A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resource and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1997

A colossal concern to the water supply has been occurred by eutrophication of water source. Algae are the great precursor to create this extensive problem. The present study has aimed to assess the troubles caused by green algae Oocystis sp. in the conventional water treatment process of coagulation and flocculation. This process was used to evaluate the removal efficiency and to understand the bad effect caused by algae. The present of algae were found that the optimum dose of alum has increased from 100 mg/I to 200 mg/I. and the turbidity removal has decreased from 98.7% to 96% with the increase of chlorophyll-a from 0 to 0.15 mg/I in sample water. Residual concentration of aluminum in drinking water treatment by the solubility diagram based on known chemical equilibrium reaction with coagulant can not be used directly due to various reasons. Practical diagrams, showing the range of residual aluminum as function of pH and chlorophyll-a were derived from various jar test data, show that the high chlorophyll a caused more residual aluminum in supernatant and the least residual aluminum in the alkaline condition. Present of chlorophyll-a which was used as the indicator of biomass also has highly influenced on the floe characteristics of the clay suspension. The observation was found that the settling velocity of clay floe was faster in the low concentration of chlorophyll-a in the surface water when coagulation and flocculation take place. Algae seem to interfere the stabilization of the clay particle.