Organics In Leachate Research Articles

Unveiling the transformation of organics in leachate during the composite anode-supported electro-hybrid ozonation-coagulation (CA-E-HOC) treatment: Significance of synergy among chlorine, coagulant, and ozone

Ozone and its advanced oxidation processes are commonly used to remove organics from leachate because of their high efficiency in eliminating toxic and resistant compounds. However, the mechanisms underlying the transformations of these organic compounds remain unclear. This study aimed to investigate the organic transformation during the composite anode (CA)-supported electro-hybrid ozonation-coagulation (CA-E-HOC) treatment of leachate, where chlorine and coagulants were coproduced on CA for ozone activation, to gain a deeper understanding of the synergistic effects when chlorine, coagulant, and ozone are simultaneously present within a single unit for leachate treatment. Reactive oxygen species and reactive chlorine species in the CA-E-HOC facilitated the degradation of unsaturated and aromatic compounds into hydrophilic organic chains or mineralisation to CO2/H2O. The aromatic carbon (C=C) and long-chain aliphatic carbon (C-C) are converted to carbonyl carbon (O-C=O), which is easily degraded by microorganisms during the subsequent treatment process. The reactive chlorine species and ozone molecules transform CHOS into CHO through −S and −SH2, whereas •OH converts CHNOS into CHNO. The enriched CHO substances were further converted into saturated fatty acids and carbohydrates through oxidation reactions (+O), making them more susceptible to conversion into CO2 and H2O by interacting with •OH and Cl•/ClO•, ultimately resulting in organic mineralisation. This study contributes to a better understanding of molecular changes in organics during leachate treatment using the CA-E-HOC process, with potential implications for practical applications.

Using landfill leachate to indicate the chemical and biochemical activities in elevated temperature landfills

Landfill leachate properties contain important information and can be a unique indicator for the chemical and biochemical activities in landfills. In the recent decade, more landfills are experiencing elevated temperature, causing an imbalance in the decomposition of solid waste and affecting the properties of the landfill leachate. This study analyzes the properties of leachate from two landfills that were experiencing elevated temperature (ETLFs), samples were collected from both elevated temperature impacted and non-impacted areas in each landfill. The accumulation of volatile fatty acids (VFA) in leachates from elevated temperature impacted areas of both landfill sites revealed that methanogenesis was inhibited by the elevated temperature, which was further confirmed by the more acidic pH, higher H/C elemental ratio, and lower degree of aromaticity of the elevated temperature impacted leachates. Also, carbohydrates depletion indicated possible enhancement of hydrolysis and acidogenesis by elevated temperature, which was supported by compositional comparison of isolated acidic species by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) at 21 T derived from both elevated temperature impacted and non-impacted areas in the same landfill site. Furthermore, leachate organics fractionation showed that leachates not impacted by elevated temperature contain less hydrophilic fraction and more humic fraction than elevated temperature-impacted leachates for both ETLFs.

Sludge-derived iron-carbon material enhancing the removal of refractory organics in landfill leachate: Characteristics optimization, removal mechanism, and molecular-level investigation

Mature landfill leachate is a refractory organic wastewater, and needs physical and chemical pretreatments contemporaneously, e.g. iron-carbon micro-electrolysis (IC-ME). In this study, a novel iron-carbon (Fe-C) material was synthesized from waste activated sludge to be utilized in IC-ME for landfill leachate treatment. The pyrolysis temperature, mass ratio of iron to carbon, and solid-liquid ratio in leachate treatment were optimized as 900 °C with 1.59 and 34.7 g/L. Under these optimal conditions, the chemical oxygen demand (COD) removal efficiency reached 79.44 %, which was 2.6 times higher than that of commercial Fe-C material (30.1%). This excellent COD removal performance was indicated to a better mesoporous structure, and uniform distribution of zero-valent iron in novel Fe-C material derived from sludge. The contribution order of COD removal in IC-ME treatment for landfill leachate was proven as coagulation, adsorption, and redox effects by a contrast experiment. The removal of COD includes synthetic organic compounds, e.g. carcinogens, pharmaceuticals and personal care products. The contents of CHO, CHON, and CHOS compounds of dissolved organic matter (DOM) in the leachate were decreased, and both the molecular weight and unsaturation of lipids, lignin, and tannic acids concentration were also reduced. Some newly generated small molecular DOM in the treated leachate further confirmed the existence of the redox effect to degrade DOM in leachate. The total cost of sludge-derived Fe-C material was only USD$ 152.8/t, which could save 76% of total compared with that of commercial Fe-C materials. This study expands the prominent source of Fe-C materials with excellent performance, and deepens the understanding of its application for leachate treatment.

