Characteristics Of R.ornithinolytica 160-1 Produced Flocculant And Its Fermentation Optimization

An efficient bioflocculant producing strain Raoultella ornithinolytica 160-1 was isolated and identified by By 16S r DNA sequencing,physiological and biochemical tests,and MALDI-TOF MS analysis.The Raoultella ornithinolytica160-1 secreted extracellular polysaccharide polymer?EPS-160?was cultured for 24 hours,and then precipitated and extracted with ethanol at 4?to obtain a crude polysaccharide.The ions and residual medium components were removed through a dialysis bag for further purification A pure polysaccharide of 2.76 g/L was obtained.The purified lyophilized polysaccharides were tested for flocculation activity and the structure and composition of the polysaccharides were examined by different methods.With the assistance of Al³⁺and Fe³⁺,EPS-160 can flocculate kaolin.With the aid of Al³⁺,the flocculation efficiency of EPS-160 is higher.When the Al³⁺concentration was 0.08 mg/m L and the EPS-160 concentration was 43.2 mg/L,the polysaccharide flocculant obtained the highest flocculation efficiency,and the highest efficiency was 97.94%.EPS-160 can be stored in a p H range of 1 to 13 and a temperature range of 40 to 100?.And EPS-160guarantee high flocculation efficiency in an environment with a p H of 3?10 and 20?100?.The experimental chemical analysis results showed that EPS-160 is mainly composed of protein?5.7%?and polysaccharide?80.3%?.The molar ratio of glucose,rhamnose and mannose in the polysaccharide components measured by high performance liquid chromatography was 3.1:1:2.4.After adding the optimal concentration of Al³⁺and flocculant,the kaolin solution significantly flocculated,the potential changed from-29.2 m V to-1.94 m V,and obvious flocculation occurred.Kaolin flocculation quickly formed a flake floc and precipitated to the bottom.The results of infrared spectroscopy indicated that functional groups such as hydroxyl,carboxyl and methoxy groups existed in EPS-160.There are three types of polysaccharides with different molecular weights measured by gel permeation chromatography.The molecular weights are 1.72×10³,1.12×10⁴and1.17×10⁶.Zeta potential and IR results show that charge neutralization and bridging are the main flocculation mechanisms of EPS-160.This study explored the fermentation conditions of R.ornithinolytica 160-1.It was determined that fermentation at 150 rpm and 25?.for 24h could obtain the highest polysaccharide flocculant with high flocculation activity.The response surface was used to optimize the fermentation production of R.ornithinolytica 160-1.When sucrose,?NH₄?₂SO₄and Mg SO₄.7H₂O were 66.41 g/L,12.84 g/L and 0.75 g/L,the maximum yield of EPS-160 was 10.11 g/L.The results of zeta potential measurements and infrared spectrometer suggested that charge neutralizationand bridging werethe main flocculation mechanism.The high flocculation rate?86.79%?was also achieved with a low-cost medium?the starch wastewater?after56h cultivation,indicating that R.ornithinolytica160-1 can be used to treat crop production wastewater,and produce flocculants with low cost fermentation.Based on a high flocculation efficiency,p H tolerance and thermal stability,EPS-160 exhibits its great potentialin industrial application.