Systematic approaches for an industrially mature halophilic bioprocess to treat residual process brine

Abstract

Residual process brines with high sodium chloride loads, generated during industrial production processes, can serve as a valuable raw material in membrane cell chlor-alkali electrolysis processes to produce chlorine and caustic soda. However, organic impurities should be removed from the brines, to ensure highly efficient chlor-alkali electrolysis processes. Biological treatment solutions for the reduction of organic content offer a sustainable alternative to chemical or physical treatment methods. For the integration of such a biological treatment process into chemical production chains, a suitable microbial system, a robust and efficient bioprocess operation, as well as reliable analytical tools are required.Therefore, the goal of this thesis was to provide an industrial mature bioprocess for the reduction of organic impurities in an industrial residual process brine. The potential of a biotechnological approach should be demonstrated to be integrated in chemical production chains. To do so, a continuous bioprocess using halophilic microorganisms should be characterized and optimized operating conditions should be provided.To demonstrate an industrial mature bioprocess, a 20-liter pilot-scale bioreactor was implemented at an industrial production site and operated continuously for >200 days. Therefore, the robustness, efficiency, and stability of the biological treatment process was proven. Moreover, a novel halophilic mixed culture consisting of three bacterial genera (Halomonas sp., Aliifodinibius sp. and Oceanobacillus sp.) was discovered, which showed excellent degradation properties for the organic contaminants. Furthermore, a reliable HPLC method for the quantification of aromatic impurities in residual process brine feed and bioreactor samples was established. In that way, peak separation and identification was improved, which enables a correct interpretation of the chromatograms. In addition, a non-invasive, and online biomass estimation was developed and successfully established, to serve as a control input for a feed-forward biomass control strategy. Thus, the acceptance to integrate bioprocesses into chemical process chains can be increased. Also, industrial mature bioprocesses require a cost-efficient operation with a minimal nutrient supplementation and an optimized process control. Therefore, critical process parameters, influencing the degradation of organic impurities, were identified, and optimized operating conditions for an efficient process were investigated and proposed.Consequently, the work showed the successful integration of extremophilic bioprocesses into chemical production chains and provides a sustainable alternative to electro-chemical or physical treatment processes. Future investigations could scope the potential of the novel halophilic mixed culture for the use with other residual process brines. Moreover, the technical transfer to production scale would be the final step of the process development.