Garbage enzyme-mediated treatment of landfill leachate: A sustainable approach

The study evaluates the soluble chemical oxygen demand (sCOD) removal efficiency from landfill leachate by treating it with four different garbage enzymes at two temperatures (room temperature 27 ± 3 °C and higher temperature 42 ± 3 °C). The four different garbage enzymes were prepared by fermenting fruit peels such as pineapple, banana, orange, and lemon peels and treated with landfill leachate at different mixing ratios of 5%, 10%, 15% and 20%. The results show that garbage enzymes made from orange (10%) and lemon (15%) have maximum sCOD reduction of 68.24% and 67.89%, respectively, at room temperature. The maximum solubilization was found in the pineapple and lemon garbage enzyme at 5% concentration. The samples kept at room temperature showed better solubilization and sCOD removal compared to the samples at higher temperatures. The study demonstrates that the garbage enzyme could be used to increase the bioavailability of organics in leachate.

Coagulation Combined with Electro-Fe0/H2O2 Reaction for Effective Treatment of Landfill Leachate Effluent of Membrane Bioreactor

In this study, coagulation combined with the electro-Fe0/H2O2 reaction was developed to treat refractory organics in the landfill leachate effluent of a membrane bioreactor (MBR), and the change in biodegradability was investigated. The results showed that polymerized ferric sulfate (PFS) was the best coagulant, with removal efficiencies of chemical oxygen demand (COD) and chromaticity of 74.18% and 72.22%, respectively, when the dosage was 2 g/L and the initial pH (pH0) was 6. Under the optimal conditions of pH0 of 3, current density of 5 mA/cm2, Fe0 dosage of 3 g/L, and H2O2 dosage of 0.059 M, the electro-Fe0/H2O2 reaction showed the removal efficiencies of COD and chromaticity for coagulated effluent were 76.68% and 74%, respectively. UV-vis and 3D-EEM spectral analysis showed that humic and fulvic acids were effectively degraded, and the effluent was mostly small molecules of aromatic protein-like substances. The whole process increased the BOD5/COD from 0.049 to 0.46, indicating that the biodegradability was substantially improved. This is due to the conjunction of the Fe0/H2O2 reaction with electrochemistry, which accelerated the reduction of Fe3+ to Fe2+ on the Fe0 surface and cathode and improved the efficiency of hydroxyl radical (•OH) generation, thus promoting the removal of pollutants. The operating cost was only 4.18 $/m3, with the benefits of less Fe0 loss and no pH adjustment. In summary, coagulation combined with the electro-Fe0/H2O2 reaction is a cost-effective method for treating refractory organics in leachate and enhancing biodegradability.

Comparative study on the treatment of refractory organics in landfill leachate by homogeneous and heterogeneous Fenton advanced oxidation processes.

With the advancement of the landfill stabilization process of municipal solid waste, landfill leachate containing a large amount of refractory organic matter is formed. In this study, homogeneous Fenton and heterogeneous Fenton-like (activation by zero valent iron (Fe0), pyrite (FeS2) and magnetite (Fe3O4) as solid iron materials) processes have been compared for the removal of refractory organics from landfill leachate. The removal efficiency of organics in the Fenton process was slightly higher than those in the Fenton-like processes. The removal efficiencies based on total organic carbon, UV absorbance at 254 nm (UV254) and colour number in the Fenton process were as high as 57.42%, 71.63% and 81.03%, respectively. In the Fenton-like processes, the Fe0/H2O2 process achieved 35.74%, 66.24% and 86.29% removal efficiencies, respectively. Moreover, the degradation effect on refractory organic substances proved to be better. In the Fenton-like processes, the activation mechanisms with Fe0 and FeS2 involve the homogeneous activation of Fe2+ in solution and heterogeneous activation of iron oxides produced during the reaction, respectively. With Fe3O4, the activation mechanism is mainly a heterogeneous process involving its intrinsic iron oxide constituents. This study may provide a theoretical basis for the treatment of refractory organics in landfill leachate.

