X-ray photoelectron spectroscopy (XPS) was used to identify Mn(II), Mn(III), and Mn(IV) in the surfaces of pure oxide standards and filtration media samples from drinking water treatment plants through the determination of the magnitude of the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line. The Mn 3p region has been widely studied by applied physicists and surface scientists, but its application to identify the oxidation state of Mn in heterogeneous oxide samples has been limited. This study shows that the use of both the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line provides a feasible means of determining the oxidation state of manganese in complex heterogeneous, environmentally important samples. Surface analysis of filtration media samples from several drinking water treatment plants was conducted. While Mn(IV) was predominant in most samples, a mixture of Mn(III) and Mn(IV) was also identified in some of the filtration media samples studied. The predominance of Mn(IV) in the media samples was felt to be related to the maintenance of free chlorine (HOCl) at substantial concentrations (2-5 mg*L(-1) as Cl2) across these filters. XPS could be a useful tool to further understand the specific mechanisms affecting soluble Mn removal using MnOx-coated filtration media.

This work highlighted practical implications of aqueous silica sorption to iron hydroxide in natural and engineered systems. Two types of surfaces were prepared by exposing 10 mg/L preformed Fe(OH)3 to aqueous silica (0-200 mg/L as SiO2) for periods of 1.5 h or 50 days. After 1.5 h, the concentration of iron passing through a 0.45 microm pore size filter at pH 6.0-9.5 was always negligible, but if zeta potential < or =-15 mV as much as 35% of the iron passed through filters after 50 days of aging. When arsenate was added to 10 mg/L iron hydroxide particles equilibrated with aqueous silica for 1.5 h, percentage arsenate removals were high. In contrast, if silica was preequilibrated with iron for 50 days, arsenate removals decreased markedly at higher pH and aqueous silica concentrations. Similar trends were observed for humic substances, although their removal was nearly completely prevented at pH 8.5 at SiO2 concentrations above 50 and 10 mg/L at 1.5 h and 50 days exposure, respectively. The mechanism of interference was hindered sorption to the iron hydroxide surface.

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Laboratory-scale filtration studies were conducted to assess the potential for soluble manganese removal within oxide-coated, mixed-media filtration systems. Filter column experiments employed both new anthracite coal and sand as well as oxide-coated media obtained from three full-scale water treatment facilities. Soluble and total manganese removals were evaluated as a function of parameters such as pH, presence or absence of an oxidant in the filter-applied water, quantity and oxidation state of the filter media surface oxide coating, and temperature. Results indicated that Mna+ removal was rapid and efficient under a variety of solution conditions. Alkaline pH conditions promoted efficient removal of Mna+ on the oxide surface. Free chlorine likewise promoted soluble manganese removal on the media surface under both alkaline and acidic pH conditions. Stronger oxidants such as KMnO,, ClOa, and O3 resulted in Mna+ oxidation immediately upon addition to the tilterapplied water. In these instances, manganese removal was accomplished by retention of colloidal MnO,(s) within the filter. Low-temperature conditions did not appear to inhibit Mna+ removal potential. The practical implications of this work for full-scale treatment operations are also discussed.