pH control in biological systems using calcium carbonate

Abstract

Due to its abundance, calcium carbonate (CaCO3) has high potentials as a source of alkalinity for biotechnological applications. The application of CaCO3 in biological systems as neutralizing agent is, however, limited due to potential difficulties in controlling the pH. The objective of the present study was to determine the dominant processes that control the pH in an acid-forming microbial process in the presence of CaCO3. To achieve that, a mathematical model was made with a minimum set of kinetically controlled and equilibrium reactions that was able to reproduce the experimental data of a batch fermentation experiment using finely powdered CaCO3. In the model, thermodynamic equilibrium was assumed for all speciation, complexation and precipitation reactions whereas, rate limited reactions were included for the biological fatty acid production, the mass transfer of CO2 from the liquid phase to the gas phase and the convective transport of CO2 out of the gas phase. The estimated pH-pattern strongly resembled the measured pH, suggesting that the chosen set of kinetically controlled and equilibrium reactions were establishing the experimental pH. A detailed analysis of the reaction system with the aid of the model revealed that the pH establishment was most sensitive to four factors: the mass transfer rate of CO2 to the gas phase, the biological acid production rate, the partial pressure of CO2 and the Ca(+2) concentration in the solution. Individual influences of these factors on the pH were investigated by extrapolating the model to a continuously stirred-tank reactor (CSTR) case. This case study indicates how the pH of a commonly used continuous biotechnological process could be manipulated and adjusted by altering these four factors. Achieving a better insight of the processes controlling the pH of a biological system using CaCO3 as its neutralizing agent can result in broader applications of CaCO3 in biotechnological industries.

Towards a low CO2 emission building material employing bacterial metabolism (1/2): The bacterial system and prototype production

“…The rate of limestone dissolution in situ is proportional to the surface area of the solids in solution as well as the acid production rate, and a large surface area was targeted in the current scenario. This is in contrast to conventional fermentation processes for acid production on a given substrate where calcium carbonate is sometimes added continuously in small amounts as a pH buffer throughout the process [26]. In this case, the goal is to produce a high amount of acid and not to dissolve a high amount of calcium carbonate.…”

Xylose utilization stimulates mitochondrial production of isobutanol and 2-methyl-1-butanol in Saccharomyces cerevisiae

“…Dry autoclaved calcium carbonate (CaCO 3 ) was added to 1% concentration to the resuspended culture to maintain a pH range of approximately 6.2–6.6 during the fermentation. We used CaCO 3 as a pH buffering agent to prevent acidification during fermentation [63, 64]. Samples of 0.3 mL were taken at different time intervals during fermentation (0, 24, 48, 72, 96, 120, 144, 168, and 192 h), and processed for HPLC analysis as described below.…”

Microorganisms meet solid minerals: interactions and biotechnological applications

“…Calcium carbonate is 60-80 % cheaper than the current neutralizing agent sodium carbonate, translating to a reduction in operational costs (Halmann and Steinfeld 2006). In addition, active pH control is not required as the use of calcium carbonate forms a self-regulating pH system in which the pH will not exceed 8.5 due to the nature of calcium carbonate (Salek et al 2015). The pH control is required in lactic acid fermentation processes, as the decrease in pH with increasing lactic acid production will result in feedback inhibition, inhibiting further production of lactic acid by the microorganisms.…”

“…Both calcite and silicate minerals are easily obtainable from natural environments. Calcium carbonate may potentially be used as a neutralizing agent in microbial biotechnological applications such as anaerobic fermentation to produce acetic and lactic acid or in wastewater treatment plants (Salek et al 2015). Calcium carbonate is 60-80 % cheaper than the current neutralizing agent sodium carbonate, translating to a reduction in operational costs (Halmann and Steinfeld 2006).…”