Bioreactor Performance and Quantitative Analysis of Methanogenic and Bacterial Community Dynamics in Microbial Electrolysis Cells during Large Temperature Fluctuations

The use of microbial electrolysis cells (MECs) for H₂ production generally finds H₂ sink by undesirable methanogenesis at mesophilic temperatures. Previously reported approaches failed to effectively inhibit methanogenesis without the addition of nongreen chemical inhibitors. Here, we demonstrated that the CH₄ production and the number of methanogens in single-chamber MECs could be restricted steadily to a negligible level by continuously operating reactors at the relatively low temperature of 15 °C. This resulted in a H₂ yield and production rate comparable to those obtained at 30 °C with less CH₄ production (CH₄% < 1%). However, this operation at 15 °C should be taken from the initial stage of anodic biofilm formation, when the methanogenic community has not yet been established sufficiently. Maintaining MECs operating at 20 °C was not effective for controlling methanogenesis. The varying degrees of methanogenesis observed in MECs at 30 °C could be completely inhibited at 4 and 9 °C, and the total number of methanogens (mainly hydrogenotrophic methanogens) could be reduced by 68–91% during 32–55 days of operation at the low temperatures. However, methanogens cannot be eliminated completely at these temperatures. After the temperature is returned to 30 °C, the CH₄ production and the number of total methanogens can rapidly rise to the prior levels. Analysis of bacterial communities using 454 pyrosequencing showed that changes in temperature had no a substantial impact on composition of dominant electricity-producing bacteria (Geobacter). The results of our study provide more information toward understanding the temperature-dependent control of methanogenesis in MECs

In Situ Photochemical Activation of Sulfate for Enhanced Degradation of Organic Pollutants in Water

The advanced oxidation process (AOP) based on SO₄^•– radicals has been receiving growing attention in water and wastewater treatment. Producing SO₄^•– radicals by activation of peroxymonosulfate or persulfate faces the challenges of high operational cost and potential secondary pollution. In this study, we report the in situ photochemical activation of sulfate (<i>i</i>-PCAS) to produce SO₄^•– radicals with bismuth phosphate (BPO) serving as photocatalyst. The prepared BPO rod-like material could achieve remarkably enhanced degradation of 2,4-dichlorophenol (2,4-DCP) in the presence of sulfate, indicated by the first-order kinetic constant (<i>k</i> = 0.0402 min^–1) being approximately 2.1 times that in the absence (<i>k</i> = 0.019 min^–1) at pH-neutral condition. This presented a marked contrast with commercial TiO₂ (P25), the performance of which was always inhibited by sulfate. The impact of radical scavenger and electrolyte, combined with electron spin resonance (ESR) measurement, verified the formation of •OH and SO₄^•– radicals during <i>i</i>-PCAS process. According to theoretical calculations, BPO has a sufficiently high valence band potential making it thermodynamically favorable for sulfate oxidation, and weaker interaction with SO₄^•– radicals resulting in higher reactivity toward target organic pollutant. The concept of <i>i</i>-PCAS appears to be attractive for creating new photochemical systems where in situ production of SO₄^•– radicals can be realized by using sulfate originally existing in aqueous environment. This eliminates the need for extrinsic chemicals and pH adjustment, which makes water treatment much easier, more economical, and more sustainable

Data_Sheet_1.pdf

<p>p-Nitrophenol (PNP) is common in the wastewater from many chemical industries. In this study, we investigated the effect of initial concentrations of PNP and glucose and applied voltage on PNP reduction in biocathode BESs and open-circuit biocathode BESs (OC-BES). The PNP degradation efficiency of a biocathode BES with 0.5 V (Bioc-0.5) reached 99.5 ± 0.8%, which was higher than the degradation efficiency of the BES with 0 V (Bioc-0) (62.4 ± 4.5%) and the OC-BES (59.2 ± 12.5%). The PNP degradation rate constant (k_PNP) of Bioc-0.5 was 0.13 ± 0.01 h^-1, which was higher than the k_PNP of Bioc-0 (0.024 ± 0.002 h^-1) and OC-BES (0.013 ± 0.0005 h^-1). PNP degradation depended on the initial concentrations of glucose and PNP. A glucose concentration of 0.5 g L^-1 was best for PNP degradation. The initial PNP increased from 50 to 130 mg L^-1 and the k_PNP decreased from 0.093 ± 0.008 to 0.027 ± 0.001 h^-1. High-throughput sequencing of 16S rRNA gene amplicons indicated differences in microbial community structure between BESs with different voltages and the OC-BES. The predominant populations were affiliated with Streptococcus (42.7%) and Citrobacter (54.1%) in biocathode biofilms of BESs, and Dysgonomonas were the predominant microorganisms in biocathode biofilms of OC-BESs. The predominant populations were different among the cathode biofilms and the suspensions. These results demonstrated that applied voltage and biocathode biofilms play important roles in PNP degradation.</p

MOESM1 of Multiple syntrophic interactions drive biohythane production from waste sludge in microbial electrolysis cells

