Inlet Loading Rate Research Articles

Biofiltration of Hexane Vapor: Experimental and Neural Model Analysis

AbstractBiofiltration is a commonly practiced biological technique to remove volatile compounds from waste gas streams. From an industrial view‐point, biofilter (BF) operation should be flexible to handle temperatures and inlet load (IL) variations. A compost BF was operated at different temperatures (30–45°C) and at various inlet loading rates (ILR; 8–598 g m−3 h−1) under intermittent loading conditions. Complete removal of n‐hexane was observed at 30 and 35°C at ILRs up to 330 g m−3 h−1. Besides, 20–75% of the pollutant was removed at 40°C, corresponding to the different ILs applied to the BF. Increasing the temperature to 45°C decreased the removal efficiency (RE) significantly. A feed forward neural network was used to predict the RE of BF with temperature and ILR as the input variables. The experimental data was divided into training (2/3) and test datasets (1/3). The best structure of neural network was obtained by trial and error on the basis of the least differences between predicted and experimental values, as ascertained from their coefficient of regression (R2) values. The modeling results showed that a multilayer network with the topology 2−10−1 was able to predict BF performance effectively with R2‐value of 0.995 for the test data. The results from this study showed the predicting capability of ANNs which can be considered as an alternative for conventional knowledge‐based models.

Removal of Ammonia from Waste Gases by a Biotrickling Filter

A laboratory-scale biotrickling filter was evaluated for its effectiveness in treating waste gases containing ammonia at different inlet loading rates. The inlet concentration of ammonia varied from 20～300mg/m3, and the air flow rates were 0.61m3/h, 0.85m3/h and 1.06m3/h, equivalent to empty bed residence time of 35s, 25s and 20s, respectively. The experimental results showed that the inlet ammonia can be efficiently removed in the biotrickling filter. The removal efficiency was nearly 100% when inlet ammonia loading rate was below 28.33g/m3·h, and the maximum elimination capacity for the biotrickling filter was determined to be about 33.99 g/m3·h. The results in microbial analyses had proven that the ammonia oxidizing bacteria and nitrite oxidizing bacteria were dominant in the biotrickling filter. These results show that the treatment system studied can be considered as a viable alternative for the treatment of gaseous emissions containing different concentrations of ammonia.

Performance Evaluation and Neural Modeling of Gas-Phase Styrene Removal in One- and Two-Liquid Phase Suspended-Growth Bioreactors

The removal of gas-phase styrene was studied in both one- and two-liquid phase continuous stirred tank bioreactors (CSTBs) inoculated with Sporothrix variecibatus. Experiments were carried out at different gas residence times and inlet styrene concentrations to reach inlet loading rates varying between 10 and 838 g m−3 h−1 in the bioreactors. The addition of 10% (v/v) silicone oil acted as a buffer for high styrene loads and improved the two-liquid phase CSTB performance 3.1-fold in comparison to the one-liquid phase CSTB, with maximum elimination capacities of 426 and 137 g m−3 h−1, respectively. The CSTBs performance was modeled using artificial neural networks (ANNs) with inlet concentration (g m−3) and unit flow (h−1) as the input variables. The best network topology, selected by a trial and error approach and by estimating the determination coefficient (R2) values, was found to be 2−5−1 and 2−6−1, respectively, for the one- and two-liquid phase CSTB.

Removal characteristics of mixed gas of ethyl acetate and 2-butanol by a biofilter packed with Jeju scoria

The removal characteristics of a mixed gas of ethyl acetate and 2-butanol by a biofilter packed with Jeju scoria were investigated. The experiments were conducted by changing the mixing ratio and the inlet loading rate of the mixed gas. There was no significant difference between the removal efficiency of ethyl acetate in the mixed gas and that of ethyl acetate in the single gas, while the removal efficiency of 2-butanol in the mixed gas was higher than that in the single gas. At the same loading rate, there was no significant difference between the removal capacity of ethyl acetate in the single gas and that in the mixed gas consisting of ethyl acetate at higher concentration than 2-butanol. However, the removal capacity of 2-butanol in the mixed gas was higher than that in the single gas when 2-butanol flowed through the biofilter at higher concentration than that of ethyl acetate.

