Stabilized landfill leachate treatment by zero valent aluminium-acid system combined with hydrogen peroxide and persulfate based advanced oxidation process

Ball-milled biochar-modified zero-valent aluminum activates peroxodisulfate for phenol degradation: Enhancement of catalysis by membrane-breaking effect

Zero-valent aluminum (ZVAl) is a potential activator for peroxodisulfate (PDS), yet the dense oxide film on its surface hampers electron transfer for the O-O bond cleavage of PDS. We synthesized zero-valent aluminum-biochar (BM-ZVAl@BC) composites through ball milling, which effectively disrupted the native oxide layer on BM-ZVAl@BC. Within the BM-ZVAl@BC/PDS system, biochar (BC) not only suppressed the rapid oxidation of BM-ZVAl@BC but also enhanced the dispersion and electron transfer rate of ZVAl, thereby improving the overall catalytic efficiency. Consequently, the phenol removal efficacy in the BM-ZVAl@BC/PDS system was notably improved. Optimal catalytic performance of the prepared BM-ZVAl@BC was achieved at a charcoal-to‑aluminum mass ratio of 2:1, resulting in 95.7 % phenol removal after 180 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that both free radicals (SO4•-, •OH, and O2•-) and non-radical species (1O2) contributed to phenol degradation, with SO4•- and •OH playing predominant roles. In summary, the BM-ZVAl@BC/PDS system represented an effective and promising technology for the remediation of phenolic water pollutants.

Process of landfill leachate pretreatment using coagulation and hydrodynamic cavitation oxidation

Landfill leachate poses a threat to the environment and human health, and its complex composition made it difficult to treat. Among the methods for treating landfill leachate, the physicochemical combination method is considered to have significant effectiveness, low cost, and application potential. In this study, we propose a new method of coagulation and hydrodynamic cavitation/chlorine dioxide (HC/ClO2) for treating landfill leachate. The optimal conditions for coagulation and HC/ClO2 treatment were investigated experimentally. Under the optimal conditions for coagulation, the COD removal rate was 60.14%. Under the optimal HC/ClO2 treatment conditions, the COD removal rate was 58.82%. In the combined coagulation and HC/ClO2 process, the COD removal rate was 83.58%. Thus, the proposed method can significantly reduce the organic load before subsequent biological treatment processes, thereby reducing the operation cycles and cost of biological treatment.

Combination of electrochemically activated persulfate process and electro-coagulation for the treatment of municipal landfill leachate with low biodegradability

To handle complex wastewater with limited biodegradability, hybrid treatment systems are necessary. The current study represents the combined effectiveness of sulfate-radical associated electro-chemical advanced oxidation process (SR-EAOP) and electro-coagulation (EC) for the treatment of stabilized landfill leachate. For SR-EAOP, Pt/Ti was employed as the anode and an iron plate as the cathode; while EC treatment was performed by switching the polarity. Hence, both electrochemical treatment was carried out in single reactor. Initially, the effects of pH, applied voltage, persulfate and Fe2+ dosage, on the performance of SR-EAOP was examined. Sulfate radical was generated in the electrolytic system via cathodic reduction of persulfate (PS) and ferrous (Fe2+) ion activation. Auxiliary processes such as anodic oxidation via Pt/Ti anode and indirect electro-chemical oxidation were also contributed for pollutant degradation. Combined process SR-EAOP followed by EC (SR-EAOP + EC) has better leachate treatment efficacy in comparison with EC + SR-EAOPs. The SR-EAOP + EC based combined treatment mechanism achieved an efficient COD reduction of 88.67% than that of EC + SR - EAOP process (74.51% COD reduction). Characterization studies have been carried out for post-treated dried-sludge using Field Emission scanning electron microscope (FE-SEM) and X-ray powder diffraction (XRD) techniques. The combined process treatment (SR-EAOP + EC) can be applied as pre-treatment for leachate decontamination.

