Engineering analysis of a packed-bed biofilter for removal of volatile organic compound (VOC) emissions

This study dealt with removal of VOC emissions from airstreams using an evolving new technology which is known as biofiltration. The basis of this technology is biodegradation of VOCs in biofilms formed around porous solids which are placed in packed-bed reactors. A detailed model describing steady state biofiltration of single and mixed VOCs was developed, and experimentally validated. The model takes into account biodegradation kinetics, the effect of oxygen, kinetic interactions among structurally similar compounds, and mass transfer from the gas phase to the biolayer. It was found that oxygen (a factor neglected in all previous studies) plays a very important role in biofiltration of VOCs, especially those which are hydrophilic. It was also found that the kinetics of biodegradation are complex, and that assumptions of zero or first order kinetics made by other researchers are invalid, and can lead to significant errors in biofilter design. Sensitivity studies with the model have shown that some of the kinetic parameters, and the biofilm surface area per unit volume of biofilter bed are important in all cases. For hydrophilic solvent vapors, sensitivity studies indicate that oxygen availability in the biolayer is also extremely important. The model was experimentally validated. In the case of single VOCs, methanol, benzene, and toluene were the model compounds. Methanol data were obtained from another study, while benzene and toluene data were generated during the course of this study from a unit 75cm-high and 10cm in diameter. For benzene removal, the residence time was varied from 2.7 min to 4.7 min, and the concentration in the inlet air from 0.07 gm-3 to 0.56 gm-3. During the experiments for toluene vapor removal, the residence time was varied from 2.7 min to 8.6 min, and the inlet concentration from 0.62 gm-3 to 2.81 gm-3. Validation of the model for the case of mixed VOCs was done with experiments involving mixtures of benzene and toluene. The unit was a three-stage glass column specifically designed during the course of this work. Each segment was 15.2cm in diameter and 30.5cm in height. Residence times varied from 0.9 min to 3.1 min, inlet benzene concentrations from 0.13 gm-3 to 0.37 gm-3, and inlet toluene concentrations from 0.21 gm-3 to 0.52 gm-3. In all cases, there was excellent agreement between model predictions and experimentally obtained concentrations. The experimental columns were continuously operated for periods over six months for single VOCs, while for mixed VOCs the column operated continuously for a year and a half. Except at start-up, in no case were additional nutrients added to the columns, while the pressure drop never exceeded 0.25 water/m of biofilter bed. Peat and perlite mixtures (2:3 volume ratio before packing) were used in all columns as solid porous support for the biofilm. Transient operation of biofilters involves, in addition to the mass transfer and reaction processes occurring at steady state, reversible adsorption of VOCs onto the packing material. This extra process was taken into account in developing a model which describes transient biofiltration of airstreams containing a single VOC. This model was experimentally validated with data for transient removal of toluene vapor. Good agreement was found between theory and experiments. The experimentally validated models developed in this study, can be used in (at least preliminary) scale-up and design of industrial biofilters

Dynamic Mathematical Modelling of the Removal of Hydrophilic VOCs by Biotrickling Filters

A mathematical model for the simulation of the removal of hydrophilic compounds using biotrickling filtration was developed. The model takes into account that biotrickling filters operate by using an intermittent spraying pattern. During spraying periods, a mobile liquid phase was considered, while during non-spraying periods, a stagnant liquid phase was considered. The model was calibrated and validated with data from laboratory- and industrial-scale biotrickling filters. The laboratory experiments exhibited peaks of pollutants in the outlet of the biotrickling filter during spraying periods, while during non-spraying periods, near complete removal of the pollutant was achieved. The gaseous outlet emissions in the industrial biotrickling filter showed a buffered pattern; no peaks associated with spraying or with instantaneous variations of the flow rate or inlet emissions were observed. The model, which includes the prediction of the dissolved carbon in the water tank, has been proven as a very useful tool in identifying the governing processes of biotrickling filtration

SYNERGISTIC HEMOLYSIS IN “NON-HEMOLYTIC” BACTEROIDES SPECIES

Bacteroides is a genus of anaerobic bacteria that are often found in high abundance in the human colon. They have a complex relationship with their human host, conferring health benefits as members of the gut microbiota but also acting as opportunistic pathogens. Though many of the virulence factors in Bacteroides have been characterized, it is currently classified as nonhemolytic. Work with Bacteroides isolates led to the observation, by happenstance, of unexpected hemolytic activity in multiple species. After incubation on blood agar plates, we observed that some isolates were clearly hemolytic, but only when plated in close proximity to certain, ‘activating’ isolates. We performed a systematic screen for hemolytic activity on a library of 94 Bacteroides isolates and identified one which was able to activate hemolysis in 30% of the collection. Using timelapse photography, we show this zone of hemolysis begins between the two colonies and proceeds in a retrograde fashion towards the ‘activated’ colony. The asymmetrical patterns of hemolysis are unlike any bacterial synergy reported to date. To investigate the mechanism behind this pattern, we combined a comparative genomics and mutagenesis approach to narrow down the genetic basis of this phenotype. Here, we characterize a unique synergistic hemolysis phenotype in Bacteroides, a genus of bacteria currently classified as nonhemolytic. This novel phenotype may provide further insight into Bacteroides as an opportunistic pathogen and may have uncovered a new mechanism by which they interact.ThesisMaster of Science (MSc

