Immobilization materials mixed with activated sludge as column biofilters for the treatment of gaseous stream containing benzene and toluene

Activated sludge has been utilized for the treatment of volatile organic compounds (VOCs) which are emitted from industrial processes. Nevertheless, activated sludge systems often suffer from the problem caused by concentration gradients as well as pressure drops. Channeling is also a major problem in the treatment process. As the bed height of the packed activated sludge system increases, the pressure drop increases accordingly. To solve these problems, we proposed immobilized activated sludge column reactors for treating VOCs in air. The immobilization material used to mix with activated sludge was properly selected in this work. Elemental compositions of these materials were analyzed. In this study, we also proposed a VOC feed system so that more stable inlet concentrations could be achieved. Hence, the equipment and operating costs were reduced and the problem of VOCs leaking from peristaltic pumps was avoided. The moisture content of the system was well maintained and better VOC removal efficiency was achieved. With an operation condition of progressive VOC inlet concentrations, better removal efficiency of benzene and toluene was then obtained. In conclusion, by the utilization of immobilization materials selected from wastes as well as immobilized activated sludge column reactors, significant removal efficiency for both benzene and toluene was demonstrated.     

Transformation of toluene and benzene by mixed methanogenic cultures

The aromatic hydrocarbons toluene and benzene were anaerobically transformed by mixed methanogenic cultures derived from ferulic acid-degrading sewage sludge enrichments. In most experiments, toluene or benzene was the only semicontinuously supplied carbon and energy source in the defined mineral medium. No exogenous electron acceptors other than CO2 were present. The cultures were fed 1.5 to 30 mM unlabeled or 14C-labeled aromatic substrates (ring-labeled toluene and benzene or methyl-labeled toluene). Gas production from unlabeled substrates and 14C activity distribution in products from the labeled substrates were monitored over a period of 60 days. At least 50% of the substrates were converted to CO2 and methane (greater than 60%). A high percentage of 14CO2 was recovered from the methyl group-labeled toluene, suggesting nearly complete conversion of the methyl group to CO2 and not to methane. However, a low percentage of 14CO2 was produced from ring-labeled toluene or from benzene, indicating incomplete conversion of the ring carbon to CO2. Anaerobic transformation pathways for unlabeled toluene and benzene were studied with the help of gas chromatography-mass spectrometry. The intermediates detected are consistent with both toluene and benzene degradation via initial oxidation by ring hydroxylation or methyl oxidation (toluene), which would result in the production of phenol, cresols, or aromatic alcohol. Additional reactions, such as demethylation and ring reduction, are also possible. Tentative transformation sequences based upon the intermediates detected are discussed.     

Factors affecting molecular packing in mixed lipid monolayers and bilayers

The nature of the molecular interactions and the factors determining molecular packing in mixed phospholipid/glyceride monolayers and bilayers were investigated by monolayer and nuclear magnetic resonance (NMR) techniques. Force-area curves were obtained at various temperatures for monolayers, at the air-water interface, of synthetic lecithins and a phosphatidyl ethanolamine mixed with di- and triglycerides in different molar ratios. The linewidths of peaks in the high resolution NMR spectra of lecithin/glyceride co-dispersions in excess water at different temperatures were used to obtain information about molecular mobilities.It was found that the molecular packing in mixed lipid monolayers and bilayers is determined by the following factors: (1) Whether lipid chains are above or below their melting point (T_C). (2) The difference between experimental temperature and T_C: the larger the difference, the smaller the effect of one component on the other. (3) The degree of similarity of the chains of the components; this influences the degree of cooperativity of chain motions and the degree of mixing of the components. (4) The nature, orientation, mutual interaction and degree of hydration of the polar groups.It is shown that mean molecular area does not always reflect the state of chain motions in lipid films, because of heterogeneity of motion and structure along the molecules. Cooperativity of motion may reduce steric requirements; other effects which are of particular importance for lecithins are interactions of zwitterions, and the influence of polar group hydration.     

