Physical and chemical parameters
The physical and chemical parameters of effluent in the planted
and unplanted beds for the two experiments are summarized in
Table 1.
3.2. COD removal
The effect of batch and continuous flow on the removal of COD,
ammonium (NH4-N), nitrate (NO3-N) and total phosphorus (TP)
were evaluated. Table 2 shows the overall average effluent
concentration and removal of the water quality parameter.
Fig. 2 presents the comparison of COD effluent concentrations
between batch and continuous flow at 4-day retention time. For the
test series of 4-day retention time, there were no significant
differences (p > 0.05) for COD removal between batch and
continuous flow modes for either the planted or unplanted treatments.
The statistical results were the same for the 2-day HRT:
there was no significant difference when the results for batch mode
were compared to that for continuous flow (Table 2). When effluent
Fig. 1. Layout of the horizontal subsurface flow constructed wetland. COD concentrations in planted versus unplanted beds were
2 D.Q. Zhang et al. / Journal of Environmental Management 96 (2012) 1e6
compared, significant differences (p < 0.05) were observed only for
those operated under continuous flow mode at the 4-day HRT.
3.3. N removal
Fig. 3 shows the comparison of NH4-N effluent concentrations
between batch and continuous modes for the test series with 4-day
retention time. In planted beds, statistical analysis showed that
there was significant enhancement (p < 0.001) of NH4-N removal in
batch flow mode (95.2%) as compared to continuous flow operation
(80.4%); while in unplanted beds, there was no significant difference
(p > 0.05) for batch flow (49.3%) as compared to the continuous
flow mode (47%). A similar conclusion was drawn for batch
and continuous flow operation at 2-day HRT. In addition, in both
batch and continuous operational modes, NH4-N removal was
significantly enhanced (p < 0.001) in the planted beds as compared
to the unplanted beds.
3.4. TP removal
Fig. 4 shows the comparison of the TP effluent concentration
between batch and continuous flow modes for the 4-day hydraulic
retention time. For both planted and unplanted beds, there was
significant enhancement (p < 0.05) in TP removal in batch flow
operation (69.6% for planted beds; 39.1% for unplanted beds) as
compared to continuous flow operation (46.8% for planted beds;
25.5% for unplanted beds). In addition, in both batch and continuous
modes, planted beds showed significantly better TP removal
efficiencies (p < 0.001) than that in unplanted beds. However, for
the test series of 2-day HRT, and in comparing the batch operation
and continuous operation, the statistical results showed significant
differences only for the planted bed.