A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

The treatment of waste-air containing mixed solvent using a biofilter 2. Treatment of waste-air containing ethanol and toluene in a biofilter

An experiment for five stages of a biofilter-run was performed to investigate the effect of hydrophilic ethanol and hydrophobic toluene on the biodegradation of hydrophobic toluene and hydrophilic ethanol, respectively, when waste-air containing toluene and ethanol was treated by a biofilter. Removal efficiencies of toluene and ethanol began to decrease when inlet load surpassed 90 g/m³/h and 100 g/m³/h consistent with maximum elimination capacities of toluene and ethanol, respectively. At the end of the biofilter-run, removal efficiencies for toluene and ethanol were decreased and maintained at 65% and 40%, respectively. The concentration of toluene at 1st sampling port was raised by factor of two in the 3rd stage of the biofilter run when the inlet load of ethanol co-feed was increased by 1.5 times, while the process conditions of toluene were maintained the same as those of the 2nd stage of biofilter-run. According to the result of Mohseni and Allen, it may be interpreted that removal efficiency of hydrophobic toluene was affected by the presence of hydrophilic ethanol when high load of hydrophobic toluene was applied like that of the 1st sampling port of the biofilter. However it was not the case when a low load of hydrophobic toluene was applied like those of the 2nd, 3rd and 4th sampling ports since hydrophobicity of toluene is much less that of α-pinene. Thus, it may be suggested that biodegradation of hydrophobic VOC was interfered by hydrophilic VOC dissolved in the biolayer and the degree of interference was proportional to the inlet load of hydrophobic VOC as well as that of hydrophilic VOC and was inversely proportional to the solubility of hydrophobic VOC. However, it was inferred that the existence of hydrophobic toluene from waste-air can hardly inversely hinder the removal of hydrophilic ethanol in the biofilter when timeevolutions of hydrophilic ethanol concentrations of this experiment were compared with those of the previous experiment of biofilter to treat waste-air containing ethanol only.     

Desorption and Biofiltration for the Treatment of Residual Organic Gases Evolved in Soil Decontamination Processses

In order to analyze the combination of a rotary kiln and a biofilter in soil decontamination processes, a previously characterized soil was artificially contaminated with toluene, ethylbenzene or p‐xylene. The desorption peak of the three compounds occurred very quickly at 20 °C, and consequently, the outlet gas flow from the rotary kiln was initially divided into two different flows. One of them was reduced to a 1/9^th fraction of the total flow to be treated in an independent biofiltration system specially acclimated to each contaminant. The sharp desorption peak observed for the three compounds at the outlet of the kiln involved a very high inlet concentration fed into the biofilters in a very short period of time (shorter than 3 h). Consequently, the removal efficiency for toluene was lower than 70 %. However, the removal efficiencies for ethylbenzene and xylene were always higher than 65 %.     

Characterization of a Spray Drying System for Soymilk

ABSTRACT

Soymilk slurries were spray dried at various combinations of inlet air temperature (1255. 265, and 275°C), feed rate (0.38 and 0.57 Lpm), and atomizer speed (119,300 and 26,800 rpm). Monitored dryer parameters included dry and wet bulb temperaturea of ambient and exhaust air, drying chamber's inlet and outlet air temperatures, product and feed temperatures, velocity pressure at exhaust pipe, atomizer speed, and feed rate. Weather data was included in the analysis.

Collected data was used to estimate the state of the outlet air using psychrometrics and assuming adiabatic saturation. Equations to predict outlet and product temperatures were developed. Average thermal and eveporative efficiencies were 65.9 and 78.4%. respectively.     

Effect of pre‐treatments based on UV photocatalysis and photo‐oxidation on toluene biofiltration performance

BACKGROUND: The integration of UV photocatalysis and biofiltration seems to be a promising combination of technologies for the removal of hydrophobic and poorly biodegradable air pollutants. The influence of pre‐treatments based on UV_{254 nm} photocatalysis and photo‐oxidation on the biofiltration of toluene as a target compound was evaluated in a controlled long‐term experimental study using different system configurations: a standalone biofilter, a combined UV photocatalytic reactor‐biofilter, and a combined UV photo‐oxidation reactor (without catalyst)‐biofilter. RESULTS: Under the operational conditions used (residence time of 2.7 s and toluene concentrations 600–1200 mg C m^?3), relatively low removal efficiencies (6–3%) were reached in the photocatalytic reactor and no degradation of toluene was found when the photo‐oxidation reactor was operated without catalyst. A noticeable improvement in the performance of the biofilter combined with a photocatalytic reactor was observed, and the elimination capacity of the biological process increased by more than 12 g C h^?1 m^?3 at the inlet loads studied of 50–100 g C h^?1 m^?3. No positive effect on toluene removal was observed for the combination of UV photoreactor and biofilter. CONCLUSIONS: Biofilter pre‐treatment based on UV_{254 nm} photocatalysis showed promising results for the removal of hydrophobic and recalcitrant air pollutants, providing synergistic improvement in the removal of toluene. Copyright © 2011 Society of Chemical Industry     