Transformation of toluene and benzene by mixed methanogenic cultures.

The aromatic hydrocarbons toluene and benzene were anaerobically transformed by mixed methanogenic cultures derived from ferulic acid-degrading sewage sludge enrichments. In most experiments, toluene or benzene was the only semicontinuously supplied carbon and energy source in the defined mineral medium. No exogenous electron acceptors other than CO2 were present. The cultures were fed 1.5 to 30 mM unlabeled or 14C-labeled aromatic substrates (ring-labeled toluene and benzene or methyl-labeled toluene). Gas production from unlabeled substrates and 14C activity distribution in products from the labeled substrates were monitored over a period of 60 days. At least 50% of the substrates were converted to CO2 and methane (greater than 60%). A high percentage of 14CO2 was recovered from the methyl group-labeled toluene, suggesting nearly complete conversion of the methyl group to CO2 and not to methane. However, a low percentage of 14CO2 was produced from ring-labeled toluene or from benzene, indicating incomplete conversion of the ring carbon to CO2. Anaerobic transformation pathways for unlabeled toluene and benzene were studied with the help of gas chromatography-mass spectrometry. The intermediates detected are consistent with both toluene and benzene degradation via initial oxidation by ring hydroxylation or methyl oxidation (toluene), which would result in the production of phenol, cresols, or aromatic alcohol. Additional reactions, such as demethylation and ring reduction, are also possible. Tentative transformation sequences based upon the intermediates detected are discussed.     

Lipid packing and transbilayer asymmetries of mixed lipid vesicles.

Predictions, based on a previously developed theory, of the radii and asymmetric lipid distribution of mixed phosphatidylcholine/lysophosphatidylcholine and phosphatidylcholine/cholesterol vesicles of variable composition are presented. The results compare well with available experimental data, except for cis-unsaturated phosphatidylcholine/cholesterol vesicles at high concentrations of cholesterol. It is concluded that specific lipid-lipid interactions need not be invoked for saturated and trans-unsaturated phosphatidylcholine mixed with lysophosphatidylcholine or cholesterol. A discussion of the effect of packing stresses on induced flip-flop and non-spherical vesicles is also presented.     

Kinetic study of the anaerobic degradation of toluene by a mixed culture

Toluene was anaerobically degraded by an enriched mixed culture under methanogenic conditions. The mixed culture was originally developed from cow-dung and sludge from a laboratory reactor, in which benzene was anerobically degraded by sulphate-reducing bacteria. First the mixed culture was enriched on toluene over a year with and without the use of sulphate in the medium. For the evaluation of growth-kinetic and maintenance parameters, namely μ_max, K_s, k_d and Y, the anaerobic degradation of toluene was carried out in batch as well as in continous reactors systems. The gas volume and the methane content in the produced gas was somewhat lover than the theoretical value expected, indicating an incomplete degradation of some of the complex intermediates of the toluene degradation pathway. However, the mixed culture was able to transform 41.3% of the toluene carbon into methane.     

Performance and macrokinetic analysis of biofiltration of toluene and p-xylene mixtures in a conventional biofilter packed with inert material

Interactions of toluene and p-xylene in air treatment biofilters packed with an inert filter media were studied. The effect of the inlet load of toluene, p-xylene and mixtures of both compounds on the biodegradation rate was analyzed in three lab-scale biofilters. A maximum elimination capacity (EC) of 26.5 and 40.3 g C m⁻³ h⁻¹ for an inlet load (IL) of 65.6 and 57.8 g C m⁻³ h⁻¹ was obtained for p-xylene and toluene biofilters, respectively. Inhibition of p-xylene biodegradation by the presence of toluene took place when the mixture was treated, whereas the presence of p-xylene had an enhancing effect on the toluene removal efficiency. Specific growth rates (μ) from 0.019 to 0.068 h⁻¹ were calculated in the mixed biofilter, where the highest values were similar to mixtures with lower p-xylene levels (IL_p-Xyl 8.84 ± 0.29 g C m⁻³ h⁻¹). Michaelis-Menten and Haldane type models were fitted to experimental EC for p-xylene and toluene biofilters, respectively.     

