Molecular-level transformations of dissolved black carbon in UV-based advanced oxidation processes.

Dissolved black carbon (DBC) released from biochar, is an essential group in the dissolved organic matter (DOM) pool and is widely distributed in aquatic environments. In various advanced oxidation processes (AOPs), DBC exhibits enhanced free radical scavenging compared to typical DOM, attributed to its smaller molecular weight and more compacted aromatic structure; however, the molecular-level transformations of DBC in different AOPs, such as UV/H2O2, UV/PDS, and UV/Chlorine, remain unclear. This study employed a DBC derived from wheat biochar for experimentation. Characterization involved ultraviolet-visible (UV-Vis) spectroscopy and fluorescence excitation-emission-matrix (EEM) spectroscopy, revealing the transformation of DBC through diminished SUVA254 values and reduced intensity of three-dimensional fluorescence peaks. Further insights into the transformation were gained through Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). After each UV-AOP treatment, a conspicuous augmentation in the oxygen content of DBC was observed. The detailed oxygenation processes were elucidated through mass difference analysis, based on 23 types of typical reactions. Results indicated that oxygenation reactions were most frequently detected in all three UV-AOP treatments. Specifically, the hydroxylation (+O) predominated in UV/H2O2, while the di-hydroxylation (+2O) prevailed in UV/PDS. UV/Chlorine treatments commonly exhibited tri-hydroxylation (+3O), with the identification of 1194 Cl-BPs of unknown structures. This study contributes to a comprehensive understanding of the molecular transformations of DBC induced by various free radicals in different UV-AOP processes, leading to a better understanding of the different fates of DBC in UV-AOP processes. In addition, the identification of DBC as a precursor of by-products will also contribute to the understanding of how to inhibit the generation of by-products.

Importance of Chain Length in Propagation Reaction on •OH Formation during Ozonation of Wastewater Effluent.

During the ozonation of wastewater, hydroxyl radicals (•OH) induced by the reactions of ozone (O3) with effluent organic matters (EfOMs) play an essential role in degrading ozone-refractory micropollutants. The •OH yield provides the absolute •OH formation during ozonation. However, the conventional "tert-Butanol (t-BuOH) assay" cannot accurately determine the •OH yield since the propagation reactions are inhibited, and there have been few studies on •OH production induced by EfOM fractions during ozonation. Alternatively, a "competitive method", which added trace amounts of the •OH probe compound to compete with the water matrix and took initiation reactions and propagation reactions into account, was used to determine the actual •OH yields (Φ) compared with that obtained by the "t-BuOH assay" (φ). The Φ were significantly higher than φ, indicating that the propagation reactions played important roles in •OH formation. The chain propagation reactions facilitation of EfOMs and fractions can be expressed by the chain length (n). The study found significant differences in Φ for EfOMs and fractions, precisely because they have different n. The actual •OH yield can be calculated by n and φ as Φ = φ (1 + n)/(nφ + 1), which can be used to accurately predict the removal of micropollutants during ozonation of wastewater.

[Comparison of Carbon Emissions in Different Treatment and Disposal Process Routes of Municipal Sludge].

With the introduction of the goal of carbon neutrality, the efficient resource recycling of municipal sludge has been given increasing attention. In order to scientifically evaluate the routes of sludge treatment and disposal from the perspective of carbon emissions, four typical routes were chosen for accounting the carbon emissions per ton for dry sludge (DS). Based on the Intergovernmental Panel on Climate Change (IPCC), combined with Chinese sludge characteristics, carbon emissions were divided into three types:the direct emissions, indirect emissions, and carbon offsets, and accounting boundaries were initiated at sludge thickening and ended at products or energies. The results showed that the total carbon emission of R4 (gravity thickening+thermal hydrolysis+anaerobic digestion+plate and frame filter pressing+transportation+land utilization) was 99.41 kg·t-1(calculated as CO2/DS, same below), which was the route with lowest carbon emissions. If the fugitive emission of CH4 from anaerobic digestion was avoided, the route (R4) could achieve carbon neutrality at this stage. Process units with larger carbon emissions should focus on optimization to reduce the carbon emissions, such as through thermal drying (1049.24 kg·t-1), deep dewatering (960.99 kg·t-1), sanitary landfill (786.24 kg·t-1), incineration (635.52 kg·t-1), aerobic composting (614.17 kg·t-1), and thermal hydrolysis (544.67 kg·t-1). The main carbon offsets were the incineration power generation (-1440.29 kg·t-1), CH4 collection of anaerobic digestion (-435.06 kg·t-1), land utilization (-415.83 kg·t-1), and building materials utilization (-169.75 kg·t-1). In summary, "anaerobic digestion and land utilization" has a great potential for carbon offsets, which should be advocated for as the widely used treatment.

