By what means is biological sewage treatment plant effluent disinfected before discharge overboard?

Correct Answer: Option C — Hypochlorite tablets or liquid solution and ultraviolet irradiation are both approved means of disinfection.

MARPOL Annex IV and 33 CFR Part 159 mandate that sewage effluent must be disinfected before overboard discharge. Approved methods include chemical disinfection using chlorine-based tablets or liquid solutions, and physical disinfection via ultraviolet light irradiation, ensuring the destruction of pathogenic organisms to meet international environmental discharge standards.