Practical Study On The Method Of Producing Bioflocculant By Culturing Aspergillus Niger From Starch Wastewater

Bioflocculants, having good flocculanting activity, are the metabolic products of the microorganisms, which mainly compose polysaccharide and protein. And they have aroused wide attention among home and foreign researchers because of their advantages of high flocculability, non-toxic and non-secondary-pollution etc. But its development is restricted by the high production costs. Potato starch wastewater, a kind of highly concentrated organic matter, is non-toxic. Therefore such thing can be a culture medium for microbial fermentation.Based on the preliminary study on a microbe of high floccubility from lab, this paper attempts to explore the attributes of flocculants produced by the said microbe. Through the study, the paper attempt to find a way to optimize the condition of culturing the said microbe in potato starch wastewater and confirm the best flocculant condition for bioflocculant to process potato starch wastewater. Meanwhile, the paper has made a comparative study on normal chemical flocculants in respect of wastewater treatment ability. Based on the study thereof, the paper attempts to explore the strengths and weakness between chemical flocculants and bio-flocculant concerning the effect of processing wastewater. So, the study can be a guide for industrialization of bio-flocculant. Main conclusions of this paper are as follows:1) The strain is identified as Aspergillus niger, which named A18 and it produces flocculant named MBFA18. The active ingredient of the flocculant is secreted by A18 and it present in the fermentation broth mainly.The flocculant products gain rate is 1.889 g/L. And the flocculant has a good heat resistance, low dosage and the flocculation rate is high. Its main composition is polysaccharide.2) The optimal and economical culture conditions for the strain producing Bioflocculant using potato starch wastewater were CODCr of wastewater about 5950 mg/L, the amount of glucose is 20 g/L and urea is 0.2 g/L, without adding the phosphorus source and adjust the pH value. Inoculating volume fraction of 10% of the spore suspension in non-sterile wastewater and cultivated for only 30 h, then 2 m L/L fermentation broth added to kaolin suspension can make the flocculating rate reach 93.4%, and the flocculant products gain rate is 0.82 g/L. The CODCr and turbidity removal rates of wastewater after microorganism cultivation were 90.33% and 80.01%, respectively.3) When the bioflocculant is used to flocculate potato starch wastewater, the optimized flocculating conditions were dosage of 2 mL/L, no need to adjust pH and 5 mol/L coagulant aid CaCl₂ adding 10 mL/L. The CODCr and turbidity removal rates after flocculation were 61.01% and 92.97%, respectively. 0.165 g/L proteic substance is recycled from the water.4) Conventional chemical flocculants Al₂?SO₄?₃ and FeCl₃ were used to treat potato starch wastewater in this paper. In their optimal treatment conditions, the CODCr removal rates were 60.22% and 66.93%, turbidity removal rates were 92.97% and 97.66%. To compare the treatment effect and costs of the two flocculants, determining the preferred starch wastewater treatment chemical flocculant is FeCl₃, its better treatment conditions as follows: the amount of flocculant is 700 mg/L, pH value of 8, 0.5 mol/L of CaCl₂ adding 5 mL/L, and the settling time for 10 min.5) The treatment efficiency and cost of MBFA18 and FeCl₃ were compared. The conclusion showed that MBFA18 has great advantages according to its simpler process, lower flocculation cost, higher treatment efficiency and economic benefit.