College of Engineering and Applied Science

The objective of this study is to obtain a fundamental understanding of the behavior of reactors with a permselective wall (membrane reactors) in terms of: design parameters (reactor length, membrane thickness); operating variables (pressure ratio, feed flow rate); physical properties (rate constant, permeability of fast gas, permselectivity, equilibrium constant); and flow patterns (recycle, cocurrent, countercurrent). Pure feed reacts on the high-pressure side of the membrane, and the product(s) formed are continuously removed to the low-pressure side so that thermodynamic equilibrium is never reached. It is shown by simulation that equilibrium shift can be enhanced by: recycling unconverted reactant; shifting feed location to separate products; and maintaining high permeation rates to reduce backreaction. It is also shown that the choice between cocurrent flow and countercurrent flow depends on the system parameters.

The purpose of this paper is to consider the well-agitated continuous stirred tank membrane reactor (CSTMR) and the plug flow membrane reactor (PFMR) from the standpoint of equilibrium shift in reversible reactions. The general behavior of both reactor types is discussed, and comparisons are made of their performance. For CSTMR, analytical criteria have been developed to predict the stability of the steady state. Results on simulation studies of ethylbenzene dehydrogenation in a

Results have been presented on the development of a structure-activity relationship for biodegradation using a group contribution approach. Using this approach, reported results of the kinetic rate constant agree within 20% with the predicted values. Additional compound studies are essential to further extend the methodology.

The toxic effects of heavy metals, zinc and copper, in unary and binary solutions were studied using the Microtox s acute toxicity test which relies upon the attenuation of light intensity emitted by Vibrio fischeri. The toxic effect G (ratio of the light intensity lost at time t to the light intensity remaining at time t) of zinc could be related to its concentration [X] by a two-parameter equation G ¼ að1 À expðÀb½X ÞÞ, where parameter a was a function of time and b equal to 0.88 L/mg. The toxic effect of zinc asymptotically approached a maximum with respect of to concentration at all times. The toxic effect of copper was fundamentally different from that of zinc, and increased exponentially with concentration without any limiting maximum value. It could also be described by a two-parameter equation, however, the equation had the form G ¼ a expðb½X Þ, where parameter a was a constant and b a function of time. The different functional dependencies (of the toxic effect on the metal concentration) of zinc and copper indicate that different toxicity/inhibition mechanisms were possibly responsible for the attenuation of light intensity for the two metals. The toxic effects of binary mixtures were substantially higher than those expected on the basis of additivity of individual metals. No simple correlations were obtained that could relate the toxic effect of binary mixture to those of individual metals. A better understanding of metal-microbe interactions is needed for achieving predictive capability for toxic effect of mixtures. r

A group contribution method has been developed that uses the LC50 values (measured for fathead minnow) for 130 diverse organic compounds. The 130 selected compounds were constituted from 16 chemical groups with -log(LCSO) values ranging from 0.85 to 6.09. The method was then used to predict the LC50 values for 10 additional compounds, not in the training set, with good agreement between the predicted and measured values.

The fate of organic chemicals in the environment depends on their susceptibility to biodegradation. Hence, development of regulations concerning their manufacture and use requires information on the extent and rate of biodegradation. Recent studies have attempted to correlate the kinetics of biodegradation with the molecular structure of the compound. This has led t o the development of structure-biodegradation relationships (SBRs) using the group contribution approach.

