5

Health Aspects of Excreta and Night Soil

Systems
bowls may block up. Fouled and unhygienic pit
latrines are found all over the wbrld, often because they
have been constructed in communities previously
accustomed to defecation on the open ground who
have also had inadequate community involvement or
health education. Fouled pit latrines become a focus of
disease transmission and may make health matters
worse than before the sanitation intervention.

the health implications of the principal varieties of excreta collection

and treatment systems are discussed. These are
separated into night soil (or "dry") and sewage (or
"wet") systems. (The health implications of reuse and
effluent-discharge practices are considered in chapter
7.) Little attention is paid here to the technical details
of the systems examined, except to those bearing on
specific health problems. The reader wishing more
information on technical aspects should consult the
second volume of this series (Kalbermatten and others
1982), the related document published by the
International
Development
Research
Centre
(Rybczynski, Polprasert, and McGarry 1978), and
standard sanitary engineering texts. In this chapter,
three excreta collection systems-the pit latrine and its
various modifications, the composting latrine, and
cartage systems-are described, and the discussion
concludes with an examination of the health
implications of dry treatment of night soil by trenching
and composting. Excreta collection and treatment by
wet systems are examined in chapter 6.
IN THIS AND THE NEXT CHAPTER,

Odor
Pit latrines with squatting slabs often are malodorous. If they are, they may not be used and thus
cannot yield any potential benefits in improved
health. Odors can virtually be eliminated by fitting a
vent pipe to the pit. This pipe should be at least 100
millimeters in diameter, painted black, and fitted on the
sunny side of the latrine so that it can heat up, the heat
creating an updraught. [See note on page 82.]
Insect breeding
Pit latrines with squatting slabs will usually become
breeding sites for flies. Flies that visit a pit latrine to
breed or feed may carry pathogens when they leave and
thus promote disease transmission. If the pits are wet,
they may also become Culex pipiens breeding sites. Well
constructed pits with pour-flush bowls will not allow
such insect breeding. If squatting slabs are used, a
vertical vent pipe 100-200 millimeters in diameter,
covered by a fly screen, and combined with a dark
interior to the superstructure-will greatly reduce
both the amount of fly breeding and the escape of any
flies that do breed. Flies breeding in the pit will be
attracted by the light coming down the vent pipe and

Pit Latrines
Pit latrines are the simplest of all on-site disposal
systems. Excreta fall into a hole in the ground, and a
new pit is dug when the hole is about two-thirds full
(see figure 5-1). A ventilated improved pit (vip) latrine,
and a modified pit latrine called a ROEC (Reed
Odorless Earth Closet), are shown in figures 5-2 and 5
3, respectively. Pits are covered by sqatting slabs, seats,
or pour-flush bowls.
Cleanliness

will attempt to escape by this route, only to be

prevented by the fly screen. The effect of vent pipes on
mosquito breeding in wet pits remains uncertain and
the latest findings are reviewed in chapter 36.

In all latrines cleanliness is of the utmost importance.

Squatting slabs easily become fouled and pour-flush

67

68

HEALTH HAZARDS OF EXCRETA

Open for
ventilation

-Removable

Vent hole

Base

Ground level _

.,.
\;u

Ground
lee

t+-B. wConcreiu
/W/

(Jr
soil cement

Soil
from pit
dug
Soil dug from pit

.,
<w.
vv
Squatting
plate

...

,,Groiunddwater

Pollution of this kind is a genuine hazard in areas

where pit latrines are widely used and where the

groundwater
is high and is used as a water source. The

Composting Toilets

Side view

~c

-=S=
-

500

, ................
pollution

subject is discussed in detail in chapter 7.'

