COAGULATION, FLOCCULATION, AND SEDIMENTATION Training Class 2020/Coag Fl… · Coagulation,...
Transcript of COAGULATION, FLOCCULATION, AND SEDIMENTATION Training Class 2020/Coag Fl… · Coagulation,...
COAGULATION, FLOCCULATION,
AND SEDIMENTATION
J.D. DouglasSt. Albans District Office Supervisor
August 21, 2018
Nature of Particulate impurities in water
• Suspended solids include settleable solids and non-settleable or colloidal mater
• Likely to include suspended and dissolved organic & inorganic matter, and biological forms such as bacteria
Coagulation, Flocculation, & Sedimentation
Need for Coagulation and Flocculation
• Remove particulate impurities, especially non-settleable solids, and color from water being treated
• Coagulation chemicals cause particles to destabilize and clump together forming floc
Coagulation, Flocculation, & Sedimentation
Coagulation
Process Description
• The term describes the effect produced when certain chemicals are added to raw water containing slowly settling or non-settling particles
• Definition of flash mixing is the addition of coagulants to raw water
Primary Coagulants cause particles to destabilize & clump together….while coagulant aids add density to slow settling floc and add toughness to reduce shear floc
• Alum (aluminum sulfate), Al2(SO4)3 • 14H20 common
• Polyaluminum chloride, Al(OH)x(Cl)y less pH adjustment
• Ferric Chloride, FeCl3 more effective than alum in some applications
• Ferric Sulfate, Fe2(SO4)3 effective & economical in some waters
• Cationic Polymers primary coagulant with alum/iron coagulants
Metallic salts may be more effective in
removing natural organic matter
Coagulation
• Coagulation is a physical and Chemical reaction occurring between the alkalinity of the water and the coagulant added to the water which results in the formation of insoluble floc
• For a specific coagulant the pH of the water determines which hydrolysis species predominate
• The best pH for coagulation usually falls in the range of 5 to 7
Basic Coagulation Chemistry
Process Performance Considerations
Mixing Method (Rapid Mix Stage)
○ Mechanical mixing○ In-line mixing○ Hydraulic mixing using
flow energy in the system○ Diffusers and grid systems○ Pumped blenders
WV-BPH design Standards require 10 to 30 seconds of mix (detention) time
Process performance considerations
• Agitation of water at low velocities for a long period of time. The process provides contact between particles to promote their gathering together of floc.
• Floc formation is controlled by the rate at which collisions occur between particles and by the effectiveness of these collisions in promoting attachment between particles.
Flocculation
Flocculation
• Best floc size ranges from 0.1 mm to about 3 mm depending on filtration process being used
• WV-BPH-EED design standards ,
Flow through velocity:
0.5 ft/minute < velocity < 1.5 ft/minute
• Detention time for floc formation ≥ 30 minutes
• Paddle speed: 0.5 ft/sec < velocity < 3.0 ft/sec
Flocculation
Process Performance Considerations
An efficient flocculation process involves the selection of the right stirring (detention) time, the proper stirring intensity, a properly shaped basin for uniform mixing, and proper mechanical mixing equipment.
Flocculation
Types of Flocculators
▪ Horizontal paddle wheels
▪ Vertical propeller, paddles, or turbines (less maintenance)
▪ Flocculator Basins (compartmentalized basins)
Flocculation
Interaction with other treatment processes
▪ Filter operations
▪ TTHM & HAA5 formation
▪ Enhanced Coagulation required? Raw vs Finished TOC & Alkalinity levels.
▪ Is proper type and amount of coagulant being used?
Sedimentation
• Zone after Coagulation & Flocculation
• Zone with no mixing or agitation
• Can provide plates for added surface to settle particles on
• Can use gravity to our advantage by forcing flow down and then back up by use of baffles
• Need to remove sludge periodically
• Normal operating condition indicators
periodic monitoring for turbidity, pH, temperature,
chlorine demand, & floc quality
• Process Actions
monitor process performance
evaluate water quality conditions (raw/tr.)
Check/adjust process controls/equipment
Visually inspect facilities
Speed adjustment of flocculators
Operating Procedures Associated with Normal Process Conditions
Should take into account:
Volume of floc to be formed: low turbidity – slower floc speeds, high turbidity – near maximum floc speeds.
Visual observations: Short circuiting may indicate insufficient mixing intensity. Floc break-up/shearing may indicate too high intensity.
Temperature: Low temps require higher mixing turbulence (so increase speed)
Operating Procedures Associated with Normal Process Conditions
The operator can approximate the correct coagulant dosage for plant use when varying amounts of turbidity, color, or other factors indicate raw water quality changes. The Jar Test is also a useful tool in evaluating new coagulants or polymers being considered for use on a plant scale.
The primary intent of the Jar Test is to define the “optimum coagulant dosage”
The Jar Test Procedurereference: California Manual, Volume 1(1989) chapter 11 lesson 5.6 &
Kawamura, “Integrated Design & Operation of Water Treatment Facilities, 2nd
edition (2000) appendix 10
The Jar Test Procedure
Other Jar Testing applications
• Determine KMnO4 feed rate
• Determine Chlorine Demand
• Enhanced Coagulation to determine optimum
Total Organic Carbon (TOC) removal
• Determine optimum lime feed rate for softening plants
• Confirm existing coagulant feed rates by placing a sample entering the plant flocculator and visually observe floc formation.
• A Stirring Machine with 6 paddles capable of variable speeds from 0 – 100 rpm
• An illuminator under the machine (optional)
• Beakers (100 mL)
• Pipets (10 mL)
• Flask, volumetric (1000 mL)
• Balance, analytical.
• Reagents
Apparatus
Clarksburg Water Board - enhanced coagulation jar test, 2002
Questions