Additional file 1: Table. S1. Similarity-based OTUs and species richness and diversity estimates of bacteria in different systems. Figure. S1. Current density of MEC fed with raw sludge (RS-MEC) and alkali-pretreated waste sludge (AS-MEC). Figure. S2. Variations of SCOD (A), soluble protein (B) and carbohydrates concentration (C) of raw sludge open-circuit MEC (RS-OCMEC), MEC fed with raw sludge (RS-MEC) or alkali-pretreated sludge (AS-MEC)

Biodegradation of Sulfonamide Antibiotics by Microalgae: Mechanistic Insights into Substituent-Induced Effects

Microalgae are a sustainable environmentally friendly wastewater treatment technology that has attracted much attention for use in the purification of antibiotic-containing wastewater. However, research into the mechanisms involved in microalgal antibiotic degradation is still in the initial stages, especially concerning the relationship between pollutant structure and removal rate. This study comprehensively analyzed the antibiotic biodegradation mechanisms in microalgae from a molecular structure perspective, examining four sulfonamide antibiotics (SAs) with different substituents as representative pollutants. Microalgae exhibited removal efficiencies of 86.15, 74.24, 60.14, and 46.60% for sulfathiazole, sulfamethazine, sulfadiazine, and sulfamethoxazole, respectively. It is noteworthy that cytochrome p450 (CYP450) played a central catalyzing role in their metabolism. Further analysis of molecular dynamics simulations and density functional theory calculations revealed that the geometric differences and electronic effect variations caused by the substituents significantly affected the catalytic activity of CYP450 as well as the overall reactivity of the SAs, resulting in different removal rates. Overall, SAs with high binding energy, low energy gap, and high electrophilicity indices were more readily catalyzed by CYP450 as evidenced by the degradation pathways. These results provide valuable insights at the molecular level into how different substituents affect the degradation rate of SAs in microalgae

Electricity Generation and Pollutant Degradation Using a Novel Biocathode Coupled Photoelectrochemical Cell

The photoelectrochemical cell (PEC) is a promising tool for the degradation of organic pollutants and simultaneous electricity recovery, however, current cathode catalysts suffer from high costs and short service lives. Herein, we present a novel biocathode coupled PEC (Bio-PEC) integrating the advantages of photocatalytic anode and biocathode. Electrochemical anodized TiO₂ nanotube arrays fabricated on Ti substrate were used as Bio-PEC anodes. Field-emission scanning electron microscope images revealed that the well-aligned TiO₂ nanotubes had inner diameters of 60–100 nm and wall-thicknesses of about 5 nm. Linear sweep voltammetry presented the pronounced photocurrent output (325 μA/cm²) under xenon illumination, compared with that under dark conditions. Comparing studies were carried out between the Bio-PEC and PECs with Pt/C cathodes. The results showed that the performance of Pt/C cathodes was closely related with the structure and Pt/C loading amounts of cathodes, while the Bio-PEC achieved similar methyl orange (MO) decoloration rate (0.0120 min^–1) and maximum power density (211.32 mW/m²) to the brush cathode PEC with 50 mg Pt/C loading (Brush-PEC, 50 mg). The fill factors of Bio-PEC and Brush-PEC (50 mg) were 39.87% and 43.06%, respectively. The charge transfer resistance of biocathode was 13.10 Ω, larger than the brush cathode with 50 mg Pt/C (10.68 Ω), but smaller than the brush cathode with 35 mg Pt/C (18.35 Ω), indicating the comparable catalytic activity with Pt/C catalyst. The biocathode was more dependent on the nutrient diffusion, such as nitrogen and inorganic carbon, thus resulting in relatively higher diffusion resistance compared to the brush cathode with 50 mg Pt/C loading that yielded similar MO removal and power output. Considering the performance and cost of PEC system, the biocathode was a promising alternative for the Pt/C catalyst

Occurrence and Profiles of Phthalates in Foodstuffs from China and Their Implications for Human Exposure

Phthalate esters are used in a wide variety of consumer products, and human exposure to this class of compounds is widespread. Nevertheless, studies on dietary exposure of humans to phthalates are limited. In this study, nine phthalate esters were analyzed in eight categories of foodstuffs (<i>n</i> = 78) collected from Harbin and Shanghai, China, in 2011. Dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP), benzyl butyl phthalate (BzBP), and diethylhexyl phthalate (DEHP) were frequently detected in food samples. DEHP was the major compound found in most of the food samples, with concentrations that ranged from below the limit of quantification (LOQ) to 762 ng/g wet weight (wt). The concentrations of phthalates in food samples from China were comparable to concentrations reported for several other countries, but the profiles were different; DMP was found more frequently in Chinese foods than in foods from other countries. The estimated daily dietary intake of phthalates (EDI_diet) was calculated based on the concentrations measured and the daily ingestion rates of food items. The EDI_diet values for DMP, DEP, DIBP, DBP, BzBP, and DEHP (based on mean concentrations) were 0.092, 0.051, 0.505, 0.703, 0.022, and 1.60 μg/kg-bw/d, respectively, for Chinese adults. The EDI_diet values calculated for phthalates were below the reference doses suggested by the United States Environmental Protection Agency (EPA). Comparison of total daily intakes, reported previously based on a biomonitoring study, with the current dietary intake estimates suggests that diet is the main source of DEHP exposure in China. Nevertheless, diet accounted for only <10% of the total exposure to DMP, DEP, DBP, and DIBP, which suggested the existence of other sources of exposure to these phthalates