Carbon-defect-driven persulfate activation for highly efficient degradation of extracellular DNA contaminant: Radical oxidation and electron transfer pathways.

Extracellular DNA (eDNA), as a dynamic repository for antibiotic-resistant genes (ARGs), is a rising threat to public health. This work used a ball-milling method to enhance defect structures of activated carbon, and carbon defects exhibited an excellent capacity in persulfate (PS) activation for model eDNA and real ARGs degradation. The eDNA removal by defect-rich carbon with PS was 2.3-fold higher than that by unmilled activated carbon. The quenching experiment, electrochemical analysis and thermodynamic calculation showed that carbon defects could not only enhance the generation of SO4•- and •OH, but formed an electron transfer bridge between eDNA and PS, leading to the non-radical oxidation of eDNA. According to molecular calculations, the nitrogenous bases of DNA were the easiest sites to be oxidized by electron transfer pathway. This research offers a new way using defective carbon materials as PS activator for eDNA pollutants, and an insight into the non-radical mechanism of eDNA degradation.

Removal and recovery of uranium (VI) from aqueous solutions by residual sludge and its biochars.

The removal and recovery of uranium (VI) from water solutions are critical for energy and environmental security. In this study, hydrochar at 100, 150, and 190 °C (HC100, HC150, and HC190) and pyrochar at 250 °C (BC250) were prepared from residual sludge (RS). The uranium (VI) adsorption behavior, recovery, and heavy metal risk of RS and its biochars were assessed. The sorption distribution coefficient of RS was higher than those of its biochars within the tested concentration range. The maximum adsorption capacity of uranium (VI) by HC190 was 121.26 mg/g at acidic pH (pH 4.5), which was higher than those of other tested biochars, previously reported unmodified biochars, and activated carbon. The zeta potential, FTIR, and XPS results implied that the adsorption of uranium (VI) by RS and its biochars was regulated by electrostatic attraction and the complexation with oxygen- and phosphorus-containing functional groups. Besides, partial reduction of uranium (VI) into uranium (IV) happened during the process of adsorption. More than 86% of the adsorbed uranium (VI) was recovered by 0.01 M hydrochloric acid and 100% by 0.01 M sodium carbonate. The leaching amount of heavy metals was greatly reduced after the sludge was converted to biochar, indicating that hydrothermal carbonization and pyrolysis can promote the stabilization of heavy metals. This work demonstrates that RS and its biochars can be implemented as low-cost, environment-friendly, and high-efficient materials for the purification of uranium (VI)-containing solutions by means of adsorption and desorption.

Effect of allelochemicals sustained-release microspheres on the ingestion, incorporation, and digestion abilities of Daphnia magna Straus.

Allelochemicals sustained-release microspheres (ACs-SMs) exhibited great inhibition effect on algae, however, few studies have focused on ACs-SMs toxicity on invertebrate. In this study, the effects of single high-concentration ACs (15 mg/L, SH-ACs), repeated low-concentration ACs (3 × 5 mg/L, RL-ACs) and ACs-SMs containing 15 mg/L ACs exposure on the ingestion, incorporation, and digestion of Daphnia magna Straus (DS) were investigated by stable isotope 15N labeling method. Meanwhile, the diversity and abundance of microflora in DS guts were determined by 16S rRNA genes and cloning methods. The results showed that SH-ACs exposure caused 50% and 33.3% death rates for newborn and adult DS, while RL-ACs exposure caused 10% death rate for newborn DS and no obvious effect on the activity of adult DS. And ACs-SMs exposure did not diminish the motility of both newborn and adult DS, indicating the lower acute toxicity of ACs-SMs. Furthermore, SH-ACs inhibited the ingestion (-6.45%), incorporation (-47.1%) and digestion (-53.8%) abilities of DS and reduced the microbial abundance (-27.7%) in DS guts. Compared with SH-ACs, RL-ACs showed relatively low impact on the ingestion (-3.23%), incorporation (-5.89%) and digestion (-23.9%) abilities of DS. Interestingly, ACs-SMs enhanced the ingestion (+9.68%), incorporation (+52.9%) and digestion (+51.3%) abilities of DS and increased the microbial abundance (+10.7%) in DS guts. Overall ACs and ACs-SMs reduced the diversity of microflora in DS guts. In conclusion, ACs-SMs can release ACs sustainably and prolong the sustained release time, which not only effectively reduce the toxicity of ACs, but also had positive effects on DS.