Pit

si

survival is of no concern because all pathogenic

organisms will be dead. In some areas, however, two
alternating pit sites are used, a pit is dug out a year or
two after closing, and the contents are used as fertilizer.
This system resembles the double-vault composting
toilet (see below) except that it operates on a longer
cycle. If the pit has been left for a minimum of one year.
there will be no viable pathogens (except, possibly, a
few Ascaris eggs). The chances of viable Ascaris eggs
being present are greater if the pit is wet and partly
below the water table. The risk involved in reusing
material that has been buried for at least 12 months is
small, however, and the pit contents may immediately
be used on the fields with confidence. [See note on page
82.7

Developed countries have shown a growing interest

in composting toilets because these sewerless facilities
_circumvent financial and ecological problems attendant on the waterborne disposal of human wastes.2
Financial considerations and the lack of municipal
effort required to maintain composting toilets make
their use attractive in some developing countries, for
o(JO which agricultural reuse of the composted product is
5------ an additional benefit. The precautions necessitated by

x'-f2~

the problem of pathogen survival in this product,

however, must be noted.3
Technical description

Alternative base using hewn logs

Figure 5-1. Convenitionial unimproued pit latrine
(dimensions in millimeters). In termite-infested areas,
use treated wood or termite barrier. From
Kalbermatten and others (1982); adapted from Wagner
and Lanoix (1958)

Pathogen suruical in the pit

Most pit latrines are filled in when two-thirds to

three-quarters full and are either never dug up again or
only dug up after many years. In either case pathogen

There are two basic kinds of composting toilets,

continuous and batch. Both require the addition of a
carbon source, such as garbage, vegetable leaves, or
sawdust. The continuous composting toilets are based
on the Swedish "multrum" toilets, and an example of
such a design is shown in figure 5-4. They have been
under trial in Tanzania and Botswana since 1977 but
have had no wide application in developing countries.
I. See the subsection "Effluent Discharge. To groundwater."
2. See chapter 1, "Characteristics of Sullage."
3. See chapter 3."Limitations in Assessing Health Benefits" and
table 3-2; see also chapter 4, "Objectives of Night Soil and Sewage

Treatments. Excreta and night soil treatment."

Fly screen

69
Flycree

50 x 100-mm wood lintel

Wood. asbestos, tile, sheet metal,

or corrugated metal roof

Open space
_uorventilatio7n
_ Brick,
adobe,
or concrete blck
OCnCCebcklocally

100- to 200-mm
diameter
vent pipe

Optional L-shaped
wall for privacy

<

_
_Optional door
or curtain of

available
. __
materials

Doorway

_ Squatting iL
5t

~~~~~plate
'

k_ 6-mm diarneter
t

_L

reintorcing

b ars or Airc mesh

/z

i\_.:
t

Lean concrete backfill

_7

_i

Front view
L-shaped wall and vent pipe not shown)

Side view (section)

~~~~~I

,j

C1

~ ~~I

-.-

I
I

I -o

~
~~I
~~I

Isometric view

,j
-

Figure 5-2. Ventilated imnproved pit (vip) latrine (dimensions in millimeters). In the side view, a pedestal seat or
bench may be substituted for the squatting plate. An opening for desludging may be provided next to the vent pipe.
Dimensions of the bricks or concrete blocks may vary according to local practice. Wooden beams, flooring, and
siding may be substituted for concrete block walls and substructure. From Kalbermatten and others (1982)

70

HEALTH HAZARDS OF EXCRETA

aI

lCD
CD

L.

Plan (with latrine superstructure removed)

Flv screen
(noncorrosie)

Wood. asbestos.
tilc. sheet metal,
or corrugated
metal roof

>

100- t 2
diame
vent pipe

Joint detail i

11)11_ concrete.
_ /'-mm,4.

Removablc
cover
sections

JOG-mm bl<
ock. .^
or-,
i
0

subStit
d fr
_

stor
E

sectons
n
Sover

manhole
C
ston
with
locascaled
m~~rlortar
or tar.,_

a-a
,

St
a

;[ <2.000to
_
31100 mm
a

_-_
a
a

___L

'~~~~~~~~~~~~~~~~~.00)
\mm

q
F
I()()~~~~~~~10-mm
concrete.,l
~~~~~lvq
7, s 2(00-mm block, or axt!6

-111"

200-mm brick liner

Section a-a

Section b-b
(vent pipe not shown)

Figure 5-3. Reed0Odorltess Earth Closet (ROEC) (dimensions in millimeters). Pedestal seat with curved chute may be
substituted forsquattingplate. Constructionmaterials and dimensions forthesuperstructuremayvary according to
local practice. From Kalbermatten and others (1982)

71

HEALTH ASPECTS OF EXCRETA AND NIGHT SOIL SYSTEMS

Fly-proof
mesh
150-mm-diameter
vent pip

Long-handled

cover to
squatting plate

_Ii
Squattingl
Removable

<t

I E

