Conventional vs. algal wastewater technologies: Reclamation of microbially safe water for agricultural reuse

Faced with the scarcity and unpredictability of freshwater supplies, the agriculture sector worldwide is finding water reclaimed from domestic wastewater as a new source of water to sustain agricultural food production. To meet this emerging trend and the higher level of treatment expected for agricultural reuse, existing wastewater treatment (WWT) facilities have to be upgraded or new-generation technologies have to be deployed. Reports on the status of existing WWT facilities have expressed strong concerns about their ecological footprint and sustainability; and, have advocated for the need for reinvented technologies to sustain the water infrastructure. Phototrophic algal-based WWT has been suggested as an option with lower life cycle impacts than the existing systems. Here, we discuss the adequacy of the existing and the algal WWT systems in serving the agricultural reuse needs in the context of the challenges and risks associated with the microbiological constituents in the reclaimed water. Recognizing some limitations of the above options, we propose a mixotrophic algal-based WWT system capable of reclaiming superior quality water meeting the reuse guidelines. Performance of this mixotrophic algal wastewater reclamation (A-WWR) system in delivering biologically safe reclaimed water appropriate for agricultural use is detailed and compared with that of the classical phototrophic algal WWT system and the conventional activated sludge-based WWT system demonstrating the potential of the A-WWR system as a greener and safer alternative.