Secondary Clarifier Design Tank

Secondary clarifier design tank  is used in ETP. We use water for many activities, most of which contaminate the water in some Way, i.e. By using detergents, chemicals, dyes t in fabric and yarn in industrial process. This contaminated water is called waste water. Water after usage is called waste water or effluent.

Main use of Secondary Clarifier

  • To Recirculation the Bacteria to the FBBR system
  • To reduce the suspended solids in the effluent
  • To avoided the Bacteria escape to other system
  • To remove the odor in the effluent in secondary clarifier design tank
  • To increase the efficiency of Electrocoagulation system
  • To reduce the current and electrode consumption in EC system
  • To increase the efficiency of FBBR system

Wastewater composition

Wastewater contains approximately 99.0% water and 1% solids maximum.

Expressed in another way, every 1000L of wastewater contains about 10kg of

Solids. The solids are organic and inorganic compounds and are suspended in the

Waste water. Volatile solids are about 70% of the wastewater solids and give the

Water its unpleasant characteristics.

The majority of the solids – carbohydrates, fats and proteins – are broken down

During treatment into more stable inorganic compounds by bacteria and other


Wastewater also contains some compounds that are resistant to normal treatment

Processes, including:


Fats, oils, grease & organic chemicals


Chlorides, heavy metals, nitrogen, phosphorus and sulphur.


Hydrogen (H2), sulphide (SO2), methane (CH4) and carbon-di-oxide (CO2).

Effluent treatment plant (etp) capacity

The Effluent treatment plant is designed to treat 2000m3 of Textile dyeing combined

Effluent generated from the process house. The plant will be capable of operating at the flow rate of 100m3/hr. The operating cycle of the plant shall be 20 hours.

Raw effluent characteristics

The effluent treatment plant is designed based on the analysis of effluent analysis report of combined effluent available with us. The relevant parameters are furnished below for your reference.

Parameter value

Ph: 9 -11

Bod: 600 mg/l

Cod: 1300mg/l

Suspended solids: 250mg/l

Total hardness: 50 mg/l

Turbidity: 150ntu

Color: 1000 pt.c0 units

Dissolved oxygen: nil

Tds: 2000 mg/l

After electro coagulation and filteration

Parameter value

Ph: 6.5-7.0

Bod: less than 50ppm

Cod: less than 150ppm.

Suspended solids: less then 5 ppm

Total hardness: 50 ppm

Turbidity: 5 ntu

Color: nil

Effluent treatment plant based on electro-coagulation and fluidized bed bio-reactor technologies.

Treatment steps

  1. Primary treatment
  2. Secondary treatment
  3. Sludge management

Primary treatment

  1. Bar screening
  2. Collection and equalization
  3. Neutralizing
  4. Fluidized bed bioreactor
  5. Secondary clarifier.
  6. Activated sludge recirculation system

Secondary treatment

  1. Electro-coagulation system
  2. Flash mixer
  3. High rate solid content clarifier
  4. Pressure sand filter
  5. Ec cleaning system

Sludge handling

  1. Sludge thickener
  2. Filter press
  3. Sludge storage

Operating cost of etp

Etp tank size and water reserve capacity-

Equalization tank= height-20feet, capacity=2000m3

Fbbr tank= height-17 feet, capacity=1200m3

Secondary clarifier=height-10feet, capacity=0.8m3

Ec feed tank= height-10feet, capacity=60m3

Hrscc tank=height-12feet, capacity=0.8m3

Filter feed tank= height-10feet, capacity-140m3

Sludge tank= height-10feet, capacity-80m3

Total electricity consumption and cost in etp per day-

88 kw per day. Unit price- 89.75 taka/kw

Total cost=7898

Ec plate consumption per day-

Destroyed metal plate per day=254.66 kg.

unit price- 82 taka/kg

total cost= 20882 taka

join coupler used per day= 768 taka

Used chemical and cost per day-

Hcl-125 liter per day. Unit price is -6.60 taka/liter

Total cost= 825 taka

Poly electrolyte-400 gm per day. Unit price is- 1250 taka/kg

Total cost=500 taka

Dap= 5 kg. Unit price is- 33 taka/kg

Total cost=165 taka

Urea=5 kg. Unit price-12 taka/kg

Total cost= 60 taka

Molasses= 10 kg. Unit price is- 36.60 taka/kg

Total cost=366 taka

Total chemical cost per day= 1916 taka.

Man power cost-

Cost per day- 600 taka

Depreciation cost

Total cost- 2, 50, 00, 000 taka

Life time of etp- 10 years

Depreciation cost per day = 6500 taka

Discharge water per day-

32, 40,000 liter per day or 3240 m3

Total cost per day-

38564 taka per day

Cost per liter-

11.90 taka per m3 for secondary clarifier design process