Experimental study on the multi-media PRB reactor for the remediation of petroleum-contaminated groundwater

The natural reactive media palygorskite, peat, and scoria were chosen for the in situ remediation of petroleum-contaminated groundwater in a northeast field of China based on its geologic and hydrogeologic characterization. The adsorption capacity of the compound media for removal of the total petroleum hydrocarbons (TPH) in the groundwater was investigated. The results indicated that the adsorption efficiency of palygorskite and peat were greatly improved after heat treatment for 2 h at 140 °C. Taking consideration of the permeability and adsorption efficiency of particle size on TPH removal of each media, the suitable particle size of 0.5–2.0 mm was selected. The optimal mass ratio of the compound reactive media was 2.0:0.8:0.2 for scoria, peat, and palygorskite, respectively, and the permeability of compounds media was 208 m/d. The results from the 31 days of operation showed that the TPH removal rate of compounds reached up to 96 %, pH varied between 7.49–7.63, and the ORP value generally decreased from −3 to −33. During the process of the cation exchange and the ion adsorption, the concentration of Ca²⁺, Mg²⁺, K⁺, Na⁺, and SO₄ ²⁻ decreased. However, the concentration of HCO₃ ⁻ increased due to the dissolved calcite of palygorskite in the slightly alkaline aqueous environment. This chemical and physical reaction allowed the TDS to gradually decrease from 717.15 to 330.94 mg/L, which then became stable after 31 days. The experiments suggested that the PRB reactor had a strong capacity to adsorb the petroleum hydrocarbon, enhance the ability of water redox state, and decrease the groundwater salinity.