2011 Honor Award - University Research

Pilot Plant Development for Fungal Value-Adding to Low-Value Ethanol Plant Co-Product

Location: Ames, Iowa
Entrant: Iowa Energy Center and Center for Crops Utilization Research, Iowa State University with MycoInnovations
Engineer in Charge: J. (Hans) van Leeuwen, Ph.D., P.E., BCEE
Media Contact: J. (Hans) van Leeuwen, Ph.D., P.E., BCEE; 515-294-5251; Leeuwen@iastate.edu

Van Leeuwen et al., 2011; Iowa Sate University and MycoInnovations	Rhizopus microsporus (oligosporus)	Preculturing
Airlift reactor	Porous diffuser	Screen harvesting

Entrant Profiles

J (Hans) van Leeuwen, BCEE, PE, Vlasta Klima Balloun Professor of Engineering BEng (Chemical), MEng, Doctor Engineering, University of Pretoria Fellow four international organizations; Honorary Member Japan Industrial Water Association Professor Environmental and Biological Engineering, Departments Civil, Construction & Environmental Engineering (CCEE); Agricultural & Biosystems Engineering (ABE); Food Science & Human Nutrition (FSHN) Iowa State University (ISU) 4 US patents, 4 pending, 3 international patents; 12 pending

Mary L. Rasmussen BA (Natural Science) College of St. Benedict MS, PhD Iowa State University (Civil Engineering, environmental engineering option) Post-doc in fungal research Winner of various awards

Daniel Erickson BS (Biology) (University of Oregon) Currently: Research Assistant in the Department of Civil, Construction and Environmental Engineering. Responsible for the day-to-day operation of the pilot plant. Completing an MS in Biorenewable Resource Technology

Christopher Koza BS (Civil Engineering, environmental engineering emphasis) (ISU) Currently: Research Assistant in the Department of Civil, Construction and Environmental Engineering. Responsible for research linked to the pilot plant. Completing an MS in Civil Engineering with Environmental Engineering option.

Brandon Caldwell BS (Industrial Technology) (ISU) Previously: Research Assistant in the Department of Civil, Construction and Environmental Engineering. Responsible for some of the construction and the day-to-day operation of the pilot plant. Currently with Modern Piping in Cedar Rapids, Iowa.

Debjani Mitra BS (Microbiology) and MS (Environmental Sciences) Currently: Research Assistant in the Department of Civil, Construction and Environmental Engineering and Food Science and Human Nutrition. Responsible for research linked to the pilot plant and other microbial value adding in the crops processing industry. Completing a double major PhD in Food Science and Biorenewable Resource Technology

Lawrence A. Johnson BS, Food Technology, Ohio State; MS, Food Science, North Carolina State; Ph.D., Food Science, Kansas State University; Dr. (h.c.) Ghent University Professor, FSHN and ABE, Director, Center Crops Utilization Research, Director BioCentury Research Farm 10 US patents, 2 pending Fellow, American Oil Chemists Society; Foreign Member, Royal Swedish Academy Agriculture & Forestry

Project Description

Introduction

Corn dry-grind ethanol plants generate ∼6 gallons leftovers/gallon ethanol after distillation - stillage. Creating value-added byproducts from stillage and recycling water is important as the annual ethanol production in the U.S. approaches eight billion gallons.

Stillage from fermentation, followed by distillation, contains fiber, yeasts, and dissolved organics in water, measured as total chemical oxygen demand (COD) of nearly 100 g/L. Most solids are removed by centrifugation and dried to distillers dried grain (DDG). The centrate, thin stillage is partially recycled directly to the fermentation process, but limited to 50% to prevent build-up of total and dissolved solids, especially lactic acid, acetic acid and glycerol. The remaining thin stillage is currently concentrated by flash evaporation - an energy - intensive process - and blended with DDG, producing DDG with solubles (DDGS). DDGS is used for livestock feed, but is low in essential amino acids, e.g., lysine, limiting its usage, particularly for hogs and chickens. Fortunately, thin stillage contains biodegradable organic compounds, sufficient micronutrients, at pH 4.5, which makes thin stillage an ideal fungal cultivation feedstock.

A fungal treatment process for thin stillage has the following merits

Energy savings by avoiding stillage evaporation,
Recovery of protein-rich fungal biomass, and
Potential for water recycling of treated effluent

Solids separation and removal of organic materials are important for recycling the effluent as process water. This research investigated the cultivation of the food-grade fungus Rhizopus microsporus on thin stillage and the potential for water recycling on a 1300L pilot plant.

Methodology

Reactor development. Cultivation of the filamentous fungus, Rhizopus microsporus required construction of a deep airlift reactor to ensure high-rate aeration for rapid fungal growth and pellet morphology.

