Sludge treatment by integrated ultrasound-Fenton process: Characterization of sludge organic matter and its impact on PAHs removal

Effective photocatalytic degradation of amphotericin B and naproxen from aqueous solutions using carbon quantum dots combined in MIL-88B(Fe) under visible light

A photocatalytic adsorbent composed of carbon dots (CD) embedded in a metal-organic framework (MOF) of MIL-88 B(Fe) was prepared by solvothermal technique. The synthesized CD@MIL-88 B(Fe) was characterized by different X-ray-based microscopic and spectroscopic methods, as well as electrochemical impedance spectroscopy, UV-Vis, FT-IR, DRS, TGA, and photoluminescence (PL) analysis. The prepared adsorbent showed a remarkable photocatalytic activity for eliminating amphotericin B (AmB) and naproxen (Nap) from aqueous solutions under visible light, reaching up to 92% and 90% removal, respectively, with an RSD value of around 5%. The parameters affecting the degradation process of pharmaceuticals were investigated. The optimal conditions for the degradation process were determined, including pH values (3 and 4 for AmB and Nap), photocatalyst concentration (0.2 g L-1), and H2O2 concentration (40-50 mM). Reactive oxidative species were also identified (·OH, ·O2) by examination of different scavengers. The adsorption isotherm and kinetic studies reveal that the synthesized photocatalyst exhibits dual functionality as an effective adsorbent (with maximum adsorption capacities of 42.5 and 121.5 mg g-1 for AmB and Nap) and a photocatalytic agent for removal purposes.

Nanobiohybrids: Synthesis strategies and environmental applications from micropollutants sensing and removal to global warming mitigation

Micropollutants contamination and global warming are critical environmental issues that require urgent attention due to natural and anthropogenic activities posing serious threats to human health and ecosystems. However, traditional technologies (such as adsorption, precipitation, biodegradation, and membrane separation et al.) are facing challenges of low utilization efficiency of oxidants, poor selectivity, and complex in-situ monitoring operations. To address these technical bottlenecks, nanobiohybrids, synthesized by interfacing the nanomaterials and biosystems, have recently emerged as eco-friendly technologies. In this review, we summarize the synthesis approaches of nanobiohybrids and their utilization as emerging environmental technologies for addressing environmental problems. Studies demonstrate that enzymes, cells, and living plants can be integrated with a wide range of nanomaterials including reticular frameworks, semiconductor nanoparticles and single-walled carbon nanotubes. Moreover, nanobiohybrids demonstrate excellent performance for micropollutant removal, carbon dioxide conversion, and sensing of toxic metal ions and organic micropollutants. Therefore, nanobiohybrids are expected to be environmental friendly, efficient, and cost-effective techniques for addressing environmental micropollutants issues and mitigating global warming, benefiting both humans and ecosystems alike.

Formation of organic chloride in the treatment of textile dyeing sludge by Fenton system

In the oxidation treatment of textile dyeing sludge, the quantitative and transformation laws of organic chlorine are not clear enough. Thus, this study mainly evaluated the treatment of textile dyeing sludge by Fenton and Fenton-like system from the aspects of the influence of Cl^-, the removal of polycyclic aromatic hydrocarbons (PAHs) and organic carbon, and the removal and formation mechanism of organic chlorine. The results showed that the organic halogen in sludge was mainly hydrophobic organic chlorine, and the content of adsorbable organic chlorine (AOCl) was 0.30 mg/g (dry sludge). In the Fenton system with pH=3, 500 mg/L Cl^-, 30 mmol/L Fe²⁺ and 30 mmol/L H₂O₂, the removal of phenanthrene was promoted by chlorine radicals (•Cl), and the AOCl in sludge solid phase increased to 0.55 mg/g (dry sludge) at 30 min. According to spectral analysis, it was found that •Cl could chlorinate aromatic and aliphatic compounds (excluding PAHs) in solid phase at the same time, and eventually led to the accumulation of aromatic chlorides in solid phase. Strengthening the oxidation ability of Fenton system increased the formation of organic chlorines in liquid and solid phases. In weak acidity, the oxidation and desorption of superoxide anion promoted the removal and migration of PAHs and organic carbon in solid phase, and reduced the formation of total organic chlorine. The Fenton-like system dominated by non-hydroxyl radical could realize the mineralization of PAHs, organic carbon and organic chlorines instead of migration. This paper builds a basis for the selection of sludge conditioning methods.

Advanced oxidation processes for the removal of mono and polycyclic aromatic hydrocarbons - A review

Aromatic hydrocarbons (AHs) are toxic environmental contaminants presented in most of the environmental matrices. Advanced oxidation processes (AOPs) for the removal of AHs in the account of complete mineralization from various environmental matrices have been reviewed in this paper. An in-depth discussion on various AOPs for mono (BTEX) and polyaromatic hydrocarbons (PAHs) and their derivatives is presented. Most of the AOPs were effective in the removal of AHs from the aquatic environment. A comparative study on the degradation of various AHs revealed that the oxidation of the AHs is strongly dependent on the number of aromatic rings and the functional groups attached to the ring. The formation of halogenated and nitrated derivatives of AHs in the real contaminated water containing chloride, nitrite, and nitrate ions seems to be a challenge in using the AOPs in real systems. The phenolic compounds, quinone, alcohols, and aliphatic acids are the important byproducts formed during the oxidation of AHs, initiated by the attack of reactive oxygen species (ROS) on their electron-rich center. In conclusion, AOPs are the adaptable method for the removal of AHs from different environmental matrices. The persulfate-based AOPs were applied in the soil phase removal as an in situ chemical oxidation of AHs. Moreover, the combination of AOPs will be a conclusive solution to avoid or minimize unexpected or other toxic intermediate products and to obtain rapid oxidation of AHs.

