Weichun Yang

Cr(III) adsorption by sugarcane pulp residue and biochar

A batch experiment was conducted to investigate the adsorption of trivalent chromium (Cr(III)) from aqueous solutions by sugarcane pulp residue (SPR) and biochar. The results show that Cr(III) adsorption by SPR and biochar is highly pH-dependent and Cr(III) adsorption amount increases with the increase of pH. The adsorption kinetics of Cr(III) fits well with the pseudo-second-order model. The maximum Cr(III) adsorption capacities of 15.85 mg/g and 3.43 mg/g for biochar and SPR were calculated by Langmuir model. This indicates that biochar has a larger ability for Cr(III) adsorption than SPR. The free energy change value (ΔG) reveals a spontaneous sorption process of Cr(III) onto SPR and non-spontaneous sorption process onto biochar. The entropy change (ΔS) and enthalpy change (ΔH) are found to be 66.27 J/(mol·K) and 17.13 kJ/mol for SPR and 91.59 J/(mol·K) and 30.875 kJ/mol for biochar which further reflect an affinity of Cr(III) onto SPR and biochar. It is suggested that biochar has potential to be an efficient adsorbent in the removal of Cr(III) from industrial wastewater.

Fungus hyphae-supported alumina: An efficient and reclaimable adsorbent for fluoride removal from water

A reclaimable adsorbent of fungus hyphae-supported alumina (FHSA) bio-nanocomposites was developed, characterized and applied in fluoride removal from water. This adsorbent can be fast assembled and disassemble reversibly, promising efficient reclamation and high accessible surface area for fluoride adsorption. Adsorption experiments demonstrate that the FHSA performed well over a considerable wide pH range of 3-10 with high fluoride removal efficiencies (>66.3%). The adsorption capacity was 105.60mgg-1 for FHSA, much higher than that for the alumina nanoparticles (50.55mgg-1) and pure fungus hyphae (22.47mgg-1). The adsorption capacity calculated by the pure content of alumina in the FHSA is 340.27mgg-1 of alumina. Kinetics data reveal that the fluoride adsorption process on the FHSA was fast, nearly 90% fluoride adsorption can be achieved within 40min. The fluoride adsorption on the FHSA is mainly due to the surface complexes formation of fluoride with AlOH and the attraction between protonated NH2 and fluoride through hydrogen bonding. Findings demonstrate that the FHSA has potential applicability in fluoride removal due to its strong fluoride adsorbility and the easy reclamation by its fast reversible assembly and disassembly feature.

Combination of microbial oxidation and biogenic schwertmannite immobilization: A potential remediation for highly arsenic-contaminated soil

Here, a novel strategy that combines microbial oxidation by As(III)-oxidizing bacterium and biogenic schwertmannite (Bio-SCH) immobilization was first proposed and applied for treating the highly arsenic-contaminated soil. Brevibacterium sp. YZ-1 isolated from a highly As-contaminated soil was used to oxidize As(III) in contaminated soils. Under optimum culture condition for microbial oxidation, 92.3% of water-soluble As(III) and 84.4% of NaHCO3-extractable As(III) in soils were removed. Bio-SCH synthesized through the oxidation of ferrous sulfate by Acidithiobacillus ferrooxidans immobilize As(V) in the contaminated soil effectively. Consequently, the combination of microbial oxidation and Bio-SCH immobilization performed better in treating the highly As-contaminated soil with immobilization efficiencies of 99.3% and 82.6% for water-soluble and NaHCO3-extractable total As, respectively. Thus, the combination can be considered as a green remediation strategy for developing a novel and valuable solution for As-contaminated soils.

A Comparative Evaluation of Different Sediment Quality Guidelines for Metal and Metalloid Pollution in the Xiangjiang River, Hunan, China

To evaluate intensively the quality of the sediments contaminated by heavy metals and metalloids in the Xiangjiang River, 52 surface sediment samples were collected at 13 sites and different combinations of empirical and theoretical sediment quality indexes, the consensus-based sediment quality guidelines, sediment toxicity degree, and equilibrium partitioning method were applied. The average contents of Cd, Pb, Cu, Zn, Hg, Cr, and As in the sampled surface sediments were significantly higher than the background values of trace elements in soils of Hunan Province, China. Moreover, speciation fraction analyses revealed that Cd, Hg, and Pb in the sediments were dominated by the more bioavailable organic or exchangeable fractions, whereas the major species of As and Cr were the less bioavailable residual fractions after strong acid treatment. In addition, all indexes showed that these metals posed a median-high degree of toxic risk to benthic organisms in sediments from nearly all of the sampling sites along the Xiangjiang River. Cd, followed by Cu and Pb, erected the most severe ecological risk. Pearson correlation and linear regression analyses between the mean PEC quotients, sediment toxicity degree, interstitial water criteria toxic units, and sediment pollution index showed that these indexes were relatively consistent to assess the quality of sediments contaminated by heavy metals and metalloids in the Xiangjiang River. Our results will facilitate the proposal of proper sediment quality guidelines for the Xiangjiang River.

