course 2 unit 7 fs_treatment (part d) [compatibility mode]

1Low-cost Options for Treating

Environmental sanitation planning and infrastructure in developing countries

gFaecal Sludges

(FS) and Wastewater in

Developing Countries

1

Countries(Part D)Doulaye KonEAWAG / SANDEC

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

Contents

Part D: Faecal sludge treatment options (design details and performance)

2

2Unplanted drying beds - WRI Accra/Ghana

3

Cross section A-A

Unplanted drying beds - WRI Accra/Ghana

Cross section B-B

4

3Design criteria


- Sludge application depth ~ 25-30 cm- Drying period to attain a 40% solids content ~ 8 - 12 days (dry weather)- TS loading ~ 100 - 200 kg TS/m2*a

* (assuming a 10-day cycle)

Approximate land requirement

- ~ 0.05 m2/cap*

Percolate quantity

~ 50 80% of FS volume

5

Design variables

- TS raw sludge concentration [kg TS/m3] - Sludge loading per day [m3 FS/day]

Fresh, undigested sludge (from public toilets) does not lend itself to dewatering !

- ~ 50-80% of FS volume

Dewaterability

Mixtures of public toilet sludge and septage (ratio 1:4) Good dewaterability, drying to max. 70% TS in 8 days


Primary pond sludge Rather good dewaterability, drying to 40% TS Public toilet sludge Fresh, nearly undigested sludge hardly

lends itself to dewatering on drying beds

Removal efficiencies(raw sludge percolate)

80

100

60

20

40

60

[%]

SS

95

%

CO

D

70-9

0%

Hel

min

th e

ggs

100

%

NH

4

40-6

0%

4Constructed wetlands - AIT Bangkok/Thailand

7-cm thickferro-cement

20-cm stainlesssteel ventilation

pipe

Outlet

2-m wood pile

0.25-cmplastic sheet

10-cm reinforcedconcrete slab

20-cm concreteblocks

1.2-cm mesh

20-cm PVCdrainage pipe

3 3 ffl t

pipe

7

Planted drying beds (constructed wetlands)- Root system allows to maintain dewatering capacity of the drying beds during several years - Low desludging requirement since sludge loading cycles may last for several years - Biosolids stabilization and dewatering in one treatment step- Plant growth has to be given particular care (water balance)- Percolate may need further treatment- Appropriate under wet-tropical climatic conditions, less appropriate under dry climatic conditions

3-m3 effluentreceiving tank

Soil filter

Underdrain and Ventilation System- Hollow concrete blocks: 20 x 40 x 16 cm- Perforated PVC pipes d=20 cm- Ventilation pipes mounted on the drainage system:

d=20cm, Height: 1m over the top edge of the units

Constructed wetlands Design and operation criteria

Soil filter- Large gravel (d=5 cm): 45 cm- Medium gravel (d=2 cm): 15 cm- Sand (d=0.1 cm): 10 cm

Vegetation- indigenous species (cattails, reeds or bulrushes)

Freeboard- 1 m

8

- Start up with plant density 8 shoots/m2

Operating conditions (for Bangkok FS)- Solids loading rate: 125 - 250 kg TS/m2*a- Septage application frequency: 1 - 2/weeks - Percolate ponding period: 2-6 days

Land requirement- ~ 0.03 m2/cap

5Constructed wetlands

9

100

Constructed wetlands Removal performances and biosolids accumulation rate

70

80

90

SS

0

20

40

60

80

[m]

20

30

40

50

60

10

SS CODtot CODfilTKN

Biosolids accumulation: 90 m of fresh FS loaded

0.9 m of dewatered, stabilized and hygienised biosolids accumulated

0

10

6Challenges and potential of co-composting

- Reuse of organic matter - Closing the nutrient cycle- Hygienic safety

Organic Waste Faecal Sludge

D t li d h

11

- Decentralised approach- Institutional and

financial setup- Socio-cultural aspects

Composting research questions

Monitoring parameters Mixing Ratio

Nitrogen Balance- Influence of temperature

pattern on HE inactivation Nitrogen Balance Maturity parameters Temperature Moisture content Helminth eggs inactivation

pattern on HE inactivation- Influence of turning frequency

on HE inactivation

12

7Heap 1, turned when temp > 60Heap 2 turned each 10 days

75Heap11 Heap12Heap21 Heap22

Temperature pattern

30

45

60Te

mpe

ratu

re (C

)

