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Doulaye Koné

EAWAG / SANDECwww.sandec.eawag.chTel.+41 44 823 55 53

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)

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Contents

Part A: Faecal sludge characteristics

Part B: Faecal sludge treatment standards

Part C: Low-cost wastewater treatment options

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Part A: Faecal sludge (FS) characteristics

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FS specific quantities

Variable Septage 1 Public toilet sludge 1 Pit latrine sludge

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Freshexcreta

BOD g/cap·day 1 16 8 45

TS g/cap·day 14 100 90 110

TKN g/cap·day 0.8 8 5 10

Volume l/cap·day 1 2(includes water for

toilet cleansing)

0.15 - 0-20 1.5(faeces

and urine)

1 Estimates are based on a faecal sludge collection survey conducted in Accra, Ghana.2 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.

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Factors influencing faecal sludge quality

Quality of Faecal Sludge

S t o r a g e d u r a t i o n ( m o n t h s t o y e a r s ) P e r fo rm a n c e o f s e p t ic ta n k

A d m ix tu re s to F S(e .g g re a se , k it c h e n / so l id w a s te ) In t ru s io n o f g ro u n d w a te rT e m p e ra tu r e

T a n k e m p ty in g te c h n o lo g y + p a t te rn

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Sludge composition - Flow Behaviour (Bösch & Schertenleib, 1985)

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60

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100

0 2 4 6 8 10 12

% Volatile (TVS)

% H

2O

1

2

3

4

Low -

Low- : Low

+

Med: m

ed +

High - : High +

1.low- viscosity zone

2.low- : low+ viscosity zone

3.med : med+ viscosity zone

4.high- : high+ viscosity zone

The latrine technology influences the FS characteristics and determines the emptying procedure and technology

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Faecal and WWTP sludges compared

Faecal sludge = wastewater offside !1 litre faecal sludge = 100 litres wastewater !

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ItemType “A”

(high-strength)Type “B”

(low-strength)

Sewage - forcomparison’s

sake

ExamplePublic toilet orbucket latrinesludge

Septage Tropical sewage

Characteri-sation

Highlyconcentrated,mostly fresh FS;stored for days orweeks only

FS of low concentration;usually stored for severalyears; more stabilised thanType “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 < 1,000 30 - 70

TS = 3.5 % < 3 % < 1 %

SS mg/l = 30,000 ˜ 7,000 200 - 700

Helmintheggs,no./litre

20, - 60,000 ˜ 4,000 300 - 2,000

Faecal sludge = wastewater offside !1 litre faecal sludge = 100 litres wastewater !

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Comparison of public toilet sludge, septageand sewage characteristics

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LocationAccra

(Ghana)Accra

(Ghana)Alcorta

(Argentina)Ouagadougou (Burkina Faso.)

Bangkok (Thailand)

Type of FSPublic toilet

sludgeSeptage Septage

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 13,50015,700

(1,200 – 76,000)

NH4-N (mg/L) 3,300 330 150 -415

(120 – 1,200)

FS characteristics in selected cities in developing countries

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Different treatment schemes and design criteria

FS Wastewater

FS Variability

Design basis: average from a large number of analyses

No standard characteristics, analysis on a case-to-case basis

Faecal sludge = wastewater offside !1 litre faecal sludge = 100 litres wastewater !

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Part B: Faecal sludge (FS) treatment standards

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Faecal sludge treatment standards

Argentina BOD=50mg/l, SS=60mg/l, FC=105/100 ml(Santa Fé) Biosolids used in agriculture: 1HE/4g TS

China 95% HE removal and 30 days storage

South Africa no viable ascaris ova/10g TS, 0 salmonella/10g TS, 1000 FC/10g TS

Ghana 90% BOD and FC removal for Teshie FSTP effluent

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Setting standards in developing countries

Development monitoring and enforcementsystems still lagging far behind

Define and set up a series of barriers (critical control points)

select a phased approachbase environmental regulations on available technology and on(local) economic and institutional resources

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Setting standards in industrialized countries

A phased approachEx. COD [mg/l]

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100

120

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180

200

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]A: Liquid effluent1. Discharge into receiving waters:

• Seasonal stream or estuary 100-200 30-60 10-30 2-5 104

• Perennial river or sea 200-300 60-90 20-50 10 105

2. Reuse:

• Restricted irrigation n.c. 1) 1 105

• Unrestricted irrigation n.c. 1) 1 103

B: Treated plant sludge

• 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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Constructed wetlandsPond systemsMacrophyte systems (e.g. duckweed; water lettuce)

Examples of treatment systems

Activated sludge systems Trickling filterRotating biodisc contactorSequencing batch reactorAerated lagoonsOxidation ditch

UASB reactorBiogas reactor

“Natural treatment systems”

“Mechanical treatment systems”

Centralised wastewater treatment

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Waste stabilization ponds in warm climates

Pond systemsW

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Degradation of organic substances inwaste stabilization pond systems

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N transformations in waste stabilization ponds

Nitrogen transformations and losses in a facultative waste stabilisationpond. The thickness of the arrows signifies the relative quantitative importance of the pathway; the broken arrows show mechanisms of net nitrogen removal.

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Constructed wetlandsW

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Constructed wetlands

From pretreatment

Variableeffluent level

Effluent

Effluent

From pretreatment

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Wetland Plants

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Mechanisms in constructed wetlands

Wastewater constituent Removal mechanisms

Suspended solids SedimentationFiltration

Soluble organics Aerobic microbial degradationAnaerobic microbial degradation

Nitrogen Ammonification followed by microbial nitrificationDenitrificationPlant uptakeMatrix adsorptionAmmonia volatilisation

Phosphorous Matrix sorption

Metals Adsorption and cation exchangeComplexationPrecipitationPlant uptakeMicrobial oxidation/reduction

Pathogens SedimentationFiltrationNatural die-offPredationUV irradiationExcretion of antibiotics from roots of macrophytes

Plant uptake

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N transformations in constructed wetlandsW

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Comparison of different systems

≤ 1 d+++Activated sludge

≤ 1 d++Oxidation ditch

≤ 1 d+Rotating biodisc reactor

< 1 d + 2)Trickling filter

2-3 d0 (+) 1)Soil-plant filter

3-5 d0Maturation pond

10 d0Facultative (non-aerated) waste stabilisation pond

Approx. hydr. retention time

[days] (in warm climate)

Rel. energy requirement for operation(gravity flow)

Relative area

requirementAerobic systems

1) (+): To remove and treat accumulated biosolids 2) (+): Recirculation

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Comparison of different systems

> 6 h(-) 3) 0 (+) 1)Upflow anaerobic sludge blanket reactor, UASB

12-15 h0 (+) 1)Anaerobic filter

≥ 3 d0 (+) 1)Anaerobic baffled reactor

1 d0 (+) 1)Septic tank

1-3 d0 (+) 1)Anaerobic pond

Approx. hydr. retention time

[days] (in warm climate)

Rel. energy requirement for operation(gravity flow)

Relative area

requirementAnaerobic systems

1) (+): To remove and treat accumulated biosolids 2) (+): Recirculation 3) (-): Gas utilization

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