primary & advanced primary wastewater treatement

Primary & Advanced Primary Wastewater TreatmentILYANA A. CAUSING ENFT-4A

Introduction: Wastewater Treatment Processes

Wastewater treatment is related to standards and/or expectations set for the effluent quality

The processes are designed to achieve improvements in the quality of wastewater

The various treatment processes aims to reduce:

1. Suspended solids

2. Biodegradable organics

3. Pathogenic bacteria

4. Nutrients

In wastewater treatment, widely used terminology refers to the three level: primary, secondary and tertiary (or advanced)

Primary Wastewater Treatment


The primary or mechanical treatment is designed to remove gross, suspended and floating solids from raw sewage

This treatment is usually the first stage in wastewater treatment

It includes screening – to trap solid objects and sedimentation by gravity –to remove suspended solids

Chemicals are often used to accelerate the sedimentation process

Examples:

1. Chemical Phosphorous Removal

2. Practice of chemically enhancing primary treatment to reduce suspended solids and organic loads from primary clarifiers


Main Objective:

1. Remove settle able organic and inorganic solids by sedimentation

2. Remove floating materials (scum) by skimming

25 – 50 % Incoming Biochemical Oxygen Demand (BOD)

50 – 70 % Total Suspended Solids (SS)

65 % Oil and Grease

Some nitrogen, organic phosphorus and heavy metals associated with solids are also

removed during primary sedimentation

The effluent from primary sedimentation – primary effluent


In industrialized countries, primary treatment is the minimum level of pre-

application treatment required for wastewater irrigation

The primary treatment can be sufficient is the wastewater will be used to irrigate

crops that will not to be consumed by humans, orchards and some processed

food crops


Primary Sedimentation Tanks / Clarifiers

May be round or rectangular basins

Typically 3-5 meters deep

Has hydraulic retention time between 2-3 hours

Settled solids (primary sludge) are removed from the bottom of tanks by sludge rakes

that scrape the sludge to a central well from which it is pumped to sludge processing

units

Primary Sludge

The scum is swept across the tank surface by water jets or mechanical

mean and pumped into sludge processing units

The primary sludge is commonly processed biologically by anaerobic

digestion

Digestion process – anaerobic and facultative bacteria metabolize

organic material in sludge thereby reducing the volume requiring ultimate

disposal

The sludge is then stable (non-putrescible) and has improved dewatering

characteristics

Primary Sludge

Digestion is done in anaerobic digesters, that is 7-14 meters deep

The time depends on the type of digester

10 days – high-rate digesters, well-mixed and heated

>60 days – standard-rate digesters

The gas produced during digestion is usually methane (60-65%) and used

as energy source

For small treatment plants the processed used are:

Aerobic digestion, storage in sludge lagoons, sludge drying beds, in-process

storage (stabilization ponds) and land application

Primary Sludge

Advanced Primary Treatment


Advanced primary treatment (APT) is a process where chemicals are added to raw sewage to enhance total suspended solids and biochemical oxygen demand removals by coagulation and flocculation

Also called Chemically Enhanced Primary Treatment (CEPT)

The chemicals added are typically metal salts and/or polymers in the form of organic polyelectrolytes

These chemicals are added to primary sedimentation basins

CEPT may be implemented using

CEPT tanks (settling tanks designed for CEPT)

Retrofitting a conventional primary treatment facility

Stabilization ponds


The chemicals will cause the suspended particles to clump up by coagulation and

flocculation

The particles aggregates or flocs and settle faster thus enhancing the treatment

The utilized chemicals are typically ferric chloride and aluminum sulfate

Primary to Advanced Primary Treatment

Primary Treatment

Consists of bar screens, a grit

chamber, and a settling tank/primary

clarifier

Upgrade to CEPT

Addition of a chemical coagulant

and flocculent (optional)

Annual Sewage Treatment Volume

1,001 million m3

• CEPT is

Efficient

Cost-effective

Easily implemented

Wastewater treatment technology

• The addition of chemical coagulants and/or

polyelectrolytes allows for the increased

removal of phosphorus, suspended solids and

its associated biochemical oxygen demand

• The increased removal efficiencies allow for

the design of smaller basins and greater

overflow rates

Quiz

1. What is the first stage in wastewater

treatment?

2. These are round or rectangular basins,

typically 3-5 meters deep and has hydraulic

retention time between 2-3 hours.

3. This is a process where chemicals are added

to raw sewage to enhance TSS and BOD

removal by coagulation and flocculation.

4. What is the treatment applied to the primary

sludge?

5. True or False? Primary Treatment has the

highest percentage in the Annual Sewage

Treatment Volume.

1. Primary or Mechanical Treatment

2. Primary Sedimentation Tanks or Clarifiers

3. Advanced Primary Treatment (APT) or

Chemically Enhanced Primary Treatment

(CEPT)

4. Anaerobic digestion

5. False

Questions Answers

primary & advanced primary wastewater treatement

Technology