[Study on redox zones of landfill leachate plume in subsurface environment]

A soil column filled with sandy soil was constructed to investigate biogeochemical process of leachate pollutants degradation and redox zones in subsurface environment, and variation of Fe3+, Fe2+, oxidation capacity (OXC) and reduction capacity (RDC) of fresh and contaminated soil were analyzed. Experimental results indicated that four sequent redox zones are appear in pollution plume, and different terminal electron acceptors (they are CO2, Fe3+, NO3- and O2) were used by microbes in different zones; Zones can be named methanogenic zone, iron reduction zone, nitrate reduction zone and oxygen reduction zone correspondingly; the indicator of the different zone is HCO3-, Fe2+, NO2- and DO, and its highest concentration is 10,353 mg/L, 13.61 mg/L, 0.097 mg/L and 5.8 mg/L respectively. OXC of the soil is increased sequentially, its lowest value is 14.18 micromol/g in methanogenic zone and highest value is 24.45 micromol/g in oxygen reduction zone; RDC of the soil is reduced sequentially, its highest value is 14.18 micromol/g in methanogenic zone and lowest value is 24.45 micromol/g in oxygen reduction zone. With the more serious contamination, Fe3+ minerals of the soil are reduced by biogeochemical process, and dissolved Fe2+ is produced. Some of the Fe2+ is released to water and the other is precipitated as sediments. Therefore, it is significant for the in situ remediation and risk assessment of the landfill contaminated site to investigate of the redox zones.