A Study Of Treatment Of Refractory Organics In Heterogeneous Catalytic

Nowadays,dyestuff has been widely used in food,printing,medical treatment,printing and dyeing as well as cosmetics industries.Statistically speaking,there are more than 100,000types of dyestuff for commercial use.Most of them are biologically toxic,teratogenic and carcinogenic.They are also difficult to degrade in the natural environment.Therefore,the problem about handling dyeing waste water becomes very significant.Advanced oxidation processes produce free radicals with strong oxidizing property through reaction which an degrade organic matter through free radical reactions.Advanced oxidation technology can be divided into two categories:homogeneous and heterogeneous.In this experiment,heterogeneous reaction was adopted to catalyze peracetic acid to gain the free radicals which are used to treat the methylene blue dye.Our catalysts are nano zero-valent iron,nano-manganese dioxide,and diatomaceous earth-supported manganese dioxide（MnO₂/diatomaceous earth）.The different effects of different calalyst dosages,oxidant dosage,reaction temperature,substrate concentration,and pH on the degradation of dyestuff were explored,and we obtained the optimum reaction condition.We also investigated the effect of manganese dioxide catalyzed by peracetic acid on the degradation of methylene blue by ultrasonic assisted.In the four reaction systems above,the free radicals generated during the peracetic acid reaction and the TOC removal rate of methylene blue were respectively verified,and we also analyzed the methylene blue UV-visible absorption spectra.The experiment results are as follows.At indoor temperature,with an 0.02g/L dosage of nZVI,the 9mmol/L dosage of PAA,and under the initial pH of the solution,we decolorized the methylene blue solution of 100mg/L,and we got our decolorization rate up to 80%30minutes later and TOC removal rate up to 71%.With a condition of room temperature,pH=7,0.04g/L dosage of nanomanganese dioxide,the 0.02mol/L dosage of peracetic acid,after 30 minutes of reaction time,we can get a good removal effect for the methylene blue of 50mg/L with the decoloration rate up to 84%,the TOC removal efficiency up to 73%.（3）Under the assistance of ultrasound and 0.3g/L dosage of nanomanganese dioxide,the0.03mol/L dosage of PAA,and 100mg/L of methylene blue was decolorized under the initial pH of the solution.After 30 minutes,the decolorization rate was up to 85%and the TOC removal rate was up to 72%.（4）At room temperature,with an 1.6g/L dosage of MnO₂/diatomite and an 0.03mol/L dosage of PAA,50mg/L of methylene blue was decolorized after 60 minutes under the initial pH of the solution.The decolorization rate was 86%.The TOC removal rate is 68%.In the four systems above,the free radical verification experiment shows that other free radicals and hydroxyl were produced in the peroxyacetic acid reaction,which can originate a combined action to degrade methylene blue.