Efficient degradation of chlorobenzene in a non-thermal plasma catalytic reactor supported on CeO2/HZSM-5 catalysts.

Chlorobenzene removal was investigated in a non-thermal plasma reactor using CeO2/HZSM-5 catalysts. The performance of catalysts was evaluated in terms of removal and energy efficiency. The decomposition products of chlorobenzene were analyzed. The results show that CeO2/HZSM-5 exhibited a good catalytic activity, which resulted in enhancements of chlorobenzene removal, energy efficiency, and the formation of lower amounts of by-products. With regards to CO2 selectivity, the presence of catalysts favors the oxidation of by-products, leading to a higher CO2 selectivity. With respect to ozone, which is considered as an unavoidable by-product in air plasma reactors, a noticeable decrease in its concentration was observed in the presence of catalysts. Furthermore, the stability of the catalyst was investigated by analyzing the evolution of conversion in time. The experiment results indicated that CeO2/HZSM-5 catalysts have excellent stability: chlorobenzene conversion only decreased from 78% to 60% after 75hr, which means that the CeO2/HZSM-5 suffered a slight deactivation. Some organic compounds and chlorinated intermediates were adsorbed or deposited on the catalysts surface as shown by the results of Fourier Transform Infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the catalyst before and after the reaction, revealing the cause of catalyst deactivation.

[Analysis of characteristics and products of chlorobenzene degradation with dielectric barrier discharge].

For non-biodegradable volatile organic compounds (VOCs) with low water solubility, the tradition biological method can not achieve a satisfactory removal efficiency, so development of high efficiency pre-treatment technology is a hot issue of research. In this experiment, using poor biodegradable chlorobenzene as the target pollutant and dielectric barrier discharge (DBD) non-thermal plasma as the pretreatment technology for biotrickling filter (BTF) , the effect of DBD on the degradation of chlorobenzene was studied by adjusting the technical parameters of DBD. The effects of the inlet concentration, residence time, humidity and peak voltage on decomposition efficiency were investigated and the decomposition products of chlorobenzene were analyzed. Experimental results showed that DBD could effectively remove waste gaseous chlorobenzene, the removal rate of chlorobenzene increased with the increasing peak voltage. When the peak voltage was ≥ 12kV, less effect of residence time on the degradation of chlorobenzene was found. The optimal humidity range of degradation chlorobenzene was 65% - 75%. Through the analysis of degradation products, the species and concentrations of degradation products increased with the increase of discharge voltage. The products were mainly consisted of organic acids and chlorinated hydrocarbons. The water solubility of degradation products was preferable. Furthermore, with the increase of discharge voltage, the biodegradability of degradation products became higher and higher and the biological toxicity was reduced. It had a promoting effect on the degradation of chlorobenzene when the voltage reached 20 kV. Meanwhile, the O3 concentration increased with the increasing discharge voltage and also enhanced with the rising humidity under the same voltage.

Conversion characteristics and production evaluation of styrene/o-xylene mixtures removed by DBD pretreatment.

The combination of chemical oxidation methods with biotechnology to removal recalcitrant VOCs is a promising technology. In this paper, the aim was to identify the role of key process parameters and biodegradability of the degradation products using a dielectric barrier discharge (DBD) reactor, which provided the fundamental data to evaluate the possibilities of the combined system. Effects of various technologic parameters like initial concentration of mixtures, residence time and relative humidity on the decomposition and the degradation products were examined and discussed. It was found that the removal efficiency of mixed VOCs decreased with increasing initial concentration. The removal efficiency reached the maximum value as relative humidity was approximately 40%-60%. Increasing the residence time resulted in increasing the removal efficiency and the order of destruction efficiency of VOCs followed the order styrene > o-xylene. Compared with the single compounds, the removal efficiency of styrene and o-xylene in the mixtures of VOCs decreased significantly and o-xylene decreased more rapidly. The degradation products were analyzed by gas chromatography and gas chromatography-mass spectrometry, and the main compounds detected were O3, COx and benzene ring derivatives. The biodegradability of mixed VOCs was improved and the products had positive effect on biomass during plasma application, and furthermore typical results indicated that the biodegradability and biotoxicity of gaseous pollutant were quite depending on the specific input energy (SIE).

[Isolation and degradation characteristics of dichloromethane-degradation bacterial strain by Methylobacterium rhodesianum H13].