Visible-light-driven photocatalytic degradation of ofloxacin by BiOBr nanocomposite modified with oxygen vacancies and N-doped CQDs: Enhanced photodegradation performance and mechanism.

The rapid recombination of photogenerated carriers and weak light absorption capacity are two major challenges for bismuth-based photocatalysts. Here, N-CQDs/BiO1-xBr micro-flower photocatalysts with the visible-light activity were fabricated through the ethylene glycol solvothermal method for the first time, and oxygen vacancies (OVs) and N-doped carbon quantum dots (N-CQDs) were simultaneously introduced on the surface of BiOBr. OVs were introduced to form defective BiOBr (BiO1-xBr). N-CQDs and BiO1-xBr formed a strong binding effect. Then, the composition, morphology, crystal structure and photoelectric property of photocatalysts were studied, and the mechanism and pathway of ofloxacin (OFL) photodegradation were studied. N-CQDs/BiO1-xBr-4 was a micro-flower composed of nanosheets with a thickness of about 60 nm, this structure produced multiple light reflections. Photoelectrochemical analysis confirmed that the synergistic effect of OVs and N-CQDs significantly promoted the electron-hole separation (3 times vs BiOBr) and enhanced the light absorption range (Eg = 2.96 eV vs 3.24 eV). Meanwhile, the removal rate of OFL by N-CQDs/BiO1-xBr-4 was 6 times higher than that by BiOBr (Kobs of N-CQDs/BiO1-xBr-4 was 32 times higher than that of BiOBr). Electron spin resonances analysis and radical quenching experiments showed that ·O2- and h+ played dominant roles in the OFL photodegradation system, and their contribution rates were 89.84% and 70.31%, respectively. There were main degradation pathways for OFL, including oxidation, dealkylation, hydroxylation and decarboxylation. This study explored the synergistic and complementary effects between OVs and N-CQDs, and provided a promising strategy for the photodegradation of toxic antibiotics by visible-light-driven photocatalysts.

Effects of different types of nitrogen sources in water on the formation potentials of nitrogenous disinfection by-products in chloramine disinfection process based on isotope labeling.

Nitrogenous disinfection by-products (N-DBPs) raise increasing concerns because of their high genotoxicity, cytotoxicity, and carcinogenicity compared to carbonaceous disinfection by-products (C-DBPs). Nitrogen-containing disinfectants, dissolved organic nitrogen (DON), and inorganic nitrogen may all promote the formation of N-DBPs. Therefore, it is urgent to explore the dominant nitrogen source of N-DBPs under the coexistence of multiple nitrogen sources. In this study, the effects of amino acids, nitrate, ammonia, and chloramine as different types of nitrogen sources on the formation of five N-DBPs were investigated systematically, including chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), dibromoacetonitrile (DBAN) and dichloroacetamide (DCAcAm). L-Aspartic acid (L-Asp) as the organic nitrogen source showed a high potential on the formation of N-DBPs by forming acetonitrile intermediates. Ammonia as the inorganic nitrogen source consumed oxidants and changed the existing form of chloramine, thus inhibiting the formation of N-DBPs. Instead of providing nitrogen to N-DBPs, nitrate as a salt promoted the volatilization of N-DBPs, thereby reducing the detected N-DBPs. Furthermore, an isotope labeling method was applied to clearly trace the nitrogen sources of N-DBPs via GC-MS with electron ionization. 15N-chloramine, 15N-amino acid, 15N-nitrate and 15N-ammonia were selected as the corresponding isotopic nitrogen sources. The results indicated that chloramine was the major nitrogen contributor to five N-DBPs during the chloramination of L-Asp under the coexistence of multiple nitrogen sources, ranging from 61 % to 79 %. The influence of environmental factors (reaction time, pH, and bromide) on the formation of N-DBPs during chloramination was also investigated. There was competition between brominated N-DBPs and chlorinated N-DBPs in chloramination. With the increase of reaction time or bromine, the formation potentials of chlorinated N-DBPs gradually decreased, while brominated N-DBPs gradually increased. Moreover, higher pH inhibited the generation of N-DBPs.

