Electrochemical impedance spectroscopy (EIS) reveals the role of microbial fuel cell-ceramic membrane bioreactor (MFC-CMBR): Electricity utilization and membrane fouling.

Ceramic membrane has become a major concern due to creasing cost and competitive efficiency. Microbial fuel cell-ceramic membrane bioreactor (MFC-CMBR) is considered alternative technology for larger-scale industrial application because of its advantages of convenient detecting and control of membrane fouling. However, MFC-CMBR are highly susceptible to membrane fouling and harsh operating requirements in these wastewaters of different compositions. This research critically discusses that electrochemical response in different types of MFC-CMBRs and control of electricity utilization on ceramic membrane fouling. The experimental results indicated that the application of sludge acclimated in coupling system with higher external resistance could ensure that lower costs (electricity utilization and membrane cleaning) provided enough membrane fouling control. The improved performance of MFC-CMBR-1 could be attributed to its enhanced nitrification/denitrification activity and capacity of electrons migration between electrode and sludge mixture. The coupling system alleviated membrane fouling and impedance increasing by improving the characteristics of sludge (increased particle size, decreased adsorption adhesion free energy), EPS (decreased hydrophobicity, molecular weight distribution regulation). And filtration tests showed that roughness and contact angle for the MFC-CMBR tend for better development compared to CMBR, dependent on the changes in the chemical surface groups as a result of electric distribution ratio. In addition, correlation analysis and filtration experiments showed that the extracellular polymer substances (EPS) enhanced the charge transfer resistance (Rct), and the protein substance in EPS was the main fouling substance when external resistance was close to the internal resistance of MFC. In summary, the low internal resistance of ceramic membrane lead to obvious better fouling control and electricity utilization than organic membrane, and the paper provides insight into the MFC-CMBR systems for a wide range of detecting membrane fouling and applications of membrane fouling mitigation.

Mechanistic insight of weak magnetic field trigger transformation of amorphous Fe(III)-(oxy)hydroxide for enhanced ferrate (VI) towards selective removal of natural organic matter.

It was important to regulate the formation of Fe-hydroxyl during ferrate (Fe(VI)) oxidation and hydrolysis which was beneficial for interfacial adsorption of natural organic matter (NOM). Based on the influence of weak magnetic field (WMF) on the physical and chemical characteristics of particles in chemistry. This study investigated the effect of WMF on Fe(VI) oxidation and Fe(III) flocculation performance by regulating iron species during hydrolysis, for NOM removal. Results indicated WMF efficiently accelerate the removal of NOM that the reactions rate constants in magnetization system was twice as much as the control group. With the structure and electrochemical analysis, WMF enhanced Hydrogen-bond and caused much polar hydroxyl groups combined with iron ions, further triggered Fe(III) transformed to amorphous Fe-hydroxide and ferrihydrite with large specific surface area and high surface activity which removed the pollutants by adsorption and co-precipitation, instead of crystalloid Fe2O3 and Fe3O4. In addition, the nucleation aggregation behavior and interaction energy of Fe-(oxy)hydroxide revealed that the lower free energy obtained in magnetization system, could lead to higher nucleation rate, and promoted the aggregation. WMF increased hydrophobicity of Fe-(oxy)hydroxides, further more easily adsorbed with humic acid (HA) and bovine serum albumin (BSA) with lower interaction energies than in control group. The selective removal mechanism of Fe-(oxy)hydroxide hardly to aggregate with pollutants which caused by the difference of electrostatic interaction, was illustrated that electronegativity HA and SA were liable to electrostatically attract with Fe-(oxy)hydroxide and removed while the low electronegativity BSA was difficult to remove which its attraction was weakened.

Biodegradation of Terrigenous Organic Matter in a Stratified Large-Volume Water Column: Implications of the Removal of Terrigenous Organic Matter in the Coastal Ocean.

Large amounts of terrigenous organic matter (TOM) are delivered to the ocean every year. However, removal processes of TOM in the ocean are still poorly constrained. Here, we report results from a 339-day dark incubation experiment with a unique system holding a vertically stratified freshwater-seawater column. The quality and quantity of dissolved organic matter (DOM), RNA-based size-fraction microbial communities, and environmental factors were high-frequency-monitored. Microbial processes impacted TOM composition, including an increased DOM photobleaching rate with incubation time. The mixed layer had changed the bacterial community structure, diversity, and higher oxygen consumption rate. A two-end member modeling analysis suggested that estimated nutrient concentrations and prokaryotic abundance were lower, and total dissolved organic carbon was higher than that of the measured values. These results imply that DOM biodegradation was stimulated during freshwater-seawater mixing. In the bottom layer, fluorescent DOM components increased with the incubation time and were significantly positively related to highly unsaturated, oxygenated, and presumably aromatic compound molecular formulas. These results suggest that surfaced-derived TOM sinking leads to increased DOM transformation and likely results in carbon storage in the bottom water. Overall, these results suggest that microbial transforming TOM plays more important biogeochemical roles in estuaries and coastal oceans than what we know before.

