NEW METHODS OF WATER PURIFICATION FOR USE IN PHARMACY

Abstract

The principle of membrane separation is widely used for water purification. Water is passed under pressure through a semi-permeable membrane. Membrane technologies differ from filtration. During filtration, particles removed from the water remain on the surface or in the filter media. During membrane filtration, two solutions are formed: filtrate (clean water) and concentrate (a solution with retained substances). The size of the membrane pores determines the size of the particles that are removed. Based on their size, membrane technologies are classified into the following types: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. The size of the membrane pores decreases when moving from microfiltration to reverse osmosis. The membrane offers greater resistance to water flow if the pore size of the membrane is small, requiring higher pressure for filtration. For coarse water purification or preparation for deep purification, microfiltration membranes with a pore size of 0.1-1.0 μm are used, which retain suspensions and colloidal particles that cause water turbidity. Ultrafiltration membranes with a pore size of 0.01‒0.1 μm, which retain trivalent iron, bacteria, viruses, large organic molecules, and colloidal particles, are used for water clarification and disinfection. Such ultrafiltration membranes have an asymmetrical structure, consisting of a porous base that provides mechanical strength and a thin layer of several tens of microns. Ultrafiltration does not retain dissolved salts and does not change the mineral composition of water. It is used in households and industry, providing high-quality purification of water from impurities without the use of chemical reagents. Thanks to this, the use of ultrafiltration is quite promising from an economic and environmental point of view. High-quality clean water is obtained thanks to nanofiltration membranes with a pore size of 0.001‒0.01 microns, which retain dangerous bacteria, viruses, colloidal particles, molecules of heavy metal salts, nitrates, nitrites, and other harmful impurities. Depending on the structure of the membrane, it allows 15-90% of mineral salts to pass through. Pure water from nanofiltration plants is used in the electronic, medical, glass, food, pharmaceutical, and other industries. Reverse osmosis membranes have the smallest pores, which trap all viruses and bacteria, allowing only water molecules, small organic compounds, and light mineral salts to pass through. Reverse osmosis membranes trap about 97‒99 % of dissolved substances. Such membranes are used to obtain high-quality water for bottling, in the food industry, in the production of alcoholic and non-alcoholic beverages, and in seawater desalination. Two-stage reverse osmosis is a good alternative to evaporative distillers and is used in many industries, such as electronics and electroplating. Different types of membranes have different water quality requirements. Microfiltration membranes and ultrafiltration membranes operate in the pH range of 1‒13 and are not affected by chlorine or high suspended solids content. Nanofiltration membranes and reverse osmosis membranes require pretreatment of water, removal of dissolved iron, neutralization of oxidants, and removal of suspended solids. All types of membranes require compliance with operating technologies, despite the high level of automation. They must be periodically flushed and cleaned to avoid irreversible contamination and failure.