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Start date: 2020Subject: search.filters.subject.570Subject: search.filters.subject.333.7

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    ItemOpen Access
    A method for 3D printing bio-cemented spatial structures using sand and urease active calcium carbonate powder
    (2020) Nething, Christoph; Smirnova, Maya; Gröning, Janosch A. D.; Haase, Walter; Stolz, Andreas; Sobek, Werner
    The substitution of Portland cement with microbially based bio-cement for the production of construction materials is an emerging sustainable technology. Bio-cemented building components such as bricks have been fabricated in molds, where bacteria-containing aggregates solidify when treated with a cementation solution. Thisrestricts component size due to the limitedfluid penetration depth and narrows options for component customization. The use of additive manufacturing technologies has the potential to overcome those limitations and toexpand the range of bio-cement applications. In the present work an automated process for the production ofspatial structures has been developed, in which sand and urease active calcium carbonate powder were selectively deposited within a print volumeand treatedwith a cementation solution.This method provided conditionsfor calcite precipitation in the powder-containing areas, whereas areas of pure sand served as removable supportstructure allowing improvedfluid exchange. The 3D printed structure was geometrically stable and had sharplydefined boundaries. Compressive strength tests on cylindricalspecimens showed thatthe used powder-sandmixwas suitable for the production of high-strength bio-cemented material. The present work demonstrates an application of bio-cement in an additive manufacturing process, that can potentially be used to produce resourceefficient sustainable building components.
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    ItemOpen Access
    Scale-up of gas fermentations : modelling tools for risk minimisation
    (2020) Siebler, Flora
    The reduction of greenhouse gas emissions is a global endeavour supported by society, politics and industry. In recent years, circular economy, reducing the exploitation of fossil energy sources, have increased the demand for new solutions when producing commodities and fine chemicals. Caboxydotrophic fermentations with acetogenic bacteria are potential processes in order to reach these goals. They convert gaseous substrates such as CO, and CO2/H2 mixtures. However, gases as sole substrate are rather challenging, not only in small lab-scales but especially in large-scale. Transferring an efficient fermentation process from experimental to industrial scales often results in unpredictable performance losses. This study presents an in silico concept minimising possible risks in gas fermentations up-scaling. First, the economical feasibility of various fermentation methods is investigated. Then, two computational tools are presented using Clostridium ljungdahlii as model organism and synthesis gas as substrate in a 125 m3 bubble column reactor. The combination of economical investigation with modelling tools show high potential for successful scale-up of gas fermentations. With this concept feasibility, reactor design, operation mode and general risk minimisation can be analysed and specified.