L-21

Development of

treatment processes

Industrial Waste Treatment

Section-II starts

Contents of unit-V

L-21 Different types of waste

treatment and their selections,

L-22 Development of treatment

flow diagram based on

characteristics of waste.

1. Contaminants Suspended solids

---: Reason for importance

Suspended solids can lead to the

development of sludge deposits and

anaerobic conditions when untreated

wastewater is discharged in the aquatic

environment.

Biodegradable organics

Composed principally of proteins,

carbohydrates and fats, biodegradable

organics are measured most commonly

in terms of BOD and COD.

If discharged untreated to the

environment, their biological

stabilization can lead to the depletion

of natural oxygen resources and to the

development of septic conditions;

Pathogens

Communicable diseases

can be transmitted by the

pathogenic organisms in

wastewater.

Nutrients Both nitrogen and phosphorus,

along with carbon, are essential

nutrients for growth.

When discharged to the water these

nutrients can lead to the growth of

undesirable aquatic life

(Euthrophication).

When discharged in excessive

amounts on land they can also lead to

the pollution of groundwater;

Refractory organics

These organics tend to resist

conventional methods of wastewater

treatment.

Typical examples include surfactants,

phenols, and agricultural pesticides;

Heavy metals

Heavy metals are usually

added to wastewater from

commercial and industrial

activities and may have to be

removed if the wastewater is to

be reused;

Dissolved inorganic

solids Inorganic constituents such as

calcium, sodium, and sulfate are added

to the original domestic water supply

as a result of water use and may have

to be removed if the wastewater is to

be reused .

Unit operations and

processes and treatment

systems used to remove

the major contaminants in

wastewater

CLASSIFICATION OF

TREATMENT METHODS

The contaminants in water and

wastewater are removed by

physical, chemical, and biological

means.

The specific methods are classified

as physical unit operations, chemical

unit processes, and biological unit

processes.

PHYSICAL UNIT OPERATIONS

Treatment operations in which

change is brought about through

the application of physical forces

are classified as physical unit

operations.

Typical unit operations include

screening, mixing, gas transfer,

sedimentation, and filtration.

CHEMICAL UNIT PROCESSES

Treatment processes in which the

removal or treatment of contaminants

is brought about by the addition of

chemicals or by chemical reactions

are classified as chemical unit

processes.

Chemical precipitation and

disinfection are two important

examples.

BIOLOGICAL UNIT PROCESSES

Treatment processes in which the

removal of contaminants is brought

about by biological means are classified

as biological unit processes.

The activated sludge process and

trickling filter used for the treatment of the

organic matter in wastewater is perhaps

the best-known example

CLASSTYPICAL CONTAMINANTS

FOUND IN WASTEWATER

Floating and

suspended

materials

Wood, rags, paper, grit, food

wastes, feces

Colloidal materials Food wastes, feces, pathogenic

bacteria, other microorganisms, silt

Dissolved materials Organic compounds (e.g. BOD)

nutrients, heavy metals, inorganic

salts

Dissolved gases Ammonia, hydrogen sulfide,

methane

Immiscible liquids Oils and greases

CONTAMINANT

UNIT OPERATION,

UNIT PROCESS, OR

TREATMENT SYSTEM

CLASSIFICATION

Suspended solids Screening and comminution

Sedimentation

Flotation

Filtration

Coagulation / sedimentation

Land treatment

P

P

P

P

C / P

P

Biodegradable

organics

Activated sludge

Trickling filters

Rotating biological

contactors

Aerated lagoons

Oxidation ponds

Land treatment

B

B

B

B

B

P / B

P / C

Pathogens Chlorination

Ozonation

Land treatment

C

C

P

Nutrients:

Nitrogen

Suspended-growth

nitrification and

denitrification

Fixed-film nitrification and

denitrification

Ammonia stripping

Ion exchange

Breakpoint chlorination

Land treatment

B

B

C / P

C

C

B / C / P

Phosphorus Metal salt coagulation/

sedimentation

Lime coagulation /

sedimentation

Biological / chemical

phosphorus removal

Land treatment

C / P

C / P

C / P

B / C

C / P

Refractory organics Carbon adsorption

Tertiary ozonation

Land treatment systems

P

C

P

Heavy metals Chemical precipitation

Ion exchange

Land treatment

C

C

C / P

Dissolved inorganic

solids

Ion exchange

Reverse osmosis

Electrodialysis

C

P

C

Theory questions

Q 1. Explain different types of contaminants

present in wastewater and suitable

treatments adopted for their removal in

practice.