Softener

Resin Basic

Groundwater is a major requisite drinking water source in the world, and its contamination has been an issue due to the presence of various pollutants such as fluoride (F−), elements causing hardness, and heavy metals. The undesirable calcium and magnesium scale deposits on a surface of any materials in contact with water frequently lead to severe technical and economic consequences when the hard water is concentrated beyond the solubility limits of inverted solubility salts (e.g., CaCO3 or MgCO3, etc.) in contact with a hot surface. Particularly, the deposition of a thick insulating scale layer probably causes pipe clogging in municipal and industrial water distribution systems, reduces the heat transfer ef- ficiency in the boilers and cooling towers, and declines the water flux in wastewater treatment membrane systems, etc.

Currently, the mostly widely utilized approach for prevention of

scale formation is the use of anti-scalants to delay or prevent the mineral crystal nucleation, owing to the effects of chelation, dispersion, lattice distortion, and threshold. Unfortunately, there is a hidden defect of the above method that the hardness ions are not removed out from the water and also probably affect the process effi- ciency in the subsequent treatment units. Lime softening method is widely utilized for water softening based on the alkalizing effect; but this treatment process produces excess sludge and increases the saltness when finally using the acid reagents to neutralize the solution pH. Ion exchange shows relatively high efficiency in hardness removal, frequent and laborious chemical regeneration is required, which is environmentally unfriendly because of producing a large volume of spent solutions of acids or salts. Precipitation of CaCO3 by electrochemistry was originally developed

by L´edion in 1969 to enhance the resistance of metal surface to corrosion by creating stable and compact covering layers. Here the metal surface was used as the cathode and becomes alkaline via the reduction of dissolved O2, resulting in an increase of local pH and an enrichment of carbonate ions. Inspired by this phenomenon, electro- chemical water softening process by cathode precipitation has been increasingly emerging as an upgraded version of chemical softening over recent decades, due to their eco-friendliness, modularity of treat- ment modes and flexibility. This treatment process is mainly based on the generation of OHˉ in situ by H2O-splitting or O2 reduction reactions at cathode, which avoids the handling of lime reagents and reduces CO2 emissions related to the lime production, shipping and waste solids treatment.

During the electrolysis process, the produced H+ and OH− are dynamically neutralized in the bulk solution, while their mass transports certainly result in an evident pH gradient between the boundary layer and bulk solution is created (Fig. 1(a)). Thus, a locally alkaline condition is created in the diffusion layer at the cathode surface, due to the production of OH− via the electrochemical reduction reactions of H2O and O2. As a result, much higher supersaturation level of CaCO3 can be locally realized than its value calculated in the bulk solution, which readily precipitates onto the cathode surface. In comparison with that of CaCO3, higher pH level is needed for the deposition of brucite (Mg(OH)2) (often pH >11). Thus, the precipitation of CaCO3 is more efficient than that of Mg(OH). At the beginning of CaCO3 electrocrystallization on the cathode surface, a thin vaterite and calcite crystals layer is initially deposited onto cathode surface. These crystals serve as crystal nucleus and will grow and promote the electrocrystallization of CaCO. Then the precipitation process turns to the next stage gradually with the coverage of cathode surface by the massive formation of precipitates.

Nature of drinking water is a major task in advanced days because of expansion in pollution of water bodies. Fluoride is one such pollutant that undermines living life forms, specifically people . Fluoride is an vital in little amount for mineralization of bone and assurance against dental caries, higher intake reasons decay of teeth enmel called fluorosis. Fluoride enters aqueous environment by weathering of fluoride rich minerals and as through anthropogenic actions, for example, industrial drains. The issue of fluoride in water bodies is serious for tropical nations, for example, such as India, Kenya, Senegal and Tanzania. The best way to pypass this issue is defluoridation. Various methods are accessible for the removal of fluoride from water, for example, precipitation-coagulation, membrane-based processes, ion –exchange and adsorption process. Lime and alum are the most usually utilized coagulants for Nalgonda technique for defluoridation of water. Expansion of lime prompts precipitation of fluoride as insoluble calcium fluoride and raises the pH value upto 11 – 12. Electrocoagulation is a technique for applying direct current to sacrificial electrodes that are submerged in an aqueous solution]. Electro-coagulation is a straightforward and efficient technique to remove the flocculating agent produced by electro- oxidation of a sacrificial anode and generally made of iron or aluminum. In this process, the treatment is performed without including any chemical coagulant or flocculants. In this way, diminishing the amount of sludge which must be disposed.

Electro Chemical

Groundwater is a major requisite drinking water source in the world, and its contamination has been an issue due to the presence of various pollutants such as fluoride (F−), elements causing hardness, and heavy metals. Even though F− is essential for humans for pre- venting dental and skeletal caries, excess intake is detrimental to human health. Hardness in water is caused by a variety of dissolved polyvalent metallic ions, predominantly calcium (Ca2+) and magnesium (Mg2+) cations. The degree of hardness of drinking water is important for aesthetic acceptability such as palatability, odor, appearance, and color. Hardness does not have a direct adverse effect on human health; however, it is troublesome for industries as well as households, causing scaling on equipment, pipelines, storage tanks etc. For removing F−, electrochemical methods have been proven as an as a water/wastewater treatment technology that has been widely employed to remove a wide range of pollutants, such as F−, organic dyes, hardness, and heavy metals effective way of treating polluted water. Moreover, Mg2+ and Ca2+ ions removal as calcite (CaCO3) and brucite (Mg(OH)2) minerals in the presence of HCO3 − ion by electrochemical methods in the vicinity of electrochemical generation of OH− ion in the cathode was reported. Common electrochemical methods are categorized as electrocoagulation (ECO), electrochemical reduction, electrochemical oxidation, indirect electro-oxidation with strong oxidants, and photo-assisted electrochemical methods

A novel continuous flow electrolysis (ELC) system comprised of non-corrosive platinum-anode and stainless steel-cathode electrodes was proposed to remove fluoride (F−) and elements that cause hardness (magnesium (Mg2+), calcium (Ca2+), and alkalinity causing ions (carbonates (CO32−) and bicarbonates (HCO3 −)) from naturally contaminated groundwater. the schematic diagram of the process is shown blow.