Evaluation of toluene dependence and cross-sensitization to diazepam

Acute effects of the abused inhalant toluene resemble those of CNS depressant drugs. Since abuse of toluene involves repeated use, the purpose of the present study was to evaluate the effects of repeated or continuous exposure to toluene and to compare these effects to those of other inhalants and depressants. In experiment 1, ICR mice exposed continuously to 250 ppm toluene via inhalation for four days developed mild dependence upon termination that was characterized by an increase in severity of handling-induced convulsions. However, administration of the convulsants, N-methyl-D-aspartate (NMDA) or pentylenetetrazole (PTZ), did not differentially affect toluene- vs. air-exposed mice. In experiment 2, CFW mice (but not ICR mice) developed cross-sensitization to the initial locomotor stimulatory effects of toluene following four days of injections with 10 mg/kg/day diazepam. Previous findings have shown that 1,1,1-trichloroethane (TCE) produced robust dependence and cross-sensitization to diazepam's locomotor effects when tested under similar conditions. The present results suggest that the dependence and cross-sensitization with diazepam produced by toluene are milder than those induced by TCE. Further, these studies add to increasing evidence that abused inhalants do not have identical pharmacological effects.     

Labor performance measurement in visual inspection and packing operations.

A methodological procedure for identifying and measuring the variables involved and their impact on labor performance in manual inspection and sorting operations is presented. The applicability of the procedure is shown as it applies in an analysis of canning asparagus spears. Worker output rates for any given spear size index tended to decrease along successive work stations, with exceptions where there were changes in proportion to specific sizes available. The canning performance was influenced by interactions among the size, positional line-load, and worker position variables as the product moved along the supply conveyer. Because linear regression equations computed to estimate the number of can per canner per minute were not effective in indicating the effect of spear size distribution nor that of interactions among other relevant variables, a more comprehensive model was developed to estimate cans per worker per minute as a function of line-load, worker position, and three binary variables representing interactions between these variables and spear-size indices. The results of this and similar studies may be used as a basis for suggesting better planning of raw product delivery schedules, introduction of innovative processes, and crew reorganization.     

Binding of lipoproteins to inert materials revisited with computer-assisted analysis

A number of studies conducted in the last decade showed that saturable ('specific') binding, by itself, does not necessarily imply biological significance. That is, biological ligands were shown to bind to inert materials as well as to biological receptors in a saturable manner. In these studies specific binding was operationally defined as binding that was displaceable by excess concentrations of unlabeled ligand. This method of measuring specific binding is now no longer considered optimal. To investigate whether optimal (computer-assisted) techniques of measuring specific binding--namely, nonlinear least-squares curve fitting of total binding data, with mathematical separation of the total binding into its various components--might ensure biological significance of measured specific binding, we studied the binding of high-density lipoproteins (HDL3) to tissue culture dishes as an example of binding without biological significance. This binding closely followed the paradigm of a ligand interacting with a class of homogeneous, saturable sites and with a class of relatively unsaturable sites, just as it would have if the HDL3 were interacting with an unpurified biological receptor. This finding indicates that computer-assisted analysis, while most accurately describing binding data, nevertheless does not ensure that measured specific binding has biological significance. Saturability is such a nonselective feature of equilibrium binding data that it should probably no longer be considered one of the criteria for deciding whether or not a defined binding site is a receptor.     

