Yu-Huei Peng

Synergistic effect of microscale zerovalent iron particles combined with anaerobic sludges on the degradation of decabromodiphenyl ether.

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardants. Owing to their toxicity and increasing accumulation in the environment, the fate of PBDEs in nature is of serious concern. The combined effects of microscale zerovalent iron (MZVI) and anaerobic sludge in decabromodiphenyl ether (BDE-209) degradation were investigated. The co-incubation resulted in 63% and 29% enhancement of removal ability when compared to the single component conditions. By-products generated during the entire process followed a stepwise sequence with non-uniform accumulation rates. Microbes hindered the accessibility of MZVI to BDE-209 and reduced the removal ability in the initial stage (<12 h). According to the analysis of the microbial community change, co-incubation with MZVI leads to the enrichment of heterotrophic microbial populations bearing nitrate- or iron-reducing activities. The interaction between MZVI and microbes contributed to the synergistic effect. Our findings provide evidence for this synergistic effect and offer an alternative for developing better remediation strategies.

The effect of cations on the aggregation of commercial ZnO nanoparticle suspension

Nanoscale ZnO materials have been largely used in many products due to their distinct properties. However, ZnO nanoparticles (NPs) are hazardous to human health and the ecosystem. The characteristics and the stability of ZnO NPs are relevant to their fate in the environment and their potential toxicities. In this study, a stable commercial ZnO NP suspension was chosen to investigate its aggregation under various salt additions. Different concentrations of NaCl, KCl and CaCl2 were chosen to represent various environmental conditions. Under pH 8–9, the surface charge of commercial ZnO NPs was negative. The behavior of the stabilized ZnO NPs in water was affected by ionic combinations and ionic strength; that is, divalent cations were more effective than monovalent ones in promoting aggregation formation. The attachment efficiencies of ZnO aggregates were calculated based upon the aggregation kinetics. The critical coagulation concentration values for this commercial ZnO NPs were higher than previous reported for ZnO NPs, indicating this ZnO NP could be stable in the aquatic environment and might have increased hazardous potentials. Based upon the Derjaguin–Landau–Verwey–Overbeek theory, interactions between ZnO NPs in the presence of different ions were evaluated to illustrate the aggregation mechanism. Our results indicated that critical ionic type and concentration promote the aggregation of stable ZnO NPs. These understandings also can facilitate the design of the precipitation treatment to remove NPs from water.

Microbial degradation of 4-monobrominated diphenyl ether with anaerobic sludge

Polybrominated diphenyl ethers (PBDEs) are widely used flame retardant additives for many plastic and electronic products. Owing to their ubiquitous distribution in the environment, multiple toxicity to humans, and increasing accumulation in the environment, the fate of PBDEs is of serious concern for public safety. In this study, the degradation of 4-monobrominated diphenyl ether (BDE-3) in anaerobic sludge and the effect of carbon source addition were investigated. BDE-3 can be degraded by two different anaerobic sludge samples. The by-products, diphenyl ether (DE) and bromide ions, were monitored, indicating the reaction of debromination within these anaerobic samples. Co-metabolism with glucose facilitated BDE-3 biodegradation in terms of kinetics and efficiency in the Jhongsing sludge. Through the pattern of amplified 16S rRNA gene fragments in denatured gradient gel electrophoresis (DGGE), the composition of the microbial community was analyzed. Most of the predominant microbes were novel species. The fragments enriched in BDE-3-degrading anaerobic sludge samples are presumably Clostridium sp. This enrichment coincides with the H(2) gas generation and the facilitation of debromination during the degradation process. Findings of this study provide better understanding of the biodegradation of brominated DEs and can facilitate the prediction of the fate of PBDEs in the environment.

Biodegradation of bisphenol A with diverse microorganisms from river sediment

The wide distribution of bisphenol A (BPA) in the environment is problematic because of its endocrine-disrupting characteristics and toxicity. Developing cost-effective remediation methods for wide implementation is crucial. Therefore, this study investigated the BPA biodegradation ability of various microorganisms from river sediment. An acclimated microcosm completely degraded 10 mg L(-1) BPA within 28 h and transformed the contaminant into several metabolic intermediates. During the degradation process, the microbial compositions fluctuated and the final, predominant microorganisms were Pseudomonas knackmussii and Methylomonas clara. From the original river sediment, we isolated four distinct strains, which deplete the BPA over 7-9 days. They were all genetically similar to P. knackmussii. The degradation ability of mixed strains was higher than that of single strain but was far less than that of the microbial consortium. The novel BPA degradation ability of P. knackmussii and its role in the decomposing microcosm were first demonstrated. Our results revealed that microbial diversity plays a crucial role in pollutant decomposition.

The effect of electrolytes on the aggregation kinetics of three different ZnO nanoparticles in water.

