Energy and Water Sustainability in the U.S. Biofuel Industry

by May Wu (Argonne National Laboratory) The progress of technology development for conventional and advanced biofuel production processes in the U.S. has been reviewed by several groups over the last two decades (Warner et al. 2017; Mueller and Kwik 2013; Wu et al. 2009; Wu 2008; Shapouri and Gallagher 2005). Together, these surveys have demonstrated a continuous improvement of productivity, diversified product portfolio, and progress in resource conservation. Data gathered on production capacity, yield, energy use, and product portfolio help to establish industrial benchmarks and to evaluate the environmental sustainability of the industry, which is critical to addressing the Food-Energy-Water (FEW) nexus that is closely linked to bioenergy production.

In 2018, Argonne National Laboratory, with support from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office, conducted a survey of biofuel producers in the United States. The survey covered a full range of plant operation parameters, including plant capacity, feedstock, product, production volume, coproducts, water resources, water treatment, water usage, wastewater management, and process fuel and electricity consumption, as reflected in 2017 plant operation data.

This report presents the most up-to-date analysis of commercial-scale plants in the U.S., including facilities producing fuels from both starch and cellulosic materials. As of this time, this is the first survey that includes the comprehensive recording of water resources, water use, and water and wastewater management for the U.S. biofuel industry at the facility level. Data presented in this study reflect primarily information on full-scale ethanol production from dry mills that was available at the time of survey. Results highlight the complexity of energy and water resource use in process steps and the role of water conservation, recycling, and reuse in advancing the production of biofuel and its contribution to the bioeconomy and the FEW nexus.

In this study, we analyze technology factors and management approaches that affect plant water footprint, water conservation, and recycle/reuse. Survey data were processed, screened and examined. Statistical analysis was applied to all 77 surveyed parameters. We conducted a rigorous analysis, which was then aggregated for presentation.

Results from this survey are compared with those of previous industry surveys, and changes that increase the environmental profile, productivity, and potential environmental benefits are estimated. The values presented in this report represent an average of current technologies weighted by the respective volumes of biofuel produced by these technologies.

The survey found that co-processing of corn kernel fiber with grain to produce ethanol has become a promising approach, with a 2.5% increase in yield compared to grain processing alone. In 2017, 2.88 gallons of denatured ethanol were produced from the starch and fiber of a bushel of grain, as compared to 2.81 gallons produced from starch alone. Forty-one percent of respondents produce ethanol from corn fiber.

The biofuel industry has made a concerted effort to conserve resources, diversify energy sources, and recycle and reuse water. Five percent of plants have implemented on-site electricity generation to replace grid electricity, and several plants have become net electricity exporters. Water intensity has decreased by 12% since 2011 and by 54% in the 19 years between 1998 and 2017.

It takes 2.65 gallons of freshwater to produce a gallon of denatured ethanol. Newer plants with improved energy and steam integration dominate biofuel plants.

CO2 extraction and export is reported in 14% of respondents. CO2 production is on the rise because of increased revenue, despite an increase in electricity expenditure for compressing CO2.

In the area of water resource use, biofuel plants have diversified their water sources by using power plant cooling water and municipal reclaimed water in addition to well water and city water supply. Water and wastewater management is progressing toward zero liquid discharge (ZLD). The survey found that 42% of facilities achieved ZLD by increasing in-plant water reuse and recycling.

Plants have also conserved water and energy by increasing production of wet distillers grain and modified wet distillers grain, reducing the demand for natural gas and electricity for drying. The water content in these coproducts is reused as a part of animals’ diets in feedlots. Analysis of the survey results demonstrated that the production practices of the biofuel industry address the FEW nexus in a way that is energy-efficient, water-efficient, and environmentally sustainable. READ MORE