Unveiling the Mechanism and Kinetics of Pollutant Attenuation by Free Radicals Triggered from Goethite in Water Distribution Systems.

Investigating the fate of persistent organic pollutants in water distribution systems (WDSs) is of great significance for preventing human health risks. The role of iron corrosion scales in the migration and transformation of organics in such systems remains unclear. Herein, we determined that hydroxyl (•OH), chlorine, and chlorine oxide radicals are generated by Fenton-like reactions due to the coexistence of oxygen vacancy-related Fe(II) on goethite (a major constituent of iron corrosion scales) and hypochlorous acid (HClO, the main reactive chlorine species of residual chlorine at pH ∼ 7.0). •OH contributed mostly to the decomposition of atrazine (ATZ, model compound) more than other radicals, producing a series of relatively low-toxicity small molecular intermediates. A simplified kinetic model consisting of mass transfer of ATZ and HClO, •OH generation, and ATZ oxidation by •OH on the goethite surface was developed to simulate iron corrosion scale-triggered residual chlorine oxidation of organic compounds in a WDS. The model was validated by comparing the fitting results to the experimental data. Moreover, the model was comprehensively applicable to cases in which various inorganic ions (Ca2+, Na+, HCO3-, and SO42-) and natural organic matter were present. With further optimization, the model may be employed to predict the migration and accumulation of persistent organic pollutants under real environmental conditions in the WDSs.

Enhanced Arsenate Immobilization by Kaolinite via Heterogeneous Pathways during Ferrous Iron Oxidation.

Clay minerals are ubiquitous in subsurface environments and have long been recognized as having a limited or negligible impact on the fate of arsenic (As) due to their negatively charged surfaces. Here, we demonstrate the significant role of kaolinite (Kln), a pervasive clay mineral, in enhancing As(V) immobilization during ferrous iron (Fe(II)) oxidation at near-neutral pH. Our results showed that Fe(II) oxidation alone was not capable of immobilizing As(V) at relatively low Fe/As molar ratios (≤2) due to the generation of Fe(III)-As(V) nanocolloids that could still migrate easily as truly dissolved As did. In the presence of kaolinite, dissolved As(V) was significantly immobilized on the kaolinite surfaces via forming Kln-Fe(III)-As(V) ternary precipitates, which had large sizes (at micrometer levels) to reduce the As mobility. The kaolinite-induced heterogeneous pathways for As(V) immobilization involved Fe(II) adsorption, heterogeneous oxidation of adsorbed Fe(II), and finally heterogeneous nucleation/precipitation of Fe(III)-As(V) phases on the edge surfaces of kaolinite. The surface precipitates were mixtures of amorphous basic Fe(III)-arsenate and As-rich hydrous ferric oxide. Our findings provide new insights into the role of clay minerals in As transformation, which is significant for the fate of As in natural and engineered systems.

Increased energy efficiency using pulse-potential electrochemical advanced oxidation processes.

The research investigated the pulse potential effect on Electrochemical Advanced Oxidation Processes (EAOPs) for benzoic acid oxidation. The current efficiency of the electrooxidation is enhanced by changing the pulse frequency and potential on electrodes. The experiments showed that there are opposing phenomena affecting energy efficiency. On the one hand, pulse potential accelerates the mass transfer of benzoic acid in an electric field. On the other hand, pulse potential increases the non-faradic current that uses energy without causing oxidation. Using the Sand equation and the electric double-layer theory, we optimized the pulse frequency and voltage amplitude to achieve the highest energy efficiency for the pulse potential EAOPs. Compared with DC (Direct current) EAOPs, the pulse potential EAOPs save 50% EE/O and have a 41 % CE for the 4_2 V cycle at 50 Hz. Therefore, pulse potential EAOPs can achieve both high pollutant degradation efficiency and low energy consumption at the same time.

Stochastic processes shape microbial community assembly in biofilters: Hidden role of rare taxa.

