Degradation of chlorobenzene by strain Ralstonia pickettii L2 isolated from a biotrickling filter treating a chlorobenzene-contaminated gas stream.

A Ralstonia pickettii species able to degrade chlorobenzene (CB) as the sole source of carbon and energy was isolated from a biotrickling filter used for the removal of CB from waste gases. This organism, strain L2, could degrade CB as high as 220 mg/L completely. Following CB consumption, stoichiometric amounts of chloride were released, and CO2 production rate up to 80.2% proved that the loss of CB was mainly via mineralization and incorporation into cell material. The Haldane modification of the Monod equation adequately described the relationship between the specific growth rate and substrate concentration. The maximum specific growth rate and yield coefficient were 0.26 h⁻¹ and 0.26 mg of biomass produced/mg of CB consumed, respectively. The pathways for CB degradation were proposed by the identification of metabolites and assay of ring cleavage enzymes in cell extracts. CB was degraded predominantly via 2-chlorophenol to 3-chlorocatechol and also partially via phenol to catechol with subsequent ortho ring cleavage, suggesting partially new pathways for CB-utilizing bacteria.

[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.

[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.

[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.

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.