Sneering ToiletToilet training

One morning, as I sat thinking about Science in the City, I looked down and realized how much we take the toilet for granted. It’s an amazing device.

Toilet in Cross-section

On the level

Next time you’re at a toilet, notice that no matter how much you pee, the level in the bowl stays the same. This is why it can be hard to tell if your tank is leaking.

You can put some food colouring in the tank to see if it bleeds into the bowl.

The direction the water swirls depends on the angle of the openings in the rim and the shape of the bowl, not the rotation of the Earth. So you shouldn’t notice any difference in Australia.

The next time you make a deposit, lift the lid of the tank and look inside. When you push down the handle, a chain pulls up the flush valve. The water in the tank rushes out the hole into the bowl through holes in the rim. The hole in the bottom of the bowl connects to a siphon jet, a tube that curves up and then down. The water level in the bowl depends on the height of the upper curve. If you add a little liquid at a time, it simply overflows down the pipe. When you flush, the rush of water fills the siphon jet and forms a siphon, which pulls the water and your contributions from the bowl.

Feeling flushed

Old toilets use up to 29 litres a flush. Low-volume toilets use six. You can reduce the amount of water in the tank with a bottle of water. Don’t use a brick. It can fall apart and mess up your toilet. If you don’t have enough water, you won’t get enough of a siphon and you’ll be left with a bowl full of doo-doo.

After the water runs out, air gets in and interrupts the siphon, which makes the gurgling sound. Meanwhile back in the tank, with the water gone, the flush valve falls back to cover the opening. At the same time, the float is no longer floating, and drops down to trigger the filler valve. This sends water into the tank and down the overflow tube to refill the bowl. When the tank gets filled enough to make the float float, the water is turned off.

The pipes are calling

In the Greater Vancouver Regional District, wastewater pipes total more than 7,000 km, which is like going to Toronto and back.

The five main treatment plants in the Greater Vancouver Regional District process 98 per cent of the wastewater captured in the region and put about 430 billion litres of treated effluent into our rivers and oceans every year. That would fill Science World a thousand times.

Wastewater travels through sewers for up to 35 km to a treatment plant. Pump stations help wastewater over high points so it can continue to flow by gravity. The path your poo takes depends on where you live. Newer sewer systems separate wastewater. Runoff from roads and roofs drains into a nearby river or ocean without treatment. Treasures from your toilet, your dirty dishwater, and other so-called sanitary waste from homes and industry, go to treatment plants.

Yellow Fish

Yellow fish painted next to sewers are not public art. They are reminders to take your nasty chemicals to a proper depot instead of dumping it down the drain and into fish habitat.

Older sewer systems, like those found in most of Vancouver, New Westminster and parts of Burnaby, have combined sewers. These carry both sanitary waste and storm water runoff to treatment plants. When it rains too much, untreated goo overflows into the Fraser River or Burrard Inlet. Think about this the next time you flush your toilet.

Special Treatment

Wastewater is treated to remove organic bits and bacteria feeding on them. These organic bits can lead to algal blooms that disrupt local ecosystems. Bacteria can use up all the oxygen in water and suffocate fish. Some bacteria, like E. coli, make people sick. Most of the sewage from our area receives only primary treatment before it gets sent out to sea. This mechanical process removes about half the floating bits and a third of the oxygen demand. Screens take out the big chunks. The rest sits in big vats where scum floats to the top and sludge settles to the bottom. The scum gets skimmed off and the sludge gets pumped out—it’s converted into Nutrifor, an agricultural fertilizer.

Iona Island Sewage Treatment Plant

Vancouver’s Iona Island treatment plant

70,000 tonnes of Nutrifor is produced each year. That weighs as much as 60 Science Worlds.

In areas where the outflow affects sensitive rivers, wastewater also goes through secondary treatment. This biological process lets bacteria break down the organic bits, reducing the oxygen demand by an additional two-thirds.

In both treatments, the remaining wastewater, or effluent, receives chlorine to kill bacteria, like in a swimming pool. Sulphur dioxide is then added to neutralize the chlorine before the effluent enters waterways.

From here, the situation becomes political. Improving systems is a murky political question involving people, money and nature. It won’t be settled easily. By doing your part to reduce what goes down the drain, you can help keep us all from going down the toilet.

This article was first published in December 2002 as part of the “Science in the City” series in The Vancouver Courier.