Isabelle Senteno 1
Installing Composting Toilets in the MODS at The Evergreen State College
Isabelle Senteno
Abstract
This paper explores the possibility of installing a composting toilet in a MOD building at The
Evergreen State College. The Background section discusses the types of composting toilets and
how they function. It explores the process of composting human waste to humanure, and the cost
of the products that do so. The Methods section includes all the calculations done in learning the
amount of water and money a composting toilet would save. It covers personal communications
with people who played a significant role in learning how these systems function and the
possibility of installing them on Evergreen. The Results, Significance/Discussion explore the
findings of this research project and why it is important. It touches on the economic benefits
versus the environmental benefits, and attempts to understand the price of cheap water.
Background
A composting toilet is a closed system where human waste is composted and returned to the
earth. This alternative to a traditional toilet saves water and reduces pollution, chemical use, and
energy used at sewage treatment plants. In traditional toilets, one flush is about 3.5 gallons and in
dual-flush toilets a flush is about 1.6 gallons.1 In America, most of the water used to flush our
waste down the toilet is potable drinking water. Every day thousands of gallons of clean drinking
water are flushed down the toilet.2
Wasting countless gallons of drinking water is a problem, especially in a time of changing
climate and increasing drought. The Evergreen State College is a place with many sustainable
endeavors and projects going on the campus. For two quarters this research project has focused
on the following main question:
If a composing toilet were installed in a MOD building, how would it benefit TESC and the
environment?
The Modular housing buildings (MODS) are student housing on The Evergreen State College
campus. Six students live together in a MOD during the school year, and many MODS are
themed around sustainability. Some MODS have solar panels, others are heated by composting,
and most have gardens in front. Because of all this, the MODs seem like the most ideal place for
a composting toilet to be installed.
Composting toilet systems are self-contained composting systems that decompose human waste
to become what is known as humanure.3 The humanure when finished can be added to gardens
1
Sloan Valve Company
WET Science Center
3
The Humanure Handbook
2
Senteno 2
or landscaping plants just as ‘normal’ compost would. However, in some states, laws prohibit
humanure being added to vegetable gardens or conventional farming. Instead, the humanure can
be added to landscaping plants that people do not eat.
There are many types of composting toilets from homemade ones to commercial ones found in
office buildings and public facilities. The composting process in these toilets is an aerobic
process, meaning one that involves oxygen.
Types of Composting Toilets:
Waterless composting toilets use no water to flush. Instead, after each use a cup of sawdust/ peat
moss is added. The pipes in a dry flush toilet must be perpendicular to the ground and the
composter must be located directly underneath the toilet.4
Low-Flush composting toilets use a small amount of water (amount varies but some models use
3-6 ounces per flush, others use 1 pint) to flush the waste down to a composter. With a low flush
toilet, the composter doesn’t need to be directly below the toilet. The water in combination with
piping allows waste to travel further than a waterless toilet does.5
Foam Flush composting toilets use a combination of biodegradable soap and two tablespoons of
water to create foam that carries the waste through the pipes down to the composter. The pipes
can be up to forty-five degrees off the vertical and waste will still travel through them.6
In the MODs, the cheapest toilet would be a waterless toilet. This would be a great way for
residents to reduce their impact. The other types of composting toilets are very expensive.
Smell is often a large concern for people installing composting toilets. All commercial toilets
have fans built into the composter that suck air continuously down the chute. This prevents the
bathroom area from smelling and provides the composter with circulation. Smell is not an issue.
Cost:
The price for a complete Phoenix composting toilet system that serves four residents is
$6,300.00.7 The price for a Clivus Multrum brand composting toilet system serving fifty uses per
day is $5,995.00.8
These are two of the main brands in the United States and many have installation project with
Zoos, public facilities, schools and residents.
4
Residential Planning Manuel, Clivus Multrum Inc.
Ibid.
6
Ibid.
7
Public Facilities Pricing 2014, Phoenix Composting Toilet System
8
Seasonal and Residential Prices 2014, Clivus Multrum Inc.
5
Senteno 3
During the composting process human pathogens are broken down inside the composter.
However, chemicals such as birth control or caffeine break down at a higher temperature. The
Bullitt Center in Seattle, WA has six floors of composting toilets. When the compost is finished,
it is shipped out to another facility where it is composted again at a higher temperature to break
down things like birth control and other drugs.9
Methods
In researching the possibility of installing a composting toilet system in a MOD, one of the main
aspects was doing calculations to determine how much water and money TESC would save.
A MOD houses six people for nine months out of the year, and they currently have dual flush
toilets that use 1.6 gallons of water per flush.10 The assumption is made that each person flushes
the toilet five times per day on average.
Water used per person per day?
1.6
5
8
gallons
flushes
gallons
per
per
per
flush
person
person
Water used per MOD per day?
8
6
48
gallons
people
gallons
per
per
per
Water used per MOD per
month?
48
30
1440
gallons
days
gallons
Water used per MOD per year?
