Biofilm-Based Biomonitoring of Treated Wastewater Using Bacillus thuringiensis : Toward Sustainable Water Reuse

Ensuring the safe reuse or discharge of treated wastewater is critical to achieving environmental sustainability, particularly in regions facing growing water stress. This study introduces a biological approach using Bacillus thuringiensis (Bt) biofilm formation as an indicator of treated wastewater quality from three wastewater treatment plants (WWTPs) in Deep East Texas. Treated wastewater samples were collected from chlorine and sulfur dioxide treatment stages at WWTPs in Nacogdoches, San Augustine, and San Jacinto counties. We assessed biofilm development through optical density and scanning electron microscopy (SEM) and evaluated changes in key anions (F − , Cl − , NO 2 − , Br − , NO 3 − , PO 4 3− , and SO 4 2− ) using ion chromatography (IC). A two-tailed Student’s t-test was used to evaluate statistical significance ( p ≤ 0.05). Remarkably, biofilm formation occurred in all samples, including those treated with chemical disinfectants, suggesting that microbial activity can still occur post-disinfection. Ion shifts, particularly the depletion of F − , NO 3 − , and SO 4 2− and the release of Cl − , NO 2 − , and PO 4 3− , highlighted active microbial processes. These findings suggest that Bt biofilms can serve as sensitive, low-cost tools to monitor treated wastewater, offering critical insights into potential reuse risks and supporting more sustainable water management.