Joseph S. Devinny

Influence of water content on degradation rates for ethanol in biofiltration

Treatment of ethanol vapor in a peat biofilter with various initial water contents (70%, 59%, 49%, and 35%) was studied. For water contents ranging from 49% to 70%, elimination capacity was about 30 g/m3/h. For a water content of 35%, elimination capacity decreased to 4 g/m3/h. A low mean CO2 yield coefficient (0.35 g CO2 produced per g ethanol consumed) was found for all of the initial water contents. The value was only 20% of the yield coefficient (1.91 g/g) predicted by stoichiometry. When the packing material was dried from 70% to 59% water content during the biofiltration process, elimination capacity dropped from 27 g/m3/h to 4 g/m3/h. After 24 hours of drying, the biofiltration experiment was restarted and run for two more weeks. During this period, the biofilter did not recover. At 59% water content, the rate of water evaporation was estimated at 59.6 g/m3/h. A simplified mass balance permitted calculation of the biological water production rate, approximately 22.1 g/m3/h.

Formation of Acidic and Toxic intermediates in Overloaded Ethanol Biofilters

Abstract Three biofilters inoculated with different amounts of active biomass were used to treat air contaminated with ethanol vapors. Chemostat-grown microbial culture was added in amounts up to 2% of the weight of the granular activated carbon (GAG) support medium. The contaminant load was 156 g ethanol per m3 biofilter per hour. The inoculation eliminated the initial period of poor treatment, which has been observed in other GAG biofilters. The most heavily inoculated biofilter, however, experienced a period of process upset. Rapid ethanol consumption was associated with production of acetaldehyde, acetic acid, and ethyl acetate. The resulting pH reduction inhibited treatment. Such upset conditions can be avoided by eliminating overload conditions and maintaining the alkalinity of the support medium.

Microbial ecosystems in compost and granular activated carbon biofilters

Compost and granular activated carbon biofilters operated at a wastewater treatment plant simultaneously removed low concentrations of hydrogen sulfide and volatile organic compounds. Through the use of phospholipid fatty acid analyses, the effects of declining pH caused by sulfide oxidation were established for microbial growth, microorganism stress, and microbial community structure. Microorganisms on both media demonstrated increases in microbial densities, varying degrees of environmental stress, and domination by gram-negative bacteria. However, the declining pH had little effect on compound removal, which was greater than 99% for the hydrogen sulfide and greater than 70% for the oxygenated and aromatic hydrocarbons. The microbial communities adjusted to difficult environmental conditions through acclimation of the species present or by growth of low-pH-tolerant species.

Treatment of hydrocarbon fuel vapors in biofilters

Abstract Industrial processes and contaminated site remediation projects produce large‐volume air discharges with low concentrations of pollutants. Biofilters can treat such effluents by passing them through a damp porous medium which supports an active community of microorganisms. This paper reports bench testing of biofilters using soil, carbon and diatomaceous earth as support media for treatment of JP‐5 jet fuel and diesel fuel vapors. Activated carbon supported higher biodegradation rates than soil, and diatomaceous earth was least effective. Jet fuel was degraded more rapidly than diesel fuel.

Treatment of gasoline residuals by granular activated carbon based biological filtration

Abstract Most biofilters use compost as the microorganism support medium. This study investigated the use of granular activated carbon (GAC) as a support medium. Its high adsorptive capacity is a feature that makes GAC a potentially good biofilter medium. A bench‐scale column provided the experimental results presented in this paper. Gasoline vapors were the contaminant treated. The GAC was seeded with microorganisms and nutrients, and the system was operated using prehumidification of the incoming gas stream only. The history of treatment efficiency indicated initial adsorption provided high percentages of removal. However, once the adsorption capacity was saturated, the treatment efficiency dropped dramatically. Later, biological activity increased to the point where effective treatment was possible. The main obstacle to effective treatment was the slow growth of biomass in the lower portions of the column. The average and maximum elimination capacities of the biofilter were high compared to published b...

A biofilter network model : importance of the pore structure and other large-scale heterogeneities

Previous efforts to describe biofiltration use continuum models with empirical relationships to describe air-flow in the biofilter, and conventional diffusion/reaction equations to describe processes in the biofilm. Biofilters are packed-bed reactors. They differ from conventional reactors because during their operation biomass is being created, which changes the beds pore structure. This may eventually clog the reactor and prevent further flow of air. All current models ignore the importance of effects that occur at the pore network level. A new biofilter network model is presented here which aims to understand the importance of the pore network structure. The model accounts for biofilm growth. With this model the biofilter removal efficiency and the pressure drop can be related to the beds pore network structure. Pressure drop changes resulting from the growing biofilm are described and explained. The effects of different initial pore size distributions on the efficiency of the biofilter are discussed. The model predicts that under certain conditions non-uniform biofilm growth will occur in the biofilter.

