LIQUID / SOLIDS SEPARATION IN WASTEWATER TREATMENT ...

[Pages:58]LIQUID / SOLIDS SEPARATION IN WASTEWATER TREATMENT & BIOSOLIDS DEWATERING

Chemical Products Lab Testing Plant Trials

LIQUID / SOLIDS SEPARATION

APPLICATIONS

Influent Water Clarification Process Water Recycling Primary Wastewater Clarification Secondary Clarification Sludge Thickening Sludge Dewatering

LIQUID / SOLIDS SEPARATION

UNIT OPERATIONS

WATER OR

WASTE WATER

SLUDGE DEWATERING

Clarifiers (Many Types) Filters (Many Types) Dissolved Air Flotation Units Induced Air/Gas Flotation Units Belt Presses Centrifuges Screw Presses Plate and Frame Presses Vacuum Filters (Rotary & Horizontal)

LIQUID / SOLIDS SEPARATION

PRODUCT TYPES

Coagulants (+) Low Mol Wt

Organic Inorganic Blended

Flocculants (+ , - , 0 ) High Mol Wt

Dry Emulsion Solution Oil-Free Flocculants

COAGULANTS AND FLOCCULANTS

Act on Insoluble Particles in Water

Oils, Grease, Blood, Insoluble Organics, Clay, Silicates, Metal Oxides/Hydroxides

Dirt, Dust, Rust & Metal Filings

Can Act on Charged Organic Compounds

Anionic Surfactants, Soaps & Dispersants

Do Not Act on Most Dissolved Solids

Salts, Acids, Nonionic Surfactants, Ammonia or Soluble Organic Compounds such as Sugar, Alcohols, etc.

SUSPENSION CHEMISTRY

THE KEY TO EFFECTIVE LIQUID / SOLIDS SEPARATION

SUSPENDED SOLIDS VARIABLES

Surface Charge Charge Density Particle Size Composition Particle Density Particle Shape

MOST IMPORTANCE

LEAST

MICROSCOPIC FORCES

ELECTROSTATIC BROWNIAN VAN DER WAALS GRAVITY

Colloidal Particle in Water

+

++ ++ +

+

+ +

+

+

+

+ +

+

++

++

++ ++ +

++

++

++

+ +

+

++ +

+

+

Almost all Particles of Industrial Interest Have a Negative Surface Charge.

The Particle is Surrounded by an Equal Number of Positive Counterions.

PARTICLES IN WATER REPEL EACH OTHER

+

++ ++

+

+

+ +

+ +

+ ++ ++++

+ +

+

+

+ +

+

+

+

++

+ ++

++ ++ +

+ +

+

+ +

++

+

++

+

+

+ +

+ + +

+ + +

++

+ +

+

+ +

+ +

+

+

+ +

+

++ +

Colloidal Particle in Water

+

++ ++ + ++

++ ++ +

+ ++ + +

+ RATIO OF EXCESS

+ + +CATIONS

++

++

++ ++

EQUAL NUMBER OF POSITIVE AND NEGATIVE CHARGES

+ +

+

++ +

+

+

DISTANCE FROM PARTICLE

ADSORPTION OF CATIONIC POLYMER NEUTRALIZES CHARGES AND COLLAPSES FIELDS

Van der Waals Force of Attraction Now Stronger Than The Electrical Force of Repulsion

NEUTRALIZED PARTICLES COAGULATE

STOKE'S LAW: = 2Gr2 ( - ) / 9

= SETTLING RATE G = GRAVITATIONAL CONSTANT r = RADIUS OF PARTICLE = DENSITY OF PARTICLE o = DENSITY OF LIQUID = VISCOSITY OF LIQUID

BIGGER SETTLES FASTER

Effect of Decreasing Particle Size

MATERIAL

Gravel Course sand Fine sand Silt Bacteria Colloidal particles Colloidal particles Colloidal particles

DIAMETER (in mm)

10 1 0.1 0.01 0.001 0.0001 0.00001 0.000001

SETTLING TIME PER METER

1 second 10 seconds 2 minutes 90 minutes 1 week 2 years 20 years 200 years

EFFECT OF COAGULATION AND FLOCCULATION

MANY SMALL

FEWER LARGE

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