What is a sand bioreactor wastewater treatment system and how does it work?
First, wastewater is screened to remove as much of the suspended solids as possible before it is flowed through beds of sand and gravel. Microbes quickly populate the surface of the sand grains and gravel pieces, and they feast on the organic matter, breaking it down and removing it from the water. The treated water runs clear.
We conducted a field test at Whitewater Processing Company, a turkey plant in southwestern Ohio that disperses 145,000 gallons of high-fat, high-organic wastewater each day. We installed a first-of-its-kind four-acre sand bioreactor system. Before treatment, the effluent at Whitewater was measured at over 800 BOD (biological oxygen demand), the standard that regulators use to measure water pollution. Normal sewage has a BOD of about 200. When Whitewater’s wastewater was tested after treatment, its BOD was less than 5, allowing it to be released directly into the Whitewater River, with the Ohio EPA’s blessing.
When you visit it, it looks sort of like a park. All you see are 12 large rectangles of gravel and grass grows all around them. Under the gravel are the pipes that carry the wastewater and spray it underground onto the sand. It’s quiet, there’s no odor, and even though most wastewater treatment plants aren’t necessarily something you want to look at, it’s not ugly. They plan to plant trees to make it even more attractive.
Is there any upkeep for such a system?
One of the challenges with the system is that operators must be sure the bioreactor doesn’t get overwhelmed and become clogged. If the sand was to get clogged, our research shows you need to turn that filter off, let it rest and send the wastewater to another cell. Then the microbes consume the wastes that have clogged the filter and unclog it. That takes about four months.
The typical loading rate for a bioreactor system is about 1.5 gallons per square foot per day. Before installing the Whitewater system, we loaded our lab system up with 6 gallons per square foot per day, and it took a year to clog the sand. Then we let it rest and after four months, it worked just like a brand new filter. You just have to let the microbes work to consume the extra organic matter that clogged the sand. At Whitewater, they require eight bioreactor cells at a time but they are building 12 cells to have the backups needed to let filters rest. Eight cells are currently online and in operation.
Are there any other positive benefits?
The cost. While still an expensive proposition — Whitewater spent $1 million to construct the system and it will cost the company $1.8 million to operate over the next 20 years — the next best alternative would have added another $10 million over that span. That would have included hooking into the local municipal wastewater treatment plant and Whitewater would still have needed to pretreat its water to remove any pollutants the municipal system couldn’t handle.
Also, this system allows Whitewater to get ahead of any forthcoming regulations that involve dispersing nutrients into navigable waters, such as phosphorus and nitrogen. There are no regulations currently but they’re on the horizon. We are conducting research on reusing the wastewater in greenhouses to fertilize flowers, grasses and other horticultural products and we envision a day where greenhouses are built on top of bioreactor systems to take full advantage of the nutrient-rich byproduct.