Simultaneous removal of hydrogen sulfide and toluene in a bioreactor: Performance and characteristics of microbial community

We investigated the correlation between performance and the bacteria community composition by H 2S and toluene co-treatment. Operation of the bioreactor was divided into four stages, in which the inlet concentration of toluene and H 2S were gradually increased. In Stage I, toluene was the sole target compound with an average removal efficiency of 86.49%. After adding H 2S in Stage II, removal efficiency of toluene decreased immediately and recovered gradually to 85.96%. When the inlet concentration of toluene and H 2S was increased in Stage III and Stage IV, respectively, the average removal efficiency for toluene increased continuously from 86.31% to 87.24%. The elimination capacities of toluene increased with increasing inlet loading rates of toluene and H 2S. Results of the PCR-DGGE analysis showed a turnover growth and decline of the microbial populations in the bioreactor. In Stage I, the dominant toluene-degrading bacteria mainly contained Pseudomonas sp. strain PS+ and Hydrogenophaga sp. In Stage IV, however, the dominant toluene-degrading bacteria was aciduric bacteria (Clostridiumpopulen). The dominant microbial community in the bioreactor enhanced the elimination capacity of toluene, and adding H 2S changed the environment of microbial growth, thus resulted in an evolution of dominant microorganisms. Analyses of microbial community and their activities provides valuable information to efficiently enhance simultaneous removal of toluene and H 2S in the bioreactor.

The performance of SBR, SCR, and MSCR for simultaneous biodegradation of high concentrations of formaldehyde and ammonia

This paper presents experimental results for the simultaneous removal of formaldehyde (CH2O) and ammonia nitrogen using three bioreactors: a sequencing batch reactor (SBR), a sequencing continuous-inflow reactor (SCR), and a novel modified moving-bed SCR (MSCR). The performance of these bioreactors was first investigated in terms of removal of CH2O and COD. The MSCR achieved the highest removal capacity: 100% of the CH2O and 97% of the COD at an inlet loading rate of 1.25kgCH2O/m3d (1.8kg COD/m3d) over a 24-h cycle time. The SCR was the next most efficient bioreactor. The nitrogen removal performance of the SCR and the MSCR was also studied. Results indicated that the MSCR removed approximately 99.9% of the nitrogen at a loading rate of 1.25kgN/m3d in the presence of 1.25kgCH2O/m3d. This work showed the MSCR to be an efficient modification of the activated sludge process for concurrently obtaining CH2O and nitrogen removal.

A strategic approach for the design and operation of two‐phase partitioning bioscrubbers for the treatment of volatile organic compounds

A strategic approach for the design of two-phase partitioning bioscrubbers (TPPBs) has been formulated using, as a basis, a re-evaluation of extensive literature data available for the degradation of benzene by Achromobacter xylosoxidans Y234 in TPPBs with n-hexadecane as the partitioning phase. Using a previously determined maintenance coefficient for benzene, we determined that an inlet benzene loading rate of 100 mg/h requires 5,928 mg cell mass at biological steady state and 243.0 mg O(2) /h. The total oxygen-transfer rates (TOTRs) into the TPPB increased by 83.5% with 33.3% of organic phase compared with a single aqueous phase and were significantly influenced by gas flow rate, whereas agitation has a minor affect. The fraction of organic phase used was suggested to be the primary parameter with which the TOTR into the TPPB may be altered. Although the presence of an organic solvent in the TPPB remarkably increased the TOTR, the total benzene transfer rate into the TPPB remained largely insensitive due to the intrinsic low Henry's law constant (or relatively high solubility) of benzene in water. Finally, we have integrated the elements of this analysis into a set of heuristic criteria that can serve as a guideline for the design of TPPB systems for future volatile organic compound treatment applications.

