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

A microwave radiation-enhanced Fe-C/persulfate system for the treatment of refractory organic matter from biologically treated landfill leachate

In this study, a microwave (MW) radiation enhanced Fe–C/PS system was used to treat refractory organic matter in biologically-treated landfill leachate. The effects of important influencing factors on the refractory organic matter in biologically treated landfill leachate were explored, and the main reactive oxygen species produced in the system were verified. The mechanism by which humus was degraded was investigated by analyzing effectiveness of organics removal in different systems, and comparative analysis was conducted on the Fe–C materials before and after the reaction. The results showed that degradation capacity and reaction rate of the system could be improved with an increase in the Fe–C/PS dosage and MW power, while initial acidic conditions were also conducive to the degradation of organic matter. Under the conditions of an Fe–C of 1 g L⁻¹, PS dosage of 30 mM, MW power of 240 W, and reaction time of 10 min, the UV₂₅₄, TOC, and CN removal efficiencies were 51.48%, 94.56%, and 51.59%, respectively. In the MW/Fe–C/PS system, a large amount of and a small amount of ˙OH were generated by the thermal activation of PS to remove organic matter. The removal efficiency of organic matter could be further improved via the homogeneous catalytic oxidation and heterogeneous adsorption catalytic oxidation of Fe–C materials. In addition, the MW/Fe–C/PS system was effective for removing refractory organic matter from the leachates from four typical treatment systems: DTRO, SAARB, MBR, and NF. The MW/Fe–C/PS system has the potential to be widely applied for the treatment of landfill leachate.

A microwave radiation enhanced Fe-C/PS system was used to treat biologically-treated landfill leachate. This process showed wide applicability in treatment of four types of leachates and has a promising potential in landfill leachate treatment.

Combining yeast MBR, Fenton and nanofiltration for landfill leachate reclamation

This study investigated the best way to combine nanofiltration (NF) and Fenton with membrane bioreactor inoculated with Saccharomyces cerevisiae (MBRy) for the treatment of landfill leachate, aiming at compliance with legislation and water reuse. Firstly, the permeate from MBRy was treated by Fenton process followed by NF (MBRy - Fenton - NF). Another alternative evaluated was the polishment of MBRy permeate by NF and treatment of NF concentrate by Fenton process (MBRy - NF - Fenton_{(concentrate)}). COD removal in the Fenton step was optimized according to central composite design (CCD) and 85.5% removal was obtained at pH = 3, Fe²⁺:H₂O₂ molar ratio = 1:9.81 and C:H₂O₂ molar ratio = 1:1.14. Increased toxicity was observed with the Fenton application (EC₅₀ = 2.45%). The NF showed the best performance treating the MBRy permeate. High permeate flux (8.9 ± 1.6 L h^-1 m^-2) and ion rejection (82 ± 4.2%), and low membrane fouling was observed in this condition. Although both NF permeate presented potential for reuse, the final COD concentration was lower in the MBRy - Fenton effluent (88 mg L^-1). The Fenton application for the NF concentrate was able to remove 87.24% of COD. With a preliminary economic analysis, it was verified that the MBRy - NF - Fenton_{(concentrate)} combination is the most advantageous due to the lower chemical reagent and membrane area requirements. Thus, this route presents itself as an alternative for landfill leachate reclamation.

Effective removal of refractory organic contaminants from reverse osmosis concentrated leachate using PFS-nZVI/PMS/O3 process

Reverse osmosis concentrated leachate (ROCL) from landfill leachate treatment contains high amounts of refractory organics. In this study, a combination of polymerized ferric sulfate (PFS) and nanoscale zero-valent iron/peroxymonosulfate/ozone (nZVI/PMS/O₃) approach was adopted to remove refractory pollutants in ROCL. The effects of coagulant species, dosage and initial pH on the pre-treatment of organics from ROCL during coagulation process were investigated. Moreover, the influences of experimental factors, including initial pH, ozone doses, PMS, and nZVI on the removal of refractory organics in ROCL from coagulation effluent were systematically studied. The characteristics of organics were determined by using microscopic, spectroscopic and electron paramagnetic resonance (EPR) analyses. The batch experimental results indicated that the refractory organic contaminants in ROCL were effectively removed through PFS-nZVI/PMS/O₃ treatment. The maximum removal efficiencies of COD and TOC were 89.1% and 83.2% under the optimum conditions: PFS of 8 g/L, ozone dose of 100 mg/min, PMS dose of 1.5 mM and nZVI dose of 10 mM, and at these conditions, the biodegradability index (BOD₅/COD) was enhanced from 0.02 to 0.32. The excitation-emission matrix fluorescence spectroscopy (EEM) analysis indicated that humic-like and fulvic-like substances in ROCL were effectively removed. According to EPR analysis, hydroxyl and sulfate radicals were the dominant reactive species for the degradation of organics in nZVI/PMS/O₃ system. Overall, the environmental and economic analysis suggested that the PFS-nZVI/PMS/O₃ system was a cost-effective method for cleaning refractory organics from ROCL.

Advanced treatment of aged landfill leachate through the combination of aged-refuse bioreactor and three-dimensional electrode electro-Fenton process

A combined process of the aged-refuse bioreactor (ARB)/three-dimensional electrode electro-Fenton (3D-EF) system was developed at lab-scale to treat aged landfill leachate. The optimum operating conditions were found to be 15 L/m³•d hydraulic loading rate for ARB; Fe²⁺ concentration 1.0 mM, initial pH 3.0, current density 30 mA/cm² and electrode distance 6 cm for 3D-EF. Under these conditions, the total removal ratios of chemical oxygen demand, NH₃-N, total phosphorus and colour were 96.2%, 94.3%, 99.2% and 93.6%, respectively. The microtoxicity of the leachate was substantially reduced after undergoing the hybrid treatment. The ARB process removed a considerable proportion of organic matter, while the 3D-EF system played an important role in removing the residue of recalcitrant substances and post-polish of final effluent. The combined process showed a promising potential for treatment of aged landfill leachate.

Importance of Combined Electrochemical Process Sequence and Electrode Arrangements: A Lab-scale Trial of Real Reverse Osmosis Landfill Leachate Concentrate

Reverse osmosis (RO) is a widely applied technique for wastewater effluent reuse and landfill leachate treatment. The latter generates a refractory RO leachate concentrate (ROLC), for which cost-effective treatment is required. This study focuses on a two-step electrochemical method consisting of aluminum-based electrocoagulation (EC), and simultaneous electrooxidation-electrocoagulation with a titanium-based lead dioxide (Ti/ß-PbO₂) anode and aluminum cathode (EO_EC) assembly. The sequence and electrode arrangements of the combined electrochemical process were investigated to determine the organic transformation, Ti/ß-PbO₂ anode viability, and energy consumption. Series-based EC-EO_EC decreased the total chemical oxygen demand (COD) from 8750 mg L^-1 to 380 mg L^-1, a 96% removal efficiency, in 3.5 hours at 141 A m^-2. Under a low energy consumption of 28.7 kWh kg_COD^-1, the ROLC biodegradability (BOD₅/COD) significantly increased from 0.015 to 0.530, which was ascribed to aromatic removal (e.g., -C=C) and an increase in -COOH functional groups. Furthermore, the rapid removal of natural organic matter and increase in pH elevation from EC suppressed the dissolution of Pb from the Ti/ß-PbO₂ anode during the subsequent EO_EC, thereby leaving 0.061 mg L^-1 in the ROLC after treatment. The treatment cost was 3.86 USD kg_COD^-1, which was approximately 34% lower than that of previously reported electrochemical processes for ROLC treatment. These findings obtained with a real RO concentrate provide a foundation for scaling up this new electrochemical treatment approach.

