National Geographic USA - August 2017

Paid by

household

Sewers

68%

Safely

managed

56%

Unsafely

managed

44 %

Latrines

28%

Open

defecation

4%

Input Containment Emptying Transport Treatment End Use

Waste treatment in Delhi, India

Schematic of a sewer

Annualized costs per capita for

waste treatment in Dakar, Senegal

Fecal sludge

management systems

Sewer-based

systems

Paid by others

Paid byutility $0.01

$1.86

Paid

by others

$0.03

Paid by

utility

$52.63

$9.74 $2.00

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The High Price

of Modern Hygiene

Sewers connected to treatment plants are the best way of removing
the hazard of human waste, especially in cities. But theyíre costly to
build and maintain. Collecting sludge from latrines or septic tanks is
an alternativeóif the sludge is properly managed. Often it isnít.

Pipes and sewers

Gravity-fed

conduits funnel

wastewater from

homes and

businesses to a

treatment plant.

Primary treatment

In a holding tank,

solids settle out

of the wastewater.

Oils and grease

DUHVNLPPHGRƂ

the top.

Aeration tanks

The wastewater

ƄRZVLQWRDHUDWHG

tanks, where

bacteria digest the

remaining solids

and nutrients.

Chemical treatment

In some communi-

ties, chemicals

such as chlorine

are added to kill

any remaining

bacteria.

AFTER THE FLUSH
Sewer systems require a
huge investment in infra-
structure to connect all
users. The process varies,
but each toilet in an urban
area must be connected to
large underground mains,
which then feed into large
waste water treatment plants.

A PRIVATE BURDEN
In Dakar, Senegal, sewer
systems were found to be
QHDUO\ƃYHWLPHVPRUHH[SHQ-
sive than collecting and
managing fecal sludge. The
latter method, however, costs
more for households, which
are responsible for their own
latrines or septic tanks.

OVERFLOWING CITIES
Sewers arenít guarantees: In
Delhi only 56 percent of waste
is safely managed, because
sewers leak and nearly a third
of the booming city isnít con-
nected. Many latrines empty
into open drains, and 4 percent
of residentsósome 700,000ó
defecate outdoors.

JASON TREAT, NGM STAFF;KELSEY NOWAKOWSKI
SOURCES: LINDA STRANDE, SWISS FEDERAL INSTITUTE OF AQUATIC
6&,(1&($1'7(&+12/2<ǖ($:$ǗEMILY C. RAND, WORLD BANK;
CENTRE FOR SCIENCE AND ENVIRONMENT, NEW DELHI