| With the development of economy and industries like building, transport, power and telecom, the demand and production of iron towers, steel frames and tires et al. increases rapidly. During the production of these products, large amount of steel and iron pickling waste acid which is hazardous is generated from surface derusting using HCL or H2SO4. The preference technology suggested for dangerous waste treatment is comprehensive utilization, that is converting the waste to resources. In Qingdao, textile industry accounts for a large proportion of the economy. The knitting printing and dyeing wastewater is difficult to treat. Especially, the treatment of the remaining dyes in the dyeing wastewater is much more difficult. Therefore, releasing dyeing wastewater with higher chroma level than standard level often occurs in dyeing enterprises, which seriously effected the natural aquatic ecosystem.The technical innovation of this study is to overcome the shortcomings of both ferrous and trivalent salt which are widely used in dyeing wastewater treatment. The ferrous could decolor the wastewater but makes the effluent yellow after treatment, and trivalent salt had good coagulation performance but couldn't decolor the wastewater perfectly. In this study, we developed two kinds of coagulant, BH-1 and BH-2, which combined the good performances of both ferrous and trivalent salt by introducing the flocculation ferric ion and aluminum ions to ferrous. BH-1 and BH-2 exhibited higher removal efficiency of both CODcr and chroma than ferrous or trivalent salt.Structure characterization of BH-1 and BH-2 was analyzed by UV-visible absorption spectra (UV-Vis), X-ray diffraction, Fe-Ferron complexation timed spectrophotometry and Al-Ferron complexation timed spectrophotometry. In the UV-Vis absorption spectra, the peak of BH-1 and BH-2 was 635nm and 618nm, respectively. For X-ray diffraction analysis, the main crystals in BH-1 was FeCl2(H2O)4(FeCl3)H2O, FeCl2·2H2O andFeCl3·6H2O, and the main crystals in BH-2 was FeCl2·2H2O, FeCl2(H2O)2, FeCl2(H2O)4, beta-Fe2(OH)3Cl, Al2(OH)5Cl·2H2O and Al10Cl3(OH)27·13H2O. The result of Fe-Ferron complexation timed spectrophotometry and Al-Ferron complexation timed spectrophotometry analysis showed that, the form of trivalent salt in BH-1was Fe (Ⅲ) and the distribution pattern was Fea. In BH-2, the trivalent salt in BH-2 was Al (Ⅲ), and its species distribution pattern was 74.8% of Ala (monomer and oligomer form) and 25.2% of Alb (medium aggregate form). No form of Alc polymer macromolecules was detected.The optimal working condition for BH-1 decolorizing coagulant is: adding 0.81.0‰decolorizing coagulant to the dyeing wastewater, then adjusting pH to 7.58.0. Under the above condition, large flocs is formed with faster sedimentation. The removal rate of CODcr and chroma is more than 55% and 95%, respectively. The quality of effluent water is up to standard DB37/533-2005. The cost of treatment is 0.40 yuan/ton. As the pH of decolorizing coagulant itself is below 1, this coagulant is suitable to treat wastewater like printing and dyeing wastewater with high pH.The BH-2 decolorizing coagulant also exhibits good settlement ability. The optimal condition for using BH-2 decolorizing coagulant is: adding 0.8‰decolorizing coagulant to the dyeing wastewater, then adjusted pH to 7.07.5. The removal rate of CODcr and chroma is 59.8% and 97%, respectively. The quality of effluent water is up to standard (DB37/533-2005), too. The cost of treatment is 0.45 yuan/ton. The pH of this coagulant is about 3.5, so it is suitable for the treatment of dyeing wastewater with low or neutral PH. In actual application, the amount and cost of coagulant used, and the removal rate of CODcr are relatively higher than those in experiment. The removal of chroma is lower than that in experiment. But the quality of effluent is still up to standard (DB37/533-2005). As the new coagulants are liquid, the labor cost for transport and preparation of stock liquid are saved. Meanwhile, the investment and maintenance fee for dissolving coagulants equipment are saved, which also decreases the cost of dyeing wastewater treatment.Dosage prediction model of GM (0, N) for BH-2 was built by Gray theory. The result showed that using Gray GM (0, N) model could be automatically adjusted the adding of BH-2 according to the changes of water quality, which could ensure the treatment effect and also save the cost of dosage.In conclusion, the new coagulants developed in this study not only make comprehensive utilization of waste acid, but also exhibit good decolorizing effect. They have good application prospects.
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