Water purification systems are used to remove harmful chemicals, particles and contaminants from your drinking water. They can be point-of-use or whole house solutions.
Using chlorine in water can create disinfection by-products that are linked to health issues such as liver and kidney damage, nervous system disorders and hardening of the arteries.
Reverse Osmosis
Reverse Osmosis, or RO for short, is a membrane-technology water filtration method that eliminates many contaminants. It gets down to a molecular level and removes chemicals, bacteria, sediments, nitrates and other minerals. It works with city or municipal water as well as private well water as long as it is pretreated for sediment and bacteria to prevent membrane fouling.
This process utilizes the natural tendency of a solvent to move across a semipermeable membrane from an area of higher concentration of solute molecules to an area of lower concentration of solute molecules. This motion is driven by the reduction in Gibbs free energy of the system, which is known as osmotic pressure. The addition of external pressure to reverse the direction of this flow creates the RO process.
Reverse Osmosis systems produce filtered water in stages. The permeate water from the first stage is combined with the permeate water from the second stage to form the final product. The reject or brine water is sent to the drain where it carries away rejected contaminants. A typical RO system is rated at 50 GPD which is enough for the average household.
Microfiltration
Microfiltration (MF) is a physical water treatment process that passes liquid through a membrane with microscopic, pore-sized holes. These pores exclude larger particles and partially dissolved solids, as well as pathogenic organisms like bacteria and protozoa. MF membranes have some of the largest pore sizes among commonly used membrane technologies, and are often used as a pre-treatment step to remove larger contamination from an upstream stream before going on to other more fine-grained processes such as ultrafiltration and nanofiltration.
Low pressure is applied to the solution side of the filtration membrane, which forces the liquid through the filter at a rate faster than diffusion alone would allow. This increases the hydrodynamic permeability of the membrane, and allows smaller molecules to pass through it at a rate proportional to their partial molar volume.
As with other membrane processes, microfiltration can also be prone to fouling, which reduces the effectiveness of the system. To prevent this, regularly scheduled Clean-In-Place is carried out. This involves circulating chemically pre-treated cleaning solutions through the membrane modules, which can be a mixture of acids (H2SO4 or HCl) and oxidizers, or bases (NaOH). The membranes are then rinsed to flush away any residue.
Ultrafiltration
Ultrafiltration is a size-exclusion process that filters out bacteria, viruses and other particles as well as turbidity, organic suspended solids and some (but not all) minerals. Unlike RO, it does not remove Total Dissolved Solids (TDS).
UF can be configured as either a spiral wound membrane or a tubular element known as hollow fiber. The feed water flows through the shell or lumen of the membrane and the membrane pore size determines which molecules can pass and which ones cannot.
PB’s UF systems utilize the revolutionary 7 Bore hollow-fiber membrane that has 7 capillaries in each individual hollow-fiber. This allows the UF membrane to handle higher fluxes and water pressure surges without losing effectiveness, which significantly extends its lifespan over traditional single-bore filtration technologies. It also eliminates the need for a storage tank and produces water on-demand, saving energy costs. Moreover, it can be “flushed” clean using a simple low foam detergent, removing the need for expensive replacement membranes and chemicals like hydrochloric acid or oxalic, sulfuric and nitric acids.
Nanofiltration
Nanofiltration is a relatively new membrane separation process that takes up the upper end of the separation size range between reverse osmosis and ultrafiltration. In addition to its separation capability, it is a highly energy efficient process. The filtration occurs by diffusion of the solvent molecules through the mass of the membrane material, driven by transmembrane pressure and not through the physical holes or pores in the membrane.
As a water purification technology, it rejects certain dissolved salts, including monovalent and divalent ions that cause hardness in the water. It also passes smaller hydrated ions. The removal of these ions and the softening of the water result in low total dissolved solids in the final product.
Pacific Water Technology offers a complete skid mounted nanofiltration system for simultaneous concentration and partial (monovalent ion) demineralization of brackish groundwater to produce potable water. These systems include a continuous antiscalant dosing system to prevent the accumulation of scale and fouling of the membrane.
Activated Carbon
Activated Carbon is the most effective method of removing organic chemicals from water. It is also the most effective in reducing harmful chlorine byproducts (such as trihalomethanes and volatile organic compounds) that can be caused by disinfectants used in treatment. These byproducts are linked to an increased risk of cancer and infant birth defects.
Generally, activated carbon is produced by heating natural coal in the presence of a strong dehydrating agent such as phosphoric acid or zinc chloride paste. This makes the carbon pores larger and improves its adsorption capacity. Activated Carbon can be found in both powdered and granular forms, the latter being the form most commonly used for domestic drinking water filtration systems.
Activated carbon removes many chemicals by attracting them to its positively charged surfaces. These contaminants are then trapped inside the pore structure. In addition, the adsorption process reduces free chlorine to chloride and breaks down chloramines through a slow catalytic reaction to ammonia, nitrogen and chlorine. Carbons capacity for chemical removal depends on a number of factors including molecular weight and concentration, operating temperature and polarity.