Tails( sic ) from the Old Rat in the Barn

1. Tails(sic) from the Old Rat in the Barn David Jenkins, Professor Emeritus University of California at Berkeley MWEA Seminar, April 29, 2008

2. Disclaimer This is not the “DJ” that most people know This talk has nothing to do with: • Filamentous microorganisms • Activated sludge • Nutrient removal

3. This is What I’m Going to Talk About

4. DJ Bio • King Edward VI School, Aston, Birmingham (1948-1954) • Birmingham Univ., B.Sc., Applied Biochemistry (1954-1957) • Univ. of Durham, King’s College, PhD, Public Health Engineering (1957-1960) • UC Berkeley, Civil and Environmental Engineering (1960-1999)

5. Topics • The case of the missing sulfite and the phantom chlorine residuals • Bad rocks on my beach • Mystery pipe scaling with no anions • A galvanicmystery • 0 ≠ zero • H2S and spina bifida

6. My Approach to Problems • Look at all data • Read the literature • Go back to first principles • Think laterally • Keep an open mind • Listen to everyone but believe nobody! • Get help if you need it

7. Objective of Talk Demonstrate these approaches with examples from my professional experience

8. The Case of the Missing Sulfite and the Phantom Cl2 Residuals • The scene of the crime! A Deox 2000 Analyzer measuring Cl2 and bisulfite residuals on tertiary filtered effluent. • Observations Although SO2 was being added in excess of the stoichiometric requirement, no residual sulfite could be detected and on occasion even Cl2 residuals were detected.

9. The Deox 2000 The Deox 2000 continuous Cl2 analyzer relies on the continuous amperometric measurement of iodine concentration to measure both residual Cl2 and bisulfite concentrations

10. Deox 2000 flow sheet KI I2and I- KH(IO3)2 Inlet Filter To Waste Sample Line Amperometric Cell Dechlorinated Effluent

11. The Deox 2000 Continuous flows of standard KH(IO3)2 solution and excess KI solution are mixed and fed at constant rates through the amperometric cell of the Deox 2000. 12 H+ + 2 (IO3)¯ + 5 I¯ (xs)  6 I2 + 6 H2O + (xs) I¯ With KI in excess this results in a mixture of I2 and I¯ flowing to the Deox 2000

12. The Deox 2000 Bisulfite detection HSO3- + I2 + 2 H2O  2 I- + SO42- + 4 H+ Cl2 detection Cl2 + 2 I-  I2 + 2 Cl-

13. The Mystery Solved (Part I) • Oxidation of HSO3- with O2 (DO) by biofilm in HSO3- sample line consumes HSO3- between sampling point and Deox 2000 result. • Result: no HSO3-

14. Demonstrating This: Bisulfiteoxidation by O2 2 HSO3- + O2 + 2 H2O  2 SO42- + 2 H+ So 1 M/L HSO3- should consume 0.5 M/L O2 and produce 1 M/L SO42- and 1 M/L strong acid (or reduce total alkalinity by 2 M H+/L, or 100 mg CaCO3/L)

15. Results

16. The Mystery Solved (Part II) • Biofilm sloughs off and partially blocks sample flow to Deox 2000. • This increases I2 concentration • Result: reads out as an increase in Cl2 concentration.

17. Demonstrating This: • Pieces of biofilm identified on Deox 2000 sample line filter • Problems with low HSO3- and phantom Cl2 residuals encountered more frequently in hot weather than when cool, and when cleaning frequency for sample line filter was low.

18. Bad Rocks on my Beach • Urea (fertilizer) production plant located near tidal bluffs. • Groundwater, contaminated by urea and ammonia, flows towards a pebble beach below bluffs • Concrete-like rocks form at water’s edge • Rocks interfere with fishing nets used by indigenous people

19. Beach rocks

20. Beach rocks

21. Objectives • Determine cause(s) of rock formation • Determine whether the cause(s) is associated with the contaminated groundwater • Determine methods for preventing rock formation

22. This is a Langlier Index Problem (in Disguise)! • Ammonia and urea get into the soil and groundwater • Carbon dioxide produced by soil microorganisms dissolves in soil water producing carbonic acid CO2 + H2O  H2CO3 • Ammonia reacts with carbonic acid producing ammonium bicarbonate • NH3 + H2CO3  NH4HCO3

23. Urea hydrolyses to ammonium carbonate CO(NH2)2 + H2O  (NH4)2CO3 Carbonic acid reacts with ammonium carbonate to form ammonium bicarbonate H2CO3 + (NH4)2CO3 2 NH4HCO3 The net result of all this is that the groundwater ammonia and alkalinity (HCO3-) concentrations both increase

24. Ground water movement Ammonia N = 100 mg/L The site Ammonia N = 1000 mg/L Bluffs Beach Pilings Beach rocks Ocean

25. “Beach Rock” Composition Mineral Sample 1(%) Sample 2(%) Quartz 46 46 K-feldspar 3 7 Plagioclase 36 26 Calcite 0 7 Aragonite 0 8 Monohydrocalcite 9 0 Clay minerals 6 6

26. Major Components of Sea Water Component Concentration (mM/L) Na+ 466 Mg2+ 56 Ca2+ 11 K+ 9.7 Cl- 535 SO42- 28 HCO3- 2.3 Br- 0.8

27. Beach Rock Formation • High pH, high alkalinity groundwater flows towards beach and meets the high Ca “sea” water. • Denser sea water forms a wedge under lower density “fresh” groundwater. • Calcium carbonate precipitates at the groundwater/sea water interface. • With pebbles (aggregate) this forms concrete.

