Chapter 10 - Cultivation of microalgae on agricultural wastewater for recycling energy, water, and fertilizer nutrients

Abstract

Agricultural production generates large amounts of solid wastes and wastewater that can be used to cultivate microalgae as a feedstock for the production of biofuels, fertilizers, animal and feed, and other bio-based chemicals. This chapter reviewed the feasibility, challenges, and enhancement strategies to grow microalgae on various agricultural wastewater for recycling energy, water, and fertilizer nutrients. Microalgae growth needs carbon, nitrogen, and phosphorus at an optimum ratio. Injection of CO2-rich flue gas, dilution of wastewater, and supplement of deficient fertilizer nutrients are necessary to prepare a wastewater-based algal culture medium with an optimum C/N/P ratio. However, as the C/N/P ratio of a specific wastewater may not be easily adjusted, a specific microalgae strain can be acclimated to the wastewater. Coculture of mixed algal strains or microalgae–bacteria consortium could lead to higher algal productivity and more effective wastewater treatment. As environmental and operational factors have effects on the microalgae growth, it is essential to study their interactive effects to optimize the algal growth conditions. Extreme environmental conditions may be used to minimize the presence of grazers and adjust microorganisms in the wastewater for the cultivation of microalgae. New attached and floating cultivation systems and new technologies including microbial fuel cells, nanotechnology, and artificial intelligence have been studied to enhance microalgae cultivation in wastewater, which have shown promising results toward the large-scale cultivation of microalgae for resource recovery and wastewater treatment.