~~~~~cover

r;

M. Air

r= .......-...
__.*

n- or A-shaped channels-

Ground level

Air
z^^>

~~~~~~~~~Air_

o
Decomposing
waste

Figure 5-4.

'tlulo

ii"

L L H~~~~~~~~~vuaulitS
)

's

c<.) *.C Gravel soakaway

continuous-composting toilet. From Kalbermatten and others (1982); adapted from a

drawing by U. Winblad

Only limited and inadequate microbiological data

exist on continuous composters (Gurak 1978; reviewed by Feachem, Mara and Iwugo 1980). The batch
composter is common in China and Vietnam, and the
most usual design is the double vault (see figure 5-5).
Again, no appreciable microbiological data on these
toilets have been located, although such data may exist
in China and Vietnam.

Pathogen
survival in product
In both kinds of composting toilet, the composted
product is used as an agricultural fertilizer and soil
conditioner. It is important, therefore, that pathogen
destruction should be as complete as possible. The two

main factors affecting the survival of excreted

pathogens are time and temperature. Temperature in
the composting pit or vault depends on the air supply,
the C:N ratio, and the moisture content. If the
digestion is anaerobic, the temperature may remain
ambient or it may rise at most to around 35C. If it is
aerobic, the temperature will rise to the 50-70C range
if the C:N ratio and moisture content are correctly
regulated. These conditions may be difficult to achieve,
especially in arid developing countries where little
organic material (needed as a source of carbon) is
available for adding to the wastes.
It is certain that double-vault composters will be
anaerobic, and it is probable that multrums will be
also. Anaerobicity and ambient temperature certainly

72

HEALTH HAZARDS OF EXCRETA

,_
r.

75-mm
unplasticized
vent pipe
Air space

.__.

Removable
superstructure
formed from
timber frame

640

1,000

690

.,

and galvanized

- -- - -jr--1-

Icr

r---1 r--~~

---

.i
L-

ON

Concrete

Concrete

,,,,~~~

~~~~~closure
cover
~~"'~~'~~'