13

300 10 20 30 40 50 60 70

Days

Windrow temperature > 45 C during 4-6 weeks

Helminth eggs (HE) inactivation

60

90

ratu

re (C

)

60

90

erat

ure

(C)

0

10

20

30

40

50

Asca

ris

Egg

s pe

r g T

S

0

30

Tem

per

0

10

20

30

40

50

0 20 40 60 80

Asc

aris

Egg

s pe

r gTS

0

30

Tem

pe

14

0 20 40 60 80

Days

HE removal in heaps turned each 3 days in the active composting period

0 20 40 60 80Days

HE removal in heaps turned each 10 days in the active composting period

8Helminth Eggs (Ascaris and Trichuris) die off during co-composting : results from Buobai Co-composting plant/Ghana

30

40Ascaris Egg/gTS

Viable Ascaris/g TS

Viability test

0

10

20

30

0 30 60 90Days

Eggs

/ g

TS

15

- HE viability in raw FS = 30-50 %- HE viability in the final co-compost: < 10 % and - Number of HE < 5/g TS in the end product )

viable HE < 0.5 HE/g TS- Recommendation for end product (3-8 HE/g TS),

Strauss & Xanthoulis, 1991

16

9Co-composting efficiency

a) Helminth eggs inactivation was not affected by the turning frequency, less frequent turning would be sufficientwould be sufficient

b) Co-composting process allowed to maintain temperature > 45C for more than 30 days.

c) Hence, high removal rate (90 to 100%) was achieved after 80 days.

17

y

d) The optimal duration of the composting process (60 + 30 days) is longer enough for the inactivation of all helminth eggs.

Drying ponds

18

10

Settling/thickening tanks

19

Settling / thickening- 2 settling/thickening units operated alternatively (e.g. 4 weeks loading / 4

weeks drying)- Performance of the tanks strongly depends on the plants state of

maintenance and operation- Problem when treating fresh public toilet sludges: bad settling behavior


20

11


21

Removal of thickened FS solids upon admixing sawdust

Waste stabilization ponds - WRI Accra/Ghana

t opt

ions

223Tr

eatm

ent

12


800010000120001400016000

[mg/l]10000

15000

20000

[mg/

l]

5060708090100

[%]

COD total

23

Eff.sed. tank

Eff.pond 1

Eff.pond 2

Eff.pond 3

Eff. pond 4

Influent0

200040006000

0

5000

[

Entire plant Sed. tank0

1020304050

86%

60%


1.00E+03

1.00E+04

1.00E+05

1.00E+06

100

ml]

5060708090100

[%]

Faecal coliforms

24

Eff.sed. tank

Eff.pond 1

Eff.pond 2

Eff.pond 3

Eff. pond 4

Influent1.00E+00

1.00E+01

1.00E+02[no.

/1


99% 0%

13


mg/

l] 800100012001400

[%] 60708090

100

Ammonium

25

Eff.sed. tank

Eff.pond 1

Eff.pond 2

Eff.pond 3

Eff. pond 4

Influent

[m


[%]

Removal efficiency

01020304050

40% 0%

Anaerobic digestion

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Anaerobic digestion- Energy production- Mechanization level higher than for e.g. pond systems - Higher operation and maintenance requirement

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Co-treatment with wastewater - UNR Alcorta/Argentina

27


C1Septage

C1C2

Sew

age

Effluent

L1 L2

Design criteria

A l ti f lid 0 02 3/ 3 FS

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- Accumulation of solids ~ 0.02 m3/m3 FS- Depth accumulated solids < 0.5 m

Approx. land requirement

- ~ 0.03 m2/cap

15


29


30

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Design and expected performance of selected low-cost options for faecal sludge treatment

Treatment process or option

Design criteria

Treatment goal / achievable removal

Solids-liquid separation

Organic pollutants in liquid fraction

Parasites (helminth eggs)

Drying/dewatering beds

100-200 kg TS/m2/year0.05 m2/cap(Accra)

SS : 60-80 % COD: 70-90 %NH4+-N : 40-60 %

To be treated for further improvement in ponds or constructed wetlands

100 % retained on top of the filtering media

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Constructed wetlands (planted drying beds)

250 kg TS/m2/yearSAR: 20 cm/year(Bangkok)

