Nitrogen removal intensification technology

We are investigating the use of a nitrogen removal intensification technology, Nuvoda’s Mobile Organic Biofilm (MOB), as a potential technology for use at the South Treatment Plant or other county facilities for either near-term optimization or to meet future nitrogen removal requirements imposed by the Department of Ecology through a Puget Sound Nutrient General Permit (PSNGP).

The Technology Assessment team is designing a pilot-scale system that will mimic South Plant’s secondary treatment process with and without the MOB technology. The pilot system is expected to operate for approximately one year. The Technology Assessment Program will be working with the University of Washington through its ongoing graduate research fellowship agreement to evaluate the performance of the technology.

The MOB technology intensifies nutrient removal by establishing and promoting multi-layered biofilms on kenaf particles and retaining those particles in the treatment process. Kenaf is a lignocellulosic material that does not readily biodegrade in an activated sludge process. Nuvoda engineers the MOB kenaf particles to be about the size of aerobic granular sludge (~1 mm) with a large surface area for biofilm growth. The MOB media operates in tandem with a traditional floc-type activated sludge and typically comprises about 30-60% of the mixed liquor suspended solids. The MOB media is added to aeration basins and is selectively retained in the secondary process by screening the media from waste-active sludge with rotary drum screens. The Solids Retention Time (SRT) for the MOB media is decoupled from the floc SRT. Due to the extended SRT of the MOB media, nitrifiers can be cultivated on the biofilm periphery in the aerobic stage. Denitrifiers that can utilize nitrate or nitrite (produced by nitrification) can grow on the inner anoxic biofilm core, allowing for Simultaneous Nitrification Denitrification (SND). The settleability of the MOB media has been shown to improve the Sludge Volume Index (SVIs) of mixed liquors in secondary clarifiers, thus potentially increasing their rated capacity.