Mark W. Fitch

Membrane process for biological treatment of contaminated gas streams.

A hollow fiber membrane bioreactor was investigated for control of air emissions of biodegradable volatile organic compounds (VOCs). In the membrane bioreactor, gases containing VOCs pass through the lumen of microporous hydrophobic hollow fiber membranes. Soluble compounds diffuse through the membrane pores and partition into a VOC degrading biofilm. The hollow fiber membranes serve as a support for the microbial population and provide a large surface area for VOC and oxygen mass transfer. Experiments were performed to investigate the effects of toluene loading rate, gas residence time, and liquid phase turbulence on toluene removal in a laboratory-scale membrane bioreactor. Initial acclimation of the microbial culture to toluene occurred over a period of nine days, after which a 70% removal efficiency was achieved at an inlet toluene concentration of 200 ppm and a gas residence time of 1.8 s (elimination capacity of 20 g m-3 min-1). At higher toluene loading rates, a maximum elimination capacity of 42 g m-3 min-1 was observed. In the absence of a biofilm (abiotic operation), mass transfer rates were found to increase with increasing liquid recirculation rates. Abiotic mass transfer coefficients could be estimated using a correlation of dimensionless parameters developed for heat transfer. Liquid phase recirculation rate had no effect on toluene removal when the biofilm was present, however. Three models of the reactor were created: a numeric model, a first-order flat sheet model, and a zero-order flat sheet model. Only the numeric model fit the data well, although removal predicted as a function of gas residence time disagreed slightly with that observed. A modification in the model to account for membrane phase resistance resulted in an underprediction of removal. Sensitivity analysis of the numeric model indicated that removal was a strong function of the liquid phase biomass density and biofilm diffusion coefficient, with diffusion rates below 10(-9) m2 s-1 resulting in decreased removal rates.

1-Butanol removal from a contaminated airstream under continuous and diurnal loading conditions.

Abstract A polysulfone microporous membrane module was investigated for control of 1-butanol-contaminated gas streams. A diurnal loading condition, using two different butanol concentrations, was used to simulate startup and stop conditions associated with shift work. The membrane module was also used to remove 1-butanol from air under continuous loading conditions in a bioreactor. The reactors were seeded with a mixed bacterial consortium capable of butanol biodegradation. Biokinetic parameters for butanol utilization were determined for the culture to be a maximum specific utilization rate (k) equal to 4.3 d−1 and a half saturation constant (Ks) equal to 8.9 mg L−1. A biofilter running only with diurnal loading conditions giving a “40-hr workweek” had an average 1-butanol removal rate of 29% (111 ppm, 74 gm−3 hr−1) from a 350-ppm influent at the end of an 8-hr operational day. End-of-day removal varied between 4 and 67% during the operational period. With continuous steady-state operation followed by placement on a diurnal loading schedule and influent butanol concentrations increased to 700 ppm, butanol removal averaged 38% (269 ppm, 145 gm−3 hr−1). Under continuous loading, steady-state conditions, 1-butanol removal from the airstream was greater than 99% (200 ppm, 73 gm−3 hr−1). These results suggest that the bioreactor can be operated on a diurnal schedule or 40-hr week operational schedule without any decline in performance.

Trichloroethylene degradation by Methylosinus trichosporium OB3b mutants in a sequencing biofilm reactor

Abstract Methylosinus trichosporium OB3b was used in a sequencing biofilm reactor to degrade trichloroethylene (TCE) in water at approximately 100 μg/l influent concentration. The reactor consisted of biofilms grown on diatomaceous earth pellets or glass beads, and was sequenced between growth cycle, in which methane and air were fed in a gas phase, and degradation cycle, in which the column was completely liquid-filled. Biomass loading on the support media was only 10 mg cell dry weight/g support media, giving a calculated biofilm thickness of 0.04 cm. Apparent psuedo-first order degradation rate constants in the system were improved by more than an order of magnitude, from 0.008 l/mg d to 0.1 l/mg d, through the use of antibiotic-resistant strains of copper-resistant organisms that express only the soluble methane monooxygenase, the enzyme responsible for trichloroethylene degradation. Also, biomass accumulation was improved through the use of a cationic coagulating polymer. However, TCE degradation was sustained only for short times, and cycling back to growth mode did not completely regenerate TCE degradation ability. Thus, biofilms of Methylosinus trichosporium OB3b did not give rise to sustained high degradation rates.

Performance of pilot-scale constructed wetlands for secondary treatment of chromium-bearing tannery wastewaters

Tannery operations consist of converting raw animal skins into leather through a series of complex water- and chemically-intensive batch processes. Even when conventional primary treatment is supplemented with chemicals, the wastewater requires some form of biological treatment to enable the safe disposal to the natural environment. Thus, there is a need for the adoption of low cost, reliable, and easy-to-operate alternative secondary treatment processes. This paper reports the findings of two pilot-scale wetlands for the secondary treatment of primary effluents from a full tannery operation in terms of resilience (i.e., ability to produce consistent effluent quality in spite of variable influent loads) and reliability (i.e., ability to cope with sporadic shock loads) when treating this hazardous effluent. Areal mass removal rates of 77.1 g COD/m2/d, 11 g TSS/m2/d, and 53 mg Cr/m2/d were achieved with a simple gravity-flow horizontal subsurface flow unit operating at hydraulic loading rates of as much as 10 cm/d. Based on the findings, a full-scale wetland was sized to treat all the effluent from the tannery requiring 68% more land than would have been assumed based on literature values. Constructed wetlands can offer treatment plant resilience for minimum operational input and reliable effluent quality when biologically treating primary effluents from tannery operations.

