Mississippi was the leader of a “green revolution” in wastewater treatment that started approximately 20 years ago growing out of research done at the Stennis Space Center by Dr. Bill Wolverton designed to treat polluted air and wastewater in future moon colonies or space stations.
What Wolverton found was that wastewater could be treated with natural plant systems that cost far less to build and operate than traditional mechanical treatment systems. With constructed wetlands, plants take up nutrients in the wastewater to grow, and microorganisms associated with the plant roots help break down pollution.
As a spin-off of the research, constructed wetlands for wastewater treatment (also known as artificial marshland wastewater treatment systems) were built not just in Mississippi, but in wide locations throughout the country. Constructed wetlands have now been built to handle waste from municipalities, industry and agriculture, and also to capture and treat stormwater runoff.
There are now a number of wastewater systems in Mississippi that use constructed wetlands technology as part of their wastewater treatment. Cities using the constructed wetlands technology include Collins, Union, Noxapater, Pelahatchie, Picayune and Ocean Springs-West Jackson County. Newer facilities include Roundrock Utilities in Pearl River County, which recently expanded its artificial wetlands, and McHenry Hills in Stone County, which includes several subdivisions. Heron Lake Estates in Stone County are also proposing the use of constructed wetlands.
But it hasn’t all been smooth sailing because while constructed wetland are far less expensive to construct and maintain than mechanical systems, with a natural plant systems one can’t just turn a knob or add more chemicals to make adjustments to meet permit limits.
“The Mississippi Department of Environmental Quality (MDEQ) does not promote or dictate the technology that is installed as long as the facilities meet the discharge limits in their permits,” said Robbie Wilbur, communications director for MDEQ. “In fact, MDEQ’s regulations do not allow approval or promotion of a certain technology. Constructed wetlands when placed in appropriate locations do provide an aesthetically pleasing alternative to wastewater treatment.”
Union was one of the first cities in the country to install a constructed wetland systems from scratch rather than add a constructed wetland to the end of another type of treatment system. The system constructed in 1991 has operation and maintenance costs that are approximately 90% less than convention mechanical systems that use a lot of energy. Don Thomas, Union water and wastewater superintendent, said their power bill is $600 per month while it would probably be close to $10,000 per month with a mechanical system.
Part of the issue with Union is it discharges into a small stream that can dry up part of the year. So, the city has to meet more stringent permit limits than if it were discharging into a large body of water such as the Mississippi River or Pearl River.
The quality of water discharged can be dependent on nature. When there are heavy rainfalls, there can be too much water for the natural system to treat completely effectively. Sometimes Thomas wishes he could just turn a knob and get different numbers on various parameters measure to determine the water is safe for discharge.
“There are pros and cons to it,” Thomas said. “The pros to artificial marshland treatment systems are you rely on nature and time to purify the water. The maintenance costs are very low. That is the big plus. But if you are out of compliance with any of the permit requirements, there is really no corrective action you can take. You can’t hold the water longer. You don’t have to be down there 24 hours a day, seven days a week like with a mechanical plant, but a mechanical plant can do things to improve your numbers because there is a mechanical way to do it.”
Constructed wetlands are at the mercy of weather. If the area gets six inches of rain, the treatment plant could have been working perfectly. But too much rain can overwhelm the capacity of the wetlands to remove pollution from the water.
When asked if he recommends constructed wetlands, Thomas said it depends on the body of water receiving the discharge. If it is only a small creek such as in Union, one might need some extra treatment because MDEQ is going to require very clean treated wastewater in order to protect people who might come into contact with the water.
“Am I pleased with it?” he asks. “It is still a work in progress. I don’t know if you can ever be pleased with wastewater because wastewater changes. I’ve been here operating it for almost 20 years. If I knew then what I know now, I would have probably done something a little different. Here lately in the past three to four years, we have put out really good numbers on biological oxygen demand (BOD) and total suspended solids (TSS). We went out on dissolved oxygen and fecal. DEQ came back and made all small systems like ours put in disinfection. So, now we have a chlorine contact chamber. It seems to be working well.”
Thomas said even if the system was perfect, when it rains one can have a lot of rainwater that enters the old sewer pipe systems that feeds into the treatment plant. And sometimes one can have industry that discharges heavy pollution into the sewer that kills all the beneficial microorganisms that are breaking down the wastewater.
“Then you start from scratch again,” he said. “If it is was just sewage from household and not extra rainwater or pollution from industry, it would probably work well. Nature will take care of it anyway if you just give it time. We have tried to condense our system on 14 acres. If we had 24 acres, it would be better to give plants the time to do their job.”
Thomas doesn’t like to report numbers to the MDEQ that are out of compliance especially as there is little he can do. “But they have been pretty lenient,” he said.
Contact MBJ contributing writer Becky Gillette at email@example.com.
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