Enhancement effects of dissolved organic matter leached from sewage sludge on microbial reduction and immobilization of Cr(VI) by Geobacter sulfurreducens.

Sewage sludge has a high concentration of dissolved organic matter (DOM) which contains compounds that can serve as electron donors or shuttles for metal reduction by dissimilatory metal reducing bacteria (DMRB). In this study, Cr(VI) removal by G. sulfurreducens, a common DMRB present in anaerobic soils, was examined in the presence or absence of sludge DOM. Two different types of sludge DOM were tested; composted sludge DOM (C-DOM) and anaerobically digested sludge DOM (A-DOM). Both sludge DOMs enhanced Cr(VI) reduction by G. sulfurreducens, but C-DOM was more effective likely because it had higher concentrations of humic substances that served as electron shuttles. Transcriptomic studies indicated that G. sulfurreducens utilizes several different mechanisms to tolerate chromium including extracellular Cr(VI) reduction and immobilization by outer membrane c-type cytochromes and electrically conductive pili, intracellular Cr(VI) reduction by triheme cytochromes and NAD(P)H FMN reductase proteins, and chromium efflux by several P-type ATPase and RND transporter proteins. Microscopy experiments also showed that Cr(III) crystals formed on the surface of the cells, indicating that extracellular Cr(VI) reduction and adsorption was involved in the chromium removal process. These results help provide insight into the potential use of sewage sludge as an additive to enhance the bioremediation of chromium contaminated soils.

Effects and mechanisms of aged polystyrene microplastics on the photodegradation of sulfamethoxazole in water under simulated sunlight.

Pharmaceutical and microplastics (MPs) have been frequently detected in aquatic environment. In this study, the effects of polystyrene MPs (PS MPs) with different aging degrees on the photolysis of sulfamethoxazole (SMX) in simulated sunlit water were investigated. The results showed that the presence of PS MPs inhibited the photodegradation of SMX, and the photodegradation rate (kobs) of SMX was negatively correlated with the aging degree of PS MPs (R2 = 0.998). The aged PS MPs would cause light-screening effect, thereby reducing the photodegradation of SMX in sunlit water. Further, the free radical quenching experiment showed that the mechanism for inhibiting the photolysis of SMX was the reduction of the triplet excited state SMX (3SMX*). According to sample characterization, aging PS MPs formed more unsaturated chromophores and produced organic intermediates that enhanced photon absorption. Additionally, aged PS MPs also decreased the types and yields of degradation products of SMX via product analysis. This study provides an insight into the environmental behaviors of SMX and the photochemical roles of aged MPs in sunlit surface waters.

Reaction kinetics of dissolved black carbon with hydroxyl radical, sulfate radical and reactive chlorine radicals.

As an important component of dissolved organic matter (DOM), dissolved black carbon (DBC) which is characterized of abundant aromatic and oxygen-containing functional groups, is widely distributed in aquatic environments. Its presence may hinder the oxidation of organic micro-pollutants during advanced oxidation processes (AOPs) via free radicals scavenging effect. However, the second-order reaction rate constants of DBC with different free radicals including hydroxyl radical (OH•), sulfate radical (SO4•-), reactive chlorine radicals (RCR) are unknown and the relationship between the chemical composition of DBC and the second-order reaction rate constants during different AOPs (UV/H2O2, UV/PDS, UV/Chlorine) is also unclear. In this study, a plant-derived DBC was extracted from wheat biochar and fractionated according to molecular weight (i.e., <10 k, <3 k, and < 1 k Da). The second order rate constants of DBC reaction with different free radicals were determined by competitive kinetic method. Besides, the chemical composition of DBC was revealed by ultraviolet-visible (UV-Vis) spectroscopy, fluorescence excitation-emission-matrix (EEM) spectroscopy Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with statistical analysis. The results showed that the second-order rate constants decreased as the molecular weight increased. For the <1 k Da DBC, the kDBC-OH•, kDBC-SO4•--, kDBC-RCR were (1.83 ± 0.06) × 104, (7.60 ± 0.21) × 103, and (1.71 ± 0.13) × 104 L·mgC-1·s-1, which were 1.98, 2.19, 1.43 times of that for the <10 k Da fraction and 1.38, 1.36, 1.24 times of that for the <3 k Da fraction in UV/H2O2, UV/PDS and UV/Chlorine processes. In addition, the results of chemical composition analysis showed that DBC mainly contained humic substances and was rich in O-containing functional groups such as CO. The second order reaction rate constants of DBC with different free radicals decreased with increasing the molecular weight of DBC due to the more aggregated structure of the small molecules that the inner carbon of DBC was not easily exposed to free radicals.