Application of membrane separation technology in the treatment of leachate in China: A review

To comprehensively investigate the application of membrane separation technology in the treatment of landfill leachate in China, the performance of nearly 200 waste management enterprises of different sizes in China were analyzed, with an emphasis on their scale, regional features, processes, and economic characteristics. It was found that membrane separation technologies, mainly nanofiltration (NF), reverse osmosis (RO), and NF + RO, have been used in China since 2004. The treatment capacity of the two most dominant membrane separation technologies, i.e., NF and RO, were both almost 60,000 m³/d in 2018, and both technologies are widely used in landfills and incineration plants. Their distribution is mainly concentrated in eastern and southwestern China, where the amount of municipal solid waste (MSW) is relatively high and the economy is developing rapidly. Membrane separation technology is the preferred technique for the advanced treatment of leachate because more contaminants can be effectively removed by the technology than by other advanced processes. However, the membrane retentate that is produced using this technology-commonly known as leachate concentrate-is heavily contaminated due to the enrichment of almost all the inorganic anions, heavy metals, and organic matter that remain after bioprocessing. An economic cost analysis revealed that the operating cost of membrane separation technology has stabilized and is between 1.77 USD/m³ and 4.90 USD/m³; electricity consumption is the most expensive cost component. This review describes the current problems with the use of membrane separation technology and recommends strategies and solutions for its future use.

Mixed culture of Lactococcus lactis and Kluyveromyces marxianus isolated from kefir grains for pollutants load removal from Jebel Chakir leachate

The wastewater from the dumping site usually contains high pollutant levels. Biological process and physico-chemical treatments are among several technologies for wastewater treatment. Using microorganisms in the treatment of landfill leachate is an emerging research issue. Furthermore, bioremediation is a feasible approach for pollutants removal from landfill leachate which would provide an efficient way to resolve the issue of landfill leachate. In this study, the performance of yeast and bacteria isolated from kefir grains was assessed for landfill leachate treatment. Kefir grains microbial composition was evaluated by molecular approaches (Rep-PCR and 16S rRNA gene sequencing). The obtained outcomes denoted that high concentrations of lactic acid bacteria and yeast populations (over 10⁷  CFU/ml) were found in the kefir grains and were essentially composed of Lactococcus lactis, Lactobaccillus kefirien, bacillus sp., L. lactis, and Kluyveromyces marxianus. The co-culture with 1% of inoculum size was demonstrated as the most efficient in the degradation of different contaminants. The overall abatement rate of chemical oxygen demand (COD), ammonium nitrogen ( NH 4 + - N ), and salinity were 75.8%, 85.9%, and 75.13%, respectively. The bioremediation process resulted in up of 75% removal efficiency of Ni and Cd, and a 73.45%, 68.53%, and a 58.17% removal rates of Cu, Pb, and Fe, respectively. The research findings indicate the performance of L. lactis and K. marxianus co-culture isolated from kefir grains for the bioremediation of LFL. PRACTITIONER POINTS: Isolation and identification of microorganisms from kefir grains was carried out. Biological treatment of LFL using monoculture of (Lactoccocus lactis; Kluyveromyces marxianus) and co-culture (5% of L. lactis and 5% K. marxianus) has been performed. Biological treatment using co-culture strain is an effective approach to remove organic matter, NH 4 + - N and heavy metals.

Molecular-level comparison study on microwave irradiation-activated persulfate and hydrogen peroxide processes for the treatment of refractory organics in mature landfill leachate

This study investigated the degradation of organics in mature leachate treated by microwave radiation-activated persulfate (MW/PS) and hydrogen peroxide (MW/H₂O₂) processes. Obvious synergistic effects existed in both the MW/PS and MW/H₂O₂ processes, but were significantly higher in the MW/PS process. Refractory organics were better degraded by the MW/PS process than the MW/H₂O₂ process due to the major contribution of SO₄-. Moreover, according to Fourier transform-ion cyclotron resonance mass spectrometry coupled with electrospray ionization analysis results, the refractory organics (e.g. polycyclic aromatics (AI > 0.66), polyphenols (0.66 ≥ AI > 0.50)) were greatly degraded by both the MW/H₂O₂ and MW/PS processes, but the MW/PS process degraded dissolved organic matter (DOM) over a wider range than the MW/H₂O₂ process due to the different dominant radicals in the two processes. In addition, after reaction in the MW/PS process, the O/C ratio of DOM in the treated effluent showed an obvious increase, which can be mainly attributed to the reaction of sulfate radicals with the N- and S- containing compounds via single electron transfer.

Catalytic ozonation of 2, 2'-methylenebis (4-methyl-6-tert-butylphenol) over nano-Fe3O4@cow dung ash composites: Optimization, toxicity, and degradation mechanisms

Composite magnetic oxide at cow dung ash, nano-Fe₃O₄@cow dung ash (nano-Fe₃O₄@CDA), was used as catalytic material for the degradation of 2, 2'-methylenebis (4-methyl-6-tert-butylphenol) (AO 2246) in real biologically pretreated landfill leachate. The Fe₃O₄@CDA composite exhibited catalytic ozonation activity and allowed material separation and magnetic recovery. The effects of several operating parameters including O₃ concentration, catalyst dosage, temperature and scavengers were evaluated in parallel. Over 70% of AO 2246 were removed by the nano-Fe₃O₄@CDA/O₃ system under optimum conditions within 120min reaction time. The EPR, GC-MS and free-radical quenching experiments expatiated the mechanism of this degradation process. It was confirmed that the AO 2246 was degraded efficiently in this catalytic micro-ozonation process, Additionally, GC-MS analysis state clearly that the 3,5-bis(1,1-dimethylethyl)phenol, 4-(1,5-dihydroxy-2,6,6-trimethylcyclohex-2-enyl)but-3-en-2-one, ethanone, 1-(1,4-dimethyl-3-cyclohexen-1-yl)-, 5-tert-butyl-6-3, 5-diene-2-one, 2-hydroxyhexanoic acid, 2-propenoic acid 1,1-dimethylethyl ester, butanoic acid, 2-methyl-, methyl ester and propanoic acid, 2, 2-dimethyl- were the dominant oxidation products (OPs) during the degradation of the AO 2246. The EPR results showed that the catalytic ozonation over Fe₃O₄@CDA led to produce more hydroxyl radicals, which were in favor of AO 2246 degradation. The toxicity evolution was also performed through a QSAR analysis calculated by the ECOSAR program which further demonstrated the different responses toward the AO 2246 and its OPs.

