How to calculate the Sewage Treatment Plant capacity for Commercial plants ?
To calculate the Sewage Treatment Plant (STP) capacity for a commercial establishment, the following steps can be followed:
Estimate the Total Wastewater Flow:
The first step is to estimate the total wastewater flow that the commercial Sewage treatment plant establishment generates. This can be done by using the water consumption data, which is usually provided by the water utility or can be measured using a water meter. The estimated water consumption needs to be multiplied by a factor that accounts for the peak wastewater flow rate and the amount of water that is lost through evaporation and other losses.
Determine the Design Flow:
The design flow is the maximum wastewater flow rate that the Sewage treatment plant should be designed to handle. It is usually calculated by adding a safety factor to the estimated peak wastewater flow rate. The safety factor depends on the variability of the wastewater flow and the reliability of the STP technology.
Determine the BOD Load:
The BOD load is the amount of organic matter in the wastewater that needs to be treated by the STP. It is usually expressed in terms of the BOD (Biochemical Oxygen Demand) concentration and the BOD load per day. The BOD load can be estimated by using the BOD concentration data of the wastewater.
Select the STP Technology:
Based on the estimated wastewater flow rate and BOD load, the most suitable STP technology can be selected. The selection of STP technology should take into account factors such as the efficiency, cost, space requirements, and maintenance requirements.
Calculate the STP Capacity:
Finally, the STP capacity can be calculated based on the design flow and the BOD load. The STP capacity should be designed to handle the maximum wastewater flow rate and the maximum BOD load, with a safety factor to account for any variations in the wastewater flow and quality.
Let’s take an example to understand how to calculate the Sewage Treatment Plant (STP) capacity for a commercial establishment.
Example: A hotel has 100 rooms, each with an average occupancy of 2 persons. The hotel provides three meals a day, and the average water consumption per person is estimated at 150 liters per day. The hotel operates for 365 days a year. The hotel is located in an area where the water supply is available throughout the year.
Step 1: Estimate the Total Wastewater Flow
Total Wastewater Flow = No. of Rooms x Occupancy x Water Consumption x Days of Operation
= 100 x 2 x 150 x 365
= 10,950,000 liters per year
= 30,000 liters per day (approx.)
Step 2: Determine the Design Flow
Design Flow = Total Wastewater Flow x Safety Factor
Assuming a safety factor of 1.5, Design Flow = 30,000 x 1.5 = 45,000 liters per day
Step 3: Determine the BOD Load
Assuming a BOD concentration of 250 mg/L and a discharge standard of 30 mg/L, the BOD load can be calculated as follows:
BOD Load = Design Flow x BOD Concentration x Discharge Standard
= 45,000 x 250 x (1 – 30/250)
= 3,825 kg/day
Step 4: Select the (Sewage Treatment Plant) STP Technology
Based on the estimated wastewater flow rate and BOD load, the most suitable STP technology can be selected. For this example, we can consider an MBBR (Moving Bed Biofilm Reactor) technology, which is a compact and efficient technology that requires minimal maintenance and has a small footprint.
Step 5: Calculate the STP Capacity
The MBBR technology has a design loading rate of 1-5 kg BOD/m3.day. Assuming a loading rate of 2.5 kg BOD/m3.day, the required STP capacity can be calculated as follows:
STP Capacity = BOD Load / Design Loading Rate
= 3,825 / 2.5
= 1,530 m3/day
