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Ji F.,Chongqing University | He L.,Chongqing University | Zhou W.,Chongqing University | He X.,Chongqing University | And 3 more authors.
Chinese Journal of Environmental Engineering

With the extensive use of biological nitrogen removal process, the setting and cancellation of primary settling tank (PST) have been controversial in academic and engineering field. A wastewater treatment plant (WWTP) was selected as object, and the importance of the PST to WWTP was discussed from the perspective of inorganic suspended solids (ISS), chemical oxygen demand (COD) and total nitrogen (TN) removal by PST. The results showed that the influent pollutant concentrations were very high under combined sewage systems, with COD of 560 mg/L, suspended solids (SS) of 1100 mg/L and ISS of 780 mg/L. The removal rates of PST for COD, SS and ISS were 61%, 78% and 85%, respectively, and the removal rate of ISS was 20% higher than COD. After PST, the ISS/COD of wastewater decreased from 1.7 to 0.7, COD/TN decreased from 8.0 to 4.3, and the median particle size (D50) decreased from 40 μm to 30 μm. PST had better removal efficiency of ISS with larger D50, but the ISS with smaller D50 suspended in mixture easily, making MLVSS/MLSS reduction. From the perspective of ISS/COD reduction and keeping a normal MLVSS/MLSS, the PST should not be canceled. Source

He L.,Chongqing University | Ji F.-Y.,Chongqing University | Lai M.-S.,Chongqing University | Xu X.,Chongqing University | And 3 more authors.
Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis

Combined with wastewater treatment process, the sewage in sunny and rainy day was collected from a wastewater treatment plant in Chongqing. Three-dimensional fluorescence spectra was used to investigate the characteristic fluorescence of dissolved organic matter (DOM). DOM dissolved organic carbon (DOC), chemical oxygen demand (COD), fluorescence index (f450/500) and fluorescence intensity ratio r(A, C) of fulvic acid in ultraviolet and visible region were used to analyze the impact of rain runoff pollution on sewage DOM. According to the experimental data, the DOM fluorescence fingerprints of this wastewater treatment plant were quite different from typical municipal sewage, and the main component was tryptophan with low excitation wavelength (Peak S), then the tryptophan with long wavelength excitation (Peak T) followed. A2/O process had an approximative degradation of the protein-like both in sunny day and rainy day, but had a better degradation of fulvic-like, DOC and COD in rainy day than that in sunny day. Morever, the fluorescence peaks got red-shifted after the biological treatment. The differences of DOM fluorescence fingerprint between sunny and rainy day were significant, the fluorescence center of UV fulvic (Peak A) in rainy day getting blue-shifted obviously, shifting from 240~248/390~440 to 240~250/370~400 nm. Although the DOM types in sunny and rainy day were the same, the source of fulvic got more complex by runoff and the component ratio of DOM also changed. Compared with the sunny day, the proportion of Peak S in DOM dereased by 10%, and the proportion of Peak A increased by 7% in rainy day. ©, 2015, Science Press. All right reserved. Source

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