Third Purification Stage

Various methods for further Sewage Purification for the purpose of separating out substances which pose a problem (e.g. Phosphates, salts, Heavy Metals) and which are not dealt with by the mechanical and Biological Purification of Sewage. Phosphates, for instance, can be precipitated out by the use of precipitating agents (e.g. iron chloride). Nitrates can be removed by Denitrification. Active charcoal filters can be used to remove substances which do not readily decompose or which are unable to decompose from the water. Third purification stages are extremely costintensive and are accordingly only used as a general rule where this is absolutely necessary due to the special nature of the pollution of the waste water or the type of Receiving Body.