Biofilm Growth-Percolation Models and Channeling in Biofilter Clogging

Abstract Biomass accumulation is a load-limiting factor in the operation of biofilters used for air pollution control. As the biofilm thickens, portions at the base are no longer exposed to contaminants and oxygen and, thus, provide no treatment. Smaller pores are filled with biomass so that air no longer flows into them. As airflow paths are restricted, air may be prevented from reaching some pores even before they are filled. Eventually blockage becomes sufficiently widespread so that increasing head loss and decreasing removal efficiency require that the system be shut down. Optimization of biofilter design requires a better understanding of the mechanisms by which biofilters clog. In this work, a numerical percolation model of the blockage process was developed for application to biofilters. It allows comparison of pore blockage histories for various pore size distributions and predicts biomass accumulation, head loss, and treatment efficiency as a function of time, as well as total time, until blockage prevents further operation. Although the model was reasonably accurate in predicting the time before complete clogging, it underestimated intermediate values of head loss. Observations of a clogged biofilter suggest that this occurs because clogging later in the process is nonuniform at scales that are large in comparison with individual pores.

Pyrolytic destruction of polychlorinated biphenyls in a reductive atmosphere

Abstract This paper discusses the development of an innovative technology for the pyrolytic destruction of halogenated hydrocarbons in a reductive environment. The technology developed demonstrated the potential for resource recovery, as reaction products could be commercially used. The process was specifically directed at the dehalogenation of polychlorinated biphenyls (PCBs), a class of chlorinated compounds most difficult to thermally decompose due to the high strength of their carbon-chlorine bonds. PCBs have extensive industrial applications, and are regarded as pollutants of serious environmental concern due to their persistence and insidious health effects. Pyrolysis experiments were conducted under controlled laboratory conditions in batch reactor systems with Aroclor 1254 (a mixture of PCB congeners) to evaluate the process feasibility, and to determine the destruction and removal efficiencies (DREs). The pyrolysis was conducted under a variety of operating conditions to investigate the effect on DREs due to changes in process variables such as reactor residence time, reaction temperature, and reactant (methane) concentration. Under optimal conditions — a residence time of 7 minutes, reaction temperature of 1000°C, and stoichiometric excess methane — a DRE of over 99.999% was achieved. The reaction products were dehalogenated hydrocarbons, hydrogen chloride, and soot. The dehalogenated compounds formed were identified as aliphatic and aromatic hydrocarbons by gas chromatography/mass spectrometry (GC /MS). The study also included a scientific analysis of free-radical reactions and associated mechanisms involved in the decomposition of the halogenated hydrocarbons. Achievement of the highest DREs suggests that the process needs further investigation as a method for dehalogenation of chlorinated hydrocarbons with the potential of product recovery for commercial use.

Removal of Ultrafine and Fine Particulate Matter from Air by a Granular Bed Filter

Abstract The removal efficiency of granular filters packed with lava rock and sand was studied for collection of airborne particles 0.05–2.5 μm in diameter. The effects of filter depth, packing wetness, grain size, and flow rate on collection efficiency were investigated. Two packing grain sizes (0.3 and 0.15 cm) were tested for flow rates of 1.2, 2.4, and 3.6 L/min, corresponding to empty bed residence times (equal to the bulk volume of the packing divided by the airflow rate) in the granular media of 60, 30, and 20 sec, respectively. The results showed that at 1.2 L/min, dry packing with grains 0.15 cm in diameter removed more than 80% (by number) of the particles. Particle collection efficiency decreased with increasing flow rate. Diffusion was identified as the predominant collection mechanism for ultrafine particles, while the larger particles in the accumulation mode of 0.7–2.5 μm were removed primarily by gravitational settling. For all packing depths and airflow rates, particle removal efficiency was generally higher on dry packing than on wet packing for particles smaller than 0.25 μm. The results suggest that development of biological filters for fine particles is possible.

Future Prospects of Biotechnology for Odor Control

The world’s populations are simultaneously growing and migrating to the cities. This produces rapid expansion of urban areas into the surrounding countryside where they encroach on land dedicated to waste treatment, industry, andagriculture.Farmersare seeking increasedefficiency throughmeasures that grow animals in dense concentrations nearer the point of consumption. Rapid development of newmaterials and new industries creates a host of exotic chemical discharges. Odors form the burgeoning fast food industry are a special problem – coffee and fried chicken may smell great when you are ready to eat, but the continuous smell of roasting beans or stale grease becomes offensive. All of these trendsmean that populations are more often living close to odorous facilities, and it means that odor control is an ever more pressing air quality problem. Cries from the farmers and treatment plant operators of “We were here first!” will have little effect. With respect toodors, ugliness is entirely in thenoseof thebeholder.Wehave evolved to recognize some compounds as associated with danger: the smell of human waste is offensive because those individuals who avoided contact with it were less likely to die of disease, and the smell of spoiled food prompts us to avoid eating meals that could threaten food poisoning. The perception that an odor is foul is the body’s way of telling the brain that it is best to go elsewhere. In modern society, we frequently encounter odors that no longer represent a health risk – it is not dangerous to be downwind of a dairy. But while the nose may not provide accurate warning of the presence or absence of a health risk in modern society, the evidence suggests that unpleasant odors can cause adverse physiological and neurogenic responses. The study by Schiffman et al. (2000) found that the most frequently reported health complaints related to odors include eye, nose, and throat irritation, headache, nausea, diarrhea, hoarseness, sore throat, cough, chest tightness, nasal congestion, palpitations, shortness of breath, stress, drowsiness, and alterations in mood. Certainly, unpleasant odors can cause human nuisance and physical discomfort. Noxious and foul odors also have economic consequences. Foul odors can reduce property values in affected neighborhoods from 15 to as much as 90% (Kleemeier et al. 2002;Weida andHatz 2002;Anstine 2003). Theoffensive odors