Irene Darku

Completed research in Pennsylvania State University

• Effect of Cell Wall Degrading Enzymes and Chemicals on Corn Stover Preservation and Pretreatment during Ensilage Processing
  Haiyu Ren, PhD Thesis – 2006
  Although the title of this dissertation does not seem to have a direct connection to my research area, it does have some relevance to the production of alcohol fuels. The main focus of the research is on how preservation method, in this case ensilage, can also give an added benefit of pre-treating the Corn Stover in preparation for eventual fermentation to ethanol.
  During the ensilage process, different cell wall degrading chemicals, purified enzymes and industrial enzymes were added to reduce the pH and to encourage lactic acid fermentation. The results showed that of the 5 application rates of purified enzyme mixtures, 13.4IUg-1DM was most significant in reducing pH and in increasing Lactic acid concentrations. It also shifted the dominant microbial region from Clostridia to Lactobacillus. Also of relevance is the cellulose: Hemi-cellulose [C: H] ratio derived from microbial source, which was found to be proportional to lactic acid content and inversely proportional to pH value. This is especially true with Trichoderma reesei enzymes; hence significant cellulose and hemicellulose degradation was observed in these high C: H ratio enzyme mixtures derived from Trichoderma reesei. The most effective fermentation resulted from the highest C:H ratio tested, which is 2.38. Industrial enzymes gave similar results but at lower cost.Experimental results of 15 chemical treatment scenarios showed chemical additives are currently more economical than enzymes. Five chemicals were used - sulfuric acid, formic acid, formaldehyde, ammonia and urea; the first 4 were found to increase sugar yield in enzymatic hydrolysis compare to fresh Stover and to samples ensiled without chemicals.
  Another interesting aspect of the project is the development of a mathematical model to predict the effect of enzyme addition on Stover preservation. Cellulose degradation process was also simulated from which a parameter to account for cellulose structural features was estimated, showing 56% of cellulose was in the non-hydrolysable region and unavailable for enzymatic hydrolysis.
• Biofilm bioreactors for biofuel productions
  Ali Demirci
  In this research, plastic composite-support (PCS) was developed to overcome micro-organism cell washout which results in low productivity in ethanol fermentation. PCS consist of up to 50% agricultural materials packed as bed reactor together with polypropylene for ethanol production. It simulates biofilm formation, which is a natural form of cell immobilization; that is it consists of natural attachment of micro-organisms to an inert support and supply nutrient to them. Various PCS biofilm reactors were evaluated and overall demonstrated up to ten times higher ethanol production rate than polypropylene-alone support (PPS) control.
• An on-line Approach to Monitor Ethanol Fermentation Using FTIR Spectroscopy
  Ennis L. Veale, Joseph Irudayarai, Ali Demirci, 2007
  This study focuses on using the Fourier Transform Infrared Spectroscopy (FTIR) to do a real time on-line monitoring of ethanol fermentation by S. Cerevisae. Three groups of models were developed alongside to analyze, assess and predict ethanol concentration, glucose concentration and optical density (OD). The purpose is to get real-time information on levels of biomass, substrate, and by-products for optimization of bioprocesses.
• The Effect of Harvest Date and Enzyme Addition on Corn Stover Silage for Bioconversion into Ethanol
  Qin Chen, Tom Richard, and Megan Marshall

  This research studies the variation in chemical composition of corn Stover at different harvest date and concludes early fall is the best time to harvest; and together with enzyme addition, parameters for ‘value-added’ preservation and bioconversion are improved.