Biogenic Fenton process - A possible mechanism for the mineralization of organic carbon in fresh waters

Degradation of different wastewater by a biological sponge iron system: microbial growth and influencing factors

The bio-ZVI process has undergone widespread development in wastewater treatment in recent years. However, there has been limited examination of the growth and degradation characteristics of functional microorganisms within the system. In the present research, strains were isolated and identified from the bio-ZVI system constructed by sponge iron (encoded as SFe-M). The consistency of operating conditions in treating different wastewater was explored. Three SFe-acclimated microorganisms exhibiting characteristics of degrading organic pollutants and participating in the nitrogen removal process were isolated. The adaptation time of these microorganisms prolonged as the substrate toxicity increased, while the pollutant degradation was related to their metabolic rate in the logarithmic phase. All these functional bacteria exhibited the ability to treat wastewater in a wide pH range (5-8). However, the improper temperature (such as 10 °C and 40 °C) significantly inhibited their growth, and the optimal working temperature was identified as 30 °C. The iron dosage had a significant impact on these function bacteria, ranging from 1 g L-1 to 150 g L-1. It was inferred that the SFe-acclimated microorganisms are capable of resisting the poison of excessive iron, that is, they all have strong adaptability. The results provide compelling evidence for further understanding of the degradation mechanism involved in the bio-ZVI process.

Advanced oxidation of bio-treated incineration leachate by persulfate combined with heat, UV254 nm, and UV365 nm: Kinetics, mechanism, and toxicity

This study compared and evaluated the ultraviolet/persulfate (UV/PS) at 254 or 365 nm and heat/persulfate (heat/PS) systems for advanced treatment of biologically pre-treated incineration leachate. The UV365 nm/PS system with the highest removal reduced chemical oxygen demand (COD) by 81.7%, total organic carbon by 73.8%, NH3-N by 96.8%, total nitrogen by 47.3%, and color by 98.6% within 24 h, separately. Kinetics tests suggested that a highest concentrations of 4.8 × 10-10 M for [SO4·-]ss and 2.8 × 10-11 M for [·OH]ss were reported in UV365/PS and UV254/PS systems, respectively. Characterization of leachate organic matter species revealed that low molecular weight organic matter < 5 kDa was preferentially degraded in three systems. Ketones are relatively easily degraded by both heat/PS and UV/PS systems, whereas esters were the most recalcitrant. Three-dimensional fluorescence analysis revealed > 99% humic acid and fulvic acid removal in all three systems. In practical applications, it is crucial to consider the pH and toxicity of SR-AOPs in the treatment of bio-treated incineration leachate. Furthermore, the ecotoxicity of MBR effluent treated by the heat/PS system and UV365 nm/PS system increased, which was caused by the strong acidity exhibited in the systems. In addition, we found that PS could interfere with 3.3% of the COD's detection. The findings of this study suggest that secondary effects of PS on water quality at high doses should be investigated in future research.

Enhanced methane oxidation efficiency by digestate biochar in landfill cover soil: Microbial shifts and carbon metabolites insights

The ability of biochar to enhance the oxidation of methane (CH4) in landfill cover soil by promoting the growth and activity of methane-oxidizing bacteria (MOB) has attracted significant attention. However, the optimal characteristics of digestate-derived biochar (DBC) for promoting the MOB community and CH4 removal performance remain unclear. This study examined how the CH4 oxidation capacity and respiratory metabolism of MOB life process are affected by the application of DBC compared with the most commonly used woody-derived biochar (WBC). The addition of both WBC and DBC enhanced CH4 oxidation, with DBC exhibiting a nearly twofold increase in cumulative CH4 oxidation mass (7.14 mg CH4 g-1) compared to WBC. The high ion-exchange capacity of DBC was found to be more favorable for the growth of Type I MOB, which have more efficient metabolic pathways for CH4 oxidation. Type I MOB which are abundant in DBC may prefer monovalent positive ions, while the charge-rich nature of DBC may also have hindered extracellular protein aggregation. The superiority of DBC in terms of CH4 oxidation thus highlights the underlying mechanisms of biochar-MOB interactions, offering potential biochar options for landfill cover soil.

