With the current national emphasis on restoring urban water quality, the City of Brockton (Massachusetts) Advanced Water Reclamation Facility wanted to stay ahead of the regulatory cycle — in particular, phosphorus discharge limits set forth by the National Pollution Discharge Elimination System program of the U.S. Environmental Protection Agency. For this region of the country, the EPA has proposed total phosphorus discharge limits of 0.1 mg/L.
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 from Aqua-Aerobic Systems. Even though the filters performed to a level well below the current phosphorus discharge limit of 0.2 mg/L, plant 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.
Full-scale testing
Following preliminary analytical evaluations of incoming phosphorus levels, the Brockton AWRF staff, working with Aqua-Aerobic Systems, 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 square meters (2,560 square feet) of filtration area and is rated for a nominal average daily flow of 1,900 cubic meters per hour (12 mgd) and a maximum daily flow of 3,800 cubic meters per 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, turbidity, pH, iron and alkalinity. Testing was conducted in three phases to explore filter performance:
1. During normal operating conditions of approximately 6 cubic meters per hour per square meter (2.4 gpm per square foot).
2. At the average design hydraulic loading rate of 8 cubic meters per hour per square meter (3.25 gpm per square foot).
3. At the peak hydraulic loading rate conditions approached 16 cubic meters per hour per square meter (6.5 gpm per square foot).
Study results
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 total suspended solids, turbidity, particle size distribution and iron concentrations and fared well during average design and peak hydraulic loading rate testing.
The plant has not observed any negative hydraulic impacts in going from the original pile cloth media (PES-13) to the microfiber media (PES-14). “We all anticipated a potential 20-25% reduction in hydraulic pressure loss across the filters,” says Norton. “I don’t believe we saw that. Also, I do not believe we have seen the increase in backwashing volume which was predicted.”
By taking the initiative, Brockton AWRF demonstrated it can meet anticipated future discharge standards. Because of this demonstrated success, the plant has installed and commissioned a third and fourth AquaDiamond CMF with the OptiFiber PES-14 microfiber media. 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.
Aqua-Aerobic Systems provides total water management solutions in aeration and mixing, biological processes, filtration, membranes, oxidation/disinfection and process control, as well as aftermarket products and services. Aqua-Aerobic Systems employs approximately 150 people in research and development, engineering, sales/marketing, manufacturing, customer service and administration.
815-654-2501 | www.aqua-aerobic.com