A new and systematic review on the efficiency and mechanism of different techniques for OPFRs removal from aqueous environments.

Organic phosphorus flame retardants (OPFRs), as a new type of emerging contaminant, have drawn great attention over the last few years, due to their wide distribution in aquatic environments and potential toxicities to humans and living beings. Various treatment methods have been reported to remove OPFRs from water or wastewater. In this review, the performances and mechanisms for OPFRs removal with different methods including adsorption, oxidation, reduction and biological techniques are overviewed and discussed. Each technique possesses its advantage and limitation, which is compared in the paper. The degradation pathways of typical OPFRs pollutants, such as Cl-OPFRs, alkyl OPFRs and aryl OPFRs, are also reviewed and compared. The degradation of those OPFRs depends heavily upon their structures and properties. Furthermore, the implications and future perspectives in such area are discussed. The review may help identify the research priorities for OPFRs remediation and understand the fate of OPFRs during the treatment processes.

Fe0-loaded superfine powdered activated carbon prepared by ball milling for synergistic adsorption and persulfate activation to remove aqueous carbamazepine.

The massive use of personal medicines makes them widely enter the aquatic environments and cause pollution, drawing a great deal of attention over the last few years. In this study, a novel nano Fe0-loaded superfine powdered activated carbon (Fe0@SPAC) was prepared via a simple ball milling method. Fe0@SPAC showed a rapid and effective removal for aqueous carbamazepine (CBZ) via the process of synergistic adsorption and persulfate (PDS) activation. The removal efficiency of CBZ (30 mg L-1) could be up to 96% by Fe0@SPAC (0.05 g L-1) with the presence of PDS (2 mM), and the maximum pseudo-first-order rate constant was 0.12 min-1. The performance of Fe0@SPAC was superior to other reported iron-bearing activator materials, and its dosage was much lower. Fe0@SPAC was also effective to remove other typical drug pollutants and had excellent reusability in five cycles. The loaded Fe0 could activate PDS to generate OH and SO4-, which played the major role for CBZ removal. It is interesting that carbon base of Fe0@SPAC could also activate PDS via surface defects, making the minor contribution to CBZ degradation. Besides, Fe0@SPAC showed rapid and high adsorption for CBZ due to the superfine particle diameter, partially contributing to CBZ removal. Finally, the possible break sites of CBZ and its degradation pathway were proposed based on DFT theoretical calculation and product identification. Fe0@SPAC would be a promising material for the removal of drug pollutants, and this study may help understand the mechanisms of synergistic adsorption and persulfate activation by carbon composite material.

Enhanced photocatalytic performance of visible-light-driven CuOx/TiO2-x for degradation of gaseous formaldehyde: Roles of oxygen vacancies and nano copper oxides.

Photocatalysis is an effective method for the removal of formaldehyde (HCHO), and high-efficiency visible-light-driven photocatalysts were urgently required. Herein, oxygen vacancies (OVs) and nano copper oxides (CuOx) synergistically modified TiO2 (CuOx/TiO2-x) photocatalysts were synthesized by one-step hydrothermal followed by impregnation method. The photocatalytic decomposition of HCHO reached 100% at initial concentration of 180 ppm under relative humidity (RH) = 60% by 0.1g CuOx/TiO2-x in 150 min visible light irradiation. Characterization results explored the complementary effect of OVs and CuOx systematically. The OVs increased the separation efficiency of photogenerated charge carriers and act as adsorption/active sites in HCHO photocatalytic oxidation. The moisture and O2 were adsorbed and actived by OVs to generate reactive oxygen species (ROS). After doped CuOx on the surface of TiO2-x, the photoexcited electrons in Cu2O could transfer to the conduction band (CB) of TiO2-x and the photoexcited electrons of TiO2-x could be captured by Cu nanoparticles. Therefore, more ROS were generated due to the synergistic effect of OVs and CuOx. The In-situ Fourier transform infrared (in-situ FTIR) measurements show the hydroxyl radical (•OH) was the dominant radical in HCHO photocatalytic oxidation, while •O2- could also upgrade the photodegradation efficiency of HCHO. Furthermore, the stability tests showed the degradation efficiency of HCHO still reached 90% after five recycles, indicating that CuOx/TiO2-x nanocomposites displayed a stable and high photoactivity in volatile organic compounds (VOCs) decomposition.

