PDA-Fe3O4 decorated carbon felt anode enhancing electrochemical performance of microbial fuel cells: Effect of electrode materials on electroactive biofilm.

Anode modification is an effective strategy for enhancing the electrochemical performance of microbial fuel cell (MFC). However, the impacts of the modified materials on anode biofilm development during MFC operation have been less studied. We prepared a novel PDA-Fe3O4-CF composite anode by coating original carbon felt anode (CF) with polydopamine (PDA) and Fe3O4 nanoparticles. The composite anode material was characterized by excellent hydrophilicity and electrical conductivity, and the anodic biofilm exhibited fast start-up, higher biomass, and more uniform biofilm layer after MFC operation. The MFC reactor assembled with the composite anode achieved a maximum power density of 608 mW m-2 and an output voltage of 586 mV, which were 316.4% and 72.4% higher than the MFC with the original CF anode, respectively. Microbial community analysis indicated that the modified anode biofilm had a higher relative abundance of exoelectrogen species in comparison to the unmodified anode. The PICRUSt data revealed that the anodic materials may affect the bioelectrochemical performance of the biofilm by influencing the expression levels of key enzyme genes involved in biofilm extracellular polymer (EPS) secretion and extracellular electron transfer (EET). The growth of the anodic biofilm would exert positive or negative influences on the efficiency of electricity production and electron transfer of the MFCs at different operating stages. This work expands the knowledge of the role that anodic materials play in the development and electrochemical performance of anodic biofilm in MFCs.

Recovery of ammonia nitrogen from landfill leachate using a biopolar membrane equipped electrodialysis system.

In this paper, a laboratory-scale electrodialysis reactor with five compartment cells separated by a bipolar membrane and ion exchange membrane was assembled to remove ammonia nitrogen from landfill leachate as a pretreatment process. The effects of humic acid, magnesium ions (Mg2+) and calcium ions (Ca2+) existing in leachate on the removal efficiency of ammonium (NH4 +) were investigated by using simulated wastewater. The results indicate that humic acid has little impact on ammonium in the presence of an electric field. High concentrations of Mg2+ and Ca2+ in solution have a substantial impact on the removal efficiency of ammonium, but the average migration rate of the three ions is NH4 + > Mg2+ > Ca2+ under the same current intensity, and NH4 + plays a major role in electromigration for mixture electrodialysis. Therefore, ammonia nitrogen can be separated from leachate and accumulated effectively. Meanwhile, the bipolar membrane near the cathode produces alkali that is released into the base cell to promote ammonia nitrogen transformation from accumulated ammonium, which creates in-site alkaline condition for ammonia nitrogen recovery by a further stripping process. When the actual leachate collected from a local municipal sanitary landfill was employed, the reactor reached 86.17% of ammonia nitrogen removal after 3.0 h reaction. Analysis of membrane scale suggests the inhibitory effect of Mg2+ on Ca2+ migration during the initial working period of the reaction can potentially slow down the membrane scaling of the cation exchange membrane. This study provides a promising technology for the removal and recovery of ammonia nitrogen from landfill leachate.

Effects of phosphorous fertilizers on growth, Cu phytoextraction and tolerance of Leersia hexandra swartz under different Cu stress levels.

In this study, the effects of Ca(H2PO4)2, KH2PO4 and (NH4)2HPO4 on growth, Cu phytoextraction and tolerance of Leersia hexandra swartz (L. hexandra) under different Cu stress levels were investigated. The results showed that KH2PO4 could most significantly increase the plant height of L. hexandra (p < 0.05), while (NH4)2HPO4 had the most significant promoting effect on its biomass (p < 0.05) by enhancing photosynthesis (chlorophyll content) (p < 0.01). The application of Ca(H2PO4)2 could most significantly improve the Cu contents in roots, stems and leaves of L. hexandra (p < 0.05). In addition, (NH4)2HPO4 could enhance the tolerance of L. hexandra to Cu by obviously reducing the content of MDA and increasing the contents of SP and MTs (p < 0.05), while Ca(H2PO4)2 could evidently improve the activity of antioxidant enzymes (SOD, POD, CAT and APX) to reduce the damage of Cu to L. hexandra (p < 0.05). Although KH2PO4 could increase the contents of SP and MTs, the L. hexandra in KH2PO4 treatment groups had the highest MDA contents, which was unfavorable to the resistance to Cu stress. These suggested that the application in combination of Ca(H2PO4)2 and (NH4)2HPO4 may be more advantageous for Cu phytoextraction by L. hexandra.