Investigation on characteristics of leachate and concentrated leachate in three landfill leachate treatment plants

Investigation of the characteristics of concentrated leachate from six municipal solid waste incineration power plants in China

The characteristics of concentrated leachate in municipal solid waste (MSW) incineration power plants were analyzed for CODCr, BOD5, the concentration of heavy metals, and spectral characteristics of dissolved organic matter (DOM). We performed correlation-principal component analysis to analyze the data. The samples were collected from leachate treatment plants of six MSW incineration power plants in China, all of which have a typical treatment process. Our study showed that the samples have high content of organic matter with extremely low biodegradability, various heavy metals, and a large amount of negative ions such as Cl-, SO4 2- and PO4 3- in the concentrated leachate. The intense fluorescent absorption peaks in the visible and ultraviolet regions of the ultraviolet-visible spectra and three-dimensional fluorescence spectra suggest that the concentrated leachate contains a large amount of refractory organic matter mainly consisting of fulvic acid. The humification indexes (HIX) of samples ranged from 1.26 to 14.24 when the biodegradability indexes (BIX) ranged from 0.10 to 2.25. Correlation analysis revealed that the concentration of Cl-, PO4 3-, and NO3 - is significantly correlated with the property of the DOM, and the concentration of Ca, Cr, and SO4 2- almost has no correlation with other indicators in the concentrated leachate. The characteristics of the concentrated leachate are reflected by three principal components: PC1 is mainly related to the DOM, which is relatively stable and hardly degrades, this component may reflect the degradability and humification degree of the concentrated leachate. PC2 reflects the degradability of the concentrated leachate; a higher score in its positive direction indicates greater degradability of the concentrated leachate. PC3 has little influence on the characteristics of the concentrated leachate. This research can provide a theoretical basis for the effective treatment of concentrated leachate of MSW incineration power plants.

Degradation of recalcitrant organics in landfill concentrated leachate by a microwave-activated peroxydisulfate process

A microwave-activated peroxydisulfate process was used to the pre-treatment for recalcitrant organics in concentrated leachate.

Advanced treatment of landfill leachate membrane concentrates: performance comparison, biosafety and toxic residue analysis

With the improvement of people's consciousness about health, more attention has been paid to the biosafety of effluent reaching conventional discharge standard. In this contribution, removal efficiency of chemical oxygen demand (COD), acute toxicity, genotoxicity and estrogenicity in landfill leachate membrane concentrates (MCs) among UV-Fenton, Fenton and activated carbon adsorption process were compared. Daphnia magna acute toxicity assay, comet assay, cytokinesis-block micronucleus and E-screen assay were performed to assess whether the effluent reaching the main parameters of Chinese Discharge Standard (GB 16889-2008) still had toxic residues. Under the conditions that COD of effluents treated by the three processes were up to the discharge standard, no obvious toxic residue was found in the effluent of UV-Fenton treatment, but effluent from Fenton or activated carbon adsorption process showed genotoxicity or estrogenicity to some extent. Dynamic analysis of UV-Fenton degradation process for estrogen simulation solutions was also conducted, and the formation of intermediates was detected by gas chromatography-mass spectrometry (GC/MS). Toxic residues might be caused by the lack of treatment duration and the formation of more toxic intermediates. UV-Fenton was found to be efficient for the treatment of MCs. Biosafety should be concerned when a new wastewater discharge standard is being established.

Organic matters removal from landfill leachate by immobilized Phanerochaete chrysosporium loaded with graphitic carbon nitride under visible light irradiation

This study investigated the technical applicability of a combination of Phanerochaete chrysosporium (P. chrysosporium) with photocatalyst graphitic carbon nitride (g-C₃N₄) for organic matters removal from landfill leachate under visible light irradiation. Photocatalyst g-C₃N₄ was well immobilized on the hyphae surface of P. chrysosporium by calcium alginate. The typical absorption edge in visible light region for g-C₃N₄ was at about 460 nm, and the optical absorption bandgap of g-C₃N₄ was estimated to be 2.70 eV, demonstrating the great photoresponsive ability of g-C₃N₄. An optimized g-C₃N₄ content of 0.10 g in immobilized P. chrysosporium and an optimized immobilized P. chrysosporium dosage of 1.0 g were suitable for organic matters removal. The removal efficiency of total organic carbon (TOC) reached 74.99% in 72 h with the initial TOC concentration of 100 mg L^-1. In addition, the gas chromatography coupled with mass spectrometry (GC-MS) measurements showed that immobilized P. chrysosporium presented an outstanding removal performance for almost all organic compounds in landfill leachate, especially for the volatile fatty acids and long-chain hydrocarbons. The overall results indicate that the combination P. chrysosporium with photocatalyst g-C₃N₄ for organic matters removal from landfill leachate may provide a more comprehensive potential for the landfill leachate treatment.

