Water from natural springs, lakes or rivers contains numerous substances, from dissolved metals to chlorine, sulfur or nitrogen compounds to organic compounds. The most well-known substances include calcium carbonate, the precursor of calcium deposits, or sodium chloride as a crucial component of salt water, which leads to increased corrosion in metals. For numerous uses of this so-called raw water, the ingredients have to be removed in order to avoid damage to or impairment of systems or process methods. The processing of used water after its use for the manufacture of products plays an equally important role.
Above all in metalworking – for example pickling iron and steel, galvanic coating with zinc for corrosion protection, precious metal for decorative purposes or copper in the field of electrical engineering – more or less large amounts of metal-containing waste water are produced. Intensive wastewater treatment has been state of the art in these areas for more than 50 years.
For some years now, in addition to pure wastewater treatment, the focus has increasingly been on reducing the amount of water used and the amount of wastewater generated for reasons of environmental protection. The aqua plus brand from Böbingen has been a constant in this industrial sector for around 25 years. Especially in the surface treatment and coating of and with metals, aqua plus devices and systems are part of production facilities worldwide. Different technologies are used for this, depending on the water treatment requirements.
Process for water treatment and purification
Membrane technology is a long-established process for removing disruptive components from raw water. Defined porous plastic membranes are used for this. Depending on the pore size, ingredients with certain particle sizes (or the size of ions or dissolved molecules) can pass through these membranes; this process is known in chemistry as diffusion. The diffusion process is intensified by the provision of differently concentrated aqueous solutions on the left and right of the membrane, possibly supplemented by the application of electrical voltage between the two sides of the membrane.
The end result is that defined components can be removed from the raw water. Another important process technology for water treatment is ion exchange. In this case, plastic granulates are used that can bind certain substances. Depending on the acidity of the aqueous solution and the type of ingredients to be removed, different types of ion exchangers are commercially available.
Almost all dissolved metals are bound by ion exchange resins as soon as they come into contact with the metals dissolved in water. In addition, sulfate, nitrate or phosphate, for example, can also be bound and removed from an aqueous solution; these constituents, known as anions, always appear in aqueous solutions as partners of dissolved metals. Ion exchangers have the great advantage that the bound substances are specifically released again in a supplementary operation, the so-called regeneration.
In this way, the bound substances can be specifically removed from a water cycle and passed on for further use (especially the metals) or disposal. The ion exchange resins are then fully functional again for the renewed metal removal process. The classic methods of work-up include the precipitation reactions.
Here dissolved substances are converted into insoluble compounds (e.g. in hydroxides) and converted into a more or less solid state as sludge. Sludge with a high water content can also be converted into a solid mass by filtering with the help of special presses and by drying. In the case of metal-containing sludge, these are often smelted in order to then participate in the material cycle again.