Advanced Reduction Processes for Degradation of Refractory Organics in Landfill Leachate

Hydroxyl radicals generated from advanced oxidation processes (AOPs) are broadly applied to mitigation of refractory organics in landfill leachate. However, following treatment by AOPs, the wastewater still contains highly oxidized organics that are recalcitrant to further chemical oxidation, thereby providing a challenge to established wastewater-treatment technologies. This study aimed to validate whether advanced reduction processes (ARPs), an emerging chemical degradation process driven by highly reductive hydrated electrons (eaq−), can effectively decompose persistent and complex organics in a Fenton pretreated landfill leachate. Results showed that ARPs poorly cleave C-C bonds in the Fenton pretreated leachate organic matter (LOM) due to low reactivity of the mixed organics toward eaq−. However, eaq− and ultraviolet (UV) irradiation during the ARP treatment could attack certain chromophores to reduce UV254 absorbance by 53%. The transformation particularly occurred to the low-molecular-weight (<10 kDa) and hydrophobic LOM fractions. Meanwhile, the carboxylic content declined after the ARP treatment, whereas the phenolic concentration remained constant, suggesting that eaq− principally reacted with electron withdrawing groups rather than electron donating moieties on the Fenton pretreated LOM. This study highlights that ARPs can serve as a promising post-treatment after AOPs for treatment of refractory organic wastes in landfill leachate.

A Combined Catalytic Ozonation-MBR Approach to Remove Contaminants from the Mature Landfill Leachate in the Yellow River Basin.

The mature landfill leachate (MLL) is characterized by a large number of fulvic acids and humic acids, which is refractory organic matter and can be cleaned by ozone oxidation. However, the poor property of mass transfer prohibits the widespread use of ozone oxidation in actual leachate treatment. Meanwhile, some combined processes are adopted to treat the mature landfill leachate, which places catalytic ozonation before the membrane bioreactor (MBR) process to enhance the biodegradability of MLL. Thus, this research is conducted to investigate the practicability of applying nano-Fe3O4 loaded cow-dung ash (Fe3O4@CDA) and biological post-treatment with MBR for the effective removal of pollutants from MLL and puts forward the variation of organics in leachate between catalytic ozonation and MBR. The addition of catalytic ozonation not only improved the removal of hazardous organics but also enhanced the biodegradability of the leachate and favored the subsequent MBR process. Chemical oxygen demand (COD) removal in the catalytic ozonation step was optimized, and 53% removal was obtained at pH = 7, catalyst dosage = 1.0 g/L, and O3 dosage = 3.0 g/L. After the MBR process, COD in effluent stabilized in the range of 57.85–65.38 mg/L, and the variation range of the ammonia nitrogen (NH3-N) concentration was 5.98–10.24 mg/L. The catalytic ozonation-MBR integrated process showed strong feasibility in dealing with the biologically pre-treated leachate.

