Transcript A Few Tales from the Old Rat in the Barn

Tails(sic) from the Old Rat in
the Barn
David Jenkins,
Professor Emeritus
University of California at
Berkeley
MWEA Seminar, April 29, 2008
Disclaimer
This is not the “DJ” that most people
know
This talk has nothing to do with:
• Filamentous microorganisms
• Activated sludge
• Nutrient removal
This is What I’m Going to Talk About
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)
Topics
• The case of the missing sulfite and the
phantom chlorine residuals
• Bad rocks on my beach
• Mystery pipe scaling with no anions
• A galvanic mystery
• 0 ≠ zero
• H2S and spina bifida
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
Objective of Talk
Demonstrate these approaches
with examples from my
professional experience
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.
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
Deox 2000 flow sheet
KI
I2 and I-
KH(IO3)2
Inlet Filter
To Waste
Sample Line
Amperometric
Cell
Dechlorinated Effluent
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
The Deox 2000
Bisulfite detection
HSO3- + I2 + 2 H2O  2 I- + SO42- + 4 H+
Cl2 detection
Cl2 + 2 I-  I2 + 2 Cl-
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-
Demonstrating This:
Bisulfite oxidation 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)
Results
Parameter
Predicted Measured
change
mM/L
mM/L
Bisulfite decrease
0.015
Sulfate increase
0.015
0.014
DO decrease
0.015
0.019
Alkalinity decrease
0.030
0.023
pH value
6.54
6.55
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.
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.
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
Beach rocks
Beach rocks
Objectives
• Determine cause(s) of rock
formation
• Determine whether the cause(s) is
associated with the contaminated
groundwater
• Determine methods for preventing
rock formation
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
• 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
Ammonia N = 100 mg/L
Ammonia N = 1000 mg/L
Bluffs
The site
Ground
water
movement
Beach
Pilings
Ocean
Beach
rocks
“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
Major Components of Sea Water
Component
Na+
Mg2+
Ca2+
K+
ClSO42HCO3Br-
Concentration (mM/L)
466
56
11
9.7
535
28
2.3
0.8
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.
Beach Rock Formation
Bluffs and beach erode and expose beach
rock at water’s edge
Sea
Groundwate
rLand, t =0
Land, t =t
Beach rock
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)
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-, undersaturation or equilibrium.
CaCO3 Saturation Results
Under
x
x
Equiulib
Slightly over
Highly over
Area of study
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)
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!!!
•
•
•
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
… 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.
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
Corrosion Cells Come in
Strange Disguises
Corrosion of steel tendons used for
post-tensioned/prestressed
concrete floors at the Watergate
Apartments (Emeryville CA)
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
Post-Tensioned Cable
Side of building
Concrete plug
Post tensioning jack
Post tensioning
cable covered
with grease
Paper wrap
on cable
Post
tensioning
directions
Edge of floor slab
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
Edge of floor slab
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)
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)
Electrochemical Cell
Internal circuit
eAnode
External circuit
(Needs aqueous environment)
Where are These 4 Components?
• Building constructed on piles containing rebar 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)
The hidden cell
Cathode
Wrapping paper
Grease Steel tendon
Floor
Rebar
Internal connections
Piles
Anode
Failure site
External
connection
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.
0 ≠ Zero
…or in plain English, a reading
of 0 does not necessarily mean
there is nothing there!
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
YSI Model 55 DO probe
Plant Upset
•
•
•
•
Black mixed liquor
Sulfide odor and detection in effluent
Turbid, high BOD , TSS effluent
DO in aeration basin apparently high
but air supply low
• All the symptoms of insufficient
aeration but with apparently high DO
Air Supply and Mixed Liquor DO
DO, mg/L and Air supply, ft3 /lbcBOD5
3
2.5
DO Concentration
2
1.5
1
Air supply
0.5
0
Date, 2004
Relationship of YSI Model 55 DO Probe
Readings to True DO Readings
YSI Zero
YSI Saturation
True Zero
( Winkler)
Increasing DO concentration
True Saturation
(Winkler)
Air Supply and Time of Winkler
DO Calibration
1.2
Winkler calibration
1
0.8
Air supply, ft
3
/lb cBOD 5
of YSI DO probe
0.6
0.4
0.2
0
Date, 2004
H2S and Spina Bifida –It’s a Gas!
