High Rate Clarifier Start-up and Operation in Shreveport, Louisiana

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 ABSTRACT

In 2004, the city of Shreveport received permits from the Louisiana Department of Environmental Quality and the U.S. Environmental Protection Agency to construct and operate a high rate clarifier (HRC) at both the North Regional and Lucas wastewater treatment plants. The HRC provides wastewater treatment for flow in excess of the peak plant capacities. Each HRC unit uses polymer and alum as wastewater conditioners and recirculates sludge to enhance
settlement of incoming wastewater. Wastewater is screened and degritted prior to entering the Lucas HRC and is screened only at the North Regional HRC. Start-up of the HRC consisted of optimization and performance testing. The manufacturer performed bench scale tests to determine the starting polymer and alum dosing rates. Once onsite and optimization started, the manufacturer adjusted the chemical dosing, the recirculation pump rates, and sludge blowdown (waste) cycle length and frequency. Throughout the optimization process, the manufacturer collected influent and effluent composite samples and tested for total suspended solids (TSS) and total biological oxygen demand (BOD5). After the system was optimized, the manufacturer began performance testing. Per the Louisiana Pollutant Discharge Elimination System (LPDES) permit, the HRC effluent must be equal or less than 45 milligrams per liter (mg/l) of BOD5 and TSS, and have a removal efficiency of equal or less than 65 percent removal of BOD5 and TSS. Since the HRC was designed to treat peak influent flows, the decision was made to operate the HRC during an actual peak storm event to determine performance. At Lucas WWTP, the high rate clarifier was operated during a high flow event on January 14th and 15th, 2007. All effluent TSS and BOD5 were within specified limits of 45 mg/L and nonsoluble BOD5 removal efficiency was greater than specified minimum of 65 percent. The performance testing for the HRC at the North Regional WWTP was conducted during a rain event on January 19th and 21st, 2007. The decision to not run the high rate clarifier on January 20th was made jointly by the contractor and city staff due to weather concerns. All of the effluent TSS and BOD5 using high flow were within specified limits of 45 mg/L and nonsoluble BOD5 removal efficiency was greater than specified minimum of 65 percent.

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