Heterogeneous viral contribution to dissolved organic matter processing in a long-term macrocosm experiment.

Viruses saturate environments throughout the world and play key roles in microbial food webs, yet how viral activities affect dissolved organic matter (DOM) processing in natural environments remains elusive. We established a large-scale long-term macrocosm experiment to explore viral dynamics and their potential impacts on microbial mortality and DOM quantity and quality in starved and stratified ecosystems. High viral infection dynamics and the virus-induced cell lysis (6.23-64.68% d-1) was found in the starved seawater macrocosm, which contributed to a significant transformation of microbial biomass into DOM (0.72-5.32 µg L-1 d-1). In the stratified macrocosm, a substantial amount of viral lysate DOM (2.43-17.87 µg L-1 d-1) was released into the upper riverine water, and viral lysis and DOM release (0.35-5.75 µg L-1 d-1) were reduced in the mixed water layer between riverine water and seawater. Viral lysis was stimulated at the bottom of stratified macrocosm, potentially fueled by the sinking of particulate organic carbon. Significant positive and negative associations between lytic viral production and different fluorescent DOM components were found in the starved and stratified macrocosm, indicating the potentially complex viral impacts on the production and utilization of DOM. Results also revealed the significant viral contribution to pools of both relatively higher molecular weight labile DOM and lower molecular weight recalcitrant DOM. Our study suggests that viruses have heterogeneous impact on the cycling and fate of DOM in aquatic environments.

Nitrifiers drive successions of particulate organic matter and microbial community composition in a starved macrocosm.

Organic carbon produced by nitrifiers plays an important role in maintaining the microbial metabolism in the aphotic ocean layer with carbon and energy scarcity. However, the contribution of nitrifiers to organic carbon processing remains unclear. To explore how nitrification impacts the material cycle in the starved ecosystem, we set up an ultra-large volume, long-term incubation experiment. Seawater collected from the Halifax coastal ocean was pumped into the Aquatron Tower Tank located at Dalhousie University, Canada, and was incubated under dark conditions for 73 days. The results indicated that the relative abundance of nitrifiers increased and nitrification was strengthened in the dark system where energy and organic carbon were scarce. The importance of nitrogenous compounds in particulate materials increased over the course of the incubation. Correlation analysis showed that the relative abundances of nitrifiers and particulate organic compounds containing nitrogen were significantly and positively correlated. Furthermore, network analysis suggested that metabolic processes related to nitrogenous and aromatic compounds are most important to particle associated bacteria. This study suggests that the nitrifiers could produce a series of organic compounds that result in the alteration of organic matter composition by promoting the degradation of recalcitrant aromatic compounds, which has important implications for organic matter processing in the starved dark ecosystem.

Coupled Carbon, Sulfur, and Nitrogen Cycles Mediated by Microorganisms in the Water Column of a Shallow-Water Hydrothermal Ecosystem.

Shallow-water hydrothermal vent ecosystems are distinctly different from deep-sea vents, as other than geothermal, sunlight is one of their primary sources of energy, so their resulting microbial communities differ to some extent. Yet compared with deep-sea systems, less is known about the active microbial community in shallow-water ecosystems. Thus, we studied the community compositions, their metabolic pathways, and possible coupling of microbially driven biogeochemical cycles in a shallow-water hydrothermal vent system off Kueishantao Islet, Taiwan, using high-throughput 16S rRNA sequences and metatranscriptome analyses. Gammaproteobacteria and Epsilonbacteraeota were the major active bacterial groups in the 16S rRNA libraries and the metatranscriptomes, and involved in the carbon, sulfur, and nitrogen metabolic pathways. As core players, Thiomicrospira, Thiomicrorhabdus, Thiothrix, Sulfurovum, and Arcobacter derived energy from the oxidation of reduced sulfur compounds and fixed dissolved inorganic carbon (DIC) by the Calvin-Benson-Bassham (CBB) or reverse tricarboxylic acid cycles. Sox-dependent and reverse sulfate reduction were the main pathways of energy generation, and probably coupled to denitrification by providing electrons to nitrate and nitrite. Sulfur-reducing Nautiliaceae members, accounting for a small proportion in the community, obtained energy by the oxidation of hydrogen, which also supplies metabolic energy for some sulfur-oxidizing bacteria. In addition, ammonia and nitrite oxidation is another type of energy generation in this hydrothermal system, with marker gene sequences belonging to Thaumarchaeota/Crenarchaeota and Nitrospina, respectively, and ammonia and nitrite oxidation was likely coupled to denitrification by providing substrate for nitrate and nitrite reduction to nitric oxide. Moreover, unlike the deep-sea systems, cyanobacteria may also actively participate in major metabolic pathways. This study helps us to better understand biogeochemical processes mediated by microorganisms and possible coupling of the carbon, sulfur, and nitrogen cycles in these unique ecosystems.