Impact of internal recycle ratio on nitrous oxide generation from anaerobic/anoxic/oxic biological nitrogen removal process

摘要

To evaluate the effects of internal recycle ratio on nitrous oxide (N2O) generation, we set up three laboratory-scale anaerobic-anoxic-oxic (A(2)O) wastewater treatment processes, with internal recycle ratios of 100%, 200%, and 300%, respectively. Total nitrogen (TN) removal was markedly enhanced from 45.8% to 61.9%, as the internal recycle ratio increased from 100% to 300%. N2O generation was increased from 3.47 to 9.81 x 10(-2) mg/L during the treatment process, with the anoxic section showing the largest N2O increment from denitrification. This phenomenon is attributed to the increased amount of nitrate (NO3--N) substrate available for denitrification, due to the increased volume of internal recycle liquid, as well as the increased amount of oxygen, which could restrain the activity of nitrous oxide reductase brought to the anoxic section. Nitrous oxide reductase was more sensitive to oxygen than nitrate and nitrite reductases. Microorganism analysis indicated that the population of nosZ gene-containing bacteria was only slightly affected by the recycle ratio. However, the number of nosZ gene copies decreased as the internal recycle ratio increased from 100% to 300%; this result reveals noticeable decreases in the denitrification capacity of the system for reducing N2O to N-2. (C) 2015 Elsevier B.V. All rights reserved.