How to Calculate the STP Plant Capacity for Schools and Colleges?

Sewage treatment plants (STPs) are essential systems in schools and colleges for treating wastewater before discharging it into the environment. These STPs must have a sufficient capacity to handle the amount of wastewater generated by the institution.  
Now, we will discuss how to calculate the sewage treatment plant capacity for schools and colleges, share the per-user water discharge, and calculate the requirement in detail as per the Indian Pollution Control Board.

Per-User Water Discharge  

Before we dive into the calculation of STP capacity, let's first understand the per-user water discharge in schools and colleges. The per-user water discharge is the amount of wastewater generated by a single person in a day. According to the Indian Pollution Control Board, the per-user water discharge in schools and colleges is 45 liters per day (L/d).

Calculation of STP Capacity          

The capacity of an STP depends on the number of users or students in the institution, the per-user water discharge, and the BOD (biochemical oxygen demand) and COD (chemical oxygen demand) levels of the wastewater. The BOD and COD levels indicate the amount of organic and inorganic pollutants present in the wastewater.

Steps: 
Here's how we can calculate the STP capacity for schools and colleges:

Step 1: Determine the total number of users or students in the institution. Let's assume that the institution has 1000 students.

Step 2: Calculate the total wastewater generated by the institution.           
As per the per-user water discharge, the total wastewater generated by the institution would be:  
                        Total wastewater generated = 1000 x 45                  
                                                                    = 45,000 L/d      

Step 3: Calculate the BOD and COD levels of the wastewater.      
The BOD and COD levels of the wastewater depend on the activities carried out in the institution. For schools and colleges, the BOD and COD levels are usually in the range of 250-350 mg/L and 500-600 mg/L, respectively. Let's assume that the BOD and COD levels of the wastewater are 300 mg/L and 550 mg/L, respectively.

Step 4: Calculate the STP capacity using the following formula:   

STP capacity = (Total wastewater generated x BOD level x Safety Factor) / (24 x BOD load x MLSS x MLVSS)

Where,

BOD load = BOD level / per-user water discharge  
MLSS = Mixed Liquor Suspended Solids (mg/L)     
MLVSS = Mixed Liquor Volatile Suspended Solids (mg/L)
Safety Factor = 1.5-2 (depends on the type of STP)

Assuming the safety factor to be 1.5, the STP capacity would be:  
STP capacity = (45,000 x 300 x 1.5) / (24 x (300/45) x 3000 x 2000)           
= 52.5 KL/d

Therefore, the STP capacity required for the institution would be 52.5 kiloliters per day (KL/d).

Conclusion:   
In conclusion, the calculation of STP capacity for schools and colleges involves determining the total number of users, per-user water discharge, BOD and COD levels, and safety factor. The capacity of the STP should be sufficient to handle the amount of wastewater generated by the institution and treat it to the required standards before discharging it into the environment.

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