Stochastic and deterministic processes are the major themes governing microbial community assembly; however, their roles in bioreactors are poorly understood. Herein, the mechanisms underlying microbial assembly and the effect of rare taxa were studied in biofilters. Phylogenetic tree analysis revealed differences in microbial communities at various stages. Null model analysis showed that stochastic processes shaped the community assembly, and deterministic processes emerged only in the inoculated activated sludge after domestication. This finding indicates the dominant role of stochastic factors (biofilm formation, accumulation, and aging). The Sloan neutral model corroborated the advantages of stochastic processes and mainly attributed these advantages to rare taxa. Cooccurrence networks revealed the importance of rare taxa, which accounted for more than 85% of the keystones. Overall, these results provide good foundations for understanding community assembly, especially the role of rare taxa, and offer theoretical support for future community design and reactor regulation.

Roles of the SOM and clay minerals in alleviating the leaching of Pb, Zn, and Cd from the Pb/Zn smelter soil: Multi-surface model and DFT study.

Soil organic matter (SOM) and clay minerals are important sinks for reactive heavy metals (HMs) and exogenous hydrogen ions (H+). Therefore, HMs are likely to be released into soil porewater under acid rainfall conditions due to the competitive adsorption of H+. However, negligible Lead, Zinc, and Cadmium (<6 ‰) in the Pb/Zn smelter soil were leached, and the effects of SOM and clay minerals on HMs leaching were unclear. Herein, the H+ consumption and HMs redistribution on SOM and clay minerals were quantitated by the multi-surface model and density functional theory calculations to reveal the roles of SOM and clay minerals in alleviating HMs' leaching. Clay minerals consumed 43.2 %-52.0 % of the exogenous H+, serving as the dominant sink for the exogenous H+ due to its high content and hindering H+ competitive adsorption on SOM. Protonation of the functional groups constituted >90 % of the total H+ captured by clay minerals. Meanwhile, some H+ also competed with HMs for adsorption sites on clay minerals due to its 0.497-fold to 1.54-fold higher binding energies than HMs, resulting in the release of HMs. On the contrary, SOM served as an accommodator for taking over the released HMs from clay minerals. The HMs complexation on the low-affinity sites (R-L-) of SOM was responsible for the recapture of HMs. In Ca-enriched soil, the released HMs were also recaptured by SOM via ion exchange on the R-L-Ca+ and the high-affinity sites (R-H-Ca+) sites due to the 30.8 %-178 % higher binding energies of HMs on these sites than those of Ca. As a result, >63.4 % of the released HMs from clay minerals were transferred to the SOM. Thus, the synergy of SOM and clay minerals in alleviating the leaching of HMs in Pb/Zn smelter soils cannot be ignored in risk assessment and soil remediation.

Decoding the influence of low temperature on biofilm development: The hidden roles of c-di-GMP.

Biofilms are widely used and play important roles in biological processes. Low temperature of wastewater inhibits the development of biofilms derived from wastewater activated sludge. However, the specific mechanism of temperature on biofilm development is still unclear. This study explored the mechanism of temperature on biofilm development and found a feasible method to enhance biofilm development at low temperature. The amount of biofilm development decreased by approximately 66 % and 55 % at 4 °C and 15 °C, respectively, as compared to 28 °C. The cyclic dimeric guanosine monophosphate (c-di-GMP) concentration also decreased at low temperature and was positively correlated with extracellular polymeric substance (EPS) content, formation, and adhesion strength. Microbial community results showed that low temperature inhibited the normal survival of most microorganisms, but promoted the growth of some psychrophile bacteria like Sporosarcina, Caldilineaceae, Gemmataceae, Anaerolineaceae and Acidobacteriota. Further analysis of functional genes demonstrated that the abundance of functional genes related to the synthesis of c-di-GMP (K18968, K18967 and K13590) decreased at low temperature. Subsequently, the addition of exogenous spermidine increased the level of intracellular c-di-GMP and alleviated the inhibition effect of low temperature on biofilm development. Therefore, the possible mechanism of low temperature on biofilm development could be the inhibition of the microorganism activity and reduction of the communication level between cells, which is the closely related to the EPS content, formation, and adhesion strength. The enhancement of c-di-GMP level through the exogenous addition of spermidine provides an alternative strategy to enhance biofilm development at low temperatures. The results of this study enhance the understanding of the influence of temperature on biofilm development and provide possible strategies for enhancing biofilm development at low temperatures.

