How Does a Composting Toilet Work To Break Down Waste?


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Does the very idea of composting human waste seem disgusting to you? If it does, it really shouldn’t. Composting toilets are becoming more and more popular in the environmentally conscious crowd these days.

Today I’ll be taking a few minutes to explain how composting toilet systems work as well as introducing you to some of the reasons that they are gaining favor with people

This first thing that many people think about when the subject of composting toilets comes up is the issue of the diseases that can be spread through human waste. While it’s true that diseases can be spread through contact with human feces, many proponents of composting human waste agree that when done properly, the disease causing bacteria and viruses are destroyed during the composting process.

That being said, you really should check your local building codes before purchasing one because most municipalities in the US have laws in place restricting their use such as forbidding the use of composted human waste on gardens that produce food that will be consumed by humans.

What is a Composting Toilet?

It is an alternative sewage treatment system that is becoming more and more popular. Instead of simply flushing waste into a septic system or into the city sewage system, the waste is decomposed on site and converted into compost that can be used as fertilizer.

Here’s a video from Sun-Mar, one of the leading manufacturers of these types of toilets, that will give you a good introduction to this technology.

How Do Composting Toilets Work?

Before we can understand the process that a compost toilet system uses to break down human waste, we need to take a look at what human waste actually is. You might not realize it but human feces are made up of about 90% water. If you remove the water content, you’re left with only 10% of the volume that you started with. Note that not all of the moisture should be removed or the length of time that is required for the waste to turn into compost is increased.

One of the first things that a compost toilet does is separate the water from the solids. This is usually done through evaporation. Some composting latrines require a source of electricity to produce the heat that is necessary to evaporate the liquid. Others are known as passive composting toilets and they use environmental factors such as the wind and the sun to evaporate it.

In order for an environmentally friendly toilet to work properly to break down the remaining solids, four components need to be in place. These critical components are oxygen, aerobic bacteria, heat, and moisture.

When these four elements are present in the right proportions, the mixture of human waste, toilet paper, and sometimes other organic plant products will decompose and create the finished product of fully composted human waste which is known as humas. Some people affectionately call it humanure.

How Does a Composting Toilet Maintain The Ideal Conditions For Decomposition?

Different manufactures maintain the balance of the four required elements in different ways. Some use manual or mechanical agitators to aerate the decomposing waste thereby maintaining the appropriate oxygen levels. Others have a separate composting bin that can be rotated to keep the compost aerated and oxygenated.

As I mentioned earlier, some use electricity to maintain the ideal temperature to keep the colony of aerobic bacteria working at optimum efficiency. Others use heat from the sun and/or natural ventilation systems that distribute warm air across the decomposing mixture. When the composting process has finished, the remaining waste can be removed and disposed of by using it as fertilizer.

How Long Does It Take To Fully Compost The Waste?

This is a difficult question to answer because there are just so many variables that come into play. Some of the factors that affect how long these eco friendly toilets take to work their “magic” are listed below.

  • The number of people using the toilet.
  • How often the toilet is used.
  • The amount of waste that the particular toilet is designed to handle.
  • Whether or not the unit is electric or non-electric.
  • Whether or not the users do a good job of making sure that the decomposing mixture remains aerated and within acceptable moisture parameters.
  • How long the system is left undisturbed between uses.
  • The design of the particular toilet.

All things considered, it may take on average between 2 to 6 months to fully compost a batch of humanuer, possibly longer.

Do Composting Waste Systems Stink?

Contrary to popular belief, if properly installed and maintained, a compost toilet should not usually have a bad odor. There are factors that could, however, cause them to start smelling bad. These factors are, whether the toilet is being used more often than it was designed to be used, whether the operator isn’t performing the regular chores to keep the unit functioning properly, and whether the toilet is in good repair. Another reason that they don’t typically smell bad is that most well designed units maintain a constant flow of air so that any odors that might be present are vented from the toilet through exhaust outlets and away from living areas.

How Much Work Is Involved In Maintaining Compostable Toilets?

Again, this depends on the particular brand that you happen to purchase. Some require that you manually manipulate the agitator bar to aerate the mixture. Others might require users to rotate the composting drum. It’s also common to add organic material like peat moss to the mixture from time to time to accelerate the decomposition process. When the process of decomposition is complete, the user will have to manually empty the remaining humus.

Are Composting Toilets Good For The Environment?

There are three main advantages that these toilets offer.

  1. Perhaps the biggest advantage is in terms of how much water they DON’T use. The amount of water that toilets use can be quite staggering. Since no water is used to flush these eco friendly toilets, the impact that using them on a large scale could conserve quite a bit of water.
  2. Another advantage is that the by-product of using them is sometimes used to fertilize plants.
  3. Yet another advantage is that they don’t contribute the strain that conventional toilets place on waste water treatment plants so they can save cities money.

Are Composting Toilets Legal To Use?

This really depends on exactly where you happen to live. Some areas are quite environmentally conscious and see the benefits that using these types of toilets can have on our ecosystem while others haven’t exactly seen the light just yet. For example, where I live, in Southern Oregon, composting toilets are permitted but you are still required to have a standard septic system which kind of defeats the purpose of installing one in the first place.

How Long Have These Types Of Toilets Been in Use?

Believe it or not, this method of disposing of human waste has been used for thousands of years and the earliest designs were nothing more than a hole in the ground. It’s only been in the last few decades that commercially available units have started to hit the market and gain favor with homeowners.

What Makes These Toilets Different Than Outhouses?

On the surface it may seem like transitioning to the use of these types of toilets is a step backwards to the days when people had to make the trip to the outhouse when they wanted to relieve themselves. The truth is that composting toilets and outhouses are very different beasts.

In a traditional outhouse, the feces pile up and create a condition where the only bacteria that thrives are of the “anaerobic variety”. This is because there isn’t any oxygen in the mixture for “aerobic bacteria” to flourish.

It’s the presence of aerobic bacteria along with the sophisticated design of modern composting toilets that make them many times more efficient at decomposing human waste. As a matter of fact, outhouses are so inefficient at the decomposition process that when they become too full, a bit of dirt is usually thrown over the hole, a new hole is dug, and the outhouse is moved to cover the the new hole.

Outhouses merely provide a final resting place for human waste while compost toilets decompose the waste.

What Can You Expect In Terms of Composting Toilet Cost?

Prices for these types of toilets can range from $1,000 to $5,000. This may seem like a lot but when you compare this price tag to how much it might cost to install a traditional in-ground septic system, the sticker shock begins to lessen. Another factor that many people don’t consider when they’re looking at the cost of composting toilet systems is the amount of money they will save over the life of the unit by not flushing three or more gallons of water down the drain every time they use it.


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