1

Practical period in Windhoek

General (plant) information Data analysis Pilot plant research Risk assessment

2

General

3

Water in Windhoek

Rainwater: limited and evaporates Rivers: >500km away Reservoirs: subjected to irregular rains (>70km) Ground water: wells >50km deep Windhoek: 250.000 inhabitants Water demand: 221 liter per person per day

Reuse since 1960s: Irrigation city parks and sports fields Drinking water supply

4

Water treatment plants

Owned by City of Windhoek, privately operated

Drinking water treatment plants: Von Bach treatment plants New Goreangab Water reclamation plant Ground water boreholes

Waste water treatment plants: Gammams water care works Otjomuize water care works

5

Gammams & NGWRP

Gammams water care works: Bar screens, sedimentation Part stream: trickling filters / humus tanks Activated sludge, sedimentation Maturation ponds: 3 – 4 days

New Goreangab Water Reclamation Plant Storage, pre-ozone, coagulation, DAF Rapid Sand filtration, ozone, BACF, GAC, GAC Ultra Filtration, chlorination

6

Sand

fil

tratio

nC

hlor

inat

ion

Coa

gula

tion

& se

dim

enta

tion

Von

Bach

wat

er tr

eatm

ent p

lant

wat

erst

orag

eFe

Cl3

Was

te

wat

er

Mix

ing

Pre

ozon

e &

Floc

cula

tion

Flot

atio

nSa

nd

filtra

tionO

zona

tion

Activ

ated

ca

rbon

Ultr

a fil

tratio

n Chl

orin

atio

n

New

Gor

eang

ab w

ater

recl

amat

ion

plan

tW

ater

stor

age

Was

te

wat

er

ScreensPrim

ary settling

Activated sludge

Secondary settling

Solid waste,

sand & grit

Sludge

Effluent

Otjom

uize waste w

ater treatment plant

ScreensPrim

ary settling

Digesters

Activated sludge

Trickling filters

Hum

us tanks

Secondary settling

Maturation ponds

Dry

sludge

Solid waste,

sand & grit

Gam

mam

s Water C

are Works

Northern industrial Area

City area 1

City area 2

City area 3

City area 4

City reservoir

City irrigation

Ground water

Goreangab dam

Von Bach dam

Gammans river

Nat

ural

wat

er s

yste

m

7

Water quantity figures

Treatment plant Amount

Production Von Bach water treatment plant (2003) 11.3

Production Goreangab water Reclamation plant (2003) 5.2

- Share of waste water effluent (Gammams MP 8) 3.6

- Share of water from Gorangab dam 1.6

Production from the boreholes (2003) 3.7

Supply of city irrigation water (2003) 1.3

Inflow in Gammams Water Care Works (2004) 11.2

8

Resource for NGWRP

City of Windhoek sets demand for individual WTP

0

5,000

10,000

15,000

20,000

25,000

1-7-2002

1-10-2002

1-1-2003

1-4-2003

1-7-2003

1-10-2003

1-1-2004

1-4-2004

1-7-2004

1-10-2004

1-1-2005

1-4-2005

1-7-2005

1-10-2005

Goreangab m3/d Gammans m3/d Production loss m3/d

9

Risk Assessment

Monte-Carlo analysis (equal MSc Thesis) Cryptosporidium DOC Data from resource Expert guess with people from WINGOC

(conservative approach based on US EPA / literature)

10

Resource concentration

Twice a week measuring Since 1996 Microscopic count Recovery 30-70%

(proven other labs) Gammams MP8 dataset of

165, 41 possitive Highest measured = 20

oocysts / liter (recovery

50%) Gamma: a=0.2; b=33

11

Removal in treatment plant

average/p90 Pre-ozonation nothing Coagulation/flocculation/DAF 0.5Log/0.4Log RSF 0.7Log/0.5Log Ozonation 2Log/1.5Log BACF/GAC/GAC 0.5Log/0.3Log UF 3Log/2.5Log Chlorination nothing

12

Results

13

Scenario’s

Mixing in distribution 1:4

Scenario Average # of infections

# of illnesses

Basic situation 3.2*10-7 oocysts/litre

0.03 per year 0.01 per year

Failure of the UF 1.3*10-3 oocysts/litre

29.7 per year 9.9 per year

Failure of the ozonation 3.3*10-5 oocysts/litre

3 per year 1 per year

Peak concentration 0.05 oocysts/litre 12 per day 4 per day

Peak concentration + Ozone 4.95 oocysts/litre 1238 per day 413 per day

14

Traffic accidents (2004)

5 fatal traffic accidents in Windhoek 57 marked serious About 1 in 4 alcohol related

What is a risk? Comments on Monte-Carlo

15

Data Analysis

Performance of UF 5 racks (A-E) Piles of data Selection: temperature adjusted permeability K=(Flux*viscosity)/TMP 360 (L Pa s)/(m2 h Bar) = 1*10-12 m 3 continues periods of operation Excluding K’s below 100 Daily average, p10 and p90

16

Results (1)

Membrane Stacks total (01-04-2003 / 31-05-2003)

