n the current Journal of Sustainable Bioenergy Systems, OMEGA system inventor Dr. Jonathan Trent and his team detail the mechanics of their innovative wastewater to algae system in the article, Microalgae Cultivation Using Offshore Membrane Enclosures for Growing Algae (OMEGA).
OMEGA has the potential of co-locating microalgae cultivation with two major waste streams from coastal cities: wastewater and CO2. By situating OMEGA systems in the vicinity of offshore wastewater outfalls and CO2 sources, such as near-shore power plants, OMEGA can transform these waste streams into resources that produce biofuels and treat wastewater without competing with agriculture for water, fertilizer, or land.
The experiments presented in the journal article explored the technical feasibility of OMEGA, using a 110-liter prototype system that was built and tested over a 23-day period. Microalgae in secondary-treated wastewater circulated through PBRs floating in seawater tanks and through a gas exchange and harvesting column, while a custom instrumentation and control system monitored and adjusted critical culture parameters.
Analyses indicated that the system was supersaturated with dissolved oxygen during the day due to photosynthesis, but at the highest light levels there was only slight photoinhibition.
The system rapidly used the NH3–N in wastewater and had a CO2 conversion efficiency of >50%; better than the 10% – 20% conversions in other systems. The areal productivity of the system averaged 14.1 g·m−2·day−1 overall with peaks above 20 g·m−2·day−1, values consistent with reported US average microalgae productivity of 13.2 g·m−2·day−1.
The microalgae consistently removed >90% of the NH3–N from the secondary-treated municipal wastewater tested. This result, combined with observations that the OMEGA system can remove other wastewater contaminants, suggests that a scaled-up system could provide effective wastewater treatment services.
Many open questions remain with regard to the feasibility of large-scale OMEGA systems. The small-scale prototype OMEGA system was intended for experimentation and was not designed for energy efficiency or economical scale up. For large-scale OMEGA deployment, dense configurations of PBRs, improved hydrodynamics, optimized pumping and mixing, and more sophisticated process control algorithms will be needed to increase yields, improve EROI, and lower operating costs.
Questions about the impact of biofouling, concerns about engineering systems that can cope with marine environments, and environmental issues around both environmental impact and environmental regulations will need to be answered. It remains to be seen if the need for sustainable biofuels will drive the innovation necessary to address these questions to develop large-scale OMEGA systems.
Read the full report of this first in a series of technical papers about OMEGA, published in an open access science journal: scirp.org/journal/jsbs/