Humic acid recovery from stabilized leachate: Characterization and interference with chemical oxygen demand-colour removal

Heterogeneous combinations of organic compounds (humic acid (HA) and fulvic acid) are the prime factor for the high concentration of colour and chemical oxygen demand (COD) in semi-aerobic stabilized landfill leachate. These organics are less biodegradable and cause a severe threat to environmental elements. Microfiltration and centrifugation processes were applied in this study to investigate the HA removal from stabilized leachate samples and its corresponding interference with COD and colour. The three-stage extraction process recovered a maximum of 1412 ± 2.5 mg/L (Pulau Burung landfill site (PBLS) leachate), 1510 ± 1.5 mg/L (Alor Pongsu landfill site (APLS leachate) at pH 1.5 and 1371 ± 2.5 mg/L (PBLS) and 1451 ± 1.5 mg/L (APLS) of HA (about 42% of the total COD concentration) at pH 2.5, which eventually indicates the process efficiency. Comparative characteristics analysis of recovered HA by scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy, and Fourier transform infrared significantly indicate the existence of identical elements in the recovered HA compared with the previous studies. The higher reduction (around 37%) in ultraviolet (UV) absorbance values (UV254 and UV280) in the final effluent indicates the elimination of aromaticity and conjugated double-bond compounds from leachate. Moreover, 36 and 39% COD and 39 and 44% colour removal exhibit substantial interference.

Sequential treatment of landfill leachate by electrocoagulation/aeration, PMS/ZVI/UV and electro-Fenton: Performance, biodegradability and toxicity studies

This study presents a systematic study on sequential treatment of highly resistant landfill leachate by electrocoagulation (EC)/aeration, sulfate radical advanced oxidation process (SR-AOP) and electro-Fenton (EF). In case of SR-AOP, peroxymonosulfate (PMS) catalyzed by zero valent iron (ZVI) and ultraviolet irradiation (UV) system was developed. Treatment process was optimized in respect to COD removal. Analysis of results revealed that sequential application of EC/aeration, PMS/ZVI/UV, and EF processes provide an extraordinary performance and meet the environmental regulations. The source of iron for EF process was provided from previous process reducing the cost of sequential process. Separately, EC/aeration (inlet COD = 4040 mg/L), PMS/ZVI/UV (inlet COD = 1560 mg/L), and EF (inlet COD = 471 mg/L) removed 61, 69 and 82% of COD respectively. Overall, sequential processes of EC/aeration, PMS/ZVI/UV and EF could remove the COD, TOC and ammonia of the landfill leachate around 98%, 93% and 94%, respectively. The comparison of different sequences of following processes indicated that current configuration (EC/aeration-PMS/ZVI/UV-EF) could meet the discharge standards. Furthermore, humification degree was significantly improved after oxidative processes. Biodegradability study was also performed by means of BOD/COD, average oxidation state (AOS), and Zahn-Wellens test, and the best results associated with these indices were obtained 0.56, 2.37, and over 98%, respectively. Phytotoxicity of leachate was remarkably reduced and the final effluent can be considered as a non-phytotoxic wastewater.

Norfloxacin removal by ultraviolet-activated sodium percarbonate and sodium hypochlorite: process optimization and anion effect

The efficiency of UV-activated sodium percarbonate (SPC) and sodium hypochlorite (SHC) in Norfloxacin (Norf) removal from an aqueous solution was assessed. Control experiments were conducted and the synergistic effect of the UV-SHC and UV-SPC processes were 0.61 and 2.89, respectively. According to the first-order reaction rate constants, the process rates were ranked as UV-SPC > SPC > UV and UV-SHC > SHC > UV. Central composite design was applied to determine the optimum operating conditions for maximum Norf removal. Under optimum conditions (UV-SPC: 1 mg/L initial Norf, 4 mM SPC, pH 3, 50 min; UV-SHC: 1 mg/L initial Norf, 1 mM SHC, pH 7, 8 min), the removal yields for the UV-SPC and UV-SHC were 71.8 and 72.1%, respectively. HCO₃^-, Cl^-, NO₃^-, and SO₄^2- negatively affected both processes. UV-SPC and UV-SHC processes were effective for Norf removal from aqueous solution. Similar removal efficiencies were obtained with both processes; however, this removal efficiency was achieved in a much shorter time and more economically with the UV-SHC process.