0

100

200

300

400

500

600

31 March 2003

07 April 2003

14 April 2003

21 April 2003

28 April 2003

05 May 2

003

12 May 2

003

19 May 2

003

26 May 2

003

02 June 2003

Per

mea

bili

ty, K

(L

Pa

s m

-2 h

-1 B

ar-1

)

0

200

400

600

800

1000

1200

10 percentile average90 percentileQperm [m3/s] QfeedD

Qfe

edD

an

d Q

per

m (

m3/

h)

17

Results (2)

Membrane Stacks total (01-08-2003 / 25-01-2004)

0

100

200

300

400

500

600

28 July 2003

25 August 2003

22 September 2003

20 October 2

003

17 November 2003

15 December 2003

12 January 2004

Per

mea

bili

ty, K

(L

Pa

s m

-2 h

-1 B

ar-1

)

0

200

400

600

800

1000

1200

10 percentile average90 percentileQperm [m3/h] QfeedD [m3/h]

Qfe

edD

an

d Q

per

m (

m3/

h)

18

Results (3)

Membrane Stacks total (01-05-2005 / 30-09-2005)

0

100

200

300

400

500

600

25 April 2005

23 May 2

005

20 June 2005

18 July 2005

15 August 2005

12 September 2005

10 October 2

005

Per

mea

bili

ty, K

(L

Pa

s m

-2 h

-1 B

ar-1

)

0

200

400

600

800

1000

1200

10 percentile average90 percentileQperm [m3/h] QfeedD [m3/h]

Qfe

edD

an

d Q

per

m (

m3/

h)

19

Data analysis, conclusions

No clear decrease in permeability Decrease of feed flow (flux) -> increase permeability Suspected effect of integrity checks Improve storage and handling of data Not just in retrospect Prediction method Often changes of settings Rack A = worse, B = best (10%)

20

Pilot plant research

21

Schematic

Drain

Feed Water

Feed water tank

Permeate water tank

Membrane module

Permeate

Backwash

Concentrate

HClNaOH & NaOCl

1 2

p10

p40 p50

p20

AV27

AV25

AV12AV11

AV23

AV30 AV31

AV33

22

Pilot plant research

Testing 40m2 membrane Comparing with 35m2 membrane module Water quality effects?

Parameter Experiment 1 Experiment 2 Experiment 3

Pilot plant – feed flow 4 m3/h 4.5 m3/h 5 m3/h

Pilot plant – flux 100 L/m2h 112.5 L/m2h 125 L/m2h

Start date 21-10-2005 9-11-2005 14-12-2005

End date 9-11-2005 14-12-2005 21-12-2005

Days of detailed research 26-10-20052-11-20059-11-2005

9-11-200516-11-200515-12-2005

16-12-200520-12-2005

23

Problems

Chemical pumps New chemical pump Algae brake through Carbon bag fibers? Many stops

24

Results (days of detailed research)

Results membrane performance

0

100

200

300

400

500

600

700

2-11-2005 11:00

2-11-2005 12:30

2-11-2005 14:00

2-11-2005 15:30

2-11-2005 17:00

2-11-2005 18:30

TM

P,

Flu

x an

d p

erm

eab

ilit

y

10

15

20

25

30

35

40

45

TMP [mBar]Flux [L m-2 h-1]Permeability (not adjusted for temperature) [L m-2 h-1 Bar-1 @ 20 °C]Permeability (adjusted for temperature) [L Pa s m-2 h-1 Bar-1]Temperature [°C]

Te

mp

era

ture

25

Results (2)

Results membrane performance

0

100

200

300

400

500

600

700

15-12-2005 8:00

15-12-2005 9:30

15-12-2005 11:00

15-12-2005 12:30

15-12-2005 14:00

15-12-2005 15:30

TM

P, F

lux

an

d p

erm

ea

bili

ty

10

15

20

25

30

35

40

45

TMP [mBar]Flux [L m-2 h-1]Permeability (not adjusted for temperature) [L m-2 h-1 Bar-1 @ 20 °C]Permeability (adjusted for temperature) [L Pa s m-2 h-1 Bar-1]Temperature [°C]

26

Results (3)

Results membrane performance

0

100

200

300

400

500

600

700

16-12-2005 9:00

16-12-2005 10:30

16-12-2005 12:00

16-12-2005 13:30

16-12-2005 15:00

16-12-2005 16:30

TM

P,

Flu

x an

d p

erm

eab

ilit

y

10

15

20

25

30

35

40

45

TMP [mBar]Flux [L m-2 h-1]Permeability (not adjusted for temperature) [L m-2 h-1 Bar-1 @ 20 °C]Permeability (adjusted for temperature) [L Pa s m-2 h-1 Bar-1]Temperature [°C]

27

Remarks

Many stops, irregular chemical cleans Little to now effects in water quality BW after chemical clean

0

2

4

6

8

0:00:00 0:05:00 0:10:00 0:15:00 0:20:00

pH

28

0

100

200

300

400

500

600

80 100 120 140

Flux (L/m2h)

TM

P (

mB

ar)

Rack D real plant (35m2) pilot plant (40m2)

Linear (Rack D real plant (35m2)) Linear (pilot plant (40m2))

29

Conclusions

40m2 membrane seems to perform better then 35m2 Effect of flux on (prevailing) fouling mechanisms

30

31

32

33

34