Engineering Surface Hydrophobicity of Porous Carriers to Enhance Algae-Bacteria Granulation and Nutrient Removal in Wastewater Treatment

Efficient and sustainable wastewater treatment increasingly depends on microbial consortia capable of simultaneous nutrient removal and biomass recovery. However, conventional systems often suffer from slow microbial aggregation, poor settling characteristics, and limited operational stability, which reduce overall efficiency. To address these limitations, this research investigates the influence of engineered surface hydrophobicity of porous biochar carriers on algae-bacteria granulation in a Sequential Batch Reactor (SBR). Porous biochar derived from agricultural biomass was modified to enhance surface hydrophobicity, thereby improving microbial adhesion and interfacial interactions between microalgae and activated sludge (AS). Selected microalgal species, including Chlorella vulgaris, Scenedesmus obliquus, Nannochloropsis oculata, Phormidium sp., and Arthrospira platensis, were co-cultivated to establish stable algal-bacterial symbiosis. Surface characterization was performed using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and contact angle measurements, confirming improved surface morphology and hydrophobic properties. It was conducted over 45 days, including granule formation (30-35 days) and maturation phases. The process enhanced Extracellular Polymeric Substance (EPS) production, facilitating rapid granulation and biomass retention. Statistical validation and modeling were performed using International Business Machines Statistical Package for the Social Sciences (IBM SPSS) to ensure data reliability. The system achieved 73.3% Total Nitrogen (TN) removal, 72.5% phosphorus removal, and 77.4% Chemical Oxygen Demand (COD) reduction. Biomass increased from 850 mg/L to 5100 mg/L, with rapid nitrate removal and improved settling velocity (VS) (5.2 m/h). One-way ANOVA assessed group differences in performance (p < 0.05). In conclusion, hydrophobic biochar-mediated algae-bacteria granulation provides a scalable and eco-friendly solution for enhanced wastewater treatment performance.