A dichloromethane-degrading bacterium Methylobacterium rhodesianum H13 which utilized the DCM as the sole carbon and energy source was isolated. According to the research, M. rhodesianum H13 could completely degrade 5 mmol x L(-1) DCM in 23 h with the initial cell concentration of 0.82 mg x L(-1), pH 7.0, 30 degrees C, and the cell yield rate was about 0.136 g x g(-1) DCM. With the degradation of DCM, Cl- concentration gradually raised (the release of Cl- concentration was about 2 times higher as the DCM), pH value dropped to 6.75, and the solution was weakly acidic. Temperature, pH, DCM concentration, Cl- concentration and other factors were investigated through the shake flask experiments, and the optimal conditions for DCM degradation were: temperature 30 degrees C, pH 7.0. The study also indicated that 5 mmol x L(-1) of DCM was the optimum concentration for M. rhodesianum H13 and high levels of DCM could inhibit the degradation. The research has an important application value for the DCM environmental pollution.

[Removal of toluene from waste gas by honeycomb adsorption rotor with modified 13X molecular sieves].

The removal of toluene from waste gas by Honeycomb Adsorption Rotor with modified 13X molecular sieves was systematically investigated. The effects of the rotor operating parameters and the feed gas parameters on the adsorption efficiency were clarified. The experimental results indicated that the honeycomb adsorption rotor had a good humidity resistance. The removal efficiency of honeycomb adsorption rotor achieved the maximal value with optimal rotor speed and optimal generation air temperature. Moreover, for an appropriate flow rate ratio the removal efficiency and energy consumption should be taken into account. When the recommended operating parameters were regeneration air temperature of 180 degrees C, rotor speed of 2.8-5 r x h(-1), flow rate ratio of 8-12, the removal efficiency kept over 90% for the toluene gas with concentration of 100 mg x m(-3) and inlet velocity of 2 m x s(-1). The research provided design experience and operating parameters for industrial application of honeycomb adsorption rotor. It showed that lower empty bed velocity, faster rotor speed and higher temperature were necessary to purify organic waste gases of higher concentrations.

[Treatment of organic waste gas by adsorption rotor].

The adsorption rotor is applicable to treating organic waste gases with low concentration and high air volume. The performance of adsorption rotor for purifying organic waste gases was investigated in this paper. Toluene was selected as the simulative gaseous pollutant and the adsorption rotor was packed with honeycomb modified 13X molecular sieves (M-13X). Experimental results of the fixed adsorption and the rotor adsorption were analyzed and compared. The results indicated that some information on the fixed adsorption was useful for the rotor adsorption. Integrating the characteristics of the adsorbents, waste gases and the structures of the rotor adsorption, the formulas on optimal rotor speed and cycle removal efficiency of the adsorption rotor were deduced, based on the mass and heat balances of the adsorbing process. The numerical results were in good agreement with the experimental data, which meant that the formulas on optimal rotor speed and cycle removal efficiency could be effectively applied in design and operation of the adsorption rotor.

Degradation of paracetamol by pure bacterial cultures and their microbial consortium.

Three bacterial strains utilizing paracetamol as the sole carbon, nitrogen, and energy source were isolated from a paracetamol-degrading aerobic aggregate, and assigned to species of the genera Stenotrophomonas and Pseudomonas. The Stenotrophomonas species have not included any known paracetamol degraders until now. In batch cultures, the organisms f1, f2, and fg-2 could perform complete degradation of paracetamol at concentrations of 400, 2,500, and 2,000 mg/L or below, respectively. A combination of three microbial strains resulted in significantly improved degradation and mineralization of paracetamol. The co-culture was able to use paracetamol up to concentrations of 4,000 mg/L, and mineralized 87.1 % of the added paracetamol at the initial of 2,000 mg/L. Two key metabolites of the biodegradation pathway of paracetamol, 4-aminophenol, and hydroquinone were detected. Paracetamol was degraded predominantly via 4-aminophenol to hydroquinone with subsequent ring fission, suggesting new pathways for paracetamol-degrading bacteria. The degradation of paracetamol could thus be performed by the single isolates, but is stimulated by a synergistic interaction of the three-member consortium, suggesting a possible complementary interaction among the various isolates. The exact roles of each of the strains in the consortium need to be further elucidated.

Removal characteristics and kinetic analysis of an aerobic vapor-phase bioreactor for hydrophobic alpha-pinene.

