Xiangling Zhang

Removal of oxygen demand and nitrogen using different particle-sizes of anthracite coated with nine kinds of LDHs for wastewater treatment.

This paper reports the application of anthracite particles of different sizes and coated with nine kinds of layered double hydroxides (LDHs) varying in MII–MIII cations, as alternative substrates in the simulated vertical-flow constructed wetland columns. Effects of LDHs-coating and particle size of modified anthracites were examined to evaluate their abilities in removing oxygen demand and nitrogen from sewage wastewater. Results showed that LDHs modification effectively enhanced the removal of nitrogen and organics. The removal efficiencies of total nitrogen (TN) , ammonia and chemical oxygen demand (COD) were best improved by 28.5%, 11.9% and 4.1% for the medium particle size (1–3 mm), followed by 9.2%, 5.5% and 13.6% for the large size (3–5 mm), respectively. Only TN removal was improved up to 16.6% for the small particle size (0.5–1 mm). Nitrate tended to accumulate and fluctuate greatly across all the treatments, probably due to the dominancy of aerobic condition in the vertical-flow columns. Overall, MgFe-LDHs was selected as the best-modified coating for anthracite. The results suggested LDHs modification would be one of the promising strategies to provide new-types of highly efficient and lasting wetland substrates.

Effects of Varying Particle Sizes and Different Types of LDH-Modified Anthracite in Simulated Test Columns for Phosphorous Removal

A comparative study was carried out for the removal of phosphorus in simulated unplanted vertical-flow constructed wetlands with different layered double hydroxide (LDHs) coated anthracite substrates. Three particle sizes of anthracites were selected and modified separately with nine kinds of LDH coating. The simulated substrates test columns loaded with the original and modified anthracites were constructed to treat the contaminated water. For the medium and large particle size modified anthracite substrates, the purification effects of total phosphorus, total dissolved phosphorus and phosphate were improved by various degrees, and the purification effect of the medium particle size anthracite is better than that of the large size one. The medium size anthracite modified by ZnCo-LDHs had optimal performance with average removal efficiencies of total phosphorus, total dissolved phosphorus and phosphate reaching 95%, 95% and 98%, respectively. The maximum adsorption capacity on ZnCo-LDHs and ZnAl-LDHs modified medium sizes anthracites were 65.79 (mg/kg) and 48.78 (mg/kg), respectively. In comparison, the small size anthracite is not suitable for LDHs modification.

Homogenous stands of a wetland grass living in heavy metal polluted wetlands harbor diverse consortia of arbuscular mycorrhizal fungi

Over the last three decades, the presence of arbuscular mycorrhizal (AM) fungi in wetland habitats had received increased attention, however, their distribution and functions have not been studied intensively. Using Illumina sequencing technology, we examined the AM fungal communities in roots of Phragmites australis living in 3 heavy metals (HMs) polluted wetlands located in Hubei Province, China. A total of 258 operational taxonomic units (OTUs) from 235,213 sequences affiliated with 6 Glomeromycota families (Glomeraceae, Paraglomeraceae, Claroideoglomeraceae, Ambisporaceae, Archaeosporaceae, and Diversisporaceae) were obtained, with Glomeraceae and Paraglomeraceae being the most and second-most dominant family, respectively. P. australis living in the HMs polluted wetlands harbored diverse AM fungi, including many non-recorded species in upland habitats, and the OTU number which we obtained in this study was higher than most of the records of upland habitats. Dry and waterlogged samples had common OTUs, however, AM fungal communities at different levels in dry and corresponding waterlogged P. australis roots were significant different. In addition, results from this study suggested that a preemption (geometric model) species abundance distributions (SAD), which might due to the distinctive features, e.g. heavy overdominance and difference in the most dominant taxon of each sample, was observed across AM fugal taxa in P. australis roots of the 3 HMs polluted wetlands.

Arbuscular mycorrhizal fungi in two vertical-flow wetlands constructed for heavy metal-contaminated wastewater bioremediation

Over the last three decades, the presence of arbuscular mycorrhizal fungi (AMF) in wetland habitats had been proven, and their roles played in wetland ecosystems and potential functions in wastewater bioremediation technical installations are interesting issues. To increase knowledge on the functions of AMF in the plant-based bioremediation of wastewater, we constructed two vertical-flow wetlands planting with Phragmites australis and investigated AMF distribution in plant roots and their roles played in purification of wastewater polluted by heavy metals (HMs), utilizing the Illumina sequencing technique. A total of 17 operational taxonomic units (OTUs) from 33,031 AMF sequences were obtained, with Glomus being the most dominant. P. australis living in the two vertical-flow constructed wetlands (CWs) harbored diverse AMF comparable with the AM fungal communities in upland habitats. The AMF composition profiles of CW1 (vegetated with non-inoculated plants) and CW2 (vegetated with mycorrhizal plants inoculated with Rhizophagus intraradices) were significantly different. CW1 (15 OTUs) harbored more diverse AMF than CW2 (7 OTUs); however, CW2 harbored much more OTU13 than CW1. In addition, a zipf species abundance distribution (SAD), which might due to the heavy overdominance of OTU13, was observed across AM fugal taxa in P. australis roots of the two CWs. CW1 and CW2 showed high (> 70%) removal capacity of HMs. CW2 exhibited significant higher Cd and Zn removal efficiencies than CW1 (CK) (p = 0.005 and p = 0.008, respectively). It was considered that AMF might play a role in HM removal in CWs.

Removal of hexavalent chromium ions by core-shell sand/Mg-layer double hydroxides (LDHs) in constructed rapid infiltration system

This study aimed to determine the efficiencies and mechanisms of hexavalent chromium (Cr(VI)) removal with modified sand coated by Mg-LDHs in constructed rapid infiltration system (CRIS). Mg-LDHs (MgAl-LDHs, MgFe-LDHs) were prepared by co-precipitation method and in situ coated onto the surface of original sand. Scanning Electron Microscope (SEM) and X-Ray Fluorescence Spectrometer (XRFS) were used to analyze physicochemical properties of sand/Mg-LDHs composites. Results obtained confirmed the successful LDHs-coating modification. During the purification experiments, the average removal rates of Cr(VI) were 47.62% for sand/MgAl-LDHs, 34.15% for sand/MgFe-LDHs and 11.61% for original sand, respectively. The sand/Mg-LDHs had a higher Langmuir adsorption capacity and desorption capability for Cr(VI) compared to original sand. The adsorption kinetic data of different adsorbents were better described by pseudo-second-order model. Intra-particle diffusion model was also used to elucidate the adsorption mechanism. Moreover, extracellular polymeric substances, biomass and enzymatic activity of microbes on the modified and original sand were testified and analyzed to study microbial effect on Cr(VI) removal in test columns. Through a rough economic estimation, the reagent cost of sand/MgAl-LDHs synthesis was only RMB ¥ 0.24/Kg. It could be concluded that MgAl-LDHs modified sand is an efficient and economical substrate of CRIS for Cr(VI) removal.