Study On Immobilization And Adsorption Of Cr(?) By Cr(?) Resistant Microorganisms

In the process of producing leather products in tanning industry,a large amount of chrome tanning agent is used,so that the concentration of Cr???in the retanning wastewater is high,which is great harm to the human health and the living environment.Our state has put forward the strict index requirement for the heavy metal chromium index in the tanning industry and the sewage discharge companies,and urges the enterprise to meet the standard of discharge.Our research groups have used the composite technology to deal with the Cr???in the retanning wastewater at the earlier stage,and found that the removal rate was good and could reach the standard of discharge.But the shortcoming of this technology is that the dosage of chemical reagent in the process is large,and will increase the treatment cost.The purpose of this study is to find a suitable way to solve the confront problems at present,which is good in remove rate,simple in preparation and low in price.In this study,the Cr???resistant microorganism FN2 was isolated from the tannery wastewater,and sodium alginate?SA?and active carbon?AC?were used as the embedding agent to prepare the AC+SA+FN2 spores?active carbon+sodium alginate+FN2 spores?.The effects of AC+SA+FN2 spores on the adsorption characteristics of Cr???under different experimental conditions were investigated,and the test conditions were optimized by the response surface method.The test results show that:?1?In a plate primary screening and a shaking flask double screening in the tanning wastewater,obtained the dominant Cr???removing microorganism FN2?fungus 2?.The spores of FN2 were observed under an optical microscope,such as the foot cells,the conidia handle,the top capsule,the primary steamed stuffed buns and the secondary buns.The scanning electron microscope?SEM?observed that the spores were in the form of round particles.The three-dimensional structure of hyphae and spores was observed by Laser Scanning Confocal Microscopy?LSCM?,and the hyphae were connected with each other.After the DNA of FN2 was amplified by PCR,the fragment size of ITS was 569 bp,and the preliminary identification of FN2 was Aspergillus sp.The strain FN2 was identified as Aspergillus oryzae by the phylogenetic tree and the strain FN2 in the growth condition of the plate.?2?The three types of immobilized microorganisms were prepared:PVA+SA+FN2 spores?polyvinyl alcohol+sodium alginate+FN2 spores?,WS+SA+FN2 spores?walnut shell+sodium alginate+FN2 spores?,and AC+SA+FN2 spores,the result found that PVA+SA+FN2 spores and Cr???were dismembered in contact,and verified by different tests,the resulting immobilized material containing PVA could not be used to treat the wastewater containing Cr???.The optimum dosage of WS+SA+FN2 spores and AC+SA+FN2 spores was:the content of SA was 10%,the content of AC?WS?was 1%,the removal rate of Cr???were 75.43%and 89.80%,respectively.Thus choose the best immobilized material was AC+SA+FN2 spores.?3?The experimental results of the removal of Cr???by AC+SA+FN2spores,AC+SA and the same amount of FN2 spore showed that:when the range of pH was 2.5-7,the removal rate of Cr???in the order was:free FN2 spores<AC+SA<AC+SA+FN2 spores.When the range of temperature was 20-43?,the removal rate of Cr???was decreased initally,and then increased,the removal rate of Cr???in the order was:free FN2 spores<AC+SA<AC+SA+FN2 spores.When the time of inoculation was 0-148 h,the removal rate of Cr???by three materials?free FN2 spores,AC+SA and AC+SA+FN2spores?increased with the increase of time,and the removal rate of AC+SA+FN2 spores was the highest.When the inital concentration of Cr???was 100-800 mg/L,the removal rate of Cr???by three materials decreased with the increase of the initial chromium concentration.When the inoculation amount was 1-8 g,the removal rate of Cr???by three materials increased with the increase of the inoculation amount.?4?The removal of Cr???by AC+SA+FN2 spores was optimized by the response surface method.The P value of the model in the variance analysis table was 0.0085,the most significant,the P value of the lake of fit was 0.2139,not significant,and the coefficient of variation C.V.was 4.87%.The model could be fitted with the experiment and the accuracy was high.The interaction of the factors was:AB>BC>AC?A is pH,B is temperature,C is time?.According to the obtained optimization scheme,the average value of the verification test was85.17%,and the difference between the predicted value and the experiment value was 4.12%,which indicated that the model can simulate the test more accurately.?5?Through observed by SEM,the spore cluster was not found in the spores of the AC+SA+FN2,after the adsorption of Cr???,and the mycelia of the AC+SA+FN2 spores and the free spores were thin and rough;there were still many holes in the AC+SA.Before and after adsorption of Cr???by AC+SA+FN2 spores and the free FN2 spores in the Fourier Transform infrared spectroscopy spectrum showed that the change of the position and shape of the peaks are obvious,especially the hydroxyl group,the alicyclic amine I and the alicyclic amine II have strong interaction with the Cr???.The position and peak of the O-H bond,the C=O bond,the C-H bond and the C-O-C bond are obviously changed before and after the adsorption of Cr???by the AC+SA.The results of X-ray diffraction indicated that after the adsorption of Cr???by the AC+SA+FN2 spores,there were CrO?OH?and Cr?CO?₆,which have an oxidation-reduction effect with the microorganisms were observed.After the adsorption of Cr???by the AC+SA,only amorphous carbon was present,and no substance combined with the chromium was present.After the adsorption of Cr???by the free FN2 spores,there was only CrO?OH?that binds to the hydroxyl groups in the cell wall was present.