Effect of dissolved organic matter on N2O generation in A2O biological wastewater treatment process
JIANG Hui-qi1, YU Pei-han1, HU Zhen1, REN Yan-gang2,3, HAO Ze-yu1, HAN Ke1, XUE Chen-yang3, WANG Jin-he4
1. School of Environmental Science and Engineering, Shandong University, Qingdao 266237, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China; 3. Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; 4. School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China
Abstract:In this study, the components of dissolved organic matter (DOM) during the anaerobic-anoxic-aerobic (A2O) biological wastewater treatment process was analyzed by using fluorescence emission excitation matrix combined with parallel factor analysis (3D EEMs-PARAFAC), and the generation of nitrous oxide (N2O) in each unit was also quantified. Additionally, machine learning model was employed to further predict the response relationship between DOM components and N2O generation. Results showed that DOM in the influent of the wastewater treatment plants (WWTP) was primarily composed of four components, including tryptophan (C1), fulvic acid (C2), humic acid (C3), and tyrosine (C4), while C1 and C4 being the dominant components. The concentration of DOM decreased progressively throughout the treatment process, while the removal efficiency of readily biodegradable DOM (such as C1and C4) were significantly higher than that of C2 and C3. N2O emission was the major component of direct carbon emissions and showed significant spatial heterogeneity. The N2O emission amount of each unit ranked from high to low were observed in the following order: oxic tank, secondary sedimentation tank, anoxic tank, anaerobic tank, grille, and primary sedimentation tank. Shapley Additive exPlanation (SHAP) analysis revealed that C1 and C2 would significantly affect the N2O generation process, while the effects of C3 and C4 were negligible. Specifically, C1would enhance N2O generation, while C2 had an adverse effect. High-throughput sequencing results indicated that Methylotenera and Terrimonas, which could utilize readily biodegradable organic matter for denitrification, were the dominant bacterial genera in the sludge of WWTP. Overall, this study revealed disparate response between N2O generation and different DOM components during the A2O process, which would help to improve the current carbon emission accounting method of WWTPs and provide theoretical support for optimizing their low-carbon operation processes.
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