COAGULATION OF COLLOIDAL MATERIAL IN SURFACE WATERS - THE ROLE OF NATURAL ORGANIC-MATTER

Organic matter has a great influence over the fate of inorganic colloi ds in surface waters, The chemical nature and structure of natural org anic matter (NOM) will be an important factor in determining whether c olloids will be stabilised or destabilised by NOM. Under environmental ly relevant conditions, the ubiquitous fulvic acids are likely to be r esponsible for coating and imparting a negative charge to colloids, If the adsorbed polyelectrolyte coating produces an increase in absolute surface potential, it will act to stabilise colloids in the water col umn. On the other hand, colloidal organic carbon, especially chain-lik e structures, has been shown to be involved in the aggregation of inor ganic colloids through the formation of bridges. It is highly probable that both adsorption and bridging flocculation are occurring simultan eously in the natural aquatic environment. The importance of each proc ess depends directly on the nature and concentration of organic matter in the system and indirectly on the productivity of the lake, its hyd rological pathways, temporal variations, temperature, etc. The present paper reports such results and emphasises the need to discriminate th e different kinds of NOM. (C) 1997 Elsevier Science B.V.