(668f) Tertiary Wastewater Treatment By Chlorella vulgaris in a Membrane Photobioreactor: Effects of Wastewater Composition and Light/Dark Cycle

Microalgae is one of the most promising and sustainable feedstock for the production of biofuels because of its high growth rate, efficient CO₂ fixation and high lipid content. These advantages had led to extensive research in the microalgae cultivation and processing. However, despite making significant progress at these fronts, production of biodiesel from microalgae remains an expensive process.

One approach to reduce the cost of microalgae cultivation is the use of urban wastewater for microalgae growth. Municipal wastewater can not only provide cheap source of organic carbon to microalgae but it also contains ample amount of nitrogen (N) and phosphorus (P) as well. The cost of microalgal biofuels can also be reduced by achieving high biomass concentration in the photobioreactor which will result in lower harvesting costs. A high biomass concentration can be achieved in continuous cultivation of microalgae in a membrane photobioreactor (MPBR), by operating it at high loading rates.

In this research, an MPBR was designed and operated for N and P removal from wastewater using Chlorella vulgaris. The effects of N/P ratio and light/dark cycle on MPBR performance and biomass accumulation were investigated. The MPBR achieved nearly complete N removal under all the operating conditions, although the removal efficiency/rates were lower when the MPBR was operated under alternating light/dark cycles. It was also observed that P removal improved at higher N loadings. The biomass composition was different at different wastewater composition, and higher amount of proteins were accumulation by microalgae, when N supply was increased. The results suggested that autotrophic microalgae can be used for effectively treating and recycling inorganic pollutants in tertiary wastewater.