Microalgae-mediated treatment of pharmaceutical contaminants: degradation pathways, advance system design, and priority research needs.

Pharmaceutical residues are increasingly detected in freshwater systems at concentrations ranging from g/L to /L, raising concerns due to their persistence, bioactivity, and potential ecological and human health impacts. Conventional wastewater treatment plants typically achieve limited removal efficiencies (often 30-60% for many compounds such as carbamazepine and diclofenac), necessitating alternative treatment strategies. This review critically evaluates microalgae-based pond and consortia systems, emphasizing the key removal pathways of bioadsorption (10-40%), bioaccumulation (up to 20-30%), and biodegradation (40-90%, compound and condition dependent). It further examines microalgal physiological responses, including oxidative stress regulation, enzymatic transformation, and adaptive metabolic shifts under pharmaceutical exposure, which influence treatment performance. Major operational constraints, including seasonal variability, affect productivity and toxicity thresholds that inhibit algal growth at elevated contaminant concentrations. Recent advances in strain engineering, co-culture consortia, and process optimization have demonstrated removal efficiencies exceeding 80% under optimized conditions. Moreover, this review provides a systematic synthesis of mechanistic pathways, integrates recent process innovations, and identifies critical knowledge gaps related to by-product toxicity, scale-up stability, and long-term system performance, offering a more quantitative and application-oriented perspective on microalgae-based pharmaceutical removal.