Coagulation Optimization: Improving the heart of the water treatment process

Transcription

1 Coagulation Optimization: Improving the heart of the water treatment process Gwyn Norman 1, Ian Douglas 1,2, Jeff Beaty 3, Josh Elliott 1,2 1 City of Ottawa Drinking Water Services 2 University of Toronto, Department of Civil Engineering 3 CH2M HILL Canada Ltd Canadian National Conference on Drinking Water Treatment Technology and Processes Coagulation/Filtration October 27, 2014

2 Coagulation: The Heart of the Process City of Ottawa Britannia & Lemieux Island WPP s Alum + Acid Activated SiO2 Cl 2 Cl 2 NH 3 NaOH HFS Anthracite Sand Ottawa River Coagulation & Flocculation Sedimentation Dual-media Filtration CT Disinfection (Clearwell) ph Adjustment & Chemical Mixing

3 Source Water Characteristics ph Turbidity NTU Dissolved Organic Carbon 6 8 mg/l UV cm 1 City of Ottawa Montreal Alkalinity Colour Temperature mg/l TCU 0 28 o C

4 Evolution of coagulation strategy 1932 enhanced coagulation, experiments with Ferric & Alum 1977: activated silica in both treatment plants 1990 s: jar testing & pilot plant studies 1997: acidified alum 1998: implemented new silica activation process 1998 coagulant optimization study (Ferric, Alum, Acid + Alum) 2008 established critical control limits for coagulation Coagulation Optimization Project: Experiments with alum, ferric, alum/ferric blends, Zeta potential measurements, polymers, etc.

5 What are our coagulation objectives?

6 Coagulation optimization project: objectives coagulation road map for optimum dose/ph strategy for monitoring the coagulation process (parameters and frequency) recommended response to raw water changes or challenging plant conditions comparison of alternative coagulants & polymers appendix with experimental results (tables, graphs) for future reference

7 Acquiring Knowledge

8 Literature Review University Expertise Operating Experience Conferences & Workshops Consultants MOE Optimization Guide

9 How do we account for changes in our source water quality?

10 1 Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec Raw Water Quality Temperature Month Temperature (C o )

11 50 Ottawa River Daily Alkalinity Levels 2012 (mg/l CaCO3) Britannia Water Purifiaction Plant Intake Alkalinity (mg/l) Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec

12 1 Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec Raw Water Quality Turbidity Month Turbiditry (NTU)

13 1 Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec Raw Water Quality UV 254 Month UV254 (cm 1 )

14 1 Jan 1 Feb 1 Mar 1 Apr 1 May 1 Jun 1 Jul 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec Raw Water Quality ph Month ph

15 Why change it? It works.

16 Coagulation objectives: i) Optimal capture and removal of suspended particles ii) Improved dissolved organic carbon (DOC) removals which in turn reduce the formation of disinfection by-products (DBPs) iii) Improved settling performance to handle higher plants loads during cold water conditions

17 What is the strategy? Jar Testing Pilot Plant Full Scale Plant

18 Jar Testing Procedure Add acid (ph correction), add coagulant 1min Rapid 100 RPM 15min stage 1 flocculation (30RPM) 15min stage 2 flocculation (15 RPM) Paddles up, Settle for 30 min Sample T=30

19 Importance of accurate jar testing: tools & tips temperature bath ph adjustment jar mock up verify micropipette duplicates randomize raw water data

20 What are the best tools to measure optimum coagulation?

21 How do we measure coagulation? Turbidity? UV 254? DOC? Zeta Potential? THM & HAA Formation Potential Dissolved Metals

22 Easiest & Most Accurate? UV 254

23 Is UV 254 a good indicator of organic removal? 10.0 UV 254 & DOC measurements in jar testing & raw water 8.0 DOC (mg/l) R² = n = UV 254 (cm 1 )

24 Coagulation road map for optimum dose/ph

25 4.0 Alum Dosing Strategy Turbidity & UV 254 at a fixed ph of 6.0 to determine optimal Alum dose in raw water Turbidity (NTU) UV254 (cm 1) 0.12 Turbidity (NTU) UV 254 (cm 1 ) Alum Dose (mg/l)

26 Alum Dosing Strategy Turbidity & UV 254 response at a fixed Alum dose of 36 mg/l in raw water at a ph range of (Cold Water Conditions) Turbidity (Cold Water) UV254 (Cold Water) 0.16 Turbidity (NTU) UV 254 (cm 1 ) ph

