Process Selection and Operating Data for Fast-Tracked Nitrification Enhancements Utilizing Magnetite as Ballast in a Sequencing Batch Reactor

Increasingly stringent effluent permits coupled with ever shrinking utility budgets require innovative solutions, particularly when the impending change to the permit is only a few months away. This was the case at the Washington County, Maryland-owned Smithsburg WWTP when in 2012, the plant was issued a more restrictive effluent ammonia permit to take effect in less than 6 months. A review of the process determined a longer solids retention time (SRT) than could be achieved by the existing infrastructure and process was required to nitrify year-round. To reliably increase the SRT, the reactors required a larger volume and/or a higher concentration of mixed liquor. The solution that could be implemented in the required timeframe was to utilize Evoqua’s BioMag® ballasted activated sludge technology to ballast the mixed liquor allowing the floc to settle more rapidly and thereby allowing the concentration of mixed liquor to be increased from 2,500 to 4,000 mg/l. This increase resulted in a sufficient SRT to reliably nitrify and meet the effluent ammonia permit. Due to the fast-tracked nature of the project the BioMag® system was implemented in a 2-phase approach. The first phase included the temporary addition of magnetite to meet the effluent goals in a matter of months. The second phase provided permanent BioMag equipment to introduce and recover the magnetite ballast used in the reactors. The system has operated for several years and the effluent ammonia permit has been reliably achieved during this time.