Experimental Data on Flocculating Activity and Optimization of Four Bacillus-derived Bioflocculants for Wastewater Treatment

This study focuses on four Bacillus species—B. thuringiensis, B. paranthracis, B. halotolerans, and B. velezensis—exploring their potential as sustainable alternatives for wastewater clarification. 1. Optimization of Flocculating Activity (FA): The effectiveness of these bioflocculants is highly sensitive to the physical and chemical environment. The study identified three primary "sweet spots" for maximum performance: Dosage: Optimal performance occurred at a relatively low concentration of 0.6–0.8 mg/mL. Beyond this range, excess bioflocculant can lead to "restabilization" of particles due to charge reversal, which actually decreases efficiency. pH Levels: Activity peaked at a neutral pH (~7.0). While bioflocculants often possess diverse functional groups (like carboxyl or hydroxyl groups), their ionization—and thus their ability to bridge particles—is most stable in neutral conditions. Thermal Stability: These bioflocculants are remarkably resilient, maintaining >80% activity up to 60°C. However, the sharp drop at 80°C suggests they are likely composed of proteins or glycoproteins that undergo thermal denaturation, losing the specific 3D structure required for particle binding. 2. Growth-Phase Correlation: A critical finding for industrial scaling is that bioflocculant production is growth-associated. Stationary Phase (72–96h): Max FA (85–90%) coincides with peak cell density. This suggests the flocculants are likely extracellular polymeric substances (EPS) secreted during the late stages of growth or released during cell lysis. Decline: Prolonged incubation leads to a slight dip in activity, possibly due to the action of extracellular enzymes (proteases or saccharases) produced by the bacteria as they enter the death phase. 3. Performance in Wastewater Treatment: In "jar-test" simulations, which mimic real-world treatment plant conditions, the Bacillus species demonstrated high-tier efficiency: These metrics are vital because Chemical Oxygen Demand (COD) reduction indicates the removal of organic pollutants that would otherwise deplete oxygen in natural water bodies. The fact that these bio-derived options match or exceed alum suggests they are not just "green" alternatives, but functionally superior ones in specific contexts. 4. Safety and Sustainability: The study also touched on antibiotic susceptibility profiling. Characterizing the resistance patterns of the Bacillus strains is essential for ensuring that the use of these bacteria in industrial processes does not contribute to the spread of antibiotic-resistant genes in the environment. Conclusion: By achieving high removal efficiencies with biodegradable, non-toxic materials, Bacillus-derived bioflocculants solve the "double-edged sword" problem of wastewater treatment: cleaning the water without introducing secondary pollutants (like residual aluminum).