Environmental monitoring of water resources around a municipal landfill of the Rio Grande do Sul state, Brazil

In Brazil, landfills are commonly used as a method for the final disposal of waste that is compliant with the legislation. This technique, however, presents a risk to surface water and groundwater resources, owing to the leakage of metals, anions, and organic compounds. The geochemical monitoring of water resources is therefore extremely important, since the leachate can compromise the quality and use of surface water and groundwater close to landfills. In this paper, the results of analyses of metals, anions, ammonia, and physicochemical parameters were used to identify possible contamination of surface water and groundwater in a landfill area. A statistical multivariate approach was used. The values found for alkali metals, nitrate, and chloride indicate contamination in the regional groundwater and, moreover, surface waters also show variation when compared to the other background points, mainly for ammonia. Thus, the results of this study evidence the landfill leachate influence on the quality of groundwater and surface water in the study area.

Leachate generation from landfill in a semi-arid climate: A qualitative and quantitative study from Sousse, Tunisia

Despite initiatives for enhanced recycling and waste utilization, landfill still represents the dominant disposal path for municipal solid waste (MSW). The environmental impacts of landfills depend on several factors, including waste composition, technical barriers, landfill operation and climatic conditions. A profound evaluation of all factors and their impact is necessary in order to evaluate the environmental hazards emanating from landfills. The present paper investigates a sanitary landfill located in a semi-arid climate (Tunisia) and highlights major differences in quantitative and qualitative leachate characteristics compared to landfills situated in moderate climates. Besides the qualitative analysis of leachate samples, a quantitative analysis including the simulation of leachate generation (using the HELP model) has been conducted. The results of the analysis indicate a high load of salts (Cl, Na, inorganic nitrogen) in the leachate compared to other landfills. Furthermore the simulations with HELP model highlight that a major part of the leachate generated originates form the water content of waste.

Molecular Insights into the Transformation of Dissolved Organic Matter in Landfill Leachate Concentrate during Biodegradation and Coagulation Processes Using ESI FT-ICR MS

Landfill leachate concentrate is a type of refractory organic wastewater with high environmental risk. Identification of refractory components and insights into the molecular transformations of the organics are essential for the development of efficient treatment process. In this report, molecular compositions of dissolved organic matter (DOM) in leachate concentrate, as well as changes after anaerobic/aerobic biodegradation and coagulation with salts, were characterized using electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). DOM in leachate concentrate were more saturated and less oxidized with more nitrogen and sulfur-containing substances (accounting for 50.0%), comparing with natural organic matter in Suwannee River. Selectivity for different classes of organics during biodegradation and coagulation processes was observed. Substances with low oxidation degree (O/C < 0.3) were more reactive during biodegradation process, leading to the formation of highly oxidized molecules (O/C > 0.5). Unsaturated (H/C < 1.0) and oxidized (O/C > 0.4) substances containing carboxyl groups were preferentially removed after coagulation with Al or Fe sulfate. The complementary functions of biodegradation and coagulation in the treatment of DOM in leachate concentrate were verified at the molecular level. Lignin-derived compounds and sulfur-containing substances in leachate concentrate were resistant to biodegradation and coagulation treatments. To treat leachate concentrate more effectively, processes aimed at removal of such DOM should be developed.

A comparison of the toxicity of landfill leachate exposure at the seed soaking and germination stages on Zea mays L. (maize)

To compare the toxicity of landfill leachate exposure at the early stages of seed soaking and germination on maize, a field experiment was conducted to evaluate the physiological aspects of growth, yield and potential clastogenicity of root-tip cells. The maizes were treated with leachate at levels of 2%, 10%, 20%, 30% or 50% (V/V). First, the change of physiological indexes, including chlorophyll (Chl), Malondialdehyde (MDA) and Reactive oxygen species (ROS) levels, combined with yield all showed that soaking with leachate, but not germination, generated a greater ecological risk on maize. After a soaking treatment of maize with 50% leachate, the Chl, MDA and ROS levels during a vigorous growth period were 47.3%, 149.8% and 309.7%, respectively, of the control, whereas the yield decreased to 68.6% of the control. In addition, our results demonstrated that the leachate at lower levels could promote growth. This is mainly embodied in that the yield of maize treated with 10% leachate at the soaking stage increased to 116.0% of the control. Moreover, the cytological analysis experiment also demonstrated that the ecological risk of leachate still exists in both cases. Furthermore, the gray relational analysis showed that the ear row number and tassel branch number were the major factors affecting the yield of maize treated with 50% leachate at the stages of soaking and germination, respectively. In general, these results are helpful in understanding the phytotoxicity of leachate, which provides additional reference data for risk assessment and management of leachate.

