2. Operation of SSF constructed wetland in
batch mode (alternating drain and fill cycles)
is a strategy that may improve both nitrogen
and phosphorus removal efficiency in
wastewater wetlands.
Studies have shown that alternating periodsStudies have shown that alternating periods
of aerobic and anaerobic soil conditions
could facilitate the sequential coupling of
nitrification and denitrification, with nitrate
generated during the aerobic phase being
denitrified in the anaerobic phase.
2
3. To evaluate the influence of batch versus
continuous mode on the removal efficiencies
of chemical oxygen demand (COD), N, and P
in tropical SSF constructed wetlands.
To evaluate the quantitative role of the higherTo evaluate the quantitative role of the higher
aquatic plants in nutrient removal in these
two alternative operational modes.
3
4. Six beds of typical SSF CW were set.
The location is a typical tropical environment
and is generally hot and humid year round.
The average temperature ranges from 23˚C
to 32˚C (74 Fe86 F).
Beds were filled with gravel.Beds were filled with gravel.
Three HSSF CWs were planted with cat-tail
(Typha Angustifolia) at a density of
approximately 14-15 plant/m2, and 3 beds
without plant. The latter were used as
“unplanted” control beds.
4
5. The operational modes included batch-
loaded and continuously loaded systems.
Two periods with identical conditions were
used. (Batch: April – June 2010, Continuous
mode: Sept. – Nov. 2010).mode: Sept. – Nov. 2010).
Effluent samples were collected same day,
time and every two and four days in 1l glass
bottles.
5
9. 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 significantanalysis 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%)
9
11. 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 significantand 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).
11
13. COD removal was not significantly affected by
the presence of plants in the batch operated
wetlands.
However, for the 4-day residence time in our
continuous flow wetlands, there was acontinuous flow wetlands, there was a
significant (p < 0.05) difference between
planted and unplanted beds, even though the
difference in removal efficiency for the
planted beds (95.9%) was only slightly better
than that for the unplanted (91.1%).
13
14. The reasons for this are unclear, but
apparently are reflective of the fact that at
least at the typical COD loading rates, the
sum of the processes of aerobic (and
anaerobic) organic carbon degradation actinganaerobic) organic carbon degradation acting
solely in a gravel filter (with no plants) are
sufficient to drive BOD5/COD degradation to
near completion without the need for either
plant rhizosphere aeration or drain and
fill operational.
14
16. Batch operation of SSF CWs has been proposed as a
method for enhancing movement of air into the
gravel pore spaces, and thereby stimulating the
oxidation of C and N and removal (adsorption) of P.
The results obtained from comparing batch versus
continuous flow modes for a tropical SSF CW,continuous flow modes for a tropical SSF CW,
showed that while these alternative loading
methods had no significant effect on C oxidation
(COD removal), both N oxidation and P removal
were significantly enhanced in the batch operation
as opposed to continuous flow mode operated at 4
day HRT.
16
17. The findings of this study imply that where
maximal N and P removal is desired, periodic
draining and filling might be the preferred
operational strategy for a full-scale SSF
constructed wetlandconstructed wetland
17
18. The results of this study on batch versus
continuous flow modes of operation for a
tropical SSF CW showed that while these
loading methods had no significant effect on
COD removal, both ammonia oxidation andCOD removal, both ammonia oxidation and
TP removal were significantly enhanced in
batch versus continuous mode.
At a 4-day HRT, the presence of plants
significantly enhanced both ammonia
oxidation and TP removal in both batch and
continuous modes of operation as compared
to that for unplanted beds.
18
19. The findings of this study imply that where
maximal N and P removal is desired, periodic
draining and filling might be the preferred
operational strategy for a full-scale SSF
constructed wetland.constructed wetland.
19
