Which chemicals are commonly used to remove phosphorus from wastewater?

The removal of phosphorus from wastewater is often achieved through chemical precipitation methods, and alum (aluminum sulfate) and ferric chloride are two of the most commonly used chemicals for this purpose.

Alum works by reacting with phosphorus to form insoluble aluminum phosphate, which can then be removed from the wastewater as sludge. This process not only helps in reducing phosphorus levels but also improves the settling characteristics of the sludge formed during sedimentation.

Ferric chloride operates in a similar manner. It reacts with phosphate ions in the wastewater to form ferric phosphate, which also precipitates out and can be easily removed. The iron based compounds are especially effective in environments with varying pH levels, making them versatile for different treatment scenarios.

Other options provided in the question serve different purposes. While sodium hydroxide and soda ash are commonly used to adjust pH or alkalinity, they are not primarily effective for phosphorus removal. Calcium nitrate and sodium bisulfite are more related to other processes, such as denitrification or controlling odors, and have limited applicability for phosphorus reduction. Chlorine and bleach are disinfectants and are typically not involved in nutrient removal processes. Thus, alum and ferric chloride stand out as effective chemicals for phosphorus removal in wastewater treatment systems.