Biological oxidation of hydrogen sulfide in mineral media using a biofilm airlift suspension reactor

Hydrogen sulfide (H 2S) removal in mineral media using Thiobacillus thioparus TK-1 in a biofilm airlift suspension reactor (BAS) was investigated to evaluate the relationship between biofilm formation and changes in inlet loading rates. Aqueous sodium sulfide was fed as the substrate into the continuous BAS-reactor. The reactor was operated at a constant temperature of 30 °C and a pH of 7, the optimal temperature and pH for biomass growth. The startup of the reactor was performed with basalt carrier material. Optimal treatment performance was obtained at a loading rate of 4.8 mol S 2− m −3 h −1 at a conversion efficiency as high as 100%. The main product of H 2S oxidation in the BAS-reactor was sulfate because of high oxygen concentrations in the airlift reactor. The maximum sulfide oxidation rate was 6.7 mol S 2− m −3 h −1 at a hydraulic residence time of 3.3 h in the mineral medium. The data showed that the BAS-reactor with this microorganism can be used for sulfide removal from industrial effluent.

Kinetics of bio-filtration of trichloroethylene by methanotrophs in presence of methanol

The biodegradation of TCE was studied in a laboratory scale biofilter packed with wood charcoal and inoculated with mixed culture of methanotrophs isolated from local soil. The removal efficiency was found to be higher than 90% up to an inlet load of 5.1 g/m 3 h. The maximum elimination capacity was 6.7 g/m 3 h at an inlet loading rate of 11.3 g/m 3 h. The reaction constants EC max, K s and K i calculated from the experimental results are also presented. The biodegradation process is found to be inhibited at higher TCE concentration. The carbon dioxide production rate has been found to be a linear function of elimination capacity. The DNA finger printing techniques has indicated the presence of functionally active methanotrophic community including Methylocystis sp. in the biofilter.

Removal of toluene vapour from air stream using a biofilter packed with polyurethane foam

Biodegradation of toluene vapour was investigated for 168 days in a polyurethane packed biofilter inoculated with a mixed microbial population. Biofilter consisted of five square cross-section modular units each of size 0.16 m × 0.16 m × 0.20 m and filled with the polyurethane foam cubes up to a height of 0.15 m. Inlet concentration of toluene was varied from 0.04 to 2.5 g m −3 and the volumetric flow rate of toluene loaded air from 0.06 to 0.90 m 3 h −1. Depending upon initial loading rates, removal efficiency ranging from 68.2 to 99.9% and elimination capacity ranging from 10.85 to 90.48 g h −1 m −3 were observed during steady state operations. More than 90% removal efficiency was observed up to an inlet loading rate of 76.3 g h −1 m −3. High carbon recovery (>90%) indicated effective biodegradation in the bed. Low variation of pH (7.2–8.8) and pressure drop (45.8–76.3 Pa) was observed. The stability of the biomass was evident from the fast response of the biofilter to shutdown and restartup.

Two‐stage gas‐phase bioreactor for the combined removal of hydrogen sulphide, methanol and α‐pinene

Biological treatment systems have emerged as cost‐effective and eco‐friendly techniques for treating waste gases from process industries at moderately high gas flow rates and low pollutant concentrations. In this study, we have assessed the performance of a two‐stage bioreactor, namely a biotrickling filter packed with pall rings (BTF, 1st stage) and a perlite + pall ring mixed biofilter (BF, 2nd stage) operated in series, for handling a complex mixture of hydrogen sulphide (H2S), methanol (CH3OH) and α‐pinene (C10H16). It has been reported that the presence of H2S can reduce the biofiltration efficiency of volatile organic compounds (VOCs) when both are present in the gas mixture. Hydrogen sulphide and methanol were removed in the first stage BTF, previously inoculated with H2S‐adapted populations and a culture containing Candida boidinii, an acid‐tolerant yeast, whereas, in the second stage, α‐pinene was removed predominantly by the fungus Ophiostoma stenoceras. Experiments were conducted in five different phases, corresponding to inlet loading rates varying between 2.1 and 93.5 g m−3 h−1 for H2S, 55.3 and 1260.2 g m−3 h−1 for methanol, and 2.8 and 161.1 g m−3 h−1 for α‐pinene. Empty bed residence times were varied between 83.4 and 10 s in the first stage and 146.4 and 17.6 s in the second stage. The BTF, working at a pH as low as 2.7 as a result of H2S degradation, removed most of the H2S and methanol but only very little α‐pinene. On the other hand, the BF, at a pH around 6.0, removed the rest of the H2S, the non‐degraded methanol and most of the α‐pinene vapours. Attempts were originally made to remove the three pollutants in a single acidophilic bioreactor, but the Ophiostoma strain was hardly active at pH <4. The maximum elimination capacities (ECs) reached by the two‐stage bioreactor for individual pollutants were 894.4 g m−3 h−1 for methanol, 45.1 g m−3 h−1 for H2S and 138.1 g m−3 h–1 for α‐pinene. The results from this study showed the potential effectiveness of a two‐stage bioreactor for treating H2S together with two hydrophilic and hydrophobic VOCs that are typically emitted from wood industries.

