University of Illinois at Urbana-Champaign Water Quality Management in Distribution Systems Vernon L. Snoeyink University of Illinois Alabama-Mississippi AWWA Education Workshop January

University of Illinois at Urbana-Champaign 2 Distribution System Problems Excessive precipitation of calcium, magnesium, and aluminum Corrosion of iron, copper, and lead, and release of corrosion products Dissolution of cement mortar lining Manganese accumulation and release Excessive biological growth Consider water quality, energy & materials

University of Illinois at Urbana-Champaign 3 Design and Operating Factors Causing Water Quality Degradation Disease outbreaks often caused by faulty distribution systems, e.g. cross connections Excessive residence times: distribution system and premises Negative pressure transients: Pressure waves owing to rapid valve closure, etc Ref: “Drinking Water Distribution Systems: Assessing and Reducing Risks”, The National Academies Press, Washington, DC 2006.

University of Illinois at Urbana-Champaign 4 Calcium Carbonate Precipitation Decreases Pipe Diameter and Increases Energy Use Control: Langelier Index, LI, useful Calcium carbonate precipitation potential, CCPP, best Calculate CCPP with RTW/Tetra model from AWWA Requires Ca, alkalinity, pH and temperature as inputs Acceptable CCPP: a few mg/L (also good for cement mortar)

University of Illinois at Urbana-Champaign 5 Al Post-Precipitation Increases Required Energy and Decreases Quality Alum is added to destabilize particles Basic reaction: Al 2 (SO 4 ) 3 + 6HCO 3 -  2Al(OH) 3 + 6CO 2 + 3SO 4 2- Very important: If not at equilibrium before distribution, or if the pH decreases during distribution, precipitation of Al(OH) 3 can occur Halton, Ont

University of Illinois at Urbana-Champaign 6 Al Post-Precipitation Increases Energy Loss Increase in roughness increases the energy, S, required to deliver a quantity Q. Hazen-Williams Equation Q = CA(0.55)D 0.63 S 0.54 Where Q = flow rate, A = pipe x-sectional area, D = pipe diameter, and S = energy slope and C = Hazen-Williams Coefficient

University of Illinois at Urbana-Champaign 7 Al Post-Precipitation Increases Energy Loss and Affects Water Quality For Halton, a C factor decrease from 135 to 85 yields a Q reduction of 37% for a fixed energy input (ie headloss) Deposits in pipes give bacteria a place to grow. As deposits increase, expect more problems with microbial growth

University of Illinois at Urbana-Champaign 8 Al Post-Precipitation and Dirty Water Complaints: Lake Erie Supply AlAl + Fe Fe

University of Illinois at Urbana-Champaign 9 Control pH to Prevent Al Post-Precipitation

University of Illinois at Urbana-Champaign 10 Post-Filter Al Depends on Temperature Chicago Example

University of Illinois at Urbana-Champaign 11 Control of Residual Aluminum Control pH, but remember the impact on total dissolved solids Alternative coagulant, e.g. FeCl 3 Remove deposit Dissolve by using water undersaturated with Al(OH) 3 Pigging

University of Illinois at Urbana-Champaign 12 Aluminum Silicate Case History San Luis Obispo, CA Al from coagulation and silica in the source water precipitate in the distribution system Al + silicate  Al silicate solid Precipitation kinetics are too slow to go to completion in the water treatment plant C factor: range (Probably lower)

University of Illinois at Urbana-Champaign 13 San Luis Obispo, CA, 2000 Aluminum Silicate scale 30” line 8” line Solution: Change to ferric coagulant and pig lines

University of Illinois at Urbana-Champaign 14 Post-Precipitation of Magnesium Silicate Austin, TX Mg 2+ + silicate  Mg silicate solid Add lime to remove calcium Finished water: –SiO 2 = 7-8 mg/L, Mg = 75 mg/L as CaCO 3. pH –Magnesium hydroxy silicate, lizardite or chrysotile. ( Ref: Price et al., Proc WQTC,Amer. Wat. Wks. Assoc., Denver, CO, 1997) Cold Hot

University of Illinois at Urbana-Champaign 15 Control of Magnesium Silicate Deposit Formation Use chemical equilibrium model 1.Reduce Mg, but not easy to change the process 2.Reduce Si, but difficult to do 3.Reduce and control pH: Best choice

University of Illinois at Urbana-Champaign Iron in Distribution Systems Corrosion, Tubercles and Iron Release 16

University of Illinois at Urbana-Champaign Available cross-section for flow – MWRA (Boston) Unlined Cast Iron Pipes Boston # 1 Boston # 3 Boston # 5 Boston # 2Boston # 4Boston # 6 17

University of Illinois at Urbana-Champaign Mississippi Unlined Cast Iron 18

University of Illinois at Urbana-Champaign A “Good” Tubercle has a Non-Porous Outer Layer From Sontheimer, Ref