Raman spectroscopic studies of the packing properties of mixed dihexadecyl- and dipalmitoylphosphatidylcholine bilayer dispersions

X-ray diffraction studies suggest the existence of two separate gel phases for mixed dihexadecylphosphatidylcholine (DHPC)/dipalmitoylphosphatidylcholine (DPPC) bilayers [Kim, J. T., Mattai, J., & Shipley, G. G. (1987) Biochemistry 26, 6599-6603; Lohner, K., Schuster, A., Degovics, G., Müller, K., & Laggner, P. (1987) Chem. Phys. Lipids 44, 61-70]. In one gel phase the lipid chains are interdigitated, while the other gel phase exhibits the conventional bilayer form. We use Raman spectroscopy to provide a detailed molecular analysis of the intermolecular and intramolecular interactions of the DHPC and DPPC molecules within these mixed bilayers. Observation of the methylene chain C-H stretching modes of DHPC and the methylene chain C-D stretching modes of DPPC-d62 for various mixed DHPC/DPPC-d62 bilayers enables the packing characteristics and conformational order of each lipid to be monitored separately. The spectral data indicate that the packing properties of DPPC-d62 in the mixed-lipid bilayers remain relatively unchanged, while the intramolecular and intermolecular properties of DHPC change dramatically as a function of the composition of the DHPC/DPPC-d62 mixed bilayer. This is consistent with a model based upon the existence of three characteristic lipid types for the mixed-lipid system, namely, domains of pure DPPC-d62 and pure DHPC species with interface lipids or boundary regions between the bulk domains.     

Preparation and performance of immobilized yeast cells in columns containing no inert carrier

Schizosaccharomyces pombe was cultivated in a medium of glucose (10 g/L) malt extract (3 g/L), yeast extract (3 g/L), and bactopeptone (5 g/L) to form flocs. More than 95% of the cell population were flocculated. Variation in glucose concentration (from 10 to 100 g/L) did not affect flocculation. Yeast extract helped induce flocculation. Application of the immobilized yeast for the continuous production of ethanol was tested in a column reactor. Soft yeast flocs (50-200 mesh) underwent morphological changes to heavy particles (0.1-0.3 cm diameter) after continuously being fed with fresh substrates in the column. Productivity as high as 87 g EtOH L(-1) h(-1) was obtained when a 150 g/L glucose medium was fed. The performance of this yeast reactor was stable over a two-month period. The ethanol yield was 97% of the theoretical maximum based upon glucose consumed.     

Dynamic bioreactor operation: effects of packing material and mite predation on toluene removal from off-gas

Recent studies have focused on using vapor-phase bioreactors for the treatment of volatile organic compounds from contaminated air streams. Although high removal capacities have been achieved in many studies, long-term operation is often unstable at high pollutant loadings due to biomass accumulation and drying of the packing medium. In this study, three bench-scale bioreactors were operated to determine the effect of packing material and fungal predation on toluene removal efficiency and pressure drop. Toluene elimination capacities (mass toluene removed per unit packing per unit time) above 100 g m(-3) h(-1) were obtained in the fungal bioreactors packed with light-weight, artificial medium, and submersion of the packing in mineral medium once per week was found to provide sufficient moisture and nutrients to the biofilm. The use of mites as fungal predators improved performance by increasing the overall mineralization of toluene to CO(2), and by dislodging biomass along the bioreactor.     

Thermodynamics of the helix-coil transition in polypeptides in mixed organic solvents: the influence of inert solvent and side chain

The thermally induced coil–helix transition of poly(γ-benzyl-L -glutamate) (PBLG) and poly(γ-methyl-L -glutamate) (PMLG) in binary solvent mixtures was investigated by calorimetric and optical rotatory dispersion (ORD) measurements. Dichloroacetic acid was the common active solvent, and the inert solvent was one of the chlorinated hydrocarbons, such as chloroform, 1,3-dichloropropane, 1-chlorobutane, or 1-chlorooctane. The thermodynamic parameters characterizing the intramolecular polypeptide and polypeptide–solvent interactions were calculated using the Karasz and Gajnos theoretical model [(1973) J. Phys. Chem. 77 , 1139–1145]. It was found that the enthalpy (ΔH₁) and entropy (ΔS₁) of helix stabilization in the absence of the active solvent depend on the inert solvent, but only in the case of PBLG. This is explained by the additional helix stabilization achieved by the stacking of the benzyl groups. The stacking is more pronounced in less polar chlorinated hydrocarbons with longer aliphatic chains. The results obtained indicate that the maximum helix stability is reached in chlorinated hydrocarbons with 12 C atoms. In the case PMLG, with an aliphatic ester side group, ΔH₁ and ΔS₁ are independent of the inert solvent. The ORD measurements were used to determine the maximum fraction of helicity attained at constant solvent composition and the transition temperature, T_c, at the point where f_H = 0.5. It was found that, for the same solvent composition, T_c was higher than the temperature of the midpoint of the calorimetric peak. This is explained by the fact that the maximum fraction of helicity is less than unity. The finite transition width was taken into account by calculating the phase boundaries for different fractions of helicity using the value of σ estimated from the calorimetric and van't Hoff enthalpies in the usual manner.     