The 1400 L airlift reactor consists of a 6m high cylindrical tank of 600 mm, with a draft tube with a diameter of 450 mm inside the tank to a height of 15' to make it possible for the liquid to circulate by flowing upwards through the draft tube and flow back through the annulus (Figure 1). Aeration of thin stillage, with fungal inoculum, is effected within the inner part using a blower with an array of seven porous diffusers. The aerated liquid moves upwards along with the bubbles, due to the lower density of the bubble-filled liquid compared with that in the annulus. The bubbles are released at the top and the liquid recirculates downwards in the annulus. procedures for designing a larger-scale airlift reactor. The aeration rate is varied to establish operational procedures for full-scale implementation. The oxygen demand of the fungi is actually the main determining factor for aeration needs.

Propagation facilities. The pilot plant has been designed and equipped with a heating system at the bottom for fungal propagation of about 10% of the main volume for better startup conditions. As alternative, we constructed two 50-L pre-propagation reactors. In each case, a pre-inoculum is prepared in 5-L shaker flasks. The ultimate aim is to operate in continuous mode.

Harvesting screen. This was built with a recirculation sump and level control.

Dewatering. The biomass is dewatered by retention on the primary screen, followed by transfer to secondary horizontal screen and final dewatering in polyethylene woven sacks.

Drying. The dewatered biomass is passed through a Cellencor microwave tunnel dryer.

Results

Fungi grew prolifically, yielding on average 20 kg of biomass per batch run from 1300L of thin stillage. The fungal pellets take 20-24h to develop, and the aeration requirements were much lower than the lab results. Removal of COD, suspended solids, glycerol, and organic acids, critical for stillage recycling, reached 60-80 %. It was ascertained that there is no need for pH control with enough acidity already in the thin stillage. The pellets are easy to harvest using the curved inclined screen and the harvested product from the primary screen contains 10-12% solids. Secondary screening, followed by gravity draining in woven polyethylene bags overnight removes about half of the remaining water, to reach a solids concentration of 22%. The biomass was dried to 8% moisture using the Cellencor microwave drying tunnel.

The fungal biomass is high in lysine and nutraceuticals chitin/chitosan, enhancing its potential as a nutritionally - beneficial livestock feed. The fungus could be co-fed with DDG to monogastrics: swine and poultry, thereby adding value to another coproduct from the ethanol industry.

Continuous operation has remained elusive due to the propensity of yeast co-cultures to develop. These are difficult to harvest. The current answer to this is regular disinfection with chlorine and steam.

Discussion

Originality and innovation. A novel, low-energy fungal process was developed that remediates dry-grind corn ethanol thin stillage with simultaneous generation of nutritious fungal biomass. The process eliminates the need for evaporation of the water to recover the dissolved organics by conversion to microbes that are readily removed by screening and dewatered further for the production of animal feed, which is to be evaluated in the next phase by feeding piglets.

R. microsporus was able to utilize most stillage organic substances, was not inhibited and it enmeshed remaining suspended solids. These are important properties in the economical operation of a full-scale fungal process.

Socio-economic impacts. The US ethanol industry consumes 35 billion gallons water per year to produce 12 billion gallons ethanol. Water consumption could be reduced by at least 10 billion gallons if all dry-grind ethanol plants recovered water by this process. The current evaporation process costs about $0.04 per gallon ethanol produced at current natural gas prices. Energy savings from eliminating stillage evaporation could save $400 million/ year nationwide. Enzymes recycled with fungal-treated water from stillage could further save $60 million in value per year. The potential revenue from high-quality livestock feed production, along with expanding the DDG market, is expected to be worth another $400 million/year. Preliminary cost estimates of implementing a fungal stillage treatment process indicate that the amortization and operational costs of the fungal fermentors and separation equipment amount to about 50% of the savings and additional income. The value of the energy savings, fungal biomass as livestock feed, and enzymes produced is estimated at 20 ¢/gal ethanol, with half of that required in alternative processing costs. Considering all these cost figures, it is estimated that the value added for the ethanol industry would be $0.6 billion per year. The fungal biomass is also an ideal source of the nutraceuticals chitin/chitosan, constituting 5-9% of the biomass, traditionally obtained from crustaceans at a cost of about $8,000 per ton. These have been demonstrated to improve animal growth and health and eliminate the need for antibiotics. This would lead to healthier meat products. Industrial implementation of fungal treatment of stillage will lead to job creation and improved rural prosperity.

Research quality. The concept has two patents pending and publications have been accepted in top journals in the field.

Screen dewatering equipment	Microwave tunnel dryer	Dewatered product fed into dryer
Dried product

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May 22, 2012

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