The Analysis Of Correlation Between DOM Fluorescence Intensity And COD Concentration During A/O/A-SBR Domestic Sewage Treatment

Dissolved Organic Matter?Dissolved Organic Matter,DOM?is widely present in all types of natural waters,whose composition and structure is very complex,and is involved in biogeochemical processes of ecosystem,greatly affect the structure and function of aquatic ecosystems,thus becoming a research hotspot and difficulty in the field of biogeochemistry and environmental science.Traditional water analysis has many drawbacks,such as time-consuming,material-consuming,producing secondary pollution easily,and only the comprehensive index of water quality can be detected through this method.The three-dimensional fluorescence spectra can effectively distinguish the composition of organic matter,and is easy to operate without secondary pollution to samples,which is widely used in the research of water organic pollutants.Thus,research on the three-dimensional fluorescence technology has significant importance on the organic detection in sewage treatment process.In this test,anaerobic-aerobic-hypoxia sequencing batch reactor?A/O/A-SBR?is used to degrade domestic sewage.We study three-dimensional fluorescence characteristics of water samples and the change of components of DOM within a typical period.A linear relationship between the fluorescence intensity and COD can be established.We can study the the influence on DOM fluorescence intensity,COD concentration and the correlation of them from different environmental factors based on this.Also,the work provides a theoretical basis for rapid determination of wastewater quality.The main results were as follows:?1?When system is running stably,three-dimensional fluorescence spectra showed that there are three main peaks in municipal sewage,which are low excitation wavelength of tryptophan,high excitation wavelength of tryptophan and humic acid,respectively.In anaerobic and aerobic segment,fluorescence intensity of low and high tryptophan excitation wavelength is significantly decreased,fluorescence intensity decreases from954.2,875.2 to 279.5,276.4,respectively;however fluorescence intensity has a slight increase in anoxic stage,fluorescence intensity increases from 279.5,276.4 to 295.2,289.3,respectively.The fluorescence intensity of humic acid changed slightly,ranges from 609.2to 561.6.The resulted effluent quality reach the standard level 1 A.[Municipal Wastewater Treatment Plant Pollutant Emission Standards]?GB18918-2002?.?2?The sum fluorescence intensity of low tryptophan excitation wavelength,high tryptophan excitation wavelength and tryptophan has a good linear relation with CODconcentration.The correlation coefficients R2 were 0.9823,0.9774,0.9809,respectively.Changes in fluorescence intensity of tryptophan was measured by three-dimensional fluorescence technique,which reflects the change of COD concentration in sewage during A/O/A-SBR process.?3?Fluorescence intensity of low and high tryptophan excitation wavelength increases as the pH increases,and relatively stable at 6?pH?8;However,the fluorescence intensity decreases along with an pH increase at pH>8 conditions.When pH<9,the humic acid fluorescence intensity increases with a pH increase;when the pH reaches 9,the fluorescence intensity reaches the maximum;After that,the fluorescence intensity starts to decrease when the pH rises again.K⁺,Mg²⁺ has no effect on fluorescence intensity of all those acid.Fe²⁺,Fe³⁺ plays a significant role in quenching the fluorescence intensity,and quenching effect of tryptophan is larger than humic acid.When Fe²⁺ concentration achieved to 400 ?mol/L,the fluorescence intensity of low tryptophan excitation wavelength,high tryptophan excitation wavelength and humic acid reduced to85.36%?89.93% ? 64.49%,respectively.When Fe³⁺ concentration achieved to 400 ?mol/L,the fluorescence intensity of low tryptophan excitation wavelength,high tryptophan excitation wavelength and humic acid reduced to 82.60%?81.78%?49.83%,respectively.When Cr³⁺ concentration achieved to 400 ?mol/L,the fluorescence intensity of low tryptophan excitation wavelength,high tryptophan excitation wavelength and humic acid reduced to51.00% ? 48.77% ? 20.55%,respectively.Cr³⁺ has the same effect on fluorescence intensity like Fe²⁺?Fe³⁺,with a relatively weak impact.?4?The COD concentration decreases as the pH value increases when pH<6;When 6? pH ? 8,the COD concentration shows a small change;when the pH>8,COD concentration increases with the pH increasing;K⁺,Mg²⁺,Fe³⁺,Cr³⁺ has no effect on COD values;COD concentration grows acceleratedly with the increase of Fe²⁺concentration;,Under neutral conditions.?5?The sum fluorescence intensity of low tryptophan excitation wavelength,high tryptophan excitation wavelength and tryptophan has a best linear relation with COD concentration when 6?pH?8.The correlation coefficient R2 fluctuate within the range of0.9262⁰.9834 ? 0.9693⁰.9827 ? 0.9521⁰.9888,respectively.When pH<6,the correlation is significantly increased with the pH increasing.The correlation coefficient R2 changes from 0.8188 to 0.9236 ? 0.8083 to 0.8813 ? 0.8199 to 0.9272 by the rise,respectively.When pH>8,the correlation decreases significantly as the pH value increases.The correlation coefficient R2 decreases from 0.8457 to 0.6433 ? 0.9006 to 0.7755 ?0.8895 to 0.7490,respectively.K⁺,Mg²⁺ has no influence on the correlation between COD concentration and the total fluorescence intensity of low tryptophan excitation wavelength,high tryptophan excitation wavelength and tryptophan.With K⁺ concentration rised from25 ?mol/L to 400 ?mol/L,the correlation coefficient R2 fluctuate within the range of0.9917⁰.9713?0.9059⁰.8935?0.9677⁰.9499,respectively.When Mg²⁺ concentration rised from 25 ?mol/L to 400 ?mol/L,the correlation coefficient R2 fluctuate within the range of 0.9742⁰.9740?0.9779⁰.9663?0.9821⁰.9739,respectively.Fe²⁺ and Fe³⁺ has an consistent correlation effects between COD concentrations and low excitation wavelength tryptophan,high excitation wavelength,humic acid,respectively.When Fe²⁺concentration rised from 25 ?mol/L to 400 ?mol/L,the correlation coefficient R2 decrease from 0.9715,0.9459,0.9953 to 0.8972,0.8843,0.9064,respectively.When Fe³⁺concentration rised from 25 ?mol/L to 400 ?mol/L,the correlation coefficient R2 decrease from 0.9261,0.9629,0.9433 to 0.7804,0.8195,0.8329,respectively.The correlation of the total fluorescence intensity of the three and COD concentrations reduced,With Fe²⁺,Fe³⁺concentration increased.Compared with Fe³⁺ concentration,Cr³⁺ has a much weaker quenching effect on low tryptophan excitation wavelength,high tryptophan excitation wavelength and humic acid,maintaining a high correlation.the correlation coefficient R2 fluctuate within the range of 0.9640⁰.9342 ? 0.9446⁰.9243?0.9510⁰.9420,respectively.