Liquid Wastewater Management

Neptune-Industrial-WastewaterThe problem of waste management in India is turning more and more terrifying by the day. Inappropriate dumping has major repercussions, such that it can change fertile soil into an arid land. Improper disposal of waste not only effects the environment but also impairs human health as it is the breeding ground of carriers like mosquitoes and flies. Drinking contaminated water causes various water borne diseases. Hence awareness about waste disposal is imperative.

The term waste broadly implies that something is unwanted. But this term is also relative.  One man’s trash is another man’s gold. A carcass of an animal is viewed as a waste but it is a scavenger’s food. Hence waste management is the process of supervising and handling these unwanted materials such that they can be reused and do not cause any potential threat to damage the environment.

Liquid waste, also called waste water, is any liquid with constituents that affect the quality of water such that it is unsuitable for use. Most waste water flows through the sewer and drains and is collected from homes, offices and industrial buildings. This wastewater is transferred to municipal treatment plants whereby the liquid is purified using various techniques.

The quality of water is measured by two parameters, namely BOD and COD. BOD or biological oxygen demand is the amount of oxygen needed by an organism in a water body to consume the organic content in one liter of water. The higher the BOD is, the poorer the water quality. COD or chemical oxygen demand is a technique to indirectly measure the water pollution in a water sample. It is primarily used to calculate the organic matter present in the sample. It too measures the oxygen depleted by the organic constituents.

There different types of wastewater are listed below:

  • Sewage wastewater
  • Agricultural wastewater
  • Industrial wastewater

Waste water contains a lot of pollutants – chemicals as well as dissolved solids and suspended solids and it requires an extensive process to purify the same. The complete process of waste water treatment can be divided into three different steps:

  • Primary treatment
  • Secondary treatment
  • Tertiary treatment



The steps involved in purifying contaminated liquid are:

  • Screening: The first step post the arrival of the waste water in a treatment plant is its screening. This step clears out objects from the water that are large and floating like sticks, rags, cans, cloth and various other objects. The screens are made up of steel bars that are spaced very few centimeters apart, preventing any large object to pass through them.


  • Grit chamber: After screening, the waste water is allowed to pass through a grit chamber and kept for enough time such that heavy materials like sand settle down.


  • Primary Settling: The waste water is then passed through a tank called the primary settling tank or the ‘primary clarifier’. It is allowed to stand for about two to three hours, enough time for the lighter suspended solids to settle down due to gravity. These suspended particles are then removed.

The effluents obtained from the primary sedimentation tanks are first subjected to systems like rotating biological contractor, trickling filters, active sludge units and oxidation ponds where they undergo aerobic oxidation. The sludge (i.e., the deposit at the bottom of the tank) obtained is allowed to undergo anaerobic oxidation in sludge digesters.



The primary treatment does not remove all the impurities present in the waste water that’s when secondary treatment comes into the picture. The use of secondary treatment is to remove the finer impurities in the water such as the biological oxygen demand (BOD) and dissolved and suspended solids. The BOD is removed by using bacteria and other microorganisms to react with the water. These processes maybe aerobic i.e. in the presence of oxygen or anaerobic i.e. in the absence of oxygen.  Thus, in secondary treatment oil, grease and organic matter (BOD) are removed to the largest extent.


The main purpose of tertiary treatment is to remove dissolved nutrients, especially nitrogen and phosphorous which has survived the primary and secondary treatment. The purpose of tertiary treatment is to provide suitable water for drinking. Therefore, besides nutrient removal, some amount of fine suspended solids, bacteria and organic materials should also be removed. This can be achieved by passing water through activated charcoal which absorbs them.



Water pollution cannot be eradicated but can be controlled through awareness.

  • Public awareness: the people must be made aware of the adverse effects of contaminated water. People who use pond, lakes etc. for washing clothes, utensils and themselves should not use the same water for drinking or cooking purposes.
  • Government awareness: Water resources belong to the nation hence government should take proper steps in the maintenance and cleanliness. Example: clean Ganga campaign.
  • Domestic awareness: domestic waste water should not be allowed to contaminate public water reservoirs or agricultural fields. Using eco-friendly soaps and detergents can make domestic water less harmful.
  • Industrial awareness: industries must not be allowed to operate without proper treatment plants. Water should be handled and be harmless before allowing it to mix with water resource.

Treatment of waste water is not only the responsibility of the government, but it is ours too. Using organic and eco-friendly substances for washing and cleaning reduces contamination of water. Fresh water is limited in nature, hence we should be careful how we use it.



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