Advances in microalgae-based livestock wastewater treatment: Mechanisms of pollutants removal, effects of inhibitory components and enhancement strategies

Livestock wastewater (LW) is characterized by the significant presence of organic matter, nitrogen (N), and phosphorus (P), as well as heavy metals (HMs), antibiotics, endocrine disruptors (EDCs), microplastics (MPs), and antibiotic resistance genes (ARGs). Microalgae-based technologies present a promising alternative for the bioremediation of LW, as they can efficiently eliminate pollutants while simultaneously utilizing renewable resources. However, microalgae-based LW treatment in remediating multiple contaminants of emerging concern (CECs) has been comprehensively evaluated by few articles. Consequently, the impact of inhibitory components in LW on microalgae and the response of microalgae to such exposure remain unclear. This review provides a critical and updated overview of the potential use of microalgae as LW bioremediation agents for the simultaneous removal of conventional pollutants and CECs. Several models and algorithms have been suggested as viable approaches for improving microalgal growth through the optimization of cultivation parameters. The effects of the inhibitory components in LW on microalgae and the removal mechanisms of hazards were comprehensively illustrated, highlighting the behavior of CECs (e.g., antibiotics, EDCs, MPs, and ARGs). Moreover, conventional and cutting-edge strategies for improving the performance of microalgae-based LW treatment, including pretreatment, optimization of the cultivation mode and light, genetic engineering, random mutagenesis, and microalgae-microbial fuel cells, were further discussed. Furthermore, perspectives for further improvement were proposed. Importantly, research should focus on verifying the specific removal mechanisms of CECs at the cellular level, distinguishing the combined effect of pollutants in LW, optimizing multi-objective microalgae-based LW treatment, and developing more sustainable and user-friendly strategies.