Biomass-Derived Porous Fe₃C/Tungsten Carbide/Graphitic Carbon Nanocomposite for Efficient Electrocatalysis of Oxygen Reduction

The oxygen-reduction reaction (ORR) draws an extensive attention in many applications, and there is a growing interest to develop effective ORR electrocatalysts. Iron carbide (Fe₃C) is a promising alternative to noble metals (e.g., platinum), but its performances need further improvement, and the real role of the Fe₃C phase remains unclear. In this study, we synthesize Fe₃C/tungsten carbide/graphitic carbon (Fe₃C/WC/GC) nanocomposites, with waste biomass (i.e., pomelo peel) serving as carbon source, using a facile, one-step carbon thermal-reduction method. The nanocomposite is characterized by a porous structure consisting of uniform Fe₃C nanoparticles encased by graphitic carbon (GC) layers with highly dispersed nanosized WC. The Fe₃C provides the active sites for ORR, while the graphitic layers and WC nanoparticles can stibilize the Fe₃C surface, preventing it from dissociation in the electrolyte. The Fe₃C/WC/GC nanocomposite is highly active, selective, and stable toward four-electron ORR in pH-neutral electrolyte, which results in a 67.82% higher power density than that of commercial Pt/C and negligible voltage decay during a long-term phase of a 33 cycle (2200 h) operation of a microbial fuel cell (MFC). The density functional theory (DFT) calculations suggest high activity for splitting the O–O bond of molecular oxygen on the surface of Fe₃C

Forward Osmosis with a Novel Thin-Film Inorganic Membrane

Forward osmosis (FO) represents a new promising membrane technology for liquid separation driven by the osmotic pressure of aqueous solution. Organic polymeric FO membranes are subject to severe internal concentration polarization due to asymmetric membrane structure, and low stability due to inherent chemical composition. To address these limitations, this study focuses on the development of a new kind of thin-film inorganic (TFI) membrane made of microporous silica xerogels immobilized onto a stainless steel mesh (SSM) substrate. The FO performances of the TFI membrane were evaluated upon a lab-scale cell-type FO reactor using deionized water as feed solution and sodium chloride (NaCl) as draw solution. The results demonstrated that the TFI membrane could achieve transmembrane water flux of 60.3 L m^–2 h^–1 driven by 2.0 mol L^–1 NaCl draw solution at ambient temperature. Meanwhile, its specific solute flux, i.e. the solute flux normalized by the water flux (0.19 g L^–1), was 58.7% lower than that obained for a commercial cellulose triacetate (CTA) membrane (0.46 g L^–1). The quasi-symmetry thin-film microporous structure of the silica membrane is responsible for low-level internal concentration polarization, and thus enhanced water flux during FO process. Moreover, the TFI membrne demonstrated a substantially improved stability in terms of mechanical strength, and resistance to thermal and chemical stimulation. This study not only provides a new method for fabricating quasi-symmetry thin-film inorganic silica membrane, but also suggests an effective strategy using this alternative membrane to achieve improved FO performances for scale-up applications

How β‑Cyclodextrin-Functionalized Biochar Enhanced Biodenitrification in Low C/N Conditions via Regulating Substrate Metabolism and Electron Utilization

Biodenitrification plays a vital role in the remediation of nitrogen-contaminated water. However, influent with a low C/N ratio limits the efficiency of denitrification and causes the accumulation/emission of noxious intermediates. In this study, β-cyclodextrin-functionalized biochar (BC@β-CD) was synthesized and applied to promote the denitrification performance of Paracoccus denitrificans when the C/N was only 4, accompanied by increased nitrate reduction efficiency and lower nitrite accumulation and nitrous oxide emission. Transcriptomic and enzymatic activity analyses showed BC@β-CD enhanced glucose degradation by promoting the activities of glycolysis (EMP), the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle. Notably, BC@β-CD drove a great generation of electron donors by stimulating the TCA cycle, causing a greater supply of substrate metabolism to denitrification. Meanwhile, the promotional effect of BC@β-CD on oxidative phosphorylation accelerates electron transfer and ATP synthesis. Moreover, the presence of BC@β-CD increased the intracellular iron level, causing further improved electron utilization in denitrification. BC@β-CD helped to remove metabolites and induced positive feedback on the metabolism of P. denitrificans. Collectively, these effects elevated the glucose utilization for supporting denitrification from 36.37% to 51.19%. This study reveals the great potential of BC@β-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for β-CD in wastewater bioremediation