Formation and Emission of Chlorinated by-Products from a Bench-Scale Packed-Bed Odor Scrubber

Abstract

The phenomenon of chlorinated byproduct formation and their possible emission from odor control systems employing chlorine scrubbing solutions was evaluated. Experiments with hypochlorite scrubbing solution were performed with a bench-scale, single-stage, packed-bed odor scrubber to explore the potential for generating toxic air contaminants (TACs) such as chloroform in full-scale operating units. Known concentrations of a mixture of volatile organic compounds (VOCs) commonly found in wastewater were introduced at realistic field concentrations in an airstream to the inlet of a counter-current packed-tower operated with different scrubbing solutions. Formation of TACs was observed in the scrubbing solution under low-, neutral- and high-pH conditions. The addition of a mixture of VOCs: acetone, methylethylketone, formaldehyde and acetaldehyde, produced chloroform under neutral to high pH conditions. Under low-to neutral-pH conditions, toluene and chlorophenol produced chlorotoluenes and chlorophenols as reaction byproducts. Under the bench-scale unit’s operating conditions, trace levels of the reaction byproducts formed were stripped from the re-circulated scrubber solution into the outlet gas. Based on the bench-scale observations and a quasi-steady-state, first-order reaction model applied to the scrubber reservoir and packed tower system, scrubber solution residence time in the liquid reservoir is hypothesized to be an important operating parameter affecting TAC formation in full-scale hypochlorite-based, packed-tower, odor control units.