In wastewater treatment plants (both urban or industrial), lime is widely used for correcting the pH balance of acidic waters, for precipitating heavy metals and phosphates, and for its flocculating action.
Lime is widely used for stabilizing industrial residual sludge or dredging sludge and for treating urban biosolids before agricultural re-use or incineration.
Lime helps coagulation, makes sludge easier to handle, prevents fermentation, limits odours, eliminates pathogens and holds metallic ions in an insoluble form. It also enriches the sludge with calcium and magnesium (when dolomitic lime is used), both of which are beneficial for agricultural use.
In addition, lime is used to treat soils polluted with hydrocarbons.
-Using in adjusting pH levels (by making them higher) can precipitate most heavy metals in the form of hydroxides.
-Precipitating phosphates and sulphates in wastewater as well as the heavy metals, in the form of insoluble salts - Ca3(PO4)2, CaSO4 - that are easy to collect.
-Neutralizing the negative charge on colloid particles contained in water and causing the flocculation of suspended impurities, acting as the flocculating agent to which metallic salts and/or polymers can also be added.
Liquid Sludge Treatment:
-Using lime milk to treat liquid sludge facilitates the coagulation of colloid particles, increasing the size of the sludge "flakes" and its dry matter content. This makes it easier to filter the sludge and also improves the performance of dehydration equipment.
-Lime is normally applied where press filters are used. However, adding lime also makes it possible to eliminate infectious germs by increasing the pH level of the sludge and preventing fermentation, thus reducing odours.