The most common technologies for water purification are listed below, as to what technologies to use is quite site-dependent and needs to be considered in the context of customer requirements.
Filtration: Such as multi-media, activated carbon, cartridge filter, micro filter filtrations, etc.
Chemical Conditioning: Chemical conditioning involves the addition into the process stream of the following chemicals, e.g., acid, caustic, sodium sulfite, sodium hypo sulfite and anti-scalents.
Ultrafiltration (UF): UF removes colloids, bacteria and silt and thus reduces SDI to < 2. UF is a cross flow filtration process in that its flow is tangential to the membrane surface and its reject stream will carry away entrained contaminant and keep the membrane in a relatively clean condition.
Reverse Osmosis (RO): Single or double pass RO can effectively remove ions, bacteria, organics and colloids.
Electrodeionization: Removes ions from water through the use of DC current and ion exchange resin, the process needs no regeneration of resins and is a continuous operation.
Electro-deionization is a membrane-separation process different from evaporative techniques, it is different in that it moves dissolved minerals away from the water rather than the other way around.In Electro-deionization process, ions are removed from water by a unique combination of ion exchange resin, ion exchange membranes, and a DC electric current. The ion exchange membranes used in this process is selectively permeable to ions, IX membranes have a fixed charge and are permeable to counter ions but impermeable to co-ions.
These membranes are arranged in alternating layers. A spacer is placed between the cation and the anion membrane to serve as a water channel to direct the flow of the purified product stream and the concentrated brine. The repeating layers of a membrane stack are called a cell pair. A cell pair consists of a cation transfer membrane, a demineralized water spacer, an anion transfer membrane, and a brine flow spacer.
As water flows down the length of the demineralized water spacer, cationic contaminants first attached onto cation exchange resin beads. Under the influence of the electrical field, these ions will migrate through the resin in the direction of the negatively charged cathode. Once the ions reach the cation permeable membrane, they are pulled through into the concentrating stream. An anion permeable membrane on the other side of that stream prevents further migration, effectively trapping the cations in the concentrating stream and allowing them to be flushed to drain. The process for anion removal is analogous, but in the opposite direction, toward the positively charged anode.
Regeneration of the ion exchange resins happens as water splitting occurs when water becomes depleted of ions. The H+ and OH- produced continuously regenerate the resin so resin can capture even weakly ionized species such as CO2 and silica.
Forced / Induced Draft Degasifier:
Removes dissolved gases from the water, CO2 in particular.Vacuum Degasifier: Vacuum Degasifier removes dissolved O2, from water. Vacuum Degasifier typically has tall columns filled with packing or trays and is used to bring a liquid phase in contact with a gas phase for the purpose of removing dissolved gases from the liquid. The liquid runs from the top of the column down around the packing. The packing creates a large surface area for the gas phase to contact the liquid phase.
Membrane Contactor Degasifier:
The membrane contactor utilizes a hydrophobic porous membrane made of PP materials. The membrane material is fabricated in the form of hollow fibers which are bundled together inside a SS outer shell. The hydrophobic porous membrane acts as a support to prevent dispersing of the water while allowing the water to come to contact with the gas phase, Vacuum is applied to reduce the partial pressure of the gas phase. And as the partial pressure of the gases on the gas phase is reduced the concentration of the gases that remain dissolved in the water is reduced in proportion to the partial pressure.
Catalytic Oxygen Removal System: The catalytic oxygen removal system uses a palladium doped anion resin to catalyze the reduction of dissolved oxygen in water or other solutions with hydrogen. The reaction takes place at ambient temperatures and a pressure of approximately 100 psi. The dissolved oxygen level can be reduced in a single pass from the 6.0 to 8.0 ppm range down to less than 10 ppb, 5 ppb or 1 ppb - depending on design.
2H2O + O2 → 2H2O
8gO2 + 1gH2 → 9gH2O
UV TOC Reducer - The 185-nm UV radiation incident on a water stream generates OH- free radicals as illustrated by the following reaction:
H2O + hι(185nm) = H• + OH•
The OH• radicals are responsible for oxidizing the hydrocarbon molecules quantified as TOC into carbon dioxide and water molecules. The OH• radical is one of the most powerful oxidizing agents known to science. The OH• radicals generated in this manner carry out the oxidation of the hydrocarbon compounds.
The 254-nm ( 1 nm = 10-9 m = 10A) UV light (also called the "germicidal light" because of its unique ability to destroy microorganisms) is employed in disinfections and ozone destruction appli-cations. It penetrates the outer cell-wall of the microorganism, passes through the cell-body, reaches the deoxyribonucleic acid (DNA) and alters the genetic materials. The microorganisms are thereby destroyed in a non-chemical manner. UV Sterilizer can effect a 99.9 % kill of microorganism.
UPT has a lot of experiences designing and integrating the above technologies. By applying practical experience to the design and installation, synergistic benefits can be realized and the net result is a cost effective, optimized, reliable, highly efficient and long lasting ultrapure water system.