Producing Fuels from Landfill Wastes: Using Algae to Convert Landfill Gases and Landfill Leachate into Oil and Biodiesel

Richard Cairncross:
Chemical & Biological Engineering

Susan Kilham:
Biology

Grace Hsuan, Mira Olson, Sabrina Spatari:
Civil, Architectural, & Environmental Engineering

This study evaluates the economic feasibility and efficiency of using landfill leachate and gas streams to produce algae oils suitable for biofuel production. To reduce landfill waste management costs and in support of domestic renewable energy, producing valuable energy products from society's urban waste holds great promise for the low-carbon, "next" generation liquid bioenergy markets. Landfills are a technologically effective, though costly, way of storing municipal solid waste in concentrated piles. As waste decomposes it produces two waste streams that pose environmental risks: (1) landfill gases composed primarily of carbon dioxide and methane and (2) landfill leachate. If designed to recover and use the two bi-product streams as feedstocks for biofuel synthesis, landfills can in turn become on-site modern biorefineries.

landfill

The project tasks include:

  • Determining the growth conditions under which algae produce the highest yield of fuel-grade lipids: batch experiments to determine the optimal leachate dilution strength and feed gas purity that support algal growth.
  • Quantifying algal oil production, leachate remediation, and CO2 consumption rates in a pilot-scale (or simulated) surface-pond algae bioreactor: pilot- or bench-scale algae bioreactors operated under various conditions to maximize algal oil production, CO2 consumption and leachate remediation.
  • Evaluation of the cost-effectiveness of converting landfill waste streams to biofuel using techno-economic analysis: analysis of the economics of landfill waste stream algae-biofuel scale-up for specific landfill operation scenarios.

Ongoing work is focused on determining the highest leachate: proteose medium ratio that supports algal growth and on fully characterizing the nitrogen dynamics during growth experiments. Also under exploration is growth medium that would not be as conducive to bacterial growth, in hopes of eliminating the necessity for heat-treatment of the leachate. Longer term goals involve characterizing the potential for leachate remediation (reduction in ammonia/ammonium) by the algae and optimizing both algae biomass production and algal lipid content. Biomass productivity and cellular lipid content are two of the major experimental factors influencing the economic feasibility of algal oil for biodiesel production. An ideal process would combine the highest biomass productivity with the highest cellular lipid content. Achieving both outputs simultaneously is difficult, since high lipid cell contents are normally produced under stress conditions such as limited food or nutrients. These stress conditions are subsequently associated with low biomass productivity and, therefore, low overall lipid productivity. Further work will determine the growth rate that maximizes overall algal oil yield.

landfill