Which of the following best distinguishes domestic wastewater from many industrial wastewaters in terms of characteristics?
- ADomestic wastewater generally has more uniform compositionCorrect
- BDomestic wastewater is always acidic in nature
- CDomestic wastewater contains heavy metals
- DThe BOD/COD ratio is very low
Solution
Concept
Comparison of domestic and industrial wastewater characteristics
Formula
NONE
Step-by-step solution
1. Domestic wastewater arises from consistent human daily routines (bathing, food preparation, sanitary waste). 2. Consequently, domestic wastewater has a relatively stable, uniform composition compared to industrial streams. 3. Industrial wastewater varies widely by factory type and manufacturing batches. 4. Hence, uniform composition is the distinguishing characteristic. Answer: A
Explanation
Domestic wastewater originates from residential plumbing fixtures and daily domestic activities, exhibiting a relatively predictable and uniform composition of organic matter, nutrients, and neutral-to-slightly alkaline pH. In contrast, industrial wastewaters vary widely in flow rate, chemical constituents, toxic contaminants, extremes of pH, and biodegradability.
Why the other options are wrong
B) Fresh domestic sewage is slightly alkaline, not acidic. C) Domestic wastewater generally lacks heavy metals, which are characteristic of industrial discharges. D) Domestic wastewater has a relatively high BOD/COD ratio (~0.4 to 0.6).
Shortcut
Domestic sewage = Predictable and uniform; Industrial effluent = Highly variable, complex.
Common mistake
Believing domestic wastewater has a low BOD/COD ratio or is acidic; fresh domestic sewage is typically slightly alkaline with BOD/COD around 0.5.
Correct answer: A) Domestic wastewater generally has more uniform composition