The Preparation And Key Constituents Analysis Of Flocculants Produced By Filamentous Fungi A80

Microbial flocculant is a kind of natural polymer produced by microorganisms,wich attracted much attention because of its safety, high efficiency,biodegradability,and no secondary pollution.In this study, we used the responsesurface method to optimize the flocculation culture conditions of Aspergillusniger A80,and then different methods were used to extract the microbial flocculant.On this basis, the combinations of chemical and instrumental analysis were applied toexplore the composition and molecular structure of microbial flocculant A80, aimingto clarify the flocculation mechanism and further promoting the practical applicationof microbial flocculants. The main results are as follows:(1)The single factor optimization shows that the dosage of carbon source andnitrogen source are respectively60g/L and1.2g/L, as well as a60%volume ratio, wecan obtain the highest flocculatin efficiency. The response surface optimizationindicates that a93%flocculating rate for Kaolin will be reached when the carbonsource dosage, culture time,volume ratio and nitrogen dosage are respectively53g/L、46h、49%and0.8g/L.(2)Four different extracellular polymers(ECP) extraction methods-thermalextraction, centrifugal sedimentation, ion exchange resin (CER) and sodiumhydroxide combined with ultrasonication,were compared on Aspergillus nigerA80,and ther results show that sodium hydroxide combined with ultrasonication canachieve the highest yield (1950mg·L-1) and no significant cell damage. Themain component of Aspergillus niger A80ECP is polysaccharide (80%), and there isalso a small amount of protein, nucleic acid. The infrared spectroscopy (FI-IR) resultsshow that the ECP has many flocculating activity groups like the carboxyl, hydroxyland amino. Gel permeation chromatography (GPC) results show that the ECP has amolecular weight distribution of2.13~7.21×104Da.(3)The crude polysaccharide purified from A-0Aspergillus niger A80ECP is divieded two components of A-1and A-2through the column chromatography.Andthe HPLC results show that A-1contains only rhamnose (neutral sugar: sugaramino: uronic acid=29:10.8:1) and its molecular weight is2.34×104Da. A-2is onlycomposed of mannose with a7.05×104Da (neutral sugar: sugar amino: uronicacid=29:10.8:1). Methylation analysis and NMR results show that:the polysaccharides A-1is most composed of [-4)-α-Rhap (1�'] and [-4)-β-Rhap (1�'] straight chain rhamnose and the small part is [-3)-α-Rhap (1�'] and[-3)-β-Rhap (;1�'] straight chain. Polysaccharide A-2contains a large number of [-2)-α-Manp (1�'] straight chain structure and a small amount of [-1)-α-Manp (1�'] structure.(4)Under the condition that pH is11and the dosages of coagulant and cultrebrothare both2mL, we can abtain the best treatment effect of100mL pig washingwastewater.