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Nutrients from Growing Coastal Communities Threaten Bio-Diversity

Wastewater treatment facility reduces effluent levels to be well below permit limits

Bio-diversity in Florida’s St. John’s River estuaries is dependent on clean water. Growth in the area’s coastal communities is adding nitrogen and phosphorous nutrients to the river through wastewater discharges. These nutrients cause rapid growth of some organisms, limit dissolved oxygen availability to others, and upset the balance of a diverse ecosystem. In 2005, the Florida Department of Environmental Protection began implementing Total Mass Discharge Limits (TMDL) for nitrogen and phosphorous from the area's wastewater treatment plants.

Challenge

A new TMDL mandated that the City of Neptune Beach reduce nitrogen discharges from its 1.5 MGD wastewater facility from 70,000 pounds to 13,000 pounds per year. To reach this 80% reduction, a total effluent discharge of 3mg/l total nitrogen needed to be achieved. In its contact stabilization mode of operation, the plant could not accommodate this requirement and needed to change its process.

 

Solution

Proven fixed-film technology enables cost-effective, space-efficient upgrade

The Neptune Beach facility did not have land available for additional tanks, and did not have an advanced control system to support implementation of a Biological Nutrient Removal (BNR) system. Initial research by the 3rd party group, Applied Technologies and Management (AT&M), found that it wasn’t feasible to build a new plant or to pump waste to neighboring community facilities. AT&M and Neptune Beach turned to Evoqua for an innovative solution. Evoqua's experts provided a comprehensive analysis of alternatives that led to selection of a Biosphere™ Moving Bed Biological System configured to operate in an integrated fixed-film activated sludge (IFAS) mode.

BioSphere®โ€‹ Biological Systems from Evoqua are fixed-film processes using thousands of patented-design biomass carriers to create a large protected surface area for biofilm growth. They can be installed either as an integrated fixed-film activated sludge (IFAS) system, or as a fixed-film system without activated sludge circulation (MBBR). They utilize a spiral role aeration pattern generated by uniquely placed diffusers to provide complete bioreactor mixing, enhanced oxygen transfer, and sloughing of old growth. Evoqua BioSphere Systems allow for capacity increases of 200% or more and compliance with ever-tightening permit limits — all within an existing plant footprint.

The plant’s original contact tank was converted into two pre-anoxic zones. A plug flow condition was created. An IFAS system was created within the original stabilization tank by reconfiguring it into four zones: - IFAS, wet well, post-anoxic, and re-aeration. Nitrification occurs in the IFAS zone which also contains the BioSphere Biological System biomass carrier. Recycle from the IFAS zone containing nitrate to be denitrified is sent back to the pre-anoxic tank where it mixes with influent flow and RAS from the clarifier. Biological nutrient removal is controlled by a SmartBNR™ Process Control System from Evoqua. All meters and instruments are integrated to provide precise control over the process. SRT is controlled either manually or by the installed TSS probes. The user can enter the desired SRT and the SmartBNR Control System calculates the required wasting rate then controls waste pump VFDs to maintain this setpointโ€‹.โ€‹

Results

New plant keeps discharges and costs under control

Despite site and time constraints, the project was successfully implemented and started up in May 2010. The new IFAS system continues to perform well, enabling consistent compliance with TMDL requirements with minimum operator attention, and does so in a plant 1/4 the size of a conventional process.

The City of Neptune Beach considers this project a successful, cost-effective solution for meeting total nitrogen discharge limits to the St. John’s River. Capital spending was minimized, and user charges remain low because an integrated BNR control system allows total operating costs to be managed to only those necessary to meet the new TMDL.