Microbial metabolic flexibility guarantees function resilience in response to starvation disturbance.

Starvation disturbance due to nutrient limitation is a common problem in bioreactors. However, an understanding of how microbial systems respond to starvation remains in its infancy. Here the metabolic response mechanism of a biofilm community to starvation was investigated using a well-controlled gaseous toluene treatment biofilter through interruption of its operation. It was found that metabolic characteristics showed significant differences before and after starvation. The dominant carbon source utilization type shifted from amino acids and carboxylic acids to esters and carbohydrates after starvation, which is more conducive to improving energy production. Metagenomic sequencing analysis supported that the changes in the dominant metabolic substrate, enhanced metabolic stability, and flexibility in the mode of energy metabolism could be the main ways to guarantee functional resilience in ecosystems after starvation. The results highlight the microbial metabolic response to starvation, which would be beneficial to the understanding of functional resilience and bioreactor stability.

Lead recovery from waste CRT funnel glass by mechanochemical reaction with reductive Al powder.

The safe disposal of waste cathode ray tubes (CRTs) has always been a serious problem due to the stable microstructure of toxic lead (Pb) located in glass. Thousands of researches have been trying to explore environmental and efficient ways to dispose of waste CRTs. To recycle lead from waste CRT funnel glass effectively, a mechanochemical reduction method has been developed in this research. Aluminum was used as a reductant, and the hydrochloric acid solution was used in the leaching process to separate lead from the solution. After mechanochemical ball milling with aluminum, lead ion in CRT funnel glass was transferred into nano-sized element lead. Lead recovery from CRT funnel glass increased significantly as compared to non-activated leaded glass. Approximately 40 % of lead was leached after mechanical activation without aluminum, while over 96 % of lead in the CRT funnel glass could be recovered after mechanochemical reduction with aluminum. Lead chloride (PbCl2) can be recycled from the leaching solution after cooling crystallization. Nano-sized Pb formation and the structural changes of leaded CRT funnel glass by mechanochemical reduction process contributed to obvious improvement in lead recovery. This research provided a high-efficiency and feasible approach for recovering lead in form of PbCl2 crystal from leaded glass.

Tracing microplastics in rural drinking water in Chongqing, China: Their presence and pathways from source to tap.

Despite the significant attention given to microplastics in urban areas, our understanding of microplastics in rural drinking water systems is still limited. To address this knowledge gap, we investigated the presence and pathways of microplastics in rural drinking water system, including reservoir, water treatment plant (WTP), and tap water of end-users. The results showed that the treatment processes in the WTP, including coagulation-sedimentation, sand-granular active carbon filtration, and ultrafiltration, completely removed microplastics from the influent. However, the microplastic abundance increased during pipe transport from WTP to residents' homes, resulting in the presence of 1.4 particles/L of microplastics in tap water. This microplastic increase was also observed during the transportation from the reservoir to the WTP, suggesting that the plastic pipe network is a key source of microplastics in the drinking water system. The main types of polymers were PET, PP, and PE, and plastic breakdown, atmospheric deposition, and surface runoff were considered as their potential sources. Furthermore, this study estimated that rural residents could ingest up to 1034 microplastics annually by drinking 2 L of tap water every day. Overall, these findings provide essential data and preliminary insights into the fate of microplastics in rural drinking water systems.

Single cobalt atoms anchored on Ti3C2Tx with dual reaction sites for efficient adsorption-degradation of antibiotic resistance genes.

