Wudneh Admassu

Feasibility of using natural fishbone apatite as a substitute for hydroxyapatite in remediating aqueous heavy metals.

Fishbone, a natural, apatite rich substance, was examined for suitability as a substitute for hydroxyapatite in the sequestering of aqueous divalent heavy metal ions. The fishbone exhibited lower metal removal capacity than pure hydroxyapatite, due primarily to its purity ( approximately 70% apatite equivalent). In other ways the fishbone behaves in a similar manner as pure hydroxyapatite in the sequestration process. It was observed that it can remove all Pb(2+), Cu(2+), Cd(2+) and Ni(2+) to below detectable levels as measured by inductively coupled plasma atomic absorption, and the rate of reaction with either Zn(2+), Ni(2+), or Pb(2+) was also found to be similar to hydroxyapatite. Also, a two level, three variable full factorial design was performed for the Pb/apatite reaction and both apatites performed similarly. The main difference, besides capacity, was on exposure to high (2.4 mM) Pb concentrations. The fishbone removed less of the Pb(2+) than capacity correction predicted.

Kinetics of the amylase system of Saccharomycopsis fibuliger

The extracellular amylases produced by Saccharomycopsis fibuliger have been studied with the intent of identifying the kinetic mechanism and product distribution, and modelling the production of d-glucose during starch hydrolysis. High performance liquid chromatography was effectively used to separate and quantify the product oligomers released. α-Amylase rapidly hydrolysed the long substrate chains into smaller oligomers which became the substrate for glucoamylase in the production of d-glucose. The formation of a rate limiting substrate occurred late in the reaction. Glucoamylase and α-amylase rates were fitted to Michaelis-Menten models with d-glucose inhibition included.

Ethanol fermentation with a flocculating yeast

Abstract A 100 cm × 5.7 cm internal diameter tower fermentor was fabricated and operated continuously for 11 months using the flocforming yeast, Saccharomyces cerevisiae (American Type Culture Collection 4097). Steady state operation of the system was characterized at 32 °C and pH 4.0 for glucose concentrations ranging from 105 to 215 g l−1. The height of the yeast bed in the tower was maintained at 80 cm. The high yeast density, ethanol concentration and low pH prevented bacterial contamination in the reactor. The concentration profiles of glucose and ethanol within the bed were described by a dispersion model. Modeling parameters were determined for the yeast by batch kinetics and tracer experiments. The kinetic model included ethanol inhibition and substrate limitation. A tracer study with step input of d -xylose (a non-metabolizable sugar for S. cerevisiae) determined the dispersion number (D/uL = 0.16) and liquid voidage (ϵ l = 0.25). Measurements taken after 6 months of continuous operation indicated that there was no significant change in fermentor performance.

Modeling of electrodialysis of metal ion removal from pulp and paper mill process stream

A theoretical model of an electrodialysis process for the removal of metal ions in process stream of the pulp and paper industry has been developed in this article. Based on a constant applied electric potential gradient as a power supply, the model starts from a differential equation of mass balance, and presents an analytical solution describing concentration profiles of cations as electrolytes in electrodialysis channels. The relationships among metal ion concentration, electrical current density, and removal efficiency are also discussed.

Growth kinetics of Clostridium bifermentans and its ability to degrade TNT using an inexpensive alternative medium

A strain of Clostridium bifermentans isolated from a munitions-supplemented anaerobic digester is known to degrade 2,4,6-trinitrotoluene (TNT) in rich media such as Brain Heart Infusion (BHI) broth. In order to make this biodegradation process commercially feasible, a new growth medium was developed. Corn steep liquor and molasses were selected as possible nitrogen and carbon sources. A medium containing 2.4% corn steep liquor and 0.4% molasses was chosen based on the value for maximum specific growth rate. The values of µm and Ks from continuous runs were of 0.029 min−1 and 0.488 g/L, respectively. To reduce the overhead cost for maintaining an anoxic environment for this obligatory anaerobic bacterium, the threshold oxygen level under which the bacterium can survive was determined. The degradation of TNT was then carried out in a batch bioreactor, and in a continuously stirred tank bioreactor. The solubility of TNT was enhanced by using the surfactant, Tween 80, and the optimal concentration of Tween 80...

