After clarification, water is filtered as a further treatment step to remove any remaining suspended particles and unsettled floc. A large variety of drum, disk, gravity and pressurised filters exist for this purpose, each having their own specific process benefits. These are used in the removal of suspended solids (turbidity), organic and micro-pollutants, heavy metals and other particles not removed by clarification.
While the most common type of filter is a rapid gravity sand filter, a variety of pressure filters can also be used. Media that can be used in filters vary from traditional sand and activated carbon, to multiple layers of various media.
Filtration may be used in the treatment of industrial effluent, process water, municipal wastewater and drinking water. It is also used as a pre-treatment step to membrane processes and desalination of seawater.
Activated carbon filtration
Activated carbon is a porous form of carbon manufactured from carbonaceous raw materials such as coal, coconut shell, peat, and wood. These products are produced in powder, granular and extruded forms. Activated carbon is an adsorbent and is utilised in the purification, separation and concentration of liquids and gases; the recovery of precious metals from ores; as a catalyst support; and in a number of other applications. The granular form of this substance is commonly used for the removal of organic constituents, residual disinfectants and disinfection by-products from water. This product also protects other water treatment units, such as the reverse osmosis membranes and ion exchange resin, from possible damage due to oxidation or organic fouling. The use of activated carbon as a water treatment technique is favoured due to its multifunctional nature and the fact that it adds nothing detrimental to the treated water. It is also ideal for use in the food and beverage industry for decolourising applications.
Veolia South Africa has an established record of success in designing, constructing and commissioning activated carbon plants. With its in-house specialists and access to global resources and knowledge, the company has reference plants in industrial, pharmaceutical, food and beverage, petrochemical, metallurgical and municipal applications.