Regeneration of granular activated carbon clogged in the treatment of leachates

Landfill leachates are highly contaminated liquids and complex to treat. Two of the processes which are promising for the treatment are the advanced oxidation and adsorption methods. With the combination of the Fenton and adsorption methods, practically all the organic load of leachates can be removed; however, this combination of processes is limited due to the soon clogging of adsorbent material, which leads to high operation costs. In the present work, the results of the regeneration of clogged activated carbon are shown after the application of the Fenton/adsorption process in leachates. This research consisted of four stages: sampling and leachate characterization, clogging of the carbon through the Fenton/adsorption process, carbon regeneration through the oxidative Fenton process, and lastly, evaluation of regenerated carbon adsorption through jar and column tests. In the experiments, HCl 3 M was used, and different concentration of hydrogen peroxide (0.15 M, 0.2 M, 0.25 M) were tested at different times (16 h and 30 h). The activated carbon regeneration through the Fenton process and the optimal peroxide dosage was 0.15 M for 16 h. The regeneration efficiency was obtained from comparing the adsorption efficiency between regenerated and virgin carbon, reaching 98.27% and can be applied up to 4 times without losing regeneration efficiency. These results prove that it is possible to restore the clogged activated carbon adsorption capacity during the Fenton/adsorption process.

Combination of zero-valent aluminum-acid system and electrochemically activated persulfate oxidation for biologically pre-treated leachate nanofiltration concentrate treatment

This study investigated the performance of combined zero-valent aluminum (ZVAl) and electrochemically activated persulfate (PS) oxidation for the leachate nanofiltration concentrate (NFC) treatment. Firstly, operating parameters in the ZVAl procedure were optimized and under the optimum conditions (ZVAl dose 1 g/L, initial pH 1.5) the removal efficiency of the chemical oxygen demand (COD), UV₂₅₄, and color were 22.39%, 29.03%, and 48.26%, respectively. Secondly, the effect of various anode types (Ti/RuO₂, Ti/IrO₂, and Ti/SnO₂) within the electrooxidation (EO) process was evaluated. The Ti/RuO₂ anode was found to be the most effective one in terms of pollutant removal efficiencies and operation cost. The efficiency of single, binary, and hybrid processes was evaluated by control experiments and the results were ranked as PS < ZVAl < ZVAl + PS < EO < EO + PS < EO + ZVAl < EO + ZVAl + PS. In the following part of the study, the Box-Behnken design was preferred to optimize the operating parameters of the hybrid EO + ZVAl + PS process. The COD, UV₂₅₄, and color removal efficiencies under optimum conditions (4.88 mM PS dose, 1.6 A current applied, and 120 min reaction time) were 62.1%, 75.2%, and 99.9%, respectively. The estimated and experimentally obtained data were close to each other. The pollutant removal efficiencies increased in parallel with the current density and reaction time; however, the effect of the PS dose remained at a negligible level. The obtained results indicate the effectiveness of the hybrid EO + ZVAl + PS process for the treatment of leachate nanofiltration concentrate under optimized conditions.

Sulfate radicals-based advanced oxidation processes for the degradation of pharmaceuticals and personal care products: A review on relevant activation mechanisms, performance, and perspectives

Owing to the rapid development of modern industry, a greater number of organic pollutants are discharged into the water matrices. In recent decades, research efforts have focused on developing more effective technologies for the remediation of water containing pharmaceuticals and personal care products (PPCPs). Recently, sulfate radicals-based advanced oxidation processes (SR-AOPs) have been extensively used due to their high oxidizing potential, and effectiveness compared with other AOPs in PPCPs remediation. The present review provides a comprehensive assessment of the different methods such as heat, ultraviolet (UV) light, photo-generated electrons, ultrasound (US), electrochemical, carbon nanomaterials, homogeneous, and heterogeneous catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS). In addition, possible activation mechanisms from the point of radical and non-radical pathways are discussed. Then, biodegradability enhancement and toxicity reduction are highlighted. Comparison with other AOPs and treatment of PPCPs by the integrated process are evaluated as well. Lastly, conclusions and future perspectives on this research topic are elaborated.

