The Preparation And Application Of Poly-phosphate-ferric-sulfate Flocculant

Eutrophication is one of the important water pollution which is seriously restrict the exploitation of water resources in recent years. The untreated domestic sewage and the effluent of the wastewater treatment plants are the significant sources of phosphorus included in the surface water. Biological phosphorus removal processes are usually utilized to remove phosphorus in the sewage treatment plants. The construction of sewage treatment plants is beneficial to reduce the phosphorus load for the surface water. However, the removal efficiency of phosphorus is not ideal under low temperature condition in the winter. In some cases, the total phosphorus is even overproof. Along with the continuous improvement of the standard of drainage, the development of economic and reasonable sewage treatment processes becomes an urgent problem to be solved in the field of water environment protection.Research of chemically enhanced phosphorus removal process was conducted, which took the effluent of Anaerobic-Contact Oxidation Process in the winer as the study object. PO₄^3- was introduced to synthetise poly-phosphate-ferric-sulfate?PPFS? by anionic modified method which used FeSO₄·7H₂O, spent H₂SO₄ and H₂O₂ as the main semifinished material. The influence of the modificatory conditions on the alkalinity of PPFS was studied. The response surface methodology was used to modify the impact of the interaction between the main synthesis factors on the total iron concentration and alkalinity of PPFS. The morphological structure of PPFS was determined by Fourier transform infrared spectroscopy, X-ray Diffraction Analysis and Scanning Electron Microscope, and the synthesis mechanism was analysed. Finnally, the removal rate of total phosphorus was investigated under different operating conditions. Several important conclusions was obtained in the research.?1?The conversion rate of Fe²⁺ could reach 99.93% in the condition such as n?H₂O₂?/n?Fe?=0.7, oxidation time is 10 min, oxidation temperature is 20?. The alkalinity of PPFS decreased with the increase of H₂SO₄/Fe and increased with the increase of P/Fe and OH/Fe. The influence of polymerization temperature and polymerization time on the alkalinity of PPFS was weak. When H₂SO₄/Fe, P/Fe, OH/Fe, polymerization temperature and polymerization time was 0.3⁰.35, 0.3, 0.3, 60? and 60 min, respectively, the alkalinity of PPFS could reach a high level.?2?The Fe??? morphological analysis of PPFS indicated that: along with the increase of P/Fe, the amount of Fea was increased; the amount of Feb was at the maximum of 18.50% when P/Fe was 0.3 and then decreased; the amount of Fec was decreased; the amount of Fec was the most. The amount of Fea was decreased with the increase of OH/Fe, however the amount of Feb and Fec was increased. XRD patterns showed that PPFS had iron-phosphate polymer, bridged by hydroxyl, which was undefined structure and mixed with the trace crystal structure. The synthesis mechanism of PPFS is that the coordination of hydroxyl and phosphate competed with iron to form different complexes, and then larger complexes was produced through the bridging by hydroxyl group.?3?The response surface method was used to modify the interaction of the operating factors on the total iron content and alkalinity of PPFS. The linear effect of OH/Fe and polymerization temperature on the total iron content of PPFS was significant; the interaction between P/Fe and polymerization temperature had significant influence on the total iron content of PPFS; the quadratic term of P/Fe, OH/Fe, polymerization temperature had significant surface effect on the total iron content of PPFS. The linear effect of H₂SO₄/Fe, P/Fe, OH/Fe and polymerization temperature on the alkalinity of PPFS is significant; the interaction between H₂SO₄/Fe and polymerization temperature had significant influence on the alkalinity of PPFS; the quadratic term of H₂SO₄/Fe, P/Fe, OH/Fe, polymerization temperature had significant surface effect on the alkalinity of PPFS.?4?In the experimental coagulation of the effluent from Anaerobic-Contact Oxidation Process, the removal efficiency of TP was increased with the dosage amount of PPFS. When the dosage of PPFS was 40 mg/L, the TP contained in the effluent of coagulation could be reduced to under 0.5mg/L. When the PPFS composed with the coagulant aids such as PAM, TP removal rate was reduced when combined with CPAM and APAM; when the dosage of non-ionic PAM was 1.2 mg/L, it is beneficial to the removal efficiency of TP. The TP removal rate of PPFS is higher than the commercial PFS. Meanwhile the dosage amount of PPFS was less, and the floc formation rate was faster, the particle density was higher, the settlement rate was higher.