Stirred anaerobic sequencing batch reactor containing immobilized biomass: a behavior study when submitted to different fill times.

The effect of the filling stage on the behavior of a mechanically stirred anaerobic sequencing batch reactor containing biomass immobilized on 1 cm polyurethane foam cubes was investigated. The reactor was made of acrylic with a capacity of 6.3 L, treating per cycle 2.5 L synthetic low-strength wastewater with a concentration of 500 mgCOD/L, at 30+/-1 degrees C. Eight-hour cycles (tC) and agitation of 500 rpm were utilized. At the beginning of each cycle 60% of the wastewater volume was treated, sufficient to completely cover the bed. The remaining volume was added at different fill times (tF) of 10, 120, 240, 260 and 480 min. The results obtained showed that ratios of tF/tC < or = 0.5 enabled organic matter removal higher than 75% and 70% for filtered and non-filtered samples, respectively. Ratios of tF/tC > 0.5, despite operation stability, resulted in loss of efficiency and formation of viscous material, similar to extra-cellular polymeric substances.

Influence of agitation rate on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass.

The present work reports on the influence of the mechanical agitation rates on the performance of a stirred anaerobic sequencing batch reactor containing immobilized biomass on polyurethane foam, as inert support, treating synthetic domestic wastewater. The reactor was operated at 30 degrees C and an 8-hour cycle was used to treat approximately 0.5 L of the synthetic substrate with a COD concentration of nearly 500 mg/L. The studied agitation rates ranged from no agitation to 750 rpm. The system attained non-filtered substrate removal efficiency greater than 83% when agitation was employed. A very short start-up period and good solid retention could be observed. The use of agitation increased the efficiency of the reactor and enabled reduction of the total cycle time. An empirical equation and a first-order kinetic model are proposed to analyze the influence of agitation rates on the reactor's performance.

Anaerobic sequencing batch reactors for wastewater treatment: a developing technology.

This paper describes and discusses the main problems related to anaerobic batch and fed-batch processes for wastewater treatment. A critical analysis of the literature evaluated the industrial application viability and proposed alternatives to improve operation and control of this system. Two approaches were presented in order to make this anaerobic discontinuous process feasible for industrial application: (1) optimization of the operating procedures in reactors containing self-immobilized sludge as granules, and (2) design of bioreactors with inert support media for biomass immobilization.

Ethanol yields during the feeding phase in fed-batch fermentation of sugar-cane blackstrap molasses.

The efficiency of ethanol yield increased from 61% to 88% of the theoretical value as the filling-up time was approached in fed-batch fermentation with Saccharomyces cerevisiae. Temporary accumulation of ethanol within the yeast cells may explain the above variation.

A general equation for the evaluation of the error that affects the value of the maximum specific growth rate.

A general equation is proposed to evaluate the absolute error that affects the maximum specific growth rate calculated from batch or continuous experiments. This error depends on the relative errors of the cell concentration measurements and on the duration of the test.

Batch ethanol fermentation of molasses: a correlation between the time necessary to complete the fermentation and the initial concentrations of sugar and yeast cells.

Batch fermentations of sugar-cane blackstrap molasses to ethanol, using pressed yeast as inoculum, demonstrated an exponential relationship between the time necessary to complete the fermentation and the initial concentrations of sugar and yeast cells. The parameters of the derived exponential equations depended on the experimental conditions.

Semi-continuous lactic fermentation of whey by Lactobacillus bulgaricus.

Semi-continuous tests of lactic fermentation of whey by Lactobacillus buigaricus were carried out using a mixture of hydrolysed milk and vitamins. The volume of the Inoculum varied from 20% to 50% of the reactor working volume. A Monod-like equation correlates the lactic acid productivity and the volume fraction of inoculum.

Invertase activity of intact cells of Saccharomyces cerevisiae growing on sugarcane molasses. II. Unsteady-state continuous-culture tests.