Removal of Elemental Mercury by Sodium Chlorite Solution

The important step for increasing gaseous elemental mercury (Hg⁰) removal in wet scrubber systems is altering the chemical form of the Hg⁰ to a water‐soluble oxidized species. This work focuses on the removal of elemental mercury from simulated flue gas by aqueous sodium chlorite in a bubble reactor. The effects of initial oxidizing solution concentration, reaction temperature, pH and mercury concentration in the inlet of the reactor on mercury oxidative absorption in sodium chlorite were investigated. The results indicate that higher concentrations of sodium chlorite favor Hg⁰ removal, with a greater efficiency observed in acidic than in alkaline solution. High temperature inhibits Hg⁰ absorption in aqueous sorbent when the reaction temperature is lower than ca. 40 °C, and the removal efficiency increases when the temperature is higher than that value. In conclusion, the major influencing factors on the levels of Hg⁰ removal are pH and chlorite concentration in solution.     

Removal of pentane and styrene mixtures from waste gases by a trickle‐bed air biofilter

The biofilter process is a relatively new technology that has been proven to be more cost‐effective than traditional technologies for treating many kinds of volatile organic compounds (VOCs) from waste gases. Pentane and styrene mixtures are commonly encountered in the manufacture of polymers such as polystyrene. This research attempts to employ a trickle‐bed air biofilter (TBAB) for treating such mixtures under different influent carbon loadings. In the pseudo‐steady‐state conditions, the elimination capacities of pentane and styrene increased but the removal efficiencies decreased with increased influent carbon loading. The removal efficiencies of styrene were higher than those of pentane, indicating that styrene is a preferred substrate and the differences were enhanced at a high carbon loading. Removal efficiencies of more than 80% were achieved with influent carbon loadings of pentane and styrene below 25 and 68 gm^?3 h^?1, respectively. The TBAB appears to be efficient for controlling VOC emissions with low pentane and medium styrene loadings, and the effectiveness could be maintained over 140 days of laboratory operation. © 2001 Society of Chemical Industry     

Effect of inlet mass loading,water and total bacteria count on methanol elimination using upward flow and downward flow biofilters

An upward flow biofilter and a downward flow biofilter using compost for removing methanol from air were investigated to compare the biofilter performance and to realize the advantages of using downward flow biofilters for accessibility to water make‐up. Both the upward flow and downward flow columns showed similar performance in terms of elimination capacity (EC) versus inlet mass loading (IC). The maximum elimination capacity (EC) from these two biofilters was approximately 101 g m⁻³ h⁻¹ with an optimum methanol loading rate at inlet (IC) of 169 g m⁻³ h⁻¹ (7.5 g m⁻³ of methanol with superficial velocity of 7.6 m h⁻¹). The effect of water movement within the bed on elimination capacity was monitored. In addition, it was found that when the water content in the compost was below 35% by weight, microbial activity was impaired. Once the compost media had dried, it became hydrophobic and could be rewetted only with great difficulty. Total bacteria count was performed on compost samples during the entire operation. The relationship between elimination capacity and total bacteria count was reported. Similar trends were shown by the variations of elimination capacity and total bacteria count with methanol loading: both initially increase, go through a plateau, then decrease with loading. © 2000 Society of Chemical Industry     

Removal of Hydrogen Sulphide by Immobilized Thiobacillus sp. strain CH11 in a Biofilter

