Byung R. Kim

Effect of substrate Henry's constant on biofilter performance

Abstract Butanol, ether, toluene, and hexane, which have Henrys constants ranging from 0.0005 to 53, were used to investigate the effects of substrate solubility or availability on the removal of volatile organic compounds (VOCs) in trickle-bed biofilters. Results from this study suggest that, although removal of a VOC generally increases with a decrease in its Henrys constant, an optimal Henrys constant range for biofiltration may exist. For the treatment of VOCs with high Henrys constant values, such as hexane and toluene, the transfer of VOCs between the vapor and liquid phases or between the vapor phase and the biofilm is a rate-determining step. However, oxygen (O2) transfer may become a rate-limiting step in treating VOCs with low Henrys constants, such as butanol, especially at high organic loadings. The results demonstrated that in a gas-phase aerobic biofilter, nitrate can serve both as a growth-controlling nutrient and as an electron acceptor in a biofilm for the respiration of VOCs with low Henrys constants. Microbial communities within the biofilters were examined using denaturing gradient gel electrophoresis to provide a more complete picture of the effect of O2 limitation and denitrification on biofilter performance.

The effect of nitrate on VOC removal in trickle bed biofilters

Abstract In response to the growing concern over volatile organic compounds (VOCs), biofiltration is becoming an established economical air pollution control technology for removing VOCs from waste air streams. Current research efforts are concentrating on improving control over key parameters that affect the performance of gas phase biofilters. This study utilized diethyl ether as a substrate, nitrate as the sole nutrient nitrogen source within two co-currently operated trickle-bed biofilters, for over 200 days. The two pelletized medium biofilters were operated at a low empty bed contact time of 25 s, inlet gas flow rates of 8.64 m 3 /day, nutrient liquid flow rates of 1 liter/day, and COD loading rates of 1.8 and 3.6 kg/m 3 per day, respectively. Operational parameters including contaminant concentration in the gas phase, nutrient nitrate concentration in the aqueous phase, and the frequency of biomass removal were considered. Special attention was given to the effect and the role of nitrate on VOC removal. Throughout the experiment, nitrate persisted in the liquid effluent and the ether removal efficiencies improved with increasing influent nitrate concentration, which suggest that the nitrate diffusion into the biofilms is rate determining. By increasing the concentration of oxygen in the feed to this biofilter from 21% (ambient air) to 50 and 100%, while maintaining an influent ether concentration of 133 ppmv and a feed nitrate concentration of 67 mg-N/liter, the performance of the biofilter was not significantly affected. These results suggest that nitrogen was rate limiting as a growth nutrient rather than as an electron acceptor for the respiration of ether. The results also indicated that removal of excess biomass is necessary to maintain long-term performance. However, the required frequency of biomass removal depends on operating parameters such as loading.

Composition and analysis of mineral oils and other organic compounds in Metalworking and hydraulic fluids

Metalworking fluids (MWFs) are the primary source of organic contaminants in oily wastewater at many manufacturing facilities. Such facilities, including those in the automotive industry, face the continuing challenge of improving wastewater treatment for organics. Hydraulic fluids (HFs), chemically similar to MWFs, have been a major source of costly soil contamination at industrial and commercial facilities. A better understanding of these organics is essential to the treatment of oily wastewater and HF decontamination. Therefore, two aspects were reviewed: (1) current and historical organic chemical compositions of MWFs and HFs and (2) existing and emerging analytical methods. Base mineral oils were emphasized, as they are the primary ingredient of these fluids and the main contaminant in oily wastewater and HF-contaminated soil. Hydrocarbon compositions of “naphthenic” (cycloalkanes) and “paraffinic” (straight and branched noncyclic alkanes) mineral oils were described, as were the chemical nature of the various MWF and HF additives. Analytical methods for gross organic measurements, individual organics, and structure- and sizebased fractions and distributions were reviewed. Most promising for characterizing the base oil fraction were gas chromatography (GC) coupled with two soft ionization mass spectrometry detection methods and comprehensive 2-dimensional GC. These methods can provide complete distributions of hydrocarbon structures and sizes and are potentially useful to monitor hydrocarbon fate in wastewater treatment, soil/sediment remediation, or other applications involving complex hydrocarbon mixtures.

