What is used to control the growth of algae and protozoa?

The correct choice for controlling the growth of algae and protozoa in water supply systems is chlorination. Chlorination involves adding chlorine or chlorine compounds to water, which acts as a disinfectant. It is effective in killing a variety of microorganisms, including algae and protozoa, thereby preventing their growth and ensuring water safety for human consumption.

While filtration is used to remove particles and some microorganisms from water, it does not specifically target the control of algae and protozoa like chlorination does. Boiling water is effective in killing many pathogens, but it is not typically used on a large scale for controlling algae growth. Flocculation is a process that helps in the aggregation of particles for easier removal from water but does not directly kill or control the growth of microorganisms. Therefore, chlorination is the preferred method for effectively managing and preventing the growth of algae and protozoa in water systems.