Drinking water defluoridation

Although a lot of research has been reported on the use of various carbonaceous materials in defluoridation, no known column or full-scale plant operation is easily available in open literature. One reason for this is that most carbonaceous materials show poor adsorption capacity (Table 4) for fluoride and therefore only laboratory-scale performances have so far been reported. Amorphous alumina supported on carbon nanotubes on the other hand show high capacity (28.7 mgF/g adsorbent) for fluoride and is therefore a promising material for drinking water defluoridation. 

Limestone is another promising geomaterial for drinking water defluoridation. However, it has only been tested in wastewater containing high concentration of fluoride. In a research work by Reardon and Wang [60], limestone was used in a two-column continuous flow system (limestone reactor) to reduce fluoride concentrations from wastewaters to below the MCL of 4 mg/L for wastewater. Calcite was forced to dissolve and fluorite to precipitate in the first column. The degassing condition in the second column (did not serve to remove fluoride) caused the... 

Using coal-based sorbents, Sivasamy et al. [62] evaluated their ability to remove fluoride from water. On equilibrium basis, Langmuir and Freundlich models were used to describe the data points, while the kinetic data points were interpreted in terms of reaction and mass transfer processes. Kaolinite, adioctahedral two-layered (silica and alumina) silicate (1 2 type), has also been tested in drinking water defluoridation. Recently, Sugita etal. [58] and earlier Kau etal. [63] and Weerasooriya et al. [10] presented fluoride adsorption results of kaolinite. The fluoride-binding sites in kaolinite consist of aluminol and silinol sites. The authors explained that the fluoride-kaolinite interaction led to the formations of both the inner- and outer-sphere complexes. 

Aluminum oxide present in soil has been utilized to make brick pieces of 15-20 mm sizes that are effective in drinking water defluoridation. When the... 

Our main focus for this review is to briefly and critically describe some of the defluoridation techniques as a means of getting a basis to support the adsorption technique, to evaluate the defluoridation adsorbents now being utilized and those novel defluoridation adsorbents reported in literature over the last two decades, with special reference to drinking water. Emphasis is laid toward the adsorbents availability, fluoride sorption capacity and where applicable their kinetic adsorption characteristics and column performances are reported. Detailed characteristics of fluoride adsorption onto surface-tailored zeolite are provided. In addition, various adsorber configurations are reexamined and challenges to and prospects for their application to less developed countries (LDCs) are discussed. 

Fluoride-related health hazards are associated with the use of fluoride-contaminated water for drinking and cooking. This corresponds only to 2-4 L per capita per day. Fluoride removal in rural areas in LDCs, where centralized water treatment and distribution facilities are unavailable, should consequently be carried out at a household level and the system applied should be simple and affordable. In this regard, tea bag POU system becomes handy. Although this kind of system has not been specifically reported for water defluoridation, it has been tested for arsenic [37,107], It is therefore a short-term potential technique worth considering. In this technique, adsorption medium is placed in a tea bag-like packet, which is subsequently placed in a bucket of water to be treated. To ensure faster defluoridation kinetics, the bag should be swirled inside the water. It therefore operates like a batch reactor and hence requires a relatively longer adsorption time to achieve the permissible levels. Since the swirling motion is supposed to be human-powered, the technique would require a material with very fast kinetics or very fine adsorption media. 

Moges et al. [56] and Agarwal et al. [109] have reported that ground-fired clay pot could effectively defluoridate drinking water. However, the process is extremely slow. The use of mud pots dates back to ancient times. When mud pots are fired, they become activated and have affinity for fluoride ions. The ability to remove the fluoride ions, however, depends on the alumina content of the soils used for molding the pots. These kinds of pots are cost effective and their use do not require any know-how. They are estimated to retail at USD 0.33/pot. 

Fluoride can also be removed from a centralized water treatment point. This is common in developed or countries in economic transition and provides a longterm solution to fluoride problem in drinking water. A full-scale water purification plant based on AA-adsorption media was reported to be in operation in Kansas, USA. In this technique, all water to the distribution system is treated irrespective of its intended use. Thus, it is unrealistic way of defluoridating water since the main concern is usually fluoride ions contained in drinking water. From the technical point of view, however, centralized water treatment guarantees the quality of drinking water since the performance of the defluoridation plant can easily be monitored. Wider application of this technique for the sole purpose of removing fluoride from water is not widely reported in literature. 

