Microbiologically induced calcium carbonate precipitation (MICP) is a technique that has received a lot of attention in the field of geotechnology in the last decade. It has the potential to provide a sustainable and ecological alternative to conventional consolidation of minerals, for example by the use of cement. From a variety of microbiological metabolic pathways that can induce calcium carbonate (CaCO₃) precipitation, ureolysis has been established as the most commonly used method. To better understand the mechanisms of MICP and to develop new processes and optimize existing ones based on this understanding, ureolytic MICP is the subject of intensive research. The interplay of biological and civil engineering aspects shows how interdisciplinary research needs to be to advance the potential of this technology. This paper describes and critically discusses, based on current literature, the key influencing factors involved in the cementation of sand by ureolytic MICP. Due to the complexity of MICP, these factors often influence each other, making it essential for researchers from all disciplines to be aware of these factors and its interactions. Furthermore, this paper discusses the opportunities and challenges for future research in this area to provide impetus for studies that can further advance the understanding of MICP.

In the present study, the optimization of the microbiologically induced calcium carbonate precipitation (MICP) to produce biosandstone regarding the compressive strength is shown. For the biosandstone production, quartz sand was treated sequentially with the ureolytic microorganism Sporosarcina pasteurii (ATCC 11859) and a reagent containing urea and calcium chloride. Response surface methodology (RSM) was applied to investigate the influence of urea concentration, calcium chloride concentration and the volume of cell suspension on the compressive strength of produced biosandstone. A central composite design (CCD) was employed, and the resulting experimental data applied to a quadratic model. The statistical significance of the model was verified by experimental data (R² = 0.9305). Optimized values for the concentration of urea and calcium chloride were 1492 mM and 1391 mM. For the volume of cell suspension during treatment 7.47 mL was determined as the optimum. Specimen treated under these conditions achieved a compressive strength of 1877 ± 240 kPa. This is an improvement of 144% over specimen treated with a reagent that is commonly used in literature (1000 mM urea/1000 mM CaCl₂). This protocol allows for a more efficient production of biosandstone in future research regarding MICP.

Microbiologically Induced Calcium Carbonate Precipitation (MICP) is a technology for improving soil characteristics, especially strength, that has been gaining increasing interest in literature during the last few years. Although a lot of influencing factors on the result of MICP are known, particle size and shape of the particles remain poorly understood. While destructive measuring of compressive strength or calcium carbonate content are important for the characterization of samples these methods give no insight into the internal structures and pore networks of the samples. X-ray microcomputed tomography (micro-CT) is a technique that is used to characterize the internals of rocks and to a certain degree MICP-treated soils. However, the impact of filtering and image processing of micro-CT Data depending on the type of MICP sample is poorly described in the literature. In this study, single fractions of local quarry were treated with MICP through the ureolytic microorganism Sporosarcina pasteurii to investigate the influence of particle size distribution on calcium carbonate content, unconfined compressive strength and the reduction of water permeability. Additionally, micro-CT was conducted to obtain insights into the resulting pore system. The impact of the Gauss filter und Non-local means filter on the resulting images and data on the pore network are discussed. The results show that particle size has a significant impact on the result of all tested parameters of biosandstone with lower particle size leading to higher strength and generally higher calcium carbonate content. Micro-CT data showed that the technology is feasible to gain valuable insights into the internal structures of biosandstone but the resolution and signal-to-noise ratio remain challenging, especially for samples with particle sizes smaller than 125 µm.

The cyanobacterium Nostoc sp. BB 92.3. had shown antibacterial activity. A cultivation as biofilm, a self‐forming matrix of cells and extracellular polymeric substances, increased the antibacterial effect. A new photobioreactor system was developed that allows a surface‐associated cultivation of Nostoc sp. as biofilm. High‐density polyethylene carriers operated as a moving bed were selected as surface for biomass immobilization. This system, well established in heterotrophic wastewater treatment, was for the first time used for phototrophic biofilms. The aim was a cultivation on a large scale without inhibiting growth while maximizing immobilization. Cultivation in a small photobioreactor (1.5 L) with different volumetric filling degrees of carriers (13.4%–53.8%) in a batch process achieved immobilization rates of 70%–85% and growth was similar to a no‐carrier‐control. In a larger photobioreactor (65 L) essentially all of the biomass was immobilized on the carriers and the space‐time yield of biomass (0.018 g_{cell dry weight} L⁻¹ day⁻​​​​​​^​1) was competitive compared to phototrophic biofilm cultivations from literature. The use of carriers increased the gas exchange in the reactor by a factor of 2.5–3 but doubled the mixing time. Enriched gassing with carbon dioxide resulted in a short‐term increase in growth rate, but unexpectedly it also adversely changed the growth morphology.

The interdisciplinary nature of science, technology, engineering, and mathematics (STEM) offers the opportunity to implement educational approaches to biotechnology and process engineering issues. The focus should be on the promotion of scientific literacy in contexts relevant to research, industry, and society. This article specifically shows the development of suitable low-level experiments to provide a milestone for the implementation of biotechnological and process engineering issues in STEM education. The experiments show the successful transfer of inquiry-based bioprocess engineering experiments with a Do-It-Yourself (DIY) bioreactor and low-cost sensors. It was possible to achieve comparable trends of process-relevant state variables like mixing time and volumetric mass transfer coefficient (k_La) for the DIY bioreactor in comparison to established commercial systems. Furthermore, microalga Microchloropsis gaditana could be successfully cultivated under different cultivation conditions in the DIY system, and the respective growth curves could be observed. The DIY system is well suited for experimental application in schools and provides a scientifically substantiated basis for data interpretation. The scientific outreach approach and cooperation in a multiprofessional team for the transfer of process engineering questions to education can be evaluated as enriching. Experiments involving educational concepts offer a variety of connecting elements in the curriculum and opportunities to foster scientific literacy.