Biological removal of organic nitrogen and fatty acids from metal-cutting-fluid wastewater

Abstract The anaerobic, anaerobic/aerobic (anaerobic followed by aerobic) and straight aerobic treatments of a simulated metal-cutting-fluid wastewater were evaluated in terms of the removal of organic nitrogen (primarily alkanolamines and heterocyclic compounds) and fatty acids, the two major constituents of many water-based metal-cutting fluids. The organic nitrogen was not well adsorbed on activated carbon but was degraded through the anaerobic/aerobic or straight aerobic treatment. It was also found that an acclimation period was necessary before the organic nitrogen could be anaerobically degraded. 2-Methylhexanoic, heptanoic, 3,5,5-trimethylhexanoic and benzoic acid, which were found in the wastewater, were degraded well both anaerobically and aerobically. The wastewater also contained a group of unidentified organic compounds that consisted of five gas chromatographic peaks (probably branched C 8 –C 10 fatty acids or their esters). These unidentified organics were partially degraded and persisted in the effluents, contributing to the non-biodegradable portion of organics. Several low molecular weight fatty acids (acetic acid, propanoic acid, 2-methylpropanoic acid, butanoic acid, 3-methylbutanoic acid and pentanoic acid) were produced during the periods when the influent chemical oxygen demand (COD) loading was varied to study the response of an anaerobic reactor to the variation. The anaerobic/aerobic treatment produced an effluent similar to that of the straight aerobic treatment with respect to fatty acid concentrations.

Mathematical model for the biodegradation of VOCs in trickle bed biofilters

The objective of this work is to develop a fundamental mathematical model that describes the biodegradation of volatile organic compounds (VOCs) in gas phase trickle-bed biofilters, and to estimate the unknown model parameters. The mathematical model considers a three-phase system (biofilm, water, and gas phase), non-uniform bacterial population, and one limiting substrate. Two pilot-scale trickle-bed biofilters were operated to remove the VOC diethyl ether from a waste gas stream. Experimental results from this system were used to estimate the unknown parameters of the steady-state model: the maximum rate of substrate utilization μ m X f / Y , the Monod constant, K s , and the ether biofilm/water diffusivity ratio, r d . While the value of μ m X f / Y was uniquely determined, the values of K s and r d were highly correlated. High values of the Monod constant and the ether diffusivity in the biofilm gave similar predictions to those corresponding to low values of both parameters. Batch studies were used to estimate the value of K s without mass transfer limitations showing that K s < 1 mg/L=2.6 mg COD/L. Using this information and biofilter operating data the true values of K s and r d were determined.

Considering age and size distributions of activated-carbon particles in a completely-mixed adsorber at steady state

A steady-state model, based on the concept of homogeneous surface diffusion, was developed to describe an activated-carbon adsorber with continuous carbon replacement. Both age and size distributions of carbon particles were incorporated into the model. Using the resulting closed-form solution, a series of simulations was made to investigate the effects of adsorption characteristics, the average age of carbon particles, surface diffusion coefficient, particle size and carbon concentration on the effluent adsorbate concentration. Although there is no single, equivalent particle size that can exactly represent a particle-size distribution, the use of a carefully chosen equivalent particle size could lead to errors in adsorber performance predictions of less than 10%. Unfortunately, there is no formal protocol for selection of the equivalent particle size and trial and error iterations are necessary.

A novel approach to paint sludge recycling: Reclaiming of paint sludge components as ceramic composites and their applications in reinforcement of metals and polymers,

About 15 × 10 6 lbs of paint sludge, produced every year at Ford plants, is disposed of in landfills. An economical alternative to this disposal method, which reclaims or recycles components of paint sludge, is highly desirable to preserve valuable natural resources. Here, we describe an alternative to landfill disposal whereby paint sludge is converted into ceramic composites that can be used as reinforcing materials. The conversion of paint sludge to ceramic composite, I/N 2 /600, is achieved by pyrolysis under a nitrogen atmosphere. Two additional composites, labeled I/N 2 /1000 and I/NH 3 /1000, respectively, are prepared by sintering I/600 at 1000 °C under N 2 and NH 3 . All three composites contain crystalline CaTiO 3 , BaTiO 3 , TiO 2 , amorphous alumina, and carbon. I/NH 3 /1000 contains an additional crystalline phase of titanium nitride. The application of these composites as reinforcing materials is demonstrated in the fabrication of representative metal matrix composites (MMCs) and reinforced plastic components.

