Treatment of real aquaculture effluent using bacteria-based bioflocculant produced by Serratia marcescens

Aquaculture effluent contributes to surface water pollution. Coagulation, flocculation, and sedimentation are currently the best practices in aquaculture effluent treatment, and the utilization of chemical coagulants or flocculants is still dominant in assisting the treatment processes. This research aimed to analyze the potential of the bacteria-based bioflocculant produced by Serratia marcescens in treating real aquaculture effluent. S. marcescens was cultivated for 24 h inside tryptic soy broth medium, and the produced bioflocculant was used in raw condition (without extraction). Jar test and one-variable-at-a-time method were used to assess the effect of bioflocculant dosage, and its performance was compared with that of alum, a commonly used coagulant. The bioflocculant produced by S. marcescens worked well with the assistance of CaCl₂. The 10% bioflocculant dosage showed a remarkable removal of turbidity and suspended solid (83.95% and 78.82%, respectively) compared with the control (80.98% and 76.99%, respectively). Increasing the bioflocculant dosage had a negative effect on color removal because the bioflocculant solution had a reddish color as a result of prodigiosin secretion by S. marcescens. Zeta potential, particle size distribution, and microscopic analyses revealed that flocculation occurred via the bridging mechanism. The utilization of CaCl₂ + bioflocculant showed notable performances in turbidity and suspended solid removal compared with the control reactor while exhibiting a similar efficiency as alum (p < 0.05). Bioflocculant extraction is suggested to be conducted in future research to eliminate its negative effect on the color parameter.