Steady- and transient-state effects during the biological oxidation of gas-phase benzene in a continuously operated biofilter

Biofiltration is an aerobic degradation process in which a well-humidified contaminated air stream is passed through a porous packed medium that supports a thriving population of microbes. The removal of benzene vapor was investigated in a laboratory-scale biofilter packed with compost, inoculated with a mixed microbial consortium. This biofilter was operated continuously in six different phases for a period of 8 months at different flow rates, 0.024–0.144 m3 h−1 with benzene concentrations ranging up to 1.7 g m−3. Under steady-state conditions, the removal efficiencies (REs) in the biofilter was consistently greater than 78% when benzene loading was less than 20 g m−3 h−1. The maximum elimination capacity (EC) achieved in this study is 64 g m−3 h−1 at an inlet loading rate of 128 g m−3 h−1. The response of the biofilter to shutdown, restart operations and fluctuations in inlet concentration, and flow rate was determined by subjecting the biofilter to inlet loads of up to 120 g m−3 h−1. The biofilter responded effectively to these loading conditions and was found to recover rapidly. The results from this study suggest that a compost biofilter is effective in treating benzene vapor under steady- and transient-conditions.

Performance of a biofilter for the removal of high concentrations of styrene under steady and non-steady state conditions

The performance of a laboratory scale perlite biofilter inoculated with a mixed culture was evaluated for gas phase styrene removal under various operating conditions. Experiments were carried out by subjecting the biofilter to different flow rates (0.15–0.9 m 3 h −1) and concentrations (0.03–17.3 g m −3), corresponding to inlet loading rates varying from as low as 3 g m −3 h −1 to as high as 1390 g m −3 h −1. A maximum elimination capacity (EC) of 382 g m −3 h −1 was achieved at an inlet loading rate of 464 g m −3 h −1 with a removal efficiency of 82%. The high elimination capacity reached with this system could have been due to the dominant presence of filamentous fungi among others. The impact of relative humidity (RH) (30%, 60% and >92%) on the biofilter performance was evaluated at two constant loading rates, viz., 80 and 260 g m −3 h −1, showing that inhibitory effects were only significant when combining the highest loads with the lowest relative humidities. Biomass distribution, moisture content and concentration profiles along the bed height were significantly dependent on the relative humidity of the inlet air and on the loading rate. The dynamic behaviour of the biofilter through vigorous short and long-term shock loads was tested at different process conditions. The biofilter was found to respond apace to rapid changes in loading conditions. The stability of the biomass within the reactor was apparent from the fast response of the biofilter to recuperate and handle intermittent shutdown and restart operations, either with or without nutrient addition.

Experimental and neural model analysis of styrene removal from polluted air in a biofilter

AbstractBACKGROUND: Biofilters are efficient systems for treating malodorous emissions. The mechanism involved during pollutant transfer and subsequent biotransformation within a biofilm is a complex process. The use of artificial neural networks to model the performance of biofilters using easily measurable state variables appears to be an effective alternative to conventional phenomenological modelling.RESULTS: An artificial neural network model was used to predict the extent of styrene removal in a perlite‐biofilter inoculated with a mixed microbial culture. After a 43 day biofilter acclimation period, styrene removal experiments were carried out by subjecting the bioreactor to different flow rates (0.15–0.9 m3 h−1) and concentrations (0.5–17.2 g m−3), that correspond to inlet loading rates up to 1390 g m−3 h−1. During the different phases of continuous biofilter operation, greater than 92% styrene removal was achievable for loading rates up to 250 g m−3 h−1. A back propagation neural network algorithm was applied to model and predict the removal efficiency (%) of this process using inlet concentration (g m−3) and unit flow (h−1) as input variables. The data points were divided into training (115 × 3) and testing set (42 × 3). The most reliable condition for the network was selected by a trial and error approach and by estimating the determination coefficient (R2) value (0.98) achieved during prediction of the testing set.CONCLUSION: The results showed that a simple neural network based model with a topology of 2–4–1 was able to efficiently predict the styrene removal performance in the biofilter. Through sensitivity analysis, the most influential input parameter affecting styrene removal was ascertained to be the flow rate. Copyright © 2009 Society of Chemical Industry

