Study On Biosorption Of Pb²⁺ From Wastewater By Immobilized Heavy Metal Tolerant Bacteria

Heavy metal pollution was a global environmental problem.The toxic enrichment of the food chain had caused serious human health problems.Compared with other heavy metals,such as Cu²⁺,Mn²⁺,Ni²⁺and so on,Lead was a more toxic heavy metal.Lead would damage human's nerves,digestion,immunity,reproductive systems,and even would affect the intellectual development of children.In view of this,many researchers at home and abroad had focused on new treatment method of heavy metal pollution.The biosorption method had many advantages such as convenient operation,high efficiency,low investment,no secondary pollution,especially in the treatment for low concentration of lead wastewater has certain advantages.Microorganisms,especially bacteria,had great potential in the respect,and they had many species and were widely distributed in nature environment and can be used as good absorbents for Pb²⁺.The efficient lead-tolerant strain H1 was isolated and screened from a dairy wastewater in Inner Mongolia by the method of isolation and purification,the strain H1was identified as Aeromonas hydrophila by 16S rDNA.The effects of different adsorbent dosages,pH,time,initial concentration of Pb²⁺and other factors on the adsorption of Pb²⁺were studied to determine the best adsorption conditions.And then immobilization technology was used to immobilize strain H1 and rubber powder by using sodium alginate,and a new biosorbent ARSIB?Alginate-Rubber powder-Strain Immobilized Beads?was synthesized to achieve solid-liquid separation between heavy metals and water.The adsorption conditions,the properties and the adsorption mechanisms of Pb²⁺were studied.The results were as follows:The strain H1 could tolerate 500 mg/L Pb²⁺.The adsorption of Pb²⁺for the free strain H1:When the conditions were as follows:pH 6.0,the initial concentration of Pb²⁺20 mg/L,the dosage of strain H1 0.64 g/L,30°C and 30 min,the removal rate of Pb²⁺reached92.27%,and the maximum adsorption capacity of Pb²⁺was 134.76 mg/g under the optimal conditions.ARSIB were synthesized under the optimal conditions as follow:4%sodium alginate,75%bacterial suspension,3.2%rubber powder and 24 h cross-linking time.The best treatment conditions of Pb²⁺by ARSIB were as follows:ARSIB dosage 12 g/L,the initial concentration of Pb²⁺100 mg/L,pH 5.0 and 3 h.In the adsorption process of Pb²⁺by ARSIB,the fitting coefficient?0.994?of Freundlich was higher than that of Langmuir?0.981?in the isotherm of Pb²⁺adsorption,which indicated that the adsorption process was more consistent with the Freundlich equation.the fitting coefficient?0.999?of pseudo-second-order kinetics was higher than that of pseudo-first-order kinetics?0.977?in the adsorption process of Pb²⁺by ARSIB,which indicated that the adsorption dynamic process was more accordance with the pseudo-second-order kinetic equation.The analysis and comparison of EDX diagram for ARSIB before and after the adsorption of Pb²⁺:There was a peak of lead in EDX after Pb²⁺adsorption,which could determine the lead precipitate.The peaks of lead in EDX of the adsorbed Pb²⁺can be found,and P,S can play an important role in the adsorption of Pb²⁺and the formation of lead-containing precipitates.At the same time,Na,Ca,etc.may also participate in the Pb²⁺adsorption process and released into the solution.By using the analysis and comparison of FTIR of ARSIB before and after the adsorption of Pb²⁺can be found:In ARSIB,there were anion groups?such as:-CH,-NH,etc.?,and the changes in the vibrational frequency of functional groups after adsorption of Pb²⁺show that these groups were involved in the adsorption process of Pb²⁺,such as the peak of 2940 cm^-1?-CH?moved to 2920 cm^-1,and the 1440 cm^-1?-NH?peak shifted to 1420 cm^-1.And then the analysis and comparison of XRD before and after the adsorption of Pb²⁺by ARSIB showed:the compounds of lead and phosphorus existed in ARSIB after the adsorption of Pb²⁺.Lead and the functional groups?such as hydroxyl group,amino group,etc.?interacted to form a complex and attach the surface,then further react with the phosphate group to form precipitation,such as Ca₃?PO₄?₂ and Pb₅?PO₄?₃?OH?,so as to effectively remove Pb²⁺from the aqueous solution.