Final Report: Developing Commercially Viable Culture Media from Wastewaters Optimized for the Emerging Microalgae-based Biofuel IndustryEPA Grant Number: SU836016
Title: Developing Commercially Viable Culture Media from Wastewaters Optimized for the Emerging Microalgae-based Biofuel Industry
Investigators: Sommerfeld, Milton , Wray, Joshua T. , Puruhito, Emil , Kent, Martha
Institution: Arizona State University
EPA Project Officer: Hahn, Intaek
Project Period: August 15, 2011 through August 14, 2012
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2011) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
As the U.S. agriculture industry continues to produce copious amounts of nutrient wastes that are highly disruptive to natural nutrient cycles and ecosystems, farmers nationwide are facing intensifying scrutiny as operations grow larger and produce more wastes. Farmers need a way to use or recycle their wastes in order to deal with increasing pressures of encroaching urbanization, the threat of lawsuits, and tightening EPA regulations.
- US agriculture is responsible for 6.5 % of the total US greenhouse gas emissions
- 80% of US nitrous oxide(US EPA, 2010)
- 70% of US methane emissions(US EPA, 2010)
- 85% of US ammonia(US EPA, 2009)
- Considerable carbon dioxide emissions
Simultaneously, the emerging algae biofuel industry is looking for a low cost nutrient media to enable the cost competitive production of microalgae for biodiesel. While much is known about wastewater treatment such as removing nutrients from municipal waste streams, relatively few studies have explored systematic approaches of extracting nutrients from waste streams utilizing biological digestion in a form suitable for the cultivation of microalgae (Bellefeuille, 2005). Understanding this process is crucial to unite this emerging industry with the proper waste nutrient streams. Once developed on a commercial scale, the algae biofuel industry not only has the potential to remove wastes from agricultural production but to also supply biofuel to the agricultural community, as well as animal feed and fertilizers from the residual biomass. This strategy would go a long way in creating a more sustainable approach to agriculture by creating a cycle of nutrient flow that incorporates feed, fuel and fertilizer. The algae biofuels industry has the potential to be a disruptive technology that would:
- Capture up to 4.3% of the total greenhouse gas emissions within the U.S.
- Change the approach of fertilizer production and application
- Change the management process for agricultural wastes (Hanson, 2006)
- Remove waste nutrients from landfills
This project is meant to explore the techniques aimed at producing cultivation media from agricultural and municipal waste streams that is suitable for culturing microalgae for biofuel production. Specifically, potential culture media for algae must be optimized with regards to the parameters listed below and has to be low cost to be suitable algae cultivation for biodiesel production.
- Key considerations in creating an algae culture media
- Nitrogen content
- Phosphorous content
- Mineral content
- pH, hardness, specific conductance, etc.
- Contaminating species present (bacteria, fungi, etc.)
Phase I of the project characterized several common wastewater sources including agricultural runoff, cattle, swine, and poultry effluents, and municipal wastewaters, and evaluated their performance in comparison to the commercially available and industry standard mediium BG‐ 11. Preliminary data was gathered on the digestion of the wastewaters to begin to track nutrient release from solid waste. This information was compiled to produce media formulations used in batch and continuous microalgae cultivation experiments using a single strain of oil‐producing microalgae to generate biomass and lipid productivity data using the digested waste waters.
The microalgae were harvested from the culture media and subjected to lipid analysis, dry weight determination, and microscopic analysis. Lipid analysis was completed on the biomass samples generated to demonstrate that the culture media derived from wastewaters could potentially be used for algae cultivation systems that yielded biomass for biodiesel production. Dry weight determination tracked the microalgae culture density during the duration of the experiment and microscopic analysis was used to check for microorganism contamination. Of particular interest was the effect of continuous microalgae cultivation in wastewater and the possibility of wastewaters introducing contamination into the microalgae cultures.
Preliminary nitric acid digestion and ICP analysis showed the wastewaters generally contained most of the nutrients necessary to sustain microalgae growth. Aerobic digestions carried out on the wastewaters showed a significant release of nutrients via ICP and flow injection analysis, although the type and quantity of nutrients released differed significantly with different wastewaters.
Turbidity caused by dissolved solids was also an issue in deriving a good culture media for algae from waste streams. If the media is turbid, this greatly reduces light penetrability into the photobioreactor, thereby reducing growth and leading to contamination with other species. Turbidity was mainly an issue with the poultry digestate, which was quite dark even upon dilution. Municipal waste was by far the best media in terms of clarity as floc from the return activated sludge (RAS) was already present, which caused suspended solids to settle rapidly.
Upon microscopic examination, the microalgae cultures grown on swine effluent showed moderate bacterial contamination in a 10‐day batch culture, while the poultry effluent culture medium had a more severe bacterial load. Clearly, more work needs to be done to done to make suitable culture media from these nutrient streams, including an assessment of the cost to reduce the bacterial load. However, the municipal digestate seemed to not only have better clarity, but also practically no contamination in the 10 day batch culture. It did however exhibit a moderate amount of contamination over a 28‐day continuous culture regime; however the results were comparable to those obtained with BG‐11 medium.
The primary goal for phase I of this project was to determine the nutrient composition on multiple wastewaters and develop a preliminary wastewater treatment protocol for the processing of waste streams into an algae culture medium suitable for growing fit‐for‐purpose algae biomass. The goal for phase I was accomplished by demonstrating that an algae culture medium could be developed that led to similar nutrient characteristics, algae growth performance and lipid content to a commercially available standard algae culture medium BG‐ 11. While some culture media exhibited microorganism contamination of the microalgae culture, the municipal wastewater stream shows the most promise by demonstrating a rapid release in nutrients and exhibiting relatively little contamination, and microalgae growth rates and lipid content similar to that found in the standard BG‐11 medium.