Immobilized Cell Biofilter: Results of Performance and Neural Modeling Strategies for NH3 Vapor Removal from Waste Gases

Artificial neural networks (ANNs) are powerful data-driven modeling tools which have the potential to approximate and interpret complex input/output relationships based on given sets of a data matrix. In this paper, a predictive computerized approach is proposed to predict the performance of an immobilized-cell biofilter treating NH3 vapors in terms of its removal efficiency (RE) and elimination capacity (EC). The input parameters to the ANN model were inlet concentration, loading rate, flow rate and pressure drop, and the output parameters were RE and EC. The data set was divided into two parts: a training matrix consisting of 51 data points, and a test matrix with 16 data points representing each parameter considered in this study. Earlier experiments of continuous biofilter operation showed removal efficiencies from 60 to 100% at inlet loading rates (ILRs) varying between 0.5 to 5.5 g NH3/m3/h. Internal network parameters of the ANN model during simulation were selected using the 2k factorial design, and the best network topology for the model was thus estimated. Predictions were evaluated based on their d coefficient values (R2). The results showed that a multilayer network (4-4-2) with a back propagation algorithm was able to predict biofilter performance effectively with R2 values of 0.9825 and 0.9982. The proposed ANN model for biofilter operation could be used as a potential alternative for knowledge-based models through proper training and testing of variables.

An intelligent neural network model for evaluating performance of immobilized cell biofilter treating hydrogen sulphide vapors

Biofiltration has shown to be a promising technique for handling malodours arising from process industries. The present investigation pertains to the removal of hydrogen sulphide in a lab scale biofilter packed with biomedia, encapsulated by sodium alginate and poly vinyl alcohol. The experimental data obtained under both steady state and shock loaded conditions were modelled using the basic principles of artificial neural networks. Artificial neural networks are powerful data driven modelling tools which has the potential to approximate and interpret complex input/ output relationships based on the given sets of data matrix. A predictive computerised approach has been proposed to predict the performance parameters namely, removal efficiency and elimination capacity using inlet concentration, loading rate, flow rate and pressure drop as the input parameters to the artificial neural network model. Earlier, experiments from continuous operation in the biofilter showed removal efficiencies from 50 to 100 % at inlet loading rates varying up to 13 g H 2 S/m 3 h. The internal network parameter of the artificial neural network model during simulation was selected using the 2 k factorial design and the best network topology for the model was thus estimated. The results showed that a multilayer network (4-4-2) with a back propagation algorithm was able to predict biofilter performance effectively with R 2 values of 0.9157 and 0.9965 for removal efficiency and elimination capacity in the test data. The proposed artificial neural network model for biofilter operation could be used as a potential alternative for knowledge based models through proper training and testing of the state variables.

NOxRemoval from Simulated Flue Gas by Chemical Absorption−Biological Reduction Integrated Approach in a Biofilter

A chemical absorption-biological reduction integrated approach, which combines the advantages of both the chemical and biological technologies, is employed to achieve the removal of nitrogen monoxide (NO) from the simulated flue gas. The biological reduction of NO to nitrogen gas (N2) and regeneration of the absorbent Fe(II)EDTA (EDTA:ethylenediaminetetraacetate) take place under thermophilic conditions (50 +/- 0.5 degrees C). The performance of a laboratory-scale biofilter was investigated for treating NO(x) gas in this study. Shock loading studies were performed to ascertain the response of the biofilter to fluctuations of inlet loading rates (0.48 approximately 28.68 g NO m(-3) h(-1)). A maximum elimination capacity (18.78 g NO m(-3) h(-1)) was achieved at a loading rate of 28.68 g NO m(-3) h(-1) and maintained 5 h operation at the steady state. Additionally, the effect of certain gaseous compounds (e.g., O2 and SO2) on the NO removal was also investigated. A mathematical model was developed to describe the system performance. The model has been able to predict experimental results for different inlet NO concentrations. In summary, both theoretical prediction and experimental investigation confirm that biofilter can achieve high removal rate for NO in high inlet concentrations under both steady and transient states.

