A widely used process for remineralization of desalinated water consists of dissolution of calcite particles by flow of acidified desalinated water through a bed packed with millimeter-size calcite particles. An alternative process consists of calcite dissolution by slurry flow of micron-size calcite particles with acidified desalinated water. The objective of this investigation is to provide theoretical models enabling design of remineralization by calcite slurry dissolution with carbonic and sulfuric acids. Extensive experimental results are presented displaying the effects of acid concentration, slurry feed concentration, and dissolution contact time. The experimental data are shown to be in agreement within less than 10% with theoretical predictions based on the simplifying assumption that the slurry consists of uniform particles represented by the surface mean diameter of the powder. Agreement between theory and experiment is improved by 1-8% by taking into account the powder size distribution. Apart from the practical value of this work in providing a hitherto lacking design tool for a novel technology. The paper has the merit of being among the very few publications providing experimental confirmation to the theory describing reaction kinetics in a segregated flow system.

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The well-established Shine-Dalgarno model suggests that translation initiation in bacteria is regulated via base-pairing between ribosomal RNA (rRNA) and mRNA. However, little is currently known about the contribution of such interactions to the rest of the translation process and to the way bacterial transcript evolve. We used novel computational analyses and modelling of 823 bacterial genomes coupled with experiments to demonstrate that rRNA-mRNA interactions are diverse and regulate not only initiation, but all translation steps from pre-initiation to termination across the many bacterial phyla that have the Shine-Dalgarno sequence. As these interactions dictate translation efficiency, they serve as a driving evolutionary force for shaping transcripts in bacteria. We observed selection for strong rRNA-mRNA interactions in regions where such interactions are likely to enhance initiation, regulate early elongation and ensure the fidelity of translation termination. We discovered selection against strong interactions and for intermediate interactions in coding regions and present evidence that these interactions maximize elongation efficiency while also enhancing initiation by ‘guiding’ free ribosomal units to the start codon.ImportancePrevious research has reported the significant influence of rRNA-mRNA interactions mainly in the initiation phase of translation. The results reported in this paper suggest that, in addition to the rRNA-mRNA interactions near the start codon that trigger initiation in bacteria, rRNA-mRNA interactions affect all sub-stages of the translation process (pre-initiation, initiation, elongation, termination). In addition, these interactions affect the way evolutionary forces shape the bacterial transcripts while considering trade-offs between the effects of different interactions across different transcript regions on translation efficacy and efficiency. Due to the centrality of the translation process, these findings are relevant to all biomedical disciplines.