Biofiltration is a relatively recent air pollution control (APC) technology in which off-gases containing biodegradable volatile organic compounds (VOC) or inorganic air toxics are vented through a biologically active material. This technology has been successfully applied in Germany and The Netherlands in many full-scale applications to control odors, VOC and air toxic emissions from a wide range of industrial and public sector sources. Control efficiencies of more than 90 percent have been achieved for many common air pollutants. Due to lower operating costs, biofiltration can provide significant economic advantages over other APC technologies if applied to off-gases that contain readily biodegradable pollutants in low concentrations. Environmental benefits include low energy requirements and the avoidance of cross media transfer of pollutants. This paper reviews the history and current status of biofiltration, outlines its underlying scientific and engineering principles, and discusses the applicability of biofilters for a wide range of specific emission sources.

This analysis offers an empirical basis for a per se limit for THC that allows identification of drivers impaired by cannabis. The limited epidemiological data render this limit preliminary.

No abstract

To date, biofilters have been used primarily to control dilute, usually odorous, off-gases with relatively low volatile organic compound (VOC) concentrations (<1 g m -3 ) and VOC loads (<50 g m -3 hr -1 ). Recently, however, U.S. industry has shown an interest in applying biofilters to higher concentrations of VOCs and hazardous air pollutants (HAPs).In this study, the behavior of biofilters under high loads of binary VOC mixtures was studied. Two benchscale biofilters were operated using a commercially available medium and a mixture of wood chips and compost. Both were exposed to varying mixtures of ethyl acetate and toluene. Concentration profiles and the corresponding removal efficiencies as a function of VOC loading were determined through frequent grab-sampling and GC analysis. Biofilter response to two frequently encountered operating problems-media dry-out and operating temperatures exceeding 40 °C-was also evaluated under controlled conditions. Microbial populations were IMPLICATIONS To date, biofilters have been used primarily to control dilute, usually odorous, off-gases with relatively low VOC concentrations. Yet there is a growing interest in expanding to higher concentrations the range of suitable applications for biological waste air treatment. However, this type of application has a high rate of system failure. Impediments for this application were reported in two recent case studies in which the treatment of high loads of ethanol from a foundry and a bakery, respectively, resulted in reduced percentage removal of the contaminants, formation of odorous acetic acid, and problems maintaining the proper moisture content because of the exothermic nature of the biodegradation process. The present study reports bench-scale operation of biofilters under high VOC loading conditions of mixed pollutant and the factors that lead to these adverse operating states also monitored to confirm the presence of organisms capable of degrading both major off-gas constituents. The results demonstrated several characteristics of biofilters operating under high VOC load conditions.• Maximum elimination capacities for ethyl acetate were typically in the range of 200 g m -3 hr -1 .• Despite the presence of toluene degraders, the removal of toluene was inhibited by high loads of ethyl acetate.• Several byproducts, particularly ethanol, were formed.• Short-term dry-out and temperature excursions resulted in reduced performance. INTRODUCTIONIt is generally thought that biofilters are suitable only for the treatment of dilute emissions of odors, volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). The large majority of biofilters installed to date treat off-gases containing organic carbon compounds at concentrations of less than 0.5 g m -3 . Corresponding VOC loads and elimination capacities rarely exceed 50 grams of organic carbon per cubic meter of biofilter material per hour (g m -3 hr). Recently, however, industrial users, particularly in the United States, and vendors of biofilters have been attr...

Foods containing seeds or oil of the hemp plant (Cannabis sativa L.) are increasingly found in retail stores in the U.S. The presence of delta9-tetrahydrocannabinol (THC) in these foods has raised concern over their impact on the results of workplace drug tests for marijuana. Previous studies have shown that eating hemp foods can cause screening and confirmed positive results in urine specimens. This study evaluated the impact of extended daily ingestion of THC via hemp oil on urine levels of its metabolite 11-nor-9-carboxy-delta9-tetrahydrocannabinol (THC-COOH) for four distinct daily THC doses. Doses were representative of THC levels now commonly found in hemp seed products and a range of conceivable daily consumption rates. Fifteen THC-naïve adults ingested, over four successive 10-day periods, single daily THC doses ranging from 0.09 to 0.6 mg. Subjects self-administered THC in 15-mL aliquots (20 mL for the 0.6-mg dose) of four different blends of hemp and canola oils. Urine specimens were collected prior to the first ingestion of oil, on days 9 and 10 of each of the four study periods, and 1 and 3 days after the last ingestion. All specimens were screened for cannabinoids by radioimmunoassay (Immunalysis Direct RIA Kit), confirmed for THC-COOH by gas chromatography-mass spectrometry (GC-MS), and analyzed for creatinine to identify dilute specimens. None of the subjects who ingested daily doses of 0.45 mg of THC screened positive at the 50-ng/mL cutoff. At a daily THC dose of 0.6 mg, one specimen screened positive. The highest THC-COOH level found by GC-MS in any of the specimens was 5.2 ng/mL, well below the 15-ng/mL confirmation cutoff used in federal drug testing programs. A THC intake of 0.6 mg/day is equivalent to the consumption of approximately 125 mL of hemp oil containing 5 microg/g of THC or 300 g of hulled seeds at 2 microg/g. These THC concentrations are now typical in Canadian hemp seed products. Based on our findings, these concentrations appear to be sufficiently low to prevent confirmed positives from the extended and extensive consumption of hemp foods.