Date of Award

Winter 2014

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

James P Malley, Jr.

Second Advisor

Kevin Gardner

Third Advisor

David G Miller

Abstract

Manganese has been a recurring seasonal issue at the Manchester, N.H. Water-Works Treatment Plant. Following pre-ozonation, Mn (II) is oxidized into colloidal MnOx solids that are difficult to remove by their anthracite and GAC biofilters without additional coagulation.

This research has investigated ways to effectively treat manganese and organic precursors by biofiltration without making major alterations to the existing treatment plant. The most promising treatment was controlling the speciation of manganese with the addition of hydrogen peroxide (H2O2) in conjunction with the existing ozone (O3) addition. Applying H2O2 immediately after ozonation appeared to convert particulate and colloidal manganese into its dissolved form (Mn2+). Biofiltration and/or MnOx filter coatings could then remove the dissolved manganese from solution.

Visually, water dosed with a high concentration of manganese (approximately 0.5-1.0 mg/L) would turn from clear to a brownish color after the addition of O3 and then return to clear if H2O2 was then added. Analyses by membrane separation followed by inductively coupled plasma emission spectrophotometry (ICP) have confirmed that O3/H2O2 treated water samples have consistently resulted in almost all manganese in dissolved form while O3 alone resulted in almost all manganese in particulate/colloidal forms.

The O3:H2O2 mass ratio controls the kinetics of converting manganese into its dissolved form. A 1:1 mass ratio of O3:H2O2 quickly (< 1 minute) converted manganese into a dissolved form while a 2:1 O3:H2O2 mass ratio also successfully converted the manganese but required a longer contact time (5 minutes). An even higher mass ratio of 4:1 O3:H2O2 did not convert the manganese into a dissolved form but rather stayed in particulate/colloidal forms regardless of contact time (> 2 hours). These results will be helpful in determining an optimal dose relationship between H2O2 and O3 such that dissolved manganese removals by either adsorption by available MnOx coatings or biological induced removals can be utilized.

In addition, phosphorous was identified as a potentially rate-limiting nutrient for Manchester's biofilters due to significant reduction by sweep-floc alum coagulation pretreatment. This research also investigated how much phosphorous was taken out of the water by alum addition and if manganese could be removed by precipitation with orthophosphate. Alum coagulation was shown to significantly reduce the concentration of phosphorous in the water and chemical simulations with Visual Minteq showed that manganese would not complex with orthophosphate or precipitate so long as oxygen was present in the water.

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