Biofiltration is considered an effective method to control volatile organic compounds (VOCs) pollution. This study was conducted to evaluate the potential use of a bacterial biofilter packed with wood chips and peat for the removal of hydrophobic alpha-pinene. When inoculated with two pure degraders and adapted activated sludge, a removal efficiency (RE) of more than 95% was achieved after a startup period of 11 days. The maximum elimination capacity (EC) of 50 g/(m3 x hr) with RE of 94% was obtained at empty bed retention time (EBRT) of 102 sec. When higher alpha-pinene concentrations and shorter EBRTs were applied, the REs and ECs decreased significantly due to mass-transfer and biological reaction limitations. As deduced from the experimental results, approximately 74% of alpha-pinene were completely mineralized by the consortiums and the biomass yield was 0.60 g biomass/g alpha-pinene. Sequence analysis of the selected bands excised from denaturing gradient gel electrophoresis revealed that the inoculated pure cultures could be present during the whole operation, and others were closely related to bacteria being able to degrade hydrocarbons. The kinetic results demonstrated that the whole biofiltration for alpha-pinene was diffusion-limit controlled owing to its hydrophobic characteristics. These findings indicated that this bacterial biofiltration is a promising technology for the remediation of hydrophobic industrial waste gases containing alpha-pinene.

Substrate interactions during the biodegradation of BTEX and THF mixtures by Pseudomonas oleovorans DT4.

The efficient tetrahydrofuran (THF)-degrading bacterium, Pseudomonas oleovorans DT4 was used to investigate the substrate interactions during the aerobic biotransformation of THF and BTEX mixtures. Benzene and toluene could be utilized as growth substrates by DT4, whereas cometabolism of m-xylene, p-xylene and ethylbenzene occurred with THF. In binary mixtures, THF degradation was delayed by xylene, ethylbenzene, toluene and benzene in descending order of inhibitory effects. Conversely, benzene (or toluene) degradation was greatly enhanced by THF leading to a higher degradation rate of 39.68 mg/(h g dry weight) and a shorter complete degradation time about 21 h, possibly because THF acted as an "energy generator". Additionally, the induction experiments suggested that BTEX and THF degradation was initiated by independent and inducible enzymes. The transient intermediate hydroquinone was detected in benzene biodegradation with THF while catechol in the process without THF, suggesting that P. oleovorans DT4 possessed two distinguished benzene pathways.

[BTF performance treating a chlorobenzene-contaminated gas stream].

In this study, biotrickling filter (BTF) inoculated with acclimated sludge was established to treat waste gas containing chlorobenzene. The BTF performance, average well color development (AWCD) values and microbial community were examined in steady state. Results revealed BTF achieved removal efficiency more than 80% of chlorobenzene under the conditions of < 0.6 g x m(-3) inlet concentration and > 45 s EBRT. Therefore, BTF have an advantage in treating low-concentration waste gas containing chlorobenzene (< or = 0.6 g x m(-3)). The overall chlorobenzene elimination capacity reached a maximum of 70 g x (m3 x h)(-1) at an inlet load of 80 g x (m3 x h)(-1). The mass ratio of carbon dioxide produced to the BTo-X removed was approximately 1.92, which confirms complete degradation of chlorobenzene, given that some of the organic carbon consumed is also used for the microbial growth. The degradation of chlorobenzene in the BTF followed Michaelis-Menten kinetic model, the maximum specific degradation rate (r(max)) was 35.6 g x (m3 x h)(-1). The AWCD values indicated that the microorganisms in the BTF showed high the microbial metabolic activity. The PCR-DGGE fingerprinting analysis on biofilm samples in the BTF indicated that the microbial community had a relative stability and complexity during the steady-state phase. The stability and complexity of microbial community could contribute to the degradation and mineralization of chlorobenzene in BTF.

[Isolation, identification and biodegradation characteristics of A new bacterial strain degrading BTEX].

A bacterial strain, able to efficiently degrade benzene, toluene, ethyl benzene, and o-xylene ( BTEX) compounds, was isolated by acclimating and enriching the activated sludge from the aeration tank in refinery wastewater treatment plant using BTEX as the sole carbon source. Based on the morphological characteristics, physiological and biochemical characteristics, sequence analysis of 16S rDNA,and Biolog identification system,the isolate was identified as Mycobacterium cosmeticum which was a newly discovered species able to degrade BTEX. The optimal conditions for the growth of the strain were at 30 degrees C and pH 7.0. The order of BTEX degradation by this isolate is benzene,toluene, ethyl benzene,and o-xylene. The specific oxygen utilization rates (SOUR) of the strain degrading benzene,toluene, ethyl benzene, and o-xylene were 165.3, 170.5, 49.3 and 57.4 mg x (min x mg)(-1), respectively. The degrading process of the strain followed the Haldane kinetic model. The maximum specific degradation rate degrading benzene, toluene, ethyl benzene,and o-xylene were 0.518, 0.491, 0.443 and 0.422 h(-1), respectively. Accordingly,the maximum specific growth rate 0.352, 0.278, 0.172 and 0.136 h(-1), respectively.