Effectiveness and longevity of a green/food waste derived compost packed column to reduce Cr(VI) contamination in groundwater

PAS100 accredited compost derived from green and food waste sources was used to remediate groundwater containing Cr(VI) at a historically contaminated site in Falkirk, Scotland, UK. The compost was mixed with gravel at a ratio of 1:1 (v/v) to provide a reactive bedding material in an upflow column. The Cr(VI) concentration in the groundwater (inlet) ranged from 0.5 to 7.8 mg L−1 during the 168 d trial period. After an acclimation period of 54 d, the flow rate was increased in the column from 5.8 to 8 mL min−1. Cr(VI) in the outlet was less than 100 μg L−1 up to 134 d, after which the concentration steadily increased till 168 d. Compost analysis following completion of the trial confirmed that Cr(VI) was captured within the column. Anaerobic microbial reduction of Cr(VI) to Cr(III) was thought to be a key mechanism responsible for the longevity of the system to remove Cr(VI) from the groundwater. Requiring no additional organic carbon or nitrogen during the trial period, this setup represents a cost-effective treatment approach for low flow-through systems.