Lime is among the chemicals used in the treatment of drinkable and industrial water resources. It’s Used by many municipalities to improve water quality, especially for water softening and arsenic removal
In water softening, the hydrated lime is used to remove carbonate hardness from water (caused by biocarbonates and calcium and magnesium carbonates). The hardness called non-carbonate hardness, which is caused by other calcium and magnesium salts, is generally treated by lime-soda treatment, which requires the precipitation of magnesium with lime. The co-produced calcium salt reacts with the soda ash to form a calcium carbonate precipitation. Lime softening can also be used to purify arsenic from water
pH Adjustment / Precipitation
The hydrated lime is widely used to adjust the pH of the water to prepare for further purification. Lime can also be used to neutralize acid water, thereby reducing corrosion of the main line pipes from acid water to prevent corrosion. Corrosive water contains excessive amounts of carbon dioxide (carbonic acid). The lime precipitates CO2 to form calcium carbonate, which provides a protective coating inside the water distribution pipes.
Lime is used in combination with alum or iron salts to remove the turbidity caused by suspended solids in raw water. It helps to maintain the appropriate pH for the most satisfactory coagulation conditions. In some water treatment plants, alum sludge is treated with lime to facilitate sludge thickening in pressure filters.
Effect on Pathogen Development
By adding lime, in 24 - 72 hours, the pH of water increases to 10.5 – 11, this will eliminate the necessary environment for the development of bacteria and certain viruses. This lime application is used in places where phenolic water is present because chlo rine application causes an unpleasant taste of water in the presence of phenol. This process so-called extreme alkalinity process also destroys heavy metals.
Removal of Trace Elements Causing Pollution
Lime is also used in the purification of manganese, fluoride, organic tannins and iron
LIME USAGE IN THE TREATMENT OF HAZARDOUS WASTES
Lime is widely used to treat hazardous wastes. Lime stabilizes most metals by converting them to more stable forms that are less likely to be chemically soluble. It can also be used to neutralize acidic substances.
LIME USAGE IN THE TREATMENT OF WASTE WATER
Lime is also used extensively in the purification of domestic waste water as well as the purification of industrial effluents.
Domestic Waste Water Treatment
In advanced wastewater treatment plants, it is used in tertiary processes where lime suspended solids and solids together with phosphorus precipitate as complex calcium phosphate. Due to the high pH of 10.5-11.0 formed by the lime, it is also facilitated to remove the other algae nutrient nitrogen. Thus, removal of phosphorus and Nitrogen helps to prevent the process of ossification (seaweed formation) in surface waters.
When alum and ferric chloride is used for precipitation, Lime is used to increase the pH value caused by these acid salts and to provide the basic environment necessary to remove the active nitrogen.
In sewage systems where sewage sludge is filtered by vacuum or by pressure filtration, lime and iron chloride are used to help sludge to stabilize the sludge and for final clarification of the active substance.
Industrial Waste Water
Limestone has numerous applications in the treatment of industrial wastewater, especially in which acidic wastes need to be neutralized. Sulfuric acid based waste pickling solutions are neutralized with lime in steel plants. Lime is also used to precipitate chromium, copper and heavy metals in the treatment of wastes of coating plants.
Lime is used to neutralize sulfuric acid wastes from artificial silk factories and to precipitate solids in solution.
Lime citrus helps in clearing waste water, clarifying waste water and processing by-products of citrus pulp.
The high degree of acidic drainage in working and abandoned mines is often neutralized with lime. Further clarification of waste is achieved by precipitating iron in the pyritic extractor. Coal washing plants use lime to neutralize acidic waste or reduce friction on steel equipment and to process the waste for reuse.