Experimental studies on the hydrodynamic properties of a deposit in rapid filters during physicochemical removal of iron from groundwater

Abstract This article presents the results of experimental studies for information support of the hydraulic compartment of the mathematical model of physicochemical iron removal from groundwater. It is experimentally established that the bound water in the deposit significantly exceeds the mineral component (chemical iron) for any waters with the different levels of iron oxidation. The deposit dehydration takes place at its boundary with the liquid phase. As a result, ferrous iron is gradually oxidized and ferric iron transforms from hydroxide forms to oxide forms, which leads to a decrease in the deposit volume and a increase in its density and strength. Further, the coefficient of the deposit hydrodynamic stability is proposed to use to take into account changes in the properties of the deposit that accumulates in the granular medium. It is experimentally determined that the iron amount remaining in the medium after backwashing increases simultaneously with the deposit's age. It will lead to a gradual reduction of the operational dirt capacity of the granular medium and a need to have measures of the filtration properties restoration or to replace the filter medium entirely.