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An Oxfam Technical Paper
Prepared by
w
J. HOWARD. FIPHE
B. LLOYD. Ph D
D. WEBBER. B Sc
OXFAM’S
SANITATION
UNIT
The design and testing
of a sanitation and
sewage treatment unit
for disasters
and long term use
I
JULY 1975 (second edition)
274 Banbury Road Oxford 0X2 7DZ Tel:(0865)56777
<
COMMUNITY HEALTH CELL
THE DESIGH AND TESTING Ur ' — rA SANITATION AND SEWAGE TREATMENT UNIT
FOR DISASTERS AND LONG TERM USE
J. HOWARD, B< LLOYD AND D. WEBBER
COMMUNITY HEALTH CELL
326, V Main, I Block
Koranic, pgala
Bangalore-560034
India
(Abstract)
Following three years research and development work including microbiological
studies a prototype sanitation unit designed and developed by Oxfam was
tested during the months of November and December 1974 at the Cholera Research
Laboratories (CRL), Dacca, Bangladesh.
The annual autumn epidemic of cholera
produced the highest number of cholera cases treated by the CRL hospital in
their recent history, and the wards thus provided an extremely potent effluent
for testing the efficiency of - the prototype in destroying or removing various
microbial pathogens, particularly V. cholerae.
The sanitation unit, which is assembled from the contents of a wooden orate
measuring 2m x 2m x Im and weighing approximately 500 kg, can be installed in a
day to provide sanitation for 500 persons.
Each unit at the time of writing costs
£1,350 i.e. £2.60 per head with an estimated working life of 5-10 years.
The
unit consists of 20 glass fibre squatting plates connected in series to two
21,000 litre flexible reinforced butyl rubber sedimentation tanks which provide
an 8 to 10 day retention time under strictly anaerobic conditions.
These tanks
may in turn be connected to an optional percolating filter, to further improve
the effluent, and this would be constructed of locally available stone.
Teets
demonstrated that during the retention period cholera vibrio counts were reduced
by as much as 100 fold, to a level far below the infective dose.
In addition
salmonellae counts were reduced by 10 to 100 fold, parallelling the reduction of
the coliform count.
Simple toxicity tests showed that the reductions in numbers
of bacteria were not attributable to disinfectant or antiobiotics released with
the hospital sewage.
Ascaris and Trichuris eggs were efficiently removed by
sedimentation to the order of 1,000 to 10,000 fold and were rarely detectable
in 100 ml of effluent from the second tank.
Introduction
In disaster situations with-high population density and especially refugee
camps, there is a very high incidence of gastro intestinal disease and often,
human degradation resulting from the non—containment of human excreta©
Oxfam
and similar relief organisations have long realised the desperate need ^o;r
efficient sanitation systems which would reduce the level of infection and attack
these diseases at the heart of their endemic foci by breaking the closed cycles
of infection, excretion and reinfection.
Traditional human waste treatment.and
containment systems such as septic tanks, trench and bore-hole latrines have been
found unsatisfactory in these circumstances.
Septic tanks take weeks to construct,
need skilled labour and costly materials such as cement, steel and bricks.
lat
rine trenches and boreholes are easily flooded and result in contamination of
the typically unprotected water supply.
Furthermore the latter cannot cope with
large numbers of people.
The exceptional circumstances prevalent in disaster
situations require a new approach, but one which must satisfy the following
criteria?
1)
2)
3)
The provision of an acceptable place for excretion®
Retention of the excreta in a protected water tight location
for adequate time to render it harmless*
mtiTnate safe disposal of the liquid effluent and of the solids©
In addition, disaster sanitation units should satisfy the following requirements?
cont’d®«•
r
-2-
4)
5)
6)
7)
8)
9)
10)
The unit must he of light weight and low bulk to facilitate
transportation, and. inexpensive• It should, be packaged, complete
with assembly instructions and. tools required for installation
and maintenance.
Rapid installation of the unit should be possible, within hours
of arrival at the intended site, by a small semi-skilled work
force, of say 4 persons.