The assimilation of antibiotic resistance genes (ARGs) by pathogenic bacteria poses a severe threat to public health. Here, we reported a dual-reaction-site-modified CoSA/Ti3C2Tx (single cobalt atoms immobilized on Ti3C2Tx MXene) for effectively deactivating extracellular ARGs via peroxymonosulfate (PMS) activation. The enhanced removal of ARGs was attributed to the synergistic effect of adsorption (Ti sites) and degradation (Co-O3 sites). The Ti sites on CoSA/Ti3C2Tx nanosheets bound with PO43- on the phosphate skeletons of ARGs via Ti-O-P coordination interactions, achieving excellent adsorption capacity (10.21 × 1010 copies mg-1) for tetA, and the Co-O3 sites activated PMS into surface-bond hydroxyl radicals (•OHsurface), which can quickly attack the backbones and bases of the adsorbed ARGs, resulting in the efficient in situ degradation of ARGs into inactive small molecular organics and NO3. This dual-reaction-site Fenton-like system exhibited ultrahigh extracellular ARG degradation rate (k > 0.9 min-1) and showed the potential for practical wastewater treatment in a membrane filtration process, which provided insights for extracellular ARG removal via catalysts design.

Ru(III)-Periodate for High Performance and Selective Degradation of Aqueous Organic Pollutants: Important Role of Ru(V) and Ru(IV).

In this study, Ru(III) ions were utilized to activate periodate (PI) for oxidation of trace organic pollutants (TOPs, e.g., carbamazepine (CBZ)). The Ru(III)/PI system can significantly promote the oxidation of CBZ in a wide initial pH range (3.0-11.0) at 1 µM Ru(III), showing much higher performance than transition metal ions (i.e., Fe(II), Co(II), Zn(II), Fe(III), Cu(II), Ni(II), Mn(II), and Ce(III)) and noble metal ion (i.e., Ag(I), Pd(II), Pt(II), and Ir(III)) activated PI systems. Probe experiments, UV-vis spectra, and X-ray absorption near-edge structure (XANES) spectra confirmed high-valent Ru-oxo species (Ru(V)=O) as the dominant oxidant in the process. Because of the dominant role of Ru(V)=O, the Ru(III)/PI process exhibited a remarkable selectivity and strong anti-interference in the oxidation of TOPs in complex water matrices. The Ru(V)=O species can undertake 1-e- and 2-e- transfer reactions via the catalytic cycles of Ru(V)=O → Ru(IV) → Ru(III) and Ru(V)=O → Ru(III), respectively. The utilization efficiency of PI in the Ru(III)/PI process for the oxidation of TOPs can approach 100% under optimal conditions. PI stoichiometrically transformed into IO3- without production of undesired iodine species (e.g., HOI and I2). This study developed an efficient and environmentally benign advanced oxidation process for rapid removal of TOPs and enriched understandings on reactivity of Ru(V)=O and Ru catalytic cycles.

Biochar-Assisted Catalytic Pyrolysis of Oily Sludge to Attain Harmless Disposal and Residue Utilization for Soil Reclamation.

Pyrolysis of oily sludge (OS) is a feasible technology to match the principle of reduction and recycling; however, it is difficult to confirm the feasible environmental destination and meet the corresponding requirements. Therefore, an integrated strategy of biochar-assisted catalytic pyrolysis (BCP) of OS and residue utilization for soil reclamation is investigated in this study. During the catalytic pyrolysis process, biochar as a catalyst intensifies the removal of recalcitrant petroleum hydrocarbons at the expense of liquid product yield. Concurrently, biochar as an adsorbent can inhibit the release of micromolecular gaseous pollutants (e.g. HCN, H2S, and HCl) and stabilize heavy metals. Due to the assistance of biochar, pyrolysis reactions of OS are more likely to occur and require a lower temperature to achieve the same situation. During the soil reclamation process, the obtained residue as a soil amendment can not only provide a carbon source and mineral nutrients but can also improve the abundance and diversity of microbial communities. Thus, it facilitates the plant germination and the secondary removal of petroleum hydrocarbons. The integrated strategy of BCP of OS and residue utilization for soil reclamation is a promising management strategy, which is expected to realize the coordinated and benign disposal of more than one waste.