Degradation of organic dye wastewater by H2O2-enhanced aluminum carbon micro-electrolysis

In this research, the treatment of methylene blue (MB) dye wastewater by a novel system that combines H₂O₂ with an aluminum-carbon micro-electrolysis (ACE) was explored. The effects of the H₂O₂ amount, initial pH, aluminum to carbon ratio, total aluminum-carbon mass, dye concentration, and reaction temperature on degradation of MB were investigated. The findings revealed that under the following conditions: H₂O₂ 34.0 mg/L, initial pH of 3.0, aluminum-to-carbon ratio of 2:1, total aluminum-carbon mass of 2.0 g/L, MB concentration of 20 mg/L, and 20 °C, the degradation rate of MB could reach 99.3% after 180 min, which is 18.4% more compared with ACE at the same conditions without H₂O₂. Through the quenching experiments, it was proved that the efficient free radicals produced during degradation are •OH and •O₂^-. Finally, a possible mechanism of H₂O₂ enhanced aluminum carbon micro-electrolysis (HP-ACE) for MB degradation was discussed.

Toward rapid reduction of carbon tetrachloride in water by zero-valent aluminum/persulfate system

The oxidation performance of the zero-valent aluminum (ZVAl)/persulfate (PS) combined system had been studied by researchers in the past, which relied on the activation of PS by ZVAl to generate potent oxidizing radicals (•OH and SO₄^•-) to degrade pollutants. However, ZVAl is a strong reductant and its reduction effect cannot be ignored. The reductive performance of the ZVAl/PS combined system is still unknown. Therefore, carbon tetrachloride (CT), an antioxidant organic pollutant, was selected as the target pollutant to test the reductive performance of the ZVAl/PS system in this study. We found a significant synergistic effect between ZVAl and PS, and the ZVAl/PS combined system could rapidly degrade CT in a wide pH range of 3-11 after an induction period. By SEM-EDS, TEM, XPS, and XRD analysis, it was found that PS could promote the corrosion of the oxide film on the ZVAl surface. The quenching experiment proved that PS could accept the electrons released from ZVAl to produce superoxide radical anion (O₂^•-), which led to the degradation of CT rather than the oxidative process by •OH and SO₄^•-. The hydrogen evolution experiment indicated that electronic reduction might play a secondary role in CT degradation. In conclusion, our study further explored the reductive performance of the ZVAl/PS combined system and expanded the pathway of CT degradation without any organic solvent addition, which provides a new strategy for the efficient degradation of refractory halogenated organic pollutants.

Mechanochemically synthesized Al-Fe (oxide) composite with superior reductive performance: Solid-state kinetic processes during ball milling

Recently, mechanical ball milling (BM), a simple and green powder processing method, has been successfully applied to improve the performance of zero-valent metals (ZVMs) for efficient water treatment. However, until now BM is still regarded as a "black box" in which the processes of the solid-state reaction during activation remain unclear. In this paper, firstly, FeSO₄·7H₂O crystal was used to activate and modify inert microscale zero-valent aluminum (mZVAl) by BM to synthesize Al-Fe (oxide)^bm composite that showed superior reactivity in reductive removal of various contaminants and excellent reusability, which may be mainly ascribed to the newly formed iron oxide layer on mZVAl by mechanochemical reaction. At the same time, the formation of iron oxides on mZVAl was closely related to BM parameters. Further kinematic analysis revealed that the occurrence of mechanochemical reaction depended on the impact energy and input energy, which BM speed and BM time were two main factors determining reaction extent on the premise that the precursors were full dose. Moreover, kinetic fitting uncovered the solid-state reaction mechanism between mZVAl and FeSO₄·7H₂O conformed to three-dimensional diffusion and phase boundary reaction models. This study ponders deeply upon the mechanochemical process and solid reaction mechanism during the preparation of Al-Fe (oxide)^bm composite, which deepens comprehensions of material synthesis procedures by BM and promotes applications of ZVM-based composite in polluted water or wastewater treatment.

