This ebook describes best practices for utilizing coagulants and flocculants in environmental applications, such as construction, mining, erosion control. and stormwater runoff.
2. Table of CONTENTS
What is Coagulation & Flocculation? 3
Types of Coagulants and Flocculants 6
Advantages and Disadvantages of Each Type 8
Settling velocity, shear strength, filterability
Sludge density, dewater-ability
Aquatic toxicity & residual testing capability
What is Enhanced Best Management Practices (eBMP)s? 17
Passive, Semi-passive, Passive w/ automation, Active Treatment
Environmental concerns and responsibilities
3. 3
Flocculation & Coagulation
‹‹ Removes suspended solids from water
‹‹ Large particles can be removed by filtration or settling, as practical
‹‹ Smaller, suspended particles (e.g. colloidal particles) are stabilized
in suspension & difficult to remove via mechanical methods:
-- Size (~0.1 to 1µm)
-- Electrically charged; repel each other; stabilize the suspension
-- Examples: clay, silica, iron, pigments, and even oil
‹‹ Flocculation & Coagulation destabilize colloidal particles to enhance
performance of mechanical separation processes
4. 4
Coagulation - Brings Particles Together
‹‹ Coagulation - destabilization of a colloid by charge neutralization
‹‹ Destabilized particles begin to collide and create small masses
–flocs or pin flocs (> 50 microns, visible)
‹‹ Requires good mix condition (e.g. static mixer)
-- Particles must come close enough to collide
-- Break apart the colloidal system
‹‹ Historical, metals salt coagulation (aluminum, iron, etc.) can create
excess sludge and/or toxicity
5. 5
Flocculation - Improves Filterability &
Settling
‹‹ Flocculation - the gathering of flocs into a network
‹‹ Anionic, cationic, neutral
‹‹ High molecular weight
‹‹ Increases floc stability
‹‹ Mixing condition essential!
-- Not to break flocs
Patching
Bridging
6. 6
Typical Coagulants
‹‹ Metal Salts
-- Alum, Ferric Chloride, etc.
-- Polymerized metal salts i.e. Polyaluminum chloride (PAC),
Aluminum Chlorohydrate (ACH), etc.
‹‹ Plant Based derivatives
-- Lignin, tannin, starch, etc.
‹‹ Synthetic derivatives
-- Polyamine, pDADMAC, etc.
‹‹ Hybrids
-- Variations or combinations of chemistries
‹‹ Synthetic derivatives
-- pDADMAC – can be coagulant or flocculant depending on
derivatization
‹‹ Polysaccharides / natural biopolymers
-- Chitosan
-- Pectin, carrageenan, alginate, etc.
-- Gums – guar, xanthan, plantago, etc.
‹‹ Polyacrylamides
7. 7
Molecular Weights of Coags, Flocs & Tackifiers
‹‹ FeCl3, Alum (Al2(SO4)3
‹‹ Polymerized metal salts – PAC, ACH
‹‹ Synthetics – pDADMAC, Polyamines
‹‹ Plant based – tannin, lignin, starch
‹‹ Chitosan biopolymer
‹‹ Gums – plantago, guar, etc…
‹‹ Polyacrylamides
‹‹ 162-342 Daltons
‹‹ 150-5,000 Da
‹‹ 150-5,000 Da*
‹‹ 500-25,000 Da
‹‹ 25,000-500,000 Da
‹‹ 1,000,000-5,000,000 Da
‹‹ 1M to 30M Daltons
* Some pDADMAC can act like flocculants 25k – 1.5M Da
Coagulants: Inorganic and Organic
Flocculants: synthetic & natural
Floc builders: act as coagulants and flocculants
8. 8
Flock Characteristics
‹‹ The following pages show characteristics to look for and awareness
of treatment through design when using:
-- Aluminum Sulfate - Alum
-- Polyaluminum Chloride (PAC)
-- Polyamine
-- pDADMAC Coagulant
-- Plant Based Derivatives
-- Natural Chitosan Biopolymer
-- aPAM blend
-- Polyacrylamide
‹‹ These characteristics are: settling velocity, settled density, shear
strength, filterability, and retained moisture content
9. 9
Aluminum Sulfate - Alum
Very fine flocks, slow to settle
Medium settled density
Flocs are very hard to see with
naked eye while under agitation
14. 14
Biopolymer – chitosan vs. chitosan + anionic
polysaccharide
Chitosan denser solids than coagulants & PAM
Dual biopolymer is even denser than chitosan only
17. 17
Best Management Practice (BMPs)
‹‹ How the chemistry is used in environmental applications
‹‹ We’ve laid out best management practices, how the density is used
for environmental applications, including:
-- Passive Treatment Systems
■■ Check Dams
■■ Baffles
■■ Slope Drains
-- Semi-Passive Treatment Systems
■■ Geotextile Bags
■■ Sedimentation Ponds
-- Active Treatments
■■ Sand Filtration
18. 18
Passive Treatment Systems (PTS)
‹‹ Gravitational flow – not pumped
‹‹ Dry flocculant usage is primary, very little liquid flocculant used in
PTS
‹‹ Variable flowrates of stormwater run-off lead to non-optimal dose
rate determination
-- Requires review of aquatic toxicity or have residual polymer
testing capabilities
‹‹ With proper jar testing to determine dose rate – PTS can typically
achieve 50-250 NTU or 75-80% reduction in Total Suspended
Solids (TSS) over same BMP without flocculant addition
19. 19
Passive – check dam channels
‹‹ Rock, wattles or filter sock
Images courtesy of North Carolina State University.
https://content.ces.ncsu.edu/fiber-check-dams-and-
polyacrylamide-for-water-quality-improvement
Photo courtesy of North Carolina State University.