Combining sequential extraction and 3D fluorescence to investigate the behavior of antibiotic and polycyclic aromatic hydrocarbons during solar drying of sewage sludge

Solar drying and liming are commonly used for sludge treatment, but little is known about their efficiency on antibiotics and Polycyclic Aromatic Hydrocarbons (PAHs) removal. This study aimed to investigate the removal of antibiotics and PAHs during solar drying of Limed Sludge (LS) and Non-Limed Sludge (NLS). Thus, organic matter fractionation and 3D fluorescence were used to assess the accessibility and the complexity of organic matter. 2 experiments have been conducted using LS and NLS for 45 days of drying in a pilot scale tunnel. Physicochemical results indicated significant decrease of water content (90%) for both sludge samples within 15 days of drying. For both treatments, the removal of total organic carbon and total nitrogen was low and similar for both treatments. Through this study, it has been confirmed that liming and drying contributed to a strong modification of the organic matter quality with an increase of its accessibility. On the other hand, drying alone increased the less accessible compartments, while the presence of lime affected the interconnexion between the organic matter pools. 3D fluorescence confirmed the obtained results and indicated that LS leads to obtaining more simple molecules in the most accessible compartments, while NLS leads to obtaining more complex molecules in the less accessible compartments. In addition, solar radiations and leaching may contribute to the significant removal (p < 0.01) of roxithromycin, benzo(a)anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo(g, h, i) perylene in the presence of lime. Furthermore, the evolution of organic matter pools in terms of accessibility and complexity may drive the bioavailability of these pollutants, leading to their significant removal.

Enhanced PAHs-contaminated site soils remediation by mixed persulfate and calcium peroxide

Polycyclic aromatic hydrocarbons (PAHs) remain in the site soils after relocated coking plants and oil refineries pose huge constraints to the subsequent land utilization. However, single persulfate (PS) or calcium peroxide (CP) remediation strategies can only inefficiently oxidize some PAHs in soil. This work sought to optimize PS/CP oxidation remediation strategy and verify its practical application effect in soil samples spiked with PAHs. The results showed that the mixed PS/CP oxidation remediation was better than the single oxidants strategies; it had high remediation performance in different particles and pollution loads of PAHs-contaminated soils. Simultaneously, reactive radicals (SO₄·^- and ·OH) were detected, and one side-product (CaSO₄) was characterized. This work optimized the mixed PS/CP system (0.3 mol/L PS, and 8 g/kg CP, together with 0.18 mol/L Fe²⁺ and 0.11 mol/L C₂O₄^2-), and the corresponding Total-PAHs removal rate was 85.41%. Compared to the cost based on benzopyrene (BaP) removal, the study provided a cost-effective mixed PS/CP oxidation remediation technique (1.22 $/ton), widely applicable in soils polluted with various organic contaminants represented such as PAHs.

Sorption of benzo[a]pyrene by Chernozem and carbonaceous sorbents: comparison of kinetics and interaction mechanisms

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon, highly persistent and toxic and a widespread environmental pollutant. Although various technologies have been developed to remove BaP from the environment, its sorption through solid matrixes has received increasing attention due to cost-effectiveness. The present research compares the adsorption capacity of Haplic Chernozem, granular activated carbon and biochar in relation to BaP from water solution. Laboratory experiments with different initial BaP concentrations in the liquid phase and different ratios of the solid and liquid phases show that Freundlich model describes well the adsorption isotherms of BaP by the soil and both sorbents. Moreover, the BaP isotherm sorption by the Haplic Chernozem is better illustrated by the Freundlich model than the Langmuir equation. The results reveal that the sorption capacity of the carbonaceous adsorbents at a ratio 1:20 (solid to liquid phases) is orders of magnitude higher (13 368 ng mL^-1 of activated carbon and 3 578 ng mL^-1 of biochar) compared to the soil (57.8 ng mL^-1). At the ratio of 0.5:20, the adsorption capacity of the carbonaceous sorbents was 17-45 times higher than that of the soil. This is due to the higher pore volume and specific surface area of the carbonaceous sorbents than soil particles, assessed through scanning electron microscopy. The sorption kinetic of BaP by Chernozem was compared with the adsorption kinetics by the carbonaceous sorbents. Results indicate that the adsorption dynamic involves two steps. The first one is associated with a fast BaP adsorption on the large available surface and inside macro- and meso-pores of the sorbent particles of the granular activated carbon and biochar. Then, the adsorption is followed by a slower process of BaP penetration into the microporous space and/or redistribution into a hydrophobic fraction. The effectiveness of the sorption process depends on both the sorbent properties and the solvent competition. Overall, the granular activated carbon and biochar are highly effective adsorbents for BaP, whereas the Haplic Chernozem has a rather limited capacity to remove BaP from contaminated solutions.