The* unit should be able to be installed in or on the ground,
regardless of waterlogged or other adverse soil conditions.
The unit should function by gravity flow and be independent of
a power source.
No chemical dosing procedures should be required.
The maintenance requirements are to keep the latrine area clean
and flushed, and periodic desludging of the first tank.
It should be possible to drain, dismantle and relocate the unit
without difficulty.
The senior author of this paper organised the installation of a sanitation
unit serving approximately 2,000 people daily in a Bengali refugee camp in 1971 •
That unit consisted of glass fibre squatting plates, plastic pipework and poly
thene sheeting for lining an open containment lagoon. The unit has been rede
signed and an effort has been made to meet all of those requirements listed
above in the new unit described here and illustrated diagramatically in Figure 1.
This sanitation unit, designed and patented by Oxfam, includes the following
3 stages of which the first, two are packed in a single wooden crate.
Stage 1 - Latrine area
This comprises two parallel rows of 10 glass fibre squatting plates. These
plates are designed to stack one inside the other for transportation. The con
necting plastic pipework is of the push-fit type requiring no jointing techniques
or special tools, and is prefabricated for immediate assembly. Where required
the main walls of the latrine area are assembled from the wooden crate which can
be used to divide the unit into male and female sections. A 20 litre flushing
tank is located at the head of the drain.
.
Stage 2 - Sewage containment or treatment
Specially designed flexible pillow tanks made of butyl rubber reinforced with
nylon comprise the main component of the sanitation unit. Each tank weighs
80 kg when empty and folds down to less than Im-}. When rolled out flat and
filled with water or sewage each tank has a maximum capacity of 21,000 litres
and measures 9m long by 2.8m wide and 0.9m high. The tanks are of standard
design, each is provided with a 100mm inlet and outlet pipe connection, a de
sludging point at a low point on the tank, and a 50mm vent pipe at the highest
point of the tank.
Each tank may be used singly as a containment unit for short term use, or
several may be connected together in series or parallel to treat sewage flowing
through the unit anaerobically. With an input of 4,600 litres per day, two
tanks in series will give an 8 day retention period whereas three tanks will
give a 12 day retention; at the same time a minimum settleable solids re
tention time of three months is provided, depending on desludging procedure.
cont’d...
E-1tic
-3Stage 3 - Percolating filter
The liquid effluent leaving the second or third tank may be passed over an
aerobic percolating filter medium of area Im x Im and a minimum of l©5m depth©
This filter medium would be locally obtained broken brick or stone recommended
sizes of between 50-75 mm. The percolating filter is fed by a simple distributor?
or mechanical tipping device© ’Hie filtrate (or effluent if no filter is to be
used) is allowed to drain to the soil in a narrow trench or ground drain.
The Cholera Research Laboratories (CRL) Dacca was chosOii as the site for the
first trials of the Stage 2 tanks because a strong sewage was available here
which was known to contain a variety of pathogens and parasites, including
high numbers of cholera vibrios.
Furthermore on site workshop and micro
biological laboratory facilities were also available.
The work undertaken
at the CRL, and described here, was to monitor and evaluate the effectiveness
of the sewage treatment provided by two flexible tanks iidiich were charged
daily with the total sewage output of the cholera wards and associated
laboratories? this amounted to 4t600 litres of crude sewage per day and in
cluded the rice water stools from cholera patients© Testing was carried/ut
over a period of 6 weeks during which time samples were taken on a daily basis
to determine the ability of the unit to remove pathogens. Routine physical
and chemical tests were carried out alongside the quantitative microbiological
ones in order to elucidate what mechanisms might be responsible for the changes
observed in the populations of pathogens, and a record of patient numbers which
would be expected to control the numbers of pathogens entering the tanks©
METHODS
Location and installation of Stage 2 at CRL
Two flexible pillow tanks were positioned end to end, on a flat open grass
area 50m from the cholera wards and laboratories and adjacent to the main 30cm
diameter hospital sewer©
The sewer was plugged below the nearest manhole
chamber and sewage allowed to surcharge the drain and manhole chamber in order
to provide an adequate volume for pumping©
As the sewer was 2m below ground
level it was necessary to raise the sewage up to the flexible tanks by means of
a 5cm centrifugal pump. To measure the quantity of sewage entering the flexible
tanks a 1,800 litre metering tank was installed between the sewer and first
flexible tank.
