Abstract:
A study has been conducted focusing on how the phosphorus renrx)val
efficiency of a constructed wetland (CW) can be optimized through
the selective enrichment of the substratum. Activated alumina and
powdered iron were examined as possible enrichment compounds.
Using packed glass column trials it was found that alumina was not
suitable for the renx)val of ortho-phosphate from solution, while
mixtures of powdered iron and quartz sand proved to be very
efficient.
The evaluation of iron/sand mixtures in CWs planted with cattails
was performed in three stages; first using an indoor lab scale
wetland, then an outdoor lab scale wetland, and finally in a small
scale pilot project. For the lab scale tests, three basic
configurations were evaluated: using the iron/sand as a pre-filter,
in the root bed. and as a post filter. Primary lagoon effluent was
applied to the test cells to simulate actual CW conditions, and the
total phosphorus and iron concentrations of the influent and effluent
were nfK)nitored. The pilot scale trials were limited to using only a
post filter design, due to in-progress research at the pilot site.
The lab scale tests achieved average renrK>val efficiencies greater
than 91% for all indoor configurations, and greater than 97% for all
outdoor configurations. The pilot scale tests had an average renK)val
efficiency of 60%. This relatively low efficiency in the pilot scale
can be attributed to the post filters being only one tenth the size of
the lab scale test in terms of hydraulic loading (6 cm/day vs. 60
cm/day).