Influence of sludge organic matter on elimination of polycyclic aromatic hydrocarbons (PAHs) from waste activated sludge by ozonation: Controversy over aromatic compounds

Ozonation has been widely used as a viable advanced oxidation process (AOP) for elimination of PAHs in waste activated sludge through effective sludge disintegration and abatement of organic pollutants. However, sludge organic matter (SOM) influences PAHs degradation during ozone treatment is still rarely understood. In this study, we investigated such an influence with the aid of solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy and the corresponding two-dimensional correlation analysis (2D-COS) strategy. The results showed that the degradation of SOM macromolecules in the order of aromatic substances > aliphatic carbon > α carbon > amides groups > O-alkyl upon ozone treatment. Moreover, the PAHs removal efficiency was positively correlated with the aromaticity of sludge (R² = 0.84-0.98), while negative associated with its aliphaticity (R² = 0.81-0.95). Lastly, humic acid (HA) was used as a proxy of aromatic SOM to further explore their interaction with PAHs in sludge matrix. The results revealed that freely dissolved (HA-D) and suspended particulates (HA-S) imposed distinctively different influence on ozone-based PAHs degradation. The HA-S facilitated the elimination of PAHs by 7.95 ± 0.11%, while those HA-D reduced the removal efficiency by 16.70 ± 0.13%.

Hydrodynamic cavitation activation of persulfate for the degradation of polycyclic aromatic hydrocarbons in marine sediments

Hydrodynamic cavitation (HC) coupled with persulfate (PS)-based that resulted in the synergistic degradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated marine sediments. The effects of HC injection pressure and Σ[PAH]: [PS] on the rate and extent of PAH degradation were studied in the pressure range of 0.5-2.0 bar, PS concentration rage of 2 × 10^-4 to 2 × 10^-2 M or Σ[PAH]: [PS] of 1:10-1000, and reaction time of 20-60 min. A pseudo-first-order rate law fitted PAHs removal kinetics well. The degradation rate constant increased with injection pressure, reaching the maximum level at 0.5 bar, then decreased at injection pressure became greater than 0.5 bar. The results showed that PAH removal was 84% by the combined HC and PS process, whereas, HC alone only achieved a 43% removal of PAHs in marine sediments under the optimal inlet pressure of 0.5 bar at PS concentration of 2 × 10^-2 M in 60 min. The HC‒PS system effectively removed PH, PY, FLU, BaA, and CH at 91, 99, 91, 84, and 90%, respectively. The maximum removal of 6-, 5-, 4-, 3-, and 2-ring PAHs was 89, 87, 84, 76, and 34%, respectively. Major reactive oxygen species (ROSs), namely, SO₄^-• and HO•, were responsible for PAHs degradation. Results clearly highlighted the feasibility of HC-PS system for the clean-up of PAHs-laden sediments in particular and other recalcitrant organic contaminants in general.

The extent of sludge solubilization allows to estimate the efficacy of ozonation for removal of polycyclic aromatic hydrocarbons (PAHs) in municipal sewage sludge

Ozone treatment has been proven as an effective technology for removing PAHs in municipal sewage sludge. However, given the complex interaction of PAHs with sludge extracellular polymeric substances (EPS), effective sludge disintegration is required to make PAHs more accessible to oxidants, which also affects PAHs partitioning. Here, we investigated two treatment systems, namely ozonation (ozone) and sequential hydrodynamic cavitation and ozonation (HC+ozone), under varied conditions, to determine whether the extent of sludge disintegration can estimate a measurable removal of PAHs. The results showed that both the PAHs removal efficiency and kinetics highly depended on pH and ozone dose. Although no significant removal of PAHs occurred during HC treatment, the observed rate constants for Σ₁₆ PAHs removal in HC+ozone system were 1.2-1.4-fold higher than those obtained in ozone system under the same condition. The accelerated PAHs removal could be attributed to the reduced flocs size (80% smaller) and increased soluble EPS concentration (5-fold higher) with HC pretreatment. Lastly, a positive correlation was noted between the PAHs removal efficiency and soluble EPS concentration (R² = 0.85), indicating the important role of dissolved and colloidal matter (DCM) for PAHs partitioning between aqueous and particulate phases.

Decomposition of oil refinery sludge using E+-Ozonation process for carbon source releasing and TPH removal

To utilize carbon source and decompose the petroleum hydrocarbon substances simultaneously, adding the electrolysis to ozonation (E⁺-Ozonation) was employed to deal with hazardous activated petroleum waste sludge (P-sludge). It was found that E⁺-Ozonation could accelerate the ozone utilization and hydroxyl radical (·OH) generation rate. Soluble chemical oxygen demand (SCOD) increased around 16.3 times than the control one (from 471 to 7700 mg/L). The potential carbon source, such as the short-chain carbon of acetate and propionate, increased from 50 to 1088 mg/L and from 27 to 614 mg/L respectively, and approximately accounted for a quarter of total SCOD. Total petroleum hydrocarbon (TPH) decomposition was observed with a much higher removal rate of 84.3% simultaneously, and the substances with the function group of C=C and C-C bonds decomposed greatly. The long- and medium-chain substances in TPH were converted into the short-chain substances (90% of C₂₈-C₄₀ of hydrocarbons was removed, while C₁₀-C₁₈ increased by 13.8%). E⁺-Ozonation process could be one of the promising methods for P-sludge decomposition through carbon source releasing and TPH removal.