Simultaneous Stripping of Ammonia from Leachate: Experimental Insights and Key Microbial Players

Air stripping is commonly used to remove the ammonia in multistage treatment systems for municipal landfill leachate (LFL). This paper proposes a novel approach combining the process of stripping with biological removal of ammonia, based on simultaneous nitrification and denitrification (SND) in a single hybrid sequencing batch reactor (HSBR). To avoid the accumulation of free ammonia (N-FAN), the shallow aeration system was used for the treatment of raw LFL with N-TAN level of 1520 mg/L and pH 9.24. The mean N-FAN removal efficiency of 69% with the reaction rate of 55 mg L−1 h−1 and mean ammonium (N-NH4+) removal efficiency of 84% with the reaction rate of 44 mg L−1 h−1 were achieved within a month in such an HSBR (R1). The comparative HSBR (R2), with conventional aeration system maintaining the same concentration of dissolved oxygen (DO ≤ 1 mg/L), was removing only trace amounts of N-FAN and 48% of N-NH4+. The quantitative analysis of 16S rRNA genes indicated that the number of total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Beta- and Gammaproteobacteria increased during the operation of both HSBRs, but was always higher in R1. Moreover, the bacterial community shift was observed since the beginning of the experiment; the relative abundance of Firmicutes, and Beta- and Gammaproteobacteria increased by 5.01, 3.25 and 9.67% respectively, whilst the abundance of Bacteroidetes and Actinobacteria decreased by 15.59 and 0.95%. All of the surveyed bacteria groups, except Gammaproteobacteria, correlated significantly negatively (p < 0.001) with the concentrations of N-NH4+ in the outflows from R1. The results allow us to suppose that simultaneous stripping and SND in a single reactor could be a promising, cost-effective and easy-to-operate solution for LFL treatment.

Stability of Nano-ZnO in simulated landfill leachate containing heavy metal ions

As the presence of nanosized zinc oxide particles (nano-ZnO) in landfill leachate increases, their interaction with coexisting heavy metal ions (HMs) also increases. The interface interaction between nano-ZnO and HMs will influence nano-ZnO stability and therefore affect its bioavailability and environmental impact. In the present study, we investigated the effects of Cu(II), Cr(III), and Cr(VI) ions on the aggregation, sedimentation, and dissolution of nano-ZnO using batch experiments with a view to better understanding their co-effect on the environment. Dynamic light scattering and UV-Vis spectroscopy results show enhanced aggregation of nano-ZnO in the presence of Cr(VI) ions under fresh landfill leachate conditions, in addition to distinct sedimentation of nano-ZnO in the presence of Cr(III) ions in both fresh and aged landfill leachate. In fresh leachate, Cu(II) ions improved the concentration of dissolved Zn from nano-ZnO. However, the effects of Cu(II), Cr(III), and Cr(VI) ions on the aggregation and dissolution of nano-ZnO were markedly reduced in aged landfill leachate. Both acetic and humic acids in landfill leachate significantly affected the stability of nano-ZnO in the presence of HMs. According to the ATR-FTIR results, Cr(III) ions reacted with hydroxyl groups on nano-ZnO to form ZnO-O bonds, which induced chains of nano-ZnO and Cr(III) complexes, and hence the increased of nano-ZnO aggregates. ATR-FTIR shows merely electrostatic adsorption effects between nano-ZnO and Cu(II) or Cr(VI) ions. In brief, the mode of interactions between HMs and nano-ZnO influenced the stability via adsorption and binding effects. The results of the present research provide insight into the potential effects of nano-ZnO on the environment in the presence of HMs in landfill leachate.

Applicability of conventional and non-conventional parameters for municipal landfill leachate characterization

The disposal of municipal solid waste (MSW) in landfills generates leachate, a highly polluting liquid to the aquatic environment. Leachate composition become a challenge to choose the best treatment process. Then, detailed techniques to determine the organic content, in terms of refractability, composition, sources and biodegradability in landfill leachate can help to choose the appropriate treatment and improve landfill management. In this sense, the aim of this study is to apply conventional and non-conventional parameters through inert chemical oxygen demand (COD) analyses and spectroscopic techniques of fluorescence and UV-vis absorbance for the characterization of municipal landfill leachate. Results indicated that physicochemical characterization cannot provided enough detailed information about leachate composition, which becomes the treatment process fragile. Inert COD, besides have high time to execution (∼30 days), presented additional information on potential of biological treatability in anaerobic conditions. Dissolved organic matter (DOM) characterization showed transitions between labile and refractory organic matter compounds. Moreover, the cost estimated showed that non-conventional parameters analysis have lower investment than conventional, being their implementation feasible. In conclusion, the synergy between conventional and non-conventional parameters, and the detailed information provided by inert COD and DOM characterization, shown a useful tool to the landfill management and, consequently, improving treatment process and its efficiency.

Effect of leachate effluent from activated sludge and membrane bioreactor systems with acclimatized sludge on plant seed germination

This research comparatively investigates the effect of landfill leachate effluent of two biological treatment schemes on germination of Lactuca sativa and Vigna radiata. The treatment schemes are two-stage activated sludge (AS) and two-stage membrane bioreactor (MBR) systems with acclimatized seed sludge. The AS and MBR are operated under two concentrations of landfill leachate influent: moderate (condition 1) and elevated (condition 2). The results show that, under condition 1, the AS and MBR efficiently remove 80-96% of organic compounds and nutrients and 81-100% of harmful micropollutants. Under condition 2 with elevated influent concentration, MBR is more effective in biodegrading micropollutants than the AS system. The germination rate (GR) and germination seed index (GSI) of L. sativa and V. radiata germinated with AS and MBR effluent from condition 1 are 100% and 1.29-1.56. Under condition 2, the GR and GSI with AS effluent are reduced to 80% and 0.65-0.77, while those with MBR effluent are 100% and 1.27-1.38. Quantitative real-time polymerase chain reaction (qPCR) analysis indicates that the bacterial community in the MBR is more abundant than in the AS, especially ammonia oxidizing bacteria, Nitrobacter, and Nitrospira, which aid heterotrophic bacteria in biodegradation of micropollutants and promote the growth of heterotrophs. The bacterial abundance and community composition render the MBR scheme more operationally suitable for elevated landfill-leachate influent concentrations. By comparison, the MBR system is more effective in removal of micropollutants than the AS, as evidenced by higher GR and GSI. The technology also could potentially be applied to water reclamation. A lack of technological and financial resources in many developing countries nevertheless precludes the adoption of MBR despite higher pollutant removal efficiency. An alternative solution is the use of acclimatized seed sludge in AS system to enhance treatment efficiency, especially in influent with low concentrations of micropollutants. In addition, the seed germination results suggest the possibility of water reuse in agriculture.