This metering tank was charged daily with a total of 4>600
litres of sewage over a six hour period, but the first 1,800 litres of each day
was passed into the treatment tanks between the hours of 08.30 and 09®30 to simu
late severe overloading conditions©
The total quantity of sewage pumped during
the period of the trials was 160,000 litres.
The final effluent from the second
flexible tank was passed by gravity to a convenient sewer connection below the
point of pumping.
Sampling procedures
500ml samples were collected daily after pumping had commenced, (at 09®00)©
Sampling points included the raw sewage inlet, the outlet of the first flexible
tank and the effluent from the second flexible tank© Sample analysis commenced
immediately following collection©
Microbiological Methods
Preliminary toxicity tests
These were undertaken to investigate whether the hospital sewage entering the
tanks contained sufficient levels of antibiotic, disinfectant or any other
cont’s...
dissolved, substances which might adversely affect the survival of bacteria
and thus artificially enhance the efficiency of the treatment process*
Four hundred millilitres of fresh sewage was pre-filtered using a Whatman
GFC grade filter pad and the filtrate filter sterilised using the membrane
filtration technique. The filtrate was used to prepare batches of
25,
5, and 1^ final strengths of filtrate in molten double strength nutrient agar.
Two freshly isolated pathogenic strains of bacteria, one of Vibrio cholerae
the other of Shigella dysenteriae, neither of which had been exposed to anti
biotics, were cultured for testing the toxicity of the sewage filtrate. Pour
plate colony counts were prepared from a 10,000 fold dilution of visibly turbid
suspensions of each culture in separate experiments. The counts of five repli
cates of each sewage filtrate concentration were compared with the same number
of replicates in filtrate—free nutrient agar after incubation at 37°C for 24
hours. It was not possible to test full strength filtrate by this technique
since the heat treatment involved in media preparation might result in the
destruction of any toxic substances present. Nonetheless the results of these
tests show that the sewage filtrate had no detectable toxic effect on
V. cholerae (Table 1), although there was a marginal effect on S. dysenteriae .
(Table 2) where the means of colony counts of all filtrate strengths tested
were below that of the control. None of these data suggests that the filtrate
could depress the counts to a significant degree, say to the order of a 10—fold
reduction. It may therefore be concluded that unadsorbed toxic substances
present in this sewage were not present at sufficient levels to have a signi
ficant effect on the survival of the pathogens tested.
Sample analysis
Gholera counts were assayed by taking a 1 ml sample of sewage andpre—
paring a 10—fold dilution series in alkaline peptone water to 10 •• Dilutions
were incubated at 37°C and subcultured onto Monsur’s medium (Monsur, 1961) and
TCBS (Kobayashi et alCT 1963) after six and twenty-four hours® Suspicious
colonies from each plate were tested against cholera antiserum by slide
agglutination® The terminal dilution at which V9 cholerae was confirmed re
presents a count of 1-9 organisms times that dilution factor® In tabulating
these results an arbitrary most probable number of 5 has been listed in front
of the log.ln of the terminal positive dilution. More accurate counts, using
say 2-fold dilutions towards the end of the dilution series, were not carried
out since a 10—fold difference between sampling points was considered to be the
minimum change worth monitoring and significantly greater differences were
anticipated.
Salmonella counts were assayed using a technique similar to that used
for cholera except that in addition the Hyflosupercel concentration technique
of Hammarstrom and Ljutov (1954) was
because much lower numbers of
salmonellae were found to be present in the raw sewage. Following dilution
or concentration in the enrichment broth of Rappaport et al®, (1956) at 37 C
for twenty—four and thirty—six hours, these cultures were plated onto.
