Waste Not, Want Not: INL Studies Potential of Municipal Solid Waste for Biofuels

The bioenergy industry has made big strides in producing fuels from non-food biomass sources. Examples include agricultural waste such as corn stover (the leaves, stalks, and cobs left after a corn harvest) and energy crops like switchgrass. However, many of these biomass sources are not available in adequate quantities throughout the year, which could result in supply challenges for biorefineries during some months or in some areas of the United States.

To address these supply challenges, an Idaho National Laboratory (INL) research team, with funding support from the U.S. Department of Energy’s (DOE’s) Bioenergy Technologies Office, has reviewed a variety of available resource blends, including portions of municipal solid waste (MSW).

One Person’s Waste Is Another Person’s Treasure?

Researchers and industry have long identified the potential of MSW as a low-cost feedstock to help meet the increasing need for domestic fuel, bio-based products, and chemical production. Using MSW to produce these bioenergy products presents an attractive alternative to sending this waste to landfills or other means of disposal. MSW represents vast, untapped sources of renewable carbon that is widely available at a lower cost than other biomass sources.

INL Researchers Assess MSW Costs and Quality

Even though MSW has great potential, not much was known about the cost and quality of feedstocks that could be derived from MSW or MSW blends for fuel production. In a recent study, INL principal investigator Vicki Thompson and her team of researchers evaluated the feasibility of MSW-biomass blending and formulation using grass clippings and non-recyclable paper and cardboard. They performed a novel, extensive multi-lab study to understand the feedstock quality and conversion efficiency to develop biofuel precursors.

INL researchers leveraged the sorting, separation, and blending capabilities at DOE’s Biomass Feedstock National User Facility (BFNUF) and created six feedstock blends that combined biomass and MSW with improved feedstock quality attributes. To understand conversion efficiency, INL then worked with researchers at DOE’s Lawrence Berkeley and Sandia National Laboratories to convert the feedstock blends to sugars and methyl ketones (chemicals that can readily be converted to biofuels) using an efficient biomass pretreatment process.

The researchers found that MSW-biomass blends could meet DOE’s cost and quality targets for conversion-ready feedstocks while successfully producing precursors to biofuels and bioproducts. The results appeared in the journal ChemSusChem.

Secrets of MSW-Biomass Blends

To develop the MSW-biomass blends, experts used the research tools available at the BFNUF, starting with the Process Development Unit, a fully integrated feedstock preprocessing facility that can process raw biomass materials from bench to pilot scale. The MSW, corn stover, and switchgrass underwent grinding and drying steps and were then sorted and separated to remove unwanted foreign materials and contaminants. Researchers at the BFNUF’s Biomass Characterization Laboratory then characterized the samples to gather data on variability and critical quality attributes needed for efficient conversion, including the content of moisture, ash and ash species, glucan, xylan, and lignin.

The Cost of Delivering MSW-Biomass Blends to the Biorefinery

To develop the lowest-cost blends while still meeting the quality specifications necessary for conversion to biofuels, researchers used the Least Cost Formulation (LCF) model developed at INL. The LCF model combines feedstock quality data along with grower payment and logistics costs to estimate the total cost of feedstocks delivered to the biorefinery.

The six feedstock blends underwent pretreatment and enzymatic hydrolysis, which resulted in good sugar production. Those sugars then underwent microbial fermentation using an engineered strain of E. coli, which yielded high-quality methyl ketones. One of the blends was scaled up 30-fold.

Biomass feedstock costs are very dependent upon location, but use of the LCF tool developed at INL demonstrated that corn stover feedstock costs could be reduced by up to 20% through blending of municipal solid waste with the corn stover¹.

INL researchers continue to identify feedstock variability factors and develop technologies to decontaminate and improve the feedstock quality. Through this research, INL will pursue the efficient utilization of various waste streams to produce a wide range of biofuels, biochemicals, and bioproducts.