Evaluation of flocculation performance for Pb2+ and Zn2+ removal from wastewater using the <i>Pseudomonas</i> sp. PR1 flocculant by response surface methodology

ABSTRACT To improve the performance of bioflocculant (PR1) in treating lead–zinc wastewater, response surface methodology (RSM), based on central composite design (CCD), was used to optimize the preparation process of bioflocculants for the treatment. The study investigated the impact of different factors, including temperature, pH, and time, on the preparation of PR1, which was further evaluated by a quadratic polynomial equation for the removal efficiency of lead–zinc in wastewater. The removal efficiency of Pb2+ by PR1 was 99.27% at the optimal conditions of temperature (35.53 °C), pH (10), and time (35.13 h). This was consistent with the RSM predictive value of 99.32% with a small deviation (0.05%) by the quadratic model (R2 = 0.9776 and Radj2 = 0.9575). The removal efficiency of Zn2+ by PR1 was 92.98% at optimal conditions of temperature (44.13 °C), pH (8.88), and time (28.27 h). This was in line with the RSM predictive value of 93.19% with a small deviation (0.21%) by the quadratic model (R2 = 0.9773 and Radj2 = 0.9568). The flocculation mechanisms of PR1 are mainly attributed to the electric neutralization and adsorption bridging. Together, PR1, optimized by RSM, was a highly efficient and promising bioflocculant for removing Pb2+ and Zn2+ from industrial wastewater.