The feasibility of in-situ bioremediation of atrazine-contaminated groundwater by Pseudomonas sp. ADP (PADP) was tested in a two-dimensional laboratory scale model aquifer. The experimental set-up consisted of three compartments: an inlet chamber, a saturated sandy aquifer with a biological permeable reactive barrier (BPRB) and an outlet chamber. Multi-layer samplers (MLSs) at 10, 25 and 40 cm from the bed base were located at 7, 28.5 (well), 42.5 (BPRB) and 55 cm from the inlet. Artificial atrazine-contaminated groundwater (1 mg/L) amended with nitrate (20 mg/L NO3- -N) flowed horizontally through the aquifer at a rate of 5.5 cm/day. Inoculation of the reactive barrier was achieved by temporarily stopping the water flow, and injecting into the reactive barrier 1 L of a PADP suspension with a concentration of 5.6 x 109 CFU/mL; water flow was resumed one hour later. To enhance bacterial activity, a citrate solution (1 g/L) was injected into the barrier twice a week. During the four months of operation, water samples were withdrawn weekly from the MLSs at each sampling station and from the inlet and the outlet, to determine the following water quality parameters: dissolved oxygen, pH, temperature, nitrate, atrazine, total dissolved solids and bacterial colony counts (CFU). The concentration of atrazine was practically unchanged from the inlet to the barrier, and an average removal of 50% was observed at the barrier. This removal in the concentration of atrazine was maintained downstream with a slight increase at the outlet, probably due to matrix heterogeneities and preferential channeling. The concentration of dissolved oxygen also decreased along the water path and the lowest value, 2.2 mg/L, was measured at the barrier and at the station downstream. A very small decline was detected in pH values, which decreased from an average of 8.4 ± 0.1 at the inlet to an average of 8.0 ± 0.1 at the outlet. The values of total dissolved solids and temperature did not change significantly throughout the aquifer. In general, low levels of nitrate reduction were detected, although up to 80% reduction was observed at the third week at location 55 cm, with no detectable decrease in the concentration of dissolved oxygen. No correlation was found between degradation of atrazine and nitrate reduction. Our results indicate that in-situ treatment may be a suitable method for the restoration of atrazine contaminated aquifers. <i> Nepal Journal of Science and Technology</i> Vol. 7, 2006
Three different types of physical substrata such as sand, granualar activated carbon (GAC) and plastic macaroni beads were selected to identify a suitable solid carrier as a course matrix for the permeable reactive barrier (PRB) in a sand filled two-dimensional laboratory-scale model aquifer. An adhesion experiment was performed and tested with Pseudomonas sp ADP (PASP) under agitated as well as static conditions. In static conditions, adhesion to GAC was the highest (80%) followed by that to beads (60%). No adhesion to sand was observed under static or agitated conditions. Since atrazine is adsorbed by GAC, its bioavailability for degradation by PADP may be affected. To test this, simultaneous loss of atrazine and release of chloride (dechlorination, the first step in the pathway of atrazine degradation by PADP) were determined in the presence and absence of GAC. Although cells remained viable, no significant chloride release was detected. Thus, plastic macaroni beads were identified and selected as the most suitable support for PADP in the biological permeable reactive barrier (BPRB) of the model aquifer.Key words: Suitable Solid; Laboratory Scale; PADPTribhuvan University JournalVol. XXV, No. 1, 2005Page:119-128Uploaded date: 26, September, 2010
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