Comparison of plate counts, Petrifilm, dipslides, and adenosine triphosphate bioluminescence for monitoring bacteria in cooling-tower waters.

Effective bacterial control in cooling-tower systems requires accurate and timely methods to count bacteria. Plate-count methods are difficult to implement on-site, because they are time- and labor-intensive and require sterile techniques. Several field-applicable methods (dipslides, Petrifilm, and adenosine triphosphate [ATP] bioluminescence) were compared with the plate count for two sample matrices--phosphate-buffered saline solution containing a pure culture of Pseudomonas fluorescens and cooling-tower water containing an undefined mixed bacterial culture. For the pure culture, (1) counts determined on nutrient agar and plate-count agar (PCA) media and expressed as colony-forming units (CFU) per milliliter were equivalent to those on R2A medium (p = 1.0 and p = 1.0, respectively); (2) Petrifilm counts were not significantly different from R2A plate counts (p = 0.99); (3) the dipslide counts were up to 2 log units higher than R2A plate counts, but this discrepancy was not statistically significant (p = 0.06); and (4) a discernable correlation (r2 = 0.67) existed between ATP readings and plate counts. For cooling-tower water samples (n = 62), (1) bacterial counts using R2A medium were higher (but not significant; p = 0.63) than nutrient agar and significantly higher than tryptone-glucose yeast extract (TGE; p = 0.03) and PCA (p < 0.001); (2) Petrifilm counts were significantly lower than nutrient agar or R2A (p = 0.02 and p < 0.001, respectively), but not statistically different from TGE, PCA, and dipslides (p = 0.55, p = 0.69, and p = 0.91, respectively); (3) the dipslide method yielded bacteria counts 1 to 3 log units lower than nutrient agar and R2A (p < 0.001), but was not significantly different from Petrifilm (p = 0.91), PCA (p = 1.00) or TGE (p = 0.07); (4) the differences between dipslides and the other methods became greater with a 6-day incubation time; and (5) the correlation between ATP readings and plate counts varied from system to system, was poor (r2 values ranged from < 0.01 to 0.47), and the ATP method was not sufficiently sensitive to measure counts below approximately 10(4) CFU/mL.

Membrane bioreactor treatment of a simulated metalworking fluid wastewater containing ethylenediaminetetraacetic acid and dicyclohexylamine.

Membrane bioreactors (MBRs) have been installed at automotive plants to treat metalworking fluid (MWF) wastewaters, which are known to contain toxic and/or recalcitrant organic compounds. A laboratory study was conducted to evaluate treatment of a simulated wastewater prepared from a semisynthetic MWF, which contains two such compounds, dicyclohexylamine (DCHA) and ethylenediaminetetraacetic acid (EDTA). Primary findings were as follows: During stable operating periods, almost all chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and EDTA were removed (by > 96%). During somewhat unstable periods, COD removal was still extremely robust, but removal of EDTA and TKN were sensitive to prolonged episodes of low dissolved oxygen. Nitrogen mass balance suggested 30 to 40% TKN removal by assimilation and 60 to 70% by nitrification (including up to 34% TKN removal via subsequent denitrification). Dicyclohexylamine appeared to be readily biodegraded. Maximum DCHA and EDTA degradation rates between pH 7 and 8 were found. An Arthrobacter sp. capable of growth on DCHA as the sole source of carbon and energy was isolated.

Approximate solution for a fluidized-bed biofilm model

Abstract An approximate algebraic solution for a fluidized-bed biofilm model, based on Monod kinetics, was developed using a one-point orthogonal collocation method. The solution was compared with an accurate numerical solution and was found to be accurate for the case where biofilm is “shallow”.