8/10/2019 Science-2012-673-Vogel - Finding a New Way to Go

1/1www.sciencemag.org SCIENCE VOL 337 10 AUGUST 2012

SPECIALSECTION

CREDIT:EAWAG-AQUATICRESEARCH,SWITZERLAND

SPECIALSECTION

At first glance, its hard to see what the labs

of stem cell researcher Michael Kallos and

petroleum engineer Ian Gates could have in

common. Excrement, however, has brought

them together. For the past year, the Uni-

versity of Calgary scientists have been col-

laborating on inventing a new kind of toilet.

Using their common expertise in designing

bioreactors, they are devising a toilet that

can convert feces and urine into fertilizer,

clean water, and a source of gas for heating

or electricity.

The world needs new toilets. The flush toi-

let has provided great service and hygiene

for 100 years or so, says Arno Rosemarin,a sustainable sanitation expert at the Stock-

holm Environment Institute in Sweden. But

it is undeniably wasteful. It uses drinkable

water to carry away urine and feces, creat-

ing wastewater that has to be cleaned with

expensive and energy-intensive technol-

ogy (see p. 674). Flush toilets make even

less sense in dry regions, and building sew-

age systems can be prohibitively expensive

in the developing world. Even in wealthy

regions, some existing systems dont treat

waste adequately, discharging pollutants

into downstream ecosystems.Sanitation engineering, however, hasnt

been one of the most innovative sectors,

says M. Sohail Khan, professor of sustain-

able infrastructure at Loughborough Uni-

versity in the United Kingdom. That may be

changing. Prompted by stricter clean water

regulations and recognition that sanitation

is key to improving public health, research

into new ways of collecting and processing

human waste is starting to catch on. Since

2010, for example, the Bill & Melinda Gates

Foundation has awarded more than 50 grants

on next-generation sanitation, including

its Reinvent the Toilet Challenge, whichaims to develop an attractive, eco- and user-

friendly toilet that can process excrement for

less than 5 cents per user per day.

One of the simplest alternatives to the

flush and forget approach is the compost-

ing toilet, in which aerobic bacteria decom-

pose waste. Given the right conditions, the

composting process generates enough heat

to kill dangerous pathogens, and with proper

design, the toilets neither attract insects

nor emit odors. Advocates have been tout-

ing compostings advantages for decades

one classic text is The Humanure Hand-

book, first published in 1995. Despite its

advocates, however, the composting toilet

hasnt caught on in private households out-

side a few ecovillages in Germany and in

Swedish summer houses. That is partly due

to psychological barriers (see p. 679), and

partly because, at least in urban areas, some-

one needs to transport the fin-

ished compost away. (One

solution to that problem is the

Arborloo, in which the com-

posting takes place in a pit dug

under the toilet. When the pit is full, usersmove the toilet and plant a tree on the site.)

One promising concept for a Toilet

2.0 is a design that keeps urine and feces

separate. The bowl has two openings, one

toward the front for urine and one toward

the back for feces. Separation has several

advantages, says Tove Larsen of the aquatic

research institute Eawag in Dbendorf,

Switzerland. Urine contains fewer patho-

gens than feces and so needs less intensive

treatment to disinfect it. Urine also contain

most of the nitrogen and much of the phos

phorus that could be used as fertilizers. I

you have the nutrients in a concentrate

solution, they are much easier to recover,

Larsen says. Finally, dry feces, not mixe

with urine or large quantities of water, em

fewer odors, take up less space, and are eas

ier to process either chemically or biologi

cally. Drying feces is also an effective disin

fection technique.

Larsen says separation toilets have prom

ise for the developing world but sees poten

tial in industrialized countries as well. Phos

phorus is one of the main pollutants targete

for removal by expensiv

water treatments. At the sam

time, it is a key component o

fertilizer, and easily exploit

able deposits are gettin

scarcer. But the element is relatively easy trecover from separated urine (compared t

mixed sewage), Larsen notes. We are per

haps a bit ahead of our time, she says. Bu

at some point you wont be able to afford t

put your urine in the nearest lake.

With her toilet challenge grant, Larsen i

working with Harald Grndl of the Austria

design firm EOOS to design a urine-divertin

toilet that would recover clean water. In con

trast, Kallos and Gatess toilet uses bacteria t

digest mixed urine and feces anaerobically. I

in a way is an extension of your gut, Kallo

says. The digester will be a bit hotter, thoughhot enough to sterilize the contents. Product

include water, fertilizer, and methane that ca

be used for heating, cooking, or to produc

electricity. Sohails project uses hydrotherma

carbonization, heating the waste under pres

sure to turn it into a coal slurry. They recove

water from the mix and burn the coal to powe

the system.

The energy potential of feces is one rea

son the Gates Foundation launched the toile

challenge, says Doulaye Kone, a senior pro

gram officer at the philanthropy. There

enough energy left [in digested food] t

heat something, to drive something, hsays. If you could harness that, you could

invent a standalone toilet that could bypas

the sewer.

On 14 August, the first eight challeng

research teams will gather in Seattle, Wash

ington, to demonstrate their prototype toi

lets. The foundation will then choose one o

two designs to develop further. So far, Kon

says, the portfolio is very, very encourag

ing. Stay tuned for Toilet 2.0.

GRETCHEN VOGE

The flush toilet was a transformative invention, but experts say its time may be past and

are pioneering ways to recover energy and nutrients from human waste

Going green.A toilet that separates urine and feces

makes it easier to recover nutrients and clean water.

Video featuring the latest

in toilet technologies.

http://scim.ag/techtoilet

Published by AAAS