using particle counters in combination with turbidimeters
TRANSCRIPT
Using Particle Counters in combination with Turbidimeters to obtain a better understanding
of coagulation and filtration performance.
Presented By: John Clark
Topics
Coagulation & Filtration Theory
Nephelometric (90o Light Scatter) Turbidimeter
Light Blocking Particle Counter
Particle Volume Distribution – Why It Matters,
Interpreting NTU & PC Data
Which Has Higher Turbidity?
A B
Both samples contain mixture of water and iron oxide (hematite)
Which Has Higher Solids?
A B
Both samples contain mixture of water and iron oxide (hematite)
Particle Size Spectrum
0.0001 0.001 0.01 0.1 1 10 100Micron(Log Scale)
RelativeSize of
Material
FiltrationTechnology
Membrane FiltrationRO NF UF MF Conventional Filtration
Dissolved OrganicsViruses
H2O
Colloidal Silica
BacteriaClay Silt Fine Sand
Amoeba
Metal Ion
ParticleSizing
Technology Light Blocking(a.k.a. Particle Counter)TDA / TEM / SEM
Small Angle X-Ray Scattering
Dynamic Light ScatteringLaser Diffraction
Imaging Analysis
X-Rays UV Near IR Far IRVisibleLight Spectrum
Coagulation Mechanisms
Alum + Raw Water
Soluble Cationic Species Al(OH)2+
Colloidal Hydroxide Precipitate Al(OH)3(s)
Amorphous Hydroxide Precipitate Al(OH)3
Enmeshment / Adsorption
Raw WaterNOM
NOMNOM
NOM
Neutralization / Complexation
Al-NOM
Al-NOM
Al-NOM
Al-NOM
AgglomerationAl-NOM Al-NOM
Al-NOM
Al-NOM
Al-NOM Al-NOMAl-NOM
Al-NOM
Al-NOM Al-NOMAl-NOM
Al-NOM
Al-NOM Al-NOMAl-NOM
Al-NOM
Colloids
Dissolved Organics
Turbidimeters(Light Scatter)
Turbidity Definition
Turbidity is a measure of water clarity, how much the material suspended in water decreases the passage of light through the water. - EPA
Turbidity is the measure of relative clarity of a liquid. - US Geological Survey (USGS)
Turbidimeter Definition
Oxford Dictionary An instrument for measuring the turbidity of
a liquid suspension, usually as a means of determining the surface area of the suspended particles.
Nephelometric Turbidimeter(90 Degree Light Scatter)
Light
Photo Detector
0.00 NTU0.20 NTU
Lens
90o
Light Scatter Behavior
Small Particles (<100 nm): Somewhat Symmetric Light Scatter
Medium Particles (100 to 500 nm): Increased Light Scatter in Forward Direction
Larger Particles (>500 nm): Extreme Scatter in Forward Direction
Rayleigh Scattering
Mie Scattering
NTU Relationship To Solids
? NTU? NTU
Iron Oxide - Nanoparticles
Impact of Particle Size On Turbidity
Demosntrating Impact Particle Size Has On Turbidity
Prior to Ultrasonication Initial Moment After Going Into Bath
10 Seconds After Going Into Bath After Ultrasonication
The agglomerations of iron particles begin to break apart.
Iron particles now disbursed as discrete submicron particles which dramatically increases turbidity.
Sample contains large agglomerations of iron particles, many larger than >10 micron
As discrete iron particles are disbursed, more surface area is exposed, increasing light scatter.
Magnetite & Hematite
PC vs NTU Response
Turbidity (Light Scatter) Summary
A qualitative measurement that determines clarity of the water, which is impacted by both number and size of particles.
10 ppb of 5 micron particles will have a lower NTU than 10 ppb of 0.5 micron particles.
Does not reliably correlate to suspended solids post coagulation due to changing distribution of particulate (post coagulation).
Offers affordable means of submicron particle detection.
Particle Counters(Light Obscuration)
The Rise of Particle Counters
Two major crypto outbreaks in the US occurred in the early 90’s which led to intense interest in particle counters in the drinking water industry as a way to hep guard against future outbreaks.
Photo Credit: H.D.A Lindquist, U.S. EPA
Particle Counter (Light Blocking)
Laser DiodePhoto Diode
Water Flow
ParticlesLight Beam
Particle Sizing
10 Micron
mV
Particle Counts
Multi-Size channel view showing counts in each size bin.
Coincidence Error
Laser DiodeOr LED Photo Diode
Water Flow
ParticlesLight Beam
Particle Count (How Many?)
Particle Volume (How Much?)