Evaluation on leachability of heavy metals from tailings: risk factor identification and cumulative influence.

The leachability of heavy metals (HMs) in tailings is significantly affected by multivariate factors associated with environmental conditions. However, the leaching patterns of HMs in molybdenum (Mo) tailings due to environmental change and cumulative influences of multi-leaching factors remain unclear. The leaching behaviors of HMs in Mo tailings were studied through static leaching tests. The key leaching factors were discussed via simulating acid rain leaching scenario in terms of global and local environmental conditions. The potential risk factors were identified, and their cumulative influences on the leachability of HMs were evaluated with boosted regression trees (BRT) and generalized additive model (GAM) analyses. Environmental factors showed interactive effects on the leachability of HMs in tailings. The leachability of HMs in tailings decreased significantly with the interaction of increasing liquid/solid (L/S) ratio and pH. Rebound of leachability was observed with high L/S ratio (> 60) and long-time leaching (> 30 h). L/S ratio and pH were the most sensitive factors to the leachability of HMs with the corresponding contribution of 40.8% and 27.1%, respectively, followed by leaching time and temperature (~ 16%). The total contribution of global climate-associated factors, i.e., L/S ratio, leaching time, and temperature to the leachability of HMs was up to 70%, while leachate pH shared the other 30%. With the increase of persistent heavy rain in summer globally, As and Cd were found to having higher leaching risks than the other HMs in tailings, although an obvious decrease in their leachability was obtained due to the improvement of acid rain pollution in China. The study provides a valuable method for the identification of potential risk factors and their associations with the leaching behaviors of HMs in tailings under the background of obvious improvement on acid rain pollution in China and global climate change.

Inactivation of Microcystis aeruginosa by H2O2 generated from a carbon black polytetrafluoroethylene gas diffusion electrode in electrolysis by low-amperage electric current.

Frequent outbreaks of cyanobacterial blooms have seriously threatened aquatic ecological environments and human health. Electrolysis by low-amperage electric current is effective for algae inactivation; however, it has no selectivity. Hydrogen peroxide (H2O2) is considered to be an efficient and selective suppressor of algae. Therefore, it is necessary to develop an electrode that can generate H2O2 to improve electrolysis technology. In this study, a carbon black polytetrafluoroethylene gas diffusion electrode (C-PTFE GDE) with good stability was prepared by a simple adhesive coating method. Then, the inactivation of Microcystis aeruginosa was conducted with electrolysis by low-amperage electric current using Ti/RuO2 as the anode and C-PTFE GDE as the cathode. When the electrode spacing was 4 cm, the current density was 20 mA cm-2, and the gas flow was 0.4 L min-1, 85% of the algae could be inactivated in 20 min. Comparing the inactivation effect of the electric field and electrogenerated oxidants, it was found that electrolysis more rapidly and strongly inactivated algae when an electric field existed. However, electrogenerated oxidants dominated algae inactivation. The concentration of H2O2 was as high as 58 mg L-1, while the concentration of chlorines was only 0.57 mg L-1, and the generation rate of H2O2 was 65 times that of chlorines. Consequently, electrogenerated oxidants dominated by H2O2 attacked photosystem II of the algae and caused oxidative damage to membrane lipids, affecting the photosynthetic capacity. Eventually, most of the algae were inactivated. The study suggested that C-PTFE GDE was promising for the inactivation of Microcystis aeruginosa in this electrochemical system.

Dissolved organic matter in complex shale gas wastewater analyzed with ESI FT-ICR MS: Typical characteristics and potential of biological treatment.