l 1l

tl |

50,
F.-

milled steel
-1

Concreteet
acs oe

access cover

lvault

-Fiberglass

I
ntosecond

oe

I__jfiio

___
450

~~~~~~Concret

Section

Plan
Model used in Botswana

50

25

3-mm ferrocement

50

450

1,050

Section

Plan
Model used in Tanzania

Figure 5-5.

Double-ivault comlposting (DVC) toilet (dimensions in millimeters). From Kalbermatten and others

(1982); top, adapted from a drawing by R. A. Boydell

73

1,420
Ash

340

~540

100

10034

storage
area
0;

Urn
outlet

Superstructure
corner posts
Plain
Bamboo wall cladding

130

~ ~
Urine

removal
port

b ,

...

1,,xv,,
250

150

,,,^sv,+
720

1140
100

, .................
1401

100

1.200
Section a-a
1,620

500

500

100
I141

<

11401-

500 O
Section b-b
Figure 5-5

(continiued)

Model used in Vietnam

100
-1

HEALTH HAZARDS OF EXCRETA

74

EXCRETA
Viruses

Bacteria

Protozoa

---

--

Composting toilet
wifh 3-month minimum
retention time.

COMPOST
Helminths

0 Helminths

Figure 5-6. Pathogenflow through a batch composting toilet (double-vault)

are the correct, conservative assumptions to make
where pathogen removal is the concern. Pathogen
removal then depends on the retention time in the unit.
There appears to be a wide variation in retention time
used in both the multrum (continuous) and doublevault (batch) systems, and the pathogen removal
efficiency of any given design can be estimated by
consulting table 5-1. It is clear from the table that a
minimum retention time of 3 months will yield a
product free of all pathogens except the more persistent
helminth eggs, as visualized in figure 5-6. Three
possible pathogen control strategies can be adopted for
compost:
* To use the compost as produced and accept the
level of risk involved. This risk could be reduced to
sufficiently low levels by using the compost only to
prepare ground prior to planting or by not
applying compost within 2 months of harvesting.

To apply the compost only to industrial or fodder

crops.

To provide further treatment for the compost

through heating it (probably impracticable) or

through mixing it with an ovicide (also often
impracticable).

above a bucket which is filled within a few days by the

excreta of an average family (see figure 5-7). The bucket
is positioned adjacent to an outside wall and is
accessible from the street or back lane. A night soil
collector ("scavenger" or "sweeper") will call
regularly-preferably every day, but more typically
once or twice a week-to empty the bucket.

Table 5-1. Probable pathogen content in final

product of anaerobic composting toilets operating at
ambient temperatures in warm climates

Cartage Systems
Cartage systems include a variety of technologies by
which night soil is periodically removed from
containers in or near the house. One of the oldestand, generally, least hygienic-systems is the bucket
latrine. A squatting slab or seat is placed immediately

6 8 10

00 0

0
0
0

0 0 0
0 0
0 0 0

00

0 0 0

++
+

++
0

++
0

+ + +
0 0 0

Viruses

Enterovirusesa
Bacteria
Fecal coliforms
Leptospira spp.
Shigella spp.
Vibrio cholerae
Protozoa
Balantidium coli

The first of these strategies is probably the most

realistic, and the quality of the product will become
better as the retention time is increased beyond 3
months.
months.

Retention time
(months)

Pathogen

Entamoeta
Giardia lamblia

~~~~~~~~~~~~~Helminth
eggs
Ascaris
lumbricoides
Hookwormsb

++
+

Schistosoma spp.
Taenia spp.

++

++

++

++

Trichuris trichiura

++

++

concontration,
a. Includes polio-, echo-, and coxsackieviruses.
b. Ancylostoma duodenale and Necator americanus.

+ + +

75

HEALTH ASPECTS OF EXCRETA AND NIGHT SOIL SYSTEMS

Squatting plate

Fly-proof door

Paved surface and drain

Ground surface

_.

:.00

~~25
mm, _ -vzt
maximuma.- _f-,,- ;eM

Soakage pit for bucket washwater

'.v:

Night-soil collection
by dipper and bucket
(here a vault rather
than a bucket is located
in house)

Bucket latrine

Night-soil bucket and scraper

Cartage wheelbarrow for three or six buckets

Figure 5-7. Bucket latrine and cartage. Fly-proof doors and paved surfaces and drains are commonly missing in
most existing bucket latrines. From Kalbermatten and others (1982); top left, adapted from Wagner and Lanoix
(1958); top right, from a photograph courtesy of Michael G. McGarry; bottom, Department of Social Welfare,
Ahmedabad, India
Many households in East Asia, and elsewhere, store
their excreta (plus the small amounts of water used for
pour flushing and anal cleansing) in sealed vaults
under or beside the house (see figure 5-8) that are
emptied by a vacuum truck about once every 2 weeks.
This system has relatively high operating costs but may
have relatively low initial costs. It is suitable for highdensity urban areas where access by truck is possible
and truck maintenance facilities exist. The health
dimensions of a cartage system depend on the manner

in which the night soil is deposited, collected,

transported, treated, and reused. Each of these will be
considered in turn.
Night soil deposition
The two normal methods of deposit are into the
bucket or vault. Both these depositories can be
satisfactory if they are hygienically maintained. The
bucket, a smaller vessel than the vault, is more likely to

