Adding carbon sources to the substrates enhances Cr and Ni removal and mitigates greenhouse gas emissions in constructed wetlands.

Constructed wetlands for wastewater treatment pose challenges related to long-term operational efficiency and greenhouse gas emissions on a global scale. This study investigated the impact of adding peat, humic acid, and biochar into the substrates of constructed wetlands and focused on Cr, and Ni removal, greenhouse gas emissions, and microbial communities in constructed wetlands. Biochar addition treatment achieved the highest removal efficiencies for total Cr (99.96%), Cr (VI) (100%), and total Ni (91.04%). Humic acid and biochar addition both significantly increased the heavy metal content in wetland plant Leersia hexandra and substrates of constructed wetlands. Further analysis of microbial community proportions by high-throughput sequencing revealed that biochar and humic acid treatments enhanced Cr and Ni removal efficiency by increasing the abundance of Bacteroidetes, Geobacter and Ascomycota. Humic acid addition treatment reduced CO2 emissions by decreasing the abundance of Bacteroidetes and increasing that of Basidiomycota. Peat treatment decreased CH4 emissions by reducing the abundance of the Bacteroidetes. Biochar treatment increased the abundance of the Firmicutes, Bacteroidetes, Proteobacteria as well as Basidiomycota, resulting in reduced N2O emissions. Biochar and humic acid treatments efficiently removed heavy metals from wastewater and mitigated greenhouse gas emissions in constructed wetlands by modifying the microbial communities.

Biosorption effects of copper ions on Candida utilis under negative pressure cavitation.

Under the optimal condition of copper ions adsorption on yeast,we found some different effects among static adsorption, shaking adsorption and negative pressure cavitation adsorption, and the methods of yeast with different pretreatments also affect adsorption of copper ions. At the same time, the change of intercellular pH before and after adsorption of copper with BCECF was studied. The copper distribution was located by using PhenGreen (dipotassium salt and diacetate), and the surface of yeast was observed by an atomic force microscope. The results showed that negative pressure cavitation can improve bioadsorption capacity of copper ions on yeast. However, the yeasts' pretreatment has a higher effect on bioadsorption. It indicates that heavy metal bioadsorption on yeast has much relation with its cellular molecule basis. With the adsorping, the intercellular pH of yeast increased gradually and changed from acidity to alkalescence. These results may suggest that negative pressure cavitation can compel heavy metals to transfer from the cell surface into inside cell and make the surface of yeast coarse.