Biological Units Need Water

We never know the worth of water till the well is dry. 

There is no other ingredient more essential to BU than water. All life as we know it, is water based. Water is essential to life because it is a unique solvent that forms the medium in which to transport many other substances, both organic and inorganic, ionized and nonionized (Section 3.2.4). 

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The unit cost of this technology, including disposal, was approximately 4/m. It is estimated that treatment will have to continue until at least 2020. This has prompted our search for alternative, less expensive techniques which take into account expected changes in mine water chemistry, as well as the decreasing load of contaminants over time. Soon after commissioning the conventional treatment plant, it became clear that a passive or semi-passive biological treatment system would be needed for the long-term. Therefore, WISMUT adopted a two-step approach, in which ... 

Zinc is found only in the + 2 state in biological systems so we need consider only this oxidation level as we examine the mechanism of carbonic anhydrase. A zinc atom is essentially always bound to four or more ligands in carbonic anhydrase, three coordination sites are occupied by the imidazole rings of three histidine residues and an additional coordination site is occupied by a water molecule (or hydroxide ion, depending on pH). Because all of the molecules occupying the coordination sites are neutral, the overall charge on the Zn(His)3 unit remains +2. 

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