Salmonella-Shigella agar and suspicious colonies tested by standard bio
chemical techniques and confirmatory agglutination against polyvalent *0e
and ,H’ salmonella antiserum.
Coliform counts were carried out by the standard membrane filtration
technique described in the U®K© Ministry of Housing and Local Government
report number
0969)®
Entero parasitic egg counts were limited to two species of nematodes®
Ova of Ascaris lumbricoides and Trichuris trichuria were found to be the most
abundant and they were counted by filtering measured volumes of sewage
conted® ®•
-5containing a little Lugol«s iodine through a membrane filter© Filters were
dried in air, cleared in immersion oil and mounted on glass slides for micro
scopic examination of the whole filter at a magnification of x 100. Thus an
accurate count of stained ova per unit volume of sewage was obtained© When
excessive organic solids impeded filtration or interfered with examination of
the sample these were hydrolysed and extracted with 50% hydrochloric acid and
ether©
Physical and Chemical Test methods
Temperatures of the samples were taken at the time of sampling©
Dissolved oxygen was measured in the metering tank and in both flexible
tanks by means of a portable oxygen meter, model 1520 (Electronic Instruments
Limited, U©Ko)© The probe was lowered into the tanks via the metering tank
lid and. gas vents respectively©
The pH of samples was measured using a Corning model 7 pH meter
(Scientific Instruments, U©S©A©)©
Suspended solids, ammonia and biochemical oxygen demand were measured
using the standard methods described in Analysis of Raw, Potable and Waste
Waters (London, 1972).
RESULTS
Microbiological date showing the effect of treatment on particular
organisms have been tabulated so that the horizontal rows include the three
samples taken on the same occasion, but it is important to note that the fate
of a given unit volume of sewage entering the system can only be found by
reading the appropriate result four days later in the outlet of the first tank
and a further four days on in the effluent of the second tank©
Therefore to
simplify evaluating the efficiency of the unit an overall mean and percentage
reduction at each stage of treatment has been calculated for each micro
Thus
organism studied and presented at the foot of all the tables of results©
for cholera (Table 3) the first tank approaches a 100 fold reduction (98$
efficiency) whilst the second tank achieves a 100 fold reduction (99%
efficiency)©
In the case of salmonellae (Table 4) the first tank achieves
efficiency
less than a 10 fold reduction (83»3%) and the two tanks together barely a 100
fold reduction ^8.8%), but if allowance is made for the much lower inlet
innoculum, by comparison with cholera, then the salmonellae data are more im
pressive since in all biological unit treatment processes the last fraction
of a percent becomes exponentially more difficult to achieve©
There is good
evidence from other sources that the members of the Enterobacteriaceae are
generally more resistant to this type of treatment process than bacteria such
The coliform populations recorded in Table 5 agrs®
as the cholera vibrio©
At each treatment stage they exhibit a percentage re
with this observation.
duction similar to that of the salmonellae despite their one million times
greater initial populations.
These results are in accord with the repeatedly
made observation that the coliform group and the pathogenic enterobacteria
have survival rates in the same order of magnitude under similar environmental
conditions©
Although the temperature of the sewage fell by 10 C, from 32 to 22,
during the period of the study this had no measurable effect upon the survival
of the bacteria monitored, neither was there a significant fall in the raw
sewage inoculum of any of the microorganisms despite the decline in both
cholera and total admissions during the same period (Figure 2).©
Other para
meters monitored which would be expected to affect the survival of the bacteria
cent8 d© • ©
COMMUNITY HEALTH CELL
47/T. (First Floor) St. Marks Fuad,
Banqalore - 5fi0 001.
•included oxygen, B.O.D., pH and solids concentration® Redox potential
measurements which, in retrospect, may have been one of the most significant
factors, were excluded.
A small amount of oxygen, 0®8 to 1.2 mg per litre
was detectable in the metering tank immediately following pumping but this
was rapidly consumed.
In the treatment tanks no oxygen was detected in the
sewage on any occasion and no aeration was possible since, apart from the
sampl ing points and gas vents, air could not enter the tanks.
