Effects of Energy Input during Orthokinetic Aggregation on the Filterability of Generated Flocs

Abstract

The implications of energy input (G value) and energy input time (t value) as well as the Gt value (Camp number) resulting from the orthokinetic particle aggregation as part of the adsorption coagulation with charge neutralization were investigated in the laboratory using a direct filtration test apparatus with a stirred reactor developed by the Wahnbach Reservoir Association. The tests were carried out at a constant particle concentration. The water was flocculated with 5 mg/l Fe3+ at pH 6. In compliance with literature references, an optimum removal of turbid matter by means of this direct filtration apparatus was achieved at G values of around 40 s−1, t values of 15-30 min and within a Gt range between 30,000-60,000 which corresponds to a GCt range of 60-120 according to Ives. Only in this range are the G values of 30-50 s−1 compatible with t values. By comparison it was shown that these values are in reasonable agreement with the results of our tests implemented on a full-scale direct filtration with two successive stirred reactors. Optimum direct filtration conditions were found to occur within a G range of 30-60 s−1, at t values of 15-20 min and within a Gt range between 15,000-40,000. From this comparison it can be concluded that results of hydrodynamic investigations into orthokinetic aggregation, which were obtained with the described laboratory floc filtration test apparatus, may well be applied as guide values in full-scale direct filtration processes.