Investigation on characteristics of landfill leachate and feasibility study of low-temperature vacuum evaporation treatment

Leachate is characterized by poor biochemical properties and complex organic matter, which is potentially harmful to the surrounding environment. Low-temperature vacuum evaporation have been intensively studied for leachate treatment, but less attention was paid to monitoring the evolution of leachate organics. In order to analyze the component characteristics (especially organic matter) of typical landfill leachate and the feasibility of low-temperature vacuum evaporation process, fluorescence Excitation Emission Matrix (EEM) measurement coupling with Parallel Factor Analysis (PARAFAC) analysis and GC-MS was used to supplement the routine monitoring in order to reveal more insights into pollutants removal during the leachate treatment. The results showed that the main organic matter of landfill leachate was humic-like organic compounds, which accounted for 75–81%. The GC-MS showed that long-chain hydrocarbons, aromatic, aldehydes and esters compounds were abundant in the raw leachates. However, the humus and protein-based organic matter could be separated in a short time through low-temperature vacuum evaporation process, and the content of protein-based organic matter in condensate could be almost 100%, thus the biochemical properties were improved. The original CC, CO, C-N, C-O-C and other groups in the raw leachate were all disappeared after the low-temperature vacuum evaporation process, which was the essential reason for the transformation of fluorophores and improvement of biochemical properties.

Persulfate-enhanced continuous flow three-dimensional electrode dynamic reactor for treatment of landfill leachate

Compared with sequencing batch reactor, continuous flow dynamic reactors are more conducive to promotion and application. In this study, the ability of a three-dimensional (3D) electrode dynamic reactor to remove pollutants in the landfill leachate was investigated, in which landfill leachate entered through continuous flow. Either increased of current density or the decreased of flow rate was conducive to the removal of pollutants. The optimal process parameters for current density and flow rate were 16 mA cm−2 and 0.75 L h−1, respectively. When the current density was constant at 16 mA cm−2 and the flow rate was kept at 0.75 L h−1, 60.02% of total organic carbon (TOC), 96.50% of chroma, 64.98% of chemical oxygen demand (COD) and 99.46% of ammonia nitrogen (NH3–N) were removed. The characteristic peaks of refractory organic pollutants were reduced by 97.95%. After the reaction, the biological oxygen demand (BOD)/COD was increased from 0.24 to 0.32. As one of the emerging trace organics in landfill leachate, 85.90% of ibuprofen (IBU) was removed. The results showed that the 3D electrode dynamic reactor constructed in this study could reduce the TOC, refractory trace organic pollutant, NH3–N and chroma in the landfill leachate. The 3D electrode dynamic reactor constructed in this research has application potential in the field of landfill leachate treatment.

Hydrogen peroxide and peroxymonosulfate intensifying Fe−doped NiC−Al2O3−framework−based catalytic ozonation for advanced treatment of landfill leachate: Performance and mechanisms

The biotreated effluent of landfill leachate still contains numerous refractory organic contaminants, which poses potential threats to human health and ecosystems. Influenced by landfill ages and other factors, the concentration of organic matter varies. Heterogeneous catalytic ozonation (HCO) is a promising technology for advanced wastewater treatment. Aiming to achieve the up−to−standard discharge of low−concentration landfill leachate (COD ≈ 108 mg·L−1) and improve the biodegradability of high−concentration landfill leachate (COD ≈ 1720 mg·L−1), the active component Fe was incorporated into a firm Ni−induced C−Al2O3−framework (NiCAF) composite support to synthesize a Fe−NiCAF catalyst for efficient catalytic ozonation. When the Fe−NiCAF dosage was 4 g·L−1, the gas flow rate was 0.5 L·min−1, and the ozone concentration was 20.0 mg·L−1, the COD of low−concentration landfill leachate effluent decreased to 43 mg·L−1, and the COD removal rate constant of low−concentration landfill leachate was 154% higher than that of pure ozone. For high−concentration landfill leachate with the BOD5/COD of 0.058, the COD removal efficiency in Fe−NiCAF/O3 increased from 39% to 57% compared with ozonation, and the effluent BOD5/COD increased to 0.282. Furthermore, the addition of hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) can further enhance the treatment performance of Fe−NiCAF/O3 process and different strengthening mechanisms were revealed. The results indicated that surface hydroxyls on the Fe−NiCAF catalyst surface were the main catalytic sites for ozone, and hydroxyl radical (•OH) and singlet oxygen (1O2) were identified as the main reactive oxygen species for the removal of organics in landfill leachate. Adding H2O2 can promote the generation of •OH for nonselective degradation of various organics, while PMS mainly enhanced the production of 1O2 to decompose macromolecular humus. This work highlighted an efficient Fe−NiCAF ozone catalyst and an innovative peroxide intensified HCO strategy for the advanced treatment of landfill leachate.

