RESEARCH ON THE EFFICIENCY OF RAPID FILTERS UNDER DIFFERENT FILTERING MODES

Increasing the duration of rapid filter operation between washings is an effective way to reduce the amount of washing water and operating costs at water treatment stations for domestic and drinking needs when drawing from surface sources. The level of pollution of surface water supply sources in Ukraine is steadily increasing. During military operations, the load on treatment facilities may rise significantly. Moreover, operating conditions can change abruptly and unpredictably. This article presents the results of a study comparing the performance of rapid filters in two filtration modes: with constant and time-varying filtration rates. The theory of low-concentration suspension filtration developed by D.M. Mints applies to the mode with a constant filtration rate. Calculations for alternative filtration modes require more general theoretical frameworks. The studies were conducted using a mathematical model. The presented mathematical model includes: the filtration equation for a low-concentration suspension, the equations of mass transfer and mass transmission of the suspended solids from the liquid phase to the solid (grains of the filter media), the formulations for determining the resistance of clean (unclogged) media and the influence of clogging on the resistance and porosity of the granular media, the expressions for calculating the adhesion (and detachment) coefficients of suspension particles on the filter media grains. The adequacy of the mathematical model at a constant filtration speed was validated by comparing the calculated results with the data obtained using the filtration theory of D.M. Mints. As a result of numerical experiments for two filtration modes, the impact of influent water turbidity on the efficiency of the rapid filter was investigated. The filter operating time between washings used as the efficiency criterion. The comparison of the two modes was conducted under the condition that the average productivity and filtration area in both cases were the same. The influence of the granular media parameters (grain size and layer thickness) was investigated. Studies have shown the advantages of operating a rapid filter in a variable filtration rate mode compared to a constant rate mode. However, the disadvantage of the variable filtration rate mode is the increased likelihood of filtrate quality deterioration at the beginning of the filtration cycle.