A Closer Look at Rapid Infiltration Basins

One of the projects I work on keeps me regularly visiting the Turfgrass Research Envirotron during summer. This summer the Envirtron’s outdoor area was a bevy of activity and building. Upon inquiry, Envirotron Biological Scientist Natasha Restuccia informed me that the build involved a rapid infiltration basin trial and that Dr. Travis Shaddox was the researcher to speak to for more. A few weeks later during a campus visit, Dr. Shaddox agreed to an interview with IrriGator about the project.

Dr. Travis Shaddox

What is the objective of this study?

TS: The project is funded by Southwest Florida Water Management District. The objective is to determine how can rapid infiltration basins (RIB) be amended to greater enhance the denitrification of nitrogen from effluent water. RIBs are areas of land (quite large in some cases, 5 acres or more) where effluent water is pumped back into the ground water. In that process, the physics behind it is that any nitrogen in the effluent water will be denitrified out. They want to know how we can amend this system so that we enhance that denitrification. The second component would be how does that system that removes nitrogen leaching compare with home lawns and spray fields? Which of these systems – spray fields, lawns or rapid infiltration basins – are the most effective at reducing nitrate leaching into the ground water?

Was there a greenhouse phase to this project?

TS: We had a greenhouse phase that was conducted in Fort Lauderdale that looked at a factorial design of many amendments – 64 columns and a manifold identical to the one we’re doing in the field. In the greenhouse we were looking at which of these amendments are most effective at reducing nitrate leaching. From the results of that greenhouse phase we selected the most effective and that’s what you see out at the Envirotron now.

Which amendments advanced from the greenhouse to field phase?

TS: What we’re dealing with is basically a bioreactor – which is a system designed to greatly enhance the microbial activities responsible for denitrification. How do we do that? We end up applying treatments that have large quantities of soluble carbon, which generally is the limiting factor in microbial growth. I’m not a microbiologist, but the literature indicates that if you add soluble carbon to certain systems you’ll see a reduction in nitrate leaching because it’s denitrifying. So the thought was let’s try this with sawdust, limestone, and biochar.

Rapid infiltration basins and lawns at the Envirotron 

We took those three amendments and then did a factorial. So we’re dealing with each individual one and then all the combinations of those three amendments and then the control which is sand. The amendments that were most effective were those containing sawdust. The amendments that did not contain sawdust had very little influence on reducing nitrate leaching. The treatments that we ended up pulling out into the field because we have such limited space are sawdust, sawdust/limestone, and sawdust/biochar. And then of course the control (sand) as well as st. augustine and bahia lawns.

How long do you anticipate this will be in the field?
TS: Well, it’s supposed to start now (summer) and it’s going to run for two years. It has to run 24 hours a day at a very very low flowrate (up to 10mL a minute) and it has to do that non-stop for two years. There are cycles when it’s flooding and cycles where it’s drying – floods for a week, dries for a week, non-stop 24 hours a day for two years straight.