Knowledge on the composition and characteristics of dissolved organic matter (DOM) in complex shale gas wastewater (SGW) is critical to evaluate environmental risks and to determine effective management strategies. Herein, five SGW samples from four key shale gas blocks in the Sichuan Basin, China, were comprehensively characterized. Specifically, FT-ICR MS was employed to provide insights into the sources, composition, and characteristics of SGW DOM. Organic matter was characterized by low average molecular weight, high saturation degree, and low aromaticity. Notably, the absence of correlations between molecular-level parameters and spectral indexes might be attributed to the high complexity and variability of SGW. The unique distribution depicted in van Krevelen diagrams suggested various sources of DOM in SGW, such as microbially derived organics in shales and biochemical transformations. Moreover, linear alkyl benzene sulfonates, as well as associated biodegraded metabolites and coproducts, were identified in SGW, implying the distinct anthropogenic imprints and abundant microbial activities. Furthermore, high DOC removal rates (31.42-79.23 %) were achieved by biological treatment, fully supporting the inherently labile nature of SGW and the feasibility of biodegradation for SGW management. Therefore, we conclude that DOM in SGW is a complex but mostly labile mixture reflecting both autochthonous and anthropogenic sources.

Recycled biochar adsorption combined with CaCl2 washing to increase rice yields and decrease Cd levels in grains and paddy soils: A field study.

Field-scale trials were conducted to remove cadmium (Cd) from paddy soil by using recycled hydroxyapatite modified biochar (HBC) plus low-level CaCl2 washing. Synergistic reduction efficiencies of total and available Cd in soil (45.6 % and 36.8 %) were achieved by the combined amendments compared with only HBC or CaCl2. The release of Cd from soil particulates was facilitated by CaCl2 washing and the increased soluble Cd in soil water (hardly removed by drainage) could be removed efficiently by recycled HBC adsorption. Significantly decreases in Cd translocation and accumulation in rice plants benefited from the decrease of Cd level and availability in soil and the increase of available silicon (Si). As a result, Cd contents in early/late rice grains decreased by ~85 % and met the Chinese national food standard. SOM, CEC, and soil nutrients after remediation were increased due to 10 %-15 % of HBC residual. Grain yields of the early and late rice increased by 34.1 % and 9.91 %, respectively. The collected HBC (>85 % of the total used HBC) was in-situ regenerated and could be used in the next field trials. The generated wastewater together with drainage from field treatment could be reused as irrigation water after the treatment with a small-scale reclamation ecosystem. The work provides a novelty remediation strategy for Cd-contaminated paddy soil. The noticeable remediation efficiency for Cd reduction in soil and grains, and improved productivity-relevant soil properties have important implications for paddy soil with poor fertility, severe desilicification, and Cd contamination in South China whereas the application of biochar or chemical washing alone did not.

Screening ionic liquids for efficiently extracting perfluoroalkyl chemicals (PFACs) from wastewater.

Liquid-liquid extraction (LLE) using ionic liquids (ILs)-based methods to remove perfluoroalkyl chemicals (PFACs), such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), from wastewater, is an important strategy. However, the lack of physicochemical and LLE data limits the selection of the most suitable ILs for the extraction of PFACs. In this work, 1763 ILs for PFACs extraction from water were systematically screened using COSMOtherm to estimate the infinite dilution activity coefficient (lnγ∞)of PFOA and PFOS in water and ILs. To evaluate the accuracy of COSMOtherm, 8 ILs with various lnγ∞ values were selected, and their extraction efficiency (E) and distribution coefficient (Dexp) were measured experimentally. The results showed that the predicted lnγ∞ decreased as the increase of experimental extraction efficiency of PFOA or PFOS, while the tendency of predicted distribution coefficient (Dpre) was consistent with the experimental (Dexp) results. This work provides an efficient basis for selecting ILs for the extraction of PFACs from wastewater.

Insight into the mechanisms of trichloronitromethane formation by vacuum ultraviolet: QSAR model and FTICR-MS analysis.