Characterization of urban and industrial wastewaters using excitation-emission matrix (EEM) fluorescence: Searching for specific fingerprints

Excitation-emission matrix (EEM) fluorescence spectroscopy has been applied to characterize several urban and industrial wastewaters (effluents from different types of industries: brewery, winery, dairy, biscuit, tinned fish industry, slaughterhouse, pulp mill, textile dyeing and landfill leachates), searching for specific fluorescence fingerprints. Tryptophan protein-like peaks (T₁ and T₂) are the predominant fluorescence in urban and food industry wastewaters (brewery, winery, dairy/milk, biscuit and fish farm industries) but no special fingerprint has been found to discriminate among them. Protein-like fluorescence also dominates the spectra of meat/fish industries (effluents from a tinned fish industry and a slaughterhouse), but in this case tyrosine protein-like peaks (B₁ and B2) also appear in the spectra in addition to tryptophan-like peaks. This fact might constitute a specific feature to differentiate these wastewaters from others, since the appearance of peaks B is quite uncommon in wastewaters. The textile dyeing effluent shows a characteristic triple humic-like fluorescence (peaks A, C₁ and C₂) that may represent a specific fingerprint for this kind of effluent. Leachates from medium-aged and old landfills might also show a specific fingerprint in their EEM spectra: the sole presence of the humic-like peak C with very high fluorescence intensity. This feature also allows differentiating them from young landfill leachates, which show predominance of protein-like peaks. The fluorescence index (FI) does not seem to be very appropriate to characterize wastewaters and its usefulness might be limited to the study of humic substances in natural waters, although further studies are needed on this topic. However, the humification index (HIX) and the biological index (BIX) do seem to be useful for studying wastewaters, since they have provided consistent results in the present work. This study shows the potential of EEM fluorescence to identify the origin of some industrial effluents, although more research is needed to check these preliminary results.

Spatial variations of heavy metal contamination and associated risks around an unplanned landfill site in India

The study highlights the impact of unplanned landfill site on quality of groundwater, soil, and plants. The site selected is the Bhalaswa landfill site located in the urbanized region of Delhi, India. The associated potential ecological and human health risks to the population residing within the catchment area of the landfill site were evaluated. The order of abundance of heavy metals (measured using atomic absorption spectrometer) in the soil was found to be Fe > Cu > Cd > Ag, with Cu and Cd exceeding the WHO (World Health Organization)-recommended limits. Translocation factor (Root_metal/Shoot_metal) for Cd in P. juliflora plant (most dominant species in the region) at the landfill site was found to be the highest. The groundwater at the landfill site, 500 m, and 1000 m distance were found to exceed the WHO recommendation limits for Cd by 14.2%, 7.1%, and 1.4%, respectively. The estimated ecological risk index (E_r) indicated a high level of contamination particularly by Cu (E_r = 90.63) and Cd (E_r = 180). Children were found to be at higher risk by ingestion of Cd contaminated water (target hazard quotient = 5.1 > 1, indicating highest risk due to noncarcinogenic effects) followed by Ag (1.5) and Cu (1.4). The strong positive correlation of Cd between various ecological compartments with distance (Spearman rho's correlation > 0.75, 99% confidence level test) implied its high mobility and easy dispersion capacity towards the residential colony around the landfill, thereby indicating high associated ecological and human health risks. To conclude, there is a need to maintain a setback distance greater than 500 m from the landfill site in order to reduce the ecological as well as health risks associated with the landfill. The findings of this study provides a brief glimpse of the scenario of heavy metal pollution around such unplanned landfill sites and aids in taking remedial steps.

Advanced landfill leachate biochemical effluent treatment using Fe-Mn/AC activates O3/Na2S2O8 process: process optimization, wastewater quality analysis, and activator characterization

A novel catalyst of Fe-Mn/AC was prepared and used as a heterogeneous catalyst to activate O₃/Na₂S₂O₈ for landfill leachate biochemical effluent treatment. The experimental results indicated that the highest COD (84%) and color (98%) removal was obtained at Fe-Mn/AC dosage 1.2 g/L, O₃ concentration 1.2 g/L, Na₂S₂O₈ dosage 6 g/L, initial pH 10, and reaction time 100 min. Three-dimensional and excitation emission matrix (3D-EEM) fluorescence spectrometry, Fourier transform infrared spectroscopy (FTIR), and gas chromatography mass spectrometry (GC/MS) of wastewater samples before and after treatment demonstrated that the leachate biochemical effluent contained a large amount of humic and fulvic acid organic compounds. After treatment with this coupling system, both the pollution level of dissolved organic matter (DOM) and the fluorescence intensity declined. The micro morphology of Fe-Mn/AC was characterized using scanning X-ray diffraction patterns (XRD), electron microscope spectra (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. It can be concluded that the microscopic morphology of the catalyst is porous. The main active components are amorphous MnO₂ and multivalent iron oxides. Furthermore, the Fe-Mn/AC catalyst showed great reusability; the removal efficiency of COD was only reduced from 84% to 79% at the fourth reaction. Moreover, the COD removal efficiency could recover to 81% after catalyst regeneration.

Benchmarking leachate co-treatment strategies in municipal wastewater treatment plants under dynamic conditions and energy prices

Combined leachate treatment at municipal wastewater treatment plants (WWTPs) is applicable to a certain extent depending on the leachate composition, treatment plant configuration and its capacity. Co-treatment of leachate at WWTPs has several advantages, but due to increasingly stringent discharge standards applied in WWTPs, it has become more problematic. This study was undertaken to investigate the impact of leachate feeding strategies on effluent quality and the aeration energy costs of WWTPs. A modified version of Benchmark Simulation Model No.1 was used to develop, test and compare several leachate feeding and WWTP control strategies in the context of dynamic pollutant loads and energy prices. The results highlighted that combined leachate treatment led to a deterioration in the quality of discharged wastewater, as indicated by a 12-20% increase in effluent quality index. Additionally, it adversely affected aeration energy demand and cost of the plant by increasing them 1.7-2.3% and 0.8-2.5%, respectively. The impacts could be mitigated by adjusting leachate flow based on effluent ammonium concentrations and by using advanced process control, i.e. feedback ammonium control for dissolved oxygen regulation in aerobic reactors. The study demonstrates that modeling can be used as a valuable tool to assess the potential impacts of leachate co-treatment and develop better management strategies.

Improved understanding of dissolved organic matter transformation in concentrated leachate induced by hydroxyl radicals and reactive chlorine species

Concentrated leachate (CL) is commonly featured with high salt and dissolved organic matters (DOM). In this study, molecular transformation of DOM was revealed to identify the reactive mechanisms with (non-) radical reactive species in ozonation, electrolysis and E⁺-ozonation processes. Chlorine ions were efficiently activated into non-radical reactive chlorine species (RCS) with 245.7 mg/L, which was more dominant in electrolysis. Compared to ozonation, C_•OH was increased from 2.6 × 10^-4 mg/L into 5.8 × 10^-4 mg/L and the generation of Cl•/ClO• could be concluded according to the decline of non-radical RCS in E⁺-ozonation process. For chromophoric and fluorescent DOM, aromatic compounds and polymerization degree dramatically decreased in E⁺-ozonation. Lipid-like and CRAM/lignin-like compounds were substantially degraded, as •OH and ClO•/Cl• shows an affinity towards oxygen-containing organic compounds via single electron transfer by attracting OH bonds. Especially, carbon/hydrogen/oxygen (CHO-containing) compounds were readily to be degraded with the removal efficiency of 92.5 %, 97.0 % and 98.4 % in electrolysis, ozonation and E⁺-ozonation, respectively. Moreover, nitrogen atoms have a negative effect on DOM degradation, and thus, carbon/hydrogen/nitrogen and carbon/hydrogen/nitrogen/sulfur (CHN- and CHNS-containing) compounds were considered as refractory compounds. This paper is expected to shed light on the synergetic effect in E⁺-ozonation and transformation of refractory DOM in CL treatment.

