Factors for selection of a treatment processFactors for selection of a treatment process

Introduction in Water TreatmentIntroduction in Water Treatment

1. Characteristics of the wastewater

- Form of pollutants suspension

colloidal

dissolved

- Biodegradability

- Toxicity of the components

2. Required effluent quality

3. Cost

4. Availability of treatment devices and area

(land)

5. Consideration for future use

Water treatment process

Pre- and

Primary

treatment

Secondary

Treatment

Tertiary

treatmentrunoff

Effluent

Mechanical Treatment

Physical Treatment

Chemical Treatment

Biological Treatment

Types of Water Treatment

Pretreatment & Primary

treatment

Secondary & Tertiary

treatment

PRE- AND PRIMARY TREATMENT

to prepare the wastewater for biological treatment

Purpose Treatment

Screening

Flotation,

Sedimentation

Coagulation

filtration

Remove large solids, grit

Remove oils, grease

and suspended solids

Adjust the pH Neutralization

SECONDARY TREATMENT

** toxic residues have to be removed prior to

biological treatment **

- Biological degradation of organic compounds

(aerobic / anaerobic)

- Microorganisms and solids will be allowed

to settle

- Recycle of a fraction of sludge

TERTIARY TREATMENT

to remove specific types of residuals

** all these processes have their place in overall

Wastewater treatment scheme **

- Filtration : removal of suspended or colloidal solids

- Adsorption, chemical oxidation : removal of organics

- Ozonation, chlorination : disinfection

Pretreatment & Primary treatment technologies

Oil

separation

Equalization NeutralizationCoagulation

and

precipitation

Flotation

Sedimentation

FiltrationSpill

basin

Source

control

EQUALIZATION

To minimize or control fluctuations in wastewater

characteristics in order to provide optimum conditions

for subsequent treatment process

Purposes of equalization for industrial treatment facilities :

1. To provide adequate dampening of organic fluctuations.

To prevent shock loading of biological systems

2. To provide adequate pH control or to minimize the

chemical requirements necessary for neutralization.

Purposes of equalization for industrial treatment facilities :

3. To minimize flow surges to physical-chemical treatment

systems and permit chemical feed rates compatible with

feeding equipment.

4. To provide continuous feed to biological systems over

period when the manufacturing plant is not operating.

5. To provide capacity for controlled discharge of wastes

to municipal systems.

To distribute waste loads more evenly.

6. To prevent high concentrations of toxic materials from

entering the biological treatment process.

Example Controlled discharge of an industrial wastewater to

a municipal plants.

Cumulative flow

Cumulative

discharge

Maximum

storage

required

Cumulative volume (million gal)

Hours of the day

Municipal

Industrial

Hours of the day

Municipal rate of flow (gal/h)

Industrial rate of flow (gal/h)

Equalization basin

Example: Submerged mixers most common method

Equalization basin may be

designed with

- a variable volume to provide a

constant effluent flow

or

- constant volume and effluent

flow that varies with influent

Flow Equalization

- The cumulative flow is plotted versus time over

the equalization period.

- The maximum volume with respect to the constant

Discharge line is the equalization volume required.

aa

b

b

a empty basin

b full basin

Application of flow equalization in the process

in-line

equalization

off-line

equalization

Application of flow equalization in the process

In-line equalization: all the flow passes through the

equalization basin.

Off-line equalization: only the flow above some

predetermined flow limit is diverted into the equalization

Basin.

References

1. George Tchobanoglous, Franklin L. Burton, H. David Stensel,

Wastewater Engineering: Treatment and Reuse. 4th ed.,

Metcalf & Eddy, Inc.,2003.

2. W. Wesley Eckenfelder, Jr. Industrial water pollution control. 3rd ed.,

McGraw-Hill, 2000.