<p>Third-generation biofuel using algal biomass as feedstock has gained importance in recent years. The present study explores an integrated approach for bioethanol production from <i>Micractinium</i> sp., biomass cultivated using nanourea (NU) as a nitrogen source. Moreover, a novel L-arginine-tagged guar gum (AGG) polymer was developed for the eco-friendly harvesting of microalgal cells. A maximum biomass yield of 5.94 ± 0.07&#xa0;g L⁻¹, productivity of 0.38 ± 0.02&#xa0;g L⁻¹ d⁻¹, and a carbohydrate content of 44.78 ± 2.09% (w/w) was observed on supplementing 2.66&#xa0;mM nanourea in a 2-L bubble column reactor. The flocculant AGG polymer showed 97.75 ± 1.12% flocculation efficiency at 100&#xa0;ppm, further improving to 99.46% with an augmentation FeCl₃ dosage (60&#xa0;ppm). The harvested microalgal biomass was subjected to microwave-assisted mixed organic acid (acetic acid and formic acid) pretreatment and subsequent enzymatic saccharification with a cocktail of cellulase and amylase (1%, w/w), giving 43.12 ± 1.05% (w/v) reducing sugars yield. These sugars were then converted into bioethanol with a yield of 0.48 ± 0.01&#xa0;g&#xa0;g⁻¹ of reducing sugars using a 250-mL conical flask. This study presents a novel and eco-friendly strategy for microalgal cultivation, harvesting, and bioethanol production, offering a significant step forward in sustainable biofuel technologies and contributing to resource efficiency.</p> Graphical Abstract <p></p>