Effective treatment of spacer tube reverse osmosis membrane concentrated leachate from an incineration power plant using coagulation coupled with electrochemical treatment processes

Membrane concentrated leachate is an important secondary pollutant in incineration plants and needs to be treated properly in order to achieve the "zero discharge" standard for pollutants from incineration plants. In this study, coagulation followed by the electro-oxidation (EO), and electro-coagulation (EC) methods were studied. Each of these processes was used to treat the spacer tube reverse osmosis membrane concentrated leachate from an incineration plant. A single factor experiment was used to determine the optimal conditions for each individual process. In addition, a two-stage electrochemical treatment was investigated after combining the optimized EO and EC processes. The results showed that the two-stage electrochemical treatment process can achieve much higher removal efficiencies than when only EO or EC are applied. The optimal conditions for the two-stage electrochemical treatment process were 180 min of the optimized EO process as the 1st stage treatment process, followed by 60 min of the optimized EC process as the 2nd stage treatment process. After the optimized coagulation-EO-EC process, the total organic carbon (TOC), UV₂₅₄, ammonia nitrogen (NH₃-N), total nitrogen (TN), color (CN), turbidity (TUB), and solution conductivity (SC) removal efficiencies were 96.19%, 98.98%, 96.54%, 88.21%, 99.72%, 98.24%, and 54.67%, respectively. This study can provide a theoretical basis for the treatment of concentrated leachate from MSW incineration plants.

Compositional characteristics of dissolved organic matter during coal liquefaction wastewater treatment and its environmental implications

The variations in the structural components of dissolved organic matter (DOM) during coal liquefaction wastewater (CLW) treatment are still unclear at present, limiting the further improvement and application of CLW treatment processes. In this study, the changes of DOM composition during air flotation, catalytic oxidation, biofiltration, ozonation, anoxic/oxic (A/O), and membrane bioreactor (MBR) which were applied in the full-scale CLW treatment, were investigated by three-dimensional excitation-emission matrix fluorescence and ultraviolet-visible spectroscopy. The dissolved organic carbon and chemical oxygen demand of the raw CLW reached 1965.2 mg/L and 5310.0 mg/L, respectively, with humic acid-like substances being as the dominant component (63.1%), and protein-like substances contributing a small amount (5.3%). Air flotation could treat humic acid-like substances more effectively. Catalytic oxidation and ozonation efficiently removed macromolecular aromatic substances with aliphatic chain substituents, resulting in the notable enhancement of the biodegradability of the organics. The DOM removal efficiency of biofiltration and A/O reached 86.0% and 92.3%, respectively, and simultaneously complex macromolecular substances with a high degree of aromaticity were formed. This study could provide a theoretical basis for optimizing the technical parameters and further improving the treatment efficiency of CLW.

UPLC Orbitrap MS/MS-based fingerprints of dissolved organic matter in waste leachate driven by waste age

Waste leachate is a pool of complicated metabolites from waste treatment and disposal as a global environmental problem. The recognition of dissolved organic matter (DOM) in leachate is crucial to improve leachate treatment efficiency and comprehend waste stabilization process. The present study acquired the molecular information for DOM in 22 waste leachate samples using ultra-performance liquid chromatography coupled with hybrid quadrupole Orbitrap mass spectrometry (UPLC Orbitrap MS/MS) based on two dimensions of retention time and mass-to-charge ratio. Unique mass peaks occupied more than 20% of the detected mass peaks in each leachate, implying that the molecular information for DOM could be the fingerprint of waste landfills and storage pits. Waste age and composition predominately accounted for this unique DOM. The double-bond equivalent increased and the H/C decreased with waste age. We further found that 57 precursor ion peaks and artificial matter (confirmed as N-butylbenzenesulfonamide) were significantly correlated with waste age by multiple test and non-target screening. These molecular characteristics of raw leachate were first determined to compensate for the evolution of leachate with waste age. The fingerprints of waste leachate can be further applied in environmental monitoring scenarios, e.g., tracing landfill leakage.

Bioremediation of landfill leachate by Aspergillus flavus in submerged culture: Evaluation of the process efficiency by physicochemical methods and 3D fluorescence spectroscopy

The present study investigates the ability of Aspergillus flavus (A. flavus) for organic and nitrogen matter removal from landfill leachate. Experiments were carried out with different types of leachate, (Young (YL), Intermediate (IL) and Old (OL)) used at different concentrations of the leachate up to 100%. The organic fraction of landfill leachate was measured by biological oxygen demand (BOD₅) and chemical oxygen demand (COD) then it was qualitatively assessed using three dimensional excitation emission matrix (3D-EEM). The nitrogen fraction was measured by ammonium (NH₄⁺) and nitrate (NO₃^-). The experiments revealed that, BOD₅, COD and NH₄⁺ removal rates after 4 weeks of treatment in flasks were within the ranges of 47.90-81.63%, 12.91-48.50% and 70.84-98.81%, respectively and that affected the reduction of the phytotoxicity in a positive way. A. flavus with 25% concentration of YL recorded the best results in reducing COD and BOD₅ with maximum removal rates of around 48.50% and 81.63%, respectively. However, the highest NH₄⁺ removal rate of 98.81% was found in 25% concentration of OL. The 3D-EEM results showed that the intensities of the fluorescent peaks for the three treated leachates have decreased sharply after treatment. This was confirmed by the increase of the organic matter complexity index for different treatments (from 0.55 to 0.87). Therefore, A. flavus may be potentially useful in the treatment of landfill leachate at a concentration of less than or equal to 50% as it was able to remove organic and nitrogen compounds, particularly in the treatment of YL leachate at a concentration of 25%.

The effect of different denitrification and partial nitrification-Anammox coupling forms on nitrogen removal from mature landfill leachate at the pilot-scale

The effects on nitrogen removal from landfill leachate were compared between the denitrification (DN) direct coupling in Partial nitrification (PN)-Anammox (DN+(PN-Anammox)) and pre-DN followed by PN-Anammox (DN-PN-Anammox). Both processes can achieve coupling and high nitrogen removal. However, the DN+(PN-Anammox) process was not conducive to the treatment of high-COD wastewater. The total nitrogen removal rate (TNRR) and total nitrogen removal efficiency (TNRE) were stable at 0.31 kg/(m³·d) and 76.3%. When UASB was added to denitrification and transform the process into DN-PN-Anammox, the influent NH₄⁺-N and COD concentrations were increased to 2230 and 2612 mg/L, TNRR and TNRE reached 0.45 kg/(m³·d) and 96.7%, respectively. The DN-PN-Anammox process not only was able to make full use of degradable COD in wastewater to realize the NO₃^--N removal, but also benefited the growth of autotrophic bacteria. The DN-PN-Anammox reduced the oxygen supply and was more conducive to the treatment of highly-concentrated mature landfill leachate.

