Pollution Control Plan isn't as bad as you might think it is — despite 20 million litres of raw sewage flowing into the facility every day.

How raw sewage is transformed into clean water and into soil for farm fields

Nature calls, technology answers . Tour P.E.I.'s largest public sewer treatment plant

5 years ago
1:00
Nature calls, technology answers . Tour P.E.I.'s largest public sewer treatment plant 1:00

The smell inside the Charlottetown Pollution Control Plan isn't as bad as you might think it is  — despite 20 million litres of raw sewage flowing into the facility every day.

"Fresh sewage doesn't have that strong of an odour," said plant superintendent Steven Stewart. "It's mostly water. It's like 99 per cent water that comes in."

The untreated sewage comes into the plant into a building called the headworks. Here a grit trap removes heavy material such as sand and gravel. (Pat Martel/CBC)

Raw sewage from the capital city enters the plant in a building called the headworks.

Before the treatment process begins, two things happen in the headworks. First, grit material such as sand, gravel and eggshells is removed. 

Steven Stewart, superintendent of the Charlottetown Pollution Control Plant, says many people are surprised to learn the raw sewage coming into the plant has little odour. (Pat Martel/CBC)

Then a trash rack removes garbage such as plastic spoons, disposal wipes and pieces of wood that people aren't supposed to flush. 

Careful what you flush

"A lot of untreatable waste that doesn't decompose should not be flushed down the toilet," said Stewart.

"Sometimes it does get through the process and it ends up in pumps, plugging pumps, plugging up different parts of our process."

Before the treatment process begins, a trash rack removes garbage such as plastic spoons, disposal wipes and pieces of wood. (Pat Martel/CBC)

The next stage, called primary clarification takes place outside, in one of the many open cement ponds. 

Here, close to 60 per cent of raw solids are removed from the stream of sewage.

Solids separated

The separated solids sink to the bottom, while the water begins a clarification process for eventual release into Charlottetown Harbour. 

"It also removes the floatable material from our waste stream — grease and fat that comes from kitchen waste and restaurants mostly and from humans as well," said Stewart.

Superintendent Steven Stewart walks along one of many treatment ponds at the Charlottetown Pollution Control Plant. (Pat Martel/CBC)

A lot of seagulls hang around this area of the facility. 

"They're feeding on food that's in the waste stream … if it floats will come to the top and the animals will pick it off. 

Before upgrades to the plant in 2007, this would have marked the last stage of the process, with the effluent going into the Hillsborough River.

Cleaner water going into river

"Now we have much cleaner, we have secondary treatment.  Primary treatment removes about 40 to 60 per cent of the waste material, and secondary treatment removes 95 to 96 per cent." 

Much of the work to clean up the water in the secondary treatment stage is done by nature, with a little help from aeration.

Air is pumped into the aeration tanks to help bacteria thrive. The bacteria actually consume the waste from the sewage. (Pat Martel/CBC)

"We add air back into our system, which supports the biological life that's in here," said Stewart.

Good bacteria eat solid wastes

"They are naturally-occurring bacteria. We just provide the right conditions and they thrive in this kind of environment and consume the waste that's in the waste stream."

The water goes through one more stage before emptying into the Hillsborough River — past some huge UV lights for disinfection. 

Steven Stewart stands on the grate covering a rack of UV lights that kills off most of the pathogens in the water that empties into the Hillsborough River. (Pat Martel/CBC)

"UV light in contact with pathogens, with bacteria and viruses, they inhibit their ability to reproduce so they end the lifecycle of those bacteria and pathogens," said Stewart.

It takes the water about 24 hours to pass through the plant. The solid waste take 20 days, and it has to go through more stages before it's clean.

This pond is about the only part of the treatment process that gives off a strong odour. It's where the solids are thickened, and settle to the bottom of yet another cement pond. (Pat Martel/CBC)

The next stage is the one that you might smell when you drive by the plant.

It's where the solids are thickened, and settle to the bottom of yet another cement pond. 

Pasteurization kills pathogens

The next stage is not what you expect to find in a sewage treatment plant.  

Pasteurization takes place in a spotlessly clean building with huge stainless steel tanks.

These giant stainless steel tanks pasteurize the separated solids at 70 Celsius for one hour, to reduce pathogens. (Pat Martel/CBC)

"We pump that solid material through a heat exchanger where we pasteurize those solids, just like you would milk — 70 Celsius for 60 minutes."

The final stage is called the anaerobic digester. It's similar to what happens in your stomach.

"Our two anaerobic digesters break down the organic matter and break down the solids. Anaerobic means there's no oxygen, so the bacteria do that job."

Turned into rich soil

After the material has been digested, it's about 20 to 25 per cent solids. It drops out in a steamy, dry form, almost like soil.

The sewage treatment process removes removes about 95 per cent of the solids before the clean water empties into the Hillsborough River. (Pat Martel/CBC)

"So the biosolids you see dropping out there, they meet the criteria for exceptional quality, Class A bio-solids," said Stewart.

"They're hauled off site and we take them and they get spread on agriculture land." 

There's one more useful by-product from this process — methane gas, which comes in handy during the winter.

After spending 20 days going through the system, the solids that entered as raw sewage are turned into rich, clean soil that is spread on farm land. (Pat Martel/CBC)

"We use that biogas in our boiler to get heat for our pasteurization and we use the heat to heat our buildings."

Making use of methane

In summer, the extra gas is flared off. That's when you might notice that Olympic-sized flame as you drive by the plant.

Steven Stewart says methane gas from sewage is not wasted. 'We use that bio-gas in our boiler to get heat for our pasteurization and we use the heat to heat our buildings,' he said. In summer, the extra gas is flared off from the flame stack. (Pat Martel/CBC)

Steven Stewart is hoping others will realize that working in the sewage treatment plant is not so bad.

"They think you're working around sewage and stuff, but it's a lot of technical. We're running the equipment more so than we're working in the sewage."

ABOUT THE AUTHOR

Pat Martel has worked with CBC P.E.I. for three decades, mostly with Island Morning where he was a writer-broadcaster and producer. He joined the web team recently to share his passion for great video. Pat also runs an adult coed soccer league in Stratford. He retired in Oct. 2019.

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