BU Constructs Submerged Wetland To Research Wastewater Treatment

With approximately one-fourth of the homes in the United States utilizing a septic tank system for on-site wastewater treatment, finding better ways to protect the surrounding environment and, ultimately, residents' drinking water is essential. But thanks to research just underway at Baylor University's Wastewater Research Program, a relatively new treatment system is being put to the test to see if it could be part of the next generation of residential treatment systems.

Dr. Joe Yelderman, Wastewater Program director, and his team have constructed a submerged gravel wetland in Waco. Mirroring the pollutant removal ability of nature, the submerged wetland relies on the gravel and plants to remove contaminants. Baylor researchers recently started studying the system to see if it meets the National Sanitation Foundation's "STANDARD 40" protocol, a widely accepted set of requirements used to test and certify individual on-site aerobic treatment systems. While submerged wetlands have been used for wastewater treatment in recent years on an individual basis, the system has never been tested against the STANDARD 40 protocol.

"As the population grows, more and more septic systems are being added to the urban fringe and a lot of them are very close to streams," explained Yelderman, who is also a Baylor geology professor. "If we're not treating the waste effectively, it could bring disease and if you have a stream that doesn't have much water, wastewater may be the dominant flow and that could harm wildlife."

Once effluent, which is treated wastewater, leaves a residential septic tank, it flows into what's called a drain field, which is an arrangement of perforated pipes that carry the effluent into the soil. In theory, the soil will further decompose the effluent, making it safer for the environment. However in many areas, the water table is either too high, which means the effluent does not have a chance to fully decompose, or the type of soil can not adequately absorb the effluent, which is the case around much of central Texas. The end result is contaminants like phosphorous and nitrate entering the groundwater.

But if a resident installed a submerged wetland, effluent leaving the septic tank would flow into the wetland, instead of a drain field, and then into the soil.

"There are a lot of places where it would be nice to build a home, but if you can't put in a septic tank because the soil can't handle a drain field, you can't build a home there. So this wetland system might allow you to build in other places and it might actually treat the wastewater more effectively," Yelderman said.

Funded by a grant from the Texas On-Site Wastewater Treatment Research Council, Baylor's submerged gravel wetland does not look like a typical wetland. Natural wetlands have water visible at the surface. A submerged wetland does not. In fact, the wastewater is flowing a full three inches under the gravel surface. Only plants and gravel are visible at the surface. Yelderman said this cuts down on odor and eliminates health risks from exposure to untreated wastewater.

The wetland is located on the Waco Metropolitan Area Regional Sewage System's (WMARSS) property. Wastewater from WMARSS is pumped three times a day to a 1,500-gallon septic tank, which then feeds into the 1000-gallon wetland. Pablo Davila, a Baylor graduate student who is writing his thesis on the wetland, tests the wastewater in three strategic locations: before the wastewater enters the septic tank, after it leaves the septic tank and then after it filters through the wetland. It takes about five days for the effluent to make it through the entire process. Once the borrowed wastewater flows through the wetland, it is then pumped back to WMARSS for continued treatment.

"Some people say plants do not play a big role in pollution reduction, others say they do. I think with the plants in place, the wetland will be highly efficient," Davila said.

Yelderman said the year long study is actually two six-month studies back to back, which will allow researchers to see the effects of the seasons and how it relates to the performance of the wetland. In addition to testing how well the wetland reduces the Biological Oxygen Demand (BOD), researchers are also studying the wetland's effectiveness in extracting nutrients from the wastewater.

"The wetland certainly has the potential to be a significant addition to the types of treatment systems," Yelderman said.

Media contact: Frank Raczkiewicz, (254) 710-1964