Elucidating the structural variation of membrane concentrated landfill leachate during Fenton oxidation process using spectroscopic analyses

Membrane concentrated landfill leachate (MCLL) contains large amounts of recalcitrant organic matter that cause potential hazards to the environment. Knowledge on the compositional variation of MCLL during treatment is important for a better understanding on the degradation pathway of organic pollutants. In this work, the structural change of MCLL during Fenton oxidation process was examined using spectroscopic techniques. The removal rates of COD, TOC and UV₂₅₄ reached 78.9 ± 1.3%, 70.2 ± 1.4% and 90.64 ± 1.6%, respectively, under the optimal condition (i.e., dosage of H₂O₂ = 9.0 mL/200 mL, H₂O₂/Fe(II) molar ratio = 3.0, pH = 3.0, time = 40 min). Spectral analyses suggested that aromatic/CC structure and CO bonds in MCLL can be successfully destroyed by Fenton oxidation, resulting in a decrease in molecular weight. One fulvic-like and one humic-like components were identified in MCLL, both of which can be removed by Fenton treatment. In addition, two-dimensional correlation spectroscopic analyses suggested the oxidative changes of MCLL structure in the order of fulvic-like component/unsaturated conjugated bond > aromatic structure > humic-like component. The results may provide a new insight to the understanding on the structure variation of MCLL during treatment, which is beneficial for the design of cost-effective treatment strategies.

Improved oxidation of refractory organics in concentrated leachate by a Fe2+-enhanced O3/H2O2 process

Concentrated leachate from membrane processes, which contains a mass of refractory organics and salt, has become a new problem for wastewater engineers. In this study, removal of organic contaminants in concentrated landfill leachate was investigated by applying the ferrous ion (Fe²⁺) catalyzed O₃/H₂O₂ process. The maximum chemical oxygen demand (COD) and absorbance at 254 nm (UV₂₅₄) removal efficiencies under the optimal conditions (initial pH = 3.0, Fe²⁺ dosage = 6.500 mM, H₂O₂ dosage = 18.8 mM and O₃ dosage = 52.65 mg min^-1) were 48.82% and 63.59%, respectively. These were higher than those achieved using the Fe²⁺/O₃, O₃/H₂O₂, and O₃ processes, and biodegradability of the leachate was improved significantly. Moreover, compared with other processes, the Fe²⁺ had a stronger catalytic effect. Molecular distribution analysis and three-dimensional excitation and emission matrix analysis both indicated that the fulvic acid and humic acid in the concentrated leachate were greatly degraded. Ultraviolet-visible spectra showed that the Fe²⁺/O₃/H₂O₂ process mainly destroyed unsaturated bonds and decreased the aromatic degree of the leachate. The reaction mechanism of the Fe²⁺/O₃/H₂O₂ process mainly was attributed to three factors: (1) O₃ and H₂O₂ reacting to produce ^•OH; (2) H₂O₂ and O₃ decomposing into ^•OH through the oxidation of Fe²⁺ to Fe³⁺; and (3) coagulation by Fe (OH)₃. The ^•OH can rapidly degrade recalcitrant organics, and coagulation also increases the removal of organic matter. Therefore, the Fe²⁺/O₃/H₂O₂ process was an effective method for treating concentrated landfill leachate.

Effective removal by coagulation of contaminants in concentrated leachate from municipal solid waste incineration power plants

Municipal solid waste (MSW) incineration is widely used in China. Concentrated leachate, containing high concentrations of pollutants, is an important type of secondary pollution produced in MSW incineration power plants and requires proper treatment. In this study, various coagulants were used to treat concentrated leachate from a nanofiltration (NF) membrane that treated leachate from an MSW incineration plant. The optimal coagulation condition was determined in this study. Under the optimal condition, removals of chemical oxygen demand, light absorbing substances (at 254 nm), total nitrogen, color and turbidity were 68.42%, 69.01%, 44.14%, 92.31% and 87.44%, respectively. Much of the refractory organic matter with relatively high molecular weight, aromaticity and humification degree was removed, and effluent had a lower molecular weight than raw NF concentrated leachate. Study also found that some parts of high molecular weight compounds from NF CL were removed by coagulation process, but the change of distribution of molecular weight was not outstanding. The NF concentrated leachate, both before and after coagulation, contained a large amount of chloride. Hence, a follow-up study should be conducted to find an effective additional processing that can remove organic matter using the high concentration of chloride in the NF concentrated leachate coagulation effluent. This study provides a theoretical basis for the treatment of concentrated leachate from MSW incineration power plants.

Electrochemical advanced oxidation processes using novel electrode materials for mineralization and biodegradability enhancement of nanofiltration concentrate of landfill leachates

The objective of this study was to implement electrochemical advanced oxidation processes (EAOPs) for mineralization and biodegradability enhancement of nanofiltration (NF) concentrate from landfill leachate initially pre-treated in a membrane bioreactor (MBR). Raw carbon felt (CF) or Fe^IIFe^III layered double hydroxides-modified CF were used for comparing the efficiency of homogeneous and heterogeneous electro-Fenton (EF), respectively. The highest mineralization rate was obtained by heterogeneous EF: 96% removal of dissolved organic carbon (DOC) was achieved after 8 h of electrolysis at circumneutral initial pH (pH₀ = 7.9) and at 8.3 mA cm^-2. However, the most efficient treatment strategy appeared to be heterogeneous EF at 4.2 mA cm^-2 combined with anodic oxidation using Ti₄O₇ anode (energy consumption = 0.11 kWh g^-1 of DOC removed). Respirometric analyses under similar conditions than in the real MBR emphasized the possibility to recirculate the NF retentate towards the MBR after partial mineralization by EAOPs in order to remove the residual biodegradable by-products and improve the global cost effectiveness of the process. Further analyses were also performed in order to better understand the fate of organic and inorganic species during the treatment, including acute toxicity tests (Microtox^®), characterization of dissolved organic matter by three-dimensional fluorescence spectroscopy, evolution of inorganic ions (ClO₃^-, NH₄⁺ and NO₃^-) and identification/quantification of degradation by-products such as carboxylic acids. The obtained results emphasized the interdependence between the MBR process and EAOPs in a combined treatment strategy. Improving the retention in the MBR of colloidal proteins would improve the effectiveness of EAOPs because such compounds were identified as the most refractory. Enhanced nitrification would be also required in the MBR because of the release of NH₄⁺ from mineralization of refractory organic nitrogen during EAOPs.

