Environmental sanitation planning and
infrastructure in developing countries
Low-cost Options
for Treating Faecal
Sludges (FS) and
Wastewater in
Developing
Countries
(Part A to C)
Doulaye Koné
EAWAG / SANDEC
www.sandec.eawag.ch
Tel.+41 44 823 55 53
1
Contents
Part A: Faecal sludge characteristics
Part B: Faecal sludge treatment
standards
Part C: Low-cost wastewater treatment
options
2
Part A: Faecal sludge (FS)
characteristics
3
FS specific quantities
Variable
Septage 1
Public toilet sludge 1
Pit latrine
sludge
Fresh
excreta
2
BOD g/cap·day
1
16
8
45
g/cap·day
14
100
90
110
0.8
8
5
10
1
2
(includes water for
toilet cleansing)
0.15 - 0-20
1.5
TS
TKN g/cap·day
Volume l/cap·day
1
2
(faeces
and
urine)
Estimates are based on a faecal sludge collection survey conducted in Accra, Ghana.
Figures have been estimated on an assumed decomposition process occurring in pit
latrines. According to the frequently observed practice, only the top portions of pit latrines
(~ 0.7 ... 1 m) are presumed to be removed by the suction tankers since the lower
portions have often solidified to an extent which does not allow vacuum emptying.
Hence, both per capita volumes and characteristics will range higher than in the material
which has undergone more extensive decomposition.
4
Factors influencing faecal sludge quality
Tank emptying technology + pattern
Storage duration (months to years)
Performance of septic tank
Quality of Faecal Sludge
Admixtures to FS
(e.g grease, kitchen / solid waste)
Temperature
Intrusion of groundwater
5
The latrine technology influences the FS
characteristics and determines the
emptying procedure and technology
% H2O
Sludge composition - Flow Behaviour (Bösch & Schertenleib, 1985)
100
1
80
2
3
60
4
40
20
0
0
2
4
6
8
10
12
% Volatile (TVS)
1.low- viscosity zone
2.low- : low+ viscosity zone
3.med : med+ viscosity zone
4.high- : high+ viscosity zone
6
Faecal sludge = wastewater  offside !
1 litre faecal sludge = 100 litres wastewater !
Faecal and WWTP sludges compared
Total solids (TS) concentration
Faecal sludge
High-strength FS
(e.g. from unsewered, low or zeroflush public toilets)
Low-strength FS
(septage)
Wastewater in the
tropics
mg TS/L
Primary and anaerobically
digested sludge
Waste activated sludge
WWTP sludge
1,000-1,500
0
10,000
20,000
30,000
40,000
50,000
7
Faecal sludge = wastewater  offside !
1 litre faecal sludge = 100 litres wastewater !
Item
Type “A”
(high-strength)
Example
Public toilet or
bucket latrine
sludge
Characterisation
Highly
concentrated,
mostly fresh FS;
stored for days or
weeks only
Type “B”
(low-strength)
Sewage - for
comparison’s
sake
Septage
Tropical sewage
FS of low concentration;
usually stored for several
years; more stabilised than
Type “A”)
COD mg/l
20, - 50,000
< 10,000
500 - 2,500
COD/BOD
2 : 1 .... 5 : 1
5 : 1 .... 10 : 1
2:1
NH4-N mg/l
2, - 5,000
TS
= 3.5 %
< 3 %
< 1 %
SS mg/l
= 30,000
˜ 7,000
200 - 700
Helminth
eggs,
no./litre
20, - 60,000
˜ 4,000
300 - 2,000
<
1,000
30 - 70
8
Comparison of public toilet sludge, septage
and sewage characteristics
9
FS characteristics in selected cities in
developing countries
Location
Accra
(Ghana)
Accra
(Ghana)
Alcorta
(Argentina)
Ouagadougou
(Burkina Faso.)
Bangkok
(Thailand)
Type of FS
Public toilet
sludge
TS (mg/L)
52,500
12,000
(6,000 – 35,000
SS)
19,000
15,350
(2,200 – 67,200)
COD (mg/L)
49,000
7,800
4,200
13,500
15,700
(1,200 – 76,000)
NH4-N (mg/L)
3,300
330
150
-
415
(120 – 1,200)
Septage
Septage
10
Faecal sludge = wastewater  offside !
1 litre faecal sludge = 100 litres wastewater !
FS  Wastewater
 Different treatment schemes and design criteria
FS Variability
 Design basis: average from a large number
of analyses
 No standard characteristics, analysis on a
case-to-case basis
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Part B: Faecal sludge (FS)
treatment standards
12
Faecal sludge treatment standards
Ghana
90% BOD and FC removal for Teshie FSTP effluent
South Africa
no viable ascaris ova/10g TS, 0 salmonella/10g TS,
 1000 FC/10g TS
China
 95% HE removal and 30 days storage
Argentina
(Santa Fé)
BOD=50mg/l, SS=60mg/l, FC=105/100 ml
Biosolids used in agriculture: 1HE/4g TS
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Setting standards in developing countries
Development monitoring and enforcement
systems still lagging far behind
base environmental
regulations on available
technology and on
(local) economic and
institutional resources
select a phased approach
Define and set up a series
of barriers (critical control
points)
14
Setting standards in industrialized countries
A phased approach
Ex. COD [mg/l]
200
180
160
140
120
100
80
60
40
20
0
1979
1985
1989
1990
Gradual development of the effluent
discharge standard in Germany.
