Pretreatment and utilization of low-value fibrous biomass for bacterial fermentation of biosurfactants

Abstract

Abstract. : Surfactants are used in many food and industrial applications, including crude oil dispersion. Synthetic surfactants are produced from petroleum-based feedstocks, which are unsustainable and potentially toxic to the environment. Biosurfactants, produced by microbial fermentations are an alternative. Low-value renewable fibrous biomasses were utilized as growth media for Bacillus subtilis which produce lipopeptide biosurfactants. Two pretreatment techniques, namely, ammonia soaking and ultrasonication, were tested on switchgrass, alfalfa, soybean hulls, soybean fiber, corn DDGS (distillers’ dry grains with solubles), and bagasse prior to enzyme hydrolysis for fermentable sugars. A combination of three Novozyme enzymes (NS22086, NS22083, and NS22119) was used at a 5% (v/v) loading. Ammonia soaking pretreatment of switchgrass, alfalfa, soy hulls and bagasse was optimum at 60°C for 12 h, resulting in hydrolysis of 72%, 70%, and 80%, 75% carbohydrate yield respectively. Ammonia soaking was not needed for soy fiber and DDGS. Ultrasonication for 3 min at 100% amplitude was optimum for soy fiber and DDGS, promoting hydrolyses of 77% and 83%, respectively. Sugars released using pretreatment and enzymatic hydrolysis of biomasses were utilized as carbohydrate sources in fermentation media growth of Bacillus subtillis. Shake flask experiments at a volume of 50 mL on glucose control based media and pretreated biomass based growth media showed heightened cell growth on the pretreated biomass hydrolysates due to increased availability of glucose. These trends were observed on optimum pretreatment hydrolysates of switchgrass and alfalfa, the soy hull pretreated hydrolysates, however underperformed compared to un-pretreated hydrolysis,