Mitigating suffusion-induced reactivity loss in sulfate-reducing barriers: Upscaling from multi-layered soil tank to...

This study examines the effectiveness of permeable reactive barriers (PRBs) in stimulating sulfate-reducing bacteria (SRB) to remove both sulfate (SO₄^2-) and metal ions (Me²⁺) from groundwater. PRBs comprising a mixture of conventional reactive materials, including livestock compost, oak sawdust, calcite, and coarse gravel, were simulated in two-dimensional tanks, to which contaminated groundwater from a smelter site in Korea was introduced. The simple placement of the materials resulted in severe depth-dependent spatial disequilibrium in SO₄^2- reduction, which was primarily attributed to the suffusion and subsequent settling of fine compost particles. Sufficient dissolved organic carbon (DOC) for SRB stimulation was provided at the lowest depth (1936.2 mg/L), whereas only 47.2-55.0 mg/L DOC was present in the upper layers. This limitation was resolved by a multi-layered configuration, wherein reactive materials were vertically segmented by acrylic plates. This configuration minimized the settling of fine particles, ensuring a uniform DOC supply at all depths. Up to 90% SO₄^2- removal was achieved during the 45-day experiment. A pilot-scale demonstration at the smelter site achieved stable SO₄^2- and Me²⁺ removal for approximately six months, even under highly variable influent conditions, underscoring the importance of barrier configuration.