A fluidized layer of granular material used for the separation of particulate impurities in drinking water treatment

Abstract

This paper deals with the application of a fluidized layer of granular material (FLGM) for the direct separation of destabilized impurities during drinking water treatment. Further, it investigates the effect of operation parameters (fluidized layer grain size, technological arrangement, velocity gradient, retention time, dosage of déstabilisation reagent and temperature) on the aggregation and separation efficiency of the layer. The tests were carried out in a pilot plant scale. Aluminium sulphate was used as the déstabilisation reagent. The highest separation efficiencies were achieved, when the particles entered the fluidized layer immediately after the dosing of the déstabilisation reagent, when they had the lowest degree of aggregation. The separation efficiency (φ) also increased with increasing velocity gradient and the maximal value was reached at the velocity gradient of about 250 s -1. The most efficient separation of aluminium was achieved at 5 °C, but the effect of temperature on the efficiency of organic matter separation (φ roc) was not very significant. The maximal efficiency of separation on the layer grains reached the values φ AI = 0.81 at the optimal dosage D AI=1.55mg L -1 and φ roc = 0.31 at the optimal dosage D AI= 2.36 mg L -1. The indisputable advantage of using FLGM for the separation of impurities is that they are intercepted on the layer grains in a form of solid, water-free shell (or coat) with the density of 2450 kg m -3, and there is no need to deal with the sludge dewatering.