Anaerobic
conditions were thus achieved and maintained in the treatment tanks within
a few hours of their being charged with sewage® The rapid fall in pH usually
occurring in the first week during conventional anaerobic digestion was not
detected at the treatment tank sampling points since there were supernatant
liquor samples containing typically high levels of ammonia (40-90 mg<l) of
human origin.
All samples were in the pH range 6c25 to 6.7 throughout the
study, and liquor pH was therefore unlikely to be a major factor affecting
the survival of bacteria in this instance.
The first tank, was observed to
gas via the appropriate vent from the end of the first week onwards and thus
indicated that the sludge accumulating here was undergoing the normal digestion
processes, including primary acidification0 Furthermore, continual gasifi—
2^ toxic
; 1. substances,
j, derived from'the hospital sewage,
cation showed that any
which may have tadsorbed
------ onto the sludge were not present at adequate levels
That the highest proportion of solids was settling
to inhibit this process.,
in the first tank is shown unambiguously by the suspended solids results in
Table 8. This has the practical implication that arrangements have to be
made for desludging the first tank after about 3 months®
There is also the
hazard that since large numbers of pathogenic bacteria have been removed from
the liquid effluent they may have been retained and even concentrated by
adsorption onto the sludge solids®
Separate sludge samples were analysed
and did not show counts of bacterial pathogens significantly higher than
those leaving the tanks, nonetheless the longevity of ova of parasites has
been extensively documented and since these are clearly concentrated in the
sludge the supervision of sludge disposal into slit trenches ano. immediate
back filling is strongly advised. The effect of treatment on the removal
of Ascaris ova is shown in Table 6 and on Trichuris ova in Table 7•
The
efficienty of removal is again impressive but attributable simple to sedi
mentation rather than to complex and ill-defined biological processes as is
more likely the case for bacteria.
DISCUSSION
The design of the system described here was primarily controlled by
public health considerations and depended partly on earlier studies of the
survival of microorganisms under anaerobic conditions® Laboratory studies
carried out by Webber (1974) and Adams (1973) showed that sewage^artificially
contaminated with cholera vibrio populations of more than 1 x 10 per ml could
be reduced to very low numbers within 7“*14 days depending on the temperature,
pH and solids concentration of anaerobic domestic sewage sludge.
The cholera
data obtained under field conditions and presented in this paper confirm that
the retention time is adequate and hence justify the design specifications of
the stage 2 tanks.
Up to 1 x 10 ^cholera vibrios per ml were entering the
tanks whereas approximately 5 x 10 Per ml were present in the effluent®
According to Cash et al., (1974) the 50 per cent infective dose able to prog
duce at least one cholera positive stool together with diarrhoea was 1 x 10
vibrios when gastric acidity was not neutraliseds no cholera positive stools
or diarrhoea was observed with a dose of 1 x IO7 vibrios per volunteer.
Extrarpolating from this information, 100 litres of the effluent from the second
tank would be required theoretically to provoke choleraic symptoms and there
fore an effective measure for the prevention of the spread of this infection
is obtained.
oont$ do © ©
■7
A less dramatic reduction of species of the Enteroba^teriaceae had been
anticipated due to the resistance which members of this group have been shown
to exhibit during conventional anaerobic .digestion® McKinney? Langley and
Tomlinson. (1958) reported 84 and 92*4 per cent reductions of Stg^hi after
six and twenty days respectively®
This represents a 10—fold reduction
approximately and is of the same order as the data presented here for salmon
ellae f excluding Sa typhi®
The numbers of salmonellae recovered from the raw
CRL sewage were low^ reflecting the low numbers of patients admitted to the
hospital with infections due to the genus Salmonella®
For example9 there was
not one typhoid case admitted to the CRL during the period of this study©
By contrast there were significant numbers of infections due to the Shigella
group? but these were regretfully excluded from the monitoring programme as
no effective quantitative isolation procedure is currently available.
