| Chlorinated aromatic compounds, a group of toxic and suspected carcinogenic refractory pollutants in industrial wastewater, are widely used in the papermaking, plastic, pesticides, pharmaceuticals, and petroleum chemicals etc., and may cause adverse effects on human health and the water system. The Nano zero valent iron（NZVI） /anaerobic granular sludge system was found to maintain a great removal efficiency of CACs, and was characterized as the most intensively investigated strategy for innocent treatment of industrial wastewater source. In this study, a novel core-shell amino-functionalized silica coated nanoscale zero valent iron（NZVI@SiO2-NH2） was prepared by surface modification method. The surface, structure and characteristics of the silica shell and amino group, the dispersibility, oxidation resistance and removal efficiency of 2,4,6-TCP of nanoparticles were all investigated. On the base of these above, the system of combined NZVI@SiO2-NH2-anaerobic granule sludge removing 2,4,6-TCP was built; the dechlorination efficiency of anaerobic granule sludge enhanced by NZVI and NZVI@SiO2-NH2 were compared; besides, we have studied the changes of sludge morphology, the fermentation way, electron transport activity, the methane-producing activity and the relative abundance of function of microorganism, found out the effect mechanism in the NZVI@SiO2-NH2-anaerobic granule sludge removing 2,4,6-TCP system and proposed the reaction mechanism of NZVI@SiO2-NH2 in anaerobic microbe environment. The main conclusions are as follows:After the surface modification, the agglomeration of NZVI@SiO2-NH2 have been relieved, and the nanoparticles have showed a clearly uniform core/shell structure with smooth surface with a diameter of 90-130 nm, silica shell of 20 nm, BET specific area of 123.38 m2/g. The XRD data have showed that NZVI particles was mainly composed of α-Fe0, amorphous SiO2, and the FTIR, EDS, C/H/N and EPMA results have also proved the existence of-NH2 group and silica shell, NZVI@SiO2-NH2 was successfully synthesized by the surface functionalization of NZVI using TEOS and APTMS.Amino-functionalized silica layer can prohibit the contact of NZVI and air, improve the oxidation resistance of nanoparticles, and let NZVI@SiO2-NH2 kept in the air for some time. The reunion and sedimentation rate of NZVI@SiO2-NH2 is far less than NZVI, because the silica coating and amino group grafting reduced the Zeta potential of NZVI, enhanced the interaction force between particles and the solvent, so the stability and dispersibility of nanoparticles in the water was improved. With thus, the removal efficiency of 2,4,6-TCP have also raised, 68.7% in 6h, and total dechlorination efficiency reached 48.3%, far higher than the unmodified NZVI particles.NZVI@SiO2-NH2 particles have an obvious promotion on anaerobic granule sludge removing 2,4,6-TCP, the order of degradation rate was: AGS<AGS/NZVI< AGS/NZVI@SiO2-NH2, and the dechlorination efficiency of AGS/NZVI@SiO2-NH2 have reached 92.4%. The added NZVI@SiO2-NH2 in microbial system can increase the cumulative amount of methane production, 169 ml CH4 of the cumulative biogas, increased by 31.3% than AGS only. The NZVI@SiO2-NH2-anaerobic granule sludge system have a wider p H range, within range of 5.0 to 8.0, the AGS/NZVI@SiO2-NH2 system can remove the pollutants totally. There were optimal conditions of the AGS/NZVI@SiO2-NH2 system according to the target pollutants concentration and the response of the anaerobic microbes, excessive dosage of NZVI@SiO2-NH2（> 2 g/L） will have an impact on the removal rate of collaborative system and methane-producing activity.In the hybrid system, the whole structure of anaerobic granular sludge was not destroyed on the degradation process when the NZVI@SiO2-NH2 was added. The concentration of main EPS was 36mg/g VSS in the hybrid system, which is twice than the an independent AGS system. The ETS was increased 21.5% and 27.9% in the combination of AGS and NZVI@SiO2-NH2 system after reaction 60 h and 120 h, respectively. The total concentration of VFA was 246.4mg/L, including 46.47% acetic acid, 25.34% propionic acid, 16.94% butyric acid, 15.62% pentanoic acid. The abundance of Syntrophomonas app., Syntrophobacter wolinii, Acetobacterium sp. E. limosum in the hybrid system was 79.3%, 81.3% and 16.3%, respectively. The abundance of Bacteria and Archaea was obviously enhanced by the NZVI@SiO2-NH2. The result was shown that NZVI@SiO2-NH2 could effectively promote the activity of anaerobic microorganism.It was observed that amino grafted silica shell still coated on NZVI after the reaction, and there are some acicular and schistose crystals lay on the surface of the shell. On the process of AGS/NZVI@SiO2-NH2 collaboratively removing 2,4,6-TCP, the released ions were mainly Fe2+, rising from 0.4mg/L to 42mg/L; Raman characteristic lines of NZVI@SiO2-NH2 showed characteristic peaks of α-Fe2O3 and α-Fe OOH at 218cm-1 and 283 cm-1; on the surface of nanoparticles, there were also distinct characteristic peaks of Fe2 p ranging from 706 e V to 730 e V, showing that the products were mainly composed of Fe O/Fe（OH）2 and some Fe OOH, the coating shell didn’t affect the reducing ability of NZVI. In addition to the physical coating, silicon hydroxyl groups and the core of NZVI has cooperation with chemical bonds.In conclusion, amino functionalized silica shell did not affect the dechlorination reaction of core NZVI. The high dispersibility and reducing ability could increase the particle surface area, enhancing the antioxidation abilities, reducing the concentration and toxic effects of 2,4,6-TCP on the anaerobic microbes, providing plenty of electron donor and mineral elements. Besides, the SiO2 shell can avoid the iron oxide depositing on the surface of the core NZVI directly, slowing down the problem of passivation. |
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