NCEES Fundamentals of Engineering (FE) Civil 2025 – 400 Free Practice Questions to Pass the Exam

Precipitation softening is a water treatment process that specifically targets the removal of hardness, which is primarily due to calcium and magnesium ions in the water. By adding lime (calcium hydroxide) and soda ash (sodium carbonate) to the water, these compounds react with the hardness ions to form insoluble precipitates. These precipitates can then be effectively removed from the water through sedimentation and filtration, leading to a significant reduction in water hardness.

The process is advantageous because it not only softens water but can also help in the reduction of other undesirable constituents by adjusting the water's pH. This makes it a widely used and effective method for treating hard water in various applications, including municipal water supplies and other treatment facilities.

The other methods do not relate to precipitation softening. For example, physical filtration methods do not chemically alter the composition of water to remove hardness. Biological agents focus on degrading organic contaminants rather than tackling inorganic hardness. Heating the water is effective for evaporation purposes but does not specifically address the removal of hardness compounds in the way that precipitation softening does. Therefore, the approach of adding lime and soda ash is uniquely suited for addressing the hardness problem in water treatment.