Inhibitory effects of antioxidant moieties in humic substances on phototransformation of chlortetracycline mediated by the algae extracellular organic matter.

In algae rich waters, sunlight-driven transformation of antibiotics could be accelerated via sensitization by algae extracellular organic matter (EOM), and this photosensitization process will be affected by coexisting humic substances. In this study, we explored the effect and mechanism of humic substances on photodegradation of chlortetracycline (CTC) mediated by EOM. We found that humic substances exhibited a marked inhibitory effect on the EOM-mediated photodegradation of CTC. Given that humic substances exhibited little effects on the EOM-mediated formation of triplet state species, the quenching effect of humic substances on reactive species was excluded. The inhibitory effect of humic substances was mainly attributed to the back reduction of CTC oxidation intermediates by the antioxidant moieties in humic substances. The ozone oxidation treatment for humic substances was applied to destroy antioxidant moieties. After ozonation, the inhibitory effects of humic substances were greatly decreased, confirming the dominant role of antioxidant moieties in humic substances, which inhibited CTC photodegradation mediated by EOM via reducing oxidation intermediates of CTC. This back reduction was further verified to be exergonic via reactive Gibbs free energy, indicating the back reduction by humic substances of CTC oxidation intermediates could occur spontaneously. The present study will be helpful for predicting the fate and risk of CTC in algae rich water environments, and is of great significance for the study of phototransformation of other antibiotics.

A critical review on bismuth oxyhalide based photocatalysis for pharmaceutical active compounds degradation: Modifications, reactive sites, and challenges.

Pharmaceutical active compounds (PhACs), as a kind of widely used pharmaceutical drugs, has attracted much attention. The bismuth oxyhalides (BiOX)-based photocatalysis can remove PhACs efficiently due to its unique layered structure, optical and electronic properties. Nevertheless, the rapid recombination of photogenerated electron-hole pairs, and the inherent instability of structure have limited its practical application. In order to solve these problems, recent modification studies tend to focus on facet control, elemental doping, bismuth-rich strategies, defect engineering and heterojunction. Therefore, the objective of this review is to summarize the recent developments in multiply modified strategies for PhACs degradation. The synthesis methods, photocatalytic properties and the enhancement mechanism are elaborated. Besides, based on theoretical calculation, the reactive sites of typical PhACs attacked by different reactive oxygen species were also proposed. Subsequently, challenges and opportunities in applications are also featured which include factors, viz., dissolution of halogen ions, instability under visible light, applications of real water/wastewater, intermediates and byproducts toxicity analysis of BiOX-based photocatalysis. Finally, the perspectives of BiOX-based photocatalysis for PhACs photodegradation in actual water applications are highlighted.

A review: Application of allelochemicals in water ecological restoration--algal inhibition.

Problems caused by harmful algal blooms have attracted worldwide attention due to their severe harm to aquatic ecosystems, prompting researchers to study applicable measures to inhibit the growth of algae. Allelochemicals, as secondary metabolites secreted by plants, have excellent biocompatibility, biodegradability, obvious algal inhibiting effect and little ecological harm, and have promising application prospect in the field of water ecological restoration. This review summarized the research progress of allelochemicals, including (i) definition, development, and classification, (ii) influencing factors and mechanism of algal inhibition, (iii) the preparation methods of algal inhibitors based on allelochemicals. The future research directions of allelochemicals sustained-released microspheres (SRMs) were also prospected. In the future, it is urgent to explore more efficient allelochemicals, to study the regulation mechanism of allelochemicals in natural water bodies, and to improve the preparation method of allelopathic algal suppressant. This paper proposed a feasible direction for the development of allelochemicals SRMs which exhibited certain guiding significance for their application in water ecological restoration.

Rapid electrochemical reduction of a typical chlorinated organophosphorus flame retardant on copper foam: degradation kinetics and mechanisms.

