Use of PAC as a Substitute for Alum in Nalgonda Technique

Fluorine, a fairly common element of earth's crust, is present in the form of fluorides in a number of minerals and in many rocks. Industrial activities involving the use of fluorine containing substances results in fluoride concentration of environment. Fluoride ion in drinking water has great significance from the physiological point of view. The problem of excess fluoride in potable water and the consequent incidences of fluorosis have been reported in India for a fairly long period. Several methods of defluoridation were suggested; but most of them suffer from some draw back. To overcome these draw backs a technique known as Nalgonda Technique was developed in 1975. Since 1960s, the National Environmental Engineering Research Institute (NEERI), Nagpur has been involved in research and development activities on defluoridation of water. NEERI, Nagpur has tried to popularize the Nalgonda Technique for defluoridation. From the literature it is seen that one of the technologies which has been successfully from the laboratory to field is the Nalgonda technology. In the Nalgonda technique, alum is added to water and water is allowed to flocculate and settle. This settle water shows reduced fluoride content water. However, the usual objection to use this process is that water defluoridation becomes costly in the context of rural water supply because of alum requirement. Defluoridation of drinking water is the only practicable option to overcome the problem of excessive fluoride in drinking water, where alternate source is not available. Many methods have been evolved over the years for the removal of fluoride content from drinking water. All these methods are based on the principle of adsorption, ion exchange, precipitation, membrane separation process, electrolytic defluoridation, and electrodialysis. Nalgonda technique is based on the principle precipitation where alum is used as coagulant. In the recent years, defluoridation of water using poly aluminium chloride (PAC) is being tried by many researchers. It is reported that use of PAC can be the only available best and cheapest alternative for the defluoridation purpose. Therefore, looking into Indian conditions, all the available technologies and limitations of Nalgonda technique using alum as basic ingredient, use of PAC can be considered as most suitable defluoridation agent. Thus, in view of various possible advantages of PAC an attempt has made in the present work to remove fluoride content from synthetic water using Nalgonda Technique by adding PAC dosages in varying percentages. Also, it can be stated that use of 5% (5gm in liter) PAC would be considered to be the optimum dosage as against 10% (10 gm in liter) of alum used in Nalgonda Technique. Thus, the experimental study indicates that use of Nalgonda Technique using PAC as defluoridation agent can be successfully used for removal of fluoride contents.