Ozone-based advanced oxidation of biologically treated landfill leachate: Oxidation efficiency, mechanisms, and surrogate-based monitoring for bulk organics

Landfill leachate effluent obtained from partial nitrification-Anammox (PNA) biological treatment still contains various recalcitrant organics. In this study, ozone-based oxidation processes (O3 and O3/H2O2) were applied to treat PNA leachate effluent. The oxidation efficiency and mechanisms were investigated by measuring chemical oxygen demand (COD), biochemical oxygen demand (BOD5), molecular size, fluorescence, UV–vis absorbance, and electron-donating capacity (EDC). Given the challenge of efficient ozone dosing, a surrogate-based monitoring approach was proposed and evaluated. Results show that leachate variability caused significant variation in the ozone utilization efficiency (O3E) for COD removal. The O3E of O3 and O3/H2O2 ranged between 0.32 and 0.47 mgCOD/mgO3, and between 0.43 and 0.73 mgCOD/mgO3, respectively. Compared to O3, O3/H2O2 was more effective to remove COD, to degrade the high molecular fraction, and to enhance biodegradability. The two-stage pseudo-first-order model (R2 > 0.90) can well describe the degradation of COD, fluorophores, UVA330, UVA254, and EDC during O3 and O3/H2O2 treatment, and the degradation rate can be ordered as follows: fluorophores > UVA330 > EDC > UVA254 > COD. Particularly, COD reduction was correlated well with surrogate reductions (i.e., fluorophores, UVA330, EDC, and UVA254) in an exponential function (R2 > 0.90), while exhibiting different steepness depending on the degradation kinetics of surrogates. The increased BOD5 showed a trend from rising and decline when presented as a function as surrogate reductions. The above correlations demonstrate the potential of surrogates to replace the conventional parameters for oxidation optimization and control. Overall, this research enriches the knowledge in the oxidation of recalcitrant organics in leachate and provides a reference for efficient ozone dosing.

Removal of nitrogen components, bulk organics, and fluorophores during one-stage partial nitrification-Anammox treatment of landfill leachate

Anammox-based processes have been intensively studied for the nitrogen removal from leachate, but less attention was paid to monitoring the evolution of leachate organics. In this study, fluorescence Excitation-Emission Matrix (EEM) measurement coupling with Parallel Factor Analysis (PARAFAC) analysis was used to supplement the routine monitoring in order to reveal more insights into pollutants removal during the leachate treatment by a one-stage partial nitrification-Anammox process (PNA). During this PNA process, up to 96% of total nitrogen and 43% of COD were removed, indicating the potential of PNA process to simultaneously remove nitrogen and organics. Fluorescence intensities and ratios clearly showed the dynamics of influent fluorophores during seasonal variations, where a high amount of protein-like compound was observed during summer months. Protein-like compound was preferentially removed (43–63%) in the PNA process, whereas humic/fulvic-like compounds exhibited recalcitrance to biodegradation. The increase of oxygen supply promoted protein-like compound degradation, which could be associated with the aerobic oxidation pathway. Furthermore, the protein-like compound removal was linearly correlated with the reduction of NH4+-N at limited oxygen conditions (i.e., air flow rate ≤1.6 Lgas/h/Lreactor) (r = 0.97, n = 65). The fluorescence directly extracted at Ex/Em:230 nm/345 nm was strongly correlated with the biodegradable chemical oxidation demand (BCOD) (r = 0.92, n = 204), showing its high potential as an indicator for biodegradable organics. Given the relatively weak correlation between fluorescence parameters and COD, EEM coupled with multivariate partial least squares (PLS) modeling was proposed and exhibited good predictive power for COD, as exemplified by a mean error of 4.5%.

