The suppressed ion chromatography (IC) and molybdenum blue methods were used to comparatively evaluate phosphorus (P) concentrations. Most of the P was more resistant to hydrolysis in ion chromatography as compared to the molybdenum blue method. However, P analysis by IC is more liable to be interfered than the molybdenum blue method because of the presence of high bivalent and trivalent metal ions. Polyvalent metal ions interfere with organic P hydrolysis or the release of P from colloids during P investigation, which leads to a difference of ortho-phosphate concentrations determined by IC and molybdenum blue methods. During the environmental samples analysis, the ortho-phosphate obtained by the IC method was usually less than that obtained by the molybdenum blue method.

In recent years, persulfate (PS) has been widely studied as a promising oxidant. In this work, a new K-Fe₂O₃ catalyst was synthesized via a facile impregnation method. K-Fe₂O₃ samples were utilized as heterogeneous photocatalysts for the degradation of aquatic organic pollutants (rhodamine, RhB, and ciprofloxacin, CIP). The catalysts showed excellent catalytic activity in the presence of PS under the irradiation of visible light, owing to the generation of SO₄˙⁻ and ·OH active radicals. The degradation ratio and COD removal ratio for RhB were 99.8% and 88.3%. More importantly, the system retained a high degradation activity for RhB within a wide operating pH range of 2.9–10. The results of cycling degradation experiments confirmed that the K-Fe₂O₃ catalyst was stable and recoverable. Large-scale experiments for treating dye wastewater under irradiation by natural sunlight were carried out, showing that this study can provide a new perspective for the treatment of wastewater.