Sam S. Sofer

Comparison of cadmium biosorption by gram-positive and gram-negative bacteria from activated sludge.

SummaryGram-positive and Gram-negative bacteria were isolated from activated sludge and used to evaluate differences in cadmium biosorption. Gram-positive bacteria exhibited approximately 20% more cadmium biosorption at 30°C and pH 6.6 than Gram-negatives. Biosorption was largely passive in both cases, although metabolic uptake appeared to occur to a higher extent with Gram-positive bacteria.

Design of a self-tuning rule based controller for a gasoline refinery catalytic reformer

Design concepts for self-tuning knowledge-based controllers are studied. To accomplish this, two interacting rule-based controllers are constructed for supervisory control and system optimization of a gasoline catalytic reformer. The knowledge bases incorporate human operator experience and basic engineering knowledge about the process dynamics. Inference is provided by a fuzzy logic engine. After manual tuning of the controller scaling coefficient is accomplished, a crisp heuristic is developed for self-tuning. The performance of the self-tuning controller is tested against perturbations of a simulation model of the catalytic reformer. >

Mechanism of cadmium uptake by activated sludge

SummaryThe significance of metabolic activity in cadmium uptake by unacclimated activated sludge was studied. Below 30 mg/l cadmium in solution, biosorption was found to follow the Freundlich isotherm, which is the most common pattern for physico-chemical adsorption. More than 95% of total cadmium uptake was achieved within 5 min metal-sludge contact time. Biosorption increased strongly when the initial cadmium concentration in solution was raised from 10 to 100 mg/l, whereas in the same concentration range the metabolic activity of the sludge, as measured by respiratory activity and extracellular protein production, was very significantly inhibited. The addition of nutrients at low but significant levels failed to increase cadmium uptake in 2 h contact time, while in 24 h the addition of nutrients caused the biosorption to increase by only 5–10% without any significant growth of the biomass. Biosorption was found to increase with temperature between 5° C and 40° C, in correlation with an increase in the metabolic activity of the sludge. Pretreatment of the sludge with metabolic inhibitors (NaN3 and UV rays) appeared to cause only a very slight decrease (5–10%) of biosorption. These results suggest that metabolic uptake of cadmium was low and that adsorption to the surface of the cells was the major mechanism of uptake.

A COMPARATIVE STUDY OF CADMIUM UPTAKE BY FREE AND IMMOBILIZED CELLS FROM ACTIVATED SLUDGE

Abstract Cadmium biosorption by free and immobilized cells from activated sludge was studied in batch experiments to determine the effects of immobilization on the biosorption properties of the microorganisms. The method of immobilization consisted of the entrapment of the microorganisms in calcium alginate beads. In a first step, the time course of cadmium uptake and the effects of pH and temperature on biosorption were studied in each case. Then the biosorption pattern and the effect of biosorbent concentration were investigated. It was found that the magnitudes of the effects of pH and temperature on biosorption were reduced by the entrapment of the cells, but the major effects of the entrapment consisted of a very high reduction of the biosorption rate and a modification of the biosorption pattern. On the one hand, cadmium biosorption by free cells followed the pattern of the Freundlich isotherm over wide ranges of cell and cadmium concentrations in solution. On the other hand, biosorption by the bead...

Design of a Self-Tuning Expert Controller for a Gasoline Refinery Catalytic Reformer

The objective is to explore design concepts for self-tuning expert controllers. To accomplish this, two interacting rule based controllers for supervisory control and system optimization are constructed to control a gasoline catalytic reformer. The knowledge bases for the controllers are established from human operator experience and basic engineering knowledge about the process dynamics. Inference is provided by a fuzzy logic engine. After manual tuning of the expert controller scaling coefficients is accomplished, a crisp heuristic is developed for self-tuning. The performance of the self-tuning expert controller is tested against perturbations of a simulation model of the catalytic reformer.