University of Illinois at Urbana-Champaign A “Poor” Scale has a Porous Outer Layer After Sontheimer, Ref. 1 20

University of Illinois at Urbana-Champaign Scale Structure: Champaign IL Tubercle Corrosion scales are porous deposits usually with a shell-like layer Permeability of shell-like layer is important Reservoir of Fe(II) ions exists in the scale interior Composition Shell-like layer: Magnetite (Fe 3 O 4 ) and goethite (  -FeOOH) Porous Interior: Fe(II) and some Fe(III) compounds Shell-like Layer Porous Interior 21

University of Illinois at Urbana-Champaign Formation of a Tubercle At C: ½O H e  H 2 O At A: Fe /2 H 2 O + ¼ O 2  Fe(OH) 3(s) + 2 H + Fe(III) ppt At A: Fe  Fe e Anode Cathode N. B.: Must balance charge at A and C Continued Fe (II) flux at A, Oxidized iron crust develops 22

University of Illinois at Urbana-Champaign 4 e + O H +  2 H 2 O Electron/Charge Flow in a Tubercle DO Present Fe 2+ Fe Shell-like layer Tubercle growth from mass increase Fe H 2 O  Fe(OH) 2(s) + 2 H + e e e X-X- X-X- X-X- 23

University of Illinois at Urbana-Champaign Iron Release – Effect of DO (NIWC Pipes) Fe (Total) in mg/L DO in mg/L Stagnation Time (hrs) 24

University of Illinois at Urbana-Champaign Iron Release from Corrosion Scales Flowing Water with oxidants Stagnant Water with oxidants “Anoxic layer” Prolonged Stagnation Oxidant supply restored Fe 2+ DO 25

University of Illinois at Urbana-Champaign Iron Release from Corrosion Scales PhysicalChemical As Fe 2+ Oxidation Particle Abrasion or Erosion Nucleation Red Water “Red Water” formation 26

University of Illinois at Urbana-Champaign Case History: MWRA pH and alkalinity are very important –MWRA (Boston) Case History –Low alkalinity (2x10 -4 ; 10 mg/L as CaCO 3 ) resulted in highly variable pH 7-10 –Result: colored water (yellow) and high lead values –Pipe loop results: 27

University of Illinois at Urbana-Champaign MWRA Rack 1 28

University of Illinois at Urbana-Champaign Important Considerations Some procedures to harden and decrease permeability of soft scales: –Constant pH (pH and alkalinity control) –Minimize stagnation –CCPP control –Orthophosphates –Polyphosphates can be used to mask color 29

University of Illinois at Urbana-Champaign 30 Biofilms Biofilms: microorganisms that grow in slimy layers attached to the pipe wall Example: Champaign-Urbana, IL –Ammonia ~1-1.5 mg/L, add chlorine to produce ~3 mg/L of NH 2 Cl as Cl 2 ; free ammonia in distribution system

University of Illinois at Urbana-Champaign 31

University of Illinois at Urbana-Champaign 32 Causes of Biofilms in Distribution Systems Ammonia and biodegradable organic matter promote the growth of biofilms. For example, the reactions NH O 2  NO H + + H 2 O and Organics + O 2  CO 2 + H 2 O + … provide the energy for the bacteria to grow.

University of Illinois at Urbana-Champaign 33 Effect and Control of Biofilms Effects Increase energy required Deplete DO and produce odors (e.g. H 2 S) Produce NO 2 - and deplete chlorine residual Growth of opportunistic pathogens Control Minimize NH3 and biodegradable organics Provide good in-plant biological treatment

University of Illinois at Urbana-Champaign 34 Final Thoughts 1.Water quality changes depend on water quality and the type of pipe material. 2.Control water quality to reduce energy required to distribute water, control biofilms and minimize metal ion release 3.Strategy to solve distribution quality problems –Compare influent and effluent quality –Monitor energy loss –Characterize scales –Bench tests or pipe loop studies may be required

University of Illinois at Urbana-Champaign Iron References 1.Sontheimer, H., Chapt in Internal Corrosion of Water Distribution Systems, AWWARF, Denver, CO, Lytle, D. et al. Effect of Ortho- and Polyphosphates on Iron Particles. J AWWA, 94(10), 87, ‘02. 3.Lytle, D. et al. The Effect of pH and DIC on the Properties of Iron Colloidal Suspensions. AQUA, 52, , Sarin, S. et al….Iron Release from … Cast-Iron Pipe. J AWWA, 95(11),85, Sarin, S., et al. Iron Release …: Effect of Dissolved Oxygen. Water Research,38(5), , March Sarin, P. et al… Model for.. Iron Release and Colored Water Formation. J Environ Engin,130(4), 364,