Abstract Description

Global water scarcity, driven by rapid urbanisation and industrialisation, has intensified wastewater pollution through increased anthropogenic activity. This escalating issue calls for sustainable and effective treatment solutions. This study aimed to isolate, characterise, and evaluate microbial bioflocculants for wastewater treatment. Bacterial and fungal strains were obtained through conventional microbiological methods and identified using 16S rRNA and ITS analysis. To enhance bioflocculant yields, factors such as temperature, pH, agitation speed, inoculum level, cultivation time, and carbon and nitrogen concentrations were optimised through Response Surface Methodology (RSM). Structural and functional properties of the bioflocculants were characterised using techniques including SEM, EDX, XRD, TGA, and FTIR. Cytotoxicity was evaluated through cell viability assays across MCF-7, HEK 293, HEPG2, and CACO-2 cell lines. Jar tests and zeta potential analysis assessed flocculation efficiency and mechanisms. Of 80 microbial isolates, Klebsiella pneumoniae and Meyerozyma guilliermondii demonstrated maximum bioflocculant production. K. pneumoniae yielded 8.60 g/L under pH 10, 20 °C, and 150 rpm. M. guilliermondii produced 5.20 g/L under pH 4, 20 °C, and a mixed nitrogen source (urea, yeast extract, ammonium sulfate). Characterisation revealed the bioflocculants Kp1 and Mg1 (from K. pneumoniae and M. guilliermondii) were glycoproteins. Kp1 exhibited a fibrous morphology, while Mg1 showed a granular structure. FTIR analysis detected hydroxyl, amine, and alkene groups as critical for flocculation. Thermal stability tests showed that Mg1 was more heat-resistant than Kp1, which decomposed completely at 1000 °C. Both bioflocculants displayed significant cytotoxicity toward MCF-7 and HEK 293 cells and moderate effects on HEPG2 and CACO-2. In pollutant removal, Kp1 and Mg1 achieved a COD removal of 90.86% and 93.12%, and a turbidity reduction of 92.65% and 92.74%, respectively. Zeta potential analysis indicated that Kp1 operated through charge neutralisation, while Mg1 used polymer bridging. In conclusion, bioflocculants Kp1 and Mg1 show strong industrial potential due to their high yield and efficient pollutant removal; however, their cytotoxic nature warrants caution in handling and application.