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CONVENTIONAL OXIDATION TREATMENTS FOR ARSENIC REMOVAL WITH CHLORINE DIOXIDE, CHLORINE, POTASSIUM PERMANGANATE AND MONOCH

2° International Conference “Metals and Related Substances in Drinking water – COST ACTION 637. CONVENTIONAL OXIDATION TREATMENTS FOR ARSENIC REMOVAL WITH CHLORINE DIOXIDE, CHLORINE, POTASSIUM PERMANGANATE AND MONOCHLORAMINE. F. Gialdini, S. Sorlini

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CONVENTIONAL OXIDATION TREATMENTS FOR ARSENIC REMOVAL WITH CHLORINE DIOXIDE, CHLORINE, POTASSIUM PERMANGANATE AND MONOCH

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  1. 2° International Conference “Metals and Related Substances in Drinking water – COST ACTION 637 CONVENTIONAL OXIDATION TREATMENTS FOR ARSENIC REMOVAL WITH CHLORINE DIOXIDE, CHLORINE, POTASSIUM PERMANGANATE AND MONOCHLORAMINE F. Gialdini, S. Sorlini Department of Civil Engineering, Architecture, Land and Environment, University of Brescia (Italy) M. Belluati Caffaro Spa, Brescia, Italy

  2. My PhD Research Present work is included in my PhD research. The topics are: • As oxidation by means of conventional oxidants • As oxidation by means of AOPs • As oxidation in a real plant (by means of biological filtration) • Management of treatment for As removal and residues produced in these treatments

  3. ARSENIC IN THE ENVIRONMENT • Widespread in soils, water and air • Natural sources and human activities • Inorganic forms (H3AsO3, H2AsO4-, HAsO42-) predominant in groundwater • As(III) predominant in deep reducing waters

  4. DIFFUSION OF ARSENIC IN ITALY

  5. ARSENIC AND HUMANS • Employed since antiquity as poison • Employed as medicament in the past • Toxicological studies have shown effects of acute and chronic poisoning • Chronic effects: skin, lungs, bladder and kidneys cancers • Not carcinogenic chronic effects: skin hyperpigmentation, keratosis and cardiovascular disorders (“blackfoot disease” (Taiwan)) LOAEL: 10-20 μg As/kg/d NOAEL: 0.4-0.9 μg As/kg/d Consumption of 14-65 μg As/kg/d

  6. REGULATIONS IARC (International Agency for Research on Cancer) • Arsenic is classified as «carcinogen of 1st Group» sure carcinogen for humans WHO Guidelines 2006 (World Health Organisation) • Recommended value for inorganic As in drinking water: 10 µg/L EPA Indications 2001 (Environmental Protection Agency) • Maximum concentration level (MCL) for As in drinking water: 10 µg/L European Directive 98/83/EU (DWD) • Limit for Arsenic in drinking water is 10 μg/L, founded on toxicological considerations and risk analysis Legislative Decree 31/01 (Italian regulation) • Arsenic limit is 10 μg/L, as implementation of Drinking Water Directive 98/83/EU

  7. ARSENIC REMOVAL PROCESSES As(V) REMOVAL Yes Yes Yes Yes As(III) REMOVAL No Yes Yes No • TREATMENTS • Precipitation + filtration • Absorption on GFH • Membranes (NF and RO) • Ion Exchange Some treatments can remove As(V) better than As(III) It is necessary to oxidize As(III): As(III) + ox  As(V) + 2e- • CLASSIFICATION OF OXIDATION PROCESSES • Chemical ( chlorine, chlorine dioxide, potassium permanganate, hydrogen peroxide, AOPs, etc.) • Fisical (UV radiations) • Biological (microorganisms)

  8. AIMS OF THIS RESEARCH • To evaluate As(III) oxidation yields in demineralised water by means of four conventional chemical oxidants: • KMnO4 • NaClO • ClO2 • NH2Cl • To study the effect of pH and oxidant/As(III) ratio (Rox/As(III)) on As oxidation in demineralised water • To evaluate the effect of natural water on As(III) oxidation yields by means of the above oxidants

  9. MATERIALS AND METHODS TESTS ON DEMINERALISED WATER (As(III)in = 300 μg/L e 50 μg/L) TESTS ON REAL WATER (As(III)in =15 μg/L e 50 μg/L) Analytical method As: stripping chronopotentiometry and HGAAS

  10. MATERIALS AND METHODS: REAL WATER Groundwater chemical characteristics Water from a deep acquifer (-150 m)

  11. RESULTS: DEMINERALISED WATER - KMnO4 [As(III)]in = 50 μg/L • Oxidation yields > 95% already with Rox/As(III) = 1 • Oxidation yields about 100% with a higher oxidant dose (Rox/As(III) = 3) • Very fast As oxidation (about 10 min) • Low influence of As initial concentration • No influence of pH [As(III)]in = 300 μg/L

  12. RESULTS: DEMINERALISED WATER - NaClO [As(III)]in = 50 μg/L • Oxidation yield about 80% with Rox/As(III) = 1 • Oxidation yields of 100% with a higher reagent dose • Fast As oxidation (1 – 2 minutes) • Low influence of pH: • higher pH improves As oxidation • influence decreases with excess of oxidant [As(III)]in = 300 μg/L

  13. RESULTS: DEMINERALISED WATER – NH2Cl e ClO2 [As(III)]in = 50 μg/L NH2Cl • With NH2Cl: • yields > 70% with Rox/As(III) = 1 and about 100% with Rox/As(III) = 3 only after 2 days contact time • With ClO2: • yields > 50% with Rox/As(III) = 3 only after 2 days • yields > 80% withRox/As(III) = 3after 6 days • With NH2Cl e ClO2: • slow reaction very long contact time • very high influence of the pH: higher yields for lower pH ClO2

  14. COMPARISON AT pH = 8 IN DEMINERALISED WATER [As(III)]in = 50 μg/L Rox/As(III) = 1 Rox/As(III) = 3 As Oxidation [%] As Oxidation [%] Time [min] Time [min] • Potassium permanganate is the best oxidant • Chlorine is an excellent oxidant if it is overdosed • Monochloramine is a quite effective oxidant and increase its oxidant power with higer dose • Chlorine dioxide is moderately effective in As oxidation

  15. RESULTS: DEMINERALISED WATER Arsenic oxidation yields after 5 minutes contact time [%]

  16. RESULTS: REAL WATER [As(III)]in = 15 μg/L • NaClO and KMnO4 are the best oxidants • Generally, yields worse when initial As(III) concentration increases (except for KMnO4) • In real water, ClO2 shows better results than demineralized water • NH2Cl is low effective also in real water (yields < 20%) [As(III)]in = 50 μg/L

  17. RESULTS: REAL WATER Tests with ClO2 with and without Fe(II) and test with chlorite

  18. CONCLUSION • INFLUENCE OF pH • pH is not influent with KMnO4 • NaClO, ClO2 e NH2Cl efficiency is influenced by pH • OXIDANT DOSES • An excess of oxidant dose increases the yields of NaClO, ClO2 and NH2Cl • An excess of KMnO4 dose is not necessary because oxidation yields are already excellent when it is dosed with the stoichiometric dose • INITIAL ARSENIC CONCENTRATION • The different initial As(III) concentration doesn’t significantly influence the oxidants behavior • COMPARISON BETWEEN DEMINERALISED AND REAL WATER • Similar behaviors for all oxidants except for ClO2 which provides better As(III) oxidation yields in real water

  19. Thank you!

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