Molecular packing of cord factor and its interaction with phosphatidylinositol in mixed monolayers.

Cord factor (trehalose 6,6'-dimycolate, CF) is a glycolipid located in the outer mycobacterial cell wall that is implicated in the pathogenesis of mycobacteria. Furthermore, CF is a convenient model for studying mycolic acid residues, the major lipid constituents of the mycobacterial cell wall that are believed to form a barrier against drug penetration. The surface properties of CF and its interactions with phosphatidylinositol (PI) have been investigated using the monolayer technique. During compression/expansion/recompression cycles, CF monolayers switch from a loosely packed to a more tightly packed structure. The change in surface properties suggests a molecular rearrangement, perhaps involving interdigitation of long and short chains of the CF molecules. In CF-PI monolayers, maximal lateral packing density occurs between 0.5 and 0.7 mole fraction CF, which is close to the relative composition of mycolic acid residues and shorter-chain lipids in the mycobacterial cell wall. Low concentrations of CF increase the order in PI monolayers, consistent with CF toxicity involving rigidification of cell membranes.     

Size exclusion chromatography on soft and semi-rigid packing materials in the dynamic axial compression mode

The effect of dynamic axial compression within a range of up to 5 bar upon the structure of the bed packed with soft and semi-rigid packing materials (Sephadex G-25, Bio-Gel P2 and Toyopearl HW-40) and the associated chromatographic parameters were studied for size exclusion chromatography. Continuous packing compression is accomplished by use of a special column with controlled external pressure applied to the packing. Compression has been shown to favor an overall increase in the resolution with pressure optima observed in some cases.     

Removal of benzene and toluene by carbonized bamboo materials modified with TiO2

Carbonized moso bamboo (Phyllostachys pubescens) was coated with TiO(2) nanoparticles to enhance its removal efficiency of harmful gases. Carbonized bamboo-TiO(2) composite (CBC) was prepared by heating mixtures of carbonized bamboo powder (CB) and TiO(2) nanoparticles, denoted as CBM, under nitrogen condition. TiO(2) nanoparticle and carbonized bamboo powder were mixed with the mass ratios of 1/1 and 2/1, respectively. At the same mass ratio of TiO(2) to CB, the benzene and toluene removal efficiencies follow the trend: CBC>CBM>CB, which is consistent with the amount of TiO(2) validated by elemental analysis. Sorption mechanism of benzene and toluene by CB, CBM and CBC might belong to hydrophobic-hydrophobic interaction, observed by depletion of untreated bamboo (UB) carbohydrates during carbonization. Sorption kinetics was further analyzed, and optimal correlation was found by fitting with the Elovich kinetic equation.     

Reversed-phase high performance liquid chromatography of the products of microbiological degradation of toluene

Conditions have been selected for a reversed-phase high-performance liquid chromatographic assay of intermediate products formed in the course of utilization of toluene by Pseudomonas putida. The composition of products indicates that degradation of toluene by strain BS590-P proceeds primarily through the formation of benzoate and catechol. This is followed by degradation of catechol via ortho-cleavage. In strain BS3701-P, toluene oxidation involves both the side chain and the aromatic ring.