28 AUG 15 | we’re talking some crap!

Brandy was really hesitant to let me write a blog post about composting toilets. I mean, she’s an artist and loves beautiful things! And for sure, at first glance, a composting toilet is ANYTHING but beautiful. First of all, we have to talk about poop to talk about composting toilets. Goodness gracious. But really, once we start looking at the other alternatives (or mainstream ways of dealing with all of our, umm, waste) composting toilets can look pretty clean and beautiful.

For real.

Composting toilets get a bad rap (or crap): people think they’re smelly and full of all kinds of viruses and pathogens and other bugs that will make you super sick. In this modern society, in the era of everyone having little tiny computers in our pockets and solar panels and electric cars and 3D printing, our society has also developed un-smelly composting toilets! True, they may not be getting quite the media coverage of driverless cars or flying robots, but they’re around and definitely pretty cool.

The amount of clean, safe drinking water used to flush minuscule amounts of human waste is just silly. The American Water Works Association Research Foundation finds that over 30% of household water is used for flushing toilets. Already the flush-less composting versions are looking way prettier, yeah??

Conventional Treatment Systems

If you live in town, you’re probably contributing to your municipal wastewater treatment plant, whereas if you live in the country, you may have your very own septic system. Both of these systems include chemicals and trucks and infrastructure, and all sorts of stuff that isn’t very earth-friendly. We’ll start with the most complicated, municipal wastewater treatment facilities.


So the easy part about this system is you flush. That’s it. Then it’s totally gone. But not really… as we know from the First Law of Thermodynamics, matter can neither be created nor destroyed. You’re just sending your poop problem somewhere else. So what happens next?

compost flush
Cartoon by Bruce Fitch

I’m going to try to make this quick, so please don’t be disappointed that it’s not too terribly detailed.

First, it whizzes through your pipes, then your neighborhood pipes, then town pipes. This stuff travels more than some people do. Once it gets to the municipal facility, the incoming matter is strained with big screens to remove all snakes, soup cans, toys, space shuttle parts, bike tires, and other weird things that inadvertently made that messy trip.

Then it’s all swirled around so that the organic matter stays suspended, while the rocks and sand sifts to the bottom. The suspended and watery stuff moves onto the next round (…movin on up, to the east side / to a deluxe apartment in the sky…) where the sludge is allowed to settle and gets pushed into sludge treatment zones, and the oils and grease floats to the top where they can get skimmed off. The de-sludged/de-oiled matter goes into secondary treatment, where it is aerated and fed to a ton of algae, bacteria, and a city of microorganisms that eat as much of the organic matter as they can.

Then it’s sent to another settling tank, where any remaining solids are allowed to settle. Since all those teeny-tiny critters were eating all of the stuff we were trying to clean out from the water, now they’re everywhere and don’t want to leave, so it all moves on to the final step: disinfection. This is pretty standard stuff that is usually not too terribly gentle on the environment: chlorine, ultraviolet lights, etc. The sludge waste that was settled out in the earlier steps is often dried on conveyor belts and taken to a special landfill site and dumped. The end. 

(If you want a little more in-depth journey through this process, there’s a video adaptation of the book, Magic School Bus at the Waterworks, available for you to watch here.)


This is a much more simple system, but there’s a few more user steps than just a flush. First of all, you probably shouldn’t use that super-soft, velvety 8-ply toilet paper if you’ll be sending it into a septic system, and every so often you’ll need to have the sludge pumped. This illustration from septicrescue.com shows how the whole system hooks up to a house.

compost septic map

Each time you flush (or use a drain), the wastewater goes out of the house and into the septic tank. A septic tank is a big concrete or plastic container that is buried in the ground near a house with wastewater pipes from the house leading to it. The sludge sinks to the bottom of the tank, and the scum and grease floats to the top. Similar to municipal system, there are bacteria and other microorganisms in the tank that help to break down the waste. As the tank fills, the de-sludged/de-oiled matter gets pushed out the other end of the tank and through a network of buried perforated drain pipe into a drainfield.

compost septic diagram

In the drainfield, the wastewater is further filtered through the rock and sand and over a long, long time and lots and lots of clarifying and filtering through sediment, percolates through the deeper soil and rejoins back up with the groundwater. The end.

The Alternative — Composting Toilets

Now that we’ve gone through the two more conventional ways of handling that messy subject, we can finally talk about composting toilets! I’m pretty jazzed.

