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Mari Chinn, Ph.D.


PMari Chinnrofessor
Biological and Agricultural Engineering

277 Weaver Labs

NC State University
Biological and Agricultural Engineering
Box 7625, Raleigh, NC 27695 

Phone: (919) 515-6744
Fax: (919) 515-7760

Curriculum Vita

Research Interests

The defined research program focuses on production of bio-based products, such as enzymes, biochemicals, and biofuels from agro-industrial residues and dedicated biomass crops.  Several areas make up the program to address the diversity of renewable resources available and various processing methods that can be applied to generate products and enhance value:

  • Semi-solid fermentation technology, including solid substrate cultivation and liquid cultivations using solid carbon sources
  • Enzymatic conversion methods and fermentation for development of effective biomass conversion processes 
  • Hybrid application of thermal and microbial conversion technologies for biofuel production from lignocellulosic biomass
  • Solvent extraction processes are also being investigated for biomass materials that contain natural colorants, nutraceuticals and other high value compounds.
  • Integrated processing systems, linking crop production and storage practices to development of conversion technology, analytical methods and process model evaluation  

The projects and activities in these areas have evolved over time, yet the primary goal of establishing functional uses of renewable materials suited to NC for industrial bioproducts that promote sustainability and enhance rural development has remained the same.  The biomass studied includes sugar, starch and lignocellulosic crops with divisions of the program developing strongly around sweet sorghum, industrial sweetpotatoes (ISP), perennial grasses, oil seeds, and single carbon gases derived from lignocellulosic materials.  The research approach involves both basic and applied objectives, leading to development of processes at various scales, lab to industrial, that often integrate multiple operations within a given system.  The program incorporates research direction for and scholarly contributions from research associates, post-docs, graduate students and undergraduate researchers.  Education and outreach activities to disseminate advances in the research are also efforts integrated into the program. 

Program Accomplishments and Key Findings

Semi-solid Fermentation Technology—Production of cost-effective enzymes can contribute to the efficient processing of feedstocks for biologically-based products.  The use of consolidated bioprocessing and microorganisms capable of converting lignocellulosic biomass with minimal inputs can lead to more effective processing options and offer greater product flexibility at the farmgate.

  • C.thermocellum is capable of growing on alternative bioenergy crops and producing ethanol in the presence of various gaseous headspaces, including syngas, making anaerobic culturing on-farm more feasible.
  • Fungi with ligninolytic enzyme systems offer a biologically based approach to removing lignin in cotton stalks, making the cellulose in the stalks more accessible to enzymes used to make fermentable sugars.  Moisture content, presence of oxygen and time influence extent of degradation and cellulose availability.  The enzymes from this system have promise in development of chemical free pretreatment methods.
  • Ligninolytic enzyme assays have been found to be effective in measuring activities of enzymes produced on pure substrates, however for those produced on lignocellulosic biomass quantification is challenging.   

Enzymatic Conversion Methods and Fermentation—Development of effective conversion systems and identification of parameters significant to the different processing steps is needed for improved understanding and to demonstrate the feasibility of the technologies. Sweet sorghum and ISPs are crops that have shown near-term potential as viable feedstocks for a biofuel industry in NC.  

  • Fermentation parameters key to sweet sorghum conversion to ethanol have been established at the lab scale.  Successful fermentation trials have been completed at the demonstration (30 gallons) and industrial (600 gallons) scales, with > 80% conversion of available sugars to ethanol.
  • A mobile demonstration scale fermentation system has been designed and fabricated for fermentation trials and outreach activities.
  • Other value added products from the sweet sorghum crop through fermentation and conversion methods, heating technologies and extraction have potential to support total utilization of the produced biomass.
  • Enzymatic conversion and fermentation parameters to effectively convert white-flesh and purple-flesh industrial sweetpotatoes to fermentable sugars and ethanol have been defined on a laboratory scale. 
    • Initial estimates indicate that 700 gallons of ethanol/acre of ISP can be achieved 
  • Completion of the scaled-up hydrolysis unit (80 gallons) for integration into the demonstration scale mobile fermentation system provides opportunities to further investigate the feasibility of using ISPs for renewable sugar feedstocks used in industrial fermentations.  
  • Fermentation studies with adapted C. beijerinckii strain SA1 for butanol production using sugars derived from sweet sorghum and perennial grasses are providing key information for the next phase of “advanced” biofuels.
  • Composition analysis and conversion work is supporting the value-added product development needs of researchers, local biomass and animal producers, and industrial stakeholders in the state.

Thermal and Microbial Conversion TechnologiesThe combined process of gasification and fermentation can offer increased carbon conversion of lignocellulosic biomass, including lignin, and a biologically based production method for ethanol and methane among other potential products.  Outside of biomass gasification, findings from this work can be extended to treatment of industrial waste carbon gas streams.

  • A strain of Clostridium ljungdahlii (OTA1) has been adapted to produce four times the ethanol yield of the wild-type strain with improved ethanol to acetate ratios.
  • C. ljungdahlii has oxidative stress enzymes that support up to 6% oxygen tolerance and influence ethanol selectivity. Sequencing of our strains has led to greater understanding of microbial performance and opportunities for metabolic manipulation.
  • The presence of sugar and syngas carbon influence metabolism, product yields and ratios.  Clostridium autoethanogenum shows great promise in use of multiple carbon streams as it can use both xylose (byproduct of conventional pretreatment and hydrolysis approach) and syngas for ethanol production. 
  • Inducing resting autotrophic Clostridia sp. could uniquely offer a more stable cell system for conversion of actual syngas streams, yet establishing metabolically active non-growing cells remains a challenge.
  • Autotrophic cells have been successfully immobilized in nanostructured polymer coatings, concentrating microbial activity and preserving viability.  This novel approach will allow for smaller reactors and improve diffusion of gaseous of substrates in the anaerobic culture system.
  • Several gasifiers have been designed and fabricated to supply biomass derived syngas for fermentations as well as support catalyst and engine research.

Solvent Extraction ProcessesHigh value compounds can be captured from specialty crops and biomass residues, generating multiple value-added product streams from renewable materials          

  • Anthocyanin compounds from the purple sweetpotato can be extracted as a co-product of starch to sugar conversion.  Improved anthocyanin and phenolic yields in combination with high sugar yields requires extraction to occur first.
  • Near infrared (NIR) spectroscopy models have been developed to estimate the composition of industrial sweetpotatoes and sorghums, reducing labor and time invested in involved analytical methods for routine processing measurements.  Similar measurement methods are being developed for sclareol and moisture in clary sage, supporting improved processing efficiency and potential commercial profits.

Integrated processing systemsLinking field operations to biomass processing can enhance system performance and support greater understanding of system limits and opportunities for value added products.   

  • Compositional changes measured in a variety of bale storage methods, including in-field stacked bales, show promise for these methods as storage solutions for biomass feedstocks in the Southeast climate.
  • Ensiled bioenergy crops offer unique storage options for biomass feedstocks used in our developing conversion processes.
  • Feeding trials with ensiled sorghum varieties have been successful and may prove a valuable near-term market for the cattle industry and early adoption farmers. 

Perennial grasses and sorghums grown on Sprayfields have shown promising establishment and dry matter yields and have potential to add value above the common Bermudagrass options.