using particle counters in combination with turbidimeters

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