Biochemical methane potential of fractions of organic matter extracted from a municipal solid waste leachate: Impact of their hydrophobic character

Many data on anaerobic digestion (AD) and co-digestion of municipal solid waste leachate (MSWL) are already available in literature. They mainly deal with its performances to decrease the chemical oxygen demand (COD) of MSWL and no information is given on the impact of the specific characteristics of the dissolved organic matter (DOM) in leachate on these performances. DOM in leachate evolves towards more aromatic and hydrophobic compounds during landfilling with increasing specific ultra-violet absorbance index (SUVA) and hydrophobic character. However, according to the humification stages, this DOM would not present the same aptitude for AD. This research thus focused on (i) optimizing a biochemical methane potential (BMP) test applied to MSWL by using the Taguchi method and (ii) evaluating the impact of the hydrophobic character of the DOM in leachate on the BMP of MSWL to finally define the humification degree more suitable for AD. Hydrophobic-like (HPO^∗) and transphilic-like (TPH^∗) compounds extracted from leachate by a fractionation protocol were tested because of their high content in MSWL during acetogenesis and methanogenesis steps. After 275days of AD, the content in hydrophobic compounds and the SUVA indexes increased in the digestates. Moreover, even if the biogas and methane productions were not significantly different during the whole tests (4072±350mLgDOC^-1 and 2370±95mLgDOC^-1 respectively), the volume of biogas produced directly correlated with the TPH^∗ fraction content in the initial digestates. On the contrary, the methane percentage in biogas was anti-correlated with the hydrophilic-like compounds content. The hydrophobic-like molecules seem thus not to be directly involved in the methanogenic step, however they promote the increase of the methane percent in the biogas.

Feasibility of sulfate-calcined eggshells for removing pathogenic bacteria and antibiotic resistance genes from landfill leachates

High abundance of human pathogen and antibiotic resistance genes (ARGs) in landfill leachate has become an emerging threat against human health. Therefore, sulfate- and calcination-modified eggshells as green agricultural bioresource were applied to test the feasibility of removing pathogenic bacteria and ARGs from leachate. The highest removal of Escherichia coli (E. coil) and gentamycin resistant gene (gmrA) from artificial contaminated landfill leachate was achieved by the application of eggshell with combined treatment of sulfate and calcination. The 16S and gmrA gene copies of E. coil declined significantly from 1.78E8±8.7E6 and 4.12E8±5.9E6 copies mL^-1 to 1.32E7±2.6E6 and 2.69E7±7.2E6 copies mL^-1, respectively, within 24h dynamic adsorption equilibrium process (p<0.05). Moreover, according to the Langmuir kinetic model, the greatest adsorption amount (1.56×10⁹ CFU E. coil per gram of modified eggshells) could be obtained at neutral pH of 7.5. The optimal adsorption eggshells were then screened to the further application in three typical landfill leachates in Nanjing, eastern China. Significant decrease in species and abundance of pathogenic bacteria and ARGs (tet, sul, erm, qnr, and ampC) indicated its great efficiency to purify landfill leachates. This study demonstrated that sulfate-calcined eggshells can be an environmentally-friendly and highly efficient bioadsorbent to the management of reducing dissemination risk of pathogen and ARGs in landfill leachate.

Ferrous ion-activated persulphate process for landfill leachate treatment: removal of organic load, phenolic micropollutants and nitrogen

The innovative [Formula: see text] treatment technology based on sulphate radicals induced oxidation was applied for the treatment of landfill leachate. The performance of chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal in the Fe²⁺-activated persulphate system was moderate; however, the results of dissolved nitrogen (DN) and total phenols removal showed significant efficacy (≤39% and ≥87%, respectively). [Formula: see text] addition to the [Formula: see text] system enhanced the treatment efficacy and resulted in supplementary 15% of COD and 5% of DN removal. Hydroxyl radical-based H₂O₂/Fe²⁺ treatment of the landfill leachate was performed as well; the results indicated higher removal efficacy of COD and DOC compared to the [Formula: see text] system. However, practical application of the H₂O₂/Fe²⁺ system is considerably influenced by temperature rise and excessive foam formation. Generally, the ferrous ion-activated persulphate treatment could be a promising technology for ex situ as well as in situ landfill leachate treatment applications.