Sulfamethoxazole degradation by alpha-MnO2/periodate oxidative system: Role of MnO2 crystalline and reactive oxygen species

Pollutant degradation via periodate ([Formula: see text]) and transitional metal oxides provides an economical, energy-efficient way for chemical oxidation process in environmental remediation. However, catalytic activation of periodate by manganese dioxide and the associated mechanism were barely investigated. In this study, four MnO₂ polymorphs (α-, β-, γ- and δ-MnO₂) were synthesized and tested to activate [Formula: see text] for the degradation of sulfamethoxazole (SMX). The reactivity of different MnO₂ structures followed the order of α-MnO₂ > β-MnO₂ > γ-MnO₂ > δ-MnO₂, suggesting that the particular crystalline structure in α-MnO₂ would exhibit higher activities via [Formula: see text] activation. Herein, in α-MnO₂/[Formula: see text] system, 91.1% of SMX was eliminated within 30 min with degradation rate constant of 0.0649 min^-1, and the neutral pH exhibited higher efficiency in SMX degradation compared with acidic and alkaline conditions. Singlet oxygen (¹O₂) was unveiled to be the dominant ROS according to the results of electron paramagnetic resonance, chemical probes and radical quenching experiments, whereas [Formula: see text] and ^•OH were mainly acted as a free-radical precursor. Six oxidation products were identified by LC-MS, and the elimination of sulfonamide bond, hydroxylation and direct oxidation were found to be the important oxidation pathways. The study dedicates to the mechanistic study into periodate activation over alpha-MnO₂ and provides a novel catalytic activation for selective removal in aqueous contaminants.

Advanced oxidation process based on hydroxyl and sulfate radicals to degrade refractory organic pollutants in landfill leachate

As a special type of wastewater produced in the landfill, leachate is mainly composed of organic pollutants, inorganic salts, ammonia nitrogen and heavy metals, and featured by high pollutants concentration, complex composition and large fluctuations in water quality and volume. Biological, chemical and physical methods have been proposed to treat landfill leachate, but much attention has been paid to the advanced oxidation processes (AOPs), due to their high adaptability and organic degradation efficiency. This paper summarizes the recent findings on the AOPs based on hydroxyl radical (OH) (e.g., ozonation and catalyzed ozone oxidations, Fenton and Fenton-like oxidations) and sulfate radical (SO₄^-) (e.g., activated and catalyzed persulfate oxidations), especially the production routes of free radicals and mechanisms of action. When dealing with some special landfill leachates, it is difficult for a single advanced oxidation technology to achieve the expected results, but the synergistic combination with biological or physical methods can produce satisfactory outcomes. Therefore, this paper has summarized the application of these combined treatment technologies on landfill leachate.

Effective degradation of azo dye from textile wastewater by electro-peroxone process

Color-producing chemicals emitted from many sources, such as textile or dye manufacturing industries, are a significant concern worldwide. The present study focuses on the electro-peroxone (EP) process for decolorizing a synthetic azo dye, C.I. Reactive Black 5 (RB5). Findings suggest that the EP process is more effective for dye degradation than ozonation and electrolysis. The EP process resulted in 100% decolorization after 60 min of contact time under optimum testing conditions such as pH 7, applied current 300 mA, and sulfate concentration 3.55 g L^-1. Based on the findings of the primary investigation, EP treatment of real textile effluent was carried out and 2 h of EP treatment resulted in 99% decolorization and 74%total organic carbon (TOC) removal. As an outcome, the EP process can treat textile wastewater in a cost-effective and environmentally friendly manner.