Enhanced in-situ electro-generation of H2O2 using PTFE and NH4HCO3 modified C/PTFE electrode for treatment of landfill leachate

In this study, the carbon black/polytetrafluoroethylene (C/PTFE) electrode was prepared under the best conditions, and then it was modified by PTFE and NH4HCO3 to make a PTFE-C/PTFE electrode. PTFE-C/PTFE electrode was used to enhance H2O2 in-situ electro-generation and the electro-peroxone process (EPP) treatment of leachate. Various analytical methods results were applied to prove that the PTFE-C/PTFE electrode greatly improved the performance of H2O2 generation and electrode stability. The effects of initial pH, current intensity, ozone flow and Cl− concentration on the removal of NH4+ and chemical oxygen demand (COD) from landfill leachate were studied in the EPP with PTFE-C/PTFE as cathode (MEPP) by one factor at a time (OFAT) method. The initial pH value 7.5, current intensity 300 mA, ozone flow 875 mg/h and Cl− concentration value 4198 mg/L were selected as the best operating parameters. A response surface methodology based on box-behnken design (BBD) was employed to optimize running conditions of the MEPP of leachate. After optimization, Mineralization efficiency of the NH4+ and COD was obtained to be 79.83% and 52.14%, and biochemical oxygen demand (BOD5)/COD ratio increased to 0.38 after 4 h. The removal curves of NH4+ and COD in the MEPP conforms to the zero-order and first-order reaction kinetics, respectively. Three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) analysis shows that MEPP has a good removal effect on organics in leachate. Energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis were carried out for the cathode sediment, which was mainly magnesium ion silicate precipitation and NaCl.

Degradation of refractory organics in pre-coagulated leachate concentrate using the Fenton process: optimization through response surface methodology

Degradation of refractory organics in pre-coagulated leachate concentrate using the Fenton process: optimization through response surface methodology

Solidification/Stabilization of Textile Sludge as Subgrade: Usage of Binders and Skeleton Material

This study investigates the disposal of textile sludge via laboratory and field tests while protecting the eco-environment. Solidification/stabilization (S/S) technology and skeleton construction method are introduced to investigate the application of S/S sludge for subgrade material. S/S is to enhance the sludge strength and stabilize the metal(loid)s and hazardous organics in the textile sludge. Skeleton construction method aims to decrease the liquid-solid ratio in mixture to reduce the binder dosage and save binder cost. In the laboratory, binders and skeleton material are implemented to investigate the differences in unconfined compressive strength (UCS) to explore the optimal mixture. Results illustrate that UCS of binder-sludge is below 100 kPa and enhanced more than 400 kPa after adding gypsum and skeleton material. Skeleton soil material with high plasticity index and low moisture content improves UCS significantly. Scanning electron microscopy test shows the physical microstructure of sludge is greatly improved for the particular space grid structure formed by the particles and cementitious products. The leaching test shows the metal(loid)s and organics in leachate are decreased after S/S treatment and below the standard value. Finally, the textile sludge was disposed for subgrade via the technology. The strength and leaching results of field tests are in good agreement with the laboratory results. The bearing capacity of the practical subgrade meets the design requirements.

Molecular-level transformation characteristics of refractory organics in landfill leachate during ozonation treatment

Macromolecular refractory organics in landfill leachate are extremely complex compounds. This study examined the molecular-level transformation characteristics of refractory organics in biologically-treated landfill leachate (i.e., membrane bioreactor (MBR) leachate) during ozonation treatment. Results indicated that higher ozone dosage and longer reaction time enhanced organics removal. When ozone dosage was 32.16 mg/min and reaction time was 30 min, the efficiencies of removing color number, chemical oxygen demand (COD), and dissolved organic carbon (DOC) were 95.16%, 51.13%, and 26.40%, respectively. Furthermore COD / DOC decreased from 3.38 to 2.24, and the content of aromatic substances and macromolecular humic substances (e.g., humic- and fulvic-like substances) substantially decreased. The MBR-treated leachate mainly contained phenolic compounds (82%, aromatic index ≤ 0.50 and H/C < 1.5), and the major elements within the dissolved organic matter in the MBR-treated leachate were C, H, O, N, and S. The CHOS and CHONS compounds in the leachate indicated that it would have a much greater biorefractory property than the natural organic matter (i.e., technical grade humic acid). After the MBR-treated leachate was treated by ozonation for 10 min, the CHO, CHON, CHOS and CHONS compounds were greatly degraded and removed, and the oxidation degree of dissolved organic matter was significantly increased owing to the strong oxidation ability of ozone. At 30 min of ozonation, CHON, CHOS and CHONS compounds were further degraded, and CHOS and CHONS compounds (as the biorefractory substances) were almost completely removed. It was noteworthy that some CHO compounds that mainly contained phenolic compounds (m/z = 250–300, carbon number > 20, and double bond equivalent < 6) with a higher bioavailability and higher saturation degree accumulated. This study provides beneficial references for practical application of landfill leachate treatment using the ozonation process.

