Modification of nitrifying biofilm into nitritating one by combination of
increased free ammonia concentrations, lowered HRT
and dissolved oxygen concentration |
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Authors: | Ivar Zekker Ergo Rikmann Toomas Tenno Anne Menert Vallo Lemmiksoo Alar Saluste Taavo Tenno and Martin Tomingas |
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Institution: | 1. Institute of Chemistry, University of Tartu, 14a Ravila St., 50411 Tartu, Estonia. E-mail: Ivar.Zekker@ut.ee 2. Tallinn University of Technology, 5 Ehitajate St., 19086 Tallinn, Estonia |
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Abstract: | 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. |
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Keywords: | moving-bed biofilm reactor free ammonia specific nitrite oxidation rate nitrite accumulation ratio |
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