Hetch Hetchy Treatability at the Sunol Valley Water Treatment Plant

Transcription

1 Operated by the San Francisco Public Utilities Commission Hetch Hetchy Treatability at the Sunol Valley Water Treatment Plant Annual Technology Transfer Workshop November 13, 2013 Enio Sebastiani, P.E., D5, T4 SFPUC Water Quality Division 1

2 Outline SVWTP Improvements HH at AE and Local Water Quality Comparison HH Filtration Results Coagulation Chemistry Mobile Pilot Plant Pilot and Laboratory Testing Full-scale Testing Results Treatment Recommendations Conclusions 2

3 SVWTP Improvements for HH Carbon dioxide injection at headworks (2003) Alkalinity adjustment (2003) SVWTP headworks caustic addition Rock River lime/tesla CO 2 /SVWTP CO 2 Filter-to-waste (2003) 3

4 Other SVWTP Improvements Fifth flocculation/sedimentation train (2013) Deep-bed filters (2013) 48 inches of anthracite over 12 inches of sand Washwater Recovery Basins Basin #3 (Phase 1 in 2003) Basin #4 (Phase 2 in 2013) 4

5 Sunol Valley Water Treatment Plant 5

6 Hetch Hetchy at AE and Local Water Comparison Water Quality Parameter Hetch Hetchy at Alameda East Calaveras/San Antonio Alkalinity (mg/l CaCO 3 ) 13 (±3) 103 (±19) ph 9.5 (±0.3) 8.6 (±0.3) Conductivity (µs/cm) 29 (±6) 314 (±67) Temperature ( F) 55 (±4) 60 (±5) Zeta-Potential (mv) to to TOC (mg/l) 1.3 (±0.3) 4.3 (±0.3) 6

7 HH Filtration Results

8 HH Filtration Results

9 HH Filtration Results

10 HH Filtration Results

11 HH Filtration Results

12 Coagulation Chemistry Particles in raw water are 0.1 to 100 microns in size Colloidal particles have a negative surface charge and do not settle out naturally TOC may be a significant contributor to negative charge in water Negative charge DECREASES with: Lower ph Higher alum dose Higher Cat-C dose 12

13 Coagulation Chemistry Alum = Al 2 (SO 4 ) 3 *14H 2 O The aluminum (Al 3+ ) in alum combines with hydroxide ions (OH - ) in water to produce one or more aluminum species: Al(OH) 2+ Al(OH) 2 + Al(OH) 3(s) Al(OH) 4 - Composition of aluminum species depends on alum dose and ph Effective ph range for alum is 5.5 to

14 Coagulation Chemistry Alkalinity provides a measure of resistance to change in ph with the addition of an acid or base Alkalinity = [HCO 3- ] + 2[CO 2-3 ] + [OH - ] [H + ] 1 mg/l of alum consumes 0.5 mg/l of alkalinity as CaCO 3 14

15 Coagulation Chemistry Charge neutralization: lower alum dose & ph Sweep floc: higher alum dose & ph Tools for determining optimal coagulant doses charge neutralization: zetapotential sweep floc: jar tests 15

16 Coagulation Chemistry Water Quality Parameter Raw Water Zeta-Potential (mv) Target Coagulated Zeta-Potential (mv) Hetch Hetchy at Alameda East Calaveras/San Antonio to to to to

17 Mobile Pilot Plant 17

18 Mobile Pilot Plant 18

19 Mobile Pilot Plant 19

20 Pilot and Laboratory Testing ph & Alkalinity Adjustment (July to Oct 2002) High & low alum dose strategies developed with carbon dioxide feed Flocculation Mixing Energy (Apr to May 2003) Confirmed literature: higher flocculation mixing intensities for direct filtration and lower for conventional treatment Tapered flocculation mixing intensities of 45, 35, 25, and 15 sec -1 recommended for SVWTP Filter Aid Dose (July to Aug 2003) Recommended initial LT-Dose of 20 ppb for High Alum Dose Recommended initial LT-Dose of 100 ppb for Low Alum Dose 20

21 Pilot and Laboratory Testing Zeta-Meter for Dose Optimization (July to Sept 2004) Investigated and refined doses for charge neutralization Spring Runoff Treatment (June 2005) Average HH raw water quality different: alkalinity lower (9.8 vs 12.5 mg/l); turbidity higher (0.8 vs 0.3 NTU); ZP lower (-21 vs -18 mv); and TOC higher (1.9 vs 1.5 mg/l) Required doses within the same range as previous studies Filter Media Size Pilot Testing (Aug to Oct 2007) Evaluated three different media size configurations All three configurations consisted of deep-bed, dual-media: 48 anthracite on top of 12 sand Filtration successful at 8 gpm/ft 2 for both HH and East Bay supplies 21

22 Full-scale Testing Tested at SVWTP for first time in more than 10 years between August and November 2005 Objectives Confirm High and Low Alum Dose treatment strategies Determine CO 2 doses required for coagulation ph adjustment 22

23 Full-scale Testing Influent Average Hetch Hetchy Water Quality Conditions ph: 9.2 Conductivity: 33.5 µs/cm Alkalinity: 10.8 mg/l as CaCO 3 Cl 2 residual: 0.86 mg/l Zeta-Potential: mv 23

24 Full-scale Testing at High Alum Dose Alum Dose = 7.5 mg/l, Cat-C Dose = 0.3 mg/l, Coagulation ph = 7.1 UFRV: ~7,300 gal/ft 2 Filter effluent turbidity: 0.06 NTU Filter effluent particles: 29.9 per ml Effluent turbidity increase observed ~5 hours after effluent particle counts increase observed 24

25 Full-scale Testing at Low Alum Dose Alum Dose = 3.0 mg/l, Cat-C Dose = 0.6 mg/l, Coagulation ph = 6.5 UFRV: ~10,500 gal/ft 2 Filter effluent turbidity: 0.05 NTU Filter effluent particles: 3.5 per ml No effluent turbidity or particle count increase observed during filter run 25

26 High Alum Dose Recommendation Alum: 7.5 mg/l Cat-C: 0.3 mg/l Filter aid: 35 ppb Coagulation Zeta-Potential: -9.0 mv (±2.9 mv) Coagulation ph Target: 7.1 (±0.2) No Carbon Dioxide 26

27 Low Alum Dose Recommendation Alum: 3.0 mg/l Cat-C: 0.6 mg/l Filter aid: 25 ppb Coagulation Zeta-Potential: -4.7 mv (±1.2 mv) Coagulation ph Target: 6.5 (±0.2) Carbon Dioxide dose of 8 to 14 mg/l 27

28 Conclusions HH water treated at SVWTP from 2005 to 2013 on 10 separate occasions. Treatment successfully produced a combined filter effluent less than 0.10 NTU on all occasions. The preferred treatment strategy for optimal filtration is a low alum dose with carbon dioxide for ph control. Zeta potential measurements are a reliable tool for coagulation control. 28

29 Questions? 29