Free and immobilized cell bioaugmentation for removing atrazine from agricultural infiltrate

Abstract

The remediation of atrazine in agricultural infiltrate by bioaugmented free and phosphorylated-polyvinyl alcohol (PPVA) immobilized cells was studied. The effects of cell-to-matrix ratio, cell loading and infiltration rate on atrazine removal efficiency were examined. Two types of bacterial cultures were used: pure and mixed cultures. The pure culture was a previously isolated atrazine degrader, Agrobacterium radiobacter J14a (J14a) while the mixed culture (MC) was enriched from atrazine-contaminated soil. This novel mixed culture degraded 33-51% of atrazine within 7 d. Two isolates, Klebsiella ornithinolytica ND2 and Agrobacterium tumefaciens ND4, which were purified from the mixed culture, contained an atrazine-degrading gene, atzA. In the PPVA immobilization process, an existing cell immobilization procedure was modified. The modified procedure provided a stable and suitable microstructure matrix and had a slight effect on bacterial cell viability. In a batch study, the atrazine removal efficiencies by the immobilized J14a and MC were better than those by the free cells. Higher cell-to-matrix ratios resulted in lower atrazine removal. The cell-to-matrix ratio of 3.5 mg/mL provided the highest atrazine removal efficiency of 40 to 50% in 5 d for both J14a and MC. For atrazine bioremediation tests in a column system, the bioaugmented J14a and MC performed similarly. During the tests at 5 pore volumes (PV), the atrazine removal by the immobilized and free cells was not significantly different. J14a degraded 50 to 100% of atrazine while MC removed 42 to 80% of atrazine. Both infiltration rate and cell loading significantly influenced the atrazine removal. The bacterial loss from the immobilized cell system was 10 to 100 times less than that from the free cell system. In the test by MC, the changes of bacterial community structure after testing for 5 PV were observed. The infiltration rate was a significant factor for the change. For long-term tests at 50 PV, the immobilized cell system provided consistent atrazine removal while the performance of the free cells declined gradually because of the cell loss