Transformation of dissolved organic matter in concentrated leachate from nanofiltration during ozone-based oxidation processes (O3, O3/H2O2 and O3/UV)

In this study, the transformation of dissolved organic matter (DOM) in nanofiltration concentrated leachate during three ozone-based oxidation processes (i.e., O₃, O₃/H₂O₂ and O₃/UV) was investigated. The transformation characteristics of DOM were evaluated by gel filtration chromatography (GFC), XAD-8 resin fractionation, excitation-emission matrix fluorescence spectroscopy (EEM) and Fourier transform infrared spectroscopy (FTIR). Compared with O₃-alone process, the removal efficiencies of COD, TOC, and color were improved in O₃-combined processes (i.e., O₃/H₂O₂ and O₃/UV) approximately by 10-15%, 7-15%, and 15-20%, respectively. Humic acid (HA) was completely degraded and preferentially reacted with the oxidants during ozonation processes. HA was first converted into fulvic acid (FA), and then the majority of these intermediates were further converted to hydrophilic fraction (HyI). The GFC results indicated that the broader molecular weight distribution of DOM was observed, and high molecular weight DOM (i.e., 0.45 μm-100 kDa) was successfully converted to low molecular weight organics in the range of 1-10 kDa after ozonation reactions. The EEM spectra also showed that HA and FA were effectively converted into HyI after ozonation for 90 min. It is suggested that ozone-based oxidation processes could effectively change the DOM distribution and fluorescence features of concentrated leachate.

Optimization of Fenton treatment process for degradation of refractory organics in pre-coagulated leachate membrane concentrates

Untreated leachate membrane concentrates are a threat to the environment. In our study, effective removal of contaminants in pre-coagulated leachate membrane concentrates was achieved using the Fenton process. The Fenton process was optimized using the response surface method, and the maximum total organic carbon (TOC), chemical oxygen demand (COD), and chromaticity reduction efficiencies reached 68.9%, 69.6%, and 100% under the conditions pH 2, H₂O₂ concentration 1mol/L, and Fe²⁺ concentration 17.5mmol/L. The COD concentration was reduced from 1120 to 340mg/L. The H₂O₂ concentration was the key factor affecting the TOC removal efficiency. Slow, continuous addition of the Fenton reagents improved the H₂O₂ utilization rate, which improved the TOC removal efficiency. Fourier-transform infrared and three-dimensional fluorescence spectroscopy showed that the majority compound of the removed organic material was humic acid. Our study provides guidelines for the treatment of leachate membrane concentrates in engineering applications.

Effective removal of contaminants in landfill leachate membrane concentrates by coagulation

Leachate membrane concentrates containing high concentrations of organics and trace toxic compounds pose a major threat to the environment, and their treatment is an urgent issue. In this work, various coagulants were used to treat leachate membrane concentrates. Appropriate pH values for treatments with FeCl₂, FeSO₄, polyaluminum chloride, and FeCl₃ were 3, 5, 5, and 4, respectively. FeCl₃ achieved the highest total organic carbon (TOC) removal efficiency. The effect of the various anions in ferric coagulants [FeCl₃, Fe₂(SO₄)₃, and Fe(NO₃)₃] on the TOC removal efficiency was negligible. The main organics remaining in the leachate membrane concentrates after coagulation were humic and fulvic acids. The conditions for coagulation with FeCl₃ were optimized using the response surface method (RSM). The highest TOC, chemical oxygen demand (COD), and chromaticity reduction efficiencies, 81%, 82%, and 97%, respectively, were achieved at pH 4 using FeCl₃ (5 g L^-1) and polyacrylamide (PAM; 0.07 g L^-1). The COD of leachate membrane concentrates was reduced from 4000 to 718 mg L^-1. The mole ratio of removed COD and Fe(III) (2.4 mol) at 5 g L^-1 FeCl₃ (pH 4, PAM 0.07 g L^-1) was lower than that (3.8 mol) at 3 g L^-1 FeCl₃ (pH 4, PAM 0.07 g L^-1); based on the cost and COD removal efficiency, the latter conditions were the best choice. Our work provides guidelines for the treatment of leachate membrane concentrates in engineering.

Simultaneous Removal of Organic and Inorganic Pollutants From Landfill Leachate Using Sea Mango Derived Activated Carbon via Microwave Induced Activation

The present work reveals the preparation and optimization of sea mango based activated carbon (SMAC) by microwave induced KOH activation for the adsorptive removal of organic and inorganic contaminants from the mature anaerobic landfill leachate using response surface methodology (RSM) technique. Chemical oxygen demand (COD) and ammoniacal nitrogen (NH3-N) are the main indicators for organic and inorganic compounds often found in aged landfill leachate. Hence, the treatment of this stabilized landfill leachate is considered to be an essential step prior to its discharge. The leachate sample was collected from Sahom Landfill site in Perak, Malaysia and the initial concentrations of COD and NH3-N were measured as 550 mg/L and 3,330 mg/L, respectively. The feasibility of converting Sea mango to activated carbon process to remove the COD and NH3-N pollutants from landfill leachate was investigated. The preparation conditions such as microwave heating at power range (350–600 W), impregnation of AC with KOH (0.5–3.0) and retention time (6–10 min) were evaluated, analyzed and optimized using response surface methodology (RSM). From the analysis of variance (ANOVA), the optimum conditions for preparation of SMAC was at 560 W of activation power, 8.4 min of activation time and 2.10 of impregnation ratios with higher adsorptive removal of COD (72.50 %), and NH3-N (79.77 %), respectively. The physical and chemical properties of SMAC were evaluated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and surface area. The findings exemplified the applicability of SMAC as an effective precursor for the simultaneous removal of organic and inorganic pollutants from mature landfill leachate.

