The Photochemical Effect Of NO₂^-/NO₃^- In Water And Research On Its Driving Organic Phosphorus Transformation

Dissolved phosphorus was widely distributed in natural water such as lakes and rivers, and its transformation to orthophosphate by biomineralization and chemical decomposition is one of the leading causes of the eutrophication in water. Nitrate and nitrite(NO2-/NO3-) existing in water play an important role in the morphological transformation of organic matter based on the photochemical activity. Therefore, basing on the photochemical activity of nitrate and nitrite, study of the degradation process and mechanism of phenol degradation was carried out. Further research about the morphological transformation of organic phosphorus with nitrite is essential to provide scientific basis for the eutrophication control in water. The main results of the research are summarized as follows:(1) Xenon lamp is adopted to simulate the sunlight, with phenol as model organisms, the photolysis processes of phenol was kinetically controlled by the reactivity of nitrate. Results suggested that the oxidation rate of phenol was in accordance with first order kinetics law, and the oxidation rate increased with an increase in nitrite/nitrate concentration. What’s more, the degradation rate of phenol oxided by nitrate is higher than that of nitrate. The study further discussed the influence of p H and the humic acid concentration on phenol photolysis in the presence of nitrite. The degradation process was favored at low p H, hindered in the presence of humic acid. When terephthalic acid was used as the hydroxyl free radical molecules probe detection, ·OH was detected in phenol photolysis process, which indicated the photochemical activity of nitrite and nitrite.(2) Measurement of the transformation of organophosphorus catalyized by photochemical activity of nitrate under sunlight was conducted, together with methyl parathion(C-O-P) as organic phosphorus, which was based mainly on the study(1) attribute. The UV-vis results showed that the longer duration of lighting was, the lower the characteristic peaks strength of methyl parathion was, with new peaks. Furthermore, a small amont of PO43- was detected in the experiment by ion chromatography. The result indicated the methyl parathion transformed in the role of photochemical activity of nitrate. When high concentration of humic acid or methyl parathion were added, methyl parathion would have inhibitory effect on photochemical conversion of itself. At the same time, the study showed that the indirect photolysis of methyl parathion was accelerated by increasing Fe3+ concentration in the system. Due to the fact that the P = S bond in methyl parathion structure is relatively stable, under the sunlight, the complete transformation of organic phosphorus to inorganic phosphorus was difficult.(3) Photochemical transformation of phosphorus in eutrophication lakes: The results show that the exogenous nitrate could promote the transformation of organic phosphorus to orthophosphate under the UV light irradiation. Compared to the UV、sunlight and dark condition, it could be found that the release flux of orthophosphate was higher in light irradiation than that of dark condition. Compared to the sterilization treatment, the release of orthophosphate was also detected, which indicated that the photochemical decomposition play an important role in orthophosphate release due to the biomineralization removed.