Reverse Osmosis (RO)
This is a membrane-technology filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side
of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be
“selective,” this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass
Pretreatment is important when working with RO and nanofiltration (NF) membranes due to the nature of their spiral wound design. The material is engineered in
such a fashion as to allow only one-way fl ow through the system. As such, the spiral wound design does not allow for back pulsing with water or air agitation to scour its surface
and remove solids. Since accumulated material cannot be removed from the membrane surface systems, they are highly susceptible to fouling (loss of production capacity). Therefore, pretreatment is a necessity for any RO or NF system. Pretreatment in SWRO systems has four major components: Screening of solids: Solids within the water must be removed and the water treated to prevent fouling of the membranes by fine particle or biological growth, and reduce the risk of damage to high-pressure pump components.
First appearing in oil filter configurations, Cartridge filters have larger surface areas compared to sand filters. This enables cartridge filters to operate for longer periods, as obstructions occur less with bigger filter surfaces. Cartridge filter systems also permit better water flow – thus, placing less strain on the filter pump. These types of filters are also easiest to clean by using a flow of high pressure water from a hose. Cartridge filters require cleaning around four to eight times a year. The filter will primarily catch larger debris while the cartridge is clean. Once the filter’s pores become clogged with larger particles, the buildup will allow the filter to trap smaller debris. The filters are actually made of polyester or some other material that can provide a superfine filtering surface. The pleats are the key to the filter’s operation. The tight pleats, or folds, allow for a large amount of material to be used in a small container. The more material used, the larger the surface area available to capture unwanted dirt or debris in the water. The fabric catches and holds the impurities until you clean or replace the filter. There 3 parts to a cartridge filter construction,end caps (made of plastic) core structure to provide strength (most often PVC) and the pleated media (most often polyester (Remay being the dominant brand).
Oxidizing biocides, such as chlorine, are added to kill bacteria, followed by bisulfi te dosing to deactivate the chlorine, which can destroy a thin-fi lm composite membrane. There are also biofouling inhibitors, which do not kill bacteria, but simply prevent them from growing slime on the membrane surface and plant walls.
(also known as antiscalants) prevent formation of all scales compared to acid, which can only prevent formation of calcium carbonateand calcium phosphate scales. In addition to inhibiting carbonate and phosphate scales, antiscalants inhibit sulfate and fluoride scales, disperse colloids and metal oxides. Despite claims that antiscalants can inhibit silica formation, there is no concrete evidence to prove that silica polymerization can be inhibited by antiscalants. Antiscalants can control acid soluble scales at a fraction of the dosage required to control the same scale using sulfuric acid.