Pre-Treatment
| Prior to arriving at the water treatment plant, several screening or pre-treatment options are available to remove not just grit and debris, but also suspended solids, from source water. Various manual and mechanical screens, screws and compactors as well as grit channels or vortex degritters are used for this purpose. Pre-treatment processes include: Clarification Clarification is typically achieved via the processes of settling or flotation during which suspended, colloidal and dissolved matter is largely removed. The process is assisted by the addition of coagulants and/or flocculants to encourage the formation of larger particles, thereby facilitating settlement or flotation. The resultant sludge produced is removed for further treatment. Chemical Coagulation Chemical coagulation in water treatment involves the addition of chemicals to alter the physical state of dissolved and suspended solids. The chemicals used include alum, ferric chloride, ferric sulphate, ferrous sulphate and lime. The destabilised colloids can then be aggregated and removed by sedimentation and/or filtration. Reactions (Precipitation) The removal of specific elements from water is possible via the formation of less soluble salt compounds and the manipulation of process conditions to cause these salts to precipitate. The addition of sodium sulphite facilitates the removal of specific metals from water in the form of metal sulphites. Another example is the removal of sulphates using barium carbonate. |
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| Softening Softening and lime softening are used worldwide as a fundamental purification step in water treatment, mainly for the removal of hardness ions in water. Lime treatment can be used effectively to achieve: * the removal of suspended solids and colloidal matter; * the partial removal of organics; * the precipitation of heavy metals, magnesium and silica; and * a reduction in carbonate alkalinity. |
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