Definition
The online total phosphorus total nitrogen analyzer is an analytical instrument used for continuous and automatic monitoring of total phosphorus and total nitrogen content in water bodies. It is usually installed at key nodes of water quality monitoring, such as the inlet and outlet of sewage treatment plants, river sections, or industrial discharge points, to achieve real-time monitoring and data feedback of water quality parameters. The instrument is capable of determining total phosphorus and total nitrogen simultaneously or separately, providing critical data support for environmental management, process control, and compliance checks.
Principle
Online total phosphorus determination is usually based on ammonium molybdate spectrophotometry. The water sample is digested to convert various forms of phosphorus into orthophosphate. Under acidic conditions, orthophosphate reacts with ammonium molybdate and potassium antimony tartrate to form phosphomolybdenum heteropolyacid, which is then reduced by ascorbic acid to blue phosphomolybdenum blue, whose color depth is directly proportional to the total phosphorus concentration, and can be photometrically determined at specific wavelengths.
The online determination of total nitrogen was mainly based on alkaline potassium persulfate digestion-ultraviolet spectrophotometry. In alkaline media, potassium persulfate oxidizes nitrogenous compounds in water samples to nitrates at high temperature and pressure. Nitrate ions have characteristic absorption in the UV region, and the total nitrogen content can be calculated by measuring UV absorbance. Some instruments also use the principle of reductive-azo colorimetry.
Measurement method
The measurement process of the instrument generally follows the automated process of sampling, pretreatment, digestion, reaction and determination. First, a representative water sample is collected through a built-in pump valve system. Subsequently, the water sample may undergo pretreatments such as filtration or homogenization to remove interfering particles. For total phosphorus determination, the samples enter the high-temperature and high-pressure digestion unit to convert organophosphate and polyphosphate to orthophosphate. For total nitrogen, it is digested and oxidized at high temperature under alkaline conditions. After digestion, the sample is programmed to mix with specific reagents and transported to a colorimetric cell or flow detection cell for photometric analysis. The built-in controller converts the measured absorbance value into concentration value according to the standard curve, and completes the data recording and output.
Influencing factors
The accuracy of the measurement results is influenced by several factors. The characteristics of the water sample body, such as turbidity, color, pH, and high concentrations of chloride ions, sulfides, and other coexisting substances, may interfere with photometric determination. The operating conditions of the instrument, including the stability of digestion temperature and time, the quality and expiration date of the reagent, the strength stability of the light source, and the sensitivity of the detector, all have a direct impact on the measurement. In addition, the representativeness of the sampling system, the presence of contamination or crystallization blockages in the pipeline, and the frequency of daily calibration and maintenance are also important aspects of ensuring data reliability.
Application:
Online total phosphorus and total nitrogen analyzer is widely used in fields that require continuous water quality monitoring. In the field of municipal sewage treatment, it is used to monitor the efficiency of nitrogen and phosphorus removal in biological treatment processes and the water quality of the final effluent. In industrial wastewater treatment, it helps monitor the quality of discharged water from specific industries such as food processing, electroplating, papermaking, and other processes. In the field of environmental monitoring, the instrument is deployed in automatic surface water monitoring stations to assess the eutrophication status of rivers and lakes, providing a scientific basis for watershed management. In addition, it is also used in waterworks, aquaculture, and other occasions where nutrient monitoring is required.
Selection
When choosing an online total phosphorus and total nitrogen analyzer, multiple technical parameters and actual needs need to be comprehensively considered. The measurement range should cover the expected concentration range of the water sample to be tested, leaving a margin. The detection limit of the instrument must meet the requirements of relevant water quality standards for low concentration monitoring. Examine the measurement cycle of the instrument, which is the time it takes to complete a complete analysis, which has an impact on the response speed of process control. The reagent consumption of the instrument is related to the amount of waste liquid generated, which is related to the long-term operating cost. The protection level and material of the equipment should adapt to the temperature and humidity of the installation site, corrosive environment and other conditions. At the same time, the instrument's data interface, remote control function, fault self-diagnosis capability, and compatibility with existing monitoring systems are also important considerations. It is recommended to refer to the relevant online water quality analyzer technical requirements standards issued by the country or industry, and conduct verification tests in combination with actual water samples.