An investigation of refractory organics in membrane bioreactor effluent following the treatment of landfill leachate by the O3/H2O2 and MW/PS processes

In this study, refractory organics in a membrane bioreactor (MBR) effluent were investigated following the treatment of landfill leachate by the ozone combined hydrogen peroxide (O₃/H₂O₂) and microwave-activated persulfate (MW/PS) processes. The treatment efficiency and the transformation characteristics of refractory organics and reactive oxygen species were determined. It was found that an acidic environment and an increase in the O₃ dosage improved the organic removal efficiency in the O₃/H₂O₂ process, and the use of H₂O₂ improved the treatment efficiency, while excessive H₂O₂ inhibited it. In the MW/PS process, an increase in the PS dosage and MW power greatly improved the treatment efficiency, while an alkaline environment inhibited it. Under the optimized reaction parameters, the O₃/H₂O₂ and MW/PS processes effectively degraded refractory organics (i.e., humic acid and fulvic acid) into components with a smaller molecular weight and simpler structure. The humification, aromaticity, and conjugation of organics in wastewater were greatly reduced. Compared to the O₃/H₂O₂ process, the MW/PS process had a better treatment effect on refractory organics, and there were more low molecular weight organics (<1 kDa) in the treated wastewater. Because O₃ is the main selective oxidant in the O₃/H₂O₂ process, a large amount of organic acids were accumulated. A large amount of hydroxyl radicals and sulfate radicals with strong oxidation ability were produced in the MW/PS process, and therefore the combined action of hydroxyl and sulfate radicals can efficiently decompose humus and intermediate organics. Overall, the MW/PS process was more effective in treating the MBR effluent than the O₃/H₂O₂ process. The results of this study provide a reference for the selection of an advanced oxidation process to eliminate refractory organics in landfill leachate.

Evaluation of coagulation-flocculation and nanofiltration processes in landfill leachate treatment

Landfill leachate consists mostly of a high content of refractory organic matter, ammonia and toxic compounds. All these compounds, regardless of their nature, have a potential pollution effect on local ground and surface waters. In this context, the purpose of the present study was to evaluate a treatment process (coagulation-flocculation with lime coupled with nanofiltration) applied to landfill leachate from Seropédica, Rio de Janeiro (Brazil). Jar tests were conducted to determine the optimum dosage of lime (ranged from 0 to 10 g L^-1) and, at optimum lime dose, ammonia nitrogen was removed during coagulation-flocculation process due to high pH. The process was settled for 6 h with slow stirring (50 rpm) to promote air entrainment and NH₃-N stripping before using the final treatment step of nanofiltration at 8 bar. After ammonia stripping, NH₃-N was reduced from 1,236 mg L^-1 to 353 mg L^-1 (71% removal efficiency). At the end of the combined treatment, TOC (total organic carbon), HS (humic substances) and COD (chemical oxygen demand) removals were 89%, 80% and 94%, respectively. The results showed that the combined process was effective in the removal of recalcitrant compounds and NH₃-N.

Impact of organic matter from leachate discharged to wastewater treatment plants on effluent quality and UV disinfection

There are growing concerns over the negative effects of leachate organic matter (LOM) on ultraviolet (UV) disinfection and effluent quality when leachate is co-treated with domestic wastewater. In this study, the effects of LOM on wastewater effluent quality were evaluated through field studies at wastewater treatment plants (WWTPs) that receive and do not receive leachate. Impacts of leachate on effluent quality were determined through UV measurements at 254 nm (UV₂₅₄), fluorescence measurements, and the quantification of conventional parameters which included nutrient and organic constituent concentrations. Results showed that some leachate impacts can be observed using UV₂₅₄ spectroscopy in wastewater influent and effluent when present at volumetric contributions as low as 0.01%. In addition, leachate impacted wastewater samples showed a higher dissolved organic nitrogen and dissolved organic carbon concentrations in the effluent relative to effluents from WWTPs without leachate. At leachate volumetric contributions greater than or equal to 0.1% (0.10-14.8%), UV₂₅₄ transmittance in wastewater effluents was below 65%. A typical guideline for effective UV disinfection at WWTPs is above 65% transmittance. Furthermore, fluorescence characterization of leachate-impacted wastewater showed a higher intensity of humic-like peaks relative to wastewater without leachate. This research provided a better understanding of the potential implications of accepting leachate at WWTPs. These effects, however, can be managed by ensuring that leachate discharge is maintained at acceptable volumetric contributions and evenly spread out over the discharge period.

Combination of self-organizing map and parallel factor analysis to characterize the evolution of fluorescent dissolved organic matter in a full-scale landfill leachate treatment plant

The dissolved organic matter (DOM) characterization in a full-scale landfill leachate treatment plant is of great importance for the design and operation of treatment processes. In this study, the long-term removal behaviors of DOM during landfill leachate treatment were explored using excitation emission matrix fluorescence spectroscopy (EEMs) coupled with parallel factor analysis (PARAFAC) and self-organizing map (SOM). Results indicated that the application of combining PARAFAC and SOM on EEMs analysis effectively characterized long-term removal behaviors of DOM during leachate treatment. The DOM in raw leachate was dominated by humic substances, while its composition exhibited significant seasonal differences. A large proportion of protein-like fluorescent dissolved organic matter (FDOM) and bulk DOM were removed within membrane bioreactor (MBR) system. Meanwhile the humic-like FDOM removal capacity in nanofiltration (NF) process was well comparable with those in the MBR system owing to the bio-recalcitrant nature of humic substances. The protein-like FDOM and bulk DOM were removed synchronously in both the process of MBR and NF. Moreover, samples distribution exhibited obvious differences among NF concentrate samples. In general, the performance of MBR-NF treatment for landfill leachate displayed reasonable stability in DOM removal irrespective of seasonal variations. This study enhanced our understanding of EEMs application in characterizing leachate-derived DOM composition and has potential implications for the associated monitoring investigations in engineered systems.

Metagenomics Response of Anaerobic Ammonium Oxidation (anammox) Bacteria to Bio-Refractory Humic Substances in Wastewater

Anammox-based processes have been widely applied for the treatment of wastewater (e.g., wastewater irrigation systems and constructed wetland) which consists of bio-refractory humic substances. Nonetheless, the impacts of bio-refractory humic substances on anammox consortia are rarely reported. In the present study, three identical lab-scale anammox reactors (i.e., HS0, HS1 and HS10), two of which were dosed with humic substances at 1 and 10 mg·L−1, respectively, were operated for nearly one year. The long-term operation of the reactors showed that the presence of humic substances in influent had no significant influence on nitrogen removal rates. Despite this, comparative metagenomics showed changes in anammox microbiota structure during the exposure to humic substance; e.g., the relative abundance of Candidatus Kuenenia was lower in HS10 (18.5%) than that in HS0 (22.8%) and HS1 (21.7%). More specifically, a lower level of humic substances (1 mg·L−1) in influent led to an increase of genes responsible for signal transduction, likely due to the role of humic substances as electron shuttles. In contrast, a high level of humic substances (10 mg·L−1) resulted in a slight decrease of functional genes associated with anammox metabolism. This may partially be due to the biodegradation of the humic substances. In addition, the lower dosage of humic substances (1 mg·L−1) also stimulated the abundance of hzs and hdh, which encode two important enzymes in anammox reaction. Overall, this study indicated that the anammox system could work stably over a long period under humic substances, and that the process was feasible for leachate treatment.