Treatment of simulated textile sludge using the Fenton/Cl- system: The roles of chlorine radicals and superoxide anions on PAHs removal

The main content of this work is to investigate the removal of polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, and fluoranthene) from simulated sludge solid phase employing an Fenton/Cl^- system under various Cl^- contents and pH values. The steady-state concentrations of the hydroxyl, chlorine, and dichloride anion radicals ([·OH]_ss, [·Cl]_ss, and [Cl₂^·-]_ss) in heterogeneous system were first measured using tert-butanol, nitrobenzene, and benzoic acid. The outcomes exhibited that increasing the Cl^- content from 50 to 2000 mg/L (pH = 3.0) or raising the pH from 3.0 to 5.0 (1000 mg/L Cl^-) caused [·OH]_ss to continuously decrease and [Cl₂^·-]_ss and the concentration of superoxide anions (HO₂·/O₂^·-) to continuously increase. When the pH was 3.0 and the Cl^- concentration was 1000 mg/L, [·Cl]_ss had a maximum value of 9.27 × 10^-14 M. Combining the results of PAH removal, radical quenching, and product analysis, it was found that ·Cl in the Fenton/Cl^- system promoted the oxidative degradation of phenanthrene without forming chlorination byproducts. Furthermore, HO₂·/O₂^·- was helpful in removing anthracene and fluoranthene. Under the environment of high Cl^- content (≥1000 mg/L), PAHs could be removed more effectively by using HO₂·/O₂^·-. This investigation underpins further study on the regulation of reactive species and the efficient degradation of target organic matter in Fenton/Cl^- system, and provides a basis for studying the formation of chlorinated or toxic byproducts in the process of treating textile dyeing sludge by Fenton.

Design and application of metal-organic frameworks and derivatives as heterogeneous Fenton-like catalysts for organic wastewater treatment: A review

Advanced oxidation process (AOP), with a high oxidation efficiency, fast reaction speed (relatively no secondary pollution), has become one of the core technologies of industrial wastewater and advanced drinking water treatment. Heterogeneous Fenton-like oxidation process (HFOP) is a kind of AOP, which developed rapidly in recent years in such a way to overcome the disadvantages of traditional Fenton reaction. Metal-organic frameworks (MOFs) and their derivatives become essential heterogeneous catalysts for organics mineralization due to the large specific surface area, abundant active sites, and ease of structural regulation. However, the knowledge gap on the mechanism and the fate of heterogeneous catalyst species during organics degradation activities by MOFs presents considerable impediments, particularly for a wide application and scaling up the process. This work has the potential to provide guidance and ideas for researchers and engineers in the fields of environmental remediation, environmental catalysis and functional materials. This review focuses on clarifying the critical mechanism of •OH production from MOFs and derivatives as well as its action on the organic's degradation process. The recent developments in MOF based HFOP are compared, and more attention is paid for the following aspects in this review: (1) classifies systematically progressive modification methods of MOFs by chemical and physical treatments; (2) analyzes the fate of catalytic species during treating organic wastewater; (3) proposes design ideas and principles for improving the performance of MOFs catalysts; (4) discusses the main factors influencing the catalytic properties and practical application; (5) summarizes the possible research challenges and directions for MOFs and their derivatives as catalysts applied to wastewater treatment in the future.

De-colourization of textile effluent using immobilized Geotrichum candidum: an insight into mycoremediation

Textile effluent is generally complicated to manage because of its extremely noxious and recalcitrant coloured compositions. Mycoremediation is an extensively used strategy for the competent degradation of hazardous pollutants present in textile effluent. Fungus could be immobilized in synthetic or natural matrices. The current study shows the decolourization of the textile effluent by 85·5 and 98·5% within 6 h using suspended and immobilized fungus, Geotrichum candidum with optimized parameters like inoculum size (5%), pH (4·5), and temperature (30°C). To maintain a high biomass of fungal population and enhance the retention of fungal strain in the contaminated sites, the fungi need to be immobilized. Hence, the fungus was immobilized naturally onto the selected inert support that is, coconut fibres by the means of adsorption, where they grew as active films on the fibres after being grown in the culture broth. The optimized process parameters of inoculum size, fibre quantity and agitation speed for immobilized G. candidum were 5%, 2·2 g l^-1 of effluent and 100 rev min^-1 respectively. High level of laccase (22 and 25 U l^-1 in suspended and immobilized fungal cells treatment respectively) was observed during the process of decolourization and it was found that decolourization was directly proportional to the laccase activity. The UV-vis, FTIR, ¹ H NMR and GC-MS analyses of treated textile industrial wastewater revealed the degradation of toxic pollutants in the textile effluent and formation of lower molecular weight intermediates. The study revealed a higher efficacy of immobilized G. candidum in comparison to suspended fungal culture, employing ligninolytic enzyme laccase, which catalyzes the degradation/transformation of aromatic dyes in the textile effluent thus decolourizing it.

Source, occurrence, migration and potential environmental risk of microplastics in sewage sludge and during sludge amendment to soil

Microplastics (MPs) are an emerging global pollutant. MPs research is mainly concentrated on water, with limited research on MPs in sewage sludge. MPs from various sources are collected into sewage and most of the MPs are trapped in the sludge during the sewage treatment process. Sludge is not only a sink of MPs, but also a source. Soil amendment with sludge provides nutrients into the soil, but it can also import substantial MPs into the soil, which has certain environmental risks. Therefore, we focused on the MPs in sludge and sludge-amended soil and conducted a literature review to summarize the sources, physical properties and fate of the MPs in sludge, as well as their separation, identification and statistical methods. MPs can accumulate in the soil, influence the properties of the soil, and also migrate, which might result in the pollution of deep soils and groundwater. In addition, the adsorption by MPs of heavy metals, organic pollutants, antibiotics and antibiotic resistance genes cannot be ignored as sewage sludge generally contains substantial concentrations of these pollutants. They can be adsorbed by the MPs and transferred into the soil with sludge amendment of soil. The combination and interaction of MPs with its adsorbed pollutants might increase environmental risk, further leading to possibility of them being uptaken by plants. The specific long-term risks to the environment caused by MPs in soil with sludge amendment require further exploration and investigation.

