Abstract: This research was to investigate the performance of a low biodegradable wastewater by means of phytotreatment prior to biological oxidation process. Four biodegradability quotients of wastewater were initially ranging from 0.05 and 0.11 and were exposed in simulated collection pond. Weekly performance on biodegradability quotients were shown to decrease linearly without phytointervension, suggesting collected wastewater became biostabilized. However, the hyacinth treatment demonstrated that the quotients were increased exponentially ranging from 3 times of the highest initial quotient and 10 times of the lowest initial quotient. The hyacinth treatment performance on increasing biodegradability were dependent on the initial COD concentration. As a result for the initial COD of less than 500 mg L-1 brought about the increasing rate and the doubling time were about 150% faster rate and 200% shorter period, respectively than those for the initial COD of more than 500 mg L-1.