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: 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

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

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 Log/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)

17. Results (2)

18. Results (3)

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

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
End date
Days of detailed research

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

24. Results (days of detailed research)

25. Results (2)

26. Results (3)

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

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