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.

Technological modeling of physicochemical removal of iron from deep groundwater

“…The technological process inside the iron removal filters proceeds fundamentally differently. Here, the progressive accumulation of the residual deposit from one filter run to another is clearly observed, which progresses from one to another filter run [ 23 ]. Its strength increases so much, due to the ongoing deep structurization with the formation of new stable chemical connections, that it is necessary to sharply increase the washout intensity and the volume of washout water in order to remove it.…”

“…The residual amount of the deposit is simply set using the hydrodynamic resistance factor . The indicated empirical coefficient characterizes the part of the non-washable deposit in the newly formed deposit and essentially depends on its age by definition [ 23 ]. Since the proportion of iron hydroxide in the deposit is stable, this coefficient can also be used to calculate the accumulation of the bound water and deposited ferric iron separately.…”

“…The basis for our developed method of technical and economic analysis of physicochemical iron removal from deep groundwater was a nonstationary nonlinear mathematical model consisting of three interconnected compartments, as well as its exact solution [ 19 ]. In order to provide the model with the initial information in full, comprehensive experimental studies were carried out in laboratory and production conditions [ [ 23 , 26 ]]. A procedure of continuous step-by-step calculations was organized and implemented using Mathcad to establish technological parameters and economic indicators with a focus on the reduced costs during the service life of the filtering material change.…”

“…It is well known that the optimization of the operation of any filtering plant consists of minimizing the total material and labor used in its construction, preparation for operation, and maintenance [ 21 ]. At the same time, it should be considered that iron removal filters operate under more difficult technological conditions than conventional filter – clarifiers for treating aqueous suspension due to the presence and the transformations of the two forms of iron, and most importantly, the progressive accumulation of the non-washable deposit [ 22 , 23 ]. Therefore, a special approach is required for calculating the filtration of water with a higher concentration of iron compounds.…”