76

HEALTH HAZARDS OF EXCRETA

Val5-mm vent pipe

Toilet-_

~Manhole

to tVacuum tanker

House

OffseVault
v

Vault below squatting plate

Vent

Hose to tanker
1

House

Offset vault

Figure 5-8. Alternative designsjor rault toilets. From Kalbermatten and others (1982)

overflow and to contaminate its surroundings. The

bucket latrine is also almost certain to be malodorous,
and this will discourage use. In contrast, the vault can
be ventilated, making a hygienic and pleasant latrine.
The possibility of fly breeding depends on the
frequency with which the depositories are emptied.
Houseflies and blowflies require a minimum of 1 week

to develop from egg to adult, and so a bucket emptied

every 5 days will not permit fly breeding, provided it is
well cleaned each time it is emptied. Vaults, however,
are emptied less frequently, and fly breeding is a
danger. Breeding can be reduced by installing a pourflush water seal to prevent access of adult flies or by
installing a vent pipe with a fly screen similar to the one

HEALTH ASPECTS OF EXCRETA AND NIGHT SOIL SYSTEMS

recommended above for pit latrines. A pour-flush

water seal is probably the only reliable method of
preventing fly breeding in vault latrines.
Night soil collection
Collection of night soil from vaults by vacuum
trucks can be hygienic and risk free-provided that the
outlet pipe from the vault is in good repair and that all
fittings on the truck and suction hose are well
maintained. A little spillage is probably inevitable, but
it can be reduced to an acceptable minimum by good
equipment and well-trained operating personnel.
By contrast, collection from bucket latrines is always
messy. The worst method is to empty the buckets and
immediately return them, which causes the latrine area
to become progressively more fouled (with consequent
risk of infection to the household, the sweeper, and
passersby). Emptying the bucket, rinsing it out, and
returning it is also undesirable and will probably result
in the washwaters being deposited in the street. The
best arrangement is to replace the bucket by another
cleaned and disinfected one, with dirty buckets being
returned to a central depot for cleaning and
disinfection. Operation of this system is facilitated by
use of a color code in which all buckets collected on
Monday, for example, are red and the replacement
buckets green. Such a bucket-replacement system is
often not feasible on a large scale because of the
difficulty of transporting large numbers of buckets. It
can, however, work well in army camps, prisons,
disaster relief camps, and other institutions of limited
size.
It is clear that the risks from a cartage system depend
greatly on the quality and regularity of the service
provided. The system is sensitive to a few days'
interruption in collections, whether from mechanical
breakdown or absence of the sweeper. 4

The differences in health risks between the

alternative bucket and vault-and-truck systems become obvious at the transport stage. The worst system
is the one in which buckets are emptied by hand into
open carts or into larger buckets, which are then
carried by hand or on yokes. Under these arrangements there will always be spillage. People who come
into contact with this fresh night soil risk infection from
any of the nonlatent pathogens (categories I and it in
4. See chapter 8. the sections "Influence of Social Structure and
Organization" and "Social and Organizational Aspects of Excreta
Cartage Systems."

77

table 2-2). This risk is not simply to the sweepers

themselves, but also to anyone who lives on or walks,
plays, or works in the streets or back lanes where the
night soil has been spilled. The risk to children is
obviously great because they commonly play in back
lanes and alleys. The latent pathogens that develop on
soil (category ti-hookworms, Ascaris, and Trichuris)
may well develop into their infective stages where they
have been spilled in fresh night soil, and there is
evidence that the cartage of night soil is partly
responsible for the high levels of Ascaris egg
contamination found in the soil of some cities. Vacuum
trucks, by contrast, can transport night soil through the
streets with minimal risk of spillage.

Night soil treatment is also discussed in conjunction

with wet systems in the next chapter. Night soil can be
digested and dewatered (as is sludge), it can be mixed
with sewage and treated in conventional plants, or it
can be sluiced into waste stabilization ponds (see
chapter 6 for descriptions of these treatments). Night
soil can also be treated by dry systems, such as
trenching or, preferably, composting. Following
adequate treatment, night soil can be used in
agriculture, aquaculture or gas production (see chapter
7).
Where trenching is used, the health implications can
be serious. A badly managed and inadequately
controlled trenching ground will be a major health
hazard to all who work on it or to those-children, for
example-who may gain access. The families and
close contacts of these people are also at risk. The
proper management of a trenching ground is largely
common sense: trenches should be at least 0.6 meters
deep and should be filled with night soil to a depth of
not more than 0.3 meters; they should then be rapidly
covered with tamped earth, to make a small mound of
earth over the trench, after which they are left for at
least 2 years. Yet, however well managed the surface of
a trenching ground is, the risk of groundwater
pollution may always be present. This risk is minimized
by careful location of the trenching ground following a
hydrogeological survey. Given these limitations, in
many situations the most appropriate and attractive
method of night soil treatment is by mixing it with
refuse and composting (see below).
Night soil reuse
Reuse is described in detail in chapter 7. The reuse of
untreated night soil in agriculture is a widespread