EFFECTS OF CHEMICAL IMPURITIES ON GAS SORPTION IN POLYMERIC MEMBRANES. I. POLYCARBONATE AND POLYSULFONE

In recent years, polymeric membranes have been increasingly used in key unit operations such as gas separations. In theory, the performance of a polymeric membrane module depends solely on the chemical structure of the polymer and the feed gas composition. It has, however, been observed that impurities in the feed stream (such as vapors from compressor oils) affect the productivity of the membrane module even at parts per million (ppm) levels. In order to understand the fundamental effects of such trace chemicals, commercial polymers were studied for their solubility and permeability characteristics in the presence and absence of such impurities. Solubilities of N2, O2, CH4 and CO2 were measured in dense homogeneous films at 35°C. Two types of compressor oils were used in doping the polymers at three concentration levels. Results from the solubility data were well described by the dual-mode model for glassy polymers that consists of a Henrys solubility term k D, Langmuir sorption capacity C′H, and an affinity constant “b.” The effect of the oil on each of the model parameters is presented. The effect of annealing on sorption in clean and doped samples of the polymers was also examined. Such thermal treatment affected the Langmuir sorption capacity C′H more than any of the other dual-mode parameters. Annealing lowered C′H because of the ensuing densification of the glassy structure. This effect was common to both clean and doped films. A good understanding of the effects of such trace chemicals on gas solubility in synthetic membranes will assist in examining effects of impurities on the overall membrane productivity and aid in designing effective polymeric membrane modules in the future.

EFFECTS OF CHEMICAL IMPURITIES ON GAS PERMEATION AND DIFFUSION IN POLYMERIC MEMBRANES

In recent years, polymeric membranes have been increasingly used in key unit operations such as gas separations. In theory, the performance of a polymeric membrane module depends solely on the chemical structure of the polymer and the feed gas composition. However, impurities in the feed stream (such as vapors from compressor oils) have been found to affect the productivity of the membrane module even at parts per million (ppm) levels. To understand the fundamental effects of such trace chemicals, commercial polymers were studied for their solubility and permeability characteristics in the presence and absence of such impurities. Two types of compressor oils were used in doping the polymers at three concentration levels. Permeabilities of N2, O2, CH4, and CO2 were measured in dense homogeneous films at 35°C. Selectivities of O2/N2 and CO2/CH4 were also calculated in the presence and absence of oil. The permeability data were used in conjunction with the sorption results as reported in previous papers to calculate diffusivities in the Henrys (D D) and Langmuir (D H) regions of the polymer. The effect of annealing on permeability and diffusivity in clean and doped samples of the polymers was also examined. Such thermal treatment reduced the diffusivity and permeability due to densification of the glassy structure. The effect was common to both clean and doped films. A good understanding of the effects of such trace chemicals on the permeability characteristics of the membrane will aid in designing effective polymeric membrane modules in the future.

EFFECTS OF CHEMICAL IMPURITIES ON GAS SORPTION IN POLYMERIC MEMBRANES. II. PC-1 AND PC-2

In recent years, polymeric membranes have been increasingly used in key unit operations such as gas separations. In theory, the performance of a polymeric membrane module depends solely on the chemical structure of the polymer and the feed gas composition. It has, however, been observed that impurities in the feed stream (such as vapors from compressor oils) affect the productivity of the membrane module even at parts per million (ppm) levels. In order to understand the fundamental effects of such trace chemicals, commercial polymers were studied for their solubility and permeability characteristics in the presence and absence of such impurities. Solubilities of N2, O2, CH4, and CO2 were measured in dense homogeneous films at 35°C. Two types of compressor oils were used in doping the polymers at three concentration levels. Results from the solubility data were well described by the dual-mode model for glassy polymers that consists of a Henrys solubility term kD , Langmuir sorption capacity CH ′, and an affinity constant “b.” The effect of the oil on each of the model parameters is presented. The effect of annealing on sorption in clean and doped samples of the polymers was also examined. Such thermal treatment affected the Langmuir sorption capacity CH ′ more than any of the other dual-mode parameters. Annealing lowered CH ′ because of the ensuing densification of the glassy structure. This effect was common to both clean and doped films. A good understanding of the effects of such trace chemicals on gas solubility in synthetic membranes will assist in examining effects of impurities on the overall membrane productivity and aid in designing effective polymeric membrane modules in the future.

Critical Change in Apparent Conductance and Ion Exchange Limit in Membrane Electrodialysis

As the rates of ion transport in membrane and electrolytic solution become comparable in membrane electrodialysis, the separation efficiency may be limited by the capability of ion exchange of the membrane. An experimental study of current vs. voltage characteristics of dilute electrolytic solutions (KCl, NaCl, and LiCl) was carried out by a laboratory scale membrane electrodialysis unit to show this phenomenon. The observed current vs. voltage characteristics show that in a low electrical field (0≤E≤100 volt/m), there is a critical change in the apparent conductance of the system with the increased initial ion concentration. This critical phenomenon suggests that in a low electrical field the ion transport is limited by the rate of ion exchange within the membrane. The sequence of these critical phenomena for the solutions of KCl, NaCl, and LiCl indicates that the ion exchange limit may be related to the ions size as well.