This Small Business Innovation Research (SBIR) Phase I project aims to develop a duckweed system for poultry waste bioremediation and use of the duckweed as a renewable feedstock for Clostridium acetobutylicum (Cac) biofuel production. Runoff from agricultural, municipal and other sources leads to eutrophication of the Chesapeake and other bays, with approximately half of the loads from agriculture, particularly poultry production on Delmarva. This work will provide an alternative nutrient reduction strategy, while simultaneously providing feedstock for clostridial biobutanol fermentation and poultry feed supplements. Current biobutanol work relies on corn hydrolysate, and duckweed is an attractive renewable feedstock. Life cycle assessments of environmental impacts indicate the ideal systems combine strategic placements of small/medium-scale wastewater remediation with biofuel feedstock production.
The broader/commercial impacts of this research are the development of poultry waste bioremedation strategies coupled with the development of that biomass for renewable chemical and biofuel technologies. The goal of this Phase I project is to maximize manure remediation while producing biomass for Cac biobutanol fermentation. Depletion of non-renewable energy sources, leading to high oil prices, highlights the importance of economically-viable technologies for production of biofuels from renewables. Renewable biomasses should be carbon-neutral and be efficiently used in biorefinery production. The economic potential of biorefineries is hindered by cellulosic materials that compete with food supply economics (i.e. corn). The commercial potential of a biomass from a nuisance plant, duckweed, combined with the use of clostridia biobutanol production is exceptional, but remains unexplored. This project aims to demonstrate this potential.
The Chesapeake Bay and Delaware Bay has long suffered from high nutrient loads causing excessive phytoplankton growth (i.e., algal blooms) which results in decreased water clarity, deposition of detritus, and hypoxia conditions (depletion of dissolved oxygen). These conditions ultimately lead to the collapse of aquatic ecosystems, forcing fish and crustacean populations out of the area. The goal of our technology is to specifically target and reduce this non-point source pollution, be it from agricultural activity or urban runoff, by using duckweed (specifically Lemna minor) as a bioremediation agent. Duckweed is a free-floating plant with an abbreviated root system and is known for its remarkably fast growth rate. Because the plants grow so quickly, they rapidly absorb nitrogen and phosphorus from the water to generate more biomass. The plants are also highly adaptive to their environment and are known to grow even upon extremely eutrophic waters. Finally, they are native to the region, so a potentially invasive species does not need to be introduced into the surrounding ecosystem. All these traits make duckweed an ideal bioremediation agent to reduce excess nutrients in eutrophic waterways. The use of duckweed as a bioremediation agent has been proposed before and is not a novel concept. However, there has always been a problem with what to do with the generated duckweed biomass. Nitrogen and phosphorous removal rates are highest when duckweed is rapidly growing which necessitates that duckweed is harvested frequently during its growth phase to achieve the highest possible remediation effects. This frequent harvesting leads to an accumulation of duckweed biomass. Elcriton is interested in using this accumulated duckweed biomass as a substrate for our microorganisms, which can produce the commodity chemical butanol. Elcriton has already developed several microorgansims to produce butanol or other commodity chemicals and has been searching for a local, sustainable biomass as a substrate for the production fermentation. Though corn stover and switchgrass, two common biomasses used a substrates, could be used, we are particularly interested in duckweed because of the potential impact on the Chesapeake Bay and Delaware Bay watersheds. Instead of using a standard agricultural crops, which could further pollute the watersheds, duckweed would actually reduce total nutrient loads in the watershed and increase the overall health of the bays. The focus of the experiments funded by this grant was proof-of-concept studies. First, we investigated the bioremediation capacity of duckweed, determining growth rates and nitrogen and phosphorous removal rates. Second, we examined the suitability of duckweed as a feedstock biomass, determining its biomass composition and evaluating methods of converting the biomass into a usable sugar solution for fermentation (termed pretreatment and hydrolysis). Finally, we assessed the ability of our microorganisms to utilize the generated sugar solutions. Overall, we found duckweed to have great potential both as a bioremediation agent and as a substrate for our microorganisms, and Elcriton is now planning and developing a larger demonstration site.