Fate of air toxics and VOCs in the odor control scrubbers at the deer island treatment plant

Process off-gases at the Deer Island wastewater treatment plant in Boston a re collected and treated and its stack emissions regulated for selected gas es including volatile organic compounds (VOCs), which are monitored as nonm ethane hydrocarbons (NMHC). The air treatment processes of countercurrent w et oxidation scrubbing and granulated activated carbon adsorption are avail able for emissions control at Deer Island. In addition, since the wastewate r treatment process of biochemical oxidation is fully enclosed at the site, microbial destruction of VOCs is an intrinsic treatment process for organi c gases. Surveyed results of wastewater research literature indicate that t he use of scrubbers for the removal of VOCs is controversial, as the fate o f volatile hydrocarbon molecules across odor control scrubbers is complex a nd not fully understood. Continuous emission monitoring tests across the De er Island scrubbers have consistently shown a VOC removal efficiency in exc ess of 50%. The fate of the scrubber inlet VOCs at Deer Island was researched as part o f a plant-wide, on-going VOC study. Removal efficiencies across the pure ox ygen bioreactors were also investigated. Preliminary results of this study indicate chemical reactions involving VOCs in odor control scrubbers partia lly oxidize and chlorinate derivatives possibly destroying a fraction of th e compounds by complete oxidation. In addition, VOC reduction across the en closed aerobic bioreactors was found to be significant. This article represents the opinions and (legal) conclusions of the authors and not necessarily those of the MWRA.