Wastewater is the water that remains after humans have used fresh water for domestic, commercial, and industrial purposes. In general, fresh water is used for a variety of domestic purposes such as washing, bathing, and flushing toilets. Washing entails washing cooking utensils, washing vegetables and other food items, bathing, washing hands, and washing clothes, etc.
The water that results from these uses contains vegetable matter, oils used in cooking, oils in hair, detergents, dirt from washed floors, soap used in bathing, and oils/greases. This water is known as wastewater or greywater.The water used to flush toilets to remove human excreta is known as "Black Water" or Sewage.
Grey water is easier to purify than black water, or sewage. However, in India, it is common practice to combine these two wastes and discharge them into a public sewer or a sewage treatment plant.
But, before building any sewage treatment plant, we must know its capacity to handle. Let’s discuss it in detail.
Why should sewage be treated?
Much of the water used in the home does not have to be potable (drinking water quality). Water used for flushing toilets, washing floors, yards, or roads, and gardening, for example, does not have to be potable. It must be treated in a scenario where fresh water is becoming increasingly scarce, and enormous volumes of sewage generated in the country are not being treated.
Discharging untreated sewage into any drain other than an underground sewerage system, or into open land, is a violation of the laws of all Pollution Control Boards in the country, and is punishable by prosecution.
Sewage must be properly treated before being reused or recycled for a variety of purposes, which do not require potable water quality. Recycling/reusing treated sewage can significantly reduce fresh water requirements, by nearly 50-60%.
How is sewage capacity estimated or calculated?
Before calculating the size and capacity of the STP, calculate the total domestic/industrial/ commercial raw water demand, required per NBC-2005, taking into account 135-150 LPCD.
· Total domestic water demand = TWD
· Estimated sewage X = 90% of total domestic (raw) water demand
· Calculate Sewerage X = 90/100 * TWD (For Example, if TWD = 1500 KLD).
· S.T.P capacity = 90 / 100 * 1500 KLD = 1350 KLD
· Space Requirement For 1350 Cum STP = Assume total depth of 3.30 Meter with free board of 300 MM (Standard Depth )
· Liquid Depth L = 3.0 Meter
· STP Size = 1350/3 = 450 =450/15 (Assumed Breadth) = 30 (Width)
· Total Area = 15303 = 1350 CUM
How much would STPs of various capacities cost?
The prices listed here are merely indicative and are intended to provide an idea. All capacities are given in KLD (Kilo litres per day).
• 5.0 KLD STP = approximately Rs.5.0 lakhs
• 10 to 15 KLD = approximately Rs.8.0 lakh
• 25 KLD = approximately Rs.15.0 Lakhs
• 35 KLD = approximately Rs.18.0 Lakhs
• 50 KLD = approximately Rs.35.0 Lakhs
• 75 KLD = approximately Rs.40.0 Lakh
Conclusion
The sewage collected from the municipal area is made up of wastewater generated by residences, commercial centers, recreational activities, and institutions, as well as industrial wastewater discharged into the sewer network, by permitted industries within the city limits.
Before designing the sewer, it is necessary to comprehend the discharge, i.e., the amount and quality of sewage.
What do we offer?
If you have any questions about sewage treatment plants, or if you would like to discuss your specific needs, please contact the Netsol Water team right away. Our team is an expert in water treatment and can help you tailor a solution, to your specific requirements.