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.

Degradation of refractory organics in concentrated leachate by the Fenton process: Central composite design for process optimization

The primary aim of this study is inert COD removal from leachate nanofiltration concentrate because of its high concentration of resistant organic pollutants. Within this framework, this study focuses on the treatability of leachate nanofiltration concentrate through Fenton oxidation and optimization of process parameters to reach the maximum pollutant removal by using response surface methodology (RSM). Initial pH, Fe2+ concentration, H2O2/Fe2+ molar ratio and oxidation time are selected as the independent variables, whereas total COD, color, inert COD and UV254 removal are selected as the responses. According to the ANOVA results, the R2 values of all responses are found to be over 95%. Under the optimum conditions determined by the model (pH: 3.99, Fe2+: 150 mmol/L, H2O2/Fe2+: 3.27 and oxidation time: 84.8 min), the maximum COD removal efficiency is determined as 91.4% by the model. The color, inert COD and UV254 removal efficiencies are determined to be 99.9%, 97.2% and 99.5%, respectively, by the model, whereas the total COD, color, inert COD and UV254 removal efficiencies are found respectively to be 90%, 96.5%, 95.3% and 97.2%, experimentally under the optimum operating conditions. The Fenton process improves the biodegradability of the leachate NF concentrate, increasing the BOD5/COD ratio from the value of 0.04 to the value of 0.4. The operational cost of the process is calculated to be 0.238 €/g CODremoved. The results indicate that the Fenton oxidation process is an efficient and economical technology in improvement of the biological degradability of leachate nanofiltration concentrate and in removal of resistant organic pollutants.

Molecular-level insights into the transformation mechanism for refractory organics in landfill leachate when using a combined semi-aerobic aged refuse biofilter and chemical oxidation process

Landfill leachate contains high concentrations of complex organic matter (OM) that can severely impact the ecological environment. If landfill leachate is to be treated using a combined “biological + advanced treatment” process, the molecular information of OM must be investigated to optimize the operation parameters of the combined process and maximize the removal of organic pollutants. This study applied ultra-high resolution mass spectroscopy to investigate the degradation and transformation characteristics of refractory OM in mature landfill leachate at the molecular level (m/z = 150–800) during biological treatment (i.e., semi-aerobic aged refuse biofilter, SAARB) and subsequent chemical oxidation (i.e., the Fenton process and ozonation). After SAARB treatment, the polycyclic aromatics (aromatic index, AI > 0.66) and polyphenol (0.66 ≥ AI > 0.50) contents increased, and the highly unsaturated phenolic compounds (AI ≤ 0.50 and H/C < 1.5), which have a high bioavailability, were mostly removed. Compared with raw leachate, SAARB effluent (i.e., SAARB leachate) contained fewer organics with short carbon chains, more organics with long carbon chains, an elevated condensation degree for organics and, thus, a considerably reduced biodegradability. Although both the Fenton and ozonation processes could remove many of the polycyclic aromatics and polyphenols, ozone produced considerable amounts of aliphatic compounds with high bioavailability. Compared to ozonation, the Fenton process utilized the hydroxyl radical to non-selectively react with OM and produced better mineralization results.