TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: The method involves (a) preparing fermentation culture medium by drying duckweed, crushing and passing through 35 meshes sieve, adding water in a ratio of 1:6-1:9 and heating, micro-boiling paste at 100 degrees C for 8-12 minutes, and complementing evaporating moisture, (b) reducing viscosity of culture medium by packaging the gelatinized culture medium into anaerobic bottle separately, cooling, adding nitrogen to remove oxygen, and sterilizing at 121 degrees C for 15-20 minutes, (c) preparing butanol producing microbial seed liquid by drying and crushing corn powder and passing through 35 meshes sieve, mixing uniformly the corn powder and water in a ratio of 1:1, boiling continuously for 1 hour into paste, packaging separately into anaerobic pipe after supplementing moisture, injecting nitrogen to remove oxygen, covering inner and outer plugs, performing sterilization for 1 hour at 121 degrees C, cooling to room temperature, absorbing the spore liquid from the seed culture medium containing acetone, inoculating Clostridium acetobutylicum (CCTCC M2010148) into newly prepared seed culture medium in a volume ratio of 1:8-1:12, subjecting to heat shock in boiling water bath for 90 seconds, static culturing at 37 degrees C for 23-25 hours, and using as seed liquid, and (d) inoculating the seed into the fermentation culture medium in a 8-12 vol.%, and static fermenting at 37 degrees C for 72-108 hours. The viscosity reduction involves adjusting pH of culture medium paste to 5.5 using 2 mol/l of vitriol, adding viscosity reducing enzyme (0.1-0.4 g/100g of mash), and shaking in water bath for 2 hours at 50 degrees C at 150 revolutions/minute, injecting into the anaerobic bottle separately, cooling and charging nitrogen to remove oxygen, and performing sterilization at 121 degrees C for 15-20 minutes. Preferred Components: The raw material is duckweed entirely. The viscosity reduction enzyme is mixture of xylanase and pectase in a ratio of 4:1.