Combined With PAM Modified Fe 3 O 4 And Bacillus EW1 To Treat The Chromium-containing Wastewater Harmlessly

With properties of hard texture,high temperature resistance,good abrasion resistance and good corrosion resistance,chromate is widely used in electroplating,tanning,dyeing and smelting industry.As a result,large amounts of chromium waste water are produced.The form of chromium in chromium waste water is mainly Cr(?).Its toxicity is 100 times as Cr(?).Cr(?)pollution is long-lasting,stable and not easy self-purification.It is very harmful to human and environment if the Cr(?)polluted water is discharged directly without treatment.In order to achieve the recycling and standard drainage of wastewater,and promote the development of environment technology,in this paper,polyacrylamide modified Fe3O4(PMMN)was applied as adsorbent to treat wastewater containing high Cr(?)concentration and bacterium EW1 was used to treat wastewater containing low Cr(?)concentration.Combine chemical and biological method to attain the innocent treatment of Cr(VI)waste water.Details are as follows:(1)Preparation,characterization and adsorption property study of PMMN:PMMN was obtained by modification of Fe3O4 with polyacrylamide(PAM)through hydrogen bonding interaction.X-ray diffraction(XRD)analysis shows that the modification of Fe3O4 did not change the structure of Fe3O4.Vibrating sample magnetometer(VSM)proves the highly saturated magnetization and superparamagnetism of PMMN,which make PMMN easily separated from liquid under magnetic field.Under the optimal experimental conditions of 400 mg/L PAM,pH of 3.0,30?,100 mg/L Cr(?),adsorption equilibrium is reached with 40 min and Cr(VI)removal efficiency is 98.3%.There is little influence of coexisting ions Na+,Fe3+,SO42-on Cr(?)removal.Pseudo-second-order kinetic model is used to fit the experiemental data and the fitting correlation coefficient R2 is larger than 0.999.Adsorption rate constant k2 is 0.372 g/(mg.min).The applicability of Langmuir and Freundlich to this experiment was investigated.Result shows that experimental data fits the Langmuir isotherm better than Freundlich.According to Langmuir,maximum adsorption amount of Cr(?)by PMMN is 35.186 mg/g.After analysis of X-ray photoelectron spectroscopy(XPS)and total Cr removal efficiency,it is proposed that the mechanism of Cr(?)wastewater treated by PMMN is adsorption-coupled reduction.PMMN regeneration is studied with NaOH solution as desorbent.The regenerated PMMN is not effective as before,but the Fe3O4 could be used to prepare PMMN to treat Cr(?)wastewater again.(2)Screening of efficient Cr(?)removal strain and its performance study:a high Cr(?)resistance(500 mg/L)strain EW1 is screened from electroplating factory wastewater.From the SEM image,EW1 is short rhabditiform,1.5-2.0 ?m in length and 0.9 ?m in diameter.After analysis of 16s rRNA,EW1 is most homologous to Bacillus axarquiensis(DQ993671).The similarity is 100%.This paper is found to be the first time Bacillus axarquiensis has the ability to treat chromium wastewater.The optimal experimental conditions are pH of 7,inoculation amount of 4%and T of 35?.Under the optimal experimental conditions,Cr(?)removal efficiency is 99.58%.The SEM analyse demonstrates that EW1 becomes longer(2.5-4.5 ?m)and narrower(0.5 ?m)after treating Cr(?).But the cellular structure is still intact.Based on analysis of SEM-EDS,XPS,XRD,FTIR and treatment effect by inactivated,living EW1 it was proposed that Cr(VI)removal was not only attributed to the reducing functional groups(-NH,-OH)on cell surface but also due to the metabolism of bacterium.And mechanism of total Cr removal was adsorption coupled with formation of chromium hydroxide precipitation.(3)Integration process combining PMMN and EW1 to treat Cr(?)wastewater and preliminary operation:A integration process combining PMMN and EW1 to treat Cr(?)wastewater is designed.The process is preliminary operated to treat simulated wastewater containing 500 mg/L Cr(?).As system expansion makes insufficient contact between PMMN and Cr(?),the desired result did not achieved at the PMMN process phase.However,Cr(?)removal efficiency reaches to 96.0%after a complete process.