BOOK OF ABSTRACTS 59 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Tuesday, 25 August 2026 / Hall B+C Technologies and Applications SL23 Precipitation of Carbonates Induced by Anoxigenic Phototrophic Sulfur Bacteria for the Capture of Carbon Dioxide Marawit Tesfa1,2*, R. Todor1, M. Carrier1, S. Dubos1, M. Peyre-Lavigne1, L. Shirokova2, M. Sperandio1, L. Menjot, A. Karen O.S. Pokrovsky2, C. Dumas1 1 TBI, Université de Toulouse, CNRS, INRAE, INSA Toulouse, France. 2 Géosciences Environnement Toulouse (GET) – Research Institute for Development [IRD]: Toulouse University, CNRS, Toulouse, France * Corresponding author: marawittesfa.research@yahoo.com To reduce atmospheric carbon (CO2) level, the presented study aims to understand the biological processes that capture CO2 by calcium carbonate precipitation (CaCO3). Two biological mechanisms precipitating carbonates occur naturally [1]: (i) an active mechanism, where bacteria precipitate carbonates thanks to their metabolism and (ii) a passive mechanism, where microorganisms change the chemical environment by increasing the pH and/ or producing exopolymers, sequentially inducing precipitation. In the presented study, the precipitation induced by anoxygenic phototrophic sulfur bacteria (APSB) was studied, pure cultures of Allochromatium Vinosum as a model microorganism. To understand this biologically induced precipitation, we attempted to reproduce the chemical environment in a lab-controlled reactor which allowed to characterize the nature of precipitated minerals, quantify their yield and rates of formation to deduce their carbon capturing capacities. These experiments were conducted in small batch and semicontinuous bioreactors, containing A. Vinosum with its inorganic growth media (vitamins, trace elements, inorganic energy source, sodium carbonates and chloride calcium). The growth media was a strictly inorganic substrate to prevent heterotrophy. To optimize carbonate precipitation and pinpoint its driving variables, some parameters such as the concentration of bacteria, elements from the growth media (Sulfate, phosphate, Magnesium) and the incubation time were modified. The chemical environment was then monitored (pH, COD, inorganic carbon, ions…) and precipitates were collected subsequently to filtration, weighted and analyzed (XRD, SEM). The incubation variation time displayed two different precipitation phases: rapid, reaching chemical equilibria within one hour, and slow, reaching equilibria within 15 days. We hypothesize the rapid kinetics was chemically driven and the slow kinetics depended on A. Vinosum growth cycle. The presence of phosphate was also shown to induce calcium phosphate
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