TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred System: In the system, the impeller is a helical impeller. One of the one or more microorganisms is a Clostridium microorganism. One or more microorganisms comprises Clostridium phytofermentans, Clostridium sp. Q.D., Clostridium algidixylanolyticum, Clostridium xylanolyticum, Clostridium cellulovorans, Clostridium cellulolyticum, Clostridium thermocellum, Clostridium josui, Clostridium papyrosolvens, Clostridium cellobioparum, Clostridium hungatei, Clostridium cellulosi, Clostridium stercorarium, Clostridium termitidis, Clostridium thermocopriae, Clostridium celerecrescens, Clostridium polysaccharolyticum, Clostridium populeti, Clostridium lentocellum, Clostridium chartatabidum, Clostridium aldrichii, Clostridium herbivorans, Acetivibrio cellulolyticus, Bacteroides cellulosolvens, Caldicellulosiruptor saccharolyticum, Ruminococcus albus, Ruminococcus flavefaciens, Fibrobacter succinogenes, Eubacterium cellulosolvens, Butyrivibrio fibrisolvens, Anaerocellum thermophilum, Halocella cellulolytica, Thermoanaerobacterium thermosaccharolyticum and Thermoanaerobacterium saccharolyticum, or its variant. The microorganism is genetically modified. Impeller has a revolution of about 10-300 rpm. The bioreactor is a stirred tank reactor, continuous stirred tank reactor, packed bed reactor, fluidized bed reactor, airlift reactor, upflow anaerobic sludge blanket reactor, or a expanded granular sludge reactor. One or more microorganisms forms a biofilm on the biomass; or one or more microorganisms forms a biofilm on the support. The support comprises metal, composite or a polymer. The biomass comprises organic matter, where the organic matter is plant matter or animal matter. Biomass comprises sawdust, wood flour, wood pulp, paper pulp, grass, switchgrass, crambe, algae, rice hulls, bagasse, jute, leaves, grass clippings, corn stover, corn cobs, corn grain, distillers grains, citrus peels, food waste, distillers grains, Distillers Dried Solubles, Distillers Dried Grains, Condensed Distillers Solubles, Distillers Wet Grains, Distillers Dried Grains with Solubles, or pectin. Preferred Method: In culturing microorganism, agitation produces a low sheer rate. Agitation does not substantially disrupt the biofilm. The biomass is agitated by the revolution of an impeller. Culturing produces a fermentation end product, where the fermentation end product is a biofuel, or alcohol, e.g. ethanol, methanol, propanol or butanol. In producing fermentation end product, the biofilm is irreversibly immobilized on the biomass. Separating is by centrifugation. The method further comprises extracting the fermentation end product by distillation. Culturing is facilitated by agitating the culture; or culturing is facilitated by static fermentation. Agitating is due to the action of an impeller. Agitation is achieved by an impeller having a revolution at a rate of 120 or 175 rpm. The biomass is 15%, 20%, or 30% (w/w) of total weight of the biomass, the medium and the one or more microorganisms, or total weight of composition. The fermentation end product is ethanol, methanol, propanol, butanol, 1,4-diacid (succinic, fumaric or malic), 2,5-furan dicarboxylic acid, 3-hydroxy propionic acid, aspartic acid, aspartate, glucaric acid, glutamic acid, glutamate, malate, itaconic acid, levulinic acid, 3-hydro xybutyro lactone, glycerol, sorbitol, xylitol/arabinitol, butanediol, an isoprenoid, or a terpene. EXAMPLE - No suitable example given.