An autotropic Thiobacillus sp. CH11 was isolated from piggery wastewater containing hydrogen sulphide. The removal characteristics of hydrogen sulphide by Thiobacillus sp. CH11 were examined in the continuous system. The hydrogen sulphide removal capacity was elevated by the BDST (Bed Depth Service Time) method (physical adsorption) and an immobilized cell biofilter (biological conversion). The optimum pH to remove hydrogen sulphide ranged from 6 to 8. The average specific uptake rate of hydrogen sulphide was as 1·02×10⁻¹³ mol-S cell⁻¹ h⁻¹ in continuous systems. The maximum removal rate and saturation constant for hydrogen sulphide were calculated to be V_m = 30·1 mmol-S day⁻¹ (kg-dry bead)⁻¹ and K_s = 1·28 μmol dm⁻³, respectively. A criterion to design a scale-up biofilter was also studied. The maximum inlet loading in the linear region (95% removal) was 47 mmol-S day⁻¹ (kg-dry bead)⁻¹. Additionally, the biofilter exhibited high efficiency (>98·5%) in the removal of hydrogen sulphide at both low (<0·026 mg dm⁻³) and high (0·078 mg dm⁻³) concentrations. The results suggested that the Thiobacillus sp. CH11 immobilized with Ca-alginate is a potential method for the removal of hydrogen sulphide. © 1997 SCI.     

Effect of temperature on the performance of a biofilter inoculated withPseudomonas putida to treat waste-air containing ethanol

The microbes ofPseudomonas putida (KCTC1768) were fixed on the biofilter-packing media comprising an equivolume mixture of granular activated carbon (GAC) and compost, by recycling the liquid medium containing incubatedPseudomonas putida (KCTC1768). A biofilter experiment was performed to observe its transient behavior under the operating condition of 2,180 ppmv of ethanol-inlet concentration and 158 g/m³/h of ethanol-inlet load for the five consecutive temperature-stages of operation ranging from 25 °C to 40 °C. For the five temperaturestages of operation their removal efficiencies were measured and were compared with each other. The optimum operating temperature of the biofilter turned out to beca. 30 °C, which was consistent with the previous experimental result of Lim and Park. However, the optimum incubation-temperatures ofPseudomonas putida (KCTC1768) and the equivalent (i.e., NCIMB8858) were announced to be of 26 °C and 25 °C by Korea Collection for Type Cultures (KCTC) and National Collections of Industrial, Food and Marine Bacteria (NCIMB), respectively. It was also confirmed by the experiment in which the microbes were incubated in the same liquid medium as in the previous work of Lim and Park at temperature ranging from 20 °C to 40 °C and their growth rates were subsequently measured. Thus, the optimum operating temperature of a biofilter inoculated withPseudomonas putida (KCTC 1768) was proved to be 30 °C, which was higher than its optimum incubation-temperature byca. 5 °C     

Simultaneous removal of gaseous pollutants with a novel swirl wet scrubber

In recent years, researchers have put a considerable effort to decrease the emission of harmful gaseous pollutants to the atmosphere. Although conventional wet scrubbers are being widely used to remove harmful gases, they have low removal efficiencies. This study reports the effect of some operating conditions on simultaneous removal of NO, NO₂, SO₂, and CO₂, using a novel swirl wet scrubber system. The gaseous pollutants were absorbed into NaOH solution. As the absorbent media was circulated continuously for removal purpose, therefore the production of chemical wastes were minimized. The effect of absorbent concentration, gas flow rate, and liquid flow rate were investigated. The best efficiencies of NO, NO₂, SO₂, and CO₂ simultaneous removal were 77, 88, 100 and 80%, respectively, with 2%, w/v NaOH as the scrubber medium. A comparison between this study and literature data shows that the liquid-gas flow rate ratio (F_L/F_G) in the novel scrubber of this work is much smaller than other gaseous pollutant removal systems. Therefore higher removal efficiency is obtained based on the same liquid flow rates.     

Comparison of biological reactors (biofilter,biotrickling filter and modified RBC) for treating dichloromethane vapors

BACKGROUND: Bioreactors used for waste gas and odor treatment have gained acceptance in recent years to treat volatile organic compounds (VOCs). Different types of bioreactors (biofilter, biotrickling filter and rotating biological reactor) have been used for waste gas treatment. Most studies reported in the literature have used one of these systems to treat several types of inorganic and organic gases either individually or in mixtures. Each of these reactors has some advantages and some limitations. Though biodegradation is the main process for the removal of pollutants, the mechanisms of removal and the microbial communities may differ among these bioreactors. Consequently their performance or removal efficiency may also be different. RESULTS: At low loading rate (<35 g m^?3 h^?1), all three bioreactors showed comparable removal efficiencies and elimination capacity, but at higher loading rates, rotating biological contactors (RBC) showed a better performance with higher removal efficiency (40–50%) than both the biofilter and biotrickling filter (20–40%). The biofilter showed a sharp drop in removal efficiency and elimination capacity at high loading rates. CONCLUSIONS: The modified RBC had no clogging problems and no increase in pressure drop when compared with the other bioreactors. It can thus handle pollutant load for a longer period of time. This is the first study attempting to compare the performance of three different bioreactors for removal of the same VOC under different conditions. Copyright © 2010 Society of Chemical Industry     

