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

Thesis (M.Eng.) - Asian Institute of Technology, 1987

One set of parallel oxidation ponds was used for comparing ·the treatment efficiency of pond system with and without water hyacinth in full-scale study under similar conditions. Experiments were performed from t he last week of October till the last week of January , 1987. Mean COD loadings to t he systems were 106 kg/(ha .d) and 98 kg/(ha.d) for the hyacinth pond and the free pond respectively. During the period of observation effluent concentrations in the hyacinth pond for hundred percent hyacinth coverage were 9 , 20 , 2 and 0 . 36 mg/L for SS, COD, TKN and TP respectively. The corresponding effluent concentrations in the free pond were 45, 94, 5.6 and 1.2 mg/L for SS, COD, TKN and TP respectively. Mean mass of COD, TKN and TP were removed at 78, 76 and 74. 8% respectively in the hyacinth pond system, whereas in the free pond system, mass COD, TKN and TP were removed at 20, 44.4 and 18.30% respectively . At 100 % hyacinth coverage, mass COD, TKN and TP removed, in the hyacinth pond were, at 84, 79.6 and 79.4% respectively. In the free pond system mass COD, TKN and TP were removed at 24, 44. 8 and 22% respectively . Hyacinth pond showed better performance than the free pond in removing SS, COD, TKN and TP from the wastewater . Laboratory experiments were conducted for comparing the efficiency of aquatic plants namely water hyacinth, water lily and salvinia. The influent loading used were 41 and 86 kg COD/ (ha. d) . Results indicated that hyacinth pond system showed the best performance in removing pollutants followed by salvinia and water lil y for t he applied loadings.