Which type of system is used for automatic regeneration in water softening?

Ion exchange systems are designed to utilize a process that allows for automatic regeneration specifically in the context of water softening. In these systems, hard water containing minerals like calcium and magnesium comes into contact with resin beads that are coated with sodium ions. As the water flows through the resin, the hard minerals are exchanged for sodium, effectively softening the water.

Over time, the resin becomes saturated with these hard minerals and loses its effectiveness. This is where the automatic regeneration process comes into play. A brine solution, which is a concentrated salt solution, is periodically flushed through the resin. This replenishes the sodium ions on the resin beads while removing the accumulated calcium and magnesium ions through another ion exchange process. This regeneration ensures that the ion exchange system continues to function efficiently and provides soft water.

The other options listed do not involve a regeneration process suitable for softening water. Reverse osmosis systems primarily focus on the removal of a wide range of contaminants through a membrane without specifically targeting hardness minerals through regeneration. Distillation systems work by boiling water and condensing the vapor, which also does not utilize automatic regeneration. Filtration systems may remove particulates and some impurities but do not soften water through an ion exchange mechanism or regeneration process.