research

"to conduct both fundamental and applied scholarly research in bioprocessing for biofuel/bioenergy production and recovery of value-added products from renewable low-cost feedstocks"

click the following links to learn more about:

(1) Anaerobic Digestion
(2) Aquaponics
(3) Biofuel
(4) Fungal Protein

Or continue reading a brief description of our work below.

  • Biochemical Conversion of High Yield Tropical Grasses into Advanced Biofuel and Biobased Product

    Napier grass, which belongs to the sugarcane family, has a high moisture content of 70-80% and reaches maturation after 8 months of planting/ratooning. The fiber yield however, remains fairly constant after 5-6 months of planting/ratooning. There is a lack of studies which examine changes in biomass composition as a result of age, and its overall effect on biomass pretreatment, enzyme hydrolysis, and fermentation into biobutanol. On the Hawaiian Islands, Napier grass is available throughout the year in all stages of growth, and can be processed green in a decentralized facility. This not only allows for onsite fractionation into solid and liquid streams during preprocessing operations, such as front-end juicing via screw pressing, but it also eliminates the need for exhaustive infrastructure for biomass harvesting, preprocessing, transportation, storage and downstream processing. The liquid stream, high in nutrients and organic content, can be collected during preprocessing and can serve as a substrate for cultivating protein-rich fungi for aquaculture feed applications in Hawaii and the Pacific region. Thus, I am exploring an innovative new concept of “green or wet processing” of Napier grass to examine how age and front-end fractionation affect the biochemical conversion of the biomass into biofuel and biobased products. The solid biomass, when preprocessed green/wet through a screw press, experiences significant physical disruption of the plant structure, thereby increasing the surface area by as much as by 75%, and eliminates the need for further size reduction. Moreover, green/wet processing reduces the need for harsh pretreatment conditions, producing fiber which can be converted to soluble sugars via commercial enzymes. The mixed sugar stream (5- and 6-carbon sugars) can be fermented to biobutanol (an advanced biofuel) using solventogenic Clostridium species. The stillage (following butanol recovery) and organic-rich effluent (after fungal biomass recovery) is digested anaerobically for biomethane production. Methane can be redirected back into the process for heat/steam or electricity generation. This research aims at developing a mobile decentralized closed-loop system for biofuel and biobased product generation with minimal environmental impacts.

  • Lignocellulosic Biomass Conversion into Biofuel through Syngas Fermentation: Evaluation of Mass Transfer and Modeling

    The goal of this research is to efficiently convert biomass-derived synthesis gas (syngas) into biofuel through anaerobic fermentation. Current approaches for syngas fermentation, however, suffer from low ethanol yield largely due to the gas/liquid mass transfer limitations of syngas (CO and H2), and kinetic limitations due to low biomass levels during fermentation. This has been the major bottleneck for the scale-up of the syngas-to-biofuel process. To overcome these limitations, I am exploring the use of innovative hollow fiber membranes (HFM) in which syngas is delivered to the attached microbes (on HFM surface) by diffusion through the walls of microporous HFM. HFM also act as support media for biofilm growth. We hypothesize that the use of HFM will eliminate the mass transfer limitation and can maintain a higher cell density in the bioreactor than traditional bioreactor designs. We are determining the volumetric mass transfer coefficients (Ka) for CO in a composite hollow fiber (CHF) membrane bioreactor. The CO concentration in the liquid phase is measured using myoglobin (Mb)-protein bioassay. Our study obtained the highest Ka value of 419.0 h-1 at a recirculation rate of 900 mL/min and at inlet gas pressure of 30 psig. The findings of this study confirm that the use of CHF membranes is effective and efficient in mass transfer of sparingly soluble gases in the liquid phase.

  • Protein-rich Fish Feed Ingredients from Biofuel Residues as a Protein Substitute for Imported Fish Meal and Other Protein Sources for Fish Feed Ingredients in Hawaii

    In this research, I am converting low-value residues (co-products) into value-added co-products using edible fungi. For example, the sugarcane-to-ethanol plants generate a considerable amount of low-value residues known as vinasse – the left-over following ethanol distillation. The residues pose a considerable disposal challenge to sugarcane ethanol industries. I am developing an innovative approach of converting low-value vinasse into high-value protein-rich fungal biomass. An FDA-approved fungus-Rhizopus microsporus is grown in an innovative air-lift bioreactor. The protein-rich fungal biomass forms pellets due to self-agglomeration and are easily recovered through gravity settling. The recovered fungal biomass is rich in protein which can be mixed with commercial fishmeal at different percentages, and would reduce the import of expensive fish feed. It may also play a role in improving fish and shrimp productivity and quality. I am also exploring the use of glycerine from biodiesel plant as a substrate to grow edible fungi. Our preliminary study shows that fungi can be grown in glycerine after dilution. The proposed research will have a significant impact in Hawaii and the Pacific region, where aquaculture is an extremely important agri-business.

  • Fungal Detoxification of Jatropha Seedcake for Aquatic Feed Applications

    My research group is investigating value-added co-product development from Jatropha-derived seedcake. Jatropha seedcake, a residue from Jatropha biodiesel production, contains high amounts of protein and essential amino acids. Thus, the use of Jatropha-derived seedcake as a protein source for aquatic feed applications is a desirable option to replace the use of commercial aquatic feeds, e.g. fishmeal and soybean meal. The protein-rich seedcake, however, contains toxic compounds including phorbol esters and curcin, which makes it unsuitable for aquatic feed applications. Therefore, detoxification is necessary before the protein-rich seedcake can be used. My research team is investigating an innovative fungal technology as a cost effective and environmentally friendly method of detoxifying Jatropha seedcake. Fungi, Rhizopus oligosporus and Phanerochate chrysosporium, are being examined in this study in solid-state fermentation.