Recirculation of reverse osmosis concentrate in lab-scale anaerobic and aerobic landfill simulation reactors

Leachate treatment is a major issue in the context of landfill management, particularly in view of the consistent changes manifested over time in the quality and quantity of leachate produced, linked to both waste and landfill characteristics, which renders the procedure technically difficult and expensive. Leachate recirculation may afford a series of potential advantages, including improvement of leachate quality, enhancement of gas production, acceleration of biochemical processes, control of moisture content, as well as nutrients and microbe migration within the landfill. Recirculation of the products of leachate treatment, such as reverse osmosis (RO) concentrate, is a less common practice, with widespread controversy relating to its suitability, potential impacts on landfill management and future gaseous and leachable emissions. Scientific literature provides the results of only a few full-scale applications of concentrate recirculation. In some cases, an increase of COD and ammonium nitrogen in leachate was observed, coupled with an increase of salinity; which, additionally, might negatively affect performance of the RO plant itself. In other cases, not only did leachate production not increase significantly but the characteristics of leachate extracted from the well closest to the re-injection point also remained unchanged. This paper presents the results of lab-scale tests conducted in landfill simulation reactors, in which the effects of injection of municipal solid waste (MSW) landfill leachate RO concentrate were evaluated. Six reactors were managed with different weekly concentrate inputs, under both anaerobic and aerobic conditions, with the aim of investigating the short and long-term effects of this practice on landfill emissions. Lab-scale tests resulted in a more reliable identification of compound accumulation and kinetic changes than full-scale applications, further enhancing the development of a mass balance in which gaseous emissions and waste characteristics were also taken into consideration. Results showed that RO concentrate recirculation did not produce consistent changes in COD emissions and methane production. Simultaneously, ammonium ion showed a consistent increase in leachate (more than 25%) in anaerobic reactors, free ammonia gaseous emissions doubled with concentrate injection, while chloride resulted accumulated inside the reactor.

Removal of humic substances from reverse osmosis (RO) and nanofiltration (NF) concentrated leachate using continuously ozone generation-reaction treatment equipment

Concentrated leachate from membrane treatment process, which contains large amount of difficult-to-degrade humic substances, can induce potential hazards to ecological environment. In this study, the concentrated leachates from reverse osmosis (RO) and nanofiltration (NF) were treated by continuous ozone generating-reaction integrated equipment, and the removal characteristics of humic substances were analyzed using gel filtration chromatography (GFC), excitation-emission matrix fluorescence spectroscopy (EEM), XAD-8 resin fractionation, and Fourier transform infrared spectroscopy (FTIR). The results of XRD-8 fractionation and SUVA254 showed that the humic substances including humic acid (HA) and fulvic acid (FA), were effectively removed along with the breakdown of aromatic hydrocarbons and decrease in the degree of humification during the ozonation process. After 110min of reaction, HA in both concentrated leachates was completely removed. GFC analysis indicated that both concentrated leachates had much broader distribution after the degradation. The high molecular weight (MW) organic matter was transformed into low molecular weight of <10kDa. The majority of high MW organics in NF concentrate were converted to low MW molecules of 10kDa-1kDa, while those in RO concentrate were decomposed to small MW molecules of <1kDa. The results of EEM analysis implied that the degradation of HA and FA led to a significant decrease in the fluorescence intensity. Though the effluent of two concentrated leachate did not meet the maximum allowable criterion for leachate direct or indirect discharge standard in China, the composition and properties of organic matters in concentrated leachate were changed significantly after entire ozonation reaction, which would be conducive to the further biological treatment or other advanced treatment.

Effect of bioavailability on the fate of hydrophobic organic compounds and metal in treatment of young landfill leachate by membrane bioreactor

Complex dissolved organic matter (DOM) present in landfill leachate provides reliable media for adsorption of highly hydrophobic contaminants, such as Di 2-ethyl hexyl phthalate (DEHP). In this research, the feasibility of submerged membrane bioreactor (SMBR) for treatment of landfill leachate (LFL) was determined. Later, the operating conditions were optimized for removal of DEHP, COD, NH4(+) and PO4(3-), and finally the effect of bioavailability was examined by introduction of different concentrations of humic acid into the influent. The result revealed that presence of complex agglomerated organic compounds increased the removal efficiency of DEHP and COD, even though DEHP biodegradation rate in sludge dramatically decreased (from 58.8% to 12.8%). MBR retention of different metals in the absence and in the presence of recalcitrant DOM was also studied. Like DEHP, ternary interaction between metals, DOM, and sludge play a pivotal role in their removal efficiency and their concentration in sludge.