Improvement of trickling biofilter purification performance on treating chlorobenzene in waste gases using surfactant

A laboratory-scale trickling biofilter column, filled with Raschig rings and inoculated with Pseudomonas putida (ATCC 1785) was used to purify chlorobenzene contained waste gases. Sodium dodecyl sulfonate (SDS) was used to enhance the performance of trickling biofilter. Purification performance of the trickling biofilter was examined for chlorobenzene inlet concentration of 1.20∼5.04 g/m3 at different EBRTs between 76∼153 s. Without SDS addition, with simultaneous increase in chlorobenzene inlet loading rate and gas flow rate, 100% removal efficiency was achieved at EBRT of 109 s and inlet loadings below 5120 mg/m3. Addition of SDS to nutrient solution led to improvement of trickling biofilter purification performance. By introducing 25 mg/L SDS, the removal efficiency was increased by 21% and elimination capacity up to 234 g/(m3·h) was achieved at chlorobenzene inlet loading of 241 g/(m3·h). Although SDS concentration experienced a low rate reduction after continuous nutrient solution recirculation, this result has little influence on trickling biofilter’s removal efficiency in monitoring period.

Performance of a Membrane Diffuser Bioreactor for the Removal of Gaseous Toluene

Hollow fiber membrane bioreactors have emerged as a promising technology for use in the treatment of volatile organic compounds (VOCs), due to their high surface area for VOC mass transfer and significant biodegradation capacity. In this study, a bioreactor operated in a diffuser mode using a submerged, hollow fiber membrane module (referred to as membrane diffuser bioreactor, MDBR) was employed in order to investigate its performance for the treatment of gaseous toluene. MDBR experiments were performed at different inlet toluene concentrations of 54, 160, and 750 ppmv, respectively. Overall, toluene removal efficiencies were maintained in the range of 60–70% at each operating condition. The biomass density in the liquid phase was changed according to the inlet loading rate, but the toluene concentrations in the liquid phase were always extremely low, indicating that the overall reaction was controlled by the mass transfer rate of toluene, rather than by the biodegradation rate. Additionally, elimination ...

Operational parameters in biofiltration of ammonia-contaminated air streams using compost–pieces of hard plastics filter media

Abstract This study evaluates the use of a mixture of compost, sludge and pieces of hard plastics as a biofilter medium to remove ammonia from a waste gas stream through a bench-scale biofilter column. This study investigated the effects of operational parameters such as inlet concentration, loading rate, retention time, pressure drop and variations of pH and alkalinity in the packing material on the performance of the biofilter. After a start-up period with an average inlet concentration of ammonia of about 51 ppm v corresponding to a loading rate of 2.15 g NH 3 /m 3 h and an empty bed residence time of 60 s, the biofilter reached a removal efficiency of more than 97.9% by day 10. The maximum elimination capacity of 9.85 g NH 3 /m 3 h was achieved at a loading rate of 9.86 g NH 3 /m 3 h, corresponding to an inlet concentration of about 236 ppm v , with the outlet concentration of NH 3 increasing for higher inlet concentrations. The pH and alkalinity of the bed medium decreased due to nitrate formation but there was no need to control them synthetically. The concentration of ammonium and nitrate in the bed medium decreased and increased, respectively. Under steady-state conditions, the number of nitrifying bacteria increased from an initial 5.6 × 10 4 cell/g wet material in the bed medium to about 2.8 × 10 8 cell/g wet material. Biological removal and nitrification were the dominant processes in ammonia removal. The maximum pressure drop during the experiment was 12 mm H 2 O for each meter of column. The minimum retention time that the system could attain at an average loading rate of ≤9.45 g NH 3 /m 3 h was 30 s.