Behavior and mechanism of low-concentration rare earth ions precipitated by the microbial humic-like acids

The disposal of bulky low-concentration rare earth solutions (usually ≤ 200 mg L^-1) is difficult and it can easily lead to the waste of rare earth resources. The precipitant separation method is a simple and effective technique that is commonly used for rare earth recovery, but the application of biological component precipitants is rarely reported. In this study, the effects of the precipitation of low concentrations of rare earth ions by excess sludge humic-like acids were evaluated. Scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and infrared (IR) spectroscopy revealed that the addition of humic-like acids to low-concentration rare earth solutions could produce a flocculent precipitate. The precipitation rate was more than 89%. The content of rare earth metals such as Nd, Y, and La in the rare earth precipitate reached 23.72%, and the elution rate of 1.25 mol L^-1 hydrochloric acid was 90.50%. It was concluded that the humic-like acids might contain many functional groups capable of adsorbing rare earth ions. It was inferred that the possible mechanism might be that rare earth ions were precipitated by a series of net catch, ion exchange, and adsorption processes. These findings provide a reference for the future recovery of rare earth resources.

Effect of magnetic powder on denitrification using the sludge alkaline fermentation liquid as a carbon source

This work evaluates the impact of the different concentrations of Fe₃O₄ on nitrate removal and organic matters utilization in the sequencing batch reactors (SBRs) using the sludge alkaline digestion supernatant as external sludge carbon source. Results indicated that the optimal concentration of Fe₃O₄ was 1 g/L for enhancing denitrification with NO₃^--N removal efficiency of 93.13% (up to a 11.93% increase) and without NO₂^--N accumulation after 18 days. The changes of soluble chemical oxygen demand (SCOD), protein, and carbohydrate during denitrification process were analyzed to gauge the utilization of sludge fermentation products by denitrifiers. The SCOD was consumed for organisms involved in NO₃^--N removal and the Fe₃O₄ could promote the utilization of carbohydrate better than protein by denitrifiers during denitrification process. Denitrification rate (V_DN) and the nitrate-to-nitrite transformation ratio (NTR), as the kinetics parameters, were also investigated in different concentrations of Fe₃O₄.

Physical-Chemical Study of Anthracene Selective Oxidation by a Fe(III)-Phenylporhyrin Derivative

In this work, we studied the anthracene oxidation by hydroxyl radicals. Hydroxyl radical was generated by reaction of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Fe (III) (TPPFe) with hydrogen peroxide under visible radiation at a nitrogen atmosphere. The TPPFe was synthesized by Adler Method followed by metal complexation with Fe (III) chloride hexahydrate. Hydroxyl radical was detected by fluorescence emission spectroscopy and we studied kinetic of anthracene selective oxidation by hydroxyl radicals through the differential method. The TPPFe was characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) measurements. The results indicated that TPPFE was compound by micro-particles with a size distribution of around 2500 nm. Kinetic results showed that the apparent rate constant for the oxidation of anthracene increased exponentially on as temperature increases, furthermore, the activation energy for the Anthracene oxidation by hydroxyl radicals under visible irradiation was 51.3 kJ/mol. Finally, anthraquinone was the main byproduct generated after oxidation of anthracene by TPP-Fe under visible irradiation.

Recycling hazardous textile effluent sludge in cement-based construction materials: Physicochemical interactions between sludge and cement

The textile industry produces a large amount of textile effluent sludge (TES). Many studies have explored the potential use of TES in cement-based materials. However, the physicochemical interactions between the TES and ordinary Portland cement (OPC) have rarely been studied. In this study, the effects of increasing dosage (0-20% by OPC) of TES on the performance of OPC-TES blends were investigated in terms of hydration progress, mechanical strength, microstructure evolution and metal leachability. The results showed that TES markedly delayed the OPC hydration at the early age, and increasing dosages of TES decreased the portlandite content at 7 and 28 days' age. Compared to the reference, the OPC-TES mortar exhibited seriously degraded mechanical strength; when using 20% TES, the decrease in compressive and flexural strength reached up to 71% and 42% respectively at the age of 28 days. Scanning electron microcopy and mercury intrusion porosimetry found the inclusion of TES introduced more weak interfaces in the cement mortar, thus increased the total porosity especially the macropores. But leachability tests revealed all the toxic metals in the TES were stabilized after the incorporation of OPC and exhibited very low metal mobility in the OPC-TES mortar, which posed no environmental risk.

Modelling PAHs removal in activated sludge process: effect of disintegration

The removal of polycyclic aromatic hydrocarbons (PAHs) in activated sludge was evaluated using two laboratory-scale bioreactors, coupled or not with a disintegration system (sonication). Mass balances performed on each system underlined that PAHs removal was significantly improved after sludge disintegration, especially for the higher molecular weight PAHs studied, which tended to adsorb to suspended matter. A model was developed in order to study the effect of sludge disintegration on the content of dissolved and colloidal matter (DCM), and to predict the potential impacts on PAHs availability and degradation. Results showed that this new model was efficient for capturing apparent degradation improvement trends and for discriminating between the involved mechanisms. This study showed that DCM content increased after sludge disintegration, and proved to be the main driver for improving PAHs apparent degradation.