Advanced treatment of stabilized landfill leachate after biochemical process with hydrocalumite chloride (Ca/Al-Cl LDH)

This study investigated the effectiveness of Ca/Al-Cl LDH for the treatment of stabilized landfill leachate. Experiments were performed including different dosage of Ca/Al-Cl LDH and comparison with different reagents, such as CaCl2 and AlCl3. As a result, Ca/Al-Cl LDH efficiently removed organic matters in stabilized landfill leachate with the maximum removal (59.41% COD, 62.06% DOC and 70.56% UV254) at the dose of 30g/L. According to UV254 and EEM, it is remarkable that the formation of Ca/Al-LDH has a greater beneficial to organic removal than other reagents, especially for fulvic acid-like and humic acid-like compounds. Moreover, the removal of fulvic acid-like compounds was much better than humic acid-like compounds. The previous compounds had more carboxylic groups, thus had a better removal selectivity.

Genotoxicity assessment of membrane concentrates of landfill leachate treated with Fenton reagent and UV-Fenton reagent using human hepatoma cell line

Membrane concentrates of landfill leachates contain organic and inorganic contaminants that could be highly toxic and carcinogenic. In this paper, the genotoxicity of membrane concentrates before and after Fenton and UV-Fenton reagent was assessed. The cytotoxicity and genotoxicity was determined by using the methods of methyltetrazolium (MTT), cytokinesis-block micronucleus (CBMN) and comet assay in human hepatoma cells. MTT assay showed a cytotoxicity of 75% after 24h of exposure to the highest tested concentration of untreated concentrates, and no cytotoxocity for UV-Fenton and Fenton treated concentrates. Both CBMN and comet assays showed increased levels of genotoxicity in cells exposed to untreated concentrates, compared to those occurred in cells exposed to UV-Fenton and Fenton reagent treated concentrates. There was no significant difference between negative control and UV-Fenton treated concentrates for micronucleus and comet assay parameters. UV-Fenton and Fenton treatment, especially the former, were effective methods for degradation of bisphenol A and nonylphenol in concentrates. These findings showed UV-Fenton and Fenton reaction were effective methods for treatment of such complex concentrates, UV-Fenton reagent provided toxicological safety of the treated effluent, and the genotoxicity assays were found to be feasible tools for assessment of toxicity risks of complex concentrates.

Heterogeneous adsorption behavior of landfill leachate on granular activated carbon revealed by fluorescence excitation emission matrix (EEM)-parallel factor analysis (PARAFAC)

Heterogeneous adsorption behavior of landfill leachate on granular activated carbon (GAC) was investigated by fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC). The equilibrium adsorption of two leachates on GAC was well described by simple Langmuir and Freundlich isotherm models. More nonlinear isotherm and a slower adsorption rate were found for the leachate with the higher values of specific UV absorbance and humification index, suggesting that the leachate containing more aromatic content and condensed structures might have less accessible sites of GAC surface and a lower degree of diffusive adsorption. Such differences in the adsorption behavior were found even within the bulk leachate as revealed by the dissimilarity in the isotherm and kinetic model parameters between two identified PARAFAC components. For both leachates, terrestrial humic-like fluorescence (C1) component, which is likely associated with relatively large sized and condensed aromatic structures, exhibited a higher isotherm nonlinearity and a slower kinetic rate for GAC adsorption than microbial humic-like (C2) component. Our results were consistent with size exclusion effects, a well-known GAC adsorption mechanism. This study demonstrated the promising benefit of using EEM-PARAFAC for GAC adsorption processes of landfill leachate through fast monitoring of the influent and treated leachate, which can provide valuable information on optimizing treatment processes and predicting further environmental impacts of the treated effluent.

Removal of refractory organics in nanofiltration concentrates of municipal solid waste leachate treatment plants by combined Fenton oxidative-coagulation with photo--Fenton processes

Removal of the refractory organic matters in leachate brines generated from nanofiltration unit in two full-scale municipal solid waste landfill leachate treatment plants was investigated by Fenton oxidative-coagulation and ultraviolet photo - Fenton processes in this study. Fenton oxidative-coagulation was performed under the condition of an initial pH of 5.0 and low H2O2/Fe(2+) ratios. After precipitate separation, the remaining organic constituents were further oxidized by photo - Fenton process. For both leachate brines with varying pollution strength, more than 90% COD and TOC reductions were achieved at H2O2/Fe(2+) dosages of 35 mM/8 mM and 90 mM/10 mM, respectively. The effluent COD ranged 120-160 mg/L under the optimal operating conditions, and the biodegradability was increased significantly. Fenton oxidative-coagulation was demonstrated to contribute nearly 70% overall removal of organic matters. In the combined processes, the efficiency of hydrogen peroxide varied from 216 to 228%, which may significantly reduce the operating cost of conventional Fenton method. Six phthalic acid esters and thirteen polycyclic aromatic hydrocarbons were found in leachate brines, and, on the average, around 80% phthalic acid esters and 90% polycyclic aromatic hydrocarbons were removed by the combined treatments.

