Variation of pH, DO, and SS
The variations of pH, DO, and SS in effluent from each cell in the
WHP are shown in Fig. 2. Algal particles (SS) from the WSP were
removed as they passed through the water hyacinth root mat (Fig. 2
(a)). In particular, algal particles were almost removed in cell #1. The
DO concentration in cell #1 decreased sharply due to endogenous
respiration of algae and probably nitrification and degradation of
organic matters because solar radiation was blocked out by a cover
plant (Fig. 2(b)). As shown in Fig. 2(c), the decrease in pH was also
caused by algal respiration. The DO concentration of cell #2, cell #3,
and cell #4 was less than that of cell #1. The DO concentration of cell
#2 to cell #4 was less than 5 mg/L during most of the operational
periods, although DO concentration varied according to algae
concentration introduced from the WSP; an anoxic zone cannot be
expected with this high a DO concentration level in bulk water.
However, an aerobic/anoxic zone would be partially formed in each
cell because the hydraulic flow pattern was very poor in the plant
zone [8].We assumed that the aerobic zone was more broadly formed
in cell #1, while the anoxic zones were more broadly formed in cell #2
to cell #4.