Design Of The Online Detecting Device For Organic Waste Water COD Based On The Method Of Double Wavelengths Ultraviolet Absorption

According to traditional chemical methods for organic waste water CODmeasurement exist problems of time consuming, operation complicated, high cost,poor stability, and this method may lead to secondary pollution easily, this paperintroduces a nondestructive testing technology based on method of doublewavelengths ultraviolet absorption, and design a set of online detecting device forreal-time detection of organic waste water COD. This method has the advantages ofsimple operation, fast speed, high credibility, no secondary pollution, low cost ofmaintenance and operation, this device also has a good application prospect andmarket value.In this paper, the main contents and the research results can be summarized asfollows:1. Analyzing and researching the various methods and techniques for organicwastewater COD measurement at home and abroad by discussing their merits andfaults, exploring the feasibility and necessity of double wavelengths ultravioletabsorption method, emphases on introducing the detecting principle and significantadvantages;2. Design a set of COD online detecting device consist of light path system,waterway system, electrical system and PLC control system, paper introduces theoverall design scheme of the device, design process and hardware composition, liststhe machine diagram of each part of the water system, amplification circuit diagramof circuit system, A/D conversion step, I/O table and PLC ladder diagram and so on,completed all device selection and installation;3. Preparation of different concentration of COD standard solution andturbidity standard solution, measuring the absorbance value respectively inwavelength of254nm and546nm, establish the COD detection model based ondouble wavelengths ultraviolet absorption method. Debugging and online simulating for the software of the PLC system, verified its reliability and real-time detection.4. By experiments, we chose organic waste water samples which from sewagetreatment plant in Hangzhou, detected respectively by means of filtration, singlewavelength ultraviolet absorption method, double wavelengths ultraviolet absorptionmethod for COD, and comparative analysis with the results of national standardmethod, verified the rapidity, accuracy and easy operability of double wavelengthsultraviolet absorption method;5. Collected different sources of organic waste water sample, detected theirCOD by the online detecting device, also comparative analysis with the results ofnational standard method, the errors are within5%, show that the device meets thedetection requirements for industrial field, and reflects the COD concentrationaccurately of actual waste water;6. Summarizes the performance index of COD online detecting device, andanalysis the uncertainty, evaluation the accuracy and practicability comprehensively.At last, the paper gropes for compatibility of the device which detecting moreparameter of water quality, mainly focus on the experiments to verify the reliabilityof turbidity and Ammonia-Nitrogen concentration measurement, expand the scope ofapplication of the device.Finally, the paper summarizes the work that has been completed, and proposesadvice to improve the device.