Nanoscale ZnO particles are receiving increasing attention because they are widely used in commercial products, but they do have potentially hazardous effects. The aggregation behavior of ZnO nanoparticles (NPs) in the environment contributes to the real risk assessment of nano-toxicity, and the real size of the nano-aggregates should be investigated. In this study, the influences of electrolytes on the stabilities of three ZnO NPs were compared: the commercial powder (NP1), the lab synthesized suspension (NP2) and the commercial suspension (NP3). The initial particle size of NP2 and NP3 in water was at a nanoscale whilst NP1 tended to form microscale aggregates. The capping reagents helped to retain their suspension. The stability of ZnO NPs depends on their zeta potential under specific pH value, ionic types and ionic strength. In general, neutralization plays a major role in aggregation. The effect of divalent counter-ions on ZnO NP aggregation was more than that of monovalent ones. The stabilities of NP2 and NP3 were confirmed by the large critical coagulation concentration (CCC) values of these particles. The experimental results also fit the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The aggregation of different ZnO NPs is relevant to their basic properties and is influenced by electrolytes, which decreases the possibility of the penetration of NPs into cells to cause toxicity in the environment. An understanding of the basic properties of NPs is crucial for assessing their fate in the environment as well as for setting up usage regulation and treatment strategy.

Influence of water chemistry on the environmental behaviors of commercial ZnO nanoparticles in various water and wastewater samples

Zinc oxide nanoparticles (ZnO NPs) are widely used nanomaterials and their environmental impacts have received increasing attention. The fate and toxicity of ZnO NPs in the environment are determined by their stability and dissolution. In this study, the influence of water chemistry on aggregation, sedimentation, and dissolution of ZnO NPs was investigated. The stabilized ZnO NPs aggregated and precipitated when the aqueous pH closed to their zero point of charge (pHzpc). Counter-ions neutralized the surface charge of NPs and promoted their destabilization. However, a high concentration of counter-ion (SO42-, >10meq/L) made the NPs more stable because of the inverted surface potential. The stability of ZnO NPs was maintained by high concentration of Suwannee River humic acid (SRHA, 10mg/L) even the concentration of electrolytes was high. The influence of water chemistry on the stability and dissolution of ZnO NPs was further demonstrated in different wastewaters. In one wastewater sample, ZnO NPs was unexpectedly stable and with a high dissolution, which was due to the effects of pH value, organic matter concentration, as well as the concentration of counter ions. Our findings facilitate the predictions of the fate of stabilized ZnO NPs in the environment.

Adsorption and sequential degradation of polybrominated diphenyl ethers with zerovalent iron.

The widely used flame retardants, polybrominated diphenyl ethers (PBDEs), have been regulated owing to their persistence and toxicity. However, the high and increasing accumulation amount of PBDEs in the environment raises a big concern for public safety. In this study, the removal processes of decabromodiphenyl ether (BDE-209) and monobromodiphenyl ether (BDE-3) with microscale zerovalent iron (MZVI) were investigated to get better understandings for the removal mechanism based upon adsorption and degradation. The removal kinetics of both compounds was analyzed and revealed two-step kinetics: a fast removal step at the beginning of the reaction and a follow-up slow removal step. By-products generated during the entire process followed a stepwise sequence. The content of brominated compounds on the surface of MZVI was measured. About 10-20% of BDE-209 and 15-30% of BDE-3 were adsorbed on MZVI. The adsorption of BDE-209 and BDE-3 on MZVI was confirmed through the Fourier transform infrared spectroscopy. Surface adsorption of PBDEs on MZVI dominates the removal mechanism in the beginning and further debromination with MZVI was found. Finally, about 70% of BDE-209 and 60% of BDE-3 was degraded by MZVI within about one month. Our findings provide evidences for understanding the removal mechanism of PBDEs with MZVI and its great longevity on the PBDE degradation, which can facilitate the remediation design.

Microbial Degradation of Some Halogenated Compounds: Biochemical and Molecular Features

Due to the advance of organic and synthetic chemistry and many applications of man-made organic compounds, lots of xenobiotic chemicals are produced and benefit our life. However, some of them are persistent in the environment and their toxicities are accumulated through the food webs. Due to the potential hazard for human and the ecosystem, the regulations on the usage of these persistent organic pollutants (POPs) and the development of safe decom‐ position methods are now in great request.

The effect of zerovalent iron on the microbial degradation of hexabromocyclododecane

Hexabromocyclododecane (HBCD), a commonly used brominated flame retardant (BFR), has been listed as a persistent organic pollutant (POP). In order to remediate HBCD in the environment, the influence of microscale zerovalent iron (MZVI) on the HBCD degrading microcosm was evaluated. In the acclimated microcosm collected from river sediment, 49% of HBCD was initially removed through adsorption and then 30% of HBCD was biodegraded through non-debromination processes. In contrast to MZVI only, over 60% of HBCD was gradually degraded by MZVI through a debromination reaction. In the microcosm-MZVI combined system, the biodegradation ability of the microcosm was inhibited. The aqueous chemistry was changed by the addition of MZVI, which led to the alteration of microbial composition and biodegradation ability. These better understandings can facilitate an evaluation of the impact of MZVI on HBCD biodegradation when ZVI was used to remediate this BFR.