Biosorption Efficiency And Mechanism Of Heavy Metal From Aquous Solution Using Aspergillus Niger Treated Rice Straw

It is an urgency of solving heavy metal pollution problems.Biosorption is very popular because of its quick,low cost,easy to do and no secondary pollution,especially in the treatment of low heavy metal ion concentration（1-100 mol/L）.Generally,biosorbents include bacteria,fungi,actinomycetes,algae,agriculture and forestry wastes,there is a single species of biosorbent in traditional treatment,biosorbing heavy metal with unmodified or physical and chemical modification.In this study,fungi and agriculture waste were combined with solid fermentation to be a new kind of biosorbent,and copper as a probe to explore the mechanism of biosorption.Liquid fermentation was instead by solid fermentation technology,and agriculture waste medium was selected by the spores production,optimizing the factors during the fermentation,and this kind of fungus-agriculture waste biosorbents were obtained.In addition,liquid fermentation production and agriculture waste as a control,solid fermentation production and fungus-agriculture waste biosorbents were studied,characterizing biosorbents with iodine value,specific surface area,Zeta potential,SEM-EDX,XPS,FTIR,FETEM and XRD.The initial solution pH,biosorbent dosage,contact time,initial concentration of the heavy metal ions biosorption were examined,Aspergillus niger spores were used to study the multicomponent competitive biosorption behavior and recycling performance;biosorption kinetics,thermodynamics and isotherm were studied,and biosorption mechanism was discussed.The iodine value of Aspergillus niger spore,solid fermented production-aerial mycelium biosorbent,liquid fermentation,Aspergillus niger treated rice straw and rice straw were 1778、1239.8、593.7、348.92 and 233.68mg/g.For the initial concentration of 30 mg/L Cu²⁺ solution,when adsorbent dosage was 0.1 g,p H was nature without any added acid and alkali,temperature was 30°C,rotating speed was100 rpm,biosorption capacity of mycelium pellets was only 8.1 mg/g,and aerial mycelium was 20.3 mg/g,Aspergillus niger spore was reached 21.3mg/g,the fermentation of straw straw for Cu²⁺ adsorption capacity 4.75mg/g also was better than that of straw stalk 1.94 mg/g.Scanning electron microscopy and energy spectrum（SEM-EDX）results show that the aerial mycelium and mycelium pellets have the similar morphology and chemical composition（C>N>P>K>O）;Fourier infrared spectroscopy（FTIR）results shown that the carboxyl（–COOH）group,amino（–NH2）,phosphate（–PO43-）and hydroxyl（–OH）were involved in the copper biosorption process.Then we have a conclusion: spores was the key factor of the high biosorptio capacity.For the initial concentration of 30 mg/L Cu²⁺ solution,when adsorbent dosage was 0.1 g,p H was nature without any added acid and alkali,temperature was 30 °C,rotating speed was100 rpm,the biosorption capacity of Pb²⁺,Hg²⁺,Cd²⁺ and Cu²⁺ were 25.3,27.9,23.4 and 22.1mg/g.In addition,spores was added to 0.5,0.4,0.6 and 0.3g,the concentration of Pb²⁺,Hg²⁺,Cd²⁺ and Cu²⁺ were reach the national standards.The effect sequence of interference cations（100-300 mg/L）on Cu²⁺ was Mg²⁺ > Ca²⁺> Na+,and negative ions SO42-and PO43-were promote the Cu²⁺ biosorption,which prove the complexation mechanism.The optimization of fermentation parameters were as follows: inoculation quantity was 1×106,temperature was 303 k,and solid-liquid ratio was 1:1.The biosorption capacity of fermented rice straw on Pb²⁺,Hg²⁺,Cd²⁺ were 16.5,23.2 and 14.9 mg/g。The best pH was natural pH 5.3,and reach the equilibrium at 60 min and 30 min,respectively.Aspergillus niger spore and fermented rice straw on Pb²⁺,Hg²⁺,Cd²⁺ was accord with second order kinetics,and isotherm model was Freundlich,this was a commom phenomenon.FTIR shown that-OH,C = O,C = O and C = C were involved in the Cu²⁺ biosorption of Aspergillus niger treated rice straw.The surface zeta potential of Aspergillus niger spores was negative,and the diameter was 2 um with ridges and grooves.The biosorption mechanism of Aspergillus niger spore on Cu²⁺ was mainly ion exchange,complexation and electrostatic attraction.Cu²⁺ in the solution was attracted by electrostatic and gathered on the surface of Aspergillus niger spore,which was full of the negative charge,and then ion exchange was happened,at the same time,complexations were formed.Biosorption process of Aspergillus niger spores on Cu²⁺ was accordence with the pseudo-second order kinetics and Freundlich model,which prove the main biosorption mechanism was chemical biosorption process and the surface of the biosorbent was multilayer and inhomogenes;Thermodynamic analysis showed that biosorption of Aspergillus niger spores on Cu²⁺ was spontaneous and endothermic.In addition,the simulation of biosorption of Aspergillus niger spores and fermented rice straw on Pb²⁺,Hg²⁺,Cd²⁺ was pseudo-second order kinetics and Freundlich model,demonstrating the similar characters on bivalent metallic cations biosorption.The effect of fermented rice straw,especially Aspergillus niger spores was excellent,which can be applied in heavy metal waste water treatment.Implements the waste resource utilization,has the double meaning in theory and reality.