Vacuum ultraviolet (VUV) photolysis is recognized as an environmental-friendly treatment process. Nitrate (NO3-) and natural organic matter (NOM) are widely present in water source. We investigated trichloronitromethane (TCNM) formation during chlorination after VUV photolysis, because TCNM is an unregulated highly toxic disinfection byproduct. In this study: (1) we found reactive nitrogen species that is generated under VUV photolysis of NO3- react with organic matter to form nitrogen-containing compounds and subsequently form TCNM during chlorination; (2) we found the mere presence of 0.1 mmol/L NO3- can result in the formation of up to 63.96 µg/L TCNM; (3) we found the changes in pH (6.0-8.0), chloride (1-4 mmol/L), and bicarbonate (1-4 mmol/L) cannot effectively diminish TCNM formation; and, (4) we established the quantitative structure-activity relationship (QSAR) model, which indicated a linear relationship between TCNM formation and the Hammett constant (σ) of model compounds; and, (5) we characterized TCNM precursors in water matrix after VUV photolysis and found 1161 much more nitrogen-containing compounds with higher aromaticity were generated. Overall, this study indicates more attention should be paid to reducing the formation risk of TCNM when applying VUV photolysis process at scale.

Electrochemical Advanced Oxidation of Perfluorooctanoic Acid: Mechanisms and Process Optimization with Kinetic Modeling.

Electrochemical advanced oxidation processes (EAOPs) are promising technologies for perfluorooctanoic acid (PFOA) degradation, but the mechanisms and preferred pathways for PFOA mineralization remain unknown. Herein, we proposed a plausible primary pathway for electrochemical PFOA mineralization using density functional theory (DFT) simulations and experiments. We neglected the unique effects of the anode surface and treated anodes as electron sinks only to acquire a general pathway. This was the essential first step toward fully revealing the primary pathway applicable to all anodes. Systematically exploring the roles of valence band holes (h+), hydroxyl radicals (HO•), and H2O, we found that h+, whose contribution was previously underestimated, dominated PFOA mineralization. Notably, the primary pathway did not generate short-chain perfluoroalkyl carboxylic acids (PFCAs), which were previously thought to be the main degradation intermediates, but generated other polyfluorinated alkyl substances (PFASs) that were rapidly degraded upon formation. Also, we developed a simplified kinetic model, which considered all of the main processes (mass transfer with electromigration included, surface adsorption/desorption, and oxidation on the anode surface), to simulate PFOA degradation in EAOPs. Our model can predict PFOA concentration profiles under various current densities, initial PFOA concentrations, and flow velocities.

Reduction of cadmium bioavailability in paddy soil and its accumulation in brown rice by FeCl3 washing combined with biochar: A field study.

Cadmium (Cd) removal from paddy soil to reduce Cd accumulation in brown rice is essential for agroecology, food safety, and human health. In this study, we demonstrate that ferric chloride (FeCl3) washing combined with biochar treatment efficiently remediates Cd-contaminated paddy soil in field trials. Our results showed that 30.9 % of total Cd and 41.6 % of bioavailable Cd were removed by the addition of 0.03 M FeCl3 at a liquid/soil ratio of 1.5:1. The subsequent addition of 1 % biochar further reduced bioavailable Cd by 36.5 and 41.5 %, compared with FeCl3 washing or biochar treatment alone. The principal component regression analysis showed that the Cd content in brown rice was primarily affected by the bioavailable Cd in soil. The combined remediation contributed to the decreased Cd contents in brown rice by 45.5-62.5 %, as well as a 2.7-11.8 % increase in rice yield. The Cd contents in brown rice decreased to 0.12 and 0.04 mg kg-1 in two cultivars of rice (Zhuliangyou189 and Zhuliangyou929), lower than the national food safety standard limit value of China (0.2 mg kg-1). Meanwhile, the combined remediation promoted the restoration of soil pH and organic matter as well as the improvement of available nutrients. This finding suggests that the combination of FeCl3 washing and biochar is an effective remediation strategy to minimize Cd bioavailability in paddy soil, and improves soil quality, thus contributing to food safety.