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Int. J. Environ. Res. Public Health 2014, 11(4), 3553-3569; doi:10.3390/ijerph110403553
Article

Effects of Sludge Retention Times on Nutrient Removal and Nitrous Oxide Emission in Biological Nutrient Removal Processes

 and *
Received: 26 February 2014; in revised form: 14 March 2014 / Accepted: 17 March 2014 / Published: 27 March 2014
(This article belongs to the Special Issue Nutrient Removal and Recovery)
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Abstract: Sludge retention time (SRT) is an important factor affecting not only the performance of the nutrient removal and sludge characteristics, but also the production of secondary pollutants such as nitrous oxide (N2O) in biological nutrient removal (BNR) processes. Four laboratory-scale sequencing batch reactors (SBRs), namely, SBR5, SBR10, SBR20 and SBR40 with the SRT of 5 d, 10 d, 20 d and 40 d, respectively, were operated to examine effects of SRT on nutrient removal, activated sludge characteristics and N2O emissions. The removal of chemical oxygen demand or total phosphorus was similar under SRTs of 5–40 d, SRT mainly affected the nitrogen removal and the optimal SRT for BNR was 20 d. The molecular weight distribution of the effluent organic matters was in the range of 500–3,000 Da under SRTs of 5–40 d. The lowest concentration of the effluent soluble microbial products concentration was obtained at the SRT of 5 d. Nitrifier growth was limited at a short SRT and nitrite existed in the effluent of SBR5. With increasing SRTs, mixed liquor suspended solids concentration increased while the excess sludge production was reduced due to the high endogenous decay rate at high SRTs. Endogenous decay coefficients were 0.020 d−1, 0.036 d−1, 0.037 d−1 and 0.039 d−1 under SRTs of 5–40 d, respectively. In BNR, the N2O emission occurred mainly during the aerobic phase and its emission ratio decreased with increasing SRTs. The ratio between the N2O-N emission and the removed ammonium nitrogen in the aerobic phase was 5%, 3%, 1.8% and 0.8% at the SRT of 5 d, 10 d, 20 d and 40 d, respectively. With low concentrations of dissolved oxygen and high concentrations of oxidized nitrogen, the N2O emission was significantly accelerated due to heterotrophic denitrification activities.
Keywords: sludge retention time; nitrous oxide; endogenous decay rate; greenhouse gas; excess sludge production sludge retention time; nitrous oxide; endogenous decay rate; greenhouse gas; excess sludge production
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Li, B.; Wu, G. Effects of Sludge Retention Times on Nutrient Removal and Nitrous Oxide Emission in Biological Nutrient Removal Processes. Int. J. Environ. Res. Public Health 2014, 11, 3553-3569.

AMA Style

Li B, Wu G. Effects of Sludge Retention Times on Nutrient Removal and Nitrous Oxide Emission in Biological Nutrient Removal Processes. International Journal of Environmental Research and Public Health. 2014; 11(4):3553-3569.

Chicago/Turabian Style

Li, Bo; Wu, Guangxue. 2014. "Effects of Sludge Retention Times on Nutrient Removal and Nitrous Oxide Emission in Biological Nutrient Removal Processes." Int. J. Environ. Res. Public Health 11, no. 4: 3553-3569.


Int. J. Environ. Res. Public Health EISSN 1660-4601 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert