Photobioreactors for microalgae-based wastewater treatment

Microalgae are being increasingly recognized as a bioremediation agent for effective nutrient recovery from various wastewaters. Microalgae have demonstrated excellent tolerance towards the harsh conditions of wastewaters, including increased organic carbon and ammonia, pollutants, such as heavy metals, organic compounds, hormones, antibiotics, and personal care products. Microalgae-based wastewater treatment has been carried out in open ponds, called waste stabilization ponds, which were upgraded as high-rate algal ponds for better algal biomass production and nutrient recovery. Closed photobioreactors have potential advantages over open systems, such as protection from contamination and high biomass productivity, while cost-effective installation and operation is a major roadblock. Recently, various photobioreactors have been applied for the treatment of wastewaters using microalgae, such as vertical column, tubular, flat plate, membrane, and biofilm-based photobioreactors. This chapter discusses in detail various photobioreactor designs applied for wastewater treatment with microalgae. The advantages, disadvantages, and opportunities of each system are presented. The challenges in using closed photobioreactors for effective and economic wastewater treatment are critically analyzed.