Structure and function of microbial community associated with phenol co-substrate in degradation of benzo[a]pyrene in coking wastewater

Coking wastewater (CWW) contains high contents of phenols and other toxic and refractory compounds including polycyclic aromatic hydrocarbons (PAHs) with the most carcinogenic benzo[a]pyrene (BaP) among them. The mechanism of PAHs/BaP degradation in activated sludge of CWW treatment with phenol as co-substrate was studied. For characterizing the structure and functions of microbial community associated with BaP degradation with phenol as co-substrate, high-throughput MiSeq sequencing was used to examine the 16S rRNA genes of microbiology, revealing noticeable shifts in CWW activated sludge bacterial populations. Major genera involved in anaerobic degradation were Tissierella_Soehngenia, Diaphorobacter and Geobacter, whereas in aerobic degradation Rhodanobacter, Dyella and Thauera prevailed. BaP degradation with phenol as co-substrate induced bacterial diversification in CWW activated sludge in opposite trends when anaerobic and aerobic conditions were applied. In order to predict the microbial community functional profiling, a bioinformatics software package of phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was run to find that some dominant genera enriched in the BaP pathway may own the ability to degrade PAHs/BaP. Further experiments should focus on testing the dominant genera in BaP degradation at different oxygen levels.

Removal of Bound PAH Residues in Contaminated Soils by Fenton Oxidation

The availability of bound residues of polycyclic aromatic hydrocarbons (PAHs), in reference to their parent compounds, can be enhanced by microbial activity and chemical reactions, which pose severe risks for the ecosystems encompassing contaminated soils. Considerable attention has been raised on how to remove these bound residues from PAH-contaminated soils. This paper provides a novel application of Fenton oxidation in the removal of bound residues of model PAHs, such as naphthalene (NAP), acenaphthene (ACP), fluorene (FLU) and anthracene (ANT), from naturally contaminated soils. The citric acid-enhanced Fenton treatment resulted in the degradation of bound PAH residues that followed pseudo-first-order kinetics, with rate constants within 4.22 × 10−2, 1.25 × 10−1 and 2.72 × 10−1 h−1 for NAP, FLU, and ANT, respectively. The reactivity of bound PAH residues showed a correlation with their ionization potential (IP) values. Moreover, the degradation rate of bound PAH residues was significantly correlated with H2O2-Fe2+ ratio (m/m) and H2O2 concentrations. The highest removal efficiencies of bound PAH residues was up to 89.5% with the treatment of chelating agent oxalic acid, which was demonstrated to be superior to other acids, such as citric acid and hydrochloric acid. This study provides valuable insight into the feasibility of citric acid-Fenton and oxalic acid-Fenton treatments in rehabilitating bound PAH residues in contaminated soils.

Removal of polycyclic aromatic hydrocarbons from different soil fractions by persulfate oxidation

Removal of polycyclic aromatic hydrocarbons (PAHs) from different soil fractions of contaminated soil was investigated by using activated persulfate oxidation remediation in our research. The results showed that the light fraction, which accounted for only 10% of the soil, contained 30% of the PAHs at a concentration of 4352 mg/kg. The heavy fraction contained more high-molecular-weight PAHs, and the total PAH concentration was 625 mg/kg. After being oxidized, the removal rate of PAHs was 39% in the light fraction and nearly 90% in the heavy fraction. Among the different fractions of the heavy fraction, humic acid contained the highest concentration of PAHs, and consequently, the highest removal efficiency of PAHs was also in humic acid. Compared with the light fraction, the heavy fraction has more aromatic compounds and those compounds were broken down during the oxidation process, which may be the removal mechanism involved in the oxidation of high-ring PAHs. Similarly, the enhancement of C=C bonds after oxidation can also explain the poor removal of high-ring PAHs in the light fraction. These results imply that different fractions of soil vary in composition and structure, leading to differences in the distribution and oxidation efficiencies of PAHs.

The role of ultrasound-treated sludge for accelerating quinoline mono-oxygenation

Activated sludge treated by ultrasound was tested as a source of exogenous electron donor to accelerate quinoline mono-oxygenation, which requires an intracellular electron donor (2H). The quinoline-removal rate was proportional to the amount of treated or untreated sludge added in flask experiments, but the best biodegradation kinetics was obtained with a mixture of 25% untreated sludge plus 75% treated sludge. The treated sludge primarily provided exogenous electron donor, while the untreated sludge provided active biomass. A biofilm system also showed the same beneficial effect of treated sludge, and the soluble fraction of the treated sludge had the greatest impact. Using treated sludge instead of a purchased electron donor provides an economic advantage for accelerating the biodegradation of contaminants whose biodegradation is initiated by an oxygenation reaction, such as quinoline.

