The City of Brockton, Massachusetts' Advanced Water Reclamation Facility (AWRF) wanted to stay ahead of the regulatory cycle -- in particular, phosphorus discharge limits set forth by the National Pollution Discharge Elimination System (NPDES) program of the Environmental Protection Agency (EPA).
The Brockton plant's existing treatment scheme included physical settling (primary treatment), activated sludge treatment (secondary treatment) and final filtration (tertiary treatment) using two AquaDiamond® cloth media filters (CMFs) from Aqua-Aerobic Systems, Inc. Although the filters performed to a level well below the current phosphorus discharge limit of 0.2 mg/L, Superintendent Dave Norton began looking for ways to not only improve the plant's removal efficiency to meet the anticipated 0.1 mg/L limit but to achieve it with minimal equipment modification and without raising operating costs with chemical addition.
Following preliminary analytical evaluations of incoming phosphorus levels, the Brockton AWRF staff, working with Aqua-Aerobic, conducted full-scale tests using OptiFiber PES-14® microfiber cloth media installed on one of the AquaDiamond filtration units and compared its performance to the unit using the existing OptiFiber PES-13® pile cloth media. Each unit provides 238 m2 (2,560 ft2) of filtration area and is rated for a nominal average daily flow of 1,900 m3/hour (12 million gallons per day [MGD]) and a maximum daily flow of 3,800 m3/hour (24 MGD).
Throughout the four-month evaluation period from December 2012 to April 2013, the two filters received common influent from the plant's secondary clarification system (which was treated with ferric chloride prior to settling). Feed quality and discharge quality were monitored for phosphorus as well as total suspended solids (TSS), turbidity, pH, iron, and alkalinity. Testing was conducted in three phases to explore filter performance.
The two filter units operated under identical flow and loading conditions during the full-scale study. The results show that the OptiFiber PES-14 microfiber media consistently reduced phosphorus levels to below the 0.1 mg/L target. Additionally, the microfiber media outperformed the existing pile cloth media with respect to final TSS, turbidity, particle size distribution, and iron concentrations, and fared extremely well during average design and peak HLR testing.
The plant has not observed any negative hydraulic impacts in converting from the original pile cloth media (PES-13) to the microfiber media (PES-14).
By taking the initiative, the Brockton AWRF has demonstrated that it can meet the anticipated future discharge standards for total phosphorus of 0.1 mg/L. Further, because of this demonstrated success, the plant, working in conjunction with Aqua-Aerobic and its consulting engineering firm, has installed and commissioned a third AquaDiamond CMF (with the OptiFiber PES-14 microfiber media), and a fourth is under construction and expected to be online in the Spring of 2014.
The AquaDiamond filter unit fitted with the original pile cloth media (the control unit in the full-scale test) is also being retrofitted with the microfiber media. According to Norton, "Retrofitting the filter units from the original pile cloth media to the microfiber media had minimal impact on the current equipment and was relatively simple."
Aqua-Aerobic Systems Inc. is an exhibitor at WEFTEC.14 and can be found at Booth 7602. For more information, visit www.aquajetaerator.com.
