| Because of the large amounts, complex components, high pollutant load and accounting for a higher proportion of paper waste water, the washing/bleaching effluent from paper mills has became one of the important source of pollution water. The conventional treatment methods are mostly limited to the primary and secondary processing, but the treated wastewater which is strongly colored and poor biodegradability still contains large amounts of lignin and its derivatives. With the state increasing standard for wastewater discharge and the increased environmental awareness of people, the traditional treatment processes have been difficult to meet the requirements. It is necessary to explore a more economical and efficient method to achieve a better treatment effect. Biomimetic, which is the direct and efficient way to achieve the"green chemistry", has both of the enzymatic catalyst and chemical catalyst characteristics. It has been studied for decades in chemical engineering field. In this study, the ferrous ions Fe(II), carboxylic acids(CA), H2O2 and O2 composed a new biomimetic system which can simulate the horseradish peroxidase in delignification. The degradation of 5-5'type,β-O-4 type lignin model compounds and milled wood lignin (MWL) in this biomimetic system were studied. The cleavages of chemical bonds in the biomimetic degradation process were speculated. Meanwhile, the copolymerization mechanism of degradation products with the metal salt flocculants was investigated. Finally, a complete theoretical system of lignin degradation, combined with followed precipitatation with flocculants was founded. It provides a theoretical basis for the application of biomimetic system in advanced treatment of papermaking wastewater.In this paper, a transition metal ion (Fe2+) and a chelating compound (CA) were used to combine a novel biomimetic system, which was characterized by FT-IR and X-ray. The results showed that they formed a new complex, which was monoclinic crystal. The synthetic route of biphenyl lignin model compound(5-5')catalyzed with laccace was investigated. The optimum conditions were obtained as following: the dosage of laccase is 16.12IU per gram of vanillin, reaction temperature is 40℃, pH is 4.5 and reaction time is 5h. In addition, theβ-O-4 type lignin model compounds were also synthesized; compared with the previous methods, the synthetic methods were modified, and the efficiency of the synthesis increased. The structures of the two compounds were characterized by FT-IR and 1H-NMR.The 5-5'type,β–O-4 type lignin model compounds and MWL were degraded successfully by the iron-based biomimetic system. The reaction products were analyzed by FT-IR and GC-MS. The FT-IR results indicated that the structural changes were very obviously after degradation; the hydroxyl and carboxyl groups of the degradation products increased significantly; the aromatic ring structures have been destroyed. The GC-MS results showed that the reaction products contained large amounts of low molecular weight phenolic compounds and carboxylic acid substances. It is suggested that the degradation process mainly contained 5-5'bond cleavage, aromatic ring opening and alkyl-aryl cleavage in the 5-5'structural degradation. In the route ofβ-O-4 degradation, the reaction mainly containedβ-O-4 ether cleavage, alkyl-aryl bond cleavage, Cα-Cβbond cleavage,aromatic ring opening and Cβ-Cr bond cleavage. The experimental results reveal the reaction route of Fe-CA/H2O2 biomimetic degradation of lignin at molecular level.The co-precipitation characteristics of coagulation of model compound of degradation products as vanillic acid/ferulic acid with two kinds of metal salt fluctuants were studied by GPC,GC-MS and nuclear magnetic resonance(NMR) techniques. The results showed that the two carboxylic acids combined with the metal salt flocculants by the coordination reaction. The way of co-precipitation was Me-OAr or Me-OOC; and macromolecular complex was gradually formed. Thus the colloid stability was destroyed with the increasing of hydrophobicity. The complex precipitated from the water, finally. The results provide a theoretical basis for the followed flocculation of the biomimetic treatment, and it is instructive for the establishment of the new wastewater treatment technology with biomimetics.In this paper, Fe-CA biomimetic-flocculation technology was used to advanced treat the washing/bleaching effluent of a paper mill. The optimal process conditions are: 10mg/L of Fe-CA complexes; 200mg/L of PFS; 150mg/L of H2O2; pH6.0; temp.30℃; reaction time 1h and sedimentation time 3h. Under these conditions, the maximum removal of CODcr and chroma achieved 71% and 80% respectively. The final CODcr was 90mg/L and chroma 40 times,and it can meet the new national discharge standard. The biodegradability index of the treated wastewater increased from 0.18 to 0.5, so that it can be completely biodegraded in the natural water area. Fe-CA biomimetic system folloed by PFS flocculation is an efficient technique in advanced treatment of pulping and papermaking effluent, because of its mild condition, high efficiency and lower running cost.
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