Treatment of a simulated sludge by ultrasonic zero-valent iron/EDTA/Air process: Interferences of inorganic salts in polyaromatic hydrocarbon removal

Understanding the occurrence states of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge is the key to their further treatment and disposal. Here, the effects of inorganic salts (silicate, sulfate, phosphate, hydroxide, and iron salts) that were typically rich in textile dyeing sludge on PAH adsorption by sludge and PAH degradation by an ultrasound (US) combined zero-valent iron/EDTA/Air (ZEA) system were studied in a simulated sludge system. The results showed that the simulated sludge containing inorganic salts had a larger specific surface area, which was beneficial for the adsorption of PAHs. More low-ring PAHs were adsorbed on the surface of the particles in the simulated sludge because of the inorganic salts, which was conducive to low-ring PAHs degradation by US/ZEA. The PAH removal rates were increased by 15.37% and 11.19%, respectively, in the presence of SiO₃^2- and HPO₄^2-. The yield of hydroxyl radicals (OH) was increased by 42.39% and 66.25% by SiO₃^2- and HPO₄^2-, respectively. The reason was that the oxidation of the ligand ([Fe^Ⅱ(EDTA)]) formed by ethylenediaminetetraacetic acid (EDTA) and divalent iron was promoted by SiO₃^2- and HPO₄^2-. The formation of OH in the US/ZEA system was inhibited by the corrosion inhibition of SO₄^2- on zero-valent iron (ZVI), the reaction of ferric salt with EDTA, and the reaction of Mg(OH)₂ with the ligand ([Fe^III(EDTA)]). This work provides an essential theoretical insight into the role of the inorganic components of sludge in the removal of PAHs by advanced oxidation processes.

Impact of Alkaline Pretreatment to Enhance Volatile Fatty Acids (VFAs) Production from Rice Husk

This study explores the use of alkaline pretreatments to improve the hydrolyzation of rice husks to produce volatile fatty acids (VFAs). The study investigated the effects of reagent concentration and pretreatment time on protein, carbohydrates, and dissolved chemical oxygen demand (SCOD) dissolution after the pretreatment. The optimum alkaline pretreatment conditions were 0.30 g NaOH (g VS)-1, with a reaction time of 48 h. The experimental results show that when comparing the total VFA (TVFA) yields from the alkaline-pretreated risk husk with those from the untreated rice husk, over 14 d and 2 d, the maximum value reached 1237.7 and 716.0 mg·L-1 with acetic acid and propionic acid and with acetic acid and butyric acid, respectively. After the alkaline pretreatment, TVFAs increased by 72.9%; VFA accumulation grew over time. The study found that alkaline pretreatment can improve VFA yields from rice husks and transform butyric acid fermentation into propionic acid fermentation. The study results can provide guidelines to support the comprehensive utilization of rice husk and waste treatment.

Characterization and carcinogenic risk assessment of polycyclic aromatic and nitro-polycyclic aromatic hydrocarbons in exhaust emission from gasoline passenger cars using on-road measurements in Beijing, China

The polycyclic aromatic hydrocarbon (PAH) and nitro-polycyclic aromatic hydrocarbon (NPAH) emissions from 16 gasoline passenger cars, encompassing five emission standards and two driving conditions, were tested using a portable emission measurement system (PEMS) in Beijing under on-road conditions. In total, 16 PAHs and 9 NPAHs were quantified in both the gaseous and particulate phases by high-performance liquid chromatography (HPLC). The results indicated that lower PAH and NPAH emissions were observed with improved emission standards, especially for China 3 to China 5 vehicles (P < 0.05). Higher emission factors (EFs) were detected on nonhighway roads than on highway roads due to incomplete combustion. Although most PAHs and NPAHs were in the gas-phase, the TEQ_BaP of the particulate-phase PAHs was 4.2 times higher than that of the gas-phase PAHs, whereas the opposite pattern was observed for NPAHs. The TEQ_BaP EFs on nonhighway roads were 1.0-2.3 times higher than those on highway roads. The results of this study will be valuable for estimating the emissions and performing carcinogenic risk assessment of PAHs and NPAHs from urban gasoline passenger cars on roads. Formulating more stringent regulations and emission control technologies for PAHs and NPAHs is important.

Ultrasound-Assisted Removal of Tetracycline by a Fe/N-C Hybrids/H2O2 Fenton-like System

In this work, the degradation of tetracycline (TC) in water by the integrated ultrasound (US)-Fenton process was investigated. For this, a new composite Fe/N-C-x (x is the molar ratio of iron salt Fe(NO₃)₃·9H₂O) catalyst was synthesized through simple carbonization of the mixture of glucose and iron salt Fe(NO₃)₃·9H₂O in the presence of ammonium chloride as the nitrogen source. The resultant catalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, vibrating sample magnetometer, and N₂ adsorption-desorption, showing a typical graphite porous structure and good magnetic properties. The results indicated that the optimized Fe/N-C-2 catalyst prepared with a mole ratio of glucose/Fe(NO₃)₃·9H₂O/NH₄Cl of 5:2:16.8 exhibited the highest TC removal in the Fe/N-C-2/H₂O₂/US system at a wide pH range from 3.0 to 11.0. At an initial pH of 7.0, TC removal in the Fe/N-C-2/H₂O₂/TC/US system was 1.83, 18.69, and 28.75 times of that in Fe/N-C-2/TC/H₂O₂, H₂O₂/TC/US, and TC/H₂O₂ systems, showing a positive synergistic action between US and Fe/N-C-2. The effects of catalyst dosage, H₂O₂ concentration, ultrasonic power, humic acid, and coexisting anions on TC removal were investigated. The preliminary analysis suggested that the Fe-N species and the graphite N dispersed in the carbon matrix are responsible for the efficient catalytic activity. By a simple magnetic separation, the Fe/N-C-2 catalyst was easily recovered and used for the next degradation experiment. Above 88% catalytic ability of Fe/N-C-2 was retained even after six successive runs, suggesting its good reusability. The simple preparation strategy, good magnetic property, and good catalytic ability of the Fe/N-C-2 materials make them promising alternative Fenton-like catalysts for the antibiotics abatement in water.

