Modification of nitrifying biofilm into nitritating one by combination ofincreased free ammonia concentrations, lowered HRTand dissolved oxygen concentration
Ivar Zekker , Ergo Rikmann , Toomas Tenno , Anne Menert , Vallo Lemmiksoo , Alar Saluste , Taavo Tenno , Martin Tomingas
DOI:
Received August 19, 2010,Revised December 18, 2010, Accepted , Available online
Volume 23,2011,Pages 1113-1121
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Nitrifying biomass on ring-shaped carriers was modified to nitritating one in a relatively short period of time (37 days) by limiting the
air supply, changing the aeration regime, shortening the hydraulic retention time and increasing free ammonia (FA) concentration in the
moving-bed biofilm reactor (MBBR). The most efficient strategy for the development and maintenance of nitritating biofilm was found
to be the inhibition of nitrifying activity by higher FA concentrations (up to 6.5 mg/L) in the process. Reject water from sludge treatment
from the Tallinn Wastewater Treatment Plant was used as substrate in the MBBR. The performance of high-surfaced biocarriers taken
from the nitritating activity MBBR was further studied in batch tests to investigate nitritation and nitrification kinetics with various FA
concentrations and temperatures. The maximum nitrite accumulation ratio (96.6%) expressed as the percentage of NO2??-N/NOx??-N
was achieved for FA concentration of 70 mg/L at 36°C. Under the same conditions the specific nitrite oxidation rate achieved was 30
times lower than the specific nitrite formation rate. It was demonstrated that in the biofilm system, inhibition by FA combined with the
optimization of the main control parameters is a good strategy to achieve nitritating activity and suppress nitrification.