This chapter is organized into two parts (i) the first part is dedicated to a review on the defluoridation processes of drinking waters (see Table 1) and (ii) the second part is based on the presentation of original results concerning a comparison study of NF and RO for a selective defluoridation of a highly fluorinated brackish water from the endemic region of Fatick (Senegal). 

The prevention of fluorosis through treatment of drinking water in rural areas is a difficult task because of economical and technological restrictions. Defluoridation of water is the only measure to prevent fluorosis and many different defluoridation techniques have been developed [17]. However, many cannot be easily implemented in areas where the problems occur. This section gives a brief overview of defluoridation methods (see Table 1). 

Membrane processes such as RO, NF, dialysis and electrodialysis have become recently developed methods for F removal from drinking waters [6,8,15,76-78] and brackish waters [7,9,79], The second part of this chapter is dedicated to the presentation of recent results obtained from the comparison of RO and NF membranes processes for a selective defluoridation of a Senegalese brackish water from the endemic region of Fatick. 

It is well known that the application of defluoridation techniques constitutes a big challenge in third world countries. Unfortunately, of the 25 countries in the world with severe fluoride problems, most have low economies. Then, two complementary approaches will have to be developed in the future depending on the local conditions (i) defluoridation using clay for rural areas and (ii) defluoridation using NF for urban areas supported by private funds, for drinking water for all. 

Y. Wang, E.J. Reardon, Activation and regeneration of a soil sorbent for defluoridation of drinking water, App. Geochem. 16 (2001) 531-539. 

C. Zevenbergen, L.P. Van Reeuwijk, G. Frapporti, R.J. Louws, R.D. Schuiling, A simple method for defluoridation of drinking water at village level by adsorption on Ando soils in Kenya, Sci. Total Environ. 188 (1996) 225-232. 

S. Hauge, R. Osterberg, K. Bjorvatn, K.A. Selvig, Defluoridation of drinking water with pottery effect of firing temperature, Scand. J. Dent. Res. 102 (1994) 329-333. 

K. Bjorvatn, A. Bardsen, R. Tekle-Haimanot, Defluoridation of drinking water by use of clay/soil, Bergen, 2nd International Workshop on Fluorosis and Defluoridation of Water, Publ. Int. Soc. Fluoride Res. 1997. 

GNDWM. Prevention and Control of Fluorosis in India Water Quality and Defluoridation Techniques, vol. 2, Rajiv Gandhi National Drinking Water Mission, Ministry of Rural Development, New Delhi, 1993. 

Graaff JWM de (1991) Decentralized defluoridation a gypsum-fluorite filter for the removal of fluoride from drinking water (in Dutch). Report Utrecht University/IWACO BV, p 54... 

Lu H., Wang B., Ban Q. Defluoridation of drinking water by zeolite NaP synthesized from coal fly ash. Energy Sources Part A, 2010 32 1509-1516. 

Essadki AH, Gourich G, Vial C, Delmas H, Bennajah M (2009) Defluoridation of drinking water by electrocoagulation/electroflotation in a stirred tank reactor with a comparative performance to an external-loop airlift reactor. J Hazard Mater 168 1325... 

Conventional methods of As removal from drinking water include oxidation/precipitation, coagulation/flocculation, adsorption, ion-exchange and membrane technologies. Similar approaches can be used also for defluoridation (Meenakshi and Maheshwari, 2006) and removal of U from driiiking water (Katsoyiannis and Zouboulis, 2013) although some of these methods have been tested at laboratory or pilot scale only. 

Ayoob, S., Gupta, A.K. Bhat, VT. (2008) A conceptual overview on sustainable technologies for defluoridation of drinking water and removal mechanisms. Critical Reviews in Environmental Science and... 

Kamble, S.P., Jagtap, S., Labhsetwar, N.K., Thakare, D., Godfrey, S., Devotta, S. Rayalu, S.S. (2007) Defluoridation of drinking water using chitin, ohitosan and lanthanum-modified ohitosan. Chemical Engineering Journal, 129, 173-180. 

The defluoridation of drinking water by EC is studied in the same reactor. Current density values j between 2.8 and 17 mA/cm are investigated, which corresponded to current (I=j-S) in the range 0.5-3 A. Samples are filtered and the concentrations of the remaining fluoride content are determined in the solution by means of a combined selective fluoride electrode 1SEC301F and a PhM240 ion-meter (Radiometer Analytical, France), using the addition of a TISAB 11 buffer solution to prevent interference from other ions. 

---