A Review on Feasibility of Conventional Fluoride Removal Techniques in Urban Areas

Present study was carried out to evaluate the feasibility of conventional rural based defluoridation technique Nalgonda technique, Activated alumina in urban areas. Nalgonda technique is being used extensively due to ease in construction of the reactor, operation & maintenance. This technique is very effective even when the fluoride concentration is above 20 mg/L. However, generation of acid or alkali water, residual aluminum, soluble aluminum fluoride complexes and fluoride contaminated sludge limits its practical applications. Above this, leakage of sulphate as aluminium sulphate with concentration as high as 400 mg/L in treated water, makes it un-potable and caused pitting effect on RCC reservoir/reactor or container. Cement paste is also employed for effective removal of F due to high concentration of Ca and additional adsorption of the remaining F into amorphous calcium phosphate. However lime creates the problem of hardness of effluent water and co-precipitation particle of CaF2 are too fine to be sedimented without coagulation. Limitation of CaF2 precipitation also includes it inability to reduce F concentration of less than 1020 mg/L against permissible limit of 1.5 mg/L. Activated Alumina though showed effective removal of fluoride, slow rate of adsorption, pH adjustment, accumulation of bacteria in the long run inhibits its commercial application. Also sludge generation is one of its main drawbacks. Application of these conventional techniques in urban areas will leads to generation of large amount of fluoride sludge which creates another issue of solid waste management. It will be advisable to set up decentralized locality based fluoride removal treatment unlike high capacity water treatment in urban areas. Tarundeep Gill et al 180