Omya Advanced Remineralization Process

    The need to develop and improve sustainable desalination processes includes also post treatment respectively remineralization of the desalinated water (permeate/distillate). From a first glance, calcium carbonate based processes are the obvious choice for the remineralization and stabilization of desalinated water. This is since calcium carbonate is itself a source of both hardness and carbonate alkalinity - the two fundamental water qualities that desal-permeate is lacking. Calcium carbonate is one of the most abundant and naturally occurring raw materials, making up just under 4% of the earth’s crust. Furthermore, calcium carbonate is regenerated through the carbonate cycle and precipitation from water bodies making it a truly sustainable alternative for post-treatment processes. 

    “…Omya has been working on processes that use Omyaqua® a micronized calcium carbonate for the remineralization of desalinated water”

    Omya advanced remineralization process 

    Despite these facts, remineralization is often performed using lime based processes. Lime is produced through calcination (burning in a kiln) of calcium carbonate. This calcination process releases large quantities of carbon dioxide to the atmosphere, resulting in a carbon footprint that is 10 times higher than calcium carbonate production and adds to the production cost of the raw material.  Further to this, lime dissolution based processes are known to be complex, fraught with issues of clogging, control over final water quality and produce up to 15% of its own weight in waste and corresponding waste treatment, handling and disposal. Finally lime processes require higher quantities of carbon dioxide for the same alkalinity addition as calcium carbonate. Lime dissolution processes have however, one distinct advantage over the calcite contactor process: calcite chips are for all intents and purposes much less reactive than calcium hydroxide, producing lower concentrated solutions and requiring a much larger footprint for dissolution. This larger footprint translates into greater capital expenditure which in many cases outweighs the advantages of the decreased operational costs. Over the course of the past few years, Omya has been working on processes that use Omyaqua® a micronized calcium carbonate for the remineralization of desalinated water and thereby exploit the technical and economic advantages that calcium carbonate has over lime, but at the same time address the drawbacks of calcite contactors, including its slow reactivity and large footprint required. The result is a new and innovative water stabilization process known as Omya Advanced Remineralization Process (OARP). A process flow diagram of the process is shown below in the Figure. At the heart of the process is the Membrane Calcite Reactor (MCR) – a reactor containing a submerged microfiltration membrane immersed in a suspension of micronized calcium carbonate. The use of modular components provides redundancy in the system, makes the process flexible in operation and allows for easy capacity expansions. Carbon dioxide is added to the calcium carbonate suspension, which in turns reacts to form a calcium bi-carbonate solution. The membrane acts as a barrier between the dissolved and undissolved calcium carbonate enabling a perfectly clear solution to be extracted from the reactor, and therefore ensuring a pristine water quality. This concentrated calcium bi-carbonate solution is then dosed into the desalination permeate to increase both the hardness and alkalinity of the mineral-deficient water. The use of submerged membranes prohibits the introduction of turbidity as seen in the current techniques, whether due to the precipitation of calcium carbonate within lime processes or from the loading of new product into the calcite contactors. The use of Omyaqua® micronized calcium carbonate with its specially engineered properties for rapid dissolution, in combination with the Membrane Calcite Reactor (MCR) allows for the generation of higher concentrations, and much decreased contact times with increased carbon dioxide efficiencies in comparison to calcite contactors. Short contact times also ensures the plant can respond very rapidly to changes in plant flow rate. Furthermore, a major advantage of the OARP process is the absence of generation of any backwash waste water since membrane backwash is made into the Membrane Calcite Reactor. This removes the requirement for backwash waste water treatment and sedimentation systems and thus allows for a zero-waste generating and handling process. 

    Omya International AG