Optimum conditions for arsenic and fluorine removal by coagulation with polyaluminum chloride

In the Centro de Ingeniería Sanitaria a process named ARCIS-UNR was developed for arsenic and fluorine removal from groundwater by means of coagulation with polyaluminium chloride (PACl) and double filtration. A treatment plant for 11,200 inhabitants was designed. During monitoring of the plant it was needed to get more data regarding removal mechanisms and relevant variables in coagulation-adsorption process in order to optimize this process and to determine its range of applicability. So, it was planned a series of trials which consist of two phases. Firstly the influence of relevant conditions were studied: pH, PAC dose and arsenic initial concentration. It was used an 2 experiment, with 3 factors and 2 levels per factor, in such a way within 8 trials all feasible arrangements and even the double interactions can be evaluated. Statistic analysis over first phase results indicated that all considered variables have effects on arsenic removal, while pH has relevant effects on fluorine removal . During second phase most relevant variables were studied one by one. The main conclusions of this second phase were: a) the optimum pH range for arsenic removal is from 6.5 to 8.0. b) Fluorine removal increase as pH decrease. c) From adsorption experiment, the results fit Freundlich isotherm. d) Optimum pH conditions for the case study water was around neutral value, in order to obtain residual arsenic, fluorine and aluminum below permissible values.