Chapter 4 - Microalgae-based technologies for circular wastewater treatment

Abstract

The realization that linear systems enhance humanity's footprint relative to the Earth's carrying capacity is challenging us to develop circular systems. In circular systems, waste is recycled back into raw materials, increasing its value. For wastewater treatment systems, this means that one needs to develop technologies that remove human pathogens and contaminants of emerging concern (CEC), while recovering water (reclaimed water), carbon, phosphate, nitrogen, macro and microelements (K, Co, Mo, etc.), metals (Cu, Zn, Fe), polymers (PHA, EPS), cellulose, fatty acids, pigments, and others. All these resources are present in wastewater and should be reused in the circular economy. Microalgae-based technologies are increasingly used for wastewater treatment as it has been shown that they are very efficient at the assimilation of nutrients and other microelements. The microalgal biomass can then be used as a raw material for the production of fertilizers, biostimulants, bioplastic, and value added products. Algae fertilizer incorporates the usual elements used in inorganic fertilizers (P, N, K), and also the microelements. Microelements are essential for crop growth, and are often overlooked in modern agriculture leading to empoverishment of our soils with decreased crop yields. This chapter discusses algae-based wastewater treatment from a circular economy perspective. We focus on current and developing technologies for resource recovery and its applications. We also discuss the bottlenecks related to the recycling of the microalgal biomass, such as residual pollutant (human pathogens and CEC) levels and desired biomass elemental composition for fertilizer application (C:N:P). Finally, we discuss how to tackle these bottlenecks to ensure a true circular wastewater treatment.