Mass transfer and benzene removal from air using latex rubber tubing and a hollow-fiber membrane module

A dense-phase latex rubber tube and a polyporous propylene hollow-fiber membrane module (HFMM) were investigated for control of benzene-contaminated gas streams. The abiotic mass flux observed through the latex tube was 3.9–13 mg/(min·m²) for 150 ppm of benzene at various gas and liquid flow rates, while a 100-fold lower mass flux was observed in the HFMM. After seeding with an aromatic-degrading culture enriched from activated sludge, the observed removal was 80% of 150 ppm, corresponding toa mass flux of 45 mg/(min·m²). The observed mass flux through the HFMM during biofiltration also rose, to 0.4 mg/(min·m²). Because the HFMM had a 50-fold higher surface area than the latex tube, the observed ben zene removal was 99.8%. Compared to conventional biofilters, the two reactors had modest elimination capacities, 2.5–18 g/(m³·h) in the latex tube membrane bioreactor and 4.8–58 g/(m³·h) in the HFMM. Although the HFMM had a higher elimination capacity, the gas-phase pressure drop was much greater.     

Application of ultra-performance liquid chromatography-tandem mass spectrometry for the determination of steroid oestrogens in wastewaters

An ultra-performance liquid chromatography method using a triple quadrupole mass spectrometer was developed and validated for the determination of steroid oestrogens in wastewater matrices. To date, analytical methods established in the literature for 17α-ethinylestradiol have been unable to achieve the proposed predicted no effect concentration of 0.1?ng?l^?1. The extensive sample pretreatment and analytical methodology proposed herein enable 17α-ethinylestradiol to be determined at very low background concentrations with a theoretical method detection limit of 0.06?ng?l^?1 which has been applied in real environmental matrices. During the validation process, a trickling filter wastewater treatment works was monitored to demonstrate the method's application. Oestrogen removal across the filters demonstrated good removals of natural free oestrogens (≥62.0%) with lower removals of the synthetic oestrogen 17α-ethinylestradiol (29.2%) from wastewaters at 10°C. The method's application illustrates its capability of detecting oestrogen concentrations in real wastewater samples comprising complex organics of comparatively high concentration. Furthermore, a complete process mass balance for 17α-ethinylestradiol is now attainable which has previously posed a challenge owing to the low environmental concentrations typically exhibited, but more significantly as a result of the lower sensitivity inherent in previously reported analytical methods.     

Development of a membrane-based vapor-phase bioreactor

A vapor-phase bioreactor has been developed utilizing porous metal membranes in a cylindrical design employing radial flow as opposed to traditional axial flow for the vapor stream. The system was evaluated for the biodegradation ofp-xylene (p-xylene) from a water-saturated air stream byPseudomonas putida ATCC 23973 immobilized onto sand. The biocatalyst was placed in the annular space between two cylindrical, porous stainless-steel membranes. Details of the reactor system are presented along with biological data verifying system performance. The feed flow rate andp-xylene concentration were varied between 60 and 130 cm³/min and 15–150 ppm, respectively. Continuous reactor operation was maintained for 80–200 h with removal efficiencies (based onp-xylene disappearance) between 80 and 95%. The effluent concentration histories were compared to determine the operating range of the bioreactor.     

Removal of chemical oxygen demand,nitrogen, and heavy metals using a sequenced anaerobic-aerobic treatment of landfill leachates at 10-30 degrees C

As a first step of treatment of landfill leachates (total chemical oxygen demand [COD]: 1.43–3.81 g/L; total nitrogen: 90–162 mg/L), performance of laboratory upflow anaerobic sludge bed reactors was investigated under mesophilic (30°C), submesophilic (20°C), and psychrophilic (10°C) conditions. Under hydraulic retention times (HRTs) of about 0.3 d, when the average organic loading rates (OLRs) were about 5 g of COD/(L·d), the total COD removal accounted for 81% (on average) with the effluent concentrations close to the anaerobic biodegradability limit (0.25 g of COD/L) for mesophilic and submesophilic regimes. The psychrophilic treatment conducted under an average HRT of 0.34 d and an average OLR of 4.22 g of ducted under an average HRT of 0.34 d and an average OLR of 4.22 g of COD/(L·d) showed a total COD removal of 47%, giving effluents (0.75 g of COD/L) more suitable for subsequent biologic nitrogen removal. All three anaerobic regimes used for leachate treatment were quite efficient for elimination of heavy metals (Fe, Zn, Cu, Pb, Cd) by concomitant precipitation in the form of insoluble sulfides inside the sludge bed. The application of aerobic/anoxic biofilter as a sole polishing step for psychrophilic anaerobic effluents was acceptable for elimination of biodegradable COD and nitrogen approaching the current standards for direct discharge of treated waste-water.     

