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

Thesis (M.Eng.) - Asian Institute of Technology, 1989

Improvement of the existing water hyacinth system by adding gravel media to remove NH3-N ·from the wastewater was evaluated in this study. The gravel was laid at the bot tom of the tank to provide support to the growth of denitrifying bacteria. Vertical baffles were constructed between width of the tank to avoid flow short circuiting . The system is termed hereafter as water hyacinth- gravel system. The study was conducted in three modes of operation. The mode 1 operation compared the treatment efficiencies of water hyacinth- gravel system with the water hyacinth system without gravel. The results obtained showed that 89.7% of NH3-N was removed in the water hyacinth- gravel system compared to 71.3% in the water-hyacinth system without gravel at the 20 d hydraulic retention time (HRT) . Other water quality parameters were also monitored which showed in a better performance of the water hyacinth-gravel system in treating wastewater than the existing water hyacinth system without gravel. In the mode 2 operation, the water hyacinth-gravel system was operated with effluent recycle. The system with effluent recycle had NH3 -N removal of 48. 496 compared to the the system without recycle which had 34 . 8% of NH3 -N removal. The mode 3 operation determined the effects of increasing the tank length by connecting the 2 water hyacinth-gravel tanks in series. It was found out that about 70% of Nff3-N was removed in the second tank compared to 25% in the first tank at the 5 d HRT. This suggests that nitrification/denitrification occurred effectively in the second tank. Over-all , water hyacinth- gravel system was found to be better in removing NH3 - N than the water hyacinth system without gravel.