Occurrence of organic micropollutants in municipal landfill leachate and its effective treatment by advanced oxidation processes

Landfilling is the most prominently adopted disposal technique for managing municipal solid waste across the globe. However, the main drawback associated with this method is the generation of leachate from the landfill site. Leachate, a highly concentrated liquid consisting of both organic and inorganic components arises environmental issues as it contaminates the nearby aquifers. Landfill leachate treatment by conventional methods is not preferred as the treatment methods are not much effective to remove these pollutants. Advanced oxidation processes (AOPs) based on both hydroxyl and sulfate radicals could be a promising method to remove the micropollutants completely or convert them to non-toxic compounds. The current review focuses on the occurrence of micropollutants in landfill leachate, their detection methods and removal from landfill leachate using AOPs. Pharmaceuticals and personal care products occur in the range of 10^-1 to more than 100 μg L^-1 whereas phthalates were found below the detectable limit to 384 μg L^-1, pesticides in the order of 10^-1 μg L^-1 and polyaromatic hydrocarbons occur in concentration from 10^-2 to 114.7 μg L^-1. Solid-phase extraction is the most preferred method for extracting micropollutants from leachate and liquid chromatography (LC) - mass spectrophotometer (MS) for detecting the micropollutants. Limited studies have been focused on AOPs as a potential method for the degradation of micropollutants in landfill leachate. The potential of Fenton based techniques, electrochemical AOPs and ozonation are investigated for the removal of micropollutants from leachate whereas the applicability of photocatalysis for the removal of a wide variety of micropollutants from leachate needs in-depth studies.

Optimization of the humic acid separation and coagulation with natural starch by RSM for the removal of COD and colour from stabilized leachate

The removal of concentrated colour (around 5039 Pt-Co) and chemical oxygen demand (COD; around 4142 mg L^-1) from matured landfill leachate through a novel combination of humic acid extraction and coagulation with natural oil palm trunk starch (OPTS) was investigated in this study. Central composite design from response surface methodology of Design Expert-10 software executed the experimental design to correlate experimental factors with desired responses. Analysis of variance developed the quadratic model for four factors (e.g. coagulant dosage, slow mixing speed and time and centrifugation duration) and two responses (% removal of colour, COD). The model confirmed the highest colour (84.96%) and COD (48.84%) removal with a desirability function of 0.836 at the optimum condition of 1.68 g L^-1 coagulant dose, 19.11 rpm slow mixing speed, 16.43 minutes for mixing time and 35.75 minutes for centrifugation duration. Better results of correlation coefficient (R² = 0.98 and 0.96) and predicted R² (0.94 and 0.84) indicates the model significance. Electron microscopic images display the amalgamation of flocs through bridging. Fourier transforms infrared spectra confirmed the existence of selected organic groups in OPTS, which eventually signifies the applied method.

Study on influence factors of treating landfill leachate by ultraviolet-activated persulfate system

In recent years, there have been many studies on treating pollutants with ultraviolet-activated persulfate (UV/PDS) system. In this paper, the biochemical treatment effluent of landfill leachate from garbage incineration power plant was treated. The effect of treating landfill leachate with UV/PDS system in the low-pressure external device and medium-pressure built-in device was compared; it was concluded that in the latter device, the photon quantity increased, the energy loss decreased, and the probability of generating free radicals in the reaction between photons and S₂O₈^2- increased, which result the treatment efficiency of this system was higher. In addition, the leachate was treated by combining the activation method of spinel composite (CuO-MgAl₂O₄) with UV activation method, called CuO-MgAl₂O₄/UV/PDS. The experimental data showed that the processing effect of segmented dosing PDS process was higher than that of one-time addition process. Under the same conditions, the removal rates of CODcr were 83.10% and 19.76%, respectively. One of the reasons for this result may be that excessive PDS in CuO-MgAl₂O₄/PDS system of the latter process inhibited the treatment effect. This paper analyzes the efficiency of UV/PDS system, as well as CuO-MgAl₂O₄/UV/PDS combination process which were used to treat landfill leachate under different conditions; the results showed that the medium-pressure built-in device and segmented-dosing process could get better treatment effect.

