Grantee Research Project Results

With the rapid growth of the biodiesel industry, the production of crude glycerol as one of the major biodiesel byproducts has been dramatically increased. Fully utilizing such a large quantity of crude glycerol is critical to the sustainability of the biodiesel industry. Lactic acid is an important industrial chemical that is widely used as a food additive for flavoring and preservative, a moistener in the cosmetic industry, and recently used as a raw material for poly-lactic acid (a biodegradable plastic) production. Some fungal strains can effectively utilize crude glycerin as a sole carbon source, and unlike its competitors of lactic acid producing bacteria, tolerate high impurities and require less nutrient supplements to grow and produce optical pure L-lactic acid. Due to the limitations of high raw material costs and nutrient requirements the bacterial lactic acid processes are currently encountering, fungal culture on a cheap feedstock of crude glycerol, along with fewer requirements of other nutrients and high tolerance on impurities in crude glycerol, could be a better solution for both biodiesel and lactic acid industries. In addition, fungal pelletization technology will overcome an inherent disadvantage in that fungal strains form cotton-like biomass, which will significantly improve mass transfer and biomass handling and further enhance lactic acid yield and productivity.

 

The goal of the project is to use the pelletized fungal fermentation on crude glycerol from biodiesel production as a nutrient source to produce an optically pure L-(+) lactic acid. The specific objectives are: (1) testing and optimizing lactic acid production using crude glycerol as carbon source; (2) maximizing lactic acid production using different culture methods; and (3) testing the economic feasibility of the process. The success of this project will turn an environmental liability of biodiesel waste into a public and private asset, which would lead to biodiesel production that is more economical and sustainable.

A pelletized fungal fermentation utilizing biodiesel waste crude glycerol as a nutrient source was undertaken to produce an optically pure L-(+) lactic acid and determine the value of crude glycerol (a market-limited and abundantly available waste) as an alternative to the commonly used carbon source of glucose in lactic acid production. The effect of crude glycerol on fungal lactic acid production has been studied to convert the crude glycerol from a waste into a resource.

 

The major contribution of this study is the utilization of biodiesel waste (crude glycerol) to produce lactic acid via pelletized fungus Rhizopus oryzae. When using crude glycerol from the biodiesel industry as a sole carbon source to culture pelletized filamentous fungus Rhizopus oryzae under optimized conditions, L-(+) lactic acid was one of the dominated metabolites in the fermentation broth. In addition, this fungal strain has lower nutrition requirements than bacteria currently used in microbial lactic acid production. Thus, using fungi can significantly reduce the fermentation cost as well as simplify the downstream product separation process. Environmental benefits and cost savings also can be realized by using crude glycerol as the carbon source. This is the first report of fungal lactic acid production on crude glycerol as a sole carbon source.