Biodegradation Capabilities of Paraquat-Degrading Bacteria Immobilized on Nanoceramics

The biodegradation of paraquat was investigated using immobilized microbial cells on nanoceramics fabricated from nanoscale kaolinite. Pseudomonas putida and Bacillus subtilis, which degrade paraquat, were immobilized separately on nanoceramics (respectively called IC_nc-P and IC_nc-B). The attachment of bacteria to nanoceramics resulted from electrostatic force interactions, hydrogen bonding, and covalent bonding (between the cells and the support materials). The initial 10 mg L^-1 concentration of paraquat in water was removed by the adsorption process using nanoceramics at 68% and ceramics at 52%, respectively. The immobilized cells on the nanoceramics were able to remove approximately 92% of the paraquat within 10 h, whereas the free cells could only remove 4%. When the paraquat was removed, the cell-immobilized nanoceramics exhibited a significant decrease in dissolved organic nitrogen (DON). IC_nc-B was responsible for 34% of DON biodegradation, while IC_nc-P was responsible for 22%. Ammonia was identified as the end product of ammonification resulting from paraquat mineralization.