SS > 80 % SAR: 20 cm/year


100% retained on top of the filtering media

Design and expected performance of selected low-cost options for faecal sludge treatment

Treatment goal / achievable removalTreatment process or option

Design criteria

Treatment goal / achievable removal

Solids-liquid separation

Organic pollutants in liquid fraction

Parasites (helminth eggs)

Settling / thickening tank

SAR*: 0.13 m3/m3of raw FSHRT: 4 hS: 0.006 m2/capAccra

SS: 60-70 % COD: 30-50 %


Concentrated in the settled and floating solids

Facultative 350 kg BOD5/ha/d N t f thi 60 % l f R d b

32

Facultative stabilization ponds

350 kg BOD5/ha/d Not for this purpose

> 60 % removal of BOD5

Removed by settlement

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Removal efficiency and challenges

Removal efficiency (%) TS COD N-NH4 Settling/Thickening Tank (septage+public toilet, 1:1)

60 40 50

Constructed wetlands (septage)

85 97 75

Drying beds

33

Drying beds (septage+public toilet, 1:1) 80 70 50


Effluent concentration Effluent concentration

TS

(mg/l) COD

(mg/l) N-NH4 (mg/l)

EC (ms/cm)

Settling/Thickening Tank (septage+public toilet, 1:1)

9,000-14,000 7,000-12,000 1,000-2,000 20-25

Constructed wetlands (septage) 1,000-6,000 300-500 50-150 3.0-3.5

34

Drying beds (septage+public toilet, 1:1) 500-1000 4000-600 300-1500 11-20

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Variable Effects and expected problems

SS - Potential difficulties in solids removal from deep ponds; - Short-circuiting due to sludge settling - Sludge drying beds to be devised as a separate treatment

NH4 / NH3 - Ammonia toxicity due to high concentration in undigested FS Inhibition to the development of facultative and maturation pond conditions;

- Eye irritation

Colouration - Dark colour of FS supernatants prevents light penetration

35

Even though the organic load can be adjusted for a polishing treatment in stabilisation ponds, the high concentrations of salinity and NH4/NH3 hinder the biochemical degradation

p p g p- Algal growth and hence facultative or maturation pond

conditions may not evolve

Pre-treatment processes

Management Pre-treatment performance Post-treatment requirements

Solids production rate and handling

frequency

Required labour

managementinput

Hygienic quality

of bBiosoli

ds

Quality of effluent for

post-treatment

Post- treatment options for solids

Post- treatment options for liquids Remarks

Planted / Not suitable for fresh

Criteria for selecting low-cost treatment options for mechanically emptied faecal sludge.

Settling / thickening tank

High medium low Low to medium

StoragePlanted / unplanted drying bedsCo-composting

Planted / unplanted drying bedsCo-treatment in WSP

Not suitable for fresh FS (TVS > 65 %)Front-end loader should be available for regular desludging

Settling / anaerobic pond

High Very High low Poor to low

StoragePlanted / unplanted drying bedsCo-composting

Planted / unplanted drying bedsCo-treatment in WSP

Not recommended as first treatmentProcess impaired by high FS ammonia content

Drying / dewatering beds (Unplanted)

High High Low to mediumMedium togood

StorageCo-composting

Planted drying bedsCo-treatment in WSP

Sand quality

36

(Unplanted) WSP

Constructed wetlands (planted drying beds)

Low Medium Good to high High Extended storageConstructed wetlands or WSP

Technology proven with specific plants (Typha and Phragmites) and Availability of proven macrophytes

Co-composing High High

High to very high No effluent

No further treatment -

O&M are highly influenced by the market demand for compost

Anaerobic digestion cum biogas production

medium high Medium -good Medium - goodPlanted / unplanted drying bedsCo-composting

Constructed wetlands or WSP

Very few existing off-site digester

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Open research questions

a) Nitrification/denitrification in vertical flow constructed wetlands treating faecal sludge: influence of bed configuration

b) Organic matter and N removal mechanisms in floating macrophytes-based system treating FS effluent/percolate

c) Enhancing FS dewaterability with bulking organic material -

37

design and operation criteria

d) Helminth eggs inactivation in biosolids generated in FS treatment plant

e) Anaerobic digestion cum biogas: off-site decentralised low-cost reactors reactor development

course 2 unit 7 fs_treatment (part d) [compatibility mode]

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