A laboratory study on the development and testing of a bioaugmentation system for contaminated soils /

The primary objective of this study was to investigate the use of water table management (WTM) as a microbial delivery system for in-situ bioaugmentation of contaminated soils. In addition, the use of Rhizobium ( R.) for PCB degradation in soils was evaluated.First, the presence and isolation of a variety of strains of Rhizobium meliloti was demonstrated using plant nodulation tests on alfalfa plants in soils that were contaminated for over 15 years with PCBs, PAHs and heavy metals. Next, R. meliloti, strain A-025, was selected based on its membrane (hydrophobicity, adhesion) characteristics and its potential to transform PCBs. This strain was delivered and implanted in sod columns, 200 mm in diameter x 1000 mm in length, packed with a sandy loam soil, using surface and subirrigation. The results of this study showed that subirrigation led to a higher number and a more uniform distribution of the bacterial cells in the soil at 60, 300, 500, and 700 mm depths, than surface irrigation.In a different setup, similar column were packed with a PCB contaminated soil. These soil columns were bioaugmented with three bacterial cultures, i.e., R. meliloti (strain A-025), Comomonas testosteroni (strain B-356) and an indigenous bacterial consortium using subirrigation. The results indicated that bioaugmentation of the PCB contaminated soil was possible by using subirrigation. Bioaugmentation with the indigenous culture was observed to be more effective in the biodegradation of PCBs than with A-025 and B-356 cultures at 140 and 340 mm depths. However, at 590 mm depth, bioaugmentation with strain A-025 was observed to be better than the other treatments. Sequential aerobic and anaerobic cycles appear to be of significance for effective dechlorination of PCB congeners to lower chlorinated congeners.In a separate exploratory study, the rhizospheric effects of alfalfa plants on R. meliloti for PCB depletion were investigated. The results suggest that the growth of alfalfa plants and bioaugmentation of soil with R. meliloti, strain A-025, increased the depletion of PCB congeners in the soil as compared to bioaugmentation alone. In other preliminary studies, the results showed that the presence of PCBs in a sandy loam soil increases the filtration of bacterial cells. Also, soil type and the presence of PCBs affected water infiltration, moisture, and hardness of the soil. Furthermore, water table management system along with bioaugmentation of soil columns with R. meliloti, strain A-025, decreased the concentration of atrazine by 31% during anaerobic and aerobic cycles and reduced the concentration of nitrate by 87% and 78% in the absence and presence of atrazine, respectively, in the drainage water.The overall results of this work indicate that water table management (subirrigation) can be used for bioaugmentation of contaminated soils. Also, use of R. meliloti may prove to be an interesting option for soils contaminated with PCBs, atrazine and nitrate