Removal of soluble iron and manganese from groundwater by chemical oxidation and oxide-coated multi-media filtration

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Virginia Tech

This study evaluated alternatives to continuously regenerated greensand for iron and manganese removal. Specific objectives were (1) to investigate the applicability for removing soluble manganese by adsorption and oxidation onto the surface of manganese oxide-coated media, and (2) to develop mathematical models to predict the removal of soluble manganese both in the presence and absence of free chlorine.

Results from a pilot-scale experiment in Columbus, Indiana, showed that when the filters were operated in a conventional oxidant addition mode (i.e., with the addition of HOCI and KMnO₄) the anthracite-sand and anthracite-sand-garnet configurations both provided efficient treatment because of the reduced rate of head loss. Further experiments, without the use of KMnO₄ or greensand, equally removed manganese by adsorption and oxidation onto oxide-coated media; however, the treatment process resulted in reduced head loss and oxidant costs.

Results from this study and other previous research demonstrated that manganese removal by oxide coatings is an efficient and functional treatment mechanism. However, little quantitative information was available to predict these processes. Therefore, mathematical models were developed to help predict design and operational conditions needed to implement oxide-coated media as a treatment process. Two separate models were developed to predict (1) the continuous removal of soluble manganese in the presence of free chlorine (continuous regeneration model), and (2) the eventual breakthrough of soluble manganese without oxidant addition (intermittent regeneration model). Each model was derived from chemical reaction, mass balance, or isotherm equations and was further developed by a sensitivity analysis and parameter estimation. The two models were then verified by predicting manganese removal from independent research.

The continuous regeneration model can help predict the removal of soluble manganese by adsorption and oxidation on the surface of oxide-coated media and is useful in the design of filters for continuous Mn(Il) removal. The intermittent regeneration model effectively predicts the performance of filters without the addition of an oxidant and is useful for treatment plants which cannot apply chlorine continuously to their filter applied water.