Defluoridation of water by the Nalgonda technique is a commonly used household process in areas of endemic fluorosis in villages around Nalgonda (Andhra Pradesh, India). The aim of this paper was to modify the existing well-known procedure minimally and without much change in the cost to bring about a greater removal of fluoride. By doubling the concentrations of alum and lime, water fluoride levels fell significantly (p<0.001) in tap water and drinking water while pH levels and other inorganic factors remained unaffected.
Keywords: Defluoridation, Nalgonda technique
Defluoridation is the removal of excess fluoride from water. The National Environment Engineering Research Institute in Nagpur, India has evolved an economical and simple method of defluoridation, which is referred to as the Nalgonda technique. ,,, The Nalgonda technique has been repeatedly proven to be an economical and effective household defluoridation technique. , In this commonly used technique, fluoride is precipitated using 500 mg/L of alum and 30 mg/L of lime. 
We have found that the removal of fluoride from potable water is not adequate when initial concentration of fluoride in the water is very high and the pH of the untreated water is alkaline. Moreover, different degrees of hardness of water require different concentrations of alum.  Therefore, we tried to modify the existing Nalgonda technique using the same materials in different concentrations. This preliminary study presents the effects of modification of the Nalgonda technique on the quality of tap water and drinking water.
Tap water (1 lit) samples were collected in plastic cans from 20 different villages in the Nalgonda district. This water originated from different bore wells that were collected in a common tank in the village. In some locations, the source of the drinking water was identical to the tap water pumped from bore wells. In other villages, separate wells were provided for drinking water; these drinking water samples were also analyzed.
Methods of defluoridation
Initially, varying concentrations of alum and lime were added to untreated water to find the combination that would decrease fluoride levels to a maximum extent. After the addition of lime and alum, water samples were allowed to stand for 30 minutes, 60 minutes, and 120 minutes to determine the shortest time for maximum flocculation [Table 1]. The weight of the sediment formed after 1 hour from 250 ml of water is also given in [Table 1]. Values are an average of results obtained from 5 water samples.
Analysis of water samples
Fluoride was analyzed using ion selective electrodes from Merck. Calcium levels in the water were analyzed by the ortho-cresolpthalein complexone method.  Magnesium was estimated by using the Magnon Complex method  and sodium and potassium were estimated using the flame photometer.  Chloride levels were measured by the Mercuric Thiocyanate method.  Iron was estimated using the Ferrozine method. . Statistical analysis was done using Microsoft Excel® (MS office, Windows 2000).
All the water samples collected were found to be clear, colorless, and odorless, tasting brackish with an absence of suspended solids and visible impurities. The average pH of the tap water and the drinking water was found to be 7.4 (± 0.2).
Various combinations of alum and lime were used to defluorinate water samples [Table 1]. Combination I was the original Nalgonda technique, combinations II and III reduced fluoride levels significantly. However, the weight of the flocculated precipitate was greater with combination IV than with combinations II and III indicating that salts were precipitated to a greater extent. Hence, combination IV was used to defluorinate further samples [Table 1].
Both tap water and drinking water samples collected from 20 villages were treated with alum and lime as in combination IV and the results were presented in [Table 2] and [Table 3]. Using the original Nalgonda technique, fluoride levels in tap water decreased by 46.4% and fluoride levels in drinking water decreased by 59%. By using combination IV of alum and lime concentrations, fluoride levels decreased by 75% in tap water and 88.2% in drinking water. The precipitation of the salts that followed treatment by combination IV was 8.6 times the original Nalgonda technique in tap water and 1.3 times in drinking water. There was no significant difference between treated and untreated water samples for sodium, potassium, chloride, magnesium, and iron levels. The average pH was increased from 7.4 to 7.6 in tap water but decreased from 7.3 to 7.1 in drinking water, indicating that the composition of tap water and drinking water was different. The addition of extra lime led to a significant increase in calcium content of the water following treatment with combination IV (p<0.01).
To increase the removal of fluoride without excessively modifying the existing well-practiced Nalgonda method, we examined if altering the concentrations of readily available materials could remove excess fluoride from drinking water without affecting the quality of water. Our results show that doubling the concentrations of alum and lime results in a significant decrease in fluoride when compared to the existing Nalgonda technique [Table 1].
However, we recommend that the water defluoridated by combination IV can be used for domestic purposes only. Further studies are required to examine the implications of use of the modified method in decreasing fluoride in drinking water.
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3]