Research studies on small constructed wetland systems are few and far between. Our Water Purification Eco-Center (WPEC) here at Rodale Institute affords us the opportunity to increase the amount of research on this kind of revolutionary system. The WPEC is an on-site wastewater treatment facility that captures rainwater and uses it several times before returning it to the soil as clean water. The system uses constructed wetlands for sewage treatment, cycling the wastewater through the wetlands landscape where the plants and surrounding microbes use nutrients from it and clean it.
Since the WPEC opened in the spring of 2011, researchers have been collecting and testing water samples between each section of the wetland and from the soil surrounding each area. The water analysis is testing for various biological contaminates to ensure the water leaving the system is clean and safe to release to the surrounding landscape. Because this system adds at least two additional cleansing steps to treat the water that would normally be released from a traditional septic system, we expect the end product to be that much cleaner.
Here is what the process of sampling looks like:
Samples are taken from “cleanest” to “dirtiest” points throughout the
system to prevent cross contamination of the samples. Christine
Ziegler-Ulsh has just finished taking a sample from the wetland
cell and is cleaning the flask and hose for the next sample.
Here April Johnson opens the
tank immediately preceeding the wetlands cell.
Tubing is lowered into the tank.
And a water sample is pumped into a flask.
The water sample is decanted into different bottles for different tests.
We are currently testing for fecal coliform, nitrates, ammonium, phosphorus,
total Kjeldahl nitrogen, carbonaceous oxygen demand and dissolved oxygen.
The process is repeated for each holding tank.
Samples packed up and ready to ship out for testing.
We send quarterly reports to the Environmental Protection Agency (EPA) with the WPEC test results and analysis. What we have seen so far has been promising and in line with our expectations:
Dissolved oxygen measures how much decomposition is going on in the water and how much (and what kinds of) microbial life can survive. The dissolved oxygen in the septic tank (from which a traditional septic system releases wastewater to the environment), is less than 1 mg/L. By the time the wastewater reaches our wetlands cell in the WPEC system, the dissolved oxygen has risen to at least 5 mg/L, a level that is high enough to support aquatic life.
Fecal coliform is an indicator of human waste. The WPEC system eliminates the fecal coliform by the time the wastewater is released to the irrigation system. Fecal coliform counts in the system’s septic tank (pre-treatment) can be over 70.000 per 100 mL, but by the time the water reaches the irrigation holding tank, fecal coliform counts drop to zero, and remain so throughout the landscape’s drip irrigation system.
Nitrates are also present in human waste. From the septic tank to the irrigation system, total levels of nitrogen fall dramatically, and that which remains is transformed into plant-available forms that can be utilized by the flowers and shrubs in the surrounding landscape via the drip irrigation system.