Study On Lipid Producing Fungal Breeding And Fermentation Technology Using Starch Wastewater

The starch is an important industrial raw material, widely applied to many industries, such as food, chemical engineering, textile, medicine. The starch production will generate a large number of organic wastewater, causing environmental pollution and resource waste if being discharged directly. Therefore, resource treatment of starch wastewater has important social and economic significance. This research was focused on microbial lipid fermentation in sweet potato starch wastewater by Cunninghamella echinulata. The pretreatment technology of sweet potato starch wastewater, breeding of high-yield lipid fungi using starch wastewater and optimization of lipid fermentation technology were systematically studied. The lipid fermentation technology using starch wastewater in an open system was also preliminary explored. The main results are as follows.(1) The technological conditions of double enzymatic pretreatment of simulated starch wastewater were investigated through orthogonal experiments. The optimum conditions of liquefaction were obtained, with 0.035g/100g starch of high- temperature amylase addition amount, 95℃of liquefaction temperature, pH 5.5 and 30min of liquefaction time. The optimum conditions of saccharification were obtained, with 0.2g/100g starch of glucoamylase addition amount, 60℃of saccharification temperature, pH 4.5 and 5h of saccharification time.(2) A laboratory preserved strain of Cunninghamella echinulata was mutation breeded through a new composite mutation technology combined UV and pulsed strong magnetic field. A mutant C108 was obtained, with 14.7 g/L of biomass, 50.2% of oil content and 7.38 g/L of lipid yield, which were increased by 16.7%, 63.0% and 90.2%, respectively, compared with original strain. The microbial lipid composition of mutant C108 was analyzed using GC-MS. The fatty acid composition of its lipid was similar to that of vegetable oil. The results of consecutive culture showed that the mutation C108 had good genetic stability.(3) The lipid fermentation process in starch wastewater was optimized using response surface design. The optimum conditions were obtained, with pH 6.14, 27.64 mL of liquid volume in 250 mL flask, 30℃of fermentation temperature, 25% of inoculation amount and 180 r/min of rotation speed. The lipid yield obtained under optimized fermentation conditions was 10.5% more than that before optimization. (4) Treatment of starch wastewater by the mutant C108 using aerobic up-flow reactors in an open system with non-sterilized starch wastewater was investigated. The COD removal rate was 50% after about 6 h of treatment. The lipid content of mycelium was 42.5%.In summary, the fungi C108 obtained by breeding through the new composite mutation technology could grow well in sweet potato starch wastewater as well as effectively produce lipid and degrade COD. The produced lipid can be used as raw material for biodiesel production. The results in this paper laid the foundation for industrial application in the resource transformation of starch wastewater.