| COD is widely used as an important indicator of the degree of contamination of sewage or wastewater around the world.Considering to the existing problems of secondary contamination,interference and the low efficiency of the samples which are exposed in the current COD analysis method,there is a need to review the development history of COD and conclude its technical features to discover innovative methods and to study new technical principles that are Eco-friendly and more practical.This thesis firstly traces the research and invention history of COD detection principle.The potassium permanganate index,potassium dichromate method,electronic-mediated measurement involving electrocatalysis,photocatalysis,photoelectrocatalytic,and ozonation oxidation have been illustrated.It also analyzes characteristics,factors and scope of various COD measurements.The problem of most commonly used COD determining method,i.e.potassium dichromate,are discussed from five aspects:selection of oxidant,scientific definition,secondary pollution,the toxic components and existence of interfering components,The principles of innovation and improvement responsible for COD measurement are also provided.Meanwhile,it also discusses the technical development and dynamic practical application of COD method,including microwave digestion technology,spectrophotometry technology,Coulomb titration technology,automatic online analysis technology and detection technology improvements.The standardization of implementation process,the batch of sample quantity,the qualcomm quantization of real-time online information and full automation are indicated,thereby improving the efficiency of COD determination.Secondly,this thesis reexamines the practical significance of COD on water environment management and water quality science.On the one hand,by summarizing the existing five species of organic COD quality-divided methods based on the design,operation and effect simulation of the optimizing biological system which can not provide a reference for the subsequent dynamic absorption of advanced treatment process.including the quality-division based on biodegradability,the quality-division based on hydrophobicity-hydrophilicity,the quality-division based on particle size,the quality-division based on molecular size and the quality-division based on fluorescence,it puts forward a organic COD quality-division method based on the penetration time of dynamic absorption as well as the principle of this method.This method chooses to examine on the four organic compounds of phenol,glucose,methanoic acid and methyl alcohol and takes activated carbon,the most commonly used adsorbent,as the filler of the dynamic absorption fixed bed,and then explores respectively the different influences on the dynamic absorption process under different initial concentration of organic compound,different water inlet speed and different height of activated carbon.The results come that,under a fixed initial concentration,water inlet speed and height of activated carbon,the penetration time of the four organic compound ranks:methyl alcohol>methanoic acid>phenol>glucose,which shows that during the dynamic absorption process,the affinity of activated carbon with the four organic compounds ranks:methyl alcohol>methanoic acid>phenol>glucose.Therefore.we can use this method to realize the quality-division of COD according to the different penetration time of different organic compounds and their homologues.On the other hand,taking the OHO process which operates steadily in the wastewater treatment process of Guangdong Shaogang Coking Plant as an example,this thesis uses a model to estimate the relations between the discharge reduction of different unit COD and the power consumption and medicine consumption,and estimates the COD which the thermal power plant discharges to get equivalent electric energy and produce corresponding medicine,and then puts forward the high-discharge conception which is covered up by the COD discharge reduction.The result shows that,the power consumption and medicine consumption in 24h produces an amount of secondary COD which counts for 29.95 of the COD reduced.So it can be concluded that it is incorrect that the less COD in the wastewater,the better treatment effect we can get.Because when the COD is reducing,there is not only the conversion of COD but also the transfer of COD.Thus,when making the wastewater discharge standards,it is necessary to find the balance between COD reduction process and COD transfer process,and take it as the basis of the most reasonable discharge limit.Finally,in order to achieve the purpose of mercury-free eliminating the interference of Cl-on COD,firstly to explore interference mechanism of Cl-on COD in different organic systems with different concentrations of organics,which indicates that in different organic systems,the contribution of Cl-on COD shows a linear relationship with almost the same and not affected by the kinds and the concentrations of organics,then using activated carbon adsorption column fixed bed as a device for separating organics and Cl-and designing an mercury-free analysis method for testing the high chlorine wastewater's COD.The results show that in four kinds of simulative wastewater containing chlorine system,the recovery of COD is in the range of 90.9%-109.1%,and the relative standard deviation(RSD)is in the range of 0.77%-4.06%,indicating that this method has the advantage of high recovery rate,low RSD.and there is no need to use HgSO4 which is highly toxic.This method will have a great chance for becoming the common laboratory analysis methods for testing the high chloride wastewater's COD.To sum up,the thinking in combination with the COD quality-division,the ultra-low emissions risk and the mercury-free COD method plays significant roles in our country's water environmental management,economic development and social progress of civilization. |
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