During unsteady-state continuous culture of Saccharomyces cerevisiae on sugarcane blackstrap molasses, the invertase activity of the intact yeast cells oscillated. Disturbances were produced by changing medium composition, air rate, impeller speed, and dilution rate. The influence of the oxygen supply rate and of the dilution rate on the invertase activity depend on the medium composition. The highest invertase activity was obtained when, after a steady-state attained using unsupplemented culture medium, nutrients were added to the feeding mash. A Monod-like equation seems to be the best representation of the correlation between the specific rate of reducing sugars consumption and the specific rate of nonreducing sugar hydrolysis by the yeast cells.

Kinetics of ethanol production during the reactor feeding phase in constant feb-batch fermentation of molasses.

During the fermentor feeding phase in constant fed-batch ethanol fermentation of molasses, the ethanol production rates are constant and are correlated to the sugar feeding rates by a Monod-like equation. The parameters of this Monod-like correlation depend on the sugars concentration of the feeding mash. A model is proposed to explain the constancy of the ethanol production rate experimentally observed. From the Monod-like correlation it is possible to evaluate the maximum value of the mash feeding rate to be used in order to have a completely fermented medium just at the end of the feeding phase.

Invertase activity of intact cells of Saccharomyces cerevisiae growing on sugar cane molasses. I. Steady-state continuous culture tests.

During the steady-state continuous culture of Saccharomyces cerevisiae on sugar cane blackstrap molasses under different experimental conditions, oscillatory variations of the invertase activity of the intact yeast cells were observed. The continuous morphological changes of the cells wall and of the periplasmic space affecting the interaction between invertase and sucrose molecules could be responsible by the observed oscillatory phenomena. The average invertase activity at the steady state is linearly correlated to the cell's growth rate.

A generalized kinetic model for the study of microbial growth.

The following general equation is proposed to represent the kinetics of microbial growth \documentclass{article}\pagestyle{empty}\begin{document}$$\phi (dR/dt) + \psi R + X = 0$$\end{document}, where phi and psi depend on several parameters of the fermenting system. The values of phi and psi were calculated based on results obtained in a batch lactic acid fermentation, a batch cultivation of yeast on diesel oil, and a continuous cultivation of yeast on sugarcane molasses.

Measurement of invertase activity of cells of Saccharomyces cerevisiae.

The determination of the invertase activity of intact yeast cells presents a critical point, that is, the blockage of the enzyme action at a given moment. In this paper seven blockage methods were compared: the addition of 0.010 M sodium hydroxide solution, addition of 0.010 M sodium carbonate solution, addition of 0.010 M sodium carbonate solution followed by centrifugation (9750g; 10 min), immersion of the reacting mixture in a boiling water bath, immersion of the mixture in a -15 degrees C bath, filtration through a Millipore membrane, and addition of the first Somogyi's reagent followed by immersion in a boiling water bath. Only the last two methods lead to a rapid and effective blockage of the invertase activity.

Some observations on oscillatory changes in the growth rate of Saccharomyces cerevisiae in aerobic continuous undisturbed culture.

Oscillatory changes in the growth rate were observed in undisturbed continuous culture of Saccharomyces cerevisiae on sugar-cane molasses media when nitrogen sources (2.56 to 6.17 g/liter of ammonium sulfate or 1.22 g/liter of urea) were added to the feeding mash and when the air rate was 1.3 to 1.6 v/v/m. The oscillations were not affected by the addition of yeast extract. The suppression of the nitrogen source during the continous test leads to a nonoscillatory transient state. No oscillations occured at all when no nitrogen source was added to the medium and/or the air rate was equal to zero or equal to about 3.3 v/v/m. The oscillatory responses of the system were affected by a previous anaerobic continuous cultivation of the yeast.

Microwave drying of microorganisms: I. Influence of the microwave energy and of the sample thickness on the drying of yeast.

The use of microwave energy for the rapid drying of yeasts is described. The influences of the microwave energy and of the sample thickness are studied. The advantages of the method over the conventional drying techniques are presented.