A system for accurate on-line measurement of total gas consumption or production rates in microbioreactors

A system has been developed, based on pressure controlled gas pumping, for accurate measurement of total gas consumption or production rates in the nmol/min range, applicable for on-line monitoring of bioconversions in microbioreactors. The system was validated by carrying out a bioconversion with known stoichiometric relation between gas consumption and substrate conversion, that is, the enzymatic oxidation of glucose to gluconic acid. The reaction was carried out in a stirred microreactor with a working volume of 100 μL, whereby the oxygen consumption was monitored on-line. Subsequently the system was applied to determine the oxygen transfer capacity of the microbioreactor. The dissolved oxygen concentration was measured with an optical dissolved oxygen sensor, which was integrated near the bottom of the reactor. Different stirrer sizes and geometries were investigated for their effect on the mass transfer of oxygen. A maximal k_La of 156±10 h⁻¹, allowing a maximal O₂-transfer rate up to 50 mmol O₂/L/h, was reached which is sufficient to grow cells aerobically in (fed-)batch mode at relatively high biomass concentrations.     

The Hagen-Poiseuille pump for parallel fed-batch cultivations in microbioreactors

We developed and applied a micropump for liquid flows of 0-150 nL/min. The operating principle of this pump is based on the Hagen-Poiseuille law. The main advantages of this pump are that an accurate continuous flow rate can be achieved, it is cheap to manufacture, easy to parallelize and easy to integrate in microtiter plates. Experiments at different flow rates showed that the flow rate remained stable in time and the measured flow rates corresponded very well to the Hagen-Poiseuille law. The applicability of the pump for reproducible feeding of microbioreactors was shown in a fed-batch system with a simple chemical reaction. Thereby the Hagen-Poiseuille pump was connected to a microbioreactor with a working volume of 100 μL. The microreactor was filled with a H₂SO₄ solution which was fed with a Na₂CO₃ solution at a constant rate, while measuring the CO₂ release on-line. This resulted in a stable CO₂ production rate. Subsequently, the pump was successful applied to carry out anaerobic fed-batch fermentations of Saccharomyces cerevisiae in the microreactor system for periods up to 20 h.     

Measuring and modeling adsorption of PAHs to carbon nanotubes over a six order of magnitude wide concentration range

Understanding the interactions between organic contaminants and carbon nanomaterials is essential for evaluating the materials' potential environmental impact and their application as sorbent. Although a great deal of work has been published in the past years, data are still limited in terms of compounds, concentrations, and conditions investigated. We applied a passive sampling method employing polyoxymethylene (POM-SPE) to gain a better understanding of the interactions between polycyclic aromatic hydrocarbons (PAHs) and multiwalled carbon nanotubes (CNTs) over a 6 orders of magnitude wide concentration range. In the low-concentration range (pg-ng L(-1)), sorption of phenanthrene and pyrene was linear on a nonlogarithmic scale. Here, sorption could thus be described using a single sorption coefficient. Isotherm fits over the entire concentration range showed that (i) monolayer sorption models described the data very well, and (ii) the CNTs sorption capacity was directly related to their surface area. Sorption coefficients for 13 PAHs (11 of which have not been reported to date) were also measured at environmentally relevant low concentrations. No competition seemed to occur in the low-concentration range and sorption affinity was directly related to the solubility of the subcooled liquid of the compounds.     

UV absorbance dependent toxicity of acridine to the marine diatom Phaeodactylum tricornutum

The present study seeks quantitative measures for photoenhanced toxicity under natural light regimes by comparing the effects of an aromatic compound under natural and laboratory light. To this purpose, the influence of light irradiance and spectral composition on the extent of photoenhanced toxicity of acridine, a three-ringed azaarene, to the marine diatom Phaeodactylum tricornutum was analyzed. Under laboratory light containing ultraviolet radiation (UV), the 72-h EC50 growth value for acridine was 1.55 microM. Under natural light, a 72-h EC50 value for acridine below the lowest test concentration (0.44 microM) was observed. Under both laboratory and natural light, the toxicity of acridine was equally enhanced by total UV (UV-A and UV-B) and UV-A radiation, while in the absence of UV no enhancement of toxicity was observed. Hence, the UV-A region of light was dominant in the photoenhanced toxicity of acridine to P. tricornutum, in accordance with its absorption spectrum in the UV-A region. Therefore, the total amount of UV radiation absorbed by aqueous acridine was calculated for each separate treatment. The amount of UV absorbed by acridine effectively described the effect of acridine on the growth of P. tricornutum in a dose-response-dependent manner. It is concluded that photoenhanced toxicity of aromatic compounds expressed as a function of the actually absorbed UV may circumvent some of the variability between studies using different concentrations of the phototoxic compounds and light sources. The UV quantity absorbed by these compounds allows a comparison with the absorption characteristics of natural waters and, thus, is a key parameter to determine the role of photoenhanced toxicity in water.     

The influence of task variation on manifestation of fatigue is ambiguous – a literature review

Task variation has been proposed to reduce shoulder fatigue resulting from repetitive hand–arm tasks. This review analyses the effect of task variation, both ‘temporal (i.e. change of work–rest ratio)’ and ‘activity (i.e. job rotation)’ variation, on physiological responses, endurance time (ET) and subjective feelings. Pubmed was searched and complemented with references from selected articles, resulting in 17 articles. Temporal variation had some positive effects on the objective parameters, as blood pressure decreased and ET increased, and on the subjective feelings, as perceived discomfort decreased. The observed findings of activity variation showed both positive and negative effects of increased activity variation, while hardly any effects were found on electromyography manifestations of fatigue. In conclusion, the evidence for positive effects of increasing the level of variation is scarce. The number of studies on variation is limited, while in most studies the findings were not controlled for the amount or intensity of work.