Effects of microbial spatial distribution on organic biodegradation and immobilization of trace metals in co-contaminated soils

Abstract

Predicting the transport and fate of organic and inorganic contaminants in co-contaminated soils is challenging, since various complex, inter-related processes are involved. In the presence of soil microbes that metabolise organic compounds (e.g., phenol), the chemical and the physical properties of the soil may alter and consequently affect the transport of inorganic trace metals e.g., Cu, Cd, Ni, Pb. However, the impact of their spatial distributions on the co-transport processes are still poorly understood and rarely available in literature. Here, we distribute the microbial colonies spatially in uniform and various non-uniform configurations and observe that the transport of weakly-sorbed Cd and Ni is greatly influenced by the distance of the colonies from the contaminant source rather than the size of the colonies. Whereas, for strongly-sorbed Pb and Cu, both the distance and the size are important. The spread of phenol in the model domain was substantially restricted by distributing the colonies more towards the transverse direction than in the longitudinal direction of the groundwater flow. In the context of co-contaminated soil remediation, this study demonstrates that optimum and efficient spatial distribution patterns can be obtained to restrict the spread of both organic and inorganic contaminants, with subsequent reduced environmental impacts.