Seperation
| Various separation technologies are applied both for pre-treatment, for tertiary water treatment to higher quality or to treat saline or polluted water sources. Strainers, Cartridge and Bag Filters (Pre-treatment) Downstream of the clarifiers and filters, but prior to tertiary treatment (membrane separation plants), it is common practice to install further filters to remove oils and finer particles before further treatment. Skimming (Pre-treatment) Floating materials such as oil, scum and foam collect on the surface of water treatment basins and, if not removed, can adversely affect the operation of a water treatment system. Mechanical or hydraulic skimming is used to remove these components from the surface of the water. Dissolved Air Floatation (Pre-treatment) Dissolved air floatation (DAF) is a unit process used to separate solid particles or dissimilar liquid droplets from a liquid phase. The process uses fine gas (mostly air) bubbles that are introduced into the liquid phase and become attached to the particles. As a result of the gas buoyancy, these bubbles rise to the surface with the attached particles, where they are collected using a mechanical sludge scraper (skimming) or by means of hydraulic desludging. DAF is a fast and highly efficient method for removing turbidity, colour, suspended solids and other contaminants from water. Membrane Separation Membrane separation involves advanced filtration systems that operate by introducing the feed stream, under pressure, over the membrane surface in a controlled flow path. Reject materials remain on the membrane surface and are flushed away. Membranes are manufactured with various rejection specifications for different applications. WSSA masters membrane technology through Proxa. Microfiltration (MF) Microfiltration is not affected by the osmotic pressure of the feed and is used for the removal of suspended solids and colloidal matter, as well as bacteria and viruses. This process is often used as pre-treatment to other membrane processes. Ultra Filtration (UF) Ultra filtration is not affected by osmotic pressures of the feed and is used in the purification of surface water contaminated with mainly bacteria, viruses and colloidal material. The process is also increasingly being used as pre-treatment for reverse osmosis to limit fouling and reduce operating costs. Nanofiltration (NF) Nanofiltration is a form of high pressure membrane filtration that differs from reverse osmosis in that it has a more open pore structure and removes multi-valent salts such as sulphate, calcium and magnesium in preference to monovalent salts such as sodium chloride. Nanofiltration is frequently applied in colour removal, softening and advanced separation processes. It is also used to produce potable water from sea or brackish water, in water softening processes, and in the removal of specific dissolved contaminants such as pesticides and natural organic matter. Reverse Osmosis (RO) This process is used to remove salts from water. Typically 97% to 99% of inorganic salts are removed by RO membranes, making the process popular for wastewater recovery, and the production of high-purity potable water from sea or brackish water. |