The basic process is, well, pretty basic:

poop + heat + oxygen + time = composted soil product

In order to compost, the waste material must have some moisture (but not be saturated) and oxygen. Aerobic bacteria is then able to convert the organic material (waste and bulk) to water and carbon dioxide, creating heat in the process, and leaving behind a plant-friendly, sanitized fertilizing soil substance. Yep, that good bacteria kills all of the viruses and illness-carrying pathogens in the process too.

Enough with all the science talk. Onto the design! Just for you Brandy. 

There’s two basic structures of composting toilet design: the self-contained one piece design and the split system. The split systems seem to mimic a standard toilet design more, but they involve a lot more plumbing and planning. This one is from Sun Mar and seems to have some pretty happy users. 

compost split toilet system

The one piece systems are pretty plug-and-play, but to the more delicate user, may be a constant reminder to you that you are sitting on a box of composting poop. Kinda like a training potty. Sigh, there are tradeoffs to everything, I guess. However, this one even has stainless steel accents, is made in USA, and it’s less than $1,000—not too bad. 

compost single piece toilet

You can even make this dry composting toilet with this tutorial!

compost toilet diy

There are some features of many composting toilets, both the self-contained and split design systems, that seem to be indispensable. One of these is a urine separator, which sounds gross but is really exactly un-gross. The liquid waste is funneled into its own storage tank where the liquid evaporates (or you take it to pour on your inedible plants, giving them tons of extra nitrogen that they LOVE–check out this article for 7 more reasons you should pee in your garden) leaving the solid waste to evaporate and break down without being soggy.

Another common feature that has a luxury by-product is a fan that sucks the air down, providing an even less smelly bathroom experience than a conventional one. Think about it, your um, bathroom fan, is pulling the stinky air directly from the, er, source, so no stinky air even enters your bathroom. Pretty lux. 

The real poop

I’m going to talk some crap here. Most people are totally disgusted by the idea that they will have to empty old, stinky, soggy poop out of their toilet. Yes, that sounds absolutely horrid, I would completely agree. And I would NEVER EVER do that either. Fortunately, as long as you don’t overload it and take care of your composting toilet, this is far from the case. The end product of all of this composting and everything is humus, the organic component of soil. Far from what many people imagine! Doesn’t this look like wonderful topsoil you’d buy at the fancy garden center?

compost compost

Yeah, that’s because that’s exactly what it is! And it doesn’t take long either. For a small amount of composting waste, it takes a few months to break down and cure or “finish” into a soil-looking substance, but for very large quantities (like at a dump site, or a large garbage bin you and your friends have been adding to for a few years) it may take a year or two. It’s like the ultimate recycling! Poop literally recycles itself into a usable product that makes your trees and flowers grow big and strong. They might even look like these ones in the Water Smart Garden at the Denver Botanic Gardens.

Roads Watersmart Garden

The rules, and bending them (not that I’m condoning or suggesting that…)

Here in Boulder CO, the Boulder County Board of Health governs all Onsite Wastewater Treatment Sysems (OWTS), including septic and composting toilets. Their official answer to composting toilets in the 2014 OWTS Regulations is that one “may be used for toilet waste where an OWTS is installed for treating wastewater remaining after removal of toilet waste.” I didn’t really like this answer, so I sent an email out to the Board of Health to ask for some clarification and try to make the case for composting toilets as an alternate to a full-on septic system.

The answer I got was that “If an owner wants to use a composting toilet, they still need to build a septic system (they get a reduction in size because it is just for graywater, not black water) and it will normally consist of a tank and leachfield.”  Well now I just got confused as to the purpose of the whole big septic tank being involved in the system, because, as we talked about a few minutes ago, the point of the tank in a septic system is to hold solids, but—assuming you’re not throwing your spare change and old carrots down your kitchen drain—if there are no solids even entering the system…hmmmm…

Turns out, this whole idea of graywater opened up another can of worms involving water rights, and the Colorado Plumbing Board. In my continuing discussion with Jessica at the Board of Health, she referred me to the Colorado Department of Public Health & Environment and their brand new Regulation 86: Graywater Control Regulation. So, although there’s no big stamp of approval that gives a homeowner the okay to use nice, effective, sustainable composting toilets in place of a giant septic system, there IS the start of a program to institute progressive graywater treatment and at-home graywater reuse at the state level, so that’s pretty darn cool.

While we’re kind of on the subject, there’s actually an article on six ways to convert poop to electricity. I’d even go as far as to say “That’s the s*#@!”


Melissa is on a quest to build a cabin in Boulder County with her very own composting toilet. [/one_half_last]