3.8. Effect of aeration tubes
The effect of the presence of aeration tubes was also tested. Two
units (W1 and W8) were similar with the only difference being
the absence of aeration tubes in unit W8. The performance of unit
W1 was clearly better. OM removal in the unit without these tubes
was about 5% lower (77.4% and 73.1% for BOD5 and COD, respectively;
Table 3), while unit W8 showed about 10% increased effluent
nitrogen concentrations (31.0 and 23.4 mg/L for TKN and NH4
+-N,
respectively) compared to unit W1. Respective differences in performance
were also observed in phosphorus removal (Table 3). The
differences in OM and nitrogen removal were found to be statistically
significant by ANOVA (Table SM-2). The vertical aeration tubes
connect the outer atmosphere with the lower layers of the bed,
something that contributes to the maintenance of aerobic conditions
within the wetland bed and consequent enhancement of the
OM decomposition and nitrification process by bacteria.