Landfill leachate treatment by persulphate related advanced oxidation technologies

Landfill leachate is produced from garbage decomposition with highly toxic and bio-refractory compounds, which poses serious harm to environmental security and human health. Thus, it is urgent to treat landfill leachate properly. Persulfate (PS) oxidation has attracted extensive attentions in terms of fast reaction speed, non-selectivity to target pollutants and thorough oxidation. In recent years, PS oxidation has been widely adopted for landfill leachate purification. However, the related results have been rarely summarized. In this review, the treatment of landfill leachate by PS oxidation system is discussed systematically including oxidants, activation modes and oxidation mechanisms. In addition, the current situation of PS oxidation system and other coupled systems for landfill leachate treatment is also summarized. Finally, the challenges and future research directions of landfill leachate treatment based on PS oxidation process are proposed. Meaningfully, this review will provide valuable references for the development of landfill leachate treatment process, promoting the application of advanced oxidation technology in landfill leachate treatment.

Electrochemical activation of peroxides for treatment of contaminated water with landfill leachate: Efficacy, toxicity and biodegradability evaluation

Contaminated water with landfill leachate (CWLL) with high salinity and high organic content (total organic carbon (TOC) = 649 mg/L and Chemical Oxygen Demand (COD) = 1175 mg/L) is a toxic and non-biodegradable effluent. The present research aimed to assess the treatment effectiveness of CWLL by electrocoagulation (EC)/oxidant process. The ferrous ions generated during the process were employed as coagulant and catalyst for the activation of different oxidants such as peroxymonosulfate (PMS), peroxydisulfate (PDS), hydrogen peroxide (HP), and percarbonate (PC) to decrease TOC in CWLL. Removal of ammonia, color, phosphorous, and chemical oxygen demand (COD) from CWLL effluent was explored at various processes. EC/HP had the best performance (∼73%) in mineralization of organic pollutants compared to others under the condition of pH 6.8, applied current of 200 mA, oxidant dosage of 6 mM, and time of 80 min. The oxidation priority was to follow this order: EC/HP > EC/PMS > EC/PDS > EC/PC. These processes enhanced the biodegradability of CWLL based on the average oxidation state and biochemical oxygen demand (BOD)/COD ratio. SUVA₂₅₄ and E₂/E₃ indices were also investigated on obtained effluents. The phytotoxicity evaluation was carried out based on the germination index, indicating that the electro-activated oxidant was an effective system to reduce the toxicity of polluted waters. EC/HP showed supremacy compared to others in terms of efficiency, cost, and detoxification. Therefore, the electro-activated oxidant system is a good means for removing organic pollutants from real wastewater.

A review of the characteristics of Fenton and ozonation systems in landfill leachate treatment

The development and application of Fenton and ozonation systems in landfill leachate treatment over the last 20 years, and the current research status are reviewed in this paper, with an emphasis on the technical and economic characteristics of Fenton and ozonation systems used to treat different types of landfill leachate. To date, a total of 101 and 78 articles have been published regarding leachate treatment by Fenton and ozonation systems, respectively. These articles considered the use of two systems to treat aged leachate, biologically treated leachate and leachate comprising the concentrated solution resulting from reverse osmosis (RO). The oxidization mechanisms of the two systems used to treat landfill leachate significantly differed in terms of their optimal process parameters (e.g., initial pH value, reagent dosage, and reaction time) and removal efficiency. The Fenton and ozonation systems outperformed persulfate-based advanced oxidation technology in terms of their improved biodegradability of landfill leachate and engineering practicability. The cost of the reagents required to treat landfill leachate by Fenton and ozonation systems accounted for at least 85% of the total operating cost. In contrast to the ozonation system, the Fenton system was more cost-effective when both systems were used to treat the same type of landfill leachate. This study provides a theoretical basis for the operation of Fenton and ozonation systems and also offers technical support for landfill leachate disposal companies that opt to use these technologies.