With the widespread use, chlorinated organophosphorus flame retardants (Cl-OPFRs) as a new emerging contaminant have been widely detected in water environments over the last few years. In this study, the degradation of a typical Cl-OPFR, TCEP (tris (2-chloroethyl) phosphate), by electrochemical reduction was investigated. It was found that copper (Cu) foam as the cathode showed more rapid and effective degradation for TCEP, compared to other cathodes. When TCEP was at the low concentrations (0.1 and 1 mg L-1), its degradation by Cu foam could reach above 95% within 20 min, and the maximum rate constant was 0.127 min-1. TCEP reduction was little influenced by the co-existing humic substance and anions, except Cl-. Compared with the reported oxidation methods, electrochemical reduction showed fast and stable degradation for TCEP. For other types of Cl-OPFRs, electrochemical reduction displayed a fast and effective removal for tris (1,3-dichloro-2-propyl) phosphate but lower removal for tris (2-cholroisopropyl) phosphate who possessed methyl units in the branched chains, influencing its reducibility. Based on the product analysis and Fukui function calculation, the bonds of TCEP molecule were found to be gradually broken, and the three oxygen-ethyl-chlorine arms were cleaved one by one. The products including C6H13Cl2O4P (MW = 249.99278 Da), C4H9Cl2O4P (MW = 221.96105 Da) and C4H10ClO4P (MW = 188.0002 Da) were detected at 60 min reaction, and those intermediates showed much lower toxicities than TCEP according to the previous report. The findings may provide a promising treatment for Cl-OPFRs removal from aqueous environments and help understand their reductive fate.

Solvothermal synthesis of multiwall carbon nanotubes/BiOI photocatalysts for the efficient degradation of antipyrine under visible light.

Antipyrine (ANT), as a widely used relieve headache, fever anti-inflammatory pharmaceutical in medical treatment, is difficult to be removed completely in water. The application of photocatalytic removal of ANT is restricted to UV light irradiation (<5% of solar energy), and the degradation pathways of ANT require more theoretical evidence. In this study, a series of three dimensions (3D) hierarchical structure multiwall carbon nanotubes/bismuth oxyiodide (MWCNTs/BiOI) photocatalysts were systematically designed and firstly applied to remove ANT through visible light (>43% of solar energy) induced photodegradation. Consequently, the as-prepared MWCNTs/BiOI photocatalysts presented superior photocatalytic activities on ANT degradation with respect to that of BiOI under 60 min visible light irradiation (100% vs 82.2%). Especially, the enhanced photocatalytic mechanism on ANT was analyzed by morphology, optical and photo-electrochemical properties. Results revealed that the designed 3D micro-mesoporous structure could promote the diffusion of photogenerated electron-hole pairs, and the utilization of photoelectrons could be efficiently improved by MWCNTs (1.5 times). Furthermore, based on radicals scavenging experiments, the photogenerated hole (h+) and superoxide radical (O2-) were demonstrated as the dominant active species in ANT photocatalytic oxidation process. The photodegradation pathways of ANT were proposed with the calculation of frontier electron densities (FEDs) and the analysis of LC-MS/MS. This study presents a feasible approach for the high efficiency removal of trace pharmaceuticals under visible light photocatalytic process.

Biochar prepared from maize straw and molasses fermentation wastewater: application for soil improvement.

A novel method was applied to improve biochar properties and its soil application by introducing molasses fermentation wastewater into a maize straw pyrolysis process. In this study, maize straw biochar (MSB) was prepared from maize straw mixed with different amounts (1, 2 and 3 mL g-1 straw, v/w) of molasses fermentation wastewater which contained high organics and nitrogen contents. Characterization results indicated that the yield, carbon content, N/C, and cation exchange capacity (CEC) of MSB increased gradually with the increasing dosage of fermentation wastewater. In addition, the prepared MSB was added into sandy soil with four mixing proportions (1%, 3%, 5% and 10%, w/w) to investigate its effects on plant growth, soil properties and soil catalase activity (CAT) by pot experiments. The results indicated that MSB amendments increased soil pH, soil total organic carbon (TOC) and nutrients contents (TN, TP). It was suggested that 5% biochar proportion in soil derived from maize straw with 2 mL g-1 fermentation wastewater addition was more suitable for ryegrass growth, soil fertility and CAT activity improvement. This study provides a promising way to realize the resource utilization of fermentation wastewater and agricultural wastes at the same time.