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.
Our results obtained from comparing batch versus 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.
These results are similar to those of Caselles-Osorio and García
(2007a) who found that although intermittently fed wetlands
operated under more oxidized conditions, there was no performance
difference in COD removal as compared to continuously fed
systems. However as pointed out by Caselles-Osorio and García
(2007a), intermittent operation (which does not involve complete
draining of the wetlands) is not equivalent to batch mode operation
which does completely drain then fill the wetlands. Apparently,
whether intermittently fed or completely drained and filled, COD
removal efficiencies are not enhanced when compared to continuous
flow systems.
On the other hand, Caselles-Osorio and García (2007b) found
that the presence of plants clearly had a significant impact on the
removal efficiency of COD, and attributed this impact to either the
convective transport of oxygen, or indirectly to increased evapotranspiration
rates which increased fluctuations in water levels
(which in turn creates a more aerobic environment). However,
surprisingly, in our SSF CWs, 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 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%). Our results then are in agreement
with that of Tanner (2001), who compared side by side studies of