Treatment Of Phenolic-contained And Chromium-contained Wastewater By Mixture Of Bacteria And Microalgae

With the rapid development of chemical industry,the productive activities of human have a serious impact on the water environment.Chromium pollution and phenol pollution are widely found in dyeing,pharmaceutical and tannery industries.In recent years,it has become a focus technology to treat phenol-containing and chromium-containing wastewater by microorganism with its low cost and no pollution characteristics.However,the existing treatment technology is limited by the degradation conditions of microbial species,so it is an inevitable trend to strengthen the technology of biological treatment of wastewater.In this paper,the degradation and removal of phenolic compounds and hexavalent chromium in wastewater were studied by using the mixed culture of different microalgae and bacteria.A strain of bacteria capable of growing with catechol as the sole carbon source and two strains capable of removing Cr(?)were isolated from printing and dyeing wastewater.The catechol-degrading strain was subjected to physiological,biochemical and 16SrRNA identification,and it was confirmed that the catechol-degrading bacteria belonged to Acinetobacter and named Acinetobacter sp.A-6.Two strains of Cr(?)degradation were found belong to the genus Serratia and the genus Delftia,named Serratia sp.S-3 and Delfitia sp.D-7,respectively.The strain A-6 was mixed with three kinds of microalgae in the laboratory for degrading catechol.The three microalgae were Chlorella pyrenoidosa?Selenastrum capricornutum and Scenedesmus obliquus,respectively.It was found that the degradation effect of the strain A-6 on catechol was the best when mixed with 10%chlorella pyrenoidosa,and the degradation rate of catechol reached above 96.53%.The degradation of catechol by temperature,pH value,concentration of catechol,amount of bacteria and volume of medium were studied after mixing the strain and the microalgae.Within a certain range,it was shown the following trends:the more the amount of bacteria,the greater the influence of on the degradation of catechol in the mixed system of bacteria and microalgae,and the faster the degradation rate of catechol.When the temperature was 33?,the mixed system had the best degradation effect on catechol,and the removal rate of 800 mg/L catechol was more than 96%in 12 h.When the pH value is 6.0,the mixed system has the highest degradation effect on catechol.In addition,the characteristics of catechol 1,2dioxygenase(C12O)in the strain A-6 showed that the degradation pathway of catechol was achieved by opening of itself benzene ring.The stable range of C12O activity was from pH6.0 to 8.0,and the optimal pH value was 7.0.The enzyme is sensitive to high temperatures and has the highest enzyme activity at 30?(2.54 U/mg).The kinetic constant of the enzymatic reaction of C12O with catechol as substrate was Km=41.54 mol/L,and Vmax=0.35 ?mol/(L·min).Under the same conditions of total bacterial inoculation,the strains S-3 and D-7 were mixed in a 1:1 ratio and the removal effect of Cr(VI)was better.Removal experiment of Cr(VI)was conducted by mixing three microalgae,namely,Chlorella pyrenoidosa,Selenastrum capricornutum and Scenedesmus obliquus,respectively,with the two strains S-3 and D-7.It was shown that the 20 mg/L Cr(?)was removed to 10.24 mg/L at 24 h with 10%of the amount of Selenastrum capricornutum in the mixed system,and the removal rate of Cr(?)reached 64.79%.Single factor experiments showed that the optimum carbon source for removing Cr(?)was glucose and sodium pyruvate.Other optimum conditions of single factor for removing Cr(?)were as follows:the optimum metal ion was Cu2+,the optimum temperature was 33?,the optimum microalgae inoculation amount was 5%,the optimum initial pH value was 6.0,and the optimum salinity was 1%,respectively.A Placket-Burman screening experiment design showed that the three key factors affecting the removal of Cr(?)were temperature,Cu2+ and glucose,respectively.The steepest climbing experiment was used to approach the maximum response region of the three key affecting factors.Box-Behnken experimental design and response surface optimization analysis showed that the optimal conditions for removing Cr(?)were as follows:the temperature was 29.74?,the Cu2+ concentration was 27.65 mg/L,the glucose content was 2.41%(w/v),the sodium pyruvate content was 2%(w/v),the inoculum was 7%,and the pH was 7.0,respectively.Under the optimized conditions,the removal rate of Cr(?)by the mixed system of bacteria and microalgae reached 97.89%.Under the same treatment time,the removal rate of Cr(?)in the optimized bacteria and algae system was increased by above 30%,and the removal effect was obvious after optimization.The relative activity of the hexavalent chromium reductase of the two strains of Cr(?)degradation S-3 and D-7 was able to reach 80%or more in the temperature range of 20-50?.The optimum pH of the hexavalent chromium reductase of the strain S-3 was 6.0,and the kinetic constant of the enzymatic reaction was Km=86.94 ?mol/L,Vmax=2.71?mol/(L·min).The optimum pH of the hexavalent chromium reductase of the strain D-7 was 7.0,and the kinetic constant of the enzymatic reaction was Km=103.18 ?mol/L,Vmax=3.38 ?mol/(L·min).The research in this paper shows that the mixed culture system of bacteria and microalgae has obvious advantages for removal effects on phenol and chromium compounds in wastewater,and also has good theoretical value and application prospects for biological treatment technology of phenol-containing and chromium-containing wastewater.