Introduction

1. STRATEGIES TO MONITOR AND REDUCE RESIDUAL ALUMINIUM IN MUNICIPAL DRINKING WATER TREATMENT SYSTEMS.Denis Bérubé* and Caetano C. Dorea***Environmental Health Centre, Health Canada, Ottawa, Canada**Dept. of Civil Eng., Univ. of Glasgow, Glasgow, UK

2. Introduction • Aluminium-based coagulation (e.g. alum, PACl, PAS) aims at: • reducing turbidity • reducing disinfection by-product (DBP) precursors • Residual aluminium must also be minimized: • Possible direct health effects • Possible indirect health hazards (problems with disinfection) • Problems in distribution • Customer satisfaction/perception (Camelford) • Good engineering practice

3. Recommended limits for residual Al concentration are variable (50 to 200 μg/L) • Recommended limits in Canada: 100 to 200 µg/L • Difficulties to meet these recommendations are largely due to seasonal changes in temperature • Temperature range: < 1 °C to > 20 °C • Temperature affects all treatment stages (coagulation, flocculation, sedimentation and filtration) • Well operated and maintained WTPs should not experience problems Morris and Knocke (1984) Van Benschoten et al. (1990 and 1994) WHO (2004)

4. Objectives • Residual aluminium occurrence throughout WTP treatment trains • Seasonal variations of residual aluminium • Strategies for residual aluminium reductions

5. Sampling programme • Three sites (A, B and C) using different Al-based coagulants were selected • Sampling was performed over winter and summer seasons • Parameters: • Aluminium (ICP-MS analysis) • Total (acid leachable, pH < 2.0) • Dissolved (0.45 μm Supor membrane) • NOM • UVA-254 nm • TOC and DOC • Turbidity • pH and temperature • Others (F, hardness, alkalinity, etc).

6. 1ary disinfection (sodium hypochlorite) pH adjustment (H2SO4) pH adjustment (NaOH & CO2) Aluminium sulfate 2ary disinfection (chloramine) Activated silica dosing Fluoridation Static mixing basins (flocculation stage) Plate settlers Dual media filtration Before flocculation After flocculation After filtration Raw water Before filtration Before distribution After coagulation Intake (raw water) Distribution (treated water) • Samples were collected at every treatment stages, e.g.:

7. Site A • Polyaluminium chloride (PACl-1) was used all year • Low NOM, low turbidity, moderate alkalinity • Pre-chlorination at the intake • No pH adjustment (~ 8.0) • Two filter configurations (two sampling points AF-a and AF-b) • Intervention: change of coagulant (PACl-2)

8. Particulate Al Total Al ≈ Dissolved Al Raw water After coag. Before floc. After floc. Before filter After filt.-a After filt.-b Before dist.

10. Redissolution in filters

11. Backwashed filter: low particulate Al End of run (< 24 hrs): breakthrough

12. Site B • Aluminium sulphate (AS) + coag. aid year-round • Moderate NOM, low turbidity, low alkalinity • Coagulation pH 7.3  6.0 (w/ H2SO4) • Intervention: precipitation by pH adjustment

13. pH 7.3 pH 6.0 pH 9.0 Precipitation?

14. Temperature-controlled jar-tests (0.1, 5.0 17.0 °C)

16. 88 μg/L 56 μg/L 44 μg/L 118 μg/L 66 μg/L 55 μg/L

18. Site C • Pre-hydroxylated aluminium sulfate (PHAS) • Polyaluminium silicate sulfate (PASS): T < 8 °C • High NOM, moderate/high turbidity, high alkalinity • No pH adjustment • Intervention: change of coagulant (PASS) - already in practice

20. Discussion and conclusions • Residual Al levels can be affected in both summer and winter seasons • Residual Al occurred mainly as dissolved Al • Year round residual Al control is possible • Seasonal monitoring of residual Al throughout WTPs give valuable insight most appropriate intervention • Operational features (e.g. filter maintenance) also play an important role • Jar-tests were useful and versatile tools in assessment of different strategies

21. Acknowledgements • Health Canada authorities • Office of the Chief Scientist • Bureau of Water, Air and Climate Change • Bureau of Environmental Health Science and Research • The staff and authorities (municipal and provincial) of the different sites.