Quantitative Determination of Glucose Transfer Between Cocurrent Laminar Water Streams in a H-Shaped Microchannel

To explore the applicability of a laminar fluid diffusion interface (LFDI) for the controlled feeding of microbioreactors, glucose diffusion experiments were carried out in a rounded H-shaped microstructure etched in a glass substrate. The diffusion channel of the microstructure had a length of 4 mm and a depth of 50 μm with a trapezoidal cross section with a width of 100 μm at the bottom and 200 μm at the surface of the channel. The microchannel was operated at residence times of less than 1 s ensuring high-mass-transfer rates. It was confirmed, both by microscopic observations as well as computational fluid dynamics (CFD) studies that the flow characteristics in the microchannel were fully laminar. Special attention was paid to flow splitting at the end of the channel, because the CFD simulations indicated that the performance of the device was sensitive to unequal flow splitting. The difference in outflow volume of the two streams was measured to be small (1.25% ± 0.6%). The measured glucose concentration in both exit ports at a fixed residence time was found to be stable in time and reproducible in multiple experiments. CFD simulation was shown to be a powerful tool for estimating the mass transfer in the LFDI, even at very short residence times. The results obtained in this work show the applicability of LFDI for the controlled diffusive supply of a solute to a water stream, with as possible application substrate and/or precursor feeding to microreactors

Influence of filter age on Fe, Mn and NH4+ removal in dual media rapid sand filters used for drinking water production

Rapid sand filtration is a common method for removal of iron (Fe), manganese (Mn) and ammonium (NH4+) from anoxic groundwaters used for drinking water production. In this study, we combine geochemical and microbiological data to assess how filter age influences Fe, Mn and NH4+ removal in dual media filters, consisting of anthracite overlying quartz sand, that have been in operation for between ∼2 months and ∼11 years. We show that the depth where dissolved Fe and Mn removal occurs is reflected in the filter medium coatings, with ferrihydrite forming in the anthracite in the top of the filters ( 1 m). Removal of NH4+ occurs through nitrification in both the anthracite and sand and is the key driver of oxygen loss. Removal of Fe is independent of filter age and is always efficient (> 97% removal). In contrast, for Mn, the removal efficiency varies with filter age, ranging from 9 to 28% at ∼2–3 months after filter replacement to 100% after 8 months. After 11 years, removal reduces to 60–80%. The lack of Mn removal in the youngest filters (at 2–3 months) is likely the result of a relatively low abundance of mineral coatings that adsorb Mn2+ and provide surfaces for the establishment of a microbial community. 16S rRNA gene amplicon sequencing shows that Gallionella, which are known Fe2+ oxidizers, are present after 2 months, yet Fe2+ removal is mostly chemical. Efficient NH4+ removal (> 90%) establishes within 3 months of operation but leakage occurs upon high NH4+loading (> 160 µM). Two-step nitrification by Nitrosomonas and Candidatus Nitrotoga is likely the most important NH4+ removal mechanism in younger filters during ripening (2 months), after which complete ammonia oxidation by Nitrospira and canonical two-step nitrification occur simultaneously in older filters. Our results highlight the strong effect of filter age on especially Mn2+but also NH4+ removal. We show that ageing of filter medium leads to the development of thick coatings, which we hypothesize leads to preferential flow, and breakthrough of Mn2+. Use of age-specific flow rates may increase the contact time with the filter medium in older filters and improve Mn2+ and NH4+ removal

Fumaric acid production by fermentation

The potential of fumaric acid as a raw material in the polymer industry and the increment of cost of petroleum-based fumaric acid raises interest in fermentation processes for production of this compound from renewable resources. Although the chemical process yields 112% w/w fumaric acid from maleic anhydride and the fermentation process yields only 85% w/w from glucose, the latter raw material is three times cheaper. Besides, the fermentation fixes CO2. Production of fumaric acid by Rhizopus species and the involved metabolic pathways are reviewed. Submerged fermentation systems coupled with product recovery techniques seem to have achieved economically attractive yields and productivities. Future prospects for improvement of fumaric acid production include metabolic engineering approaches to achieve low pH fermentations

Studies in Delft of the thermodynamics of life

A review with 6 refs. on research done at the Tech. University at Delft and the Swiss Federal Institute of Technol. at Lausanne on the thermodn. of complex bioprocesses, esp. thermodn. effects on proteins. [on SciFinder (R)