1. Waste water – What is it and its types ?

Wastewater or sewage is water that has been adversely affected in quality by containing wastes from residential, commercial, and industrial processes. Waste water encompass a wide range of hazardous dissolved toxins and chemicals, whiles others contain particles, sediments and suspended matter of all sizes. Waste water requires treatment to remove pollutants prior to discharge.

Wastewater Treatment Plant

Wastewater comes in three main types namely Black water, Gray water and Yellow water.

1. Black water : Black water is from toilets fixtures and kitchen sinks and known to be highly contaminated with dissolved chemicals, particulate matter and is very pathogenic.

2. Grey water : This is wastewater that originates from non-toilet and food fixtures such as bathroom sinks, washing machines, bathtubs, dishwashers and sinks and so on.

3. Yellow water : This is basically urine collected with specific channels and not contaminated with either black water or gray water.

2. What is Waste Water Treatment and why it is required ?

Waste water treatment is the process of converting wastewater – water that is no longer needed for use and that can be discharged back into the natural environment. In other words converting used water into environmentally acceptable water is called wastewater treatment.

The main objective of wastewater treatment or waste water management is to allow human and industrial effluents to be disposed of without leaving danger or harm to the human health and the natural environment. These dangerous wastes must be taken out of the water and treated safely and hence waste water treatment is required. The source of a wastewater will determine its characteristics and how it must be treated.

3. Types of waste water treatment process or methods :

Some of the important types of wastewater treatment plants are as follows:

1. Effluent Treatment Plants (ETP)

2. Sewage Treatment Plants (STP)

3. Common and Combined Effluent Treatment Plant (CETP)

The above listed wastewater treatment plants are not generic and they vary from one locale to another.

Step by step of waste water treatment process involved during waste water disposal or how waste water comprising domestic, industrial and commercial waste is treated for disposal is categorized as follows :

1. Preliminary Treatment :

The main purpose of this treatment is to protect the operation of the wastewater treatment plant and it removes waste water constituents which can damage or clog pumps.

The incoming wastewater, called influent, passes through screens that remove bulky suspended or floating solids and that can be skimmed off.

After screening wastewater passes into a grit chamber which is another component of this treatment where cinders, sand, and small stones settle to the bottom.

It uses comminuters for grinding large sized suspended solids to smaller size and is usually provided in large plants. Clarifiers are used for continuous removal of solids being deposited by sedimentation.

2. Primary Treatment :

The wastewater, with large debris and grit removed in preliminary treatment is then subjected to primary treatment system.

When waste water is subjected to primary sedimentation tank where heavy particles sink and light particles float.

Sedimentation often uses chemicals like flocculants and coagulants and the effluent from primary sedimentation units is referred to as primary effluent.

During this treatment, about 70% of total suspended solids and 60% of oil, grease and plastic products are removed.

The partially treated wastewater from primary setting tanks are then directed to the next phase i.e. secondary treatment system to become bio-solids.

3. Secondary Treatment :

It's objective is the further treatment of the effluent from primary treatment to remove residual solids and organics.

The main principal of secondary treatment is it uses a process known as “activated sludge” (sludge with high levels of bacteria).

In this process about 80% of organic matter in the sewage will be removed by making use of bacteria in it.

During this treatment, sedimentation tank that allows both solids and microorganisms to form clumps and settle to the bottom as secondary sludge.

4. Tertiary Treatment :

Tertiary treatment involves advanced treatment processes that generate a higher quality effluent than secondary/primary treatment can produce.

This stage has the ability to remove up to 99% of the impurities from the wastewater.

Tertiary treatment includes filtering, disinfecting and preparing wastewater for recycling.

It includes a disinfection process using UV light, chlorination or ozone treatment to remove bacteria and viruses before it's release into the environment.

It utilizes some form of filtration to achieve a higher level of suspended solids removal than is possible through primary and secondary screening and sedimentation.

5. Waste Water Recycling :

Water resources are depleting day by day and hence recycling and reuse of wastewater is extremely important to preserve our precious resources for domestic, agriculture, commercial and industries. Treating waste water using waste water treatment plants/methods produce high quality recycled water that is suitable to meet a number of needs in many sectors and its usage has grown significantly in the last several years.

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