pH in wastewater engineering: Evaluate the statements—(A) Determining the pH of sewage is important. (R) The efficiency of several treatment methods depends on pH. What is the correct A–R relationship?
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ABoth A and R are true and R is the correct explanation of A
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BBoth A and R are true but R is not a correct explanation of A
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CA is true but R is false
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DA is false but R is true
Answer
Correct Answer: Both A and R are true and R is the correct explanation of A
Explanation
Introduction / Context:pH fundamentally influences chemical equilibria and biological activity in wastewater systems. Accurate pH measurement guides process control for coagulation, digestion, nitrification, disinfection, and corrosion control in sewers and plants.
Given Data / Assumptions:
- A: pH determination is important.
- R: Process efficiency depends on pH availability/control.
- Typical unit processes are pH sensitive.
Concept / Approach:
Many unit operations have optimum pH windows: alum/iron coagulation, biological nitrification (around neutral), anaerobic digestion stability (alkalinity and pH), and chlorine disinfection efficacy. Therefore, knowing and adjusting pH is integral to achieving treatment goals, explaining why pH measurement is important.
Step-by-Step Solution:
Identify pH-sensitive processes (coagulation, biological steps, disinfection).Relate target performance to pH control bands.Conclude that pH measurement is essential because process efficiency relies on it.Verification / Alternative check:
Process control charts show reduced efficiency outside pH setpoints; jar tests and upstream alkalinity additions demonstrate dependence.
Why Other Options Are Wrong:
Options (b)–(d) contradict the well-established causal link between pH and treatment efficiency.
Common Pitfalls:
Calibrating pH meters infrequently; ignoring temperature effects; relying on grab pH only when diurnal variation is significant.
Final Answer:
Both A and R are true and R is the correct explanation of A