  • Anaerobic Digestion of Green Grass for Bioenergy Production

    I am an internationally known researcher in the anaerobic digestion area and published a bestseller book which is being adapted by researchers, instructors, and consulting engineers globally. For nearly five years, I did not conduct research in this area, but in Hawaii, I saw a great opportunity to continue my anaerobic digestion research. My research mainly focuses on the anaerobic digestion of green grass for biomethane production and life cycle analysis. Grassland is a beneficial landscape as it sequesters carbon into the soil which is not released following harvesting. Moreover, biomethane produced from green grass has been shown to offer better net energy return than the first generation liquid biofuels such as ethanol. These findings have resulted significant interest on grasslands and other green grasses as potential sources of renewable feedstocks for sustainable bioenergy production. However, higher storage loss of organic matter and slow hydrolysis during digestion are the major constraints in the anaerobic digestion of grass for methane production. Thus, there is critical need of an appropriate and low-cost pretreatment method that minimizes storage loss while enhancing hydrolysis during anaerobic digestion. In this research, we are investigating ensilage with biological additives as pretreatment to enhance biomethane production during anaerobic digestion, and conducting complete life-cycle analysis of grass-to-gas.

  • Nitrogen Transformation in Aquaculture System and Its Implication to Climate Change

    Aquaculture is an important agro-based industry in Hawaii and the Pacific Islands, and is a major revenue source for many small to medium-size fish/shrimp farms in the islands. Typically in aquaculture, protein-rich feed is metabolized into different forms of nitrogen by fish/shrimp and by the microbial community present in the ponds. Nitrous oxide (N2O) is one such form that is produced through nitrification and denitrification processes. Nitrous oxide is a potential greenhouse gas (GHG) that is over 300 times more detrimental than carbon dioxide on a molecular basis. Aquaculture could become an increasingly important source of N2O emission and thus, may contribute to climate change. In addition, the accumulation of high ammonia and nitrite, particularly evident in closed recirculating systems, imposes toxic conditions to fish in aquaculture systems. In this research, I am evaluating the nitrogen transformation in aquaculture, and identifying key factors responsible for nitrogen transformation and N2O formation.
  • grants


    University of Hawaii
    • Conversion of High-Yield Tropical Biomass into Sustainable Biofuels. [Co-PI]
      -Funding Agency: USDA and USDOE, Amount: $6,000,000 (Apr 2012 - Mar 2016), (Khanal: $700,000).
    • Green Processing of High Yield Tropical Grass to Biobased Product and Biobutanol. [PI]
      -Funding Agency: Sun Grant Western Regional Center, Amount: $200,000 (Sep 2011 - Aug 2013).
    • Global Mapping of N2O Emission from Aquaculture and Its Implications to Climate Change: Fate of N2O in Water Recirculating Aquaponic System. [US Lead Researcher]
      -Funding Agency: National Research Foundation of Korea, Amount: $270,000 (Oct 2011 - Sep 2014).
    • • An Integrated BioGas-Solar Dehydration System: Increasing Sustainability through Value-Added Agriculture. [Lead University Partner]
      -Funding Agency: Small Business Innovative Research (SBIR) Phase II-USDA-NIFA, Amount: $500,000 (Khanal: $50,000)(Sep 2011 - Aug 2013).
    • Nitrogen Transformation in Aquaculture-Aquaponic System and Its Implication to Climate Change. [PI]
      -Funding Agency: USDA HATCH, Amount: $61,000 (Jan 2011 - Dec 2012).
    • Lignocellulosic Biomass Conversion into Ethanol Through Syngas Fermentation with Simultaneous Recovery of Acetic Acid using Mesoporous Silica Nanoparticle Materials. [PI]
      -Funding Agency: USDA T-STAR Pacific, Amount: $144,807 (Sep 2009 - Aug 2012).
    • A Collaborative Effort for Utilizing Regionally-based Feedstocks and Co-Products for Aquaculture Livestock Feeds. [Co-PI]
      -Funding Agency: USDA ARS, Amount: $200,478 (Jan 2010 - Dec 2011).
    • Integrated Education and Research in Clean Energy and Island Sustainability (Lead researcher, Biofuel and Bioenergy section)
      -Funding Agency: USDOE, Amount: $2.5 million (2010 - 2013).
    • Tropical Grass into Biofuel and Biobased Products: Biorefinery Approach. [PI]
      -Funding Agency: USDOE (Oct 2009 - Sep 2012).
    • Value-added Processing of Sugarcane-ethanol Vinasse: Production of Protein-rich Fungal Biomass as a Fish Feed Ingredient. [PI]
      -Funding Agency: USDA ARS, Amount: $79,987 (Sep 2008 - Aug 2012).
    • Wood utilization research on US biofuels, bioproducts, hybrid biomaterials production, and traditional forest products. [PI]
      -Funding Agency: USDA-CSREES (HATCH) (Oct 2008 - Jun 2009).
    • Effect of ultrasonic pretreatment on the biochemical conversion of banagrass to ethanol. [PI]
      -Funding Agency: USDOE (Jul 2008 - Jun 2009).
    • Value-added processing of sugarcane-ethanol vinasse: production of protein-rich fungal biomass as a fish feed ingredient. [PI]
      Funding Agency: USDA-ARS (Sep 2008 - Aug 2011).
    Iowa State University
    • Syngas fermentation to ethanol using innovative hollow fiber membrane with simultaneous recovery of acetic acid. [PI]
      Funding Agency: ConocoPhillips (Jan 2008 - Dec 2009).

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