Wastewater disinfection methods: Which options list the common and widely implemented disinfection approaches used at municipal and industrial wastewater treatment plants?

Introduction:
Disinfection in wastewater treatment reduces pathogens before discharge or reuse. Practical plant-scale methods must be effective, safe, and economical at high flow rates. Chlorination and ultraviolet (UV) irradiation are the two most widely applied options globally due to proven performance and established design guidance.

Given Data / Assumptions:

• Wastewater effluents contain suspended solids that can shield microbes.
• Systems must be scalable and continuously operable.
• Residual control and by-product formation are considered in method choice.

Concept / Approach:
Chlorination (gas chlorine or hypochlorite) provides a measurable residual and broad-spectrum efficacy but can form chlorinated by-products; dechlorination may be needed. UV disinfection inactivates microorganisms by damaging nucleic acids without leaving a chemical residual, avoiding formation of halogenated by-products but requiring low UV transmittance attenuation and clean lamp sleeves. Many facilities use either method depending on effluent quality and regulatory goals.

Step-by-Step Solution:
Identify proven, scalable methods: chlorination and UV are both mainstream.Exclude nonstandard or impractical options for high flows (e.g., phenolic solvents, boiling).Select the inclusive option listing both chlorination and UV.

Verification / Alternative check:
Design manuals provide dosage–contact time (CT) guidelines for chlorine and UV dose–response curves, underscoring their prevalence in plant design.

Why Other Options Are Wrong:

• Phenolic solvent: Not a practical or permitted method for large-scale wastewater disinfection.
• Boiling: Impractical at plant scale due to enormous energy demand.

Common Pitfalls:
Ignoring upstream solids removal; poor clarification can reduce UV efficacy and chlorine demand estimates.

Final Answer:
both (a) and (b)