78

HEALTH HAZARDS OF EXCRETA

practice, but one that is to be strongly condemned for

its health hazards. There is much evidence that the use
of untreated night soil on crops contributes to the
transmission of infection to those working in the fields
and. to a lesser (but still significant) degree, to those
handling or consuming the crops. Treatment or
storage of night soil should therefore always be
provided prior to its reuse.

Composting
Again it must be stressed that temperature and time
are the two most important factors in the achievement
of low pathogen survival in waste treatment processes.
In the treatment of night soil or sludge for reuse, an
almost pathogen-free product is required. This is only
achieved by processcs incorporating long retention
times (such as ponds or protracted digestion and
drying; see the next chapter), heat (such as thermophilic digestion; see the next chapter), or thermophilic
composting (discussed here). The attraction of
thermophilic composting is that it can yield a safe
product for reuse in a relatively short time (<2
months) and that it does not require an external source
of energy for heat. In addition, composting technologies are available that are relatively low cost and
labor intensive. The compost produced is a useful soil
conditioner and source of plant nutrients that may
increasingly be in demand among poor farmers as the
cost of industrially produced fertilizers rises (Food and
Agriculture Organization 1975).
Composting has been thoroughly reviewed by
Gotaas (1956), and more recent accounts are provided
by Haug (1979); Polprasert, Wangsuphachart, and
Muttamara (1980); and Shuval, Gunnerson, and Julius
(1981). A wide range of fecal composting technologies
are available. They all incorporate the mixing of night
soil or sludge with a carbon source (such as refuse or
sawdust) to achieve a C:N ratio of approximately
20-30. Moisture content (20-60 percent) must also be
regulated for optimal performance, with wetting or
turning (for drying) at appropriate intervals.
The most important feature of composting, from the
health viewpoint, is the temperature achieved-and
this depends on the oxygen content of the pile, C:N
ratio, moisture content, particle size, and pH. If the
process is anaerobic, temperatures will remain at (or
only a little above) ambient temperature, and
mesophilic microorganisms will predominate. Foulsmelling gases are usually produced, and the process of
degradation proceeds slowly. If the process is aerobic,
substantial heat is generated by the proliferation of

thermophilic microorganisms, and degradation is

more rapid and usually free of odor.
A newly erected compost pile will contain entrapped
oxygen and, if the other factors mentioned above are
correctly regulated, thermophilic aerobic processes
will be established and the temperature at the center of
the pile will rapidly rise to 55C or above. As the
available oxygen is used up, however, the process will
become progressively more anaerobic and temperatures will fall. There are three methods commonly used
to sustain the supply of oxygen and therefore maintain
thermophilic temperatures: the pile is regularly turned,
or ventilation tubes are arranged in the pile, or forced
aeration is provided by blowers or suckers. In the last
two cases, the pile is usually lagged to prevent heat loss.
Temperatures can rise to 80C in these well-managed,
thermophilic, aerated composting systems, and it is
possible to ensure that all parts of the pile spend several
hours at temperatures above 60C-of the utmost
importance in curtailing pathogen survival.

