Study On The Effect And Mechanism Of Desizing Wastewater Treatment By Zero Valent Iron

Desizing wastewater containing high concentrations of polyvinyl alcohol (PVA) has been amajor problem in the field of wastewater treatment. Due to the poor biodegradability of PVA,traditional biochemical process is difficult to achieve ideal effect.In order to effectively degradePVA and further improve its biodegradability, the study selects self-made nanoscale zero valentiron (nZVI) and zero valent iron (ZVI) combined with microbubbles in the treatment of desizingwastewater containing PVA. The main factors of PVA degradation and mechanism of ZVI andnZVI are studied respectively.The results obtained are as following:（1）It is shown that PVA could be efficiently removed by nZVI. The effect of the initial pHof the solution, dissolveed oxygen (DO) of solution, the dosage of nZVI, the concentration of PVAand the temperature on the degradation of PVA are studied respectively. The degradation kineticsand thermodynamics are also analyzed. The reaction rate constant decreases with the rising of pHand the initial concentration of PVA increases with increasing temperature and nZVI dosage. Theactivation energy of the reaction is45.98KJ/mol.（2）PVA could be efficiently removed by ZVI. The effect of the initial pH of the solution,the dosage of nZVI, the concentration of PVA, the temperature and microbubbleon the degradationof PVA are studied respectively. The results indicate that after5minutes’ reaction the removal rateof PVA increases from22%to43%, nearly doubled, under the condition of microbubble aeration.The total removal rate increases by10%from49%to59%.（3）The study analyzes the reaction mechanism of nZVI and ZVI respectively, which resultsthat ZVI and nZVI have different reaction mechanisms in the degtradation process of PVA. Thedegradation of PVA by ZVI under acidic condition is dominated by hydroxyl radicals. Itspeculates that nZVI reaction is dominated by High iron and Oxygen free radical. By thecomparison of nZVI and ZVI adsorption reaction, it is found that the adsorption rate of PVA is8.59%,4.81%1.39%by nZVI, ZVI, MB combined with ZVI respectively. ZVI can generates a large number of hydroxyl radicals and nZVI can generates a small amount of hydroxyl radicalsunder acidic conditions by electron spin resonance (ESR).（4）At the beginning of the reaction process of ZVI dissolving PVA, MB takes theadvantage of it’s character of high speed, it can provide relatively high dissolving oxygen amountfor the system in the very moment. It results that after5minutes’ reaction, under the condition ofmicrobubble aeration the removal rate of PVA was59%, and under the condition of air bubbleaeration the removal rate of PVA was49%.