Nanoremediation of cadmium contaminated river sediments: Microbial response and organic carbon changes.

The application of nanomaterials to contaminated river sediments could induce important changes in the speciation of heavy metals with potential impacts on ecosystem. Here, rhamnolipid (RL)-stabilized nanoscale zero-valent iron (RNZVI) was conducted to test its potential performance in changing the mobility and speciation of cadmium (Cd) in river sediments, with consideration of the influences of microbial community and organic carbon (OC). Compared to NZVI, RNZVI was more effective in transforming labile Cd to stable fraction with a maximum residual concentration increasing by 11.37 mg/kg after 42 days of incubation. Bacterial community structure was tracked using high-throughput sequencing of 16S rRNA genes. Results indicated that the application of RNZVI changed the bacterial community structure and increased the relative abundance of Fe(III)-reducing bacteria, which could redistribute Fe combined Cd into a more stable Fe mineral phase. The contents of OC were gradually decreased and became stable, might resulting from OC bioavailability's being stimulated by RNZVI through changing the bacterial community composition. This study indicates that abiotic process (i.e., from reaction with NZVI) and biotic process fueled by RNZVI lead to the immobilization of Cd in river sediments.

Nanoscale zero-valent iron assisted phytoremediation of Pb in sediment: Impacts on metal accumulation and antioxidative system of Lolium perenne.

Lead (Pb) is a highly toxic environmental pollutant, and could result in toxic effects on living organisms. The effects of 0, 100, 200, 500, 1000 and 2000 mg/kg of nZVI on plant growth, Pb accumulation and antioxidative responses of Lolium perenne were investigated. Results showed that the total Pb contents in L. perenne with the treatment of low concentrations of nZVI (100, 200 and 500 mg/kg) were higher than those in the non-nZVI treatments, and the highest Pb accumulation capacity of 1175.40 µg per pot was observed in L. perenne with the treatment of 100 mg/kg nZVI. However, the total Pb contents in L. perenne decreased at high concentrations of nZVI (1000 and 2000 mg/kg). This might be resulted from the decrease of photosynthetic chlorophyll content and the aggravated oxidative stress induced by the high concentration of nZVI, which caused the decrease of plant biomass and metal accumulation capacity in plant. Moreover, the sequential extraction experiments results showed that the lowest acid soluble fraction of Pb in the sediments was found in the treatment with 100 mg/kg of nZVI, indicating that 100 mg/kg was the optimum concentration for nZVI to assist the phytoremediation of Pb-polluted sediment. To conclude, these findings provide a promising method to remediate Pb-polluted sediment by nZVI assisted phytoremediation.

Cadmium immobilization in river sediment using stabilized nanoscale zero-valent iron with enhanced transport by polysaccharide coating.

Proper management of metal-contaminated sediment plays a key role in sediment recovery and reuse. This study synthesized two kinds of stabilized nanoscale zero-valent iron (nZVI) with starch (S-nZVI) and carboxymethyl cellulose (C-nZVI) for the in situ immobilization of Cd(II) in river sediment and investigated their transport in porous media. Experimental data showed that when the sediment sample was treated with C-nZVI for 56 days at a dosage ranging from 5 to 10 mg/g-sediment as Fe0, the TCLP (toxicity characteristic leaching procedure) leachability of Cd(II) in the sediment decreased by 93.75-96.43%, and the PBET (physiologically-based extraction test) bioaccessibility of Cd(II) decreased by 22.79-71.32%. Additionally, the acid soluble fraction of Cd(II) was partially transformed to a residual fraction, resulting in a 32.4-33.1% decrease of acid soluble Cd(II) and a 125.4-205.6% increase of the residual-Cd(II) fraction. Surface complexation with iron oxyhydroxide minerals might be the main mechanism of Cd(II) immobilization in sediment. Column experiments indicate that starch or carboxymethyl cellulose (CMC) could extend the travel distance of nZVI, but inherent site physical and chemical heterogeneities still posed challenges for nanoparticle transport. Over all, this study verifies the effectiveness of stabilized nZVI for Cd(II) immobilization in sediment and discusses the potential immobilization mechanism.

Sorptive removal of ionizable antibiotic sulfamethazine from aqueous solution by graphene oxide-coated biochar nanocomposites: Influencing factors and mechanism.

Significant concerns have been raised over antibiotics pollution in aquatic environments in recent years. In this study, sorption of sulfamethazine (SMT) by novel graphene oxide-coated biochar nanocomposites (GO-BC) based on graphene oxide (GO) with bamboo sawdust biochar (BC) was investigated. In comparison with the original BC, the sorption capacity of GO-BC for SMT increased by 1.14 times. Sorption of SMT onto GO-BC was proved to be dominantly by chemisorption, and Freundlich isotherm described the sorption adequately. It was found that variation of pH and ionic strength obviously affected the sorption of SMT, and GO-BC had a good sorption effect on SMT at pH 3.0-6.0 and lower ionic strength. Obvious enhancement (by 30%) in sorption of SMT on GO-BC was observed, which might be attributed to the increase of functional groups on the surface of GO-BC. Moreover, the main sorption mechanism for SMT was π-π electron-donor-acceptor interaction, while auxiliary sorption mechanisms were inferred as pore-filling, cation exchange, hydrogen bonding interaction and electrostatic interaction. The results indicated that GO-BC sorption was an efficient way for the removal of SMT.