China
Africa
Explore chapters and articles related to this topic
Microbial Distributions, Activities, and Movement in the Terrestrial Subsurface: Experimental and Theoretical Studies
Published in R.J. Wagenet, P. Baveye, B.A. Stewart, Interacting Processes in Soil Science, 2020
A number of recent studies have utilized nitrogen isotope fraction, which has long been used to investigate microbially-mediated changes in inorganic nitrogen in surface environments, to study denitrification in contaminated and uncontaminated groundwater (e.g., Bengtsson and Annadotter, 1989; Wilson et al., 1990; Bottcher et al., 1990; Mariotti et al., 1988). Stable N isotope fraction measurements can be combined with other geochemical assays to yield useful insight about the significance of denitrification with respect to degradation of organic carbon within the aquifer. Mariotti (1986) lists three geochemical methods for identification of denitrification in groundwater: (1) identification of a redox gradient which generates the appropriate sequence of oxidation-reduction reactions; (2) determination of dinitrogen gas in oversaturation; and (3) the use of 15N natural isotope abundance tracing. In the Smith et al. (1991b) study, a combination approach using field mass balance, stable istope analysis, and laboratory incubations led to the determinations that denitrification was much more significant than dissimilatory reduction of nitrate to ammonium and was the major terminal electron-accepting process in the upgradient portion of the 4 km-long plume of sewage-contaminated groundwater in Cape Cod, MA.
Electrochemically Assisted Artificial Wetlands, Generating Electricity From Wastewater Treatment
Published in María del Carmen Durán-Domínguez-de-Bazúa, Amado Enrique Navarro-Frómeta, Josep M. Bayona, Artificial or Constructed Wetlands, 2018
María Guadalupe Salinas-Juárez
The differences between the MFC-LH and the EACW are the carbon source and that in the wetlands, the main objective is the wastewater treatment with the added value of the electricity generation in a simultaneous process. However, the EACW require a drastic improvement in terms of power generated and coulombic efficiency implicated for that power generation (Xu et al. 2015). A challenge in scaling the system up is to allocate the electrodes in an arrangement that optimize the potential redox gradient in the wetland, and the organic matter degradation feed the bacteria at the anode but does not interfere with the reduction reaction at cathode. An additional challenge regarding the design of the EAAW involves the optimal use of oxygen as final electron acceptor at the cathode and, besides that, ensuring that oxygen doesn’t interfere with the anodic reactions of oxidation.
Nanogels for Brain Targeting
Published in Raj K. Keservani, Anil K. Sharma, Rajesh K. Kesharwani, Nanocarriers for Brain Targeting, 2019
Nagarjun Rangaraj, Sunitha Sampathi
Redox cleavable crosslinks are governed by the redox gradient between the oxidative extracellular medium and reductive intracellular environments (Saito et al., 2003). The cancer tumors are found to have high levels of Glutathione (GSH) as compared to the normal cells (Gupte et al., 2009, Russo et al., 1986) The disulfide bonds are efficiently cleaved under intra-cellular reductive conditions enabling the rapid release of drug and hence site-specific delivery of the antitumor drug (Qiao et al., 2011, Whittell et al., 2011). Dithiothreitol (DTT) also showed the cleavage of the disulfide bonds leading to the formation of water-soluble polymers which were assumed to promote kidney elimination (Zhang et al., 2015).
Energy harvesting using exoelectrogenic Shewanella oneidensis bacteria
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Young H. Park, Edward Park, Geoffrey Smith
These two experiments showed that the reactor is stratified due to biological redox potential difference between Reference and various locations along the column. Ntarlagiannis et al. (2007) used isogenic mutants that produce non-conductive nanowires to investigate the role of fully functional nanowires in developing electrical signals. In their work, they showed that in the absence of electron conductive pathways (nanowires) within the columns, redox gradient alone cannot induce electric potential. The electric potentials measured in our system also cannot be explained by a galvanic cell model whereby the electric potential signal is the result of electrode reactions and the electrons are transferred through the instrumentation wiring since our experimental setup does not have the external circuit. The electric potential difference is indeed associated with the electron flow in the conductive nanowire.
Performance of vertical up-flow-constructed wetlands integrating with microbial fuel cell (VFCW-MFC) treating ammonium in domestic wastewater
Published in Environmental Technology, 2023
Nguyen Xuan Phuong Vo, Dat Dang Nguyen Hoang, Thuy Doan Huu, Tuan Doan Van, Hien Lam Pham Thanh, Que Vo Nguyen Xuan
This study demonstrates the potential to enhance -N removal and electricity generation via anaerobic processes in the up-flow CW-MFC system treating domestic wastewater with relatively high COD:N ratios (5:1–6:1). The balance of microbial composition and activities involved in N removal and electricity generation strongly depended on influent pH, hydraulic retention time, and mass loading rate. The presence of plants in up-flow CW-MFCs could improve treatment performance. Plant root development within the cathode layer filled with a mixture of clay soil and sand was an effective modification to maintain an appropriate redox gradient for effective power recovery. Preliminary results suggested that the constructed model of up-flow CW-MFCs is worth further investigation into the proliferation of active microbial groups involved in N removal and power generation. The long-term response of CW-MFC units should be investigated after pertaining to the steady-state. The polarization analysis should be conducted to understand the behaviour of MFC units integrated into up-flow CWs. The lifetime of the electrode would have a great influence on the real-life applicability of the CW-MFC technology.
Recent advances in improving the remediation performance of microbial electrochemical systems for contaminated soil and sediments
Published in Critical Reviews in Environmental Science and Technology, 2023
Ruixiang Li, Jinning Wang, Tian Li, Qixing Zhou
A typical SMES consists of an anode and a cathode that is connected via an external circuit (Wang & Ren, 2013). The electrodes function as non-exhaustible electron acceptors, or even donors, thus alleviating the lack of electron donors and acceptors in the soil (Gustave et al., 2021). The microorganisms can be used to convert toxic large-molecule pollutants into nontoxic small-molecule substances via integrating microbial and electrochemical processes (Logan & Rabaey, 2012). In some cases, to overcome the thermodynamic barrier and improve the remediation performance of complex pollutants, a constant additional power supply is required to drive the electron flow to the cathode, which is known as SMECs (Zhang et al., 2021). Generally, SMECs require relatively low energy input (0.2–0.8 V) compared to traditional water electrolysis (1.8–3.5 V) and can be supplied by a small solar panel or MFCs (Lu & Ren, 2016). In SMESs, the general mechanism of soil/sediment remediation is to use the redox gradient between the electrodes and the pollutants, which is mainly attributed to the activities of different microorganisms (Fig. 1) (Kumar et al., 2017). Although biodegradation plays a dominant role in pollutant removal, there are still some pollutants that are removed by other mechanisms (Wu et al., 2020). In this section, the bioremediation mechanisms on different electrodes are highlighted. Then, the other remediation mechanisms are briefly discussed.