Florida Drinking Water Operator "B" Practice Test

During reverse osmosis, which of the following compounds primarily causes scaling?

1. Iron compounds

2. Calcium carbonate

3. Sodium chloride

4. Silica

The correct answer is: Calcium carbonate

During reverse osmosis, calcium carbonate is the primary compound that causes scaling. Scaling occurs when dissolved salts precipitate out of solution and accumulate on the membrane surface, which can lead to reduced efficiency and increased maintenance needs. Calcium carbonate is particularly prone to precipitation when water undergoes temperature changes or when it is concentrated during the reverse osmosis process. As the concentration of calcium ions and carbonate ions increases, they can exceed their solubility limit and start to form solid deposits on the membrane. This scaling reduces the membrane's permeability to water and can significantly affect the overall performance of the reverse osmosis system. In contrast, while iron compounds, sodium chloride, and silica can also affect reverse osmosis systems, they do not typically contribute to scaling to the same extent as calcium carbonate. Iron may lead to fouling but is less common as a scaling agent. Sodium chloride, being highly soluble, does not precipitate under normal operating conditions of reverse osmosis. Silica can cause problems as well, but its behavior in terms of scaling is quite different from that of calcium carbonate, which is more straightforward and predictable in terms of precipitation under these conditions.