What if there were pooping cars?

An investigation into waste treatment in my city

Eila

May 18, 2024

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This morning I awoke with a burning question.

“What if there were pooping cars?” I rolled over and woke up Steve to ask for his opinion. Two answers popped up immediately in response to this question:

Cars already poop, in a way. We feed them gasoline, and they poop out nitrogen, carbon dioxide, and water vapours.1
We used to have pooping cars, they were called horses.

However, these two answers were not exactly what I had in mind when I asked the question. To be more specific: “What if there was a car that could take kitchen scraps, convert them to compost, and also be able to drive from the excess energy?”

I have no idea if this would be technologically feasible, however it did get me curious about what we do with waste, and raise some interesting ideas about energy capture and the conversion of pollutants into riches. Let’s dive in.

The oldest kind of pollution

A pollutant is substance that makes the water, air or soil harmful or poisonous to people, plants, or animals.

The first pollutant made by humans was our excrement. Riddled with bacteria, pathogens, and parasites, we are hardwired to avoid our own feces due to the risk of getting sick from it. This was easy enough when people lived nomadic lifestyles. They were constantly migrating to new areas before the environment could become saturated with waste. However it became a major problem upon the discovery of agriculture, when it became much more difficult to avoid coming into contact with water or soil that had not been contaminated by the generations of feces limited to a relatively small area.

The oldest pollutant is also the oldest example of turning a waste into a resource.

In rural China, it used to be good manners to poop at your neighbour’s house. If someone hosted you over for a meal, it was generally seen as a courteous thing to pay a visit to their outhouse on the way home and lay down a token of appreciation. The muck from the outhouse would be added to compost heaps, and fermented until it was sterile enough to be re-used as fertilizer to grow better crops, without causing the spread of disease.2 By donating a poop, you were contributing to the wealth of your hosts, and leaving a little something behind in exchange for their hospitality.

So, what happens when we flush?

Nowadays, us city-dwellers send all of our wastewater through a massive underground sewage system to a water treatment facility. You could drive a bus down some of these pipes, they are so large. The sewage looks like a giant, dirty, underground river, with little tributaries from every single building in the city.

In Ottawa, the sewage all goes to the Robert O. Pickard Environmental Center, which from satellite looks like a giant grid with 16 massive circular ponds arranged into four quadrants. It also has some covered sections along the west side and long troughs down the middle.

At this centre, it undergoes both primary and secondary treatment. For primary treatment, the water passes through screens to remove large sticks and detritus, the grit chamber separates out sands and fine rocks, and the sedimentation tank drastically slows down the flow of the water, to allow time for the minute particles of organic and inorganic matter to settle to the bottom of the tank.The product of the sedimentation tanks are ‘biosolids’, formerly known as sludge.3 More on those later.

To further clean the wastewater, it passes through a secondary treatment. In this treatment, naturally occurring bacteria that feed off the organic material are encouraged by the addition of air to the system. The water goes to another tank to settle, and any sludge that settles to the bottom is pumped back to the aeration tanks to continue feeding the bacteria population and encourage the bio degradation of the organic particles in the water.

After these two treatments, the water is chlorinated to kill off any remaining pathogens, then another chemical is added to remove excess chlorine before it’s pumped back out into the Ottawa river.

The sludge from the settling tanks is sent to anaerobic chambers (no air) for further fermentation. This process creates a product called biosolids, with carbon dioxide and methane byproducts. In Ottawa last year, we (the poopers) produced just shy of 50 metric tonnes of biosolids, which have all been either directly applied to agricultural land, or processed into soil products.4

As for the methane byproduct? That’s put to use as well - it’s burnt in engines and boilers, which produces heat and electricity to run the plant.5

All in all, it’s a far cry from the early 1960s, when Ottawa was dumping raw sewage and industrial waste directly into the river, to the point that it was dangerous to swim in or drink the water.6

Back to the pooping car

Let’s take another look at that methane byproduct. It turns out the Bristol sewage treatment plant in the UK has managed to use methane to run a car. They report that the waste flushed down the toilets of 70 homes is enough to run the “Bio-Bug” for a year.7 So a poop car already exists! Add in the fact that the Bristol treatment plant has expanded to include a green bin program and is generating compost and methane byproduct from kitchen scraps, it does seem like there is an indirect answer to my question:

“What if there was a car that could take kitchen scraps, convert them to compost, and also be able to drive from the excess energy?”

The Bio-Bug is not eating kitchen scraps and pooping compost, but it is burning a byproduct of the composting process which otherwise could go completely to waste, and that is pretty darn cool.

Ottawa’s green bin program does create compost, however it’s not yet capturing methane as a byproduct. That system will have to be an investigation for another day.

That’s all for now. If you enjoyed this and would like to receive my weekly update, make sure you are subscribed! And let me know - would you drive a pooping car?