Innovative Waste Biomass Derived Organic Acids Synthesis, Immobilization and Purification System

Grant # 07-02
Principal Investigator: Shihwu Sung
Organization: Iowa State University
Technical Area: Renewable Energy


The goal of the proposed project is to develop a commercially feasible waste biomass derived organic acids synthesis, reclamation and purification system to enhance the rural Iowa economy.

Waste biomass, which has been one of the major environmental concern in the world owing to growing environmental awareness and public health concerns, may become a plentiful and inexpensive substrate for the chemical production. The conversion of waste biomass i.e. corn stover/stalk and animal manure into useful chemicals is an environmentally sound solution to decrease the dependency on fossil fuels, reduce the global warming and lower the pollution potential.

A mixture of low-molecular weight carboxylic organic acids such as acetic acid, propionic acid, butyric acid, lactic acid, etc. can be easily produced from various complex organics by an indigenous mixed microbial community. The production of a mixture of organic acids generally does not require non-sterile condition, expensive tanks or enzymes. If organic acids could be separated from the fermented liquor, it would be thermally and chemically converted to mixed alcohols, liquid fuels. Furthermore, individual organic acids themselves are feedstock of many chemical processes and are widely used in food industries. As a leading agricultural state, Iowa produces various waste biomass such as corn stover and animal manure. This waste biomass could be ideal candidates for organic acids production.

However, the economic feasibility of converting waste biomass to soluble chemicals is heavily depending on how to separate organic acids from the bulk solution. For the selective separation of organic acids, several unit operations such as adsorption, precipitation, solvent extraction, pertraction, ion-exchange and electrodialysis have been tried. Nevertheless, the separation/purification is still regarded as the highest cost associating with harvesting organic acids from biomass.

A novel method to separate organic acids from the bulk solution is proposed. Iowa State University (ISU) patented mesoporous silica (MPS) materials will be used as the media to adsorb organic acids. The MPS media provides a highly-ordered matrix in which all of the surface area is accessible to the bulk solution. The media has extremely high surface area-to-mass ratio of more than 700 m(squared)/g which warrants a fast binding kinetics and a high adsorption capacity. The MPS will be permanently bound with amine group, which selectively adsorb organic acids in the bulk solution.

The proposed system would consist of three unit processes, an acid bioreactor for organic acids synthesis, an adsorption column for organic acids immobilization, and a recovery unit for organic acids purification and media regeneration. Each unit processes will be optimized during the project. Acid bioreactor coupled with a cost-effective non-woven cloth membrane unit, which has been successfully developed and operated at ISU for the past six years, will be fed with a mixture of corn stover and swine manure as substrates. The membrane bioreactor is able to deliver solids free permeate which is ideal for the following adsorption column. The adsorption column will be packed with the MPS media. The adsorption step would also act as the acid concentrating process to improve the efficiency of the subsequent purification step. In the media regeneration, absorbed organic acids will be washed off with acid and purified to produce final products, while media will be reactivated by a base solution e.g., NaHCO3. Finally, a pilot-scale system will be designed and operated to evaluate the commercial viability of a full-scale acids reclamation/recovery process as it applies to waste biomass, and particularly its use in the Iowa rural site. and more general commercial applications.