Abstract
Microbial residue-mineral composites are important components of stabilizing soil carbon pool, and sorption/desorption of organic contaminants on the composites affects their transport in the soil. Here, we obtained the microbial residue-mineral composites by inoculating the model soil (33% Hematite + 67% Quartz sand (FQ), or 33% Montmorillonite + 67% Quartz sand (MQ), w/w) with natural soil microorganisms and adding different substrate-C (Glycine (G), Glucose (P), or 2, 6-Dimethoxyphenol (B)) for incubation, which were named as GF, PF, BF, GM, BM, PM, respectively. Then performed batch adsorption and desorption experiments of phenanthrene (PHE) and ofloxacin (OFL). Composites cultured with 2,6-dimethoxyphenol had the highest carbon content (0.98% on FQ, 2.11% on MQ), whereas those cultured with glycine had the lowest (0.24% on FQ, 0.64% on MQ). And the carbon content of composites incubated with MQ (0.64%~2.11%) was higher than that with FQ (0.24%~0.98%) at different carbon matrix additions, indicating that more microbial residues were formed on composites incubated with MQ compared to FQ. Perhaps montmorillonite facilitated the accumulation of microbial residues due to its large specific surface area. The sorption of PHE by composites, especially BM, was higher than MQ but lower than FQ. Moreover, the sorption of OFL was related to properties of microbial residues. The release ratio (RR) of PHE adsorbed by composites had positively correlated with the concentration in the solid phase. The RR of OFL is almost zero for both high and low concentrations, indicating that sorption of OFL on composites is stable. Thus, microbial residue-mineral composites can reduce the risk of migration of organic contaminants in soil, especially the ionic organic contaminants.