ARTICLE Converting Corn Wet-Milling Effluent Into High-Value Fungal Biomass in a Biofilm Reactor Nagapadma Jasti, 1 Samir K. Khanal, 2 Anthony L. Pometto III, 3 J. (Hans) van Leeuwen 1,3,4 1 Department of Civil, Construction and Environmental Engineering, Iowa State University, 376 Town Engineering Building, Ames, Iowa 50011; telephone: 515-294-5251; fax: 515-294-8216; e-mail: leeuwen@iastate.edu 2 Department of Molecular Biosciences and Bioengineering, University of Hawai’i at Ma ¯noa, Honolulu, Hawaii 3 Department of Food Science and Human Nutrition, Iowa State University, Ames, Iowa 4 Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa Received 5 February 2008; revision received 26 April 2008; accepted 27 May 2008 Published online 4 June 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bit.22007 ABSTRACT: Rhizopus microsporus was grown in an attached growth system using corn wet-milling effluent as a growth medium. This strain was chosen due to its ability to effec- tively degrade organic matter in corn wet-milling effluent and for its properties to produce significant levels of protein, chitin and chitosan. Fungal growth and organic removal efficiency were examined under both aseptic and non-asep- tic conditions with and without nutrient supplementation. Plastic composite support (PCS) tubes, composed of 50% (w/w) polypropylene (PP) and 50% (w/w) agricultural products were used as support media. Significantly higher organic removal measured as chemical oxygen demand (COD) and biomass yield were observed in the bioreactor with PCS tubes than in two control bioreactors; that is with PP tubes alone and suspended growth (without support media). This confirmed that the PCS support medium with agricultural components enhanced fungal growth and organic removal. The results showed that supplementation of nutrients (e.g., mineral salts) under aseptic conditions enhanced the COD removal from 50% to 55% and observed biomass yield from 0.11 to 0.16 g (dry-weight)/g COD removed (i.e., from 0.10 to 0.14 g volatile solids (VS)/g COD removed approximately). Non-aseptic operation without nutrient supplementation resulted in an observed biomass yield of 0.32 g volatile suspended solids (VSS)/g COD removed with no significant improvement in COD removal (53%); whereas with nutrient supplementation, the observed biomass yield increased to 0.56 g VSS/g COD removed and COD removal improved to 85%. The fungal system was able to degrade the organic matter with concomitant production of high- value fungal biomass. This is the first study that examined the conversion of corn milling waste stream into high value fungal protein. Biotechnol. Bioeng. 2008;101: 1223–1233. ß 2008 Wiley Periodicals, Inc. KEYWORDS: attached growth; corn wet-milling effluent; fungal process; plastic composite support (PCS) medium; resource recovery; Rhizopus microsporus Introduction One-third of all the corn in the United States is processed through wet corn milling. A typical wet-milling plant processes at least 2,500 tons of corn per day year-round (Rausch, 2002). Corn wet-milling involves separation of starch, protein, fiber, corn syrup, and oil for producing commercial co-products, such as corn gluten meal and feed, ethanol, corn oil, sugars, specialty starches, etc. These plants also provide pure starch products (>99.5%) for the paper and corrugating industries, modified starches for food ingredients and high fructose corn syrup. Currently, conventional aerobic biological treatment, particularly the activated sludge process is employed to treat such waste streams, which produces large amounts of low- value bacterial biomass. The excess bacterial biomass requires additional treatment and disposal, contributing 40–60% to the operating cost (Canales et al., 1994). On the other hand, fungi are often cultivated commercially as a source of high-value byproducts under aseptic conditions on relatively expensive substrates such as starch or molasses (Barbesgaard et al., 1992). The use of molds (microfungi) is an attractive approach since the fungal process converts the organics into high-value fungal biomass that can be used as a Correspondence to: J. (Hans) van Leeuwen Contract grant sponsor: Cooperative State Research, Education, and Extension Service Contract grant sponsor: U.S. Department of Agriculture (USDA) ß 2008 Wiley Periodicals, Inc. Biotechnology and Bioengineering, Vol. 101, No. 6, December 15, 2008 1223