Our Town

A Bug’s Life: The end of the line for the little bugs that could

The water from these taps was once our waste and is now ready to be used for irrigation. - Sally MacDonald photo
The water from these taps was once our waste and is now ready to be used for irrigation.
— image credit: Sally MacDonald photo

In the conclusion of a three-part series on how Cranbrook turns sewage into water, we learn how the bugs in our wastewater change as the effluent moves through the wastewater system.

Bugs have a vital role in helping Cranbrook get rid of the roughly 2 million gallons of wastewater that we produce every day.

We are learning how microorganisms do away with our feces in the most unappetizing way at the city’s wastewater lagoons.

On a tour of the site with Director of Public Works Joe McGowan, we’ve learnt how the city filters out “floaties” and foreign materials from the wastewater, before billions of microorganisms go to work breaking down the organic material like they’re Lance Armstrong in the Tour de France.

There are three lagoons at the wastewater site. Each lagoon is slightly lower than the last, and the wastewater flows from the first pond into the second and then the third.

Each lagoon has a different colony of microorganisms. The first pond receives more oxygen, so it has bugs that do much of the hard work breaking down organic materials.

McGowan describes the bugs in the first lagoon as grizzly bears.

“It’s like a bunch of people standing around a Las Vegas buffet. They don’t care what they are presented with, they are going to eat it in huge quantities.”

In the second pond, the bugs get what’s left over – they are lean runners with a narrower diet.

And the third lagoon’s bugs are essentially vultures – they will eat anything.

What’s more, the temperature in the lagoons gets cooler the further from the source. The first pond is on average seven or eight degrees warmer than the third. There’s two reasons for that: first, wastewater is warm when it leaves your home, because the water picks up the heat in your home as it passes through. Second, the microorganisms generate heat as they are feeding on the organic material.

Once the wastewater has flown through the lagoons, it’s now considered “effluent” - treated sewage. When it leaves the third lagoon, it goes through another screener – that conveyer belt that it first met at the head of the lagoons – which picks up anything that has fallen into the lagoons along the way, such as bulrushes.

It then flows into a large underground chamber. From there, pumps pick up the effluent and force it up the hill into a trunk main that carries the wastewater to Cranbrook’s spray irrigation fields in Mayook.

Here, the wastewater sits in two ponds, which add more oxygen to the water so that bugs can continue to work on the little organic material that’s left. Then the effluent – now containing little more than water – goes through an ultraviolet facility the city built in 2012.

Here, the water is sent through pipes that contain dozens of fluorescent lights, which kick off pathogens in the water. The ultraviolet light doesn’t kill the bugs, but it renders them infertile.

If you turn on the tap inside the ultraviolet facility, water gushes out – water that bares little resemblance to sewage because the bugs have done such a thorough job of cleaning it.

The water is then piped all over the spray fields – 900 hectares of pastures where cattle graze and hay crops grow.

Only about 10 per cent of Cranbrook’s wastewater is not used on the spray fields. That 10 per cent is piped to the opposite end of the spray fields to a third lagoon, built in 2011.

Before it goes into that lagoon, the water is treated again – at a building that’s the only place a chemical is added to the wastewater.

Here, alum is added to the water, a chemical that settles out the phosphorous. There’s about a thimble full of alum added to each cubic metre of water.

From the third lagoon, the water is treated for a final time at a second ultraviolet facility. That is essentially the end for Cranbrook’s hardest working bugs. Their job complete, they are put to rest as the little leftover wastewater is sent into the Kootenay River.

Each fall, for two or three weeks, the city empties what is left of the irrigation water it no longer needs into the river, ready to start collecting wastewater over the winter for the coming farming season.

McGowan explains that, thanks to those dedicated, hungry bugs, the water the city sends into the Kootenay River is better quality than the spring melt that is already in the river.

 

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