Although
a regular 10 to 1.00-fold reduction of salmonellae was observed these results
are more difficult to interpret in terms of their public health value because
published data on the infective dose of salmonellae are highly variable©
The
coliform count may be considered as a general index of the efficiency of the
tanks in reducing the populations of most members of the Enterobacteriaceae
including the entero pathogenic species and again a 10 to 100—fold reduction
was observed between the inlet and. effluent from the second tank®
Although it
cannot be claimed that the unit will reduce pathogenic populations of this
taxonomic group to a safe level? nonetheless a significant reduction of their
numbers entering the environment should make a positive contribution by lower
ing the probability of infection©
The data showing the removal of enteroparasitic ova by sedimentation were
as encouraging as those for the removal of cholera vibrios©
However the ex““
tremely high incidence of infections with Ascaris lumbricoides and Trichuris
trichiura throughout Bangladesh make it pointless to suggest that the further
spread of these parasites may be prevented in disaster situations in that
country since a high percentage of the human population there is already in
fected.
Nonetheless in many other areas the containment provided by this
sanitation unit offers a valuable public health measure for the prevention of
spread of enteroparasitic eggs and cysts.
The removal of ova of Ascaris sp©
and Triphuris sp© may be taken as an index of the efficiency of the unit in
removing the dispersal phase of many other parasites such as the much larger
Fasciolopsis buski and even the small cysts of Entamoeba hystolytica for
example®
Additional advantages observed with this unit were the absence of flies
and noxious odours©
The unit was originally conceived as a short-term
solution to sewage containment problems in disaster situations but the progress
achieved within the research and development show clearly that the unit is a
major advance in sanitation and sewage treatment systems for long-term use particularly in poorer parts of the world®
It could for example be used to
advantage in crowded, slum communities? providing the flexible tanks were pro
tected from damage by adequate fencing and supervision©
It is intended to
test the long-term durability of the principal components and the various uses
and acceptability of the unit commencing in the Spring of 1975 ^7 installing
complete units in selected refugee camps and possibly at the CRL hospital in
Mat lab Bazaar in Bangladesh®
ACKNOWLEDGMENTS
This project was made possible by the generous financial support of the Lever—
hulme Trust Fund and by the Overseas Development Ministry of the U.K© government
which funded the apiipment. The authors are also grateful for facilities provided
at the Cholera Research Laboratories? Dacca? Bangladesh? and at the Loughborough
and Surrey Universities? U.K® Particular thanks are due to Dr® W© Verwey, Director
and Mr© Mark Tucker? Engineer? and the engineering and laboratory staff of CRL?
Dacca? for their encouragement? advice and practical assistance; and to
Mr© J© Pickford? Senior Lecturer, Civil Engineering Dept®? University of Technology?
Loughborough, and Mr® J® McoL® Fraser? WHO? Consultant Chartered Engineer, for
their signifleant contribution's to the design of the unit®
REFERENCES
Adams, J. (1973)
University of Surrey, Oxfam Project Report.
Cash, R.A., Music, S.I., Libonati, J.P., Snyder, M.J., Wenzel, R.P.
and Hornick, R.B. (1974) J.Inf.Bis. 129, (1), 45*
Hammarstrom, E. and Ljutov, V. (1954) Acta.path, microbiol.scand.,
365.
Kobayashi, T., Enomoto, S., Sakazaki, R. and Kuwahara, S. (1963)
Jap.J.Bact., 18, 387
McKinney, R.E., Langley, H.E. and Tomlinson, H.P. (1958) Sewage
Ind.Wastes, 30, 12, 1469*
Monsur, K.A. (1961)
Trans. Royal Soc.Trop.Med.Hyg.,
Rappaport, F., Konforti, N. and Navon, B. (1956)
, 440 •
J.clin.Path. 9., 261.
Webber, B. (1974) University of Surrey, Oxfam Project Report.
Analysis of Raw, Potable and Waste Waters (1972)
H.M.S.O. London.
Report No. 71 (1969) Reports on Public Health and Medical Subjects,
H.M.S.O. London.