1440
9
12,960
per
per
day
day
person
MOD
MOD
per
day
per
day
per
per
per
MOD
month
MOD
per
day
per
month
gallons
months
per
per
per
month
gallons
per
MOD
school
year
year
per
MOD
In one MOD building the installation of a composting toilet would save 12,960 gallons of water
over a school year. Because composting toilets are so expensive it is important to calculate how
much money would be saved by not paying for all that water.
9
Bullitt Center, Seattle, WA
Sloan Valve Company
10
Senteno 4
In Seattle, the monthly bill for a family of four using fifty gallons per person per day is $42.15. 11
What is the price per gallon of water?
4
50
200
$42.15
30
$1.4050
$0.0070
People
Gallons
gallons
Cost
Days
Cost
cost
use
per
per
per
per
per
per
Person
House
Month
Month
Days
Gallon
per
per
day
day
per
day
per
day
per
per
day
day
per
day
per
month
The above calculation shows that the cost of water is super cheap.
Cost per 1.6 gal flush?
1.6
$0.0070
$0.0112
gallons
cost
cost
per
per
per
Flush
Gallon
Flush
Cost per person per day?
5
$0.0112
$0.0560
flushes
cost
cost
per
per
per
Person
Flush
person
Cost per MOD per day?
6
$0.0560
$0.3360
people
cost
cost
per
per
per
MOD
Person
MOD
Cost per MOD per month?
$0.3360
30
$10.0800
cost
days
cost
per
per
per
MOD
Month
MOD
Cost per year (9 months) per
MOS?
$10.0800
9
$90.72
cost
months
per
per
per
MOD
MOD
per
school year
per
year
11
Circle of Blue’s Urban Water Pricing Survey
month
Senteno 5
This summer (2015) one of the MODs will be remodeled, and I met with Joe Martino, head of
RAD Sustainability at Evergreen, to discuss the possibility of a composting toilet being installed.
When the above figures were presented to Joe Martino, he said the biggest challenge with a
project like this would be the cost. To further the process, outside grants would need to be
written and approval by CLUC (the Campus Land Use Committee) would be needed.
I also spoke with Brian Barry, a representative from Clivus Multrum, Inc., a company making
commercial composting toilet systems. Years ago Clivus Multrum partnered with Warren Wilson
College to install two composting toilets in their Eco-Dorms.12 When speaking with Brian, I
inquired about the possibility of retrofitting a structure to accommodate a composting toilet
system. The answer was that it is possible but very difficult and typically very costly. A
composting toilet system works best with a building that is designed to accommodate one.
Results
The calculations show that a MOD with a composting toilet would save 12,960 gallons of water
per school year and $90.72 on the cost of water. A composting toilet is difficult to retrofit
buildings for, and many companies partner with institutions to create projects around green
building with composting toilets as part of the design.
Significance and Discussion
My original hypothesis predicted that even though the price of a composting toilet system is
high, it would pay off because of the amount of water it would save. At this point I did not fully
understand the price of water. The price of water as calculated above is $0.007 per gallon.
The composting toilet technology that saves thousands of gallons of water only saves a measly
$90.00 during nine months. From a purely economic standpoint the savings don’t make sense.
To install a composing toilet system one must value the environmental benefits over the
economic input, and be invested in long term pay offs.
Often we forget that the cycle doesn’t stop after our waste is flushed down the toilet. A sewage
treatment plant uses many chemicals to treat the water, and a lot of electricity to run the
machines that do so. A composting toilet eliminates not only water, but energy used to pump the
water to a household, energy used to carry the sewage to the treatment plant, and then the energy
used at the treatment plant to appropriately treat the sewage. A composting toilet eliminates all
these steps and potential complications with chemicals in our watersheds. Our waste is returned
to the soil and the cycle becomes a closed system.
12
Warren Wilson College
Senteno 6
Acknowledgements
I would like to acknowledge E.J. Zita for all the help with the calculations and mentoring; Brian
Barry for sending Clivus Multrum pricing documents and resources; Joe Martino with RAD for
taking the time to meet about this project.
Bibliography
Bullitt Center, Seattle, WA. http://www.bullittcenter.org/ Date Accessed: March 6, 2015
Circle of Blue’s Urban Water Pricing Survey. http://www.circleofblue.org/waternews/wpcontent/uploads/2010/04/allstats.pdf Date Accessed: March 6, 2015.
Jenkins, Joseph. http://humanurehandbook.com/manual.html. Date Accessed: March 6, 2015.
Public Facilities Pricing 2014, Phoenix Composting Toilet System. PDF.
Residential Planning Manuel, Clivus Multrum Inc. PDF.
Seasonal and Residential Prices 2014, Clivus Multrum Inc. PDF.
Sloan Valve Company. http://www.sloanvalve.com/Our_Products.aspx. Date Accessed: March
6, 2015.
Warren Wilson College. http://inside.warrenwilson.edu/~ELC/New_ELC_Website_/compostingtoilet.php Date Accessed: March 6,
2015
WET Science Center, Olympia, Washington. http://www.lottcleanwater.org/education.htm Date
Accessed: March 6, 2015