| The use of zero valent iron, permeable reactive barriers (PRBs) for groundwater remediation continues to increase. An exciting variation of this technology involves introducing anaerobic bacteria into these barriers so that both biological and abiotic pollutant removal processes are functional. This work evaluated the hypothesis that a system combining a mixed culture of sulfate reducing bacteria (SRB) with zero valent iron would have a greater Cr(VI) removal efficiency and a greater total Cr(VI) removal capacity than a zero valent iron system without the microorganisms. Hence, the overall goal of this research was to compare the performance of these types of systems with regard to their Cr(VI) removal efficiency and total Cr(VI) removal capacity. Both batch and continuous flow reactor systems were evaluated.; In batch studies using Cr(VI)-unacclimated and Cr(VI)-acclimated cultures, and an initial concentration of 2.0 mM for both cultures, Cr(VI) was removed most rapidly in the treatments in the following order: Fe(0) + SRB + Lactate > Fe(0) + SRB > Fe(0) > SRB + Lactate.; Two continuous-flow column studies were conducted, a short-term study for a period of 58 days and a longterm study for a period of 360 days. In each study, columns were packed with 5 g of steel wool and selected columns were seeded with a SRB stock culture. The columns (2.25 cm dia. x 9.2 cm long) were fed via a syringe pump at a flow rate of 10 mL/d. The results clearly showed that seeding the columns with the SRB culture greatly improved their Cr(VI) removal performance.; In the 58-day study, the influent Cr(VI) concentration ranged from 380 μm to 19.2 mM. The ratio of the overall performance of the column pairs, based on total mass of Cr(VI) removed during the study, was: Fe(0) + SRB compared to Fe(0) (143%); Fe(0) + SRB + Lactate vs. Fe(0) (178%); and Fe(0) + SRB + Lactate vs. Fe(0) + SRB(123%).; In the 360-day study, the influent Cr(VI) concentration ranged from 190 μM to 3.08 mM. The performance of the columns in terms of the ratio of the total mass of Cr(VI) removed by each was as follows: Fe(0)+SRB vs. Fe(0) (207%); Fe(0) + SRB+Lactate vs. Fe(0) (575%); Fe(0) + SRB+Lactate vs. Fe(0) + SRB (278%). |