F17/75
•<
/
FLUSHING TANK
Squatting plates
TANK 2
TANK 1
Q
o
o o o o o
o o o o o
o o
o o
o
o
PERCOLATING
FILTER
DESLUDGE TRENCH
PLAN
Stage 1 — Latrine Area
Stage 2 — Sewage Treatment
Partition
X-------- lH Earth plinth =
i ■>
.
Ground level
Primary Sedimentation
Secondary Sedimentation
ELEVATION
GENERAL LAYOUT OF SANITATION UNIT
Stage 3 — Filter
32
SEWAGE TEMPERATURE °C
31
I = Inlet
30 —|Q
0
Outlet of the 1st tank
29
28
27 —
26 —
25 —
24 —
23 —
J
__ 1_
December
1
UNovember
__ __ 1
J
CRL HOSPITAL ADMISSIONS
Total number
55—
5C—
45—
4C—
35—
3C —
25;
A
Confirmed cholera \
1C —
cases
]___ [I
5November
y
I
I
I I
I I
18
20
22 24
26
26
28
/ \
V
L I
30 December 6
1 fid
8
10
Figure 2. Some of the factors expected to affect the inoculupi
of microorganisms in the treatment tanks
12
TABLE 5.
TABLE 4.
IEEE CT OP TREATMENT ON THE
EFFECT 01’’ TREATMENT ON THE
COUNT OF OOLIFORMS EEL? 1 ML SAMPLE
COUNT OF SALMONELLAE PEI? 100 ML SAMPLE
Outlet first tank
Effluent second tank
Sampling
date
Raw sewage
- inlet
Outlet first tank
Effluent second tank
Nov. 14
500 x 10A
50 x 10A
20 x 10A
20
400 x 10A
50 x 10A
5 X 10A
22
550 X 10
80 x 10A
0.5 x 10A
28
400 x 10A
40 x 10A
50
190 x 10A
50 x 10A
8 x 10A
5 X 10A
2
50 x 10A
6 x 10A
0.5 X 10A
Sampling
date
Raw Sewage
- inlet
5 x 10 5
,2
5 x 10‘
5 x 1O1
Nov. 14
18
5 x 10,5
2
5 x 10'
5 x 10.1
20
2
5 x 10'
2
5 x 10*
5 x 101
5 x 10*
.2
5 X 10'.2
5 x IO1
25
1
5 x 101
5 X 10.0
5 x 10,0
5
5 x -IOA
5 x 10.0
0
4
40 x 10A
10 x 10A
5 x 10A
8
5 x 10,5
2
5 x 10‘
5 x 101
8
400 x 10A
50 x 10A
4 x 10A
11
5 x 10 3
,2
5 X 10‘
5 x 101
10
110 x 10A
50 x 10A
10 x 10A
5 x 10,5
5 x 10
5 x 10'.0
11
50 x 10A
13
200 x 10A
500 x 10A
50 x 10A
’
13
20 x 10A
7 x 10A
Mean
265 x 104
56 x 104
8.5 x 104
11
11
11
86.4
96.5
Dec.
Mea'a
Number
of results
Percentage
of bacteria
removed
2
Dec.
3-4 x IO1
2.9 x 103
3.4 x 10
9
9
9
88.3
98.8
Number
of results
Percentage
of bacteria
removed
TABLE 5.
EFFECT OF TREATiOTT ON THE
COUNT OF CHOLERA VIBRIOS PER 1 ML SAMPLE
Table 1. The effect of CRL sewage filtrate on the viability
of a standard inoculum of Y.cholerafi measured by pour plate
colony counts in nutrient agar»
Replicate
number
Final strength of sewage filtrate in nutrient agar
50 %
25 %
5%
1%
Control
Sampling
date
Raw Sewage
- inlet
Outlet first tank
Effluent second tank
Nov. 14
5 x 104
5 x 10.2
’
5 x 10.2
’
60
42
47
41
65
18
5 x 10-.5
5 x 10->3
5 x 10*
2
64
43
65
45
55
20
5 x 10.5
5 x 10-.3
5 x 101
5 x 10.2
’
5 x lo3
3
60
62
63
45
56
22
5 x 104
4
35
56
54
53
ss
27
5 x 10A
5
63
55
43
54
51
28
5 x 10A
30
5 x 1O>3:
2
5
5 x 10A
5 x 10A
7
5 x 10A
8
56.4
Mean
51.6
54.4
47.6
56.0
Dec.