A comparative study of gel entrapped and membrane attached microbial reactors for biodegrading phenol

A comparative study between two reactors, one using microorganisms entrapped in calcium alginate gel, and the other using microorganisms attached on the surface of a membrane (polymeric microporous sheeting, MPSTM) to biodegrade phenol is performed. Results indicate that the alginate bead bioreactor is efficient at higher phenol concentrations while the membrane bioreactor shows better performance at lower phenol concentrations. This unique response is primarily attributed to the different techniques by which the microorganisms are immobilized in the two reactors.In batch mode, below a starting concentration of 100 ppm phenol, biodegradation rates in the membrane bioreactor are (7.58 to 12.02 mg phenol/h · g dry biomass) atleast 10 times the rates in alginate bead bioreactor (0.74 to 1.32 mg phenol/h · g dry biomass). Biodegradation rates for the two reactors match at a starting concentration of 250 ppm phenol. Above 500 ppm phenol, the rates in the alginate bead bioreactor are (7.3 to 8.1 mg phenol/h · g dry biomass) on an average 5.5 times the corresponding rates in the membrane bioreactor (2.18 to 1.03 mg phenol/h · g dry biomass).In continuous feed mode the steady state degradation rates in the membrane bioreactor are one to two orders of magnitude higher than the alginate bead bioreactor below 150 ppm inlet phenol concentration. At an inlet concentration around 250 ppm phenol the rates are comparable. Above 500 ppm of phenol the rates in the alginate bioreactor are an order of magnitude high than the membrane bioreactor.Due to substrate inhibition, and its inability to sustain a high biomass concentration, the membrane bioreactor shows poor efficiencies at phenol concentrations above 250 ppm. At low phenol concentrations the apparent reaction rates in the alginate bead bioreactor decrease due to the diffusional resistance of the gel matrix, while biodegradation rates in the membrane bioreactor remain high due to essentially no external diffusional resistance.Results indicate that a combined reactor system can be more effective for bioremediation than either separate or attached microbial reactors.

Biodegradation of benzene and a BTX mixture using immobilized activated sludge

Abstract Aerobic biodegradation was studied using activated sludge immobiized in calcium alginate gel. Hydrogen peroxide provided the dissolved oxygen source in a recirculation reactor that was operated batchwise and continuously. Responses to changes in benzene concentrations, flow rates, and biomass loadings were measured. Sixty percent of the benzene was biologically degraded in batch tests after 24 h using an initial concentration of 100 mg/L. A residence time of 17.14 h was required to biologically reduce benzene concentrations from 600 ppm to below the detection limit (1 ppm) during continuous operation. The system was modeled using Monod kinetics for substrate utilization. The apparent km values changed with biomass loadings, but were independent of the initial benzene concentrations. The aromatic species in BTX mixtures (i.e., benzene, toluene and o‐, m‐ and p‐xylene) can all be degraded at the same time.

Towards an on-line biochemical oxygen demand analyser

A simple, and effective tool to measure BOD with a 98% correlation to theoretical BOD values has been developed using a technique of continuous short term measurements of O2 consumption rates. Measurement times are in the range of 5 to 10 h depending on the initial BOD, instead of 5 days required in the conventional BOD5 analysis. A bioreactor containing calcium alginate entrapped activated sludge microorganisms was used with phenol and hydroxybutyric acid (HBA) as model substrates.

A spiral bioreactor for removal and recovery of metals from aqueous wastes

Microorganisms from activated sludge were immobilized on a spiral reactor fabricated from a PVC-Silica based biosupport, and used to biosorb lead from synthetic waste streams. Biosorption parameters determined for lead from Freundlich isotherms indicate that 89% of the binding capacity of that observed in suspended cell system is retained in the spiral bioreactor. More than 87% of biosorbed lead was recovered each time after breakthrough by dilute acid washing between the pH of 2 to 2.5. No significant changes in the biosorption pattern was observed over several adsorption and recovery cycles that were conducted. The spiral bioreactor is better than suspended cell systems because it provides comparable surface area as that in the suspended cell system in an immobilized (small volume) form. It is also better than the entrapped microbial cell reactors because it eliminates mass transfer resistance across the external matrix, which may reduce the inherent binding capacity.

A Polymeric Membrane Reactor for Biodegradation of Phenol in Wastewater

Microorganisms from activated sludge were immobilized by at tachment to microporous plastic sheets [MPS™]. Biodegradation of phenol was accomplished by pumping a phenol solution through a reactor containing microorganisms attached to the MPS™ sheet. Biodegradation was the pri mary removal mechanism, with only 5% removal by abiotic means. Experi ments were conducted in batch recirculation flow and continuous flow con figurations. In batch mode biodegradation rates showed a strong dependency on recirculation flow rates. In continuous mode, a residence time of 1.4 hours was needed for 50% conversion at steady state. Consumption of phenol and dis solved oxygen showed parallel trends throughout the experiments.