Abstract
This study assessed the feasibility of utilizing activated carbon and clay minerals for treating water impacted with the bittering agent denatonium benzoate (DB). Our specific study objectives were to 1) evaluate denatonium ion sorption to smectite clay minerals (bentonite and hectorite) and activated carbon (powdered and granular) at constant pH and ionic strength and 2) examine the impact of pH on denatonium ion sorption to each solid material. The experimental results indicated that high doses (33,000 mg/L) of as-received granular activated carbon and as-received clay minerals completely removed denatonium from aqueous solutions containing 100 - 1000 mg/L denatonium benzoate. Powdered activated carbon at doses of 5 - 100 mg/L exhibited favorable monolayer sorption of denatonium ions from a pH 6.95, 70 mg/L aqueous denatonium benzoate solution with a Langmuir separation factor (r) of 0.481, a maximum sorption capacity (Sm) of 74 mg/g, and a Langmuir constant of 15.3 L/g. A maximum removal of 23% of denatonium was achieved at the highest powdered activated carbon dosage employed. Denatonium ion removal with peroxide treated bentonite and peroxide treated hectorite did not result in complete removal of the ion and exhibited favorable sorption as evidenced by Freundlich 1/n values ranging from 0.803 to 1.194; Freundlich constants (Kf) ranged from 8 ng/L to 575 ng/L. Denatonium ion sorption to peroxide treated bentonite appeared to depend on pH while hectorite sorption of denatonium ions was independent of hydrogen ion concentrations. For powdered activated carbon adsorption, as pH increased denatonium ion sorption decreased. Overall, the work demonstrates that denatonium can be effectively removed from water via activated carbon or clay mineral sorption.
Highlights
The protection of drinking water supplies from industrial and household contaminants along with the treatment of waters impacted by hazardous and undesirable constituents often involves chemical partitioning at the solid-solution interface [1]
We studied the constant temperature sorption of denatonium ions to common sorbents utilized in water treatment processes
Crosson et al between powdered activated carbon (PAC) and aqueous denatonium benzoate, a 27% percent decrease in denatonium ion concentration was observed at the highest PAC dose utilized, while decreases of 16% and 23% occurred for 50 mg/L and 75 mg/L PAC doses, respectively
Summary
The protection of drinking water supplies from industrial and household contaminants along with the treatment of waters impacted by hazardous and undesirable constituents often involves chemical partitioning at the solid-solution interface [1]. Denatonium benzoate, shown, is a water soluble, bittering agent legislatively mandated to be added to antifreeze formulations in at least seventeen American states [2]; the denatonium ion is responsible for imparting the bitter taste. Given the large water solubility of denatonium benzoate (42,400 mg/L at 20 ̊C), irreversible sorption to soils and sediments may not occur resulting in denatonium benzoate seepage into ground waters or runoff into surface waters used as sources for drinking water treatment facilities. As highlighted in a meeting before a congressional subcommittee considering federal legislation mandating the addition of denatonium benzoate to antifreeze formulations, a dearth of knowledge exists related to 1) the environmental fate of denatonium benzoate and 2) the feasibility of current water and wastewater treatment practices for removing denatonium benzoate from impacted waters [5]
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