TITLE:
Microalgae Cultivation Using Offshore Membrane Enclosures for Growing Algae (OMEGA)
AUTHORS:
Patrick Wiley, Linden Harris, Sigrid Reinsch, Sasha Tozzi, Tsegereda Embaye, Kit Clark, Brandi McKuin, Zbigniew Kolber, Russel Adams, Hiromi Kagawa, Tra-My Justine Richardson, John Malinowski, Colin Beal, Matthew A. Claxton, Emil Geiger, Jon Rask, J. Elliot Campbell, Jonathan D. Trent
KEYWORDS:
Biofuels; Wastewater Treatment; Microalgae; Photobioreactor; CO2 Mass Transfer; Fast Repetition Rate Fluorometry; Instrumentation and Control
JOURNAL NAME:
Journal of Sustainable Bioenergy Systems,
Vol.3 No.1,
March
27,
2013
ABSTRACT: OMEGA is a system for
cultivating microalgae using wastewater contained in floating photobioreactors
(PBRs) deployed in marine environments and thereby eliminating competition with
agriculture for water, fertilizer, and land. The offshore placement in
protected bays near coastal cities co-locates OMEGA with wastewater outfalls
and sources of CO2-rich flue gas on shore. To evaluate the feasibility
of OMEGA, microalgae were grown on secondary-treated wastewater supplemented
with simulated flue gas (8.5% CO2 V/V) in a 110-liter prototype
system tested using a seawater tank. The flow-through system consisted of
tubular PBRs made of transparent linear low-density polyethylene, a gas
exchange and harvesting column (GEHC), two pumps, and an instrumentation and
control (I&C) system. The PBRs contained regularly spaced swirl vanes to
create helical flow and mixing for the circulating culture. About 5% of the
culture volume was continuously diverted through the GEHC to manage dissolved
oxygen concentrations, provide supplemental CO2, harvest microalgae
from a settling chamber, and add fresh wastewater to replenish nutrients. The
I&C system controlled CO2 injection and recorded dissolved
oxygen levels, totalized CO2 flow, temperature, circulation rates,
photosynthetic active radiation (PAR), and the photosynthetic efficiency as
determined by fast repetition rate fluorometry.
In two experimental trials, totaling 23 days in April and May 2012, microalgae
productivity averaged 14.1 ± 1.3 grams of dry biomass per square meter
of PBR surface area per day (n = 16), supplemental CO2 was converted
to biomass with >50% efficiency, and >90% of the ammonia-nitrogen was recovered
from secondary effluent. If OMEGA can be optimized for energy efficiency and
scaled up economically, it has the potential to contribute significantly to
biofuels production and wastewater treatment.