Acid mine drainage from abandoned mines and acid mine pit lakes is an important environmental concern and usually contains appreciable concentrations of heavy metals. Because sulfate-reducing bacteria (SRB) are involved in the treatment of acid mine drainage, knowledge of acute metal toxicity levels for SRB is essential for the proper functioning of the treatment system for acid mine drainage. Quantification of heavy metal toxicity to mixed cultures of SRB is complicated by the confounding effects of metal hydroxide and sulfide precipitation, biosorption, and complexation with the constituents of the reaction matrix. The objective of this paper was to demonstrate that measurements of dissolved metal concentrations could be used to determine the toxicity parameters for mixed cultures of sulfate-reducing bacteria. The effective concentration, 100% (EC100), the lowest initial dissolved metal concentrations at which no sulfate reduction is observed, and the effective concentration, 50% (EC50), the initial dissolved metal concentrations resulting in a 50% decrease in sulfate reduction, for copper and zinc were determined in the present study by means of nondestructive, rapid physical and chemical analytical techniques. The reaction medium used in the experiments was designed specifically (in terms of pH and chemical composition) to provide the nutrients necessary for the sulfidogenic activity of the SRB and to preclude chemical precipitation of the metals under investigation. The toxicity-mitigating effects of biosorption of dissolved metals were also quantified. Anaerobic Hungate tubes were set up (at least in triplicate) and monitored for sulfate-reduction activity. The onset of SRB activity was detected by the blackening of the reaction mixture because of formation of insoluble ferrous sulfide. The EC100 values were found to be 12 mg/L for copper and 20 mg/L for zinc. The dissolved metal concentration measurements were effective as the indicators of the effect of the heavy metals at concentrations below EC100. The 7-d EC50 values obtained from the difference between the dissolved metal concentrations for the control tubes (tubes not containing copper or zinc) and tubes containing metals were found to be 10.5 mg/L for copper and 16.5 mg/L for zinc. Measurements of the turbidity and pH, bacterial population estimations by means of a most-probable number technique, and metal recovery in the sulfide precipitate were found to have only a limited applicability in these determinations.

The adverse effects of copper and zinc on an acetate-utilizing mixed cultures of sulfate-reducing bacteria (SRB) at concentrations below the toxic concentration (minimum metal concentration at which no sulfate reduction is observed) are reported in this paper. Mathematical models were developed to incorporate the toxic and inhibitory effects (defined as the reduction in bacterial population upon exposure to the metal and the decrease in the metabolic rate of sulfate reduction by the SRB, respectively) into the sulfate-reduction biokinetics. The characteristic toxicity and inhibition constants were obtained from the measurements of bacterial populations and dissolved metal concentrations in serum bottle studies conducted at 35°C and pH 6.6. Both copper and zinc had toxic and inhibitory effects on SRB. The toxicity constants for copper and zinc were 10.6 and 2.9 mM−1, respectively, indicating that exposure to copper resulted in a higher mortality of SRB than did exposure to zinc. The values of the inhibition constants were found to be 17.9 ± 2.5 and 25.2 ± 1.0 mM−1 for copper and zinc, respectively. This implies that dissolved zinc was slightly more inhibitory to SRB than copper. The models presented in the paper can be used to predict the response of a sulfate-reduction bioreactor to heavy metals during acid mine drainage treatment. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 306–312, 2003.

A membrane biofilter is used to biodegrade toluene in the gas phase. Active microorganisms are immobilized on the outside of a hollow fiber membrane cartridge and air containing toluene as the contaminant is passed through the membrane fibers. A porous polysulfone membrane containing water in the pore is used through which both toluene and oxygen are diffused to the biofilm attached to the outside surface. High conversion of toluene (84%) is achieved with a 16 second gas-phase residence time, based on total internal volume of the hollow fibers. A mathematical model is then developed to estimate toluene removal efficiencies at higher air flow rates.

Acid mine drainage (AMD), an acidic metal-bearingwastewater, poses a severe pollution problem attributedto post mining activities. The metals usuallyencountered in AMD and considered of concern for riskassessment are arsenic, cadmium, iron, lead, manganese,zinc, copper and sulfate. The pollution generated byabandoned mining activities in the area of Butte, Montanahas resulted in the designation of the Silver Bow Creek–ButteArea as the largest Superfund (National Priorities List) sitein the U.S. This paper reports the results of bench-scalestudies conducted to develop a resource recovery basedremediation process for the clean up of the Berkeley Pit.The process utilizes selective, sequential precipitation (SSP)of metals as hydroxides and sulfides, such as copper, zinc,aluminum, iron and manganese, from the Berkeley Pit AMDfor their removal from the water in a form suitable foradditional processing into marketable precipitates and pigments.The metal biorecovery and recycle process is based on completeseparation of the biological sulfate reduction step and themetal precipitation step. Hydrogen sulfide produced in the SRBbioreactor systems is used in the precipitation step to forminsoluble metal sulfides. The average metal recoveries usingthe SSP process were as follows: aluminum (as hydroxide) 99.8%,cadmium (as sulfide) 99.7%, cobalt (as sulfide) 99.1% copper(as sulfide) 99.8%, ferrous iron (sulfide) 97.1%, manganese(as sulfide) 87.4%, nickel (as sulfide) 47.8%, and zinc (as sulfide)100%. The average precipitate purity for metals, copper sulfide,ferric hydroxide, zinc sulfide, aluminum hydroxide and manganesesulfide were: 92.4, 81.5, 97.8, 95.6 , 92.1 and 75.0%, respectively.The final produced water contained only calcium and magnesiumand both sulfate and sulfide concentrations were below usablewater limits. Water quality of this agriculturally usable watermet the EPA's gold standard criterion.

