Investigation into struvite precipitation: A commonly encountered problem during fermentations on chemically defined media

Biotechnology and Bioengineering, vol. 121, pp. 1076–1089

Abstract

Abstract Chemically defined mineral media are widely used in bioprocesses, as these show less batch to batch variation compared with complex media. Nonetheless, the recommended media formulations often lead to the formation of precipitants at elevated pH values. These precipitates are insoluble and reduce the availability of macronutrients to the cells, which can result in limiting growth rates and lower productivity. They can also damage equipment by clogging pipes, hoses, and spargers in stirred tank fermenters. In this study, the observed precipitate was analyzed via X‐ray fluorescence spectroscopy and identified as the magnesium ammonium phosphate salt struvite (MgNH 4 PO 4 × 6H 2 O). The solubility of struvite crystals is known to be extremely low, causing the macronutrients magnesium, phosphate, and ammonium to be bound in the struvite crystals. Here, it was shown that struvite precipitates can be redissolved under common fermentation conditions. Furthermore, it was found that the struvite particle size distribution has a significant effect on the dissolution kinetics, which directly affects macronutrient availability. At a certain particle size, struvite crystals rapidly dissolved and provided unlimiting growth conditions. Therefore, struvite formation should be considered during media and bioprocess development, to ensure that the dissolution kinetics of struvite are faster than the growth kinetics.

Authors 8

1. Thomas Steimann Aachen AVT‑Biochemical Engineering

   RWTH Aachen University

   Affiliation as printed

   AVT—Biochemical Engineering RWTH Aachen University Aachen Germany

2. David Wollborn Aachen AVT‑Biochemical Engineering

   RWTH Aachen University

   Affiliation as printed

   AVT—Biochemical Engineering RWTH Aachen University Aachen Germany

3. Florian Röck Aachen AVT‑Biochemical Engineering

   RWTH Aachen University

   Affiliation as printed

   AVT—Biochemical Engineering RWTH Aachen University Aachen Germany

4. Rebekka Horstmann Aachen AVT‑Biochemical Engineering

   RWTH Aachen University

   Affiliation as printed

   AVT—Biochemical Engineering RWTH Aachen University Aachen Germany

5. Elina Schmitt Aachen AVT‑Biochemical Engineering

   RWTH Aachen University

   Affiliation as printed

   AVT—Biochemical Engineering RWTH Aachen University Aachen Germany

6. Jonas Johannes Christ Aachen iAMB-Institute of Applied Microbiology

   RWTH Aachen University

   Affiliation as printed

   iAMB—Institute of Applied Microbiology RWTH Aachen University Aachen Germany

7. Lars M. Blank Aachen iAMB-Institute of Applied Microbiology

   RWTH Aachen University

   Affiliation as printed

   iAMB—Institute of Applied Microbiology RWTH Aachen University Aachen Germany

8. Jochen Büchs corresponding Aachen AVT‑Biochemical Engineering

   RWTH Aachen University

   Affiliation as printed

   AVT—Biochemical Engineering RWTH Aachen University Aachen Germany