Apply flocculant on and around wattle.
Depending on % solids – flocculant
can be sprinkled on wattles & matting.
More contact flocculant has with
turbid water the better the dosing.
Flocculant
20. 20
Sediment Basins with porous baffles
Flocculant is added up stream of basin or forebay. Purpose of the
baffles is to disperse the energy of flowing water and allow to settle.
When combined with flocculant enhancement can improve 75-80%
performance on water quality.
21. 21
Case Study – Passive wattle & porous baffle
sediment basin - Raleigh NC
Passive: Wattle check dam and matting channel, to sediment pond with porous
baffles and floating skimmer.
From Left:
Influent: >4000 NTUs calc’d. 5400
End of channel: 260 NTUs
Skimmer effluent: 28 NTUs
22. 22
Passive - Slope Drain flocculant application
Dry flocculant sock deployed inside of slope drain, allows for high
agitation of flocculant - then treated water can be directed to
sediment basin, vegetated buffer or check dam channel prior to
discharge.
Drawing courtesy of Dober Chemical
23. 23
Semi-Passive Treatment Systems (SPTS)
‹‹ Pumped water
‹‹ Known flowrate improves dose rate calculations and thus improves
flocculant performance.
‹‹ Dry or liquid flocculant used – dry is more common
‹‹ With proper jar testing to determine dose rate – PTS can typically
achieve 25-150 NTU or 85-95% reduction in Total Suspended
Solids (TSS) over same BMP without flocculant addition
‹‹ Flocculant enhanced geotextile dewatering/filtration
-- Non-woven geotextile bags typically filter down to 150-200
microns
-- Woven geotextile bags typically filter down to 500-700 microns
-- With correct flocculant can improve filtration 75-80% +
Bottles from right to left:
1. Influent from sediment pond 450-560 NTUs
2. Directly from geobag 56-89 NTUs
3. After 50 ft of vegetative buffer 18-27 NTUs
WARNING: Do NOT over pressurize!!!
Unless you want to get DIRTY and WET
24. 24
Passive Treatment Systems with automation
‹‹ Gravitational flow of water
‹‹ Automated detection of flowrate and proportionally dosed liquid
flocculants greatly improves dose rate calculations and thus
improves flocculant performance
‹‹ liquid flocculant typically used
‹‹ With proper jar testing to determine dose rate – PTS can typically
achieve 10-25 NTU or 95-99% reduction in Total Suspended
Solids (TSS) over same BMP without flocculant addition
25. 25
Passive & Semi-Passive w/automation
‹‹ Sedimentation pond with forebay and weir:
‹‹ Automation unit monitors and optimal doses liquid flocculant
system
Forebay and settling pond w. EDD unit and PV, battery
“green power” package shown.
**Generators can be added to/or in replacement of
green power package**
26. 26
Automation controls dosing and records
results
‹‹ Can collect data every 15 seconds
‹‹ Flow activate
‹‹ Optimal dosing
‹‹ Remote monitoring capability
27. 27
Active Treatment System
‹‹ Very high quality water results.
-- Typically less than 10 – 20 NTUs, often < 5 NTUs
-- Secondary remediation options (ie. GAC, ion exchange or
membranes)
‹‹ Proven track record of billions of gallons treated
‹‹ Flocculant must have high filterability with depth media
filtration
‹‹ Allows for flow through treatment.
-- Minimize storage demands
-- Can be fully automated
‹‹ Biopolymer with Sand Filtration:
Drawing courtesy of Dober Chemical
28. 28
ATS is custom designed for each site
Photos of various parts of treatment train including ponds, settling
tanks, automation, filtration and remediation equipment
29. 29
Residual testing vs. Whole Effluent Toxicity
(WET)
‹‹ Current residual polymer test commercially sold for biopolymers
-- Actually crosslinking, filtering and staining of polymer
‹‹ Metal test for metal salts currently available
-- Polymerized metal salts may not be detectable unless specialist
testing
‹‹ Some companies have protocols using clay solution to detect any
floccing in treated effluent
-- Not a direct detection of polymer, only looking for the “effects of
the polymer”
‹‹ Florescence “dyes or tagging” of polymers has been demonstrated
in scientific research, however not aware of commercially available
polymers with florescent tags
If no residual testing is available and product is being dosed at or near
the effect concentration for coag or floc being used, then typical is
batch treatment and sending treated water out to be WET tested.
‹‹ Whole Effluent toxicity testing
-- 0 – 100% of treated effluent (typical 5 dilutions) is tested for acute
or chronic aquatic toxicity
-- acute is usually 24-96 hrs
-- Chronic is typically 7 days
-- Ideally 100% survivability over control
