Coagulation and flocculation Flashcards
Coag aids add
Density to slow settling floc and add toughness to floc so they will not break up during mixing and settling
Importance of floc speed (3)
1.If flocculator speed is too slow short circuiting may occur
2. Velocity 1 ft/sec
3. Create floc in 0.1-0.3mm in density
Jar test (2)
Procedure with multiple glass jars with different dosages under same conditions
80% settled in less than 2 minutes floc is too heavy
(3) uses of coag aids
- Lime
- Weighting agents
- Polymers
- cationic +
- anionic -
- nonionic
Baffles
prevent short circuiting and direct flow
Inlet should be designed to
Minimize high flow near bottom
Weirs have
V notches at every foot
A physical and chemical reaction occurring between the alkalinity of the water and coagulant added
Coagulation
4 factors that effects coagulation and flocculation
Temp
PH
Alkalinity
Specific conductance
The ability of water to conduct an electrical current and provide an estimate of dissolved solids
Specific conductance
Purpose of coag and floc
Remove turbidity
Detention time for coag and floc
Up to 30 minutes
(7) factors affects coag and floc process
- Best pH ( alum,5-7 Fe,5-8)
- Alk of water
- Concentrations of salts
- Turbidity
- Types of coags used
- Temp
- Adequacy of mixing
(5) uses of alum
- Most used coag
- Effective pH rang 5-7 6.5 best
- Effective color rang ~ 5.5
- Reacts with alk to form floc
- For every 2mgl alum, 1mgl lime is used to replaced alk; caustic soda can also be used
(5) uses of ferric sulfate and lime
- Combination produces ferric hydroxide
- PH Rand 8.4-9.0
- Oxygen must be added aeration or chemical by chlorine
- Very effective for turbidity
- Care must be taken because color not removed at high pH
Coagulant flash mixing (3)
- flash mixing to rapidly mix coag throughout water
- first results form very small particles
- if most floc settles within 1-2 minutes too much coag was added
(3) things about coag mixing
- Devices- mechanical, diffusers, pumps, hydraulic use
- 5-7 fps mixing velocity
- Coags added in first chamber
(3)floc process
- Slow stirring process from small to larger particles
- Achieves best with 3 basins by baffles to prevent short circuiting
- Colder temps require longer detention times
Condition where some water travels faster than other areas in tanks or basins
Short circuiting
(3) desirable floc quality
- Popcorn flake desirable appearance
- Too much alum if milky appearance or bluish tint
- Described discrete and fairly dense
Most important consideration in coag floc process control is
Proper type and amount of coag added
Jar test procedures (3)
Flash mix- 1min at 80 rpm
Floc- 30 min at 20 rpm
Settling- 30 min
Turbidity measured
Every 4 hours or continuously and reported