28. Beach Rock Formation Bluffs and beach erode and expose beach rock at water’s edge Sea Groundwater Land, t =0 Land, t =t Beach rock

29. Last Steps • Assume a 1:1 mixture of groundwater and sea water at the interface • Calculate averages for total alkalinity, Ca2+ • Back calculate average pH from Alk = Ct(α1 + 2α2) + Kw/[H+] – [H+] using equilibrium constants corrected for temperature and salinity (ionic strength)

30. Last Steps • Calculate CO32- from: Alk = Ct(α1 + 2α2) + Kw/[H+] – [H+] • Solve for Ct, then for [CO32-] = Ctα2 • Determine Ksp for CaCO3(s) = [Ca2+][CO32-] • Compare Ksp with observed [Ca2+][CO32] and determine whether over-, under- saturation or equilibrium.

31. Under Equiulib x Slightly over Highly over CaCO3 Saturation Results x Area of study

32. Mystery Pipe Scaling with No Anions • Where: Reno NV apartment buildings at extremity of water distribution system • What: Pitting corrosion of hot water copper piping combined with erosion corrosion (high water velocity) • Pits occurred in regions where turbulent flow had eroded a soft white scale (precipitate)

33. The Scale • To solve murders you must determine how many bodies there are and then identify all of them • Analysis of dry scale (% by weight): Cations: Al = 9.6; Si = 37.4 Anions: NONE!!!

34. Because electroneutrality must be conserved the anions must have been: Lost during analysis Not detected by analysis The only anion that fits both of these categories is hydroxide. Hydroxides dehydrate to oxides during drying and oxides are not detected by anion analysis

35. … so it looks like we have a mixture of aluminum oxide (alumina, Al2O3) and silicon dioxide (silica, SiO2)… lets check it out! Al = 27, Si = 28, O = 16, Al2O3 = 102, SiO2 = 60 If Al = 9.6%, then Al2O3 = (102/54) x 9.6 = 18.1% If Si = 37.4% then SiO2 = (60/28) x 37.4 = 80.1% And 80.1 + 18.1 = 98.2% so this accounts for virtually all of the dry weight and we have a scale consisting of about 80% silica and 20% alumina.

36. How is This Possible? • Reno water supply is from Truckee River which comes from a granite basin and contains siliceous material • Reno water treatment plant used alum coagulation / flocculation then sedimentation but NO FILTRATION…so alum-flocculated silica particles could escape into the distribution system • Apartments were at extremities of distribution system and flocs settled out and were washed into the apartment water lines

37. Corrosion Cells Come in Strange Disguises Corrosion of steel tendons used for post-tensioned/prestressed concrete floors at the Watergate Apartments (Emeryville CA)

38. The Situation • Apartment concrete floors strengthened by post-tensioned steel cables coated in grease, wrapped in paper and fitted through a jack at either end of the floor slab. • Floor is poured then cables are pulled and the tensioned cables are held under tension by the jacks. • Jacks are covered with a concrete plug for aesthetic purposes

39. Post-Tensioned Cable Side of building Concrete plug Post tensioning jack Post tensioning directions Post tensioning cable covered with grease Paper wrap on cable

40. Edge of floor slab

41. What Happened? • Shortly after completion aesthetic concrete plugs began to spall off the buildings revealing the jacks • Inspection showed the jacks had moved outwards indicating tendon failure • This was confirmed and examination of the tendons showed damage consistent with stress corrosion cracking

42. Edge of floor slab

43. Stress Corrosion Cracking • Not classical corrosion (like rusting) since it occurs at the cathode (not the anode). It is the result of hydrogen formation within the structural lattice of a metal that literally blows it apart. • Cathodic reaction is: e- + H+ ½ H2(g)

44. An Electrochemical Cell is Needed for Corrosion to Occur Electrochemical cell consists of: • Anode (electrons produced) • Cathode (electrons consumed) • Internal circuit (electrons flow) • External circuit (ions flow)

45. Electrochemical Cell Internal circuit e- Cathode Anode External circuit (Needs aqueous environment)

46. Where are These 4 Components? • Building constructed on piles containing re-bar which is tied to re-bar in floor (internal circuit) • Piling re-bar electrical potential differs from one pile to another so floor re-bar varies with location in slab (anode and cathode) • During tendon assembly, wrapping paper tears and allows contact between re-bar and steel tendon at some locations • At other locations wrapping paper tears but tendon and re-bar do not touch leaving a moist layer between them (external circuit)

47. The hidden cell Cathode Wrapping paper Grease Steel tendon Failure site Floor Anode Rebar External connection Internal connections Piles

48. Solution Existing construction • Replace steel tendons as they fail with slightly smaller tendons wrapped in plastic sheathing. This eliminates internal and external circuits New construction • Use plastic wrapped tendons and tie all rebar, tendons and slab conduit together to ensure constant potential throughout metal in slab and piles. This eliminates internal and external circuits anode and cathode.

49. 0 ≠ Zero …or in plain English, a reading of 0 does not necessarily mean there is nothing there!

50. DO Control Procedure • Aeration basin blowers controlled by in situ Zulig DO probes (old) • Daily calibration of Zulig probes by handheld YSI Model 55 DO probe • YSI probe can be calibrated on site for 100% saturation but not for 0% saturation