The inhibitory effects of reject water on nitrifying populations grown at different biofilm thickness
Journal article, 2016
Suppression of nitrite oxidizing bacteria (NOB) is of vital importance to achieve successful, energy efficient,
mainstream anammox processes for wastewater treatment. In this study, biofilm carriers from a
fully nitrifying MBBR system, fed with mainstream wastewater, were temporarily exposed to reject water
from sludge dewatering, to evaluate this as a possible strategy to inhibit NOB and achieve nitrite production
under realistic conditions. Two different carrier types were compared, in which biofilm thickness
was maintained at approximately 400 and 50 mm, respectively, and reject treatment was tested at
different exposure time and loading rates. Reject exposure almost always resulted in an increased nitrite
production in the thinner biofilm, and overall, nitrifiers growing in the thin biofilm were more sensitive
than those grown in the thicker biofilm. The effect from reject exposure remained in the systems for four
days after returning to mainstream operation, with nitrite production gradually increasing for three days.
Increased concentrations of free ammonia correlated with reject exposure and may be the cause of inhibition,
although other factors cannot be excluded.
Optical coherence tomography