Geosmin reduction by algaecide application to drinking water: field scale efficacy and mechanistic insights

Abstract

Ten years of field data from an Oklahoma drinking water utility were analyzed for the effects of an acid-stabilized, ionic copper algaecide/bactericide called EarthTec on geosmin concentrations in the water traveling by pipeline from the source lake to a water treatment plant. The data show that geosmin already present in the raw water is reduced more during periods of applying algaecide than when not. Median reduction in geosmin concentration from pipe intake to pipe outfall by natural degradation without addition of algaecide was 5.6 ng/L removed (56.7% reduction) and improved to 126 ng/L removed (83% reduction) during periods the algaecide was being dosed at 1 μL/L, equivalent to 0.06 mg/L as copper. A laboratory study to replicate the phenomenon at bench-scale showed that either the algaecide itself or its copper-free acidic carrier can be used to depress pH and drive a reaction converting geosmin to an odorless dehydration product, argosmin. Algaecides intuitively reduce the organisms that produce geosmin, but this study shows that geosmin already present in the water is also being reduced through chemical conversion to the odorless argosmin, representing a novel means of geosmin removal in drinking water.

Algaecide Controls Geosmin in Tulsa

“…Table 1 shows the median reduction in geosmin concentration from the pipe intake to pipe outfall by natural degradation without addition of algaecide, which was estimated to be 5.6 ng/L removed (57% reduction). This improved to 126 ng/L removed (83% reduction) during periods when the algaecide was dosed at 1 μL/L, equivalent to 0.06 mg/L as copper (Hammond et al 2021).…”

“…Over a period of seven years, staff collected more than 1,100 separate geosmin measurements. The reductions from dosing the acidic algaecide were statistically significant (Hammond et al 2021).…”

“…This improved to 126 ng/L removed (83% reduction) during periods when the algaecide was dosed at 1 μL/L, equivalent to 0.06 mg/L as copper (Hammond et al 2021).…”

“…The phenomenon was subsequently confirmed at lab scale, and the removal mechanism was determined to be chemical conversion via acidic dehydration from geosmin to argosmin. While humans are sensitive to geosmin at low concentrations, argosmin is odorless (see Hammond et al 2021).…”