Promoted oxidation of polycyclic aromatic hydrocarbons in soils by dual persulfate/calcium peroxide system

In situ chemical oxidations (ISCO) have been demonstrated as effective ways for remediating soils contaminated with organic pollutants by complete mineralization. This work aims to develop a technology for the oxidation remediation of soils contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) using a dual calcium peroxide (CP)/persulfate (PS) oxidant system activated by oxalic acid (OA)-chelating Fe²⁺. The dual peroxide system was set up, and the effects of 5 single factors (i.e., CP dosage, PS dosage, Fe²⁺ dosage, OA concentration, and soil/water ratio) on PAHs degradation were studied using the single-factor experiment. The response surface method was then introduced to obtain the optimized experimental conditions (CP dosage, PS dosage, OA concentration) of the dual peroxide system. The result shows that the dual peroxide system significantly increased the PAHs degradation and the maximum PAHs degradation efficiency (70.8%) was achieved by the dual peroxide system under optimal conditions (PS dosage, CP concentration, Fe²⁺/PS ratio, and Fe²⁺/OA ratio was 8.89 g/kg, 0.18 mol/L, 1/4 and 0.62) at neutral soil condition. This study is an illustration of the promising efficiency of the dual peroxide system for PAH oxidation in the neutral soil and has great potential for remediation of PAHs contaminated farmland soils.

Iron-based persulfate activation process for environmental decontamination in water and soil

Sulfate radical based advanced oxidation processes have been extensively studied for the degradation of environmental contaminants. Iron-based materials such as ferrous, ferric, ZVI, iron oxides, sulfides etc., and various natural iron minerals have been explored for activating persulfate to generate sulfate radicals. In this review, an overview of different iron activated persulfate systems and their application in the removal of organic pollutants and metals in water and soil are summarised. The chemistry behind the activation of persulfate by homogenous and heterogeneous iron-based materials with/without the assistance of electrochemical techniques are also discussed. Besides, the soil decontamination by iron persulfate system and a brief discussion on the ability of the persulfate system to reduce metals presence in wastewater are also summarised. Finally, future research prospects, believed to be useful for all researchers in this field, based on up to date research progress is also given.

A novel Co(OH)2/Cu2O nanocomposite-activated peroxydisulfate for the enhanced degradation of tetracycline

Football like Co(OH)2/Cu2O nanospheres were developed and used as efficient catalysts in the catalytic system of PDS activation for environmental protection.

Microbial response during treatment of different types of landfill leachate in a semi-aerobic aged refuse biofilter

In this research, for the first time, three kinds of landfill leachate (young (YL), mature (ML) and mixed (MYL) leachate) were treated in a semi-aerobic aged refuse biofilter (SAARB) to compare the effectiveness of, and microbial changes in, this biofilter when treating leachates that have significantly different characteristics. The SAARB achieved stable removal of organic matter from all three leachates and reduced the concentrations of aromatic substances. The best treatment was achieved with YL, followed in order by MYL and ML. The removal of nitrogen from all three leachates by the SAARB was particularly significant. The microbial abundance and diversity in the media of the SAARB changed after treatment of the three leachates, and the order of change from small to large was ML# < MYL# < YL#. The microbial communities were mainly affected by (and negatively correlated to) the relative content of refractory organics in leachate. Proteobacteria was the dominant microorganism. Deinococcus-thermus responded most to the quality of leachate being treated, increasing in relative abundance as the content of refractory organics increased. This was opposite to the response of Chloroflexi. In YL# the dominant species at the genus level was Thauera, and in ML# the dominant species were Truepera and Iodidimonas. The microbial activity and metabolic intensity were enhanced after treatment of the different leachates. The expression of nitrification-related genes was the strongest and the total abundance was the highest when YL was treated. This study promotes the optimization and application of SAARB.