Use of Treated Effluent Water in Cellulosic Ethanol Production

The food-water-energy nexus is the inextricable relationship between our supplies of these three indispensable resources. We are all dependent on our nation's agricultural system, but crop production accounts for a whopping 80% of the country's water use. Agriculture also consumes a great deal of energy, not just in the form of fuel for tractors and other farm equipment, but also for processing agricultural goods in factories, pumping groundwater, and producing fertilizers (to name a few examples).

So, what if agriculture could "produce" energy and do so using recycled water? ISTC's associate director for applied research, Kishore Rajagopalan, and a team from the University of Illinois Urbana-Champaign's Department of Civil and Environmental Engineering and Department of Agricultural & Biological Engineering investigated a way to do just that.

Agriculture has already started producing energy, through the fuel ethanol industry in the United States (U.S.). At present, corn-based dry grind and wet milling facilities account for 95% of the fuel ethanol produced in the U.S. (Zheng et al., 2009). Most commercial bioethanol plants are based on fermentation of sugars from starch in corn grain or other high-sugar crops. However, concerns about the competing demands on our nation's food supply have prompted a move toward cellulosic feedstocks that can produce ethanol from non-food crops (e.g., perennial grasses, trees, and others). Lignocellulosic feedstocks could also lower greenhouse gas emissions, reduce cost pressure on food and feed markets, and make use of land which is unsuitable for row crops.

While cellulosic ethanol production represents a significant advancement in our nation's energy portfolio, unfortunately, the process consumes a great deal of water. Use of fresh water in ethanol plants depletes a precious natural resource and cannot be sustained in the long term. Thus, water management technologies are critical for the successful operation of an ethanol plant.

Current water consumption rates in corn dry grind ethanol plants are 3 to 4 gallons of water per gallon of ethanol produced (gal/gal) and 6 to 10 gal/gal for cellulosic ethanol plants. The research team's main goal was to examine the use of treated wastewater effluent in place of potable freshwater for cellulosic ethanol production (in both hydrolysis and fermentation). The effects of using two different types of filtered treated effluent - Bloomington-Normal, IL (predominantly residential type) and Decatur, IL (industrial/residential mix type) - on hydrolysis, the rate of fermentation, and final ethanol yield were evaluated.

During hydrolysis, glucose is produced from lignocellulosic feedstock material; then the glucose is used in the fermentation step to produce ethanol.arial photograph of an ethanol plant Glucose and ethanol concentrations arising from these processes were similar for the control treatment (deionized water) and both types of treated wastewater effluent, despite the difference in the nature of water samples being used. Thus, with proper characterization, the use of treated effluent water is feasible in cellulosic ethanol production in both the hydrolysis and fermentation steps.

This research was funded in part by the Illinois Hazardous Waste Research Fund (Grant Number: HWR12227) and resulted in the master's thesis of Divya Ramchandran from the University of Illinois at Urbana-Champaign. A news article in Ethanol Producer Magazine by Holly Jessen, titled, "Dropping Water Use," also discusses this project and several other water saving projects conducted by ISTC.