Simultaneous immobilization of cadmium and lead in contaminated soils by hybrid bio-nanocomposites of fungal hyphae and nano-hydroxyapatites

Self-aggregation of bulk nano-hydroxyapatites (n-HAPs) undermines their immobilization efficiencies of heavy metals in the contaminated soils. Here, the low-cost, easily obtained, and environment-friendly filamentous fungi have been introduced for the bio-matrices of the hybrid bio-nanocomposites to potentially solve such problem of n-HAPs. According to SEM, TEM, XRD, and FT-IR analyses, n-HAPs were successfully coated onto the fungal hyphae and their self-aggregation was improved. The immobilization efficiencies of diethylene-triamine-pentaacetic acid (DTPA)-extractable Cd and Pb in the contaminated soils by the bio-nanocomposites were individually one to four times of that by n-HAPs or the fungal hyphae. Moreover, the Aspergillus niger-based bio-nanocomposite (ANHP) was superior to the Penicillium Chrysogenum F1-based bio-nanocomposite (PCHP) in immobilization of Cd and Pb in the contaminated soils. In addition, the results of XRD showed that one of the potential mechanisms of metal immobilization by the hybrid bio-nanocomposites was dissolution of n-HAPs followed by precipitation of new metal phosphate minerals. Our results suggest that the hybrid bio-nanocomposite (ANHP) can be recognized as a promising soil amendment candidate for effective remediation on the soils simultaneously contaminated by Cd and Pb.

Combination of bioleaching by gross bacterial biosurfactants and flocculation: A potential remediation for the heavy metal contaminated soils

Combining bioleaching by the gross biosurfactants of Burkholderia sp. Z-90 and flocculation by poly aluminium chloride (PAC) was proposed to develop a potential environment-friendly and cost-effective technique to remediate the severely contaminated soils by heavy metals. The factors affecting soil bioleaching by the gross biosurfactants of Burkholderia sp. Z-90 were optimized. The results showed the optimal removing efficiencies of Zn, Pb, Mn, Cd, Cu, and As by the Burkholderia sp. Z-90 leachate were 44.0, 32.5, 52.2, 37.7, 24.1 and 31.6%, respectively at soil liquid ratio of 1:20 (w/v) for 5 d, which were more efficient than that by 0.1% of rhamnolipid. The amounts of the bioleached heavy metals by the Burkholderia sp. Z-90 leachate were higher than that by other biosurfactants in the previous studies, although the removal efficiencies of the metals by the leachate were relatively lower. It was suggested that more heavy metals caused more competitive to chelate with function groups of the gross biosurfactants and the metal removal efficiencies by biosurfactants in natural soils were lower than in the artificially contaminated soils. Moreover, the Burkholderia sp. Z-90 leachate facilitated the metals to be transformed to the easily migrating speciation fractions. Additional, the results showed that PAC was efficient in the following flocculation to remove heavy metals in the waste bio-leachates. Our study will provide support for developing a bioleaching technique model to remediate the soils extremely contaminated by heavy metals.

Discerning three novel chromate reduce and transport genes of highly efficient Pannonibacter phragmitetus BB: From genome to gene and protein

Here, Pannonibacter phragmitetus BB was investigated at genomic, genetic and protein levels to explore molecular mechanisms of chromium biotransformation, respectively. The results of Miseq sequencing uncovered that a high-qualified bacterial genome draft was achieved with 5.07 Mb in length. Three novel genes involved in chromate reduce and transport, named nitR, chrA1 and chrA2, were identified by alignment, annotation and phylogenetic tree analyses, which encode a chromate reductase (NitR) and two chromate transporters (ChrA1 and ChrA2). Reverse transcription real-time polymerase chain reaction (RT-qPCR) analyses showed that the relative quantitative transcription of the three genes as the maximum reduction rate of Cr(VI) were significantly up-regulated with the increasing initial Cr(VI) concentrations. However, at the maximum cell growth points nitR was in a low transcription level, while the transcription of chrA1 and chrA2 were hold at a relatively high level and decreased with the increasing initial Cr(VI) concentrations. The ex-situ chromate reducing activity of NitR was revealed a Vmax of 34.46 µmol/min/mg enzyme and Km of 14.55 µmol/L, suggesting feasibility of the reaction with Cr(VI) as substrate. The multiple alignment demonstrates that NitR is potentially a nicotinamide adenine dinucleotide phosphate (NADPH) dependent flavin mononucleotide (FMN) reductase of Class I chromate reductases. Our results will prompt a large-scaled bioremediation on the contaminated soils and water by Pannonibacter phragmitetus BB, taking advantage of uncovering its molecular mechanisms of chromium biotransformation.