有机废气处理生物膜滴滤塔操作方式研究

通过对生物膜滴滤塔降解VOC数学模型进行的因次分析,分析了操作方式对生物膜滴滤塔降解性能的影响,并通过实验研究获得了操作方式对滴滤塔降解低浓度甲苯废气的净化性能、填料床内温度分布以及气体进出口温差的影响规律。实验结果表明:相比顺流操作而言,逆流操作时系统的净化效率高,气体进出口温差大;操作方式的不同直接导致了塔内温度分布的改变,在顺流操作时塔上部温升迅速,底部温升平缓;而逆流操作时塔下部温升迅速,顶部温升较小。     

Significance of fluid regime and wetted area in biofilm reactors

Mass transfer within microbial films was described using Monod-type biological kinetics in terms of properties of filter media and feed solution. The performance characteristics of a trickling filter were thus modeled. The model enables one to consider the effect of inlet substrate concentration and flow rate upon the removal efficiency. For this purpose a second-order partial differential equation describing the dispersion phenomena inside the liquid layer was solved under special boundary conditions and used to determine substrate flux into the biofilm. A uniform biofilm thickness was considered. The model is based on computer techniques and the numerical evaluation of the normalized biofilm mathematical model. A design procedure was also given to calculate biological filters. The numerical model was also applied to experimental data to demonstrate its validity.     

A study on performance characteristics of granular-media trickling filters

Mass transfer within microbial films is described using Monod type biological kinetics in terms of the properties of packing material and the feed solution. For this purpose computer techniques have been first developed for the numerical evaluation of the normalized biofilm mathematical model. A second-order partial differential equation describing the mechanism of dispersion phenomena inside the liquid layer is then solved to determine the mass transfer coefficient. The application of the theory to experimental data reported in literature has also been demonstrated using the values of mass transfer coefficients and the computer programs developed.     

Biofiltration of 1,1,1-trichloroethane by a trickle-bed air biofilter

The performance of a trickle-bed air biofilter (TBAB) in the removal of 1,1,1-trichloroethane (TCLE) was evaluated in concentrations varying from 0.025 to 0.049 g/m³ and at empty-bed residence time (EBRT) varying from 20 to 90 s. Nearly complete TCLE removal could be achieved for influent carbon loading between 0.98 and 5.88 g/m³ h. The TBAB appeared efficient for controlling TCLE emission under low-carbon-loading conditions. Carbon recoveries higher than 95% were achieved, demonstrating the accuracy of results. The carbon mass rate of the liquid effluent was approximately two orders of magnitude less than that of the effluent CO₂, indicating that dissolved TCLE and its derivatives in leachate were present in negligible amounts in the TBAB.     

Colmatage des réacteurs gaz–liquide à lit fixePlugging in two-phase flow packed beds

A 1-D transient two-fluid deep-bed filtration model was formulated for the capture of colloidal fines in porous media experiencing gas–liquid trickling and dispersed bubble flow regimes. The deposit prediction resulted from solving the coupled volume-average fines' advection–dispersion, Navier–Stokes, volume and mass conservation equations for the three phases. To make the system solvable, it was augmented by auxiliary closures expressing the coupling between fluids and porous medium via the drag interfacial forces, the filter coefficient in the so-called mono- and multi-layer modes, and the growth of the specific surface area of the filter bed for liquid-solid drag. To cite this article: I. Iliuta, F. Larachi, C. R. Mecanique 330 (2002) 563–568.     

Effect of temperature on biofiltration of nitric oxide

Applied Biochemistry and Biotechnology -