Degradation of gaseous volatile organic compounds (VOCs) by a novel UV-ozone technology

In this study, a UV-assisted ozonation (UV/O₃) process for the degradation of VOCs emissions with a final scrubbing phase was implemented to evaluate the removal efficiency of toluene and to prevent the release of polluting intermediates of the single-step process. Inlet toluene concentration and applied voltage were varied in order to investigate several operating conditions. The results highlighted that at higher inlet concentration the abatement of toluene was lower, while increase in ozone concentration led to an increase of the degradation efficiencies. The additional water scrubbing step enhanced the abatement of UV/O₃ up to 98.5%, due to the solubilisation of ozone and by-products in the process water and, thus, the further oxidation of the contaminants within this phase. A maximum Elimination Capacity (EC_max) of 22.6 g m⁻³ h⁻¹ was achieved with the UV/O₃ + Scrubbing. The combined system boosted higher performance and stability compared to the stand-alone (UV/O₃) process along with a more economical and environmental sustainability.

Degradation of diclofenac via sequential reduction-oxidation by Ru/Fe modified biocathode dual-chamber bioelectrochemical system: Performance, pathways and degradation mechanisms

A sequential reduction-oxidation for DCF degradation was proposed by alternating anaerobic/aerobic conditions at Ru/Fe-biocathode in a dual-chamber bioelectrochemical system (BES). Results showed that Ru/Fe-electrode was successfully fabricated by in-situ electro-deposition, which was rough and uniformly distributed with Ru⁰ and Fe⁰ particles. The morphologic changing and biocompatibility were favorable to increase the surface area and enhance microbial adhesion on Ru/Fe-electrode. At an applied voltage of 0.6 V, the potential and impedance of Ru/Fe-biocathode were -0.80 V and 26 Ω, respectively, lower than that of carbon-felt-biocathode. It led to a higher DCF degradation efficiency of 93.2% under anaerobic conditions, which was superior to that of 88.0% under aerobic conditions. Using NaHCO₃ as carbon source, DCF removal efficiency increased with increasing applied voltage, but decreased with increasing initial DCF concentration. Thirteen intermediates were measured, and two degradation pathways were proposed, among which sequential reduction-oxidation of DCF was the main pathway, dechlorination intermediates were first generated by [H] attacked under anaerobic conditions, further oxidized by microbes and OH attacked under aerobic conditions, achieving 69.6% of mineralization. After 4 d of reaction, microcystis aeruginosa growth inhibition rate decreased from 22.9 to 8.0%, signifying a significant reduction in biotoxicity. Bacteria (e.g. Nitrobacter, Nitrosomonas, Pseudofulvimonas, Aquamicrobium, Sulfurvermis, Lentimicrobiaceae, Anaerobineaceae, Bacteroidales, Hydrogenedensaceae, Dethiosulfatibacter and Azoarcus) for DCF degradation were enriched in Ru/Fe-biocathode. Microbes in Ru/Fe-biocathode had established defense mechanisms to acclimate to the unfriendly environment, while Ru/Fe-biocathode possessed higher nitrification and denitrification activities than carbon-felt-biocathode, and Ru/Fe-biocathode might be of aerobic and anaerobic biodegradation activities. DCF could be mineralized by the synergistic reaction between Ru/Fe and bacteria under sequential anaerobic/aerobic conditions.

