Question

The Biochemical Oxygen Demand (mg/l, max) of effluents discharged in Public Sewers should be less than .......

• A. 50
• B. 150
• C. 350
• D. 600

Hint:

Remember the three standard BIS BOD discharge limits:
1. Inland surface waters: \( 30 \text{ mg/L} \)
2. Land for irrigation: \( 100 \text{ mg/L} \)
3. Public sewers: \( 350 \text{ mg/L} \)

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Biochemical Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen required by aerobic microorganisms to decompose organic matter in a water sample over a specific period (usually 5 days at \( 20^\circ\text{C} \)).
It is an important parameter used to assess the organic strength of food industry wastewater before it is discharged.

Step 2: Detailed Explation:
Environmental protection regulations establish discharge standards for industrial effluents to protect tural water bodies and sewage treatment infrastructure.
When effluents are discharged directly into municipal public sewers, the standards are less stringent than those for inland surface waters because the municipal plant will provide further biological treatment.
According to the standards set by the Central Pollution Control Board (CPCB) and Bureau of Indian Standards (BIS: 2490), the maximum permissible BOD limit for discharging industrial wastewater into public sewers is \( 350 \text{ mg/L} \).
Discharges with BOD levels higher than this can overload the aeration basins of municipal treatment plants, leading to process failure and septic conditions.
In contrast, the limit for discharging wastewater into inland surface waters is much stricter, typically restricted to \( 30 \text{ mg/L} \).
The limit for land application (irrigation) is generally set at \( 100 \text{ mg/L} \).

Step 3: Fil Answer
The maximum permitted BOD limit for discharging wastewater into public sewers is \( 350 \text{ mg/L} \).