Coagulation-flocculation Processes in Water/wastewater Treatment: the Application of New Generation of Chemical Reagents

The aim of this paper is to provide an overall description of coagulation-flocculation process and its applications in water and wastewater treatment. The significance of coagulation – flocculation in the area of water and wastewater treatment is reviewed and evaluated, emphasizing on the series of applications employed, including destabilization of colloids, removal of inorganic and organic matter (particulate and/or dissolved), removal of metals and anions (arsenic, phosphate etc), as well as removal of pathogen microorganisms. Furthermore, the latest developments in the coagulation field, regarding the evolution of the coagulation reagents, are also under investigation. The development of simple pre-polymerized coagulants (i.e. polyaluminium chloride,) seems no longer to be sufficient enough. The need for more effective coagulants has lead to the development of new coagulant categories, via the introduction of various additives in the structure of pre-polymerized coagulants. The first effort was reported 15 years ago, suggesting the use of silica in the form of polysilicates for such a purpose. Nowadays, the range of additives has expanded, including organic compounds, such as anionic, cationic or non-ionic polyelectrolytes, leading to new composite coagulants. Overall, it is evident that the tendency in the coagulation field nowadays is the production of modified composite coagulants, which they are becoming more and more complicated, regarding their composition, but also more effective, when compared with the traditionally applied reagents. Key-Words: Coagulation; flocculation; composite coagulants; inorganic additives; organic additives.