What Is More Important?
Idealized Size Distribution
This size distribution model states that for every 10 µm particle there will be one million 0.1 µm particles in the sample.
A single 10 µm particle has the same volume as one million 0.1 µm particles.
Particle Size vs Volume
2 micron = 4.2 µm³
10 micron = 524 µm³
* At concentration of 1 count per mL
0.1 micron = 0.0005 µm³
524 ppt*
4.2 ppt*
0.0005 ppt*
Real World Filter Effluent Data
0.35% of counts >5 um
80% of volume >5 um23% 20%20%
18%12%
7%
94.5%
5.1%
0.28%0.04%
0.02%0.007%
Particle Volume Readout
An important feature of some online particle counters is a volumetric concentration readout
Biologically Active Filters
Total Counts with PPB
Before Chlorine Addition
Before
After Chlorine Addition
After
Filter Backwashes
(120 hr)
Particle Detachment
Surface Removal (Straining)
Large floc particles lead to rapid head loss, shorter filter run times.
Filter media
Top of filter
Attachment Filtration
Smaller floc particles allow more of the filter media to be utilized, allowing for longer filter run times
Filter media
Top of filter
Attachment Filtration Mechanism
Particles attach to filter media by way of electrostatic forces / van der Waals forces Enhanced with metal hydroxide (coagulant) or
polymer (filter aid).
Particles are “stored” and not “trapped”.
Probability of detachment & breakthrough increases as solids loading and internal pore velocity increases.
Detachment
FLOW
Internal Pore
Impact Of Flow Rate Changes
Combined Filter Particle Counts
Filter #1 Turbidity
Filter #1 Particle Counts
Filtration Rate Head Loss
End of Filter Runtime Particle Breakthrough
Filtration Stages
RipeningStage Working Stage Breakthrough
Stage
e.g. 120 Hours
Backwashes Often Performed Many Hours Before Initial
Breakthrough Occurs
InitialBreak-through
RapidIncline
End of Filter Run Breakthrough
DateTime
Patic
le co
unt 2
-10 m
icron
(par
ticles
per m
L)
Turb
idity
NTU
g End of run filter breakthrough trends for particle count and turbidity
1/2/2013 6:00:00 AM 1/2/2013 9:00:00 AM 1/2/2013 12:00:00 PM 1/2/2013 3:00:00 PM0 0
5 0.01
10 0.02
15 0.03
20 0.04
25 0.05
30 0.06
35 0.07
40 0.08
45 0.09
50 0.1Particle Count (2-10 um)F4_FT660scF4_1720 Tubidimeter
Particle CounterLaser Diode TurbidimeterTungsten Lamp Turbidimeter
Filter Integrity
Early Warning Of Filter Problems
Depression in media caused by damaged underdrain
Coagulation Upsets
Coagulation Upsets
Backwash solids accidentally recycled at too high of a concentration Coagulant Feed Temporarily Lost.
Getting The Full Picture
Turbidity Particle Counts
TSS
Baseline 0.04 NTU 10 cnts/ml <1 ppb
#1 Event
0.30 NTU 30 cnts/ml 30 ppb
#2Event
0.10 NTU 120 cnts/ml 60 ppb
Getting The Full Picture
Turbidity Particle Counts
TSS
Baseline 0.04 NTU 10 cnts/ml <1 ppb
#1 Event
0.30 NTU 30 cnts/ml 30 ppb
#2Event
0.10 NTU 120 cnts/ml 60 ppb
The Takeaway Turbidimeters offer affordable detection of
submicron particulate, very informative in terms of coagulation performance. But the reduced response to larger particles has potential implications in regards to early detection of filter performance issues.
Particle Counters offer affordable, very sensitive detection of larger particles. These larger particles can signal the beginning of the end of a filter run, a developing filter integrity issue, or excessive biological shedding.
Only when particle counters and turbidimeters are used together do we have the most complete picture of coagulation & filtration performance.
Questions?
References
Turbidity Science, Michael J. Sadar, Hach Monitor Water Filtration Processes For Optimum Particle Removal,
John Gregory, University College London Particles Contributing To Turbidity, EPA Guidance Manual Turbidity
Provisions http://www.hielscher.com/nano_01.htm; Ultrasonic Devices To
Disperse Nanomaterials Deep Bed Filtration: Modeling Theory and Practice, G. Keir; V.
Jegatheesan; S. Vigneswaran Particle Counting In Real World Water Treatment Plant Operations,
Thomas M. Ginn,Jr., P.E.; G. Ricky Bennett; Gregory D. Wheatley; Cobb County-Marietta Water Authority