Tcb?e 2. The effect of CRL sewage filtrate on the viability
measured by pour
of a standard inoculum of
plate colony counts in nutrient agar.
I
Replicate
Final strength of sewage filtrate in nutrient agar
5%
1%
Control
339
354
392
349
328
359
350
484
342
422
327
463
476
4
468
336
364
415
458
5
413
390
365
349
467
404.0
363.0
353.4
393.8
446.8
50%
25%
1
381
2
416
3
number
Mean
12
1
5 x 10.2
‘
,2
5 x io1
5 x IO1
5 x 10>2
‘
t
5 x 10*2
5 x 1O1
5 x IO1
5 x 'O>5
5 x 1O.2
‘
,2
5 x 1O‘
9
5 x 10-.5
5 x 101
5 x 10'
11
5 X 10A
5 x 10A
5 x 10,3
12
5 x 10,3
5 x 10A
5 X io1
13
5 x 10,5
5 x 10 5
5 x 101
5 x 104
9.5 x !(?
53 » 102
15
13
14
93.
99.
Mean
Number
of results
Percentage
of vibrios
removed
5 x 101
5 x 101
i
TABLE 7EFEE CT OF TREATMENT ON THE
COUNT OF TRI (HURTS OVA PER 100 ML SAMPLE
TABLE 6.
EFFECT OF TREATMENT ON THE
COUNT OF AS CARLS OVA PER 100 ME SAMPLE
Sampling
date
Raw sewage
- inlet
Outlet first tank
Effluent second tank
Nov. 18
560
0
0
20
200
0
0
22
760
10
0
0
25
520
20
0
20
0
28
1,160
0
0
500
0
2
1,050
0
0
0
5
700
0
0
65
Sampling
date
Raw sewage
- inlet
Outlet first tank
Effluent second tank
Nov. 17
6,000
0
0
18
5,560
60
0
20
2,540
0
0
22
5,200
10
25
2,760
28
5,460
50
Dec.
Dec.
2
9,750
100
9
7
1,800
0
0
11,500
45
0
8
100
12
0
5
12,700
14-0
12
10
800
10
0
7
8
6,100
172
0
11
200
0
0
10
15,200
4-10
4
12
4-00
0
0
9,000
190
20
15
550
0
0
11
12
8,000
570
4-
Mean
646
4-
0
15
8,000
720
4
Number of
results
15
15
15
Mean
Number of
results
Percentage
of ova removed
7,612
175
5.5
14
15
15
97-7
99-95
99-53
100
w O
2$
c
<» o
c'n 0)
__ CD
C
Percentage of
ova removed
■>
_ «> o
03
n.
5
o
c ‘
o
H
? -<
- T
£2 m
I
J>
o
p
1
TABLE S',
EFFECT OF TREATMENT ON THE
SUSPENDED SOLIDS IN MG PER LITRE OF SAMPLE.
I
Effluent second tank
Sampling
date
Raw sewage
- inlet
Outlet first tank
Nov. 14
240
71
39
18
452
61
50
20
332
50
44
22
950
68
32
25
612
52
30
27
352
54
33
28
1604
58
38
29
1810
43
36
30
2020
52
30
1
1400
52
24
2
1325
49
36
3
2010
46
24
4
1940
38
19
5
1900
41
28
7
1620
54
28
8
2020
57
28
9
1900
40
26
IO
1750
53
26
11
1790
47
27
12
2380
74
27
1420
53
31
20
20
20
96*27
97 >82
Dec.
MEAN
Number of results
Percentage of
solids removed
Position: 1793 (3 views)