Not being able to use chlorine as a water disinfectant has taken its toll on equipment at the El Dorado Hills Wastewater Treatment Plant as large amounts of algae grows continually, forcing employees to take extra time to remove it. During a recent meeting of the El Dorado Irrigation District directors, staff requested and obtained funding approval to help with the problem.
“The plant permit requires Trihalomethane reduction,” said senior engineer Tim Sullivan. “The THM is a byproduct of chlorine disinfection. Back in 2010 we installed a UV disinfection system in order to meet that very stringent requirement and subsequent to that, the plant discontinued the use of chlorine, including the plant service water.”
Sullivan added currently there is a high level of algae growth and plants and that has increased the manual labor that is used to remove them.
“Without the mitigation of algae growth operating costs will continue to be impacted,” he said. “Algae is manually removed by the use of a high pressure hose and the removal is a time-consuming process especially in summer when we have more sunlight.”
Sullivan said the two secondary clarifiers at the plant which are about 100 feet in diameter are not covered and fall victim to the algae growth. The algae attaches to the walls and forms a thick layer.
“Algae in the launderer degradate effluent quality,” he said. “Those pieces can detach and raise turbidity levels. It also can impede the flow around the clarifier. It can also negatively affect the downstream processes.”
He said the solution to the growth is to block sunlight on the clarifier launders by the use of fiberglass covers over the launders.
“Did you have the algae problem when there was chlorine treatment or was it only triggered by putting the UV in?” asked Director George Wheeldon. “Could we use a chlorine supplement to help?”
Sullivan said this level of algae issues was triggered by the UV installation and added using any type of chlorine at the plant will cause issues with the THM requirement permit.
“So this is just an unintended consequence of converting to UV,” Director George Osborne added.
The lowest bid came in at $107,300, with capitalized labor costs at $23,442, a contingency of $16,095 included, bringing the project subtotal is $146,837. The project already has a balance of $15,000, therefore the requested amount is $131,837.
Funding for the project was included in the Capital Improvement Project list of Sept. 26, 2011.
After further discussion Directors Wheeldon, Osborne, Bill George, Alan Day and John Fraser all voted to OK the funding.