Pathogen survival
Pathogen survival in compost systems depends
upon the time-temperature characteristics of various
parts of the pile. The death curves derived for some
pathogens, discussed further in Part Two, are plotted
in figure 5-9. Time-temperature points above the curve
for each pathogen represent certain, total destruction.
It is clear that enteroviruses and Ascaris eggs are the
most hardy, but the time-temperature combinations
given in the note to figure 5-9 will ensure their
destruction. If all parts of a compost pile can be
brought to a time-temperature state within the "safety
zone" in figure 5-9, complete pathogen destruction
should be guaranteed (see figure 5-10). There are two
possible exceptions. First, spore-forming bacteriasuch as Clostridium perfringens, discussed in chapter
4-are more resistant but present little risk. Second,
hepatitis A virus appears to resist rapid heating, and its
ability to survive temperatures around 60'C for several
hours is unknown.
Much of the literature on pathogen survival in
compost, which has previously been reviewed by others
(for intance, Kawata, Cramer, and Burge 1977; Krige
1964; Nell and Wiechers 1978; Reeves 1959; Shuval,
Gunnerson and Julius 1981; Wiley 1962; Wiley and
Westerberg 1969; WHO Intemational Reference
Centre for Wastes Disposal 1978) is reported in Part
Two. This literature indicates that a well-designed
system under good management produces a pathogenfree, or almost pathogen-free, compost if all sections of
the pile reach the required temperature for the required

HEALTH ASPECTS OF EXCRETA AND NIGHT SOIL SYSTEMS

79

70

70
Enteric
viruses

65

65

Shigella

60

\/

SAFETY ZONE

so-

60

50

'N

Vibrio cholerae

45

G.

45
45'

N.

40 -N

35

30

25

20
0.1

Ascaris -40
Salmonella

'N

N\>

&

35

;_30

,Emn-aoba
',histolytica

I
1

10

I
I day

100
I week

1,

1 '
00
I month

25

1 20
I'
I year

Time (hours)

Figure 5-9. Influence of time and temperature on selected pathogens in night soil and sludge. The lines represent
conservative upper boundaries for pathogen death-that is, estimates of the time-temperature combinations
required for pathogen inactivation. A treatment process with time-temperature effects falling within the "safety
zone" should be lethal to all excreted pathogens (with the possible exception of hepatitis A virus at short retention
times). Indicated time temperature requirements are at least: I hour at >62C, I day at >50'C, and I week at
>, 46C. For more detail on the time-temperature combinations lethal to these and other pathogens, see the graphs

in chapters 9, 15-17, 20, 22, 23, 32, and 34 of Part Two (from which this composite was made)

80

HEALTH HAZARDS OF EXCRETA

EXCRETA
Viruses

Bacteria

---

--

3m

Protozwoa

Wel/-managed (olparts of the pilet

required time-temperature)
thermophiiic compostinIg.
COMPOST

Helminths

>

Figure 5-10. Pathogenflow throuigh a well-managed thermophilic compostinlg process

time. The organism most likely to survive this

treatment is Ascaris, and Ascaris eggs may therefore be
used as the indicator of successful composting.
Fly breeding

One of the major problems in managing composting

operations is fly control. All raw materials used for
composttflies
and are good media for fly
brmpee ting.Flies cattract
eggs in the material attheplace
breeding. Flies can lay eggs in the material at the place
of collection or during the handling of the material at
the compost site. Different species predominate under
different conditions, but good control measures should
affect them all. Fly larvae cannot survive temperatures
above 50'C, and so, as for other pathogens, the
achievement of high temperatures in all parts of the pile
is the essential requirement for control. Fly larvae may
however, migrate along temperature gradients to seek
the cooler parts of the pile (such as the edges or the

areas near ventilation shalts). These larvae may be

destroyed by effective and well-controlled turning orby
lagging unturned piles. The use of insecticides in
compost piles is not desirable unless it has been
demonstrated that these chemicals will not affect the
composting process or the acceptability of the product
to farmers.
Fly breeding may pose a general problem in all
composting systems. The level of fly breeding provides
some gauge ofhow successfully the pile is managed and
whether it is being thoroughly heated, with minimum
fly breeding an explicit goal for the management of all
compstig
It splnts
pssibe t montorthe eve of
composthng plants. It ISpossible to monitor the level of

useful to the staffin charge. Fly breeding will, of course,

fluctuate markedly with the seasons, irrespective of the
condition of the compost pile.
Literature Cited
Feachem, R. G. A., Mara, D. D. and Iwugo, K. 0. (1980).
Alternative Sanitation Technologies for Urban Areas in

Africa. Appropriate Technology for Water Supply and

Sanitation, vol. 7. Washington, D.C.: The World Bank,
Transportation,
Water and Telecommunications
Department.
Food and Agriculture Organization (1975). Organic
materials as fertilizers. Soils Bulletin, 27.
Gotaas H. B. (1956). Composting. Sanitary disposal and
reclaniation of organic wastes. Monograph Series no. 31.
Geneva: World Health Organization.