• Trunk sewer carrying high BOD
canning wastewater runs down
residential street.
• Significant H2S generation especially
during warm weather.
• City seals manholes so H2S travels up
house laterals and vent pipes.
• Residents sue City claiming H2S passes
thru’ toilets into bathroom and causes
high incidence of spina bifida.
My Job as Expert
• What is rate and amount of H2S that can
pass thru’ water in toilet to bathroom ?
You are
here
Sewer vent
To house
lateral
P-trap
A (Not Trivial) Diffusion Problem
• H2S in water exists as H2S(aq), HS- and
S2-, all of which diffuse at different rates
• Assume water pH = 5, so that only H2S,
with the lowest diffusion coefficient, is
present
• Each time toilet is flushed, diffusion
starts all over again
• Do calculations for longest common
“undisturbed” time (72 h = long
weekend)
Common Problem for Engineers and
Scientists in Courtroom Situations
• Even with simplifying assumptions
the defining equations are:
• Diffusion
(CS – CA)/CS = erf (X/2√Dt)
• Flux
= [{-2D(CS – C0)}/√4πDt] exp{-X2/4Dt}
• Explain that to a jury!
Results
• The calculation shows that over a long
weekend about 9 x 10-4 μg H2S /m3 will
diffuse into the bathroom.
• Threshold odor limit of H2S is 1 μg/L or
1.4 μg H2S / m3 …some 1600 times
higher!
• But even these numbers are likely to
make the eyes of an average citizen
glaze over… so how can we tie this to
something that they really understand?
Other Sources of H2S in a Bathoom
• You’ve guessed it…flatus!
• This led me into a fascinating
study of the subject of flatology
• Journal of Emergency Medicine ,
Vol. 10, pp. 79-88. (1992)
…and the Moral of These Stories
is:
“If you hear hoofbeats, think
horses, not zebras”
(but remember there may be a
zebra in that pack of horses)
Questions?
Topics
• The case of the missing sulfite and
the phantom chlorine residuals
• Mystery pipe scaling with no
anions
• A galvanic mystery
• H2S and spina bifida
• If this mechanism is true then
the molar concentrations of
ammonia and total alkalinity
in the groundwater plume
should be equal ….
3. 5
3
Log Alkalinity
2. 5
2
1. 5
1
0. 5
0
-3
-2
-1
0
1
-0. 5
-1
Log NH4+
2
3
4
Guess who paid to rip out all the
pipes, replace them and fix all the
water damage!
All Data are Useful
• Investigation of lead levels in water
delivered to apartments
• Lead standard for drinking water:
90% of samples < 15 μg/L.
• MDL for Pb = 5 μg/L
• Many samples below MDL
Pb Concentration, data > MDL
100
Pb, μg/L
50
20
10 MDL= 5 μg/L
5
2
1
10
30 50 70 90
% less than
99 99.9 99.99
Standard Met?
• It is a close call!
• More data would be helpful
• Data sets contained many “Nondetects” below MDL
• Lab notebooks reviewed and
sample readings below MDL
converted to μg Pb/L
Conclusions
• Data below MDL belong to the same
statistical distribution as those > MDL
• Including all data provides more
confidence that Pb standard is met.
• Eliminates the skewing of data
introduced by assuming some fixed
value for data <MDL
Pb concentration, All Data
100
Pb, μg/L
50
20
10
MDL= 5 μg/L
5
2
1
10
30
50 70
90
% less than
99
99.9 99.99