Phosphorus Removal From The Eutrophic Water By Iron Internal Electrolysis Process

As a related project of the application of "Technology and Equipment of the Advanced Catalytic Reduction" (an 863 research project in the 10th Five-year plan) to the treatment of natural water, this thesis had performed a primary investigation into the efficiency and mechanism of phosphorous removal from eutrophic water by Iron Internal Electrolysis process.The effect of phosphorous removal by Iron Internal Electrolysis was investigated initially. Results show that the total phosphorus (TP) concentration in the iron-added reactor decreased from 0.57 mg/L to 0.23 mg/L after a 23-day operation, and the lowest concentration even reached 0.16 mg/L. In contrast, the control experiment without iron scraps did not show any TP decrease. Furthermore, the pH value of the overlying water in the iron-added reactor only reduced by 0.23, indicating that the method of Iron Internal Electrolysis will not bring apparent effect on pH value of water body. Further investigation on phosphorus fractions in sediment found that the addition of iron scraps leaded to an increase in Fe-bound phosphorus. In contrast, Fe-bound phosphorus decreased in the control experiment. The TP concentration of sediment in both reactors decreased, and concentration in the one with iron was 34% lower than the other one without iron. Results reveal that the addition of iron scraps not only decreases TP in the overlying water, but also prevents or reduces phosphorous release from sediment to water, leading to an increase in the load of phosphorus adsorption. Meanwhile, the addition of iron scraps enhances the phosphorus fixation capacity of the sediment in acidic condition, and weakens the phosphorus release intensity of the sediment in basic condition. The XRD analysis of the iron scraps surface oxide shows that it contains various metal oxides, including two dominant ferric oxides: (?)FeOOH (goethite) and amorphous hydrous iron oxide. Researches on phosphorus adsorption indicated that hydrous ferric oxide (HFO) can serve as an effective pH buffer substance.Furthermore, both the adsorption velocity and efficiency by the three kinds of HFOs in acidic condition are higher than those in basic one. Experiment results also show that the formation of deposited FePO₄ in the phosphorus adsorption process is negligible. By the end, experiments on the chlorella cultivation show that the influence of chlorella growth depends on the Fe³⁺ concentration. However, the pH variation caused by the addition of ferric ion can affect the growth of chlorella directly or indirectly.