For sewage treatment plants > 100,000 p.e.
(Bode, 1998)
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Suggested standards for developing countries
BOD [mg/l]
total
filtered
NH4-N
[mg/l]
Helminth eggs
[no./liter]
FC
[no./100 ml]
 104
 105
•
A:
Liquid effluent
1. Discharge into receiving waters:
Seasonal stream or estuary
100-200
30-60
10-30
 2-5
•
Perennial river or sea
200-300
60-90
20-50
 10
2. Reuse:
•
Restricted irrigation
n.c.
1)
1
•
Unrestricted irrigation
B:
Treated plant sludge
n.c.
1)
1
 105
 103
•
Use in agriculture
n.c.
n.c.
 3-8/ g TS 2)
3)
1)  Crop’s nitrogen requirement (100 - 200 kg N/ha.year)
2) Based on the nematode egg load per unit surface area derived from the WHO guideline for wastewater irrigation (WHO, 1989)
and on a manuring rate of 2-3 tons of dry matter /ha·year (Xanthoulis and Strauss, 1991)
3) Safe level if egg standard is met
n.c. – not critical
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Appropriate FS treatment options in developing countries
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Part C: Low-cost wastewater
treatment options
Comment: This part is not essential: you can see it as a
reminder about how constructed wetlands and
anaerobic ponds work
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Centralised wastewater treatment
Wastewater treatment
Examples of treatment systems
“Natural treatment
systems”
“Mechanical treatment
systems”
Constructed wetlands
Pond systems
Macrophyte systems (e.g.
duckweed; water lettuce)
Activated sludge systems
Trickling filter
Rotating biodisc contactor
Sequencing batch reactor
Aerated lagoons
Oxidation ditch
UASB reactor
Biogas reactor
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Pond systems
Wastewater treatment
Waste stabilization ponds
in warm climates
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Wastewater treatment
Degradation of organic substances in
waste stabilization pond systems
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Wastewater treatment
N transformations in waste stabilization ponds
Nitrogen transformations and losses in a facultative waste stabilisation
pond. The thickness of the arrows signifies the relative quantitative
importance of the pathway; the broken arrows show mechanisms of net
nitrogen removal.
22
Wastewater treatment
Constructed wetlands
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Constructed wetlands
Wastewater treatment
From
pretreatment
Variable
effluent level
Effluent
From
pretreatment
Effluent
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Wetland Plants
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Mechanisms in constructed wetlands
Wastewater treatment
Wastewater constituent
Removal mechanisms
Suspended solids
Sedimentation
Filtration
Soluble organics
Aerobic microbial degradation
Anaerobic microbial degradation
Ammonification followed by microbial nitrification
Denitrification
Plant uptake
Matrix adsorption
Ammonia volatilisation
Matrix sorption
Plant uptake
Adsorption and cation exchange
Complexation
Precipitation
Plant uptake
Microbial oxidation/reduction
Sedimentation
Filtration
Natural die-off
Predation
UV irradiation
Excretion of antibiotics from roots of macrophytes
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Nitrogen
Phosphorous
Metals
Pathogens
Wastewater treatment
N transformations in constructed wetlands
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Comparison of different systems
Rel. energy
requirement
for operation
(gravity flow)
Approx. hydr.
retention time
[days] (in
warm climate)
Facultative (non-aerated)
waste stabilisation pond
0
10 d
Maturation pond
0
3-5 d
Soil-plant filter
0 (+) 1)
2-3 d
Trickling filter
+
<1d
Rotating biodisc reactor
+
Oxidation ditch
++
≤1d
Activated sludge
+++
≤1d
Aerobic systems
1)
Relative
area
requirement
(+): To remove and treat accumulated biosolids
2)
≤1d
2)
(+): Recirculation
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Comparison of different systems
Rel. energy
requirement
for operation
(gravity flow)
Approx. hydr.
retention time
[days] (in
warm climate)
Anaerobic pond
0 (+) 1)
1-3 d
Septic tank
0 (+) 1)
1d
Anaerobic baffled reactor
0 (+) 1)
≥3d
Anaerobic filter
0 (+) 1)
12-15 h
Wastewater treatment
Anaerobic systems
Upflow anaerobic sludge
blanket reactor, UASB
1)
Relative
area
requirement
(-) 3) 0 (+) 1)
(+): To remove and treat accumulated biosolids
3) (-): Gas utilization
2)
>6h
(+): Recirculation
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