Another experiment was a 3-tank system (Fig. 2). The size of three water tanks was same as those used in the 9-tank system. Total nitrogen concentration in the water was kept at 50 mg/L. The produced water hyacinth was harvested in a similar manner as the 9-tank system and operated from April 2007 to October 2008. Both the 9-tank system and the 3-tank system were independently installed in the green house without direct connection to the existing natural waste treatment system.
The third experiment was a 2-tank system (Fig. 3). The radius of the tanks was 0.9 m and the height was 0.9 m. A similar harvest method as the other two systems was used and these tanks were operated from August 2006 to September 2008. The water supplied to these two tanks was the effluent from the fish growing tanks and it contained approximately 2 mg/L total nitrogen. The second and the third set of experiments were conducted to investigate the difference of biomass production influenced by nitrogen level and growth space. All of the harvested water hyacinth was removed from the tank water surface, allowed to drain to remove the surface water and finally weighed (wet basis).