Which treatment level contains less suspended solids and lower CBOD5?

Which treatment level contains less suspended solids and lower CBOD5?

• A. Level I
• B. Level II
• C. Level III
• D. Level IV

Answer: (D)

Higher treatment levels correspond to more thorough removal of solids and organic matter, so the effluent has less suspended solids and a lower CBOD5. Level IV involves the most advanced treatment, often including polishing or tertiary steps that remove remaining fine particles and reduce biodegradable organic matter further. This combination yields the smallest amount of suspended solids and the lowest CBOD5 among the options, producing cleaner effluent. The earlier levels focus on basic screening, settling, or primary/secondary treatment, which remove a substantial portion but not as much of the solids and CBOD5 as Level IV.

Higher treatment levels correspond to more thorough removal of solids and organic matter, so the effluent has less suspended solids and a lower CBOD5. Level IV involves the most advanced treatment, often including polishing or tertiary steps that remove remaining fine particles and reduce biodegradable organic matter further. This combination yields the smallest amount of suspended solids and the lowest CBOD5 among the options, producing cleaner effluent. The earlier levels focus on basic screening, settling, or primary/secondary treatment, which remove a substantial portion but not as much of the solids and CBOD5 as Level IV.