Simultaneous modelling of coagulant recovery and reuse by response surface methodology

Surface water from rivers, lakes, reservoirs etc. needs to be treated prior to municipal supplies. The treatment scheme includes coagulation, flocculation, sedimentation, filtration and finally disinfection process. Huge volume of sludge or waste is generated during the coagulation-flocculation. Disposal of the sludge so generated in the treatment plants require careful consideration for managing it sustainably and in an environment friendly manner. Constructive utilization of the inevitable waste may help in finding a sustainable solution to sludge disposal problems. Presently, response surface methodology (RSM) with central composite design (CCD) has been applied to simultaneously model coagulant recovery as well as reuse parameters. In order to simplify the process and increase the applicability, the effect of three significant variables, acid dose, sludge ratio, and recovered coagulant dose are studied. A second order regression model has been developed which gave the optimum combination of acid dose of 30 ml/L, sludge ratio of 1% and recovered coagulant dose of 12 ml/L for maximum turbidity removal. The predicted value of turbidity removal is 95.4%. In the confirmatory experiments, the turbidity removal value was observed to be about 96.2%, which is in good agreement with the predicted value. In addition to turbidity removal, it also helps to effectively remove other impurities from the raw water for it to meet the standards prescribed for potable supply. Thus, the regenerated alum or recovered coagulant has the potential to substitute the conventional coagulants, fully or partially at water treatment plants.