THE ALGAE PROBLEM IN THE NETHERLANDS FROM A WATER-TREATMENT PERSPECTIVE

Surface-water treatment in the Netherlands has received increased atte ntion lately, emphasising the need for recognition, characterisation a nd evaluation of the 'algae problem'. Investigations and analysis carr ied out at five drinking-water production locations in the Netherlands , using surface water (60% of the overall Dutch surface water producti on), show that the most significant problem causing algae are the cyan obacteria. Seasonal blooms of Microcystis aeruginosa and Oscillatoria aghardii force short- and long-term process modifications, with signif icant negative economic effects. Assessment of possible solutions to t he problem indicates that apart from the application of appropriate wa ter-quality management measures, new insights and knowledge on efficie nt (pre-) treatment processes are recognised as essential. Regarding t reatment, the agglomeration (coagulation/flocculation) phase is consid ered to be essential for the removal of algae. It should be correlated with pre-treatment preceding it (application of chemical oxidant/s, a nd/or microstraining), as well as with the applied solid liquid separa tion (pre-) treatment process. Bearing in mind the natural tendency of algae to float, as well as world-wide noted positive references, DAF (dissolved air flotation) emerges as a strong possible solution. Exist ing literature and practice discrepancies support related process rese arch and leave space for possibly emerging theoretical and practical i mprovements. These should be supported with deeper insights into;algae morphology and physiology, known to influence treatment efficiency.