Multilayer Immobilizing of Denitrifying Bacillus Sp. and TiO2-AgNPs on Floating Expanded Clay Carrier for Co-Treatment of Nitrite and Pathogens in Aquaculture.

Nitrite contamination and the spread of pathogens can seriously degrade water quality. To simultaneously control these factors, an innovative approach of fabricating a remediation agent that contained denitrifying bacteria and TiO2-AgNPs co-immobilized on floating expanded clay (EC) was proposed in this study. The EC was fabricated from a mixture of clay and rice husk through pyrolysis at a high temperature of 1200 degrees C, followed by a rapid cooling step to create a porous structure for the material. TiO(2)NPs were modified with Ag to shift the absorbance threshold of TiO2-AgNPs into the visible region of 700-800 nm. The experimental results showed that the stirring speed of 250 rpm was suitable for immobilizing TiO2-AgNPs on EC and achieved the highest Ti and Ag content of 639.38 +/- 3.04 and 200.51 +/- 3.71 ppm, respectively. Coating TiO2-Ag/EC with chitosan (0.5%) significantly reduced the detachment level of immobilized TiO2-AgNPs compared to that of the material with no coating. In particular, this functionalized material inhibited 99.93 +/- 0.1% of Vibrio parahaemolyticus pathogen but did not adversely affect the denitrifying bacteria after 2 h of visible light irradiation. Based on the electrostatic bond between oppositely charged polymers, the denitrifying bacteria, Bacillus sp., in alginate solution was successfully immobilized on the chitosan-coated TiO2-Ag/EC with a bacteria density of (76.67 +/- 9.43) x 10(7) CFU g(-1), retaining its nitrite removal efficiency at 99.0 +/- 0.27% through six treatment cycles. These findings provide solid evidence for further investigating the combination of biodegradation and photodegradation in wastewater treatment.