A mathematical model for the anaerobic treatment of Baker's yeast effluents

Baker's yeast fermentation produces high strength wastewaters containing high concentrations of organic materials that cannot easily be degraded by biological processes. A two-stage (anaerobic-aerobic) treatment system has been used in order to treat this effluent efficiently. Most of the COD reduction takes place during the anaerobic degradation. The objective of this study was to generate a simple mathematical model for the anaerobic stage. The model, which is based on the elimination of COD, assumes that only three consecutive reactions namely hydrolysis, acidogenesis and methanogenesis are significant. In the laboratory-scale experiments, feed strength was increased from 3600 to 14,000 mg O2 l-1 in a batch reactor. Three reaction rate constants were found as 0.08, 0.004, 0.06 h-1 by analyzing data from the laboratory experiments. The model was tested and found to be congruent with the daily operation data, which were collected from the Pakmaya Baker's Yeast Kocaeli Factory Plant. This plant contains three Upflow Anaerobic Sludge Blanket reactors, which are run in series. The rate constants of the hydrolysis and methanogenesis were similar to the batch experiment case.     

Fetal toxoplasmosis and negative amniocentesis: necessity of an ultrasound follow-up

Prenatal diagnosis of congenital toxoplasmosis relies on the PCR test on amniotic fluid and ultrasound follow-up of the fetus. We report two cases of toxoplasma infection during the first trimester of gestation with a discrepant diagnosis of fetal infection. PCR performed more than four weeks after the estimated date of contamination was negative. Ultrasound follow-up was normal up to the third trimester when major hydrocephalus was detected, leading to pregnancy termination. In both cases, post-mortem examination revealed a diffuse infection with severe brain lesions. These observations confirm the necessity to continue a monthly ultrasound follow-up, even if amniocentesis is negative, in case of fetal toxoplasma infection in pregnancy. Copyright © 2003 John Wiley & Sons, Ltd.     

An experimental and theoretical analysis of the effect of added weight on the energetics and hydrostatic function of the swimbladder of European sea bass (Dicentrarchus labrax)

We conducted experiments to determine the effect of the increasing ultrasonic/radio transmitter weight on the routine metabolic rate of sea bass. We measured the oxygen consumption (MO₂) of fish tagged externally with a dummy transmitter made of a hollow pipe, the weight of which was adjusted with lead to represent in water 0, 1 and 4% (R_tf) of the animal weight. We then developed a theoretical model to estimate, for a given fish size, the range of added weight that fish can compensate for through swimbladder regulation. When R_tfБ%, MO₂ of untagged and tagged fish did not differ significantly. However, when R_tf reached 4%, fish that carried a tag incurred a significant elevation of oxygen consumption, which represented 28% of their total useable power (or metabolic scope). This result strongly supports the view that a high R_tf ratio contributes to a decrease in available metabolic energy by diverting energy from, e.g., growth or swimming performance. A comparison between the tagged fish and the theoretical model reinforced the hypothesis that, when R_tf attained 4%, the increase in metabolic rate reflected a supplementary and costly swimming effort necessary to maintain vertical position. In this condition, the swimbladder cannot regulate the buoyancy of tagged fish.