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Environmental sanitation planning and infrastructure in developing countries

Low-cost Options for Treating Faecal for Treating Faecal Sludges (FS) and Wastewater in

Developing Countries

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Doulaye KonEAWAG / SANDEC

www.sandec.eawag.chTel.+41 44 823 55 53

(Part A to C)

Contents

Part A: Faecal sludge characteristics

Part B: Faecal sludge treatment standards

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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/capday 1 16 8 45

TS g/capday 14 100 90 110

TKN g/capday 0.8 8 5 10

Volume l/capday 1 2(includes water for

toilet cleansing)

0.15 - 0-20 1.5(faeces

and urine)

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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

Storage durat ion (months to years) Performance of septic tank

Tank emptying technology + pattern

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Admixtures to FS(e.g grease, kitchen / solid waste) Intrusion of groundwaterTemperature

Sludge composition - Flow Behaviour (Bsch & Schertenleib, 1985)100

H2O

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

40

60

80

% H

1

2

3

4

6

0

20

0 2 4 6 8 10 12% Volatile (TVS)

1.low- viscosity zone2.low- : low+ viscosity zone

3.med : med+ viscosity zone 4.high- : high+ viscosity zone

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Faecal and WWTP sludges compared

Total solids (TS) concentration

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

Total solids (TS) concentration

Faecal sludge

High-strength FS(e.g. from unsewered, low or zero-flush public toilets)

Low-strength FS(septage)

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WWTP sludge

Wastewater in thetropics

mg TS/L 10,000 20,000 30,000 40,000 50,0000

Waste activated sludge Primary and anaerobicallydigested sludge

1,000-1,500

Item Type A(high-strength)Type B

(low-strength)Sewage - forcomparisons

sakePublic toilet or

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

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

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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

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Comparison of public toilet sludge, septageand sewage characteristics

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Location Accra (Ghana)Accra

(Ghana)Alcorta

(Argentina)Ouagadougou (Burkina Faso )

Bangkok (Thailand)

FS characteristics in selected cities in developing countries

(Ghana) (Ghana) (Argentina) (Burkina Faso.) (Thailand)

Type of FS Public toilet sludge Septage Septage

TS (mg/L) 52,500 12,000 (6,000 35,000 SS) 19,00015,350

(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)

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(120 1,200)

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FS Wastewater

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

Different treatment schemes and design criteria

FS Variability

Design basis: average from a large number of analyses

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of analyses

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

Part B: Faecal sludge (FS) treatment standards

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Faecal sludge treatment standards

A ti BOD 50 /l SS 60 /l FC 105/100 l

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

Setting standards in developing countries

Development monitoring and enforcementsystems still lagging far behind

Define and set up a seriesselect a phased approachbase environmental

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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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60

80

100

120

140

160

180

200

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0

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1979 1985 1989 1990

Gradual development of the effluent discharge standard in Germany.

For sewage treatment plants > 100,000 p.e. (Bode, 1998)

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

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B: Treated plant sludge Use in agriculture n.c. n.c. 3-8/ g TS 2) 3)1) Crops 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 /hayear (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

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Comment by Elisabeth: This part is not essential: you can see it as a reminder about how constructed wetlands and anaerobic ponds work

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Examples of treatment systems

Centralised wastewater treatment

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

Activated sludge systems Trickling filterRotating biodisc contactorSequencing batch reactorAerated lagoons

Natural treatment systems

Mechanical treatment systems

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tew Aerated lagoons

Oxidation ditch

UASB reactorBiogas reactor

Waste stabilization pondsin warm climates

Pond systems

in warm climates

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Degradation of organic substances inwaste stabilization pond systems

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N transformations in waste stabilization ponds

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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 wetlands

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Constructed wetlands

From pretreatment

Variableeffluent level

Effluent

From pretreatmentw

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Effluent

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 exchangePlant uptake

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Metals Adsorption and cation exchangeComplexationPrecipitationPlant uptakeMicrobial oxidation/reduction

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

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N transformations in constructed wetlands

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Comparison of different systems

Approx. hydr. retention time

[days] (in warm climate)

Rel. energy requirement for operation(gravity flow)

Relative area

requirementAerobic systems

< 1 d+ 2)Trickling filter

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

3-5 d0Maturation pond

10 d0Facultative (non-aerated) waste stabilisation pond

)(g y )

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1 d+++Activated sludge

1 d++Oxidation ditch

1 d+Rotating biodisc reactor

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

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Comparison of different systems

Approx. hydr. retention time

[days] (in warm climate)

Rel. energy requirement for operation(gravity flow)

Relative area

requirementAnaerobic systems

12-15 h0 (+) 1)Anaerobic filter

3 d0 (+) 1)Anaerobic baffled reactor

1 d0 (+) 1)Septic tank

1-3 d0 (+) 1)Anaerobic pond

warm climate) (gravity flow)

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

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

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