What Are Chemical Dosing Tanks And Why Are They Necessary?
Reverse osmosis (RO) is now widely perceived as the ultimate technology for use in the purification of liquids and it has become invaluable for the treatment of water for drinking purposes and in any application in which an exceptionally high degree of purity is required. It is a modification of osmosis, the process used by plants to control the movement of water necessary to maintain their rigid stems and in which pressure applied to a liquid forces it through a semi-permeable membrane, leaving any dissolved solids behind. To extend the useful life of RO membranes, it has become necessary to introduce dosing tanks.
To understand the need for them, it helps to understand a little more about reverse osmosis. To simulate the effect of a plant cell’s wall, man-made systems employ a membrane prepared from a porous polymer, such as cellulose acetate. Its pores are of a size that permits the passage of water molecules, while obstructing anything larger. In effect, this is filtration on a molecular scale. Membranes are costly and easily blocked by particulate matter, so chemical dosing tanks are necessary to form part of a pretreatment regime designed to minimise this risk, which could otherwise lead to membranes becoming clogged, possibly with substances that encourage bacterial growth, in addition to physical damage and reduced efficiency, prompting the need for premature replacement.
While these systems have the potential to operate efficiently for years, such longevity is only possible with the constant monitoring of factors, such as the efficiency of pretreatments performed in chemical dosing tanks and the condition of the raw water supply that is to be treated, while also keeping an eye open for any visible signs that the system’s membranes might be affected by fouling. Many of the constituents of the raw water supply have the potential to cause fouling. Among the more common micro-foulants are iron, metal oxides, and hydroxides, as well as silt, bacteria, and other organic matter. But the greatest risk is the presence of calcium carbonate, the compound responsible for scaling in taps, kettles, and washing machines. Specialised scale inhibitors introduced into chemical dosing tanks provide the necessary pretreatment to prevent deposits of the insoluble compound from causing fouling in RO systems and have replaced the previous use of acid for this purpose.
But before attempting to apply any pretreatment procedures, it will first be necessary to carry out a chemical analysis of the raw water source in order to identify any substances present that might interfere with the operation of a reverse-osmosis system. Once the precise composition is known, any counteragents that may be required can then be added via a system’s chemical dosing tanks in the precise concentrations needed to negate their potential ill effects. Both the food and beverage industry and the manufacturers of pharmaceuticals are heavily dependent on eater of exceptional purity, as are the companies involved in producing the specialised semiconducting materials employed in a plethora of technological applications, such as solar panels. On the domestic front, much of the water we may be drinking in future years is likely to have been produced in a desalination plant. Consequently, the demand for reverse-osmosis systems and the chemical dosing tanks that help increase their operational efficiency has been growing at an unprecedented rate in recent years and there can be little doubt that this demand is set to accelerate in the future.
Chemicals, of course, are not the only potential threat to the efficiency of the reverse-osmosis process. Steps also need to be taken to prevent the growth of microorganisms in components such as pipelines and cartridge filters. On occasion, bacterial growth may even be detected in a system’s chemical dosing tanks. The presence of a visible biofilm is often the clue and the most suitable remedy for bio-fouling, as it is commonly known, will most likely be a multi-stage cleaning programme that alternates between the use of surfactants and non-oxidising biocidal preparations. Reverse osmosis technology has been improving and becoming cheaper as a result of ongoing research and development and it seems likely that the future will see it used in many more applications. That said, for the moment at least, careful monitoring and maintenance of the systems will remain necessary to ensure peak efficiency. For the supply of world-class water treatment solutions, including reverse osmosis and chemical dosing tanks, many South African companies now choose WaterIcon.