Nitrogen removal from wastewater by algae provides the potential benefit of producing lipids for biodiesel and biomass for anaerobic digestion. Further, ammonium is the renewable form of nitrogen produced during anaerobic digestion and one of the main nitrogen sources associated with wastewater. The wastewater isolates Scenedesmus sp. 131 and Monoraphidium sp. 92 were grown with ammonium, nitrate, or urea in the presence of 5 % CO2, and ammonium and nitrate in the presence of air to optimize the growth and biofuel production of these chlorophytes. Results showed that growth on ammonium, in both 5 % CO2 and air, caused a significant decrease in pH during the exponential phase causing growth inhibition due to the low buffering capacity of the medium. Therefore, biological buffers and pH controllers were utilized to prevent a decrease in pH. Growth on ammonium with pH control (synthetic buffers or KOH dosing) demonstrated that growth (rate and yield), biodiesel production, and ammonium utilization, similar to nitrate- and urea-amended treatments, can be achieved if sufficient CO2 is available. Since the use of buffers is economically limited to laboratory-scale experiments, chemical pH control could bridge the gap encountered in the scale-up to industrial processes.
Bibliographical noteFunding Information:
Acknowledgments The authors would like to thank the Montana State University Algal Biofuels Group for intellectual support and Lauren Franco for 18S rRNA gene sequence interrogations of Scenedesmus sp. 131. Also of special note is the MSU Center for Biofilm Engineering for instrumental support. Funding was provided by the Montana State Board of Research and Commercialization Technology Grant 10–40 and the National Science Foundation under CHE-1230632.
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- Fatty acid methyl ester (FAME)
- Nitrogen removal
- pH Control