This paper is concerned with an important aspect of process control design—synthesis of the control structure. Synthesis of control structures has long been practiced by experienced control engineers, who relied on intuition, insight and judgment to pick a feasible solution from the vast number of alternatives that were possible. This paper describes a systematic procedure to generate these alternatives based on the cause-and-effect representation of the process. The final product is a set of control schemes from which the final system may be selected or evolved. The work is significant in that it is the first attempt to apply non-numerical problem-solving techniques to the problem of synthesizing process control structures. As such, it gives a new way of studying and teaching chemical process control.

One of the major concerns regarding municipal wastewater treatment plant discharge is the rising concentration of nutrient compounds, specifically nitrogen and phosphorus.
Nitrogen and phosphorus are the primary causes of cultural eutrophication (i.e., nutrient enrichment due to human activities) in surface waters. The most recognizable manifestations of this eutrophication are algal blooms that occur during the summer. Chronic symptoms of over-enrichment include low dissolved oxygen, fish kills, murky water, and depletion of desirable flora and fauna.

In this paper, a process that can simultaneously, but independently recover nitrogen and phosphorus from wastewater will be presented. This process can enable municipalities to develop useful fertilizer products from the nitrogen and phosphorus, that are present in wastewater.

A mathematical model has been developed to simulate the Texaco downflow entrained-bed pilot-plant gasifier using coal liquefaction residues and coal-water slurries as feedstocks. This model describes the physical and chemical processes occurring in an entrained coal gasifier. The gasification kinetics describes different complex reactions occurring in the gasifier and the hydrodynamics describes mass, momentum and energy balances for solid and gas phases. Temperature, concentration and velocity profiles along the reactor height were obtained by solving the mass, momentum and energy balances. Parameter studies were made to provide a better understanding of the reactor performance for various inlet feed conditions utilizing the model.

Commercially available biojiltration systems have used natural bioactive materials in packed beds due to low media cost and easy availability. Detailed understanding and modeling of biojiltration systems are lacking in existing literature. Experimental studies on the isopentane treatment in air using peat-and compost-packed beds were conducted with inlet isopentane concentrations of 360 to 960 ppmv, and empty-bed gasphase residence times of 2 to 10 min. High removal efficiencies ( > 90%) were achieved at low contaminant concentrations ( < 500 ppmv) and large empty-bed gas-phase residence times ( > 8 min). For both peat and compost biojilters, there was an "optimal" water content that gave the highest removal eficiency. For higher water content, mass transfer of isopentane through the liquid phase controlled the biojiltration removal efficiency. A t low water content, irreversible changes in the bioactivity of peat and compost occurred, resulting in an irrecoverable loss of removal eficiency. Increases in biofilter bed temperature from 25 to 40°C improved the remoual eficiency. A mathematical model incorporating the effect of water content and temperature was developed to describe the packed-bed biojilter performance. Model predictions agreed closely with experimental data.

The development of processes requires the consideration of a wide variety of reactions which are required to transform raw materials into desired products, solve separation problems, and heat or cool process streams. These reactions have to be evaluated on the basis of raw material costs, kinetics, potential separation difficulties, catalyst costs, safety and reliability, as well as other factors that would arise in their industrial implementation. In this paper, the current status of research in reaction path synthesis has been reviewed. Details have been presented on the REACT program that has been developed for the synthesis of reaction paths for industrial organic chemicals.