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.

Effectiveness of Porous Covers for Control of Ammonia, Reduced Sulfur Compounds, Total Hydrocarbons, Selected Volatile Organic Compounds, and Odor from Hog Manure Storage Lagoons

Abstract Anaerobic lagoons are a major source of odor at concentrated animal feeding operations. Seven different kinds of artificial (geotextile and polyethylene foam) and natural (straw and redwood) permeable lagoon covers were evaluated for their potential to reduce odorous emissions generated by anaerobic waste lagoons. A novel floating sampling raft was constructed and used to simultaneously evaluate the effectiveness of lagoon covers on an operating swine waste lagoon. The air collected from the raft was evaluated for odor, total reduced sulfur (TRS) compounds, ammonia, total hydrocarbons, dimethyldisulfide, and trimethylamine. The emission rates from the lagoon were highly variable both temporally and spatially. All of the lagoon covers substantially reduced TRS emissions and odor. Geotextile fabric and a recycled foam cover exhibited the greatest reduction in total hydrocarbon emissions; natural covers were less effective. Because of consistently low emission rates of ammonia, no statistically significant reduction of ammonia emissions were observed from any of the lagoon covers.

Steady-State Performance of an Activated Carbon Biofilter Degrading Styrene: Effects of Residence Time and Inlet Concentration

Abstract A granular-activated-carbon-packed biofilter receiving a constant loading rate of styrene was subjected to changes in residence time and concentration, and the effects on performance characteristics and the composition of biofilm along the bed height in the biofilter were studied. This study was carried out during the last 3 months of the entire biofilter operation of 16 months. The total bed height of the biofilter was physically divided into four individual reactor stages in series. This configuration permitted measurement of the leachate pH in each stage. Also, between-stage mixing of the culture was minimized. Each reactor stage was loaded in an upflow mode. The shortest residence time tested, 1.05 min, resulted in a decrease of removal efficiency to 95% (from 100% achieved at longer residence times). The shorter residence time nonetheless resulted in a higher elimination capacity in the higher stages of the filter bed. In the first two stages, the leachate pH values were 6.4 and 6.6, slightly lower than in higher stages (pH 7). A decrease of the styrene concentration along the bed height significantly affected the total cell number of immobilized cells whereas the number of degraders, Pseudomonads, and eukaryotes changed only a little. Microbial analysis of the mixed culture showed the presence of four bacterial strains and three fungi.

Impact of biocatalyst and moisture content on toluene/xylene mixture biofiltration

The objective of this work was to determine the influence of microbial inoculation on degradation efficiency. Three biofilters were used for the treatment of waste gas. A mixture of compost and perlite (8:2) served as the packing material. One biofilter was inoculated with a constructed microbial population. The second remained uninoculated, having the natural population present in the compost. The third biofilter was uninoculated and the packing material was sterilized. The degradation ability of the uninoculated biofilter started to drop after 18 days, while the removal efficiency of inoculated biofilter was stable. The sterile biofilter proved to have no removal efficiency. Moisture content of the packing and ability of the packing to keep moisture was tested. The results showed a significant dependence of the degradation efficiency on the packing moisture content, with highest removal efficiency observed at 70 % moisture content.

Mine-Impacted Water and Biochemical Reactors

Abstract Biochemical reactors (BCRs) biologically reduce sulfate to treat mine-impacted water. Generally, the BCR is a pondlike system containing a permeable bed including organic material. That organic material is used as an electron donor and sulfate in the metal-containing water is transformed during electron acceptance to sulfide, which precipitates many metals in an insoluble form. Adsorption and coprecipitation are other possible mechanisms of metals removal in BCRs. The key design parameter is the rate of sulfate reduction, which is determined by the rate at which the organic material, usually a woody material, is consumed. A wide range of sulfate reduction rates have been reported, presumably due to differences in degradability of the organic substrate. The hydraulics of a BCR is another design consideration, particularly because operational problems are most often related to flow patterns in the bed.

Abatement of synthetic landfill gas including limonene by biotrickling filter and membrane biofiltration

In this study, a single silicone rubber membrane biofilter was compared to a lava rock biotrickling filter to examine the aerobic biofiltration of synthetic landfill gas including odorous limonene. The membrane bioreactor and biotrickling filter showed, respectively, maximum elimination capacities of 17 g m−3 h−1 and 31.3 g m−3 h−1 for limonene and removal efficiencies of 11 % and 18 % for methane. The membrane bioreactor was apparently mass transfer-limited and the biotrickling filter was reaction-limited.