Softening:
When water contains a significant amount of calcium and magnesium, it is called hard water. Hard water is known to clog pipes and to complicate soap and detergent dissolving in water.
KASRAVAND Water softening technology is a technique that serves the removal of the ions that cause the water to be hard, in most cases calcium and magnesium ions. Iron ions may also be removed during softening.
The best way to soften water is to use a water softener unit and connect it directly to the water supply.
Water softeners are specific ion exchangers that are designed to remove ions, which are positively charged.
Softeners mainly remove calcium (Ca2+) and magnesium (Mg2+) ions. Calcium and magnesium are often referred to as 'hardness minerals'.
Softeners are sometimes even applied to remove iron. The softening devices are able to remove up to five milligrams per liter (5 mg/L) of dissolved iron.
Softeners have different types such as automatic, semi-automatic, or manual. Each type is rated on the amount of hardness it can remove before regeneration is necessary.
Ion exchangers are often used for water softening. When an ion exchanger is applied for water softening, it will replace the calcium and magnesium ions in the water with other ions, for instance sodium or potassium. The exchanger ions are added to the ion exchanger reservoir as sodium and potassium salts (NaCl and KCl)
Types of Water Hardness
Temporary Hardness
this refers to hardness which effects can be removed by boiling the water in an open container. Such waters have usually percolated though limestone formations and contain bicarbonate HCO3– along with small amounts of carbonate (CO3)2– as the principal negative ions. Boiling the water promotes the reaction by driving off the carbon dioxide gas.
2 HCO3– → (CO3)2– + CO2
The (CO3)2– reacts with Ca+2 or Mg+2 ions, to form insoluble calcium and magnesium carbonates which precipitate out. By tying up the metal ions in this way, the amounts available to form soap scum are greatly reduced. While boiling is not an economical way to soften water, the chemistry demonstrated by boiling defines the difference in temporary and permanent hardness.
Permanent Hardness
Waters that contain other anions such as chloride or sulfate cannot be softened by boiling, and are said to be "permanently" hard. These must be softened by other methods, including lime soda or, more frequently, ion exchange softening.
A water softener typically consists of two tanks, a larger one into which rock or pellet salt is added and a smaller tank containing the ion exchange resin through which the hard water passes. A control valve fixed atop the resin tank of the industrial water softener causes the system to recharge or regenerate based on passage of a pre-set time or it meters the water treated and initiates regeneration based on a pre-set number of gallons treated.
When regeneration is initiated, the first step is to backwash the resin bed with raw water to fluff the resin and remove entrained dirt and sediment. Then brine is slowly deducted from the salt tank at a set flowrate for a specific time (set as a function of the resin volume and the influent water hardness), followed by a slow draw of raw water to slowly displace the brine solution. This is followed by a faster flow of raw water to thoroughly flush any remaining salt from the resin bed. During this entire process, the control valve either prevents raw water from flowing to service or allows raw water to by-pass the softener during regeneration. Often two parallel industrial water softeners are operated together, in order to avoid any interruption to soft water.
Disadvantages to conventional softening are consumption of copious volumes of salt and the discharge of highly saline waste water from the regeneration step.
Given proper consideration of raw water quality and ultimate end use of the treated water, the application of precipitation processes has few limitations. However, operational difficulties may be encountered unless the following factors are controlled:
Temperature: Cold and warm units are subject to carryover if the temperature varies more than 4°F/hr (2°C/hr). Hot process units are less sensitive to slight temperature variations. However, a clogged or improper spray pattern can prevent proper heating of the water, and carryover can result.
Hydraulics: In any system, steady-state operation within design limits optimizes the performance of the equipment. Rapid flow variations can cause severe system upsets. Suitable treated water storage capacity should be incorporated into the total system design to minimize load swings on the softener.
Chemical Control: This should be as precise as possible to prevent poor water quality. Because of the comparatively constant quality of most well waters, changes in chemical feed rates are largely a function of flow only. However, surface water quality may vary hourly. Therefore, for proper control, it is imperative that users perform frequent testing of the raw water as well as the treated effluent, and adjust chemical feed accordingly.