Mass transfer of volatile organic compounds from drinking water to indoor air: The role of residential dishwashers

Contaminated tap water may be a source of volatile organic compounds (VOCs) in residential indoor air. To better understand the extent and impact of c hemical emissions from this source, a two-phase mass balance model was deve loped based on mass transfer kinetics between each phase. Twenty-nine exper iments were completed using a residential dishwasher to determine model par ameters. During each experiment, inflow water was spiked with a cocktail of chemical tracers with a wide range of physicochemical properties. In each case, the effects of water temperature, detergent, and dish-loading pattern on chemical stripping efficiencies and mass transfer coefficients were det ermined. Dishwasher headspace ventilation rates were also measured using an isobutylene tracer gas. Chemical stripping efficiencies for a single cycle ranged from 18% to 55% for acetone, from 96% to 98% for toluene, and from 97% to 98% for ethylbenzene and were consistently 100% for cyclohexane. Exp erimental results indicate that dishwashers have a relatively low but conti nuous ventilation rate (similar to 5.7 L/min) that results in significant c hemical storage within the headspace of the dishwasher. In conjunction with relatively high mass transfer coefficients, low ventilation rates generall y lead to emissions that are limited by equilibrium conditions after approx imately 1-2 min of dishwasher operation.