Survival,oxidative stability,and surface characteristics of spray dried co-microcapsules containing omega-3 fatty acids and probiotic bacteria

The objective of the study was to determine optimum inlet and outlet air temperatures of spray process for producing co-microcapsules containing omega-3 rich tuna oil and probiotic bacteria L. casei. These co-microcapsules were produced using whey protein isolate and gum Arabic complex coacervates as shell materials. Improved bacterial viability and oxidative stability of omega-3 oil were used as two main criteria of this study. Three sets of inlet (130°C, 150°C, and 170°C) and outlet (55°C, 65°C, and 75°C) air temperatures were used in nine combinations to produce powdered co-microcapsule. The viability of L. casei, oxidative stability of omega-3 oil, surface oil, oil microencapsulation efficiency, moisture content, surface elemental composition and morphology of the powdered samples were measured. There is no statistical difference in oxidative stability at two lower inlet air temperatures (130°C and 150°C). However, there was a significant decrease in oxidative stability when higher inlet temperature (170°C) was used. The viability of L. casei decreased with the increase in the inlet and outlet air temperatures. There was no difference in the surface elemental compositions and surface morphology of powdered co-microcapsules produced under these nine inlet/outlet temperature combinations. Of the range of conditions tested the co-microcapsules produced at inlet-outlet temperature 130–65°C showed the highest bacterial viability and oxidative stability of omega-3 and having the moisture content of 4.93?±?0.05% (w/w). This research shows that powdered co-microcapsules of probiotic bacteria and omega-3 fatty acids with high survival of the former and high stability against oxidation can be produced through spray drying.     

Influence of nitrogen on the degradation of toluene in a compost‐based biofilter

Two identical laboratory‐scale bioreactors were operated simultaneously, each treating an input air flow rate of 1 m³ h^?1. The biofilters consisted of multi‐stage columns, each stage packed with a compost‐based filtering material, which was not previously inoculated. The toluene inlet concentration was fixed at 1.5 g m^?3 of air. Apart from the necessary carbon, the elements nitrogen, phosphorus, sulfur, potassium and other micro‐elements are also essential for microbial metabolism. These were distributed throughout the filter bed material by periodic ‘irrigations’ with various test nutrient solutions. The performance of each biofilter was quantified by determining its toluene removal efficiency, and elimination capacity. Nutrient solution nitrogen levels were varied from 0 to 6.0 g dm^?3, which led to elimination capacities of up to 50 g m^?3 h^?1 being obtained for a toluene inlet load of 80 g m^?3 h^?1. A theoretical analysis also confirmed that the optimum nitrogen solution concentration lays in the range 4.0–6.0 g dm^?3. Validation of the irrigation mode was achieved by watering each biofilter stage individually. Vertical stage‐by‐stage stratification of the biofilter performance was not detected, ie each filter bed section removed the same amount of pollutant, the elimination capacity per stage being about 16 g m^?3 h^?1 per section of column. © 2001 Society of Chemical Industry     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

ABSTRACT

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10–20% of solids was dried at different inlet air temperatures (120–160°C), air flow rate of 0.19 kg dry air s^?1 and different feed rates (1.4 ? 4.2 × 10^?4 kg dry solids s^?1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

High-Rate Anaerobic Treatment of Malting Waste Water in a Pilot-Scale EGSB System Under Psychrophilic Conditions

The feasibility of the expanded granular sludge bed (EGSB) system for the treatment of malting waste water under psychrophilic conditions was investigated by operating a pilot-scale 225·5 dm³ EGSB-reactor system in the temperature range from 13 to 20°C. The concentration of chemical oxygen demand (COD) in the malting waste water was between 282 and 1436 mg dm⁻³. The anaerobically biodegradable COD of the waste water was about 73%, as determined in the batch bioassays. During reactor operation at 16°C, the COD removal efficiencies averaged about 56%, at organic loading rates (OLR) ranging between 4·4 and 8·8 kg COD m⁻³ day⁻¹ and a hydraulic retention time (HRT) of approximately 2·4 h. At 20°C, removal efficiencies were approximately 66% and 72%, respectively, at OLRs of 8·8 and 14·6 kg COD m⁻³ day⁻¹, corresponding to HRTs of 2·4 and 1·5 h. The specific methanogenic activity with the sludge from the reactor, assessed on acetate and volatile fatty acids mixture as substrates, significantly increased (80%) in time, indicating an enrichment of methanogens and acetogens even at the low temperatures applied. These findings are of considerable practical importance because they indicate that anaerobic treatment of low strength waste waters at low temperature might become a feasible option. © 1997 SCI.     

