Which of the following is an example of a tertiary treatment method?

Tertiary treatment methods are advanced processes used in wastewater treatment that go beyond primary and secondary treatments to remove remaining contaminants and enhance water quality before final discharge or reuse. Filtration and disinfection are key examples of tertiary treatment.

Filtration involves passing wastewater through various media to remove particulate matter, while disinfection typically employs chemical agents (such as chlorine) or physical methods (like ultraviolet light) to eliminate pathogens. These processes significantly improve the quality of the effluent, making it safer for the environment or human use.

In contrast, settling tanks and gravity separation focus on removing solids through sedimentation, which is part of primary treatment, while composting refers to the conversion of organic matter into compost, not specifically a wastewater treatment process. Therefore, filtration and disinfection represent the advanced level of treatment that characterizes tertiary methods, making this the correct answer.