Which type of water treatment system may require a holding tank for effective iron removal?

Aeration systems are designed to remove dissolved gases and volatile contaminants from water, and one of their primary functions is the removal of iron from groundwater. When iron is present in its dissolved form, it can be oxidized into a solid precipitate through aeration, which makes it easier to remove from the water.

A holding tank is often necessary in conjunction with aeration systems because it allows for adequate contact time between the air and the water. This contact time is essential for the oxidation process to occur effectively. After aeration, the oxidized iron forms tiny particles that can settle out of the water. The holding tank provides a space for these particles to aggregate and settle, improving the efficiency of the iron removal process.

The other treatment systems mentioned do not typically require a holding tank for the purpose of iron removal. For instance, granular activated carbon systems focus primarily on removing organic compounds and chlorine but are not specifically designed for iron removal. Membrane systems, such as reverse osmosis, primarily function through filtration mechanisms rather than oxidation processes. Aerobic systems may address some biological contaminants but do not directly facilitate the oxidation process needed for effective iron removal in the same way that an aeration system does.