Microbes team with nanoscale zero-valent iron: A robust route for degradation of recalcitrant pollutants

Modified nano zero-valent iron coupling microorganisms to degrade BDE-209: Degradation pathways and microbial responses

Polybrominated diphenyl ethers (PBDEs) in soil and groundwater have garnered considerable attention owing to the significant bioaccumulation potential and toxicity. Currently, the coupling treatment method of nano zero-valent iron (nZVI) with dehalogenation microorganisms is a research hotspot in the field of PBDE degradation. In this study, various systems were established within anaerobic environments, including the nZVI-only system, microorganism-only system, and the nZVI + microorganisms system. The aim was to investigate the degradation pathway of BDE-209 and elucidate the degradation mechanism within the coupled system. The results indicated that the degradation efficiency of the coupled system was better than that of the nZVI-only or microorganism-only system. Two modified nZVI (carboxymethyl cellulose and polyacrylamide) were prepared to improve the coupling degradation efficiency. CMC-nZVI showed the highest stability, and the coupled system consisting of microorganisms and CMC-nZVI showed the best degradation effect among all of the systems in this study, reaching 89.53% within 30 days. Furthermore, 22 intermediate products were detected in the coupling systems. Notably, changing the inoculation time did not significantly improve the degradation effect. The expression changes of the two reductive dehalogenase genes, e.g. TceA and Vcr, reflected the stress response and self-recovery ability of the dehalogenating bacteria, indicating such genes can be used as biomarker for evaluating the degradation performance of the coupling system. These findings provide a better understanding about the mechanism of coupling debromination process and the direction for the optimization and on-site repair of coupled systems.

Combining nanoscale zero-valent iron and anaerobic dechlorinating bacteria to degrade chlorinated methanes and 1,2-dichloroethane

Nanoscale zero-valent iron (nZVI) has the potential to degrade a diversity of chlorinated compounds, and it is widely used for remediation of contaminated groundwaters. However, some frequently detected contaminants such as dichloromethane (DCM) and 1,2-dichloroethane (1,2-DCA) have shown nearly no reactivity with nZVI. Here, we tested the feasibility of combining anaerobic dechlorinating bacteria, Dehalobacterium and Dehalogenimonas, and nZVI as a treatment train to detoxify chlorinated methanes (i.e., chloroform-CF- and DCM), and 1,2-DCA. First, we showed that CF (500 μM) was fully degraded by 1 g/L nZVI to DCM as a major by-product, which was susceptible to fermentation by Dehalobacterium to innocuous products. Our results indicate that soluble compounds released by nZVI might cause an inhibitory impact on Dehalobacterium activity, avoiding DCM depletion. The DCM dechlorination activity was recovered when transferred to a fresh medium without nZVI. The increase in H2 production and pH was discarded as potential inhibitors. Similarly, a Dehalogenimonas-containing culture was unable to dichloroeliminate 1,2-DCA when exposed to 1 g/L nZVI, but dechlorinating activity was also recovered when transferred to nZVI-free media. The recovery of the dechlorinating activity of Dehalobacterium and Dehalogenimonas suggests that combination of nZVI and bioremediation techniques can be feasible under field conditions where dilution processes can alleviate the impact of the potential inhibitory soluble compounds.

Environmental occurrence, toxicity and remediation of perchlorate - A review

Perchlorate (ClO4-) comes under the class of contaminants called the emerging contaminants that will impact environment in the near future. A strong oxidizer by nature, perchlorate has received significant observation due to its occurrence, reactive nature, and persistence in varied environments such as surface water, groundwater, soil, and food. Perchlorate finds its use in number of industrial products ranging from missile fuel, fertilizers, and fireworks. Perchlorate exposure occurs when naturally occurring or manmade perchlorate in water or food is ingested. Perchlorate ingestion affects iodide absorption into the thyroid, thereby causing a decrease in the synthesis of thyroid hormone, a very crucial component needed for metabolism, neural development, and a number of other physiological functions in the body. Perchlorate remediation from ground water and drinking water is carried out through a series of physical-chemical techniques like ion (particle) transfer and reverse osmosis. However, the generation of waste through these processes are difficult to manage, so the need for alternative treatment methods occur. This review talks about the hybrid technologies that are currently researched and gaining momentum in the treatment of emerging contaminants, namely perchlorate.