MBBR Ammonia Removal: An Investigation of Nitrification Kinetics, Biofilm and Biomass Response, and Bacterial Population Shifts During Long-Term Cold Temperature Exposure

New federal regulations with regards to ammonia in wastewater effluent discharge will require over 1000 existing wastewater treatment facilities to be upgraded. Although biological treatment is the most common and economical means of wastewater ammonia removal, nitrification rates can be completely impeded at cold temperatures. Moving bed biofilm reactors (MBBR) have shown promise as an upgrade nitrifying unit at pilot-scale and full-scale applications with respect to low temperature nitrification. MBBR technologies offer the advantages of less space requirement, utilizing the whole tank volume, no sludge recycling, and no backwashing, over other attached growth systems.;Two laboratory MBBRs were used in this study to investigate MBBR nitrification rates at 20°C, after long-term exposure to 1°C, and at the kinetic threshold temperature of 5°C. Furthermore, the biologically produced solids from the MBBR system 20°C and after long-term exposure to 1°C, and the Arrhenius temperature correction models used to predict nitrification rates after long-term exposure to 1°C. The nitrification rates at 1°C over a four month exposure period as compared to the rate at 20°C were 18.7 ± 5.5% and 15.7 ± 4.7% for the two reactors. The nitrification rate at 5°C was 66.2 ± 3.9% and 64.4 ± 3.7% compared to the rate measured at 20°C for reactors 1 and 2, respectively, and as such was identified as the kinetic temperature threshold. The quantity of solids detached from the nitrifying MBBR biocarriers was low and did not vary significantly at 20°C and after long-term exposure to 1°C. Lastly, a temperature correction model based on exposure time to cold temperatures, developed by Delatolla et al. (2009) showed a strong correlation to the calculated ammonia removal rates relative to 20°C following a gradual acclimatization period to cold temperatures.;Biofilm morphology along with biomass viability at various depths in the biofilm were investigated using variable pressure electron scanning microscope imaging (VPSEM) and confocal laser scanning microscope (CLSM) imaging in combination with viability live/dead staining. The biofilm thickness along with the number of viable cells showed significant increases after long-term exposure to 1°C while the dead cell coverage did not show significant increases after long-term exposure to 1°C while the dead cell coverage did not show significant changes. Hence, this study observed higher cell activities at warm temperatures and a slightly greater quantity of biomass with lower activities at cold temperatures in nitrifying MBBR biofilms. Using DNA sequencing analysis, Nitrosomonas and Nitrosospira (ammonia oxidizers)as well as Nitrospira (nitrite oxidizer) were identified in which no population shift was observed during 20°C and after long-term exposure to 1°C. Furthermore, a number of non-nitrifiers were identified in the biofilm during warm and cold temperatures presenting the possibility that their presence may have provided some form of protection to the nitrifiers during long-term temperature exposure.