Chlorine Dioxide Application for Microbial Control on Polyamide Membranes During Seawater Desalination

Transcription

1 American Water Works Association 2009 Water Quality Technology Conference Chlorine Dioxide Application for Microbial Control on Polyamide Membranes During Seawater Desalination Tai J. Tseng, Robert C. Cheng, Dian Tanuwidjaja, and Kevin L. Wattier Long Beach Water Department November 17, 2009

2 Presentation Outline Long Beach Overview Research Initial Bench Studies Full Scale Studies Conclusion 2009 WQTC LBWD 2

3 Presentation Outline Long Beach Overview Research Initial Bench Studies Full Scale Studies Conclusion 2009 WQTC LBWD 3

4 Long Beach Water Department California s 5th most populous city (~500,000 residents) 70,000 AF of drinking water per year 8,000 AF of reclaimed water per year Operate largest GW treatment plant in US 900+ miles of drinking water lines 750+ miles of sewer lines 2009 WQTC LBWD 4

5 LBWD s Resource Mix Reclaimed 6% Conservation 14% Imports 42% Reclaimed 12% Conservation 15% Imports 30% Groundwater 38% Groundwater 33% Desal 10% 2009 WQTC LBWD 5

6 LBWD s Desalination Program A $20 M, 10-year investment Leverage various partnerships for technical input and other support Federal / State / Local Funding Pretreatment NF 2 or RO Post treatment / Distribution Under Ocean Floor Intake and Discharge Prototype UV/ClO 2 for disinfection and biofouling control DBP Control Stability of Disinfectant Residual Mitigation of WQ impacts due to integration of new source 2009 WQTC LBWD 6

7 Presentation Outline Long Beach Overview Research Initial Bench Studies Full Scale Studies Conclusion 2009 WQTC LBWD 7

8 Background Looking for ways to help meet primary disinfection while minimizing O&M costs through controlling fouling. UV Energy Recovery Disinfectant Cartridge Filter Energy Recovery 1 st Pass NF 2 nd Pass NF Pre-Treatment Cartridge Filter ClO 2 1 st Pass NF 2 nd Pass NF 2009 WQTC LBWD 8

9 Initial Bench Studies Initial Bench Testing using SEPA Cell System operated in recirculation mode. ClO 2 generated using Cl 2 gas & NaClO WQTC LBWD 9

10 Initial Bench Studies Rapid deterioration in salt rejection after ClO 2 exposure Salt rejection decreased by ~ 50% in 4 days suggest the ClO 2 was rapidly destroying the PA membrane. Concentration of ClO 2 (mg/l) 5.0 ClO2 100% 4.5 Rejection 90% % % % % % % % % 0.0 0% 11/16 11/17 11/18 11/19 11/20 11/21 Rejection 2009 WQTC LBWD 10

11 Initial Bench Studies Many ways to generate ClO 2. 2NaClO 2 + Cl 2 (g) 2ClO 2 (g) + 2NaCl. 2NaClO 2 + HOCl 2ClO 2 (g) + NaCl + NaOH. 5NaClO 2 + 4HCl 4ClO 2 (g) + 5NaCl + 2H 2 O. Electrolytic generation. Depending on the generation method, free Cl 2 may be present. The key is to generate ClO 2 without generating free Cl WQTC LBWD 11

12 Initial Bench Studies Revised Bench SEPA Cell testing Operated in once-thru mode. Acid / chlorite method ( free Cl 2 free) WQTC LBWD 12

13 Initial Bench Studies SEPA Cell testing using ClO 2 generated via acid generation method over 14 days Salt rejection was 100% 90% stable thru the 14 80% day test period. 70% Provided 60% 50% reasonable 40% assurance to 30% proceed to testing 20% 10% on full-scale 0% Rejection (%) Rejection ClO2 id /1 7/6 7/11 7/16 7/21 l ClO 2 Residual (mg/l) 2009 WQTC LBWD 13

14 Initial Beach Studies Parallel SEPA Cell testing Chlorite System operated in once-thru mode. 0.5 mg/l of sodium chlorite was feed to one cell while the other acted as a control WQTC LBWD 14

15 Initial Bench Studies 7.E-06 MF permeate MF permeate mg/l chlorite Permeate quality essentially identical 7.E-06 MF permeate MF permeate mg/l chlorite Flux, m/s 6.E-06 6.E-06 5.E-06 5.E-06 4.E-06 8/17 8/19 8/21 8/23 8/25 8/27 8/29 8/31 9/2 9/4 Permeate Conductivity, us/cm Flux decline follows similar patterns /15 8/20 8/25 8/30 9/4 SEPA Cell testing using sodium chlorite shows no added benefit but also no noticeable degradation 2009 WQTC LBWD 15