Effects of concentrated leachate injection modes on stabilization of landfilled waste

Injection of concentrated leachate to landfills is a simple and cost-effective technology for concentrated leachate treatment. In this study, the effects of injection mode of concentrated leachate and its hydraulic loading rate on the stabilization of landfilled waste were investigated. Compared with the injection of concentrated leachate, the joint injection of leachate and concentrated leachate (1:1, v/v) was more beneficial to the degradation of landfilled waste and mitigated the discharge amount of pollutants at the hydraulic loading rate of 5.9 L m(-2) day(-1). As the hydraulic loading rate of the joint injection of leachate and concentrated leachate was increased from 5.9 to 17.6 L m(-2) day(-1), the organic matter, biologically degradable matter, and total nitrogen of landfilled waste were degraded more rapidly, with the degradation constant of the first-order kinetics of 0.005, 0.004, and 0.003, respectively. Additionally, NO2(-)-N and NO3(-)-N in the concentrated leachate could be well removed in the landfill bioreactors. These results showed that a joint injection of concentrated leachate and raw leachate might be a good way to relieve the inhibitory effect of high concentrations of toxic pollutants in the concentrated leachate and accelerate the stabilization of landfilled waste.

Treatment of landfill leachate using immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO₂ nanoparticles

This study investigated the performance of immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO2 nanoparticles in the treatment of raw landfill leachate with a very low biodegradability ratio (BOD5/COD) of 0.09. The effects of various operating parameters, such as initial chemical oxygen demand (COD) concentration, pH, temperature, and biosorbent dosage, were evaluated with respect to the removal efficiency of total organic carbon (TOC) and ammonia nitrogen (NH3-N). For the immobilized biosorbents, an optimum pH of 6.0 for TOC and 7.0 for NH3-N were found suitable for TOC and NH3-N removal at temperature of 37°C, respectively. The most superior removal efficiencies of TOC and NH3-N of landfill leachate were over 75% and 74% in 72 h at an initial COD concentration of 200 mg L(-1), respectively. In addition, heavy metals were partly removed by the immobilized biosorbents during the process of landfill leachate treatment. The species and mass percentage of organic compounds in landfill leachate after the treatment were found to have considerably declined according to the gas chromatography coupled with mass spectrometry (GC-MS) system. These results indicate that the immobilized P. chrysosporium loaded with nitrogen-doped TiO2 nanoparticles could be a convenient and efficient method for the treatment of landfill leachate.

Pretreatment of concentrated leachate by the combination of coagulation and catalytic ozonation with Ce/AC catalyst

A raw concentrated leachate produced from membrane bioreactor-nanofiltration (MBR-NF) was taken from Chengdu Chang'an Waste Landfill Site, China. The major fraction of this concentrated leachate was large refractory humic substances. A coagulation-ozonation process was applied to treat this leachate, aiming at enhancing chemical oxygen demand (COD) removal efficiency and increasing its biodegradability. Meanwhile the molecular size distribution of the leachate, before and after coagulation and ozonation treatment, was analyzed by using ultrafiltration membrane separation. Coagulation pretreatment effectively removed varieties of large molecules in the raw concentrated leachate. The addition of Ce/AC greatly improved the oxidative ability of O3 in COD removal in the ozonation of coagulated leachate. The biochemical oxygen demand (BOD5)/COD ratio increased from 0.011 for the untreated concentrated leachate to 0.30 for the effluent of the coagulation-catalytic ozonation process, which indicated that a subsequent biological treatment could be readily conducted. The stability test demonstrated that the Ce/AC catalyst was effective and stable in the catalytic ozonation process. According to the results of molecular size distribution analysis, a direct correlation was observed between the increase of BOD5/COD and the decrease of apparent molecular weight.

Characterization of a joint recirculation of concentrated leachate and leachate to landfills with a microaerobic bioreactor for leachate treatment

With comparison of a traditional landfill, a joint recirculation of concentrated leachate and leachate to landfills with or without a microaerobic reactor for leachate treatment was investigated in this study. The results showed that the joint recirculation of concentrated leachate and leachate with a microaerobic reactor for leachate treatment could not only utilize the microaerobic reactor to buffer the fluctuation of quality and quantity of leachate during landfill stabilization, but also reduce the inhibitory effect of acidic pH and high concentrations of ammonium in recycled liquid on microorganisms and accelerate the degradation of landfilled waste. After 390 days of operation, the discharge of COD and total nitrogen (TN) from the landfill with leachate pretreatment by a microaerobic reactor was 7.4 and 0.9 g, respectively, which accounted for 0.7% and 2.6% of COD, 1.9% and 7.5% of the TN discharge from the landfills without recirculation and directly recirculated with leachate and concentrated leachate, respectively. The degradation of the organic matter and biodegradable matter (BDM) in the landfill reactors could fit well with the first-order kinetics. The highest degradation of the organic matter and BDM was observed in the joint recirculation system with a microaerobic reactor for leachate treatment with the degradation constant of the first-order kinetics of 0.001 and 0.002.

