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\bibitem{Peng_etal2020} {\textquotedblleft}\textit{Return-sludge treatment with endogenous free nitrous acid limits nitrate production and N$_{2}$O emission for mainstream partial nitritation/anammox}{\textquotedblright}. Peng L, Xie Y, Van Beeck W, Zhu W, Van Tendeloo M, Tytgat T, Lebeer S, Vlaeminck SE, Environmental Science \& Technology \textbf{54}, 5822 (2020).   http://doi.org/10.1021/ACS.EST.9B06404

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