16 Presentation Outline Long Beach Overview Research Initial Bench Studies Full Scale Studies Conclusion 2009 WQTC LBWD 16

17 Full Scale Studies Closer examination of cartridge filter ΔP Cartridge Filter Train 1 Pre-Treatment Initially No ClO 2 Started ClO 2 Stopped ClO 2 Cartridge Filter Train 2 Initially With ClO 2 Stopped ClO 2 Started ClO WQTC LBWD 17

18 Full Scale Studies Short experiments to evaluate ClO 2 T1 DP T2 DP T1 Flow T2 Flow /24 04/25 04/26 04/27 04/28 Delta Pressure (psi) 04/29 04/30 Stopped ClO2 Injection Started ClO2 Injection Stopped ClO2 Injection Started ClO2 Injection Flow (GPM) 2009 WQTC LBWD 18

19 Full Scale Study 20 With ClO2 No ClO 2 Addition Started ClO 2 Addition Without ClO2 CF Differential Pressure (psi) /28 2/16 4/7 5/27 7/16 9/ WQTC LBWD 19

20 Full Scale Study With ClO2 Without ClO2 Membrane Differential Pressure (psi) 12 No ClO 2 Addition Started ClO 2 Addition /28 2/16 4/7 5/27 7/16 9/ WQTC LBWD 20

21 Full Scale Study Specific Salt Rejection Di-valent salts such as Ca 2+ and SO 4 2- were rejected at greater than 99%. Mono-valent salts were rejected near 90% initially but did show some decline over time. Percent Removal in First Pass Calcium Sodium Sulfate Chloride 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 3/28 5/17 7/6 8/ WQTC LBWD 21

22 Full Scale Studies Performance of SWRO and NF Membranes with ClO 2 Average ClO 2 exposure ~ 0.6 mg/l. Total exposure ~ 350 ppm-hours for SWRO. Total exposure > 1000 ppm-hours for NF. Conductivity (ms/cm) NFNF SWRO WQTC LBWD 22

23 Full Scale Study Conductivity Temperature Temp or Cond ( o C or ms/cm) No Apparent Damage by ClO 2 Changed O-Rings Plant shut down without flushing Water quality deteriorated 0 3/28 4/12 4/27 5/12 5/27 6/11 6/26 7/11 7/26 8/10 8/25 9/ WQTC LBWD 23

24 Full Scale Study King Lee Technologies Cleaning Data Sheet Commercial Information Technical Information Manufacturing Test Specifications Date Element Rec'd 10/16/2009 Element Manufacturer FilmTec Net Pressure 72 Psig Client Long Beach Water Co. Element Model NF Recovery 15% Contact Tai Tseng/ Jason Allen Productivity, GPD 9500 Temperature 77 PO# DPW %Rejection 97.00% Test Solution 2000 ppm MgSO4 Date S/N Cleaner Soak Time Circ Time Differential Pressure DP Perm Pressure Pp Feed Pressure Pc Feed Temp Tf Perm Flow Fp Conc Flow Fc Feed Cond. Cf Perm Cond. Cp Norm GPD Norm %Rej % Nominal Product. 19-Oct F Pretest % 39.3% 19-Oct F Pretest % 40.2% 19-Oct F Pretest % 51.1% 4-Nov F Hi Pressure % 28.3% Notes: S/N Weight # Autopsy of F ; brown layer on membrane. Foulant laid down in patterns looking like channeling or pressure vessel drained. F Foulant gel like at feed end.dry at concentrate end. Membrane embossed. Both CV and CR dye test were negative. F F WQTC LBWD 24

25 Presentation Outline Long Beach Overview Research Initial Bench Studies Full Scale Studies Conclusion 2009 WQTC LBWD 25

26 Conclusions Generation method for ClO 2 is key. Bench results show that direct chlorite addition did not degrade the membranes, however, it also did not show flux enhancement. ClO 2 showed definitive benefits in terms of controlling organic-related fouling across both the cartridge filters as well as the membrane system. ClO 2 was applied to two types of membranes and for the NF90 membranes, it was successful over 1,000 ppm-hours without noticeable damage to the membranes WQTC LBWD 26

27 Next Steps Salt passage did increase in the system but autopsy results show no visible oxidative damage to PA membranes. Continuing our investigation into the cause of the salt passage. Re-started the chlorine dioxide test on a new set of membranes to confirm previous findings WQTC LBWD 27

28 Acknowledgement Funding partners: US Bureau of Reclamation Ca Dept of Water Resources Los Angeles Dept of Water and Power LBWD WQ Lab & Research Staff 2009 WQTC LBWD 28

29 Questions 2009 WQTC LBWD 29