February 22, 2012 By Brian Heaton
A number of new technology additions are helping the Rocky River Wastewater Treatment Plant in Anderson, S.C., discharge cleaner and clearer water back into the environment.
Last fall, the facility replaced its old chlorine water disinfection process with an ultraviolet (UV) light system. In addition, in order to meet environmental regulations, the plant also began removing phosphorus from the water by using sand filters and expanded its daily treatment capacity by 3.4 million gallons per day.
Jeff Caldwell, utilities director for Anderson, said the uptick in water quality is obvious to anyone watching the water come off the plant’s cascade into the receiving stream.
“You can tell a physical difference,” Caldwell said. “It’s a much cleaner and clearer quality of water, but as far as the nutrients that are dissolved in that water, other than the phosphorus, that hasn’t changed.”
Wastewater comes in the Rocky River plant and is sent to a primary clarifier where heavy solids are sifted out. Then it heads to a trickling filter to remove further pollutants using microorganisms, then over to rotating biological contactors, which remove dissolved and suspended biological matter. After that, the water is sent through a final clarifier before it’s released.
To remove the phosphorus, however, the facility added another step prior to the final clarifier, where a chemical mixture called Alum is introduced that binds the lighter particles together, so they get heavier and settle out. The water then heads to a sand filter, which gets rid of the finer particles that weren’t removed.
The project cost approximately $30 million and took two years to complete. The work took place while the plant was in operation, so it was done in a phased approach that resulted in a setup of equipment being brought online before older components were taken down.
But in a time of budget shortfalls, why make the move to a UV system, particularly if chlorine is cheaper to use and has been used successfully at the plant for years?
Caldwell explained that since the equipment at Rocky River was due for an upgrade to its chlorine equipment anyway, the city compared chemical costs against power use and once transportation and storage for chlorine factored in, the choice became a no-brainer.
“Throw in the risk component of having several one-ton chlorine cylinders onsite and having to truck them through our city streets … eliminating that risk to our employees and citizens is what put it over the top and made it a more effective solution for us,” he said.
In addition to environmental and safety benefits, the new process also makes things a little easier on workers. Using chlorine, workers took a sample of water and from that, determined what dosage level of the chemical was needed to disinfect the water.
UV is a little different. The amount of UV that goes into the water depends on the flow. As the water passes through the channel where the UV lights are located, it’ll sense whether the water is degraded at all and automatically turn on more lights to disinfect based on the need. So while workers still need to remain attentive, the system is more reactive to the flow and the water coming to it than the chlorine process was.
The added bonus is now employees won’t have huge chlorine cylinders to deal with or a concern over potential leaks and the health impacts that could result. While UV rays are dangerous, Caldwell said the risk of UV exposure is minor, as long as the bulbs are kept at an appropriate depth underwater.
He added that the improvements made to separate phosphorus will also allow the plant to limit the amount of nitrogen that can be in the water, should regulators impose any future mandates.
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