Wastewater treatment processes dedicated to metal finishing lines are realized by specific Waste Water treatment plants equipped with different purification stages depending on pollution quality.
In many cases Waste Water treatment plant must realize a special purification able to leave a Reuse of the same water treated.
Chemical Phisical Plants are currently used wherever it is necessary to remouve metals and to neutralize or remouve some Anions such Sulphates, Fluorides, Phosphates.
In chemistry, neutralization or neutralisation (see spelling differences), is a chemical reaction in which an acid and a base react quantitatively with each other. In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in solution. The pH of the neutralized solution depends on the acid strength of the reactants. Neutralization is used in many applications.
Metal remouval is currently realized by neutralization in the Ph range of 7-9. They precipitate as sludge in form of Hydroxide : Fe(OH)3, Al(OH)3, Zn(OH)2 and so on.
Main organics found in Metal finishing lines come from oils or dirty fats or Surfactants. The remouval of them is usually realized by addition of Oils adsorbers, special blend of Charcoal.
MST Chemicals developed specialties called PuroSorb able to remouve more than 90% of organics, however, in some cases, it is necessary to realize a drastical Oxidation using a dedicated technology based on strong oxidizing agents and Inorganic Acids.
Waste Water: Pressure vessels with sand or other loose media are widely used in industrial filtration applications. During the cleaning cycle, called “backwash”, the bed is lifted (or “fluidized”) to loosen the filter media and release trapped dirt which is removed in the backwash flow.
Filtration is the most widely used method in the treatment of sludge produced by wastewater treatment. It can consist just in dreinage though sand beds or it can be mechanical under vacuum middle or high pressure conditions which require more sophisticated equipment. Filter presses operate applying very high pressures to the cake (from 5 to 15 bars and sometimes even more). Alternative system such Bend Filter or vaccum filter are not popular because of the final sludges have a superior % of water and this generate automatically higher volume of waste sludges to dump.
Flocculation and sedimentation are widely employed in the purification of drinking water as well as in sewage treatment, storm-water treatment and treatment of industrial wastewater streams. Typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection. Flocculation is used after neutralization of chemical-phisical plants dedicated to metal removing. A dedicated stage is required and the use of special polyelectrolyte substances is necessary.
MST Chemicals developed superior quality flocculants called PuroFloc to be used at very low concentration (5-10 ppm), with strong flocculation cost reduction.
Ultrafiltration (UF) is a variety of membrane filtration in which forces like pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate. This separation process is used in industry and research for purifying and concentrating macromolecular (103 – 106 Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from microfiltration. Both of these separate based on size exclusion or particle capture. It is fundamentally different from membrane gas separation, which separate based on different amounts of absorption and different rates of diffusion. Ultrafiltration membranes are defined by the molecular weight cut-off (MWCO) of the membrane used. Ultrafiltration is applied in cross-flow or dead-end mode. UF is used often before R.O.
Nanofiltration is a relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter. Nanofiltration is also becoming more widely used in food processing applications such as dairy, for simultaneous concentration and partial (monovalent ion) demineralisation.
Reverse Osmosis technology (RO) is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential differences of the solvent, a thermodynamic parameter. Reverse osmosis can remove many types of dissolved and suspended species from water, including bacteria, and is used in both industrial processes and the production of potable water.
MST Chemicals developped special Chemicals for periodical cleaning of membranes, called PurOsmo.
Evaporation is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase that is not saturated with the evaporating substance. The other type of vaporization is boiling, which is characterized by bubbles of saturated vapor forming in the liquid phase.
Steam produced in a boiler is another example of evaporation occurring in a saturated vapor phase.Evaporators are currently used in ZLD plants as final step of a full recycling process.
The water obtained is “distilled” water with approx zero salinity and perfect for reuse.
There are 3 evaporation technology: Heat pump, thermo compression and Multistage system. While Heat pump and Thermocmpression use Electricity, Multistage (double or triple stage) use hot water or steam and can accept any waste calor sorce available recovering energy.In addition Multistage can be equipped with strong advantages with COGENERATION units with approx 70% of energy cost reduction.