Bench-Scale Testing for Controlling Desalinated Seawater Quality Tai J. Tseng, Robert C. Cheng, Cynthia Andrews-Tate, and Kevin Wattier Long Beach Water Department November 17, 2008 2008 WQTC, Cincinnati, OH 1
LBWD s s Seawater 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 $2 M project $1 M funded by DWR through Prop 50 2
Elements of Interest in Seawater H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Nb Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 3
Select Water Quality Parameters Raw seawater Br mg/l 72 TOC mg/l 0.35 ph units 7.6 TDS mg/l 34130 Alk-T mg/l-caco 3 100 Ca mg/l 424 Mg mg/l 1110 SO 4 mg/l 2393 DI DW DSW ND 0.6 0.07 0.11 0.12 2.0 7.4 7.3 8.3 7.0 60 260 3.6 15 117 ND 0.3 28 ND <0.5 7.2 ND <10 50 4
Concerns with Seawater Quality Higher-than than-normal normal levels of bromide Disinfection byproducts (DBP) formation skewed towards brominated compounds? Residual stability issues associated with brominated acids? Perform bench-scale DBP tests Corrosion low minerals content Leaching of minerals? Perform corrosion tests Evaluate corrosion indices 5
Bench-Scale DBP Testing Will desalinated waters, by itself or in a blend, cause residual instability? DBP compliance issues? Evaluated 6 different waters deionized water (DI) - control existing distribution system water (DSW) 100% desalinated seawater (DW) by NF2 process 25% DW 75% DSW 50% DW 50% DSW 75% DW 25% DSW 6
Bench-Scale DBP Testing Test sequence Free chlorine residual at 2.5 mg/l at end of 45 min. Blends adjusted to ~ ph = 8 using phosphoric acid NH 3 added for a 5:1 Cl 2 :NH 3 ratio (t = 0) Each time and blend sampled from individual headspace-free bottle, held in the dark Analyzed for ph, Cl 2, NH 3, THM, HAA9 Analyzed at t = 0.5, 1, 2, 4, 8, 12, 24, 48, 72, 96, 120 hrs 7
3.0 Chlorine Residual Results 2.5 DI Cl 2 (mg/l) 2.0 1.5 DSW 100% DW 50% DW 25% DW 1.0 75% DW 0.5 0.0 0 12 24 36 48 60 72 84 96 108 120 Time (hrs) 8
40 35 DSW TTHM Results 30 TTHM (µg/l) 25 20 15 25% DW 50% DW 75% DW 10 5 0 0 12 24 36 48 60 72 84 96 108 120 Time (hrs) 100% DW DI 9
BDCM Results 20 18 16 BDCM level noted as level of concern BDCM (µg/l) 14 12 10 8 6 4 2 0 0 12 24 36 48 60 72 84 96 108 120 Time (hrs) DW DSW 75% DW 25% DW 50% DW DI 10
HAA9 Results 18 16 DSW HAA9 (µg/l) 14 12 10 8 6 4 25% DW 75% DW 50% DW 2 0 100% DW DI 0 12 24 36 48 60 72 84 96 108 120 Time (hrs) 11
DBP Testing Results Chlorine degradation 60% less Cl 2 in DW as compared to DSW over 120 hours Blending stabilized the effect (13% decrease in 50% DS) TTHM production No increase observed with desalinated seawater BDCM levels all less than 18 µg/l HAA9 production No increase observed with desalinated seawater 12
Corrosion indices Corrosion Testing general prediction based on source water quality advantage simple to use disadvantage not completely accurate Bench-scale tests marble test gauge of CaCO 3 saturation pipe section test expose water to actual pipes better predictor than indices, but still batch tests Pipe-loop test allows for flow-through testing of waters on different pipe materials provides most accurate results of all tools 13
LBWD Pipe Materials Cast iron (CI, oldest) used until 1950s 225 miles Asbestos cement (AC, no longer used) available from 1940 until 1990s 400 miles Ductile iron (DI, currently used) available from 1970s on 203 miles 14