27 Physics: Impact of mixing speed and duration, order of addition, neat vs. dilute

28 1.4 Mixing Speed & Duration Fixed Alum Dose = 36 mg/l, Fixed ph = Turbidity (NTU) Super Low Mixing Low Mixing Medium Mixing Jar Testing Mixing Plant Mixing Jar Testing + Plant Mixing Mixing Speed & Duration Combinations

29 Mixing Speed & Duration 0.12 Fixed Alum Dose = 36 mg/l, Fixed ph = UV 254 (cm 1 ) Super Low Mixing Low Mixing Medium Mixing Jar Testing Mixing Plant Mixing Jar Testing + Plant Mixing Mixing Speed & Duration Combinations

30 Can we further reduce Disinfection by-product (DBP) precursors?

31 HAA & THM (µg/l) Disinfection by-productformation (Alum vs. Ferric) DBP formation & UV 254 response dosing optimum & supersaturated Alum & Ferric in raw water HAA THM UV Alum Alum Ferric Ferric 36 mg/l 54 mg/l 8 mg Fe/L 12 mg Fe/L Coagulant & Dose

32 What other coagulants can we try?

33 AluFer Dosing Strategy 0.15 UV 254 : Fixed AluFer 3330 = 3.27 mg Al/L & 3.0 mg Fe/L, Alum 36 mg/l, and Ferric 12 mg Fe/L, ph range = (cold water) Alufer 3.27 mg Al /L mg Fe /L Alum 36 mg/l Ferric 12 mg Fe/L 0.10 UV 254 (cm 1 ) 0.05 Raw Water UV 254 = 0.28 cm ph

34 Polymer performance vs. activated silica

35 Polymer Selection versus current SiO Turbidity: Alum Dose = 36 mg/l, Fixed ph 5.8, Polymer = mg/l, water temp = 5.5 o C 3.0 Turbidity (NTU) None Si02 A 1883 A 1883 A 1883 A 1883 C 492 C 492 C 492 C 492 Floc Aid Dose (mg/l)

36 Polymer Selection versus current SiO UV 254 : Alum Dose = 36 mg/l, Fixed ph 5.8, Polymer = mg/l, water temp = 5.5 o C UV 254 (cm 1 ) None Si02 A 1883 A 1883 A 1883 A 1883 C 492 C 492 C 492 C 492 Floc Aid Dose (mg/l)

37 Where do we go from here? Narrow down the sweet spot amalgamating datasets from each coagulant and giving operators the ultimate coagulation road map Take a closer look at AluFer, including the potential for more organic removal & lower DBPs Trial each optimum coagulant dose & ph conditions in the pilot plant Try other potential polymers versus activated silica

38 Questions? Thank-you

39 Order of Addition of Chemicals Fixed Alum Dose = 36 mg/l, Fixed ph = Turbidity (NTU) Acid Before Alum Alum Before Acid Alum & Acid at the same time Order of Addition Acid, then 50% 50% Alum dose, Alum dose, 1 then Acid, then min delay, then remaining 50% remaining Alum Alum dose (1 dose min after initial Alum Dose) Acid, then 50% Alum dose, 5 min delay, remaining 50% Alum dose

40 Order of Addition of Chemicals 1.5 Fixed Alum Dose = 36 mg/l, Fixed ph = Turbidity (NTU) Acid Before Alum Alum Before Acid Alum & Acid at the same time Order of Addition Acid, then 50% Alum dose, 1 min delay, then remaining Alum dose 50% Alum dose, then Acid, then remaining 50% Alum dose (1 min after initial Alum Dose) Acid, then 50% Alum dose, 5 min delay, remaining 50% Alum dose

41 Order of Addition of Chemicals 1.5 Fixed Alum Dose = 36 mg/l, Fixed ph = Turbidity (NTU) Acid Before Alum Alum Before Acid Alum & Acid at the same time Order of Addition Acid, then 50% Alum dose, 1 min delay, then remaining Alum dose 50% Alum dose, then Acid, then remaining 50% Alum dose (1 min after initial Alum Dose) Acid, then 50% Alum dose, 5 min delay, remaining 50% Alum dose

42 Order of Addition of Chemicals 0.12 Fixed Alum Dose = 36 mg/l, Fixed ph = UV 254 (cm 1 ) Acid Before Alum Alum Before Acid Alum & Acid at the same time Order of Addition Acid, then 50% Alum dose, 1 min delay, then remaining Alum dose 50% Alum dose, then Acid, then remaining 50% Alum dose (1 min after initial Alum Dose) Acid, then 50% Alum dose, 5 min delay, remaining 50% Alum dose