Performance of an industrial biofilter from a composting plant in the removal of ammonia and VOCs after material replacement

BACKGROUND: Biofiltration is a suitable odor reduction technique for the treatment of gaseous emissions from composting processes, but little is known about the start-up of full-scale biofilters after material replacement and their performance after several years of operation. - RESULTS: Biofilter material (wood chips used previously as bulking agent in a composting process) can effectively remove ammonia and most of the volatile organic compounds (VOCs) content, achieving removal efficiencies greater than 70% for VOCs and near 90% for ammonia immediately after material replacement. These removal efficiencies were maintained for several months after material replacement. In the studied full-scale biofilter no lag phase was observed in the removal of ammonia whereas in the case of VOCs different patterns were detected during biofilter start-up. For the old biofilter material, after 4 years of operation, a statistically significant decrease of removal efficiency for ammonia in comparison with the new material was detected. No statistically significant differences were found in the case of VOCs. - CONCLUSIONS: Data on the emissions of several pollutants from biofilters treating composting exhaust gases have been systematically obtained. The tested filtering media presented adequate properties for biofiltration of gases emitted during the composting process

Abatement of styrene waste gas emission by biofilter and biotrickling filter: comparison of packing materials and inoculation procedures

The removal of styrene was studied using 2 biofilters packed with peat and coconut fibre (BF1-P and BF2-C, respectively) and 1 biotrickling filter (BTF) packed with plastic rings. Two inoculation procedures were applied: an enriched culture with strain Pseudomonas putida CECT 324 for biofilters and activated sludge from a municipal wastewater treatment plant for the BTF. Inlet loads (ILs) between 10 and 45 g m-3 h-1 and empty bed residence times (EBRTs) from 30 to 120 s were applied. At inlet concentrations ranging between 200 and 400 mg Nm-3, removal efficiencies between 70 and 95% were obtained in the 3 bioreactors. Maximum elimination capacities (ECs) of 81 and 39 g m-3 h-1 were obtained for the first quarter of the BF1-P and BF2-C, respectively (IL of 173 g m-3 h-1 and EBRT of 60 s in BF1-P; IL of 89 g m-3 h-1 and EBRT of 90 s in BF2-C). A maximum EC of 52 g m-3 h-1 was obtained for the first third of the BTF (IL of 116 g m-3 h-1, EBRT of 45 s). Problems regarding high pressure drop appeared in the peat biofilter, whereas drying episodes occurred in the coconut fibre biofilter. DGGE revealed that the pure culture used for biofilter inoculation was not detected by day 105. Although 2 different inoculation procedures were applied, similar styrene removal at the end of the experiments was observed. The use as inoculum of activated sludge from municipal wastewater treatment plant appears a more feasible option

Mechanism of olfactory masking in the sensory cilia

Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide–gated (CNG) and Ca2+-activated Cl− (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane

Medical Waste Management and Control

Medical centers including hospitals, clinics and places where diagnosis and treatment are conducted generate wastes that are highly hazardous and put people under risk of fatal diseases. Although the understanding of medical waste management and control techniques is important, technical elective courses that are offered in undergraduate chemical, civil or environmental engineering place less emphasis on this area of education. In this paper, the meaning of medical waste, the risks of exposure, medical waste management regulatory acts, medical waste management procedures and control techniques are presented. The contents presented in this paper served as a supplementary material in an undergraduate elective course on waste management and as an educational guide for medical staff training on waste handling

Selection of sustainable technologies for reducing emission of volatile organic compounds and greenhouse gases

Selection of sustainable and environmental friendly technologies is very important in meeting strict environmental regulations on industrial emissions of volatile organic compounds and greenhouse gases. Many of the industrial volatile organic compounds are toxic and carcinogenic, and they are regulated under Clean Air Act for hazardous air pollutants. Similarly, global environmental agreements such as European Union’s 2015 Paris Agreement and Kyoto Protocol restrict carbon emission, which is responsible for global warming, sea-level rise, flooding, and ecological imbalance. It is essential that industries choose suitable technologies that reduce not only toxic volatile organic compounds in the air but also greenhouse gas emissions. In this communication, biotechnological methods are discussed and compared with conventional processes, which are used for control of volatile organic compounds. The readers may find this article useful in the selection of an appropriate technology for their application while minimizing the greenhouse gas emissions. </jats:p

A synthetic biofilter media for ammonia (NH3) removal

In this work, a patented biofilter media is used in treating air contaminated with ammonia (NH3). The data shows up to 200 ppm of NH3 can be removed with over 93% removal efficiency at 30 s Empty Bed Residence Time (EBRT). At the start-up conditions, the results also indicated that the humidifier can be utilised for buffering concentration fluctuations. The design correlation developed based on the zero-order model can be used as a preliminary estimate for sizing biofilters for NH3 removal. The results show that predictions using the design correlation are in good agreement with the experimental data