waste water treatment

Waste water Treatment

 When effluent discharged into a river body such as lake, river or sea a number of process occur like physical, chemical and biological characteristics of water change which cause loss of organism. The extent of damage depend upon type pf pollutant present in effluent. Non bio-degradable pollutant like mercury are most deadly as they accumulate in aquatic organism which lead to Biomagnifications. Large quantity of biodegradable waste can affect living organism in the water bodies in which waste are discharged. are It is necessary to treat effluent or waste water before discharging in water body. The treatment procedure are generally divided into three groups:
1. Primary Treatment or Mechanical Treatment
2. Secondary Treatment or Biological Treatment
3. Tertiary Treatment or Advance Biological or Chemical Treatment.

Primary Treatment

 In primary treatment suspended solid and floating material is removed. Effluent is passes through a screen which is used to remove certain material like wood pieces, plastic , paper, floating debris. Then effluent is passed through chamber which is known as grit chamber.

 -Fatty and oily substance can be removed by flotation method. In order to trap fatty and oily substance a instrument called Centrifugal Separator is used in this process fatty substance are reached to outside and clean water remain in the center of cyclone. 

- The water is passed in Settling Tank in which water remain for a long time in which suspended particles are settled down this process is known as Sedimentation. 

-Sedimentation can be accelerated by adding chemical substance known as Coagulant like Alum.

- Some small particles may be separated by Floatation Method . In this method bubble of air pass through the bottom of tank and small particles come in the contact with bubble come out on the surface of water. 

- Colloidal particles can be removed by Flocculation and Precipitation.

-Physical Treatment

a) Screening
b) Grit Chamber
c) Floatation or skimming tank

- Chemical Treatment

-Sedimentation
- Coagulation
- Flocculation
- Filteration 

Secondary Treatment or Biological Treatment 

It is the process in which microorganism play a very important role for the treatment of effluent. Microorganism like bacteria, fungi decompose the organic waste and convert into simpler form. The main function of secondary treatment is to convert the reaming organic matter of sewage into stable form by oxidation and nitrification. 

Biological Treatment Can be classified into

 1. Aerobic Treatment 

 a) Activated Sludge Process 

 b) Trickling Filter

2. Anaerobic Treatment

Aerobic Treatment :

 The treatment which is carried out by microorganism in the presence of oxygen.

Anaerobic Treatment : 

The treatment which is carried out by aerobes in the absence of oxygen. The need of oxygen is supplied by oxidation of oxygenated compound for e.g SO2

Tertiary Treatment (Advance waste water treatment) 

The main function of tertiary treatment is to decrease the load of nitrogen and phosphorous compound present in the effluent by the following process. 

a) Precipitation 

b) Nitrogen Stripping 

c) Chlorination 

a) Precipitation: The effluent received after the secondary treatment is mixed with calcium oxide. The lime then react with phosphorous compound in waste to from insoluble calcium phosphate, which then settle down a the bottom of settling tank.

b) Nitrogen Stripping Nitrogen present in waste water is generally in the form of ammonia gas , nitrates and nitrites. Ammonia is highly undesirable in streams and lakes because it is extremely lethal to aquatic biota. Nitrogen eventually enhance Eutrophication In order to remove nitrogen air is forced through the effluent which thereby result in the removal of ammonia gas. 

C) Chlorination It is the process in which chlorine is used to kill micro-organism .The main purpose of chlorination are - To assist in the formation of floc in the process of coagulation together with other chemical. - To prevent corrosion of sewers. - To prevent spread of epidemic.