11-27: Production of bioethanol from spent of levan fermentation

This is to investigate using the spent of levan fermentation for the production of bioethanol. The process involves separation of levan product and glucose remnant in the broth of levan fermentation by using ultrafiltration, followed by fermenation of the glucose remnant by Z. Mobilis to produce bioethanol. High amount (~60 g/L) of levan was produced when B. subtilis (natto) was cultivated in sucrose medium; In addition, high amount of glucose and fructose by-products were also produced in the broth after 24h of fermentation. The levan product and small sugar molecules were easily separated by ultrafiltration through a membrane of 5 kDa cutoff. The levan in the concentrate was precipitated by addition of cold ethanol; the filtrate was cultivated by Zymomonas mobilis for ethanol production. Nutritional and operational factors were investigated for optimal ethanol production; the results showed that incubation of Z. mobilis in the medium containing glucose remnant, supplemented with Yeast extract 1%, KH₂PO₄ 0.1%, (NH₄)₂SO₄ 0.1%, MgSO₄.7H₂O 0.05%, at 30°C, pH 6.5, standing for 48 h gave the highest 31.84 g l^-1 (E_y 93.78%�AY_P/S 0.49 g/g) of bio-ethanol.

This is an excellent example of the use of tandem fermentation for the production of fructose polymer from readily available sucrose followed by the intermediate processing from the waste to be used in the second fermentation for bioethnaol; such efficiencies are important for the development of cost effective bio-refineries that maximise useful product formation from the available biomass. The process and the products thus produced are economically and environmentally friendly.