World Student Community for Sustainable Development

by Philip Sheehy, Research Assistant, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA

Having sown many a seed for technological innovation, the Massachusetts Institute of Technology now finds itself in a different role: testing ground. Atop its cogeneration power plant, a slipstream with 1 percent of the flue gases emitted is being biologically scrubbed by algae to reduce nitrogen oxides (NOx) and carbon dioxide (CO2) as part of a beta test by GreenFuel Technologies Corporation. The algae can be harvested and put to a variety of uses, including conversion it to biodiesel, neutraceuticals production, or production of plastics. Many green-oriented energy firms promise long-term savings and minimization of negative environmental impacts, often with high capital costs. With lower capital investments, GreenFuel is already delivering results.

Using algae to capture emissions is not a new idea. In the late 1970s, the US Department of Energy tried pumping emission gases through the base of a pond and growing algae on the surface. The project was eventually abandoned, in part because the algae were difficult to harvest and the energy required to “churn†the pond to ensure full algal exposure to sunlight was expensive. GreenFuel has succeeded in reducing the capital investment by streamlining the harvesting of algae, limiting the energy required to operate the system, automating many of the necessary controls (e.g., flow controllers and gas uptake), and minimizing the physical space required. Applying these systemic innovations to the known capacity of algae to capture of emissions has caught the attention of academics, energy providers, and, most importantly, investors.

Nitrogen oxides are pollutants that are precursors to air quality problems including smog. The preliminary tests of the algal bioreactor, conducted by CK Environmental Inc. over a seven-day period, demonstrated an 85 percent reduction in NOx emissions. GreenFuel currently claims that the cost of its system is 40-60 percent lower than that of the existing technology of selective catalytic reduction (SCR). Despite being the only option, SCR is not an attractive one for power plants interested in reducing their NOx emissions. The implementation costs have been increasing steadily since the 1990s due to lower labor productivity (with labor accounting for nearly half the implementation cost), as well as costly modifications and/or upgrades to existing equipment. GreenFuelâ€^TMs system operation is entirely external to the power plant: all it requires is a stream of flue gases. The SCR method requires toxic catalysts and reagents, posing an entirely different environmental problem. The algae uptake of NOx is a natural chemical reaction and is not dependent on sunlight, thus allowing reductions around the clock.

The photosynthetic growth of the algae is primarily dependent on three simple factors: CO2, water, and — the only factor GreenFuel cannot control — sunlight. Even so, the results of the tests are remarkable. On cloudy or rainy days, a 50 percent reduction in CO2 was reported, while on sunny days an 82 percent reduction was observed. Although initiatives to reduce carbon dioxide emissions in the US at the national, state, and local levels are voluntary to date, there are rumblings about carbon trading and other market-based mechanisms. Based on GreenFuelâ€^TMs potential to reduce CO2, one can be sure they — and their investors — are eager to demonstrate the capacity of a full-scale implementation of their algal bioreactors, which they say should be ready within the next two years. If, and more likely when, a market for CO2 trading develops in the US, GreenFuel is positioning itself to be a major player.

The initial tests demonstrate that GreenFuelâ€^TMs technology is capable of taking out two birds — NOx and CO2 — with one stone. And although GreenFuel itself has not made use of the harvested algae on a large scale to date, the potential is real. The opportunity to reduce emissions and comply with regulatory standards is already attractive. The tax incentives and potential profit to be made from natural and renewable biodiesel make for an even more intriguing proposition. GreenFuel has proven not only that it can take out two birds, but that it will also retrieve the stone for you.