Gurak, R. S. (1978). Final Report on the Alternative Waste

Disposal Methods Project in Tanzania, East Africa:
Chemical, Microbiological and Parasitological Results.

Ottawa: International Development Research Centre.

Haug, R. T. (1979). Engineering principles of sludge
composting. Journal of the Water Pollution Conjtrol
Federation, 51, 2189-2206.
Kalbermatten, J. M., Julius, D. S., Gunnerson, C. G. and
Mara. D. D. (1982). Appropriate Sanitation Alternatives:
Plannling and Design Manual. World Bank Studies in
Water Supply and Sanitation 2. Baltimore. Md.: Johns
Hopkins University Press.
Kawata, K.. Cramer, W. N. and Burge. W. D. (1977).
Composting destroys pathogens in sewage solids. Water
and Sewage Works, 124, 76-79.
Krige. P. R. (1964). A survey of the pathogenic organisms and
helminthic ova in composts and sewage sludge. Journal

fly breeding by positioning flytraps at appropriate sites

and Proceedingsof the Institute of Sewage Purification,part

around the plant and recording the daily gatch. This

provides a continuous and immediate check of
management and temperature control that is most

3, 215-220.
Nell, J. H. and Wiechers, S. G. (1978). High temperature
composting. Water South Africa, 4, 203-212.

HEALTH ASPECTS OF EXCRETA AND NIGHT SOIL SYSTEMS

Polprasert, C., Wangsuphachart, S. and Muttamara, S.

(1980). Composting night soil and water hyacinth in the
tropics. Compost Science/Land Utilization, 21, 25-27.
Reeves, J. B. (1959). Sanitary aspects of composted sewage,
sludge and sawdust. Sewage and Industrial Wastes, 31,
557-564.
Rybczynski, W., Polprasert, C. and McGarry, M. G. (1978).
Lowv-Cost Technology Options fbr Sanitation: A State-ofthe-Art Review and Annotated Bibliography. IDRC-102e.
Ottawa: International Development Research Centre.
Shuval, H. I., Gunnerson, C. G. and Julius, D. S. (1981).
Night-soil Composting. Appropriate Technology for Water
Supply and Sanitation, vol. 10. Washington, D.C.: World
Bank, Transportation, Water and Telecommunications
Department.

81

Wagner, E. G. and Lanoix, J. N. (1958). Exereta Disposalfor

Rural Areas and Small Communities. Geneva: World
Health Organization.
Wiley, B. B. and Westerberg, S. C. (1969). Survival of human
pathogens in composted sewage. Applied Microbiology, 18,
994-1001.
Wiley, J. S. (1962). Pathogen survival in composting
municipal wastes. Journal of the Water Pollution Control
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WHO, International Reference Centre for Wastes Disposal
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Note added in proof

Since this chapter was written, there have been a number of developments in the design of
ventilated improved pit latrines, especially with regard to ventilation mechanisms (wind shear
across the top of the vent pipe is now known to be more important than absorption of solar
radiation) and the use oftwin pit V IP latrines (which are permanentstructures requiringeach pit to
be emptied in alternate years). There have also been significant developments in superstructure
design, notably the spiral shape used in Zimbabwe which obviates the need for a door, while still
ensuring privacy and good fly control. In rural Zimbabwe spiral latrines have been built almost
entirely out of local materials and at a financial cost to the householder of only US$tO. These and
other developments are described in a series ofworking papers and technical notes prepared by the
Technology Advisory Group established by the World Bank as executing agency for the United
Nations Development Programme Interregional Project INT1 81,/047 "Development and
Implementation of Low-cost Sanitation Investment Projects", they may be obtained by writing to
The Project Manager, UNDP INT/81/047, Transportation and Water Department, World Bank.
1818 H St NW, Washington DC 20433. USA.