Wenyu Zhang

Optimization of the medium and process parameters for ethanol production from kitchen garbage by Zymomonas mobilis.

Plackett-Burman design was employed to screen 13 parameters for ethanol production from kitchen garbage by Zymomonas mobilis in simultaneous saccharification and fermentation. The parameters were seven enzymes for the fermentation, four kinds of nutrition salts, and two physical-chemical parameters. Only the protease and glucoamylase were determined to be significantly affecting factors for ethanol production. As a follow-up, a single factor experiment was carried out to determine the optimum usage of these two enzymes. They both showed the optimum effect at the usage of 100 U/g. Then the optimization for physical-chemical parameters during the fermentation were determined as follows: the solid to liquid ratio was 1:0.5, the initial pH 5, the incubation temperature 35°C, the inoculum size 10%, the culture time 40 h, and the corresponding ethanol yield was 53.40 g/L.

RESEARCH ON THE ADOPTION OF LACTIC ACID BACTERIA IN FOOD WASTE STORAGE AND ETHANOL PRODUCTION

The preservation and de-odorization of food waste are very important for its utilization in fuel ethanol production as raw materials. In this paper, the inoculation of lactic acid bacteria (LAB) was carried out for food waste storage and its further fermentation for ethanol. Four contamination prevention methods, anaerobic storage, autoclaving, acid usage, the inoculation of LAB, were compared in this study. The optimum conditions for inoculation of LAB into food waste as well as the fermentation characteristic were studied. The optimum inoculum size and storage time of LAB for food waste were 0.5% (V/V) and 2 days, respectively. The quantities of microorganisms such as Escherichia coliform (E. coli) and Methicillin Resistant Staphylococcus aureu (MRSA) could not be detected in the final phase of fermentation. It proved that the inoculation of LAB in food waste could prevent the growth of putrefying bacteria. The low pH or metabolic product by lactic acid (LA) fermentation was the reason for contamination prevention.

Research on Biodiesel and Ethanol Production from Food Waste

In order to solve the pollution caused by food waste, research was carried out to test the feasibility of biodiesel and ethanol production from food waste. With separation process, waste oil and rudimental solid component of food waste were obtained. Chemical synthesis was utilized for biodiesel production with oil and fermentation was chosen for ethanol production from solid parts. The result demonstrated that biodiesel produced from waste oil were mixed fatty acid methyl esters with the main components of Octadecenoic acid methyl ester, Octadecadienoic acid methyl ester and Hexadecanoic acid methyl ester. Since they were similar to the composition to those produced with other traditional raw biodiesel materials, it demonstrated that this was a possible way to utilize waste oil. Furthermore, the solid part of food waste could produce 44 g/L ethanol under 35°C for 3 days with yeast cultured. Ethanol and biodiesel production from food waste could to a large extent save the production cost as well as solve the pollution problem.

Pilot-scale open fermentation of food waste to produce lactic acid without inoculum addition

Lactic acid (LA) production through non-sterilized open fermentation of food waste without inoculum addition was investigated. Results from laboratory-scale experiments indicated that the optimal solid–liquid ratio was 1 : 1 (water content 91.7%). Addition of α-amylase could significantly accelerate the hydrolysis of food waste and consequently increase LA productivity. During the pilot-scale fermentation, the highest LA concentration (21.5 g L−1) was achieved at 48 h. After 48 h, the LA concentration decreased and the byproducts (mainly acetic acid and propionic acid) concentration increased, which was likely caused by the increased cell density of microorganisms other than lactic acid bacteria. After 48 h of fermentation, the total sugar and suspended solids concentration decreased by 65.7% and 61.8%, respectively, suggesting that the LA fermentation was beneficial to achieve the harmless reduction of food waste. The results from this study demonstrated the feasibility of LA production from food waste fermentation without sterilization and extra inoculum addition.