Insights into carbon isotope fractionation on trichloroethene degradation in base activated persulfate process: The role of multiple reactive oxygen species

Understanding the role of reactive oxygen species (ROS) is essential to elucidate the mechanism of contaminants degradation in in-situ chemical oxidation (ISCO). In this study, compound specific isotope analysis (CSIA) and radicals quenching methods were integrated to investigate the roles of hydroxyl radical (HO), sulfate radical (SO₄^-), and superoxide radical (O₂^-) on trichloroethene (TCE) degradation during persulfate (PS) activated with base. The carbon isotope fractionation of TCE was found to be dependent of the base:PS ratios, yielding carbon enrichment factors (ε values) from -9.8 ± 0.5‰ to -16.7 ± 1.0‰ at base:PS molar ratios between 0.5:1 and 10:1, which was attributed to multi-pathways degradation of TCE by multiple ROS. The expected ε value (-31.6 ± 1.6‰) for TCE degradation via O₂^- attacking pathway, was more negative than those values via SO₄^- or HO pathways. The relative contributions of HO, SO₄^- and O₂^- for TCE degradation during base activated PS were estimated with observed ε values. HO and O₂^- were the predominant ROS for TCE degradation (with the relative contribution of 55-69% and 22-45%, respectively) in base activated PS. This work highlights the prospect of CSIA application for identifying degradation pathways of contaminants with ROS in environment.

Simultaneous mineralization of 2-anilinophenylacetate and denitrification by Ru/Fe modified biocathode double-chamber microbial fuel cell

A double-chamber microbial fuel cell (MFC) with Ru/Fe-modified-biocathode was constructed for simultaneous mineralization of 2-anilinophenylacetate (APA) and denitrification. The factors on performance of simultaneous APA degradation and denitrification were explored. The contributions of ROS to APA degradation were evaluated by EPR and quenching experiments. The microbial community of Ru/Fe-modified-biocathode was determined by high-throughput sequencing. Results showed that low resistance accelerated APA degradation by Ru/Fe-modified-biocathode, while higher initial APA concentration inhibited microbial activity of the biocathode. The optimum ammonia concentration was 50 mg L^-1, while too high or too low ammonia concentration did not favor APA degradation. The APA degradation efficiency of Ru/Fe-modified-biocathode-MFC was higher than that of other modified-cathode-MFCs. The APA degradation process confirmed to the pseudo-first-order kinetic model, and APA degradation kinetic constant, the maximum removal efficiency of TOC, ammonia and TN were 2.15d^-1, 59.70%, 99.20% and 44.56% respectively, signifying a simultaneous APA mineralization and denitrification performance of Ru/Fe-modified-biocathode-MFC. The coulombic efficiency decreased with APA concentration increase. OH was the primary radical in APA degradation progress. Eight kinds of intermediates were measured, and two APA degradation pathways were proposed, among which APA hydroxylation was the main pathway. The microbial community of Ru/Fe-modified-biocathode was dominated with Nitrosomonas at genus level, and enriched with various APA-degraders, nitrifiers, and denitrifiers such as Pseudomonas, Nitrospira, Nitrobacter, Paracoccus, Thermomonas, Dechloromonas, and Clostridium_Sutra_stricto_1. COG analysis showed the redox reaction of Ru/Fe might affect signal transduction and environment adaptation, while FAPROTAX analysis suggested that Ru/Fe-modified-biocathode exhibited higher nitrification activity than that of carbon-felt-biocathode. The synergistic mechanism of simultaneous APA mineralization and denitrification was mainly redox reaction of Ru/Fe and supplemented by aerobic biodegradation.

Identifying driving factors of humic acid formation during rice straw composting based on Fenton pretreatment with bacterial inoculation

The aims of this study were to identify the driving factors of humic acid (HA) during rice straw composting based on Fenton pretreatment with bacterial inoculation. Rice straw was pretreated by Fenton reactions and then inoculated during composting, which was set up CK (control), FeW (Fenton pretreatment) and FeWI (Fenton pretreatment + functional bacterial agents). Results indicated that Fenton pretreatment and inoculation of functional bacteria increased the concentration of HA components, which was due to that bacterial composition was changed and bacterial diversity was decreased. Moreover, Fenton pretreatment and inoculation of functional bacteria increased the bacterial amounts of shikimic acid metabolism genes and the correlation between HA components and shikimic acid metabolism genes. Therefore, the functional bacteria were core driving factors, and NH₄^--N, pH, cellulose and bacterial diversity as key environmental factors to promote the formation of HA components.