| Beside the characteristics of general heavy oil wastewater, such as high concentration of pollutants, complex composition and relatively poor biochemical characteristics, Heavy Oil Petrochemical Wastewater (HOPW) is more complex and stable than heavy oil wastewater, due to using many chemicals additives in the refining process and fluctuation of quality and quantity. Because many heavy oil refineries located in the Liaohe River basin, HOPW has become important pollution sources of Liaohe River. To treat the HOPW, the refineries have built a large number of wastewater treatment facilities. However, as the local environmental laws and regulations stringent increasingly, the treatment effect of the facilities cannot meet the requirements of environmental protection. It has become a common problem for many petrochemical enterprises to find an economical and feasible way to treat the HOPW, especially to enhance the existing wastewater treatment process.Based on the status of the HOPW treatment technology and the characteristics of raw water and biochemical treated water, a new kind of cationic polymer flocculants were synthesized to improve the efficiency of pre-processing and enhanced flocculation of the bio-treaded water and resolved the contradiction between the meeting the pollutant emission standards and the high cost of the HOPW treatment.The efficiency of flocculants is key factor to effect HOWP treatment. Therefore, according to the shortcomings of the current flocculants and the water characteristics, new kinds of Poly Ferric Silicate Sulphate phosphate (PFSiSp) were synthesized by composite anions modified copolymerization method base on Poly Ferric Silicate Sulphate (PFSiS). Moreover, the synthesis factors, component ratios and application conditions properties of PFSiSp discussed by investigating the pollutants'removal efficiency of treating the simulated water and the actual HOPW samples.The polysilicate (PS) synthesis conditions were determined by experiments as follows: Si concentration of 0.5 mol·L-1; activation pH of 4, synthesis temperature of 25℃. PFSiS synthesis conditions as follows: initial Fe ion concentration of 0.3 mol·L-1, NaHCO3 as alkalization agent, aging temperature at 60℃and aging time of 2h. Using the PFSiS to treat simulated wastewater and HOPW, at different basicities (B value) and Fe/Si molar ratios, the results showed that PFSiS had a good flocculation performance in appropriate scale of B value and Fe/Si. The 1.0PFSiS5.0 (B=1.0, Fe / Si=5.0) had the best performance in the all flocculants. The same conclusions were obtained in treating the actual HOPW. The 1.0PFSiS5.0 is the most effective to remove oil and COD than the others in the experimental scale. Experiment results of the 1.0PFSiS5.0 Stability indicated that it can storage stably more than 60 days when NaH2PO4 was used as the stabilizer and the Fe/P value of 10. Moreover, adding phosphate can improve the floccunlant efficiency. Finally, the optimal ratios of PFSiSp were selected as follows: B = 1.0, Fe/Si = 5.0, Fe/P = 10.The pretreatment results of the actual HOPW exhibited that PFSiSp can remove 65% COD and 96% oil in the appropriate scale of dosages and suitable pH values conditions. The B/C (BOD/COD) value of the pretreated wastewater can be increased 10% than the raw wastewater. The change of B/C values indicated that PFSiSp can remove the nonbiodegradable COD efficiently. To optimize the application conditions, PFSiSp also was used as flocculant to decrease COD remaining in bio-treated HOPW by enhanced flocculation method. The results proved that nearly 50% COD can be removed under the dosage at 40 mg·L-1 and the setting time of 120 min conditions.To study the impact of the synthesis conditions on the composition of Fe (Ⅲ) hydrolysis and polymerization products, RSM experiment method was adopted. Using the method, the multiple regression analysis models were established between the B value and Fe / Si corresponds to Fea, Feb and Fec respectively. In experiment scales, the errors between the models predicted values and the measured values less than 5%. Using the models can decrease the selecting range of synthesis conditions. Furthermore, PFSiS flocculants were characterized by FTIR, XRD and SEM methods. The results indicated that Si participate the Fe (Ⅲ) hydrolysis and polymerization processes and conjoin with Fe atoms through the Fe-Si and Fe-O-Si bonds. Besides a few of hexagonal and orthorhombic crystals, most of the substances in PFSiSp were amorphous materials. SEM results exhibited that main substance existing in PFSiSp is two kinds of amorphous materials and mixed crystals.Using ICP-AES, IC, and GC-MS methods, the characteristics of HOPW were analyzed. The HOPW samples were collceted from the distillation, catalytic cracking, coking processes and the treatment plant's inlet. The results showed that it is low heavy metals content, lack of phosphorus and the major organic pollutants are composited of alkanes, methyl phenols, small molecular organic acids and amines. Most of the alkanes contained more than ten carbon atoms. All the HOPW samples contain Polycyclic Aromatic Hydrocarbons (PAHs) in different degrees and the majority of PAHs are naphthalenes, anthracenes, phenanthrenes, pyrenes and their derivatives.Field experiments results showed that more than 92% of oil, nearly 60% COD and 39.3% of phenols can be removed using the PFSiSp as flocculant in the pretreatment of the actual HOPW. All the PFSiSp performance and removal rates stability are superior to LHSH-1 flocculant, which is a single component polymer of iron salt and used in this field. On the aspect of removing sulfide, PFSiSp and LHSH-1 can remove about 85% of sulfide. During the field experiments of enhanced flocculation for bio-treated HOPW, PFSiSp can remove COD steadily and the average COD removal rate is 44.35%; The COD remains in supernatant less than 50 mg·L-1 and meet the local emission standards in Liaoning Province. The running cost of PFSiSp is 0.83 RMB·t -1.
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