Spray Drying of Yogurt: Optimization of Process Conditions for Improving Viability and Other Quality Attributes

Plain yogurt was subjected to spray drying to determine the optimum processing conditions that yield maximum survival ratio of lactic acid bacteria, maximum overall sensory attributes, minimum color change, and acceptable moisture content. The inlet (150–180°C) and outlet air temperatures (60–90°C) and the feed temperature (4–30°C) were the independent factors. A pilot-scale spray dryer was used to conduct a set of drying experiments where the process conditions were selected according to central composite rotatable design (CCRD). The resulting yogurt powder at each condition was also subjected to the measurement of some physical properties (water activity, titratable acidity [lactic acid, %] and pH) to determine the effects of spray-drying conditions. The morphological structure of the powder was inspected by scanning electron microscopy (SEM) analysis. Optimization by the application of the desirability function method resulted in air inlet temperature of 171°C, air outlet temperature of 60.5°C, and feed temperature of 15°C as the optimum processing condition. The mathematical optimum condition was experimentally verified.     

The effect of noncondensable gas on heat transfer in the preheater of the sewage sludge drying system

We used a shell-and-tube type preheater to investigate the effect of noncondensable gas on heat transfer. In the preheater of the drying system, heat is exchanged between steam-air mixed gas which is dryer outlet gas and sewage sludge. To evaluate the performances of the preheater, water was first used in the tube-side material instead of sewage sludge and steam-air mixed gas in the shell-side material. The test variables were as follows: mixed gas inlet temperatures range from 95 to 120 °C; inlet air content, m _air /m _steam from 55 to 83%; tube-side water flow rate from 42 to 62 kg/h. The shell-side heat transfer coefficient varied from 150 to 550W/m²K, which corresponds to the amount of noncondensable gas in the steam-air mixed gas and the overall heat transfer coefficient varied from 60 to 210W/m²K. Using sewage sludge as a tube-side material the overall heat transfer coefficient varied from 60 to 130W/m2K and the outlet temperature of sewage sludge was above 90 °C, which is high enough for reducing energy consumption in the dryer by preheating the sewage sludge.     

Spray Drying and Agglomeration of Instant Bayberry Powder

Optimum technology of spray-dried bayberry powder was studied using D-optimal experimental design. The operating conditions were varied within the following ranges: inlet air temperature 140–160°C, outlet air temperature 65–85°C, maltodextrin DE values 12 and 19, and feed concentrations of 7–17°B. The spray-dried bayberry powder was analyzed for moisture content and color. Moisture content of spray-dried powder was determined mainly by the inlet and outlet air temperatures, DE value, and the feed concentration. The inlet and outlet temperature had important effects on powder color. Finally, instant bayberry powder for beverages was produced by agglomeration of the spray-dried product.     

Integrated air stripping and biofiltration for remediation of soils contaminated by organic compounds

This paper presents the results of a laboratory scale investigation on the remediation of a soil contaminated by a mixture of organic compounds using a two‐step process consisting of stripping and biofiltration. The biofilter was packed with the soil under examination in order to use autochthonous microorganisms. To assess the effects of both temperature and superficial velocity of the air stream on process performance different sets of experimental tests were carried out at two air temperatures (50 and 80 °C), and at two superficial air velocities (41.0 and 82.0 m h^?1), corresponding to apparent air residence times in the biofilter column of 38 and 19 s respectively. The stripping rate proves to be inversely correlated with the soil–water partitioning coefficient, while no evident correlation was found with the Henry coefficient. It can therefore be concluded that soil–water partitioning is limited by mass transfer while air–water partitioning reaches equilibrium. Temperature influences both stripping rate in the stripping column and degradation capacity in the biofilter. A stripping temperature of 80 °C combined with a biofiltration temperature of 34 °C provides the best process performance. Copyright © 2007 Society of Chemical Industry