Decomposition characteristics of humic-like matters with the hollow ellipsoid structure sludge inoculated from decayed soil in mature landfill leachate

The organics in mature leachate are mainly humic-like matters, which account for over 80% weight of the total organics. In this work, the microorganisms in decayed soil were found to be capable of decomposing the humic-like matters evidently using an anaerobic-aerobic/anoxic bioprocess in two sequencing bio-reactors. The 3D excitation-emission matrix and Fourier transform infrared (FT-IR) were applied to characterize the variation of dissolved organic matters in mature leachate while sludge morphology was characterized by scanning electron microscopy. The intensities of fluorescence peaks A and C of leachate effluents were 71.66% and 48.75% lower than those of influents, respectively, which indicated the extraordinary degradation ability of microorganisms inoculated from the decayed soil. Meanwhile a kind of distinctive hollow ellipsoid structure sludge organized by tiny soil particles was observed, which might favour the humic-like matters' decomposition and has never been reported before as we know. The formation mechanisms of hollow ellipsoid structure sludge will need further study.

Removal of refractory contaminants in municipal landfill leachate by hydrogen, oxygen and palladium: a novel approach of hydroxyl radical production

Municipal solid waste (MSW) leachate contains various refractory pollutants that pose potential threats to both surface water and groundwater. This paper established a novel catalytic oxidation process for leachate treatment, in which OH is generated in situ by pumping both H2 and O2 in the presence of Pd catalyst and Fe(2+). Volatile fatty acids in the leachate were removed almost completely by aeration and/or mechanical mixing. In this approach, a maximum COD removal of 56.7% can be achieved after 4h when 200mg/L Fe(2+) and 1250mg/L Pd/Al2O3 (pH 3.0) are used as catalysts. After oxidation, the BOD/COD ratio in the proposed process increased from 0.03 to 0.25, indicating that the biodegradability of the leachate was improved. By comparing the efficiency on COD removal and economical aspect of the proposed Pd-based in-situ process with traditional Fenton, electro-Fenton and UV-Fenton for leachate treatments, the proposed Pd-based in-situ process has potential economic advantages over other advanced oxidation processes while the COD removal efficiency was maintained.

Effect of Fenton oxidation on biodegradability, biotoxicity and dissolved organic matter distribution of concentrated landfill leachate derived from a membrane process

The treatment of concentrated landfill leachate from membrane process is a troublesome issue due to high concentrations of biorecalcitrant pollutants. In this study, the effect of Fenton process on dissolved organic matter (DOM) distribution (i.e. humic acid (HA), fulvic acid (FA) and hydrophilic fraction (HyI)), chemical forms of toxic organic compounds and metals, and their biotoxicity were investigated. In the concentrated leachate, toluene, ethylbenzene and chlorobenzene predominated in the HyI fraction, while phthalate esters (PAEs) were mainly absorbed on the HA and FA fractions. PAEs were more readily removed from the HA and FA fractions than that from the HyI fraction in the Fenton process. The complexing abilities of DOM varied with types of metal in the concentrated leachate. The biotoxicities of the DOM fractions to luminescent bacteria (Photobacterium phosphoreum T3 mutation) were HA > FA > - HyI. The biotoxicities of the hydrophobic organic contaminants to luminescent bacteria were not obvious in the concentrated leachate due to their low concentrations. Metals might be the main contributor to the biotoxicity to luminous bacteria in the concentrated leachate. These results indicated that Fenton process could influence the pollutants distribution in DOM and their biotoxicities through the breakdown of HA and FA in the concentrated leachate.

Supercritical Water Oxidation of Fulvic Acid as a Model Organic Compound in Landfill Leachate

Fulvic acid (FA) is a common refractory organic compound in landfill leachate. The degradation of FA in supercritical water oxidation (SCWO) was conducted in a SS 316 batch reactor. The effects of temperature, pressure, residence time, oxidation ratio and initial FA concentration on the degradation of FA were investigated. Results showed that FA could be easily destructed in SCWO process, and a total organic carbon (TOC) removal efficiency of 98.0% was available at 600 °C, 420 s, 25 MPa and 1% FA. Oxidation coefficient had a significant positive effect on the degradation of FA. Total carbon (TC) and TOC removal efficiencies increased from 78.9 % to 97.2 % and from 86.4 % to 97.2, respectively, when oxidation coefficient increased from 0 to 4. Benzene, phenol and naphthalene could be regarded as the intermediate products in SCWO.