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

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

Development and Validation of a Practical Model for Transient Biofilter Performance

Biofilters are biological air-phase packed-bed reactors used for the removal of industrial air pollutants such as volatile organic compounds (VOCs) and odors. Because of the economic and environmental benefits, biofilter technology is preferred in applications such as wastewater treatment plants, waste recycling facilities, and several chemical industries over conventional treatment methods such as adsorption, absorption, and thermal oxidation processes. In order to predict the performance of biofilters, mathematical models under steady-state and transient conditions are needed. The transient biofilter models for gas-phase bioreactors are highly complex, as they involve several parameters that are not easily determined for industrial applications. In this work, a practical transient biofilter model is developed and an analytical solution for the transient model is obtained. When this model is compared with the published but more complex model, this new transient model produces almost the same level of prediction with equal comparisons of experimental data for VOCs, benzene, and toluene. This simple model has fewer parameters and will be very useful and practical for industrial applications for the analysis of transient biofilter performance

Toxic and Environmental Effects of Neonicotinoid Based Insecticides

The insecticide known as neonicotinoid has negative impacts on the ecosystem, human health, and the environment; specifically, its effects on the relationship between crop yields and the death rate of natural pollinators, such as bees, affect food security. The active ingredients in neonicotinoids include imidacloprid, clothianidin, thiamethoxam, acetamiprid, sulfoxaflor, and thiacloprid, which are sold under various trade names. For many of the components of these toxic insecticides, patents have been expired; however, farmers and consumers who continue to use these chemicals are unaware of the products’ toxicity and the environmental effects they have. Thus, agricultural industries are required to consider diverse methods to minimize neonicotinoid use in farming operations and move away from the current prevailing methods. In this short review, the negative effects of neonicotinoid use; the toxic components, health effects, and environmental regulations of neonicotinoids; and sustainable methods to minimize their use are examined