How do root exudates of bok choy promote dibutyl phthalate adsorption on mollisol?

This study investigates the interaction between the bok choy root exudates and dibutyl phthalate (DBP) onto mollisol during the adsorption. The result elucidated that the adsorption reached equilibrium within 12 h, the adsorption capacity of rhizosphere mollisol containing root exudates and ordinary mollisol were 243.46 mg kg^-1 and 281.95 mg kg^-1, separately. The adsorption kinetics and isotherm model followed the pseudo-second order and the Frendlish model, respectively, which hinted that the adsorption process was multi-layer heterogeneous chemisorption. We characterized the root exudates and analyzed its effects on soil physical and chemical properties and structure. The result revealed that the root exudates contained hydrocarbons, sulfur compounds and acids. Root exudates made the dissolved organic matter (DOM) dissolution from soil and the increase of organic matter, which might be one of the reasons that root exudates promote DBP adsorption on mollisol. We selected three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence and Fourier transform infrared spectroscopy (FTIR) to analyze the interactions between root exudates and DBP, DOM and DBP, respectively. Fluorescence spectrum revealed that the main component of root exudates was protein, for DOM was humic acid, the fluorescence of root exudates and DOM gradually disappeared with the increase of DBP concentration. FTIR revealed that -COO in root exudates and -CH₂ in DOM respectively reacted with DBP. The results of this study are of great importance to reveal that the root exudates are significant in the environmental behavior of DBP adsorption on mollisol, and also provide more useful information for phytoremediation of organic pollutants in the mollisol.

The relationship between volatile fatty acids accumulation and microbial community succession triggered by excess sludge alkaline fermentation

The volatile fatty acids (VFAs) accumulation pattern and microbial community succession were studied during excess sludge (ES) alkaline fermentation at pH of 10.0 with expanded granular sludge blanket reactor over 5 cyclers. Microbial community shifted conspicuously as ES suffered alkaline fermentation. Both VFAs and acid-producing bacteria increased rapidly during the first 8 days fermentation time, and they showed a quite positive correlation relationship. In addition, soluble chemical oxygen demand (SCOD) also dramatically increased during the first 8 days, which implied 8 day was the optimum sludge retention time (SRT) for ES alkaline fermentation and VFAs accumulation time. Illumina Miseq Sequencing analysis indicated that Clostridium, Bacillus, Amphibacillus and Peptostreptococcaceae were the dominant bacteria genus to produce VFAs. Acetic acid took about 84% in total VFAs because among the total acid-producing bacteria most bacteria could produce acetic acid.

Treatment of Cutting Fluid Waste using Activated Carbon Fiber Supported Nanometer Iron as a Heterogeneous Fenton Catalyst

Addressing the problem of high chemical oxygen demands (COD) of cutting fluid waste generated in the machining process, its complex composition, and the specific conditions required for the treatment process, a heterogeneous Fenton fibre catalyst (NZVI@ACF) made of nanometer-iron supported on activated carbon fiber using dip-molding was developed. NZVI was homogeneously loaded onto ACF surfaces to form NZVI@ACF, with a specific surface area (S_BET) of 726.3642 m²/g. Using a multistage chemical pretreatment, the NZVI@ACF/H₂O₂ system was used to effectively treat cutting fluid waste. The results indicated that the rate of COD removal in the cutting fluid waste liquid pretreated with NZVI@ACF/H₂O₂ system was 99.8% when the reactions conditions were optimized to 20 nmol/L H₂O₂, 6 g/L NZVI@ACF, total reaction time of 120 min and pH 5. The treated waste solution passed China’s tertiary wastewater discharge standards. NZVI@ACF/H₂O₂ demonstrated an excellent catalytic performance compared to the traditional Fenton catalyst, increased the effective pH reaction range and had an adsorption effect on the waste liquid after the reaction.

Solubilization of polycyclic aromatic hydrocarbons (PAHs) with phenol in coking wastewater treatment system: Interaction and engineering significance

Polycyclic aromatic hydrocarbons (PAHs) are accumulated in the sludge collected from the coking wastewater treatment. Phenol with its efficient degradation observed in biological treatment promotes the solubility of PAHs in aqueous phase. The interaction mechanism of phenol and PAHs in aqueous and sludge phases was systematically studied in two full-scale engineering projects composed of anaerobic-oxic-oxic (A-O₁-O₂) and anaerobic-oxic-hydrolytic-oxic (A-O₁-H-O₂) sequences. The results showed that reasonable use of phenol facilitates solubilization of PAHs alleviating their emission problems. The ΔPAHs/Δphenol mass ratio in the sludge phase of A-O₁-H-O₂ system (146.3) exceeded that in A-O₁-O₂ one (63.80), exhibiting a good solubilization effect on PAHs with their more efficient degradation in the former. The full-scale observations were verified in laboratory solubilization experiments using phenanthrene (Phen), pyrene (Pyr) and benzo[a]pyrene (Bap) as the models of 3-, 4- and 5-ring PAHs, respectively. The binding energies of [phenol^-PAHs] complexes were calculated using computational density functional theory showing consistency with the experimentally observed phenol-facilitated solubilization efficiencies in the row of Phen>Pyr>Bap. The results showed the fate and distribution of PAHs in coking wastewater treatment affected by the presence of phenol serving as a cost effective reagent for enhanced solubilization of PAHs from the coking wastewater sludge.