MECHANISTIC STUDY OF RAW WATER BIOFILTRATION FOR SURFACE WATER MANGANESE CONTROL

Abstract

Biofiltration is a sustainable method for removing dissolved manganese (Mn) from water. This treatment is well established in groundwater studies, where a simple aeration-biofiltration designs are used to remove Mn, iron (Fe), and ammonium (NH4+) simultaneously from water. Biofiltration has been studied for Mn removal from surface water but is much less understood. Improved understanding of this technology, specifically the mechanisms of removal, are needed to develop design guidance.

The objectives of this work were designed to expand understanding of Mn removal across surface water biofilters. In particular, aerated biofilters treating raw (i.e., untreated) surface water were studied as a potentially sustainable pre-treatment for Mn. Results show that this technology can be an effective tool for controlling Mn, even outperforming full-scale permanganate, clarification, and filtration treatment. A toolset was developed to improve understanding of dissolved Mn removal mechanisms across biofilters, with a comprehensive analysis approach targeting the broad categories of homogeneous (oxidation and precipitation by dissolved oxidants), heterogeneous (adsorption and catalytic oxidation by abiotic surfaces), and biological removal (adsorption and oxidation by biofilms). It was determined that raw surface water biofilters removed Mn by a combination of heterogeneous and biological mechanisms, which contrasts with well established groundwater biofilters where removal is driven by heterogeneous mechanisms with possible contributions from homogeneous removal. A final experiment was conducted to address raw water biofiltration head loss and start-up concerns, including head loss and long start-up periods. A bioreactor containing large-grained Mn-oxide media was tested in a recirculating experiment. The results of this experiment demonstrated that a raw water bioreactor may be a viable tool for removing Mn from untreated surface waters.