Aeration is primarily used to treat which of the following contaminants in water?

Aeration is primarily effective for treating dissolved iron and manganese in water. The process of aeration involves introducing air into the water, which helps in oxidizing these dissolved metals, transforming them into particulate forms that can then be filtered out. When oxygen is introduced into the water, it reacts with dissolved iron and manganese, causing them to precipitate as solid particles.

This precipitation allows for easier removal through filtration or sedimentation, improving the overall water quality. The treatment is particularly important in groundwater sources where iron and manganese can cause staining and taste issues in water, making aeration a suitable method for their remediation.

While suspended solids, chlorine residual, and heavy metals may also require treatment, the specific process of aeration directly targets the transformation and removal of dissolved iron and manganese, making it the correct answer in this context.