Treatment of MEK and toluene mixtures in biofilters: Effect of operating strategy an performance during transient loading

Abstract

In recent years, biofiltration has been increasingly applied as an air pollution control technology to minimize or eliminate emissions of volatile organic compounds from industrial sources and environmental remediation activities. Although the ability of this technology to maintain high removal efficiency during relatively steady loading conditions has been well established for many waste streams, relatively little research has focused on development of operating strategies that could improve treatment performance during transient loading conditions typical of industrial operations. In the research described herein, two operating strategies were evaluated over a period of 295 days in biofilters treating a model waste gas stream containing a two-component mixture of methyl ethyl ketone (MEK) and toluene. One biofilter was operated as a sequencing batch biofilter (SBB), and the other was operated as a conventional continuous-flow biofilter (CFB). During "normal" steady loading conditions, the model waste stream contained MEK concentrations ranging from 80 to 89 ppmv and toluene concentrations ranging from 28 to 30 ppmv. Both biofilter operating strategies resulted in stable long-term performance with greater than 99% contaminant removal during these normal loading conditions. On a regular basis, the influent MEK and toluene concentrations were temporarily increased to five times the normal influent concentration for the duration of 1 h to test performance during transient "shock loading" conditions. Biofilter performance during the model shock loading conditions demonstrate that SBB operating strategies can result in superior treatment in two important areas: (1) overall mass of contaminants removed and (2) minimum instantaneous removal efficiency.

Biofilter Treatment of Volatile Organic Compound Emissions from Reformulated Paint: Complex Mixtures, Intermittent Operation, and Startup

“…Low head loss observed in these biofilters was likely attributable in part to the highporosity polyurethane foam packing, which allows substantial accumulation of biomass without a concomitant increase in pressure drop. 11,15,31 CONCLUSIONS Results presented herein demonstrate that the synthetic gas stream representative of emissions from reformulated paints can be treated effectively using biofilters even in cases with intermittent operation. With use of an acclimated enrichment culture, successful startup was achieved under intermittent or continuous loading conditions; however, high removal efficiency was achieved more quickly in the continuously loaded system.…”

“…This is also consistent with previous reports that microbial growth is generally highest near the inlet of biofilter systems. 12,15 The second trend revealed by the SEM photos was that biofilm coverage of the packing medium in the continuously loaded biofilter (Biofilter 1) was higher than that in the intermittently loaded biofilter (Biofilter 2). In Biofilter 1, the surface of foam media was almost completely covered by biomass by day 22 (see Figure 6a).…”

“…Decanted liquid was then diluted with nutrient solution, and a 3.5-L volume was transferred into a 4-L glass kettle reactor. The glass kettle reactor was then operated as a sparged-gas reactor 15 to enrich for microorganisms able to degrade VOCs used in subsequent biofilter experiments. The reactor, stirred by a Teflon-coated magnetic stir bar, was supplied with a VOC-contaminated airstream that entered via a gas diffuser stone.…”

“…10 -11,15 Analytical Techniques VOC concentrations in gas samples collected from biofilter monitoring ports using glass gas-tight syringes (Hamilton) were measured using a Hewlett Packard 6890 series gas chromatograph equipped with a DB-624 Special Analysis Column (60 m ϫ 320 m ϫ 1.80 m, Hewlett Packard) and a flame-ionization detector (FID) as described previously. 15 Calibration was performed using certified gas standards (BOC Gases).…”

“…Laboratory and pilot-scale biofilters treating mixtures of ketones and aromatic hydrocarbons have revealed that removal of ketones generally precedes that of aromatic compounds. [7][8][9]11,15 Faster removal of ketones may result because of physical-chemical properties of higher aqueous partitioning coefficients and aqueous solubilities leading to faster mass transfer. It may also result from inherent differences in rates of enzyme-catalyzed reactions.…”