Corrosion Indices Langelier Saturation Index (LSI) Indicator of whether conditions favorable for CaCO 3 precipitation f(ca,, ph, TDS, T, Alk-T) Most other common corrosion indices based on calcium carbonate Calcium Carbonate Precipitation Potential (CCPP) Ryznar Saturation Index (RSI) Aggressiveness Index (AI) for AC pipes only Calculated with Rothberg Tamburi Windsor (RTW) model 15
Comparison of Indices Condition LSI RSI CCPP AI Corrosive < - 0.5 > 6.0 < -5 <12.0 Passive -0.5 - +0.5 6.0-5 - 0 Scaling > 0.5 < 6.0 > 0 > 12.0 16
LSI is representative of other indices 25 Corrosion Index (CCPP, Ryznar or AI) 20 15 10 5 0 CCPP y = 14.89(LSI) - 0.67 R 2 = 0.9411 Aggressiveness Index y = 1.01(LSI) + 11.81 R 2 = 0.9989 Ryznar Saturation Index y = -0.93(LSI) + 8.23 R 2 = 0.787-5 -10-1.0-0.5 0.0 0.5 1.0 1.5 2.0 LSI 17
Marble Test SM2330c Over- or undersaturation with CaCO 3 Measures ph of sample before and after CaCO 3 addition 300 mg CaCO 3 :300 ml sample Would expect results to correlate well with LSI 18
LSI vs. Marble Test Corrosion Control = ph adjustment (8.0) 1.0 LSI Marble Test Index (LSI or Marble Test) 0.5 0.0-0.5 DSW Acceptable LSI level for distribution system operations DS 25% DS 50% DS 75% -1.0 Marble test = ph (before CaCO 3 addition) ph (after CaCO 3 addition) -1.5 19
LSI vs. Marble Test Corrosion Control = OPO 4 addition (ph = 7.5) 1.0 LSI Marble Test Index (LSI or Marble Test) 0.5 0.0-0.5-1.0 Acceptable LSI level for distribution system operations DS 25% DS 50% DS 75% -1.5 Marble test = ph (before CaCO 3 addition) ph (after CaCO 3 addition) -2.0 20
Pipe Section Test AWWA C104 (Ductile iron pipe) Section 5.2 Testing of Seal Coat protocol Tested sections of ductile-iron iron pipe seal-coated and unsealed up to 15, 12 x 4 4 pipes determined that minimum 5 sections required for statistically significant results Tested for 72 hrs changed water every 24 hrs analyzed for ph, T, alkalinity, TDS, Ca, Mg, Cl,, SO 4 Provides indication of the stability of water as related to pipe material 21
Pipe Section Test Setup 22
Water Conditioning Aerate desalinated water (DW) Allows for CO 2 absorption, lower ph from > 9 to ph 7 Add 40 mg/l of baking soda to provide 25 mg/l alkalinity as CaCO 3 Blend DW with DSW at following ratios 75:25, 50:50 or 25:75 Final ph adjustment as needed 23
Comparison of LSI for DSW Sealed and Unsealed DIP 1.4 1.2 1.0 Unsealed DIP Sealed DIP 0.8 LSI 0.6 0.4 0.2 Acceptable LSI for distribution system operations 0.0 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 24
Comparison of LSI for Various Waters Unsealed DIP 6.0 5.5 5.0 4.5 4.0 3.5 DI 3.0 LSI 2.5 2.0 1.5 DSW 50% DW, ph 8 50% DW, OPO 4 1.0 0.5 0.0-0.5-1.0 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 25
Comparison of LSI for Various Waters Sealed DIP 6.0 5.5 5.0 4.5 4.0 3.5 3.0 LSI 2.5 2.0 1.5 1.0 0.5 0.0-0.5 DI DSW 50% DW, ph 8 50% DW, OPO 4-1.0 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 Day 1 Day 2 Day 3 26
Corrosion Testing Results Indices Aggressiveness index, RSI, and CCPP correlated well with LSI Indicated that up to 50% DS blend should be acceptable Bench-scale tests marble tests correlated well with LSI pipe section tests provides better indication of behavior of water with specific pipes Pipe material Seal-coating provides better protection against corrosion than no seal coat 27
Unresolved Issues/Future Work Microbial growth issues Exposure of existing pipe to new water blends Reaction of various residential plumbing materials (copper, galvanized) to new water blends Pipe loop testing for 12 months 28
Acknowledgement 29
www.lbwater.org 30