COD的测定---快速消解法(英文版)

ExperimentⅩthe determination of chemicaloxygen demand——the Rapid Digested Spectrophotometry method The purpose and requirements of the experiment1.Learn the Rapid Digested Spectrophotometryto determinateMethodCOD.pare the advantages and disadvantage of Potassium Dichromate MethodwithSpectrophotometry.3.Learn why and how to eliminate the influence of Chloridion.4.Know whether shake up the solution in different circumstances when we usespectrophotometry to determinate samples.Experimental program1.Experimental instruments and drugsDigester device12 digester tubes, pipetteSpectrophotometerDigestive juice IIScreening agentCatalyst2.Experimental stepsThe preparation of sample wastewater: take 3 parts 3mL sewage, 2 parts vacant sample water and 2 parts 3mL, 2 parts 5mL, 10mL 20mL 40mL respectively 1 part standard solution into 12 digester tubes, then add 1mL screening agent3mL digestive juice II and 5mL catalyst into it, finally screw their lids andshake up.Digester and Determining: put tubes into digester device and setDigester device’s temperature in 160 and time in 25 min. when time is up, let tubes in digester for cooling 15 minutes, the next let it cool in air for 10min. after add respectively 3mL clean water into 12 digester tubes.set the wavelength of Spectrophotometer in 600nm. The first determine 4 dishes difference and markwhich tube is put into which dish to determine, then determine each tubes and writ every data down table. Let the Abs be the ordinate and the concentration of standard solution be the abscissa and draw up the graph. Through the graph, calculate the COD.Experimental result and data handlingThe Abs and the standard solution dataFig. 1 Abs-the concentration of standard solutionAccording to fig. 1 and the following formula we can calculate the COD in the sewage.)/()(2L mg K F A O COD ⨯⨯=Notes: A refers to the absorbance of sample sewage. F refers to dilution multiple.K refers to reciprocal of curve slopeThe data of detainment and calculate about sewageConclusion1. Data reliability analysis2. Data reliability analysisFrom the formula we can see R 2 which mean the requirement quite well995.06383.02≤=R The average of the concentration434)397337567(311x 1=++==∑=ni i x nThe standard deviation of the concentration119213699409176891)(σn1i 2=++=--=∑=n x x iThe relative standard deviation of data%51.27%100434119%100s1=⨯=⨯=xCV From the data, we can see that our R 2 is severely lower standard data which mean that the standard solution data have big error when we digested and determinated. Similarlythe relative standard deviation (CV 1=27.51%) is very bad which mean the data have a lot of fluctuation. It is obvious that the first data is very higher than other data. When we remove it, CV 1 become to 11.56%, but it is still big than credible value.In my opinion, the experimental error mainly comes from the phase of digested, when we opened the lids, we found the solution intube have been reduced and the reduced value is different. Hereby, after we added 3mL clean water, every tube’s concentrationis also different. I think that we have mistaken the meaning of adding 3mLwater which should be adding clean water to 15ml. We should pay attention to the attitude about experiment steps.3.Some standard specifications of total chromium andhexavalent chromium in GBCOD emission limit in <Integrated Wastewater Discharge Standard>(GB 8978-1996)The standard limited value of chemical oxygen demand (COD) in <Surface Water Environment Quality Standard> (GB3838-2002)From the standard, we can the sample water have exceeded standard of surface water more than 10 times, if compare with integrated wastewater dischargestandard it is accord Ⅲstandard. But compare withthe last report in Potassium dichromate method, the value have exceeded nearly 3 times. From the words of teacher, we know the method is hardly to determinate accurately. Although the method is quickly, errors are easy appearing.4.Treatment technologiesPhysical method:the methods mainly wipe off the big organic that will cost oxygen in physical methodincluding filtering, precipitation, centrifugal separation.Chemicalmethod: we can add some Chemical substances in wastewater to react with the organic pollutants substance that cost oxygen, such as Oxidation reduction, Chemical PrecipitationBiological treatment: by microbial metabolism, we transform the organic pollutants and microbial inorganic nutrients into stable, harmless substance, like Activated Sludge Process, Biological Membrane method, Wetland Treatment. Questions and discussion1.Look up some material to explain the measuring methods of COD and theiradvantages and disadvantages of.Answer:from materials we can found these methods: Potassium Dichromate Standard Method, Potassium Permanganate Standard Solution, and Microwave Digester Method.Potassium Dichromate Standard Method and Potassium Permanganate Standard Solution are both accurate highly and smart applicability. But both methods have to cost much time to heat reflux and they also produce new pollution, such as mercury and silver.Microwave Digester Method is faster than Potassium Dichromate Standard Method and Potassium Permanganate Standard Solution, and it cost less time and drugs, its operation is also easy. But it is hard to determinate with high accuracy.2.Look up some material to explain how Chloride affects the determination ofCOD, and how to overcome it.Answer: Chloride in solution can consume catalyst and oxidant which is used to react with sample water. In other word, if there are many Chlorides, it will pull up the value of COD. We can add screening agent (mercury sulfate solution) into solution to react with Chlorides before adding catalyst.3.How to determinate COD in the water with low COD (20mg/L) and highconcentration of Chloride (more than 60000mg/L).Because the concentration of Chloride is very high, it can’t be added screening agent to cost so many Chlorides. But we can put silver pillar into sample water, when Chloride get through the resin of silver pillar, it can react with the silver ion in resin pillar, after reacted they will become Silver chloride precipitation. And silver pillar can’t react with other ion except Chloride, so it will not affect the constitution of sample water. By the method, we can only reduce concentration of Chloride, we can determinate COD by ordinary methods.。