The Mechanism Of Nitrogen Removal In A Microaerobic Wastewater Treatment System Based On The Detection Of Signal Molecule AHLs

Piggery wastewater has the characteristics of high ammonium(NH4+-N) and low C/N ratio, which is difficult to treat, especially for nitrogen removal. A novel upflow microaerobic sludge reactor(UMSR) has been constructed to treat manure-free piggery wastewater characterized by high concentration of ammonium and low ratio of chemical oxygen demand(COD) to total nitrogen(TN). The reactor has an excellent removal efficiency of COD, but the understanding of the mechanism of biological nitrogen removal is not thorough. It has been found up to now that the anammox bacteria are gram negative bacteria(G-), can secrete a kind of signal molecule called N-acyl homoserine lactones(AHLs), stimulating growth and metabolic activity of bacteria, this is termed quorum sensing. In this work, taking activated sludge of UMSR for research objects, the key signal molecule in microaerobic nitogen removal system has been studied, further revealed the mechanism of biological nitrogen removal in microaerobic system.First, an ultra performance liquid chromatography tandem mass spectrometry method was developed for the detection of AHLs in UMSR, which can simultaneously detect the 9 kinds of AHLs signal molecules of the G- flora rapidly and accurately. The analysis could be finished within 6.5 min,detection limits were 0.01~0.5 μg/L with high recovery and low relative standard deviation. Resluts showed that many kinds of nitrogen removal pathway exist in the system including autotrophic denitrification and heterotrophic denitrification, among them Anammox was the main nitrogen removal mechanism of UMSR.High C/N ratio caused by volatile fatty acids(VFAs) and urea and other hydrolysis products have a serious impact on the removal efficiency of microaerobic activated sludge. The increase of C/N ratio under the control of propionate c an effectively improve the denitrification efficiency of the system, but high C/N ratio can cause a marked inhibition of Anammox in the activated sludge system. For the UMSR system, the appropriate C/N of influent is about 1. In the presence of urea, the main nitrogen removal mechanism of UMSR is also anammox. Increase of C/N ratio caused by urea can inhibit anammox sludge severely, but shortcut denitrification still maintain a high metabolic activity.Through batch culture test of activated sludge in UMSR, different kinds of AHLs have indicative significance for the metabolic characteristics of activated sludge. C14-HSL is the key signal molecule in the heterotrophic metabolism of UMSR activated sludge, C6-HSL and 3-oxo-C8-HSL are the key signal molecules of aerobic respiration, C4-HSL is the key signal molecule of fermentation and C14-HSL characterizing the strength of heterotrophic bacteria and nitrite reduction activity.It was found that 3-oxo-C14-HSL and C14-HSL were the key signal molecules in the Anammox, and the ratio of these two compunds could characterize the metabolic activity of the Anammox bacteria. When 3-oxo-C14-HSL/C14-HSL>1, Anammox was inhibited. And when 3-oxo-C14-HSL/C14-HSL<1, Anammox can be carried out smoothly. The higher the accumulation of 3-oxo-C14-HSL was, the stronger Anammox was inhibited.