Inorganic coagulation is both cost-effective and applicable for a broad variety of water and wastewater. Inorganic coagulant treatment is particularly effective on raw water with low turbidity (total suspended solids concentration) and will often treat this type of water when organic coagulants cannot.
Once added to water, inorganic coagulant chemicals react with the alkalinity and hydrate to form metal (aluminum or iron) hydroxide precipitates, which act as a sweep-floc mechanism. This mechanism can be compared to snowfall on dirty air. As the snow falls, it adsorbs particulates in the air, which coprecipitate, thus cleaning the air. In water treatment, the metal hydroxide sweep-floc acts on water the way a snowfall acts on air. Many difficult-to-treat colloidal suspensions can be effectively treated using inorganic coagulants.
Although the metal hydroxide precipitate sweep-floc is advantageous in water cleaning, these precipitates add to the overall sludge volume that must be treated and removed. These precipitates also tend to lower the overall density and dewaterability of sludge versus precipitates created with organic coagulants. For influent or raw water applications where the sludge is generally non-hazardous, the penalty for creating more sludge with higher water content is small. For wastewater applications with hazardous sludge, the economic penalty can be significant.