Raw wastewater CBOD concentration of 450 ppm is most likely due to:

• A. High organic load
• B. Low organic load
• C. Septic condition
• D. Alkaline condition

Answer: (A)

CBOD measures the amount of carbon-containing, readily biodegradable organic material in wastewater. A value of 450 ppm in raw wastewater indicates a large amount of such organic matter entering the system, which translates to a high organic load. The higher the organic load, the more oxygen is needed by microorganisms to oxidize that material, so CBOD rises accordingly. The other options don’t explain a high CBOD: a low organic load would produce a much lower CBOD, alkaline conditions don’t directly determine CBOD values, and while septic conditions involve microbial activity, they don’t specifically indicate the quantity of biodegradable carbon that CBOD measures.