Practical reduction of arsenic from groundwater: - PowerPoint Presentation

1. Practical reduction of arsenic from groundwater: Two towns with two different solutions Devendra Borikar, Lindsay Ariss, Laura Zettler, Geoff Graham, Elliot Jones, Ryan DeVries, Stephen Burnett, Souleymane NdiongueApril 26, 2021OWWA Annual Virtual Conference, Ontario

2. Outline of PresentationIntroductionCase Study 1: - Objectives, set-up and resultsCase Study 2: - Objectives, set-up and resultsDiscussion of the similarities and differences found between the cases2

3. IntroductionArsenic (As) is classified as a human carcinogen (Health Canada, 2006).In January 2018, the MECP lowered the maximum acceptable concentration (MAC) of As in treated water from 25 µg/L to 10 µg/L.Any drinking water systems with As levels between 10-25 µg/L in their finished water need to upgrade treatment.3

4. Typical Treatment Technologies Precipitative and membrane processes - oxidation (chlorination) + filtration (microfiltration)Adsorptive processes - oxidation followed by adsorption on alumina/iron based adsorbentsIon exchange processes - uses anionic resins in chloride form, regenerated with salt - exchanges all negative ions with chloride ions4

5. ObjectivesOverall the goal is to reduce As in the treated water, using a process suitable for the existing system.Specific objectives: - To reduce As in the treated water to ≤ 5 µg/L (treatment goal). - To reduce iron (Fe) in the treated water as low as possible for aesthetic purposes.5

6. Case Study 1Town has population under 10,000Avg. As levels in well: 10.4 µg/LAvg. Fe levels in well: 0.06 mg/L Fe/As ratio: 5.8Existing treatment - chlorination and sequestering with CalciQuest (to keep Fe in dissolved form)Town has a sewer system6

7. Lowest dissolved As level achieved 6.5 µg/L at 4 mg/L Cl dose Raw water: - 0.37 mg/L total Fe - 0.34 mg/L dissolved FeAfter filtration:- ≤ 0.02 mg/L FeJar Testing Results: Optimizing Chlorine Dose7

8. Lowest dissolved As level achieved 7.6 µg/L 28% reductionTotal Fe in treated water increased from 0.35 to 0.85 mg/L. After filtration:- ≤ 0.02 mg/L FeJar Testing Results : Optimizing Ferric Chloride Dose8

9. Pilot Scale Set-up

10. Adsorptive media filter: - 0.47 µg/L As avg. (95% reduction)1 µm + 0.35 µm cartridge filters (in series): - 9.8 µg/L As avg. (4% reduction)Arsenic Reduction Effectiveness with Contact Chamber10

11. Adsorptive media filter: - ≤ 0.2 µg/L As avg. (> 98% reduction)1 µm and 0.35 µm cartridge filters (in series): - 10.4 µg/L As avg. (2% reduction)Arsenic Reduction Effectiveness without Contact Chamber11

12. Through chlorine oxidation (4 mg/L), As was reduced from 9.6 µg/L to 6.5 µg/L (32% reduction) during jar testing.Cartridge filters (1 µm and 0.35 µm) were ineffective at removing As (2-4% reduction).Adsorptive media filtration provided significant arsenic reduction (greater than 95%) to provide treated water arsenic levels ≤ 0.5 µg/L. Case Study 1: Conclusions12

13. Case Study 2Town has a population under 1,000.Avg. As levels in well : 11.4 µg/LAvg. Fe levels in well : 0.59 mg/L Fe/As ratio: 51.8Existing treatment - Chlorination and sequestering with sodium silicate (to keep Fe in dissolved form)Town does not have sewer system13

14. Pilot Scale Set-up

15. Lowest dissolved As level achieved:2.05 µg/L at 3 mg/L chlorine dose (81% reduction)4 mg/L was used for pilot as it was current plant dosage to meet CT requirements.Jar Testing Results: Optimizing Chlorine Dose15

16. Addition of ferric chloride had a positive effect on As reduction.Increased total Fe levels, however filtered iron was still ≤ 0.02 mg/L.Jar Testing Results: Optimizing Ferric Chloride Dose16

17. Cartridge filter series (50-5, 1 and 0.35 µm):-Avg. As concentration ≤ 3.7 µg/L (72% reduction)- ≤ 0.02 mg/L Fe Arsenic Reduction Effectiveness with Contact Chamber17

18. Cartridge filter series (50-5, 1 and 0.35 µm):3.5 µg/L As avg. (67% reduction)Fe levels were reduced to 0.02 - 0.04 mg/LContact chamber provided no significant change in performance Arsenic Reduction Effectiveness without Contact Chamber18

19. Arsenic Reduction Effectiveness without Contact Chamber19Cartridge filter series changed to (75-25, 5 and 1 µm):≤ 5.6 µg/L As avg. (44 % reduction)≤ 0.05 mg/L Fe

20. Chlorine oxidation (4 mg/L) reduced As level to 2.4 µg/L in treated water (80% reduction) [Jar Test 1].Ferric chloride oxidation had a positive effect on As reduction [Jar Test 2].On-site pilot experiment’s results summary: Case Study 2: Conclusions20Experiment No. Chlorine Contact ChamberDepth filter (µm)Cartridge filters (µm)Treated As levels (µg/L)1, 2, 3Yes50-51, 0.353.74, 5, 6No50-51, 0.353.56, 7No75-255, 15.6

21. Case Similarities21The chlorine contact chamber did not provide a significant change in arsenic reduction Jar testing was effective for optimizing dosages prior to pilot testingThe addition of ferric chloride provided additional reduction of arsenicRaw arsenic levels: Town 1 - 10.4 µg/LTown 2 - 11.4 µg/L

22. Case Differences22 Iron levels differed: Town 1 - 0.06 mg/L Fe (Fe:As ratio 5.8)Town 2 - 0.59 mg/L (Fe:As ratio 51.8)Town 1 had a sewer system while Town 2 did not (limiting potential treatment technologies)Treatment technologies therefore differed: Town 1 – Chlorination followed by adsorptive mediaTown 2 – Chlorination followed by 50-5 µm depth filter and 1 & 0.35 µm cartridge filters

23. Lessons Learned23In spite of similar As concentrations, suitable treatment technologies differed based on the existing site-specific conditions.The process is dependant on the raw water chemistry and not one size fits all.On-site pilot testing provided confirmation of selected treatment technologies.This approach was especially helpful to consultants as site-specific data was gathered and info for scalability of the selected treatment could be provided.

24. Ontario Regulation 169/03. Ontario Drinking Water Quality Standards. Available from https://www.ontario.ca/laws/regulation/0301692. Ontario MOE. Technical support document for Ontario drinking water standards, objectives and guidelines. Ontario Ministry of the Environment, Ontario, 2003. Available from http://www.ontla.on.ca/library/repository/mon/6000/10313601.pdfReferences24

25. Thank you! Questions? dborikar@wcwc.caVisit our website for more information on our pilot testing services!25