2.3. Sequence of wastewater treatment
The original wastewater treatment system comprised of a primary sedimentation tank (T1), a facultative tank (T2), a water hyacinth tank (T3) and a treated effluent tank (T4). The sequence and water sampling points are shown in Fig. 1. The hydraulic residence time (HRT) for T1–T4 was expected to be 1, 7, 27 and 1 day, respectively.
The water surfaces of T1 and T2 were almost completely covered with the plastic netting bags of the sliced water hyacinth stalks. Water hyacinth with an average height of about 30 cm (including leaves and stalk) were placed in T3 in late March 2008. They covered less than 1/10 of the water surface, and did not grow well until June. By mid-July, the plants reached a maximum height of about 70 cm forming a dense mat over the entire water surface in the tank.