Method and system for monitoring total phosphorus and total nitrogen of water quality on line

The invention relates to a method and a system for monitoring total phosphorus and total nitrogen of water quality on line. The monitoring method comprises the following steps of: a, acquiring a water sample; b, performing ultraviolet digestion on the acquired water sample according to the principle of ultraviolet digestion and ultraviolet absorption methods; and c, discharging the digested water sample into a cuvette to perform ultraviolet absorption through ultraviolet light, and meanwhile calculating light intensity through a light sensitive sensor to obtain the concentration of pollutants. The detection system comprises a PLC, a CPU, a sample pretreatment device, a multi-way sampling valve, an injector, a reactor, a detector, a human-computer interface and a communication interface, wherein the sample pretreatment device, the injector, the reactor and the detector are connected to the multi-way sampling valve through pipelines respectively. The method and the system can efficiently, quickly, stably and accurately perform continuous detection, storage and forwarding on the concentrations of the total phosphorus and the total nitrogen, and have the advantages of high measurement precision, stable performance, high efficiency, small volume, light weight, convenient assembly and debugging, low cost, low energy consumption, independent use, long-term continuous work and the like.