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This case study presents a pioneering approach for in-situ immobilization of Chlorella sp. microalgae in photobioreactors, achieved through the synergistic combination of immobilization within a polymeric gel and adsorption on a Nylon mesh, termed the CIPGA system. By applying Buckingham's Pi theorem, correlations among governing variables of the CIPGA were established, and a comprehensive full factorial experimental design assessed the significance of light intensity, reactor diameter, and volumetric airflow. Optimal immobilization conditions for Chlorella sp. were determined: light intensity of 71 μmolm−2s−1, photobioreactor diameter of 0.15 m, and aeration air flow rate of 6.7 × 10−6 m3 s−1. A non-linear three-dimensional model utilizing dimensionless parameters was formulated, exhibiting strong accuracy in predicting scaling-up conditions. The CIPGA system demonstrated remarkable efficacy, forming extensive microalgal strands and a biofilm within a complex three-dimensional architecture. Characterization through FTIR spectra analysis revealed significant attributes, including proteins, polysaccharides, and lipid substances. Notably, the presence of exopolysaccharides emerged as a key factor driving microalgal adhesion to hydrophobic surfaces. The versatile applications of this innovative immobilization approach encompass various bioprocesses, including high-value product generation (biohydrogen, biodiesel, photopigments), nutrient and heavy metal ion removal, biosensors, and wastewater treatment processes.

In recent decades, the extensive use of synthetic dyes in dye-based industries, particularly the textile sector, has led to environmental contamination, raising concerns about water quality and human health. This study aimed to develop a sustainable approach for treating wastewater contaminated with indigo dye through a hybrid approach combining bioremediation and nanofiltration for reuse. In the first stage, two bioaugmentation strategies were compared: using native microorganisms in the wastewater (R-1) and activated sludge from a municipal wastewater treatment plant (R-2). Both strategies effectively reduced chemical oxygen demand (COD) to 200 mg/L and eliminated over 90% of the color. Statistical analysis showed no significant difference in COD removal efficiencies between R-1 and R-2. Correlation analysis revealed a strong association (>99%) between COD, suspended solids (SS) concentration, and color in the reactors, providing insights into sustainable monitoring for wastewater treatment, with potential cost reductions and environmental benefits. In the second stage, nanofiltration (NF) with organic membranes was employed to obtain high-quality permeate for reuse in denim washing. Permeability measurements for R-1 demonstrated similar membrane behavior (NF 270 and Alfa Laval NF) at various transmembrane pressures (TMPs). Both membranes achieved color rejection rates exceeding 96% and COD removal efficiency over 80% for all TMPs. NF tests with R-2 effluent revealed higher permeate flux of 23.71 L·h−1·m−2 at a TMP of 5 bar, with Alfa Laval NF membrane exhibiting superior COD and color rejection compared to NF 270 membrane. The techno-economic analysis showed the hybrid approach of biological treatment/NF to have a mean unit cost of 0.97 USD/m3, indicating economic feasibility and competitiveness against commercial purification processes for sustainable water reuse.