Investigation Of The Influence Of Organic Matter Type On The Determination Of BOD-Q As Water Quality

Organic matter is one of the main pollutants in water,and microbial metabolism is the main method to remove organic pollutants.Therefore,biodegradable organic matter（BOM）is a key index of water quality.5-day biochemical oxygen demand（BOD₅）,which is the traditional method to determine BOM,has some problems,such as long determination time,complicated operation and poor reproducibility.Compared with BOD₅,biochemical oxygen demand-Q（BOD-Q）,which uses microbial fuel cell（MFC）as biochemical reaction system,has the advantages of short determination time,simple operation and good reproducibility,and it has a broad application prospect in the determination of BOM.The determination of BOD-Q is closely related to the degradation and electricity generation of organic matter in MFC.Previous studies have shown that the degradation and electricity generation of different types of organic matter in MFC are different,which may lead to differences in the determination of BOD-Q.Therefore,it is necessary to study the determination of BOD-Q for different types of organic matter and analyze the applicability of determining BOM by BOD-Q,so as to be more suitable for the application scenario of BOD-Q.Meanwhile,volatile fatty acids（VFAs）is typical chain organic matter,which is biodegradable.VFAs in effluent is an important control indicator of the anaerobic digestion process.It is an extension of BOD-Q to combine the result of BOD-Q with the concentration of VFAs in anaerobic digested effluent.Therefore,using BOD-Q to determine the concentration of VFAs in anaerobic digested effluent has important practical application value.Therefore,the following two aspects of research were carried out in this paper:Firstly,based on the molecular structure of different organic matter,7 kinds of cyclic organic matter including phenol and 3 kinds of chain organic matter including sodium acetate were selected as samples,and the determination of BOD-Q of these samples was investigated.The results showed that the determination value of BOD-Q was generally lower than that of BOD₅ for cyclic organic matter samples,and the determination value of BOD₅ was more than 2 times that of BOD-Q.But the determination value of BOD-Q was higher than that of BOD₅ for imidazole.The determination value of BOD-Q was higher than that of BOD₅ for chain organic matter samples,and the determination value of BOD-Q was 1 to 2 times that of BOD₅.When phenol and benzoic acid were taken as samples,which were cyclic organic matter,the linear correlation between determination values of BOD-Q and organic matter concentrations was poor（R²<0.09）.When sodium acetate and mucic acid were taken as samples,which were chain organic matter,the linear correlation between determination values of BOD-Q and organic matter concentrations was good（R²>0.96）.When determining BOD-Q of cyclic organic matter samples and chain organic matter samples,the degradation efficiency of organic matter was both higher.However,when determining BOD-Q of cyclic organic matter samples,the electron transport rate was slower and the efficiency of chemical energy converted into electric energy was lower in the MFC system,which was not conducive to the determination of BOD-Q.And when determining BOD-Q of chain organic matter samples,the electron transport rate was faster and the efficiency of chemical energy converted into electric energy was higher in the MFC system,which was conducive to the determination of BOD-Q.Secondly,on the basis of the above studies,a kind of typical chain organic matter VFAs was further focused,and the feasibility of using BOD-Q to determine the concentration of VFAs by taking simulated anaerobic digestion effluent as water sample was studied.The relationship between BOD-Q and VFAs concentrations,the performance of MFC in the determination process,the influence of common oxidized ions and the influence of external resistance were investigated.The results showed that there was a good linear relationship between determination values of BOD-Q and VFAs concentrations（R²=0.9998）,so that the concentration of VFAs could be determined at the same time as the determination of BOD-Q in water sample,then the function of BOD-Q could be expanded.In the determination process,the electron transport rate was faster,the efficiency of chemical energy converted into electric energy was higher,the degradation efficiency of VFAs was higher and the p H and conductivity environment was more stable in the MFC system,which was conducive to the determination of BOD-Q.SO₄^2-of 1～5 m M had little influence on the determination of BOD-Q.With the increase of NO₃^-concentrations between 0.2 and 1.0 m M,the determination value of BOD-Q would decrease,the electron transport rate and efficiency of chemical energy converted into electric energy in the MFC system would decrease.However,NO₃^-had little influence on the degradation efficiency of VFAs and the p H and conductivity environment.There was a good linear relationship between determination values of BOD-Q and VFAs concentrations（R²>0.99）under different external resistances.With the decrease of external resistance,the electron transfer rate in the MFC system would increase and the determination time would be shortened,but the fluctuation of current would increase.The research in this paper deepens the understanding of BOD-Q as water quality,which is of great significance to the application and expansion of BOD-Q method.