Practical period in Windhoek General (plant) information Data analysis Pilot plant research Risk assessment

General

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

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

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

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

Resource for NGWRP City of Windhoek sets demand for individual WTP

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)

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

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

Results

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

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

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

Results (1)

Results (2)

Results (3)

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%)

Pilot plant research

Schematic

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 21-12-2005 Days of detailed research 26-10-2005 2-11-2005 16-11-2005 15-12-2005 16-12-2005 20-12-2005

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

Results (days of detailed research)

Results (2)

Results (3)

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

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