Microalgae Cultivation Using Offshore Membrane Enclosures for Growing Algae (OMEGA)

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 CO 2-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% CO 2 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 CO 2 , harvest microalgae from a settling chamber, and add fresh wastewater to replenish nutrients. The I&C system controlled CO 2 injection and recorded dissolved oxygen levels, totalized CO 2 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 CO 2 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.

Botryococcus braunii for biodiesel production

“…A very interesting closed system design for cultivating green microalgae (Desmodesmus sp.) using wastewaters is the Offshore Membrane Enclosures for Growing Algae (OMEGA) system [79]; however, there has been no report on its application for B. braunii cultivation.…”

Theoretical Calculations on the Feasibility of Microalgal Biofuels: Utilization of Marine Resources Could Help Realizing the Potential of Microalgae

“…Several reports estimated microalgal biofuel productivity using solar irradiance information , but they only analyzed a few locations or considered only land area when determining biofuel potentials. Land‐based open raceway ponds (ORPs) and closed photobioreactors (PBRs) have been the major technologies employed for algal cultivation, but development of water‐based algal culture systems has been reported recently, claiming various advantages over conventional land‐based systems . Thus, it would be worth including the vast ocean area in analysis of maximum microalgal biofuel productivity.…”

Fabric‐hydrogel composite membranes for culturing microalgae in semipermeable membrane‐based photobioreactors

“…Recognizing this situation, a few research groups have begun development of ocean-based microalgal cultivation systems, focusing on delivering technology platforms for affordable and sustainable production of biofuels. 7,8 Ocean-based culture can have *Present address: Z-Hun Kim great benefits of inexpensively utilizing various natural resources, including aqueous nutrients, sunlight, and energy from tidal waves, not to mention the huge cultivable area. In a photobioreactor (PBR) floating on the ocean, nutrients diffuse across a reactor wall made of semipermeable membranes (SPMs) due to a concentration gradient, while algal cells are retained inside.…”