1) Enhancing highly viscous fermentations by multiple-phase cultivation technology<\/em><\/strong><\/p>\n By suspending an aqueous culture in an immiscible oil phase, we confine the viscosity-causing mechanisms in aqueous droplets.\u00a0 This mechanism keeps the bulk viscosity manageable, although the aqueous phase may approach semi-solid gel particles.\u00a0 However, the complex multiple-phase characteristics of the new cultivation technology pose serious fundamental and process challenges to bioengineers, especially in predicting the change in droplet size and the phase inversion from W\/O to O\/W under certain culture conditions.\u00a0 These studies have been mostly limited to xanthan fermentation.<\/p>\n (2) Exploring nitrate-respiring fermentation technology<\/em><\/strong><\/p>\n Oxygen supply often limits the performance of aerobic bioprocesses, due to the poor solubility of oxygen in aqueous media.\u00a0 Many microorganisms are, however, capable of anaerobic respiration using chemical oxidants such as nitrate, nitrite, sulfate, carbonate, ferric ion, etc.\u00a0 Nitrate respiration (such as denitrification and dissimilative ammonification) is among the most well known and energy favorable.\u00a0 In this research we examine the feasibility of enhancing the productivity of oxygen-limiting fermentations by combining aerobic and anaerobic respiration mechanisms.\u00a0 Current example studied is the rhamnolipid production by Pseudomonas<\/em>.\u00a0 Its highly foaming characteristics restricts the functional aeration rate.\u00a0 The ability of Pseudomonas’s active<\/em> denitrification is used to improve the fermentation.\u00a0 Medium design has to be modified significantly to accommodate the fundamental change in biochemistry.<\/p>\n (3) Photobioreactor for algal and cyanobacterial culture<\/em><\/strong><\/p>\n We are examining ways of improving light delivery in photobioreactors.\u00a0 Among the many unique products from algal and cyanobacterial culture, the focus of our current study is the protein-layered, sub-micron, hollow, gas vesicles.\u00a0 We have demonstrated their function as ideal gas carriers, e.g. for oxygenation in shear sensitive culture.\u00a0 Other medical applications are being identified.<\/p>\n (1) Study of environmental bioprocesses using culture fluorescence<\/em><\/strong><\/p>\n Many fluorophores, intracellular and extracellular, are present in biological processes.\u00a0 The variations of their concentrations are closely linked with the biological activities and, therefore, can be used as effective metabolic and\/or process indicators.\u00a0 Among the best studied biofluorophores are NAD(P)H, i.e., the reduced coenzyme nicotinamide adenine dinucleotide and its phosphorylated form.\u00a0 Having both oxidized NAD(P)+ and reduced NAD(P)H forms, coenzymes NAD(P) are the key intermediate electron acceptors in cellular metabolism.\u00a0 Because only the reduced coenzymes are fluorescent, the NAD(P)H fluorescence reflects the intracellular redox state, in addition to the cell concentration.\u00a0\u00a0 We have used on-line NAD(P)H fluorescence in various environmental studies including biological wastewater treatment, microbial nitrate respiration (i.e. denitrification and dissimilative ammonification) and nitrification.\u00a0 We have studied its application in sludge digestion processes.\u00a0 Systematic scanning for other extracellular biofluorophores is also performed to generate a more complete understanding of the culture fluorescence profile and its relationship to the biological activities.<\/p>\n<\/h1>\n
Environmental Bioengineering<\/h1>\n