Identification of organic compounds in landfill leachate treated by advanced oxidation processes

Landfill leachates are considered to be complex effluents of a variable composition containing many biorecalcitrant and highly toxic compounds. Considering the shortage of studies concerning the treatment of landfill leachates using ozone, as well as its combination with catalysts, the aim of this paper was to identify the organic compounds in this effluent treated with advanced oxidation processes (AOPs) of ozonation (O₃), and heterogeneous catalytic ozonation with TiO₂ (O₃/TiO₂) and with ZnO (O₃/ZnO). In addition, this study sought to assess the efficiency of the removal of the organic matter present in the leachate. For the pre- and post-AOPs, the leachate was characterized through physicochemical parameters and identification of organic compounds using gas chromatography coupled to the mass spectrometry (GC-MS). The three processes studied (O₃, O₃/TiO₂, and O₃/ZnO) presented color removal, turbidity, BOD above 95%, and lower COD removals (19%, 24%, and 33%, respectively). All AOPs studied promoted a similar reduction of organic compounds from leachate, some of which with toxic and carcinogenic potential, such as p-cresol, bisphenol A, atrazine, and hexazinone. In addition, upon the removal of organic matter and organic compounds, the heterogeneous catalytic ozonation processes proved more efficient than the process carried out only with ozone.

Leachate generation rate modeling using artificial intelligence algorithms aided by input optimization method for an MSW landfill

Leachate is one of the main surface water pollution sources in Selangor State (SS), Malaysia. The prediction of leachate amounts is elementary in sustainable waste management and leachate treatment processes, before discharging to surrounding environment. In developing countries, the accurate evaluation of leachate generation rates has often considered a challenge due to the lack of reliable data and high measurement costs. Leachate generation is related to several factors, including meteorological data, waste generation rates, and landfill design conditions. The high variations in these factors lead to complicating leachate modeling processes. This study aims at identifying the key elements contributing to leachate production and developing various AI-based models to predict leachate generation rates. These models included Artificial Neural Network (ANN)-Multi-linear perceptron (MLP) with single and double hidden layers, and support vector machine (SVM) regression time series algorithms. Various performance measures were applied to evaluate the developed model's accuracy. In this study, input optimization process showed that three inputs were acceptable for modeling the leachate generation rates, namely dumped waste quantity, rainfall level, and emanated gases. The initial performance analysis showed that ANN-MLP2 model-which applies two hidden layers-achieved the best performance, then followed by ANN-MLP1 model-which applies one hidden layer and three inputs-while SVM model gave the lowest performance. Ranges and frequency of relative error (RE%) also demonstrate that ANN-MLP models outperformed SVM models. Furthermore, low and peak flow criterion (LFC and PFC) assessment of leachate inflow values in ANN-MLP model with two hidden layers made more accurate values than other models. Since minimizing data collection and processing efforts as well as minimizing modeling complexity are critical in the hydrological modeling process, the applied input optimization process and the developed models in this study were able to provide a good performance in the modeling of leachate generation efficiently.

Removal of phthalic acid dieters with dissolved organic matter by an anaerobic/anoxic/oxic leachate treatment process

The removal of di-n-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) with dissolved organic matter (DOM) was studied in a laboratory scale anaerobic/anoxic/oxic reactor for landfill leachate treatment. The removal rate was up to 98.0% for DBP and 78.2% for DEHP, which was related to humification of DOM (i.e., the aromaticity and molecular weight (MW) of humic substances in landfill leachate). The dissolved organic carbon (DOC) was mostly humic acid and fulvic acid in the fraction of 1–100 kDa MW, indicating strong aromaticity and a high DBP/DEHP concentration. With complete removal of the fraction, the removal rate of DBP/DEHP was also high. The positive correlation of the DOC and DBP/DEHP concentration in raw leachate and the effluent from each reactor showed that the interaction between DOM and DBP/DEHP facilitated the removal of organic pollutants.

The removal of di-n-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) with dissolved organic matter (DOM) was studied in a laboratory scale anaerobic/anoxic/oxic reactor for landfill leachate treatment.

Research on the treatment of biologically treated landfill leachate by joint electrochemical system

Biologically treated landfill leachate (BTLL) is typically characterized by significantly high amount of total nitrogen (TN) and chemical oxygen demand (COD), and it has low biodegradability. In this study, a joint electrochemical system (JES) composed of iron anode reactor (IAR) and Ti/RuO₂ anode reactor (TAR) was constructed to remove both TN and COD from BTLL and improve its biodegradability. The IAR and TAR with the same structure but using different anodes. As a result, JES could simultaneously remove COD and TN by 90.9 ± 0.3% and 90.2 ± 1.0%, respectively. Reduction of nitrite-N by Cu/Zn cathode in IAR and oxidation of ammonium-N by active chlorine in TAR were the major pathways for TN removal, while the COD could be removed by coagulation of iron flocs and oxidation by hydroxyl radicals and active chlorine. Fluorescence spectrum and parallel factor analysis showed that the main components of organics in BTLL were humic-like substances, fulvic-like substances, and soluble microbial degradation products. Humic-like substances were particularly removed by JES, and the remaining organics after electrolysis were some alkanes (e.g., heptane and nonane). Furthermore, decrease in molecular weight and aromaticity and increase in biodegradable substances indicated that the biodegradability of BTLL was effectively improved by the JES. The developed JES is a promising approach for application in the BTLL treatment.

A review of landfill leachate induced ultraviolet quenching substances: Sources, characteristics, and treatment

Landfill leachate contains extremely diverse mixtures of pollutants and thus requires appropriate treatment before discharge. Co-treatment of landfill leachate with sewage in wastewater treatment plants is a common approach because of low cost and convenience. However, some recalcitrant organic compounds in leachate can escape biological treatment processes, lower the UV transmittance of waste streams due to their UV-quenching properties, and interfere with the associated disinfection efficacy. Thus, the leachate UV quenching substances (UVQS) must be removed or reduced to a level that UV disinfection is not strongly affected. UVQS consist of three major fractions, humic acids, fulvic acids and hydrophilics, each of which has distinct characteristics and behaviors during treatment. The purpose of this review is to provide a synthesis of the state of the science regarding UVQS and possible treatment approaches. In general, chemical, electrochemical, and physical treatments are more effective than biological treatments, but also costlier. Integration of multiple treatment methods to target the removal of different fractions of UVQS can aid in optimizing treatment. The importance of UVQS effects on wastewater treatment should be better recognized and understood with implemented regulations and improved research and treatment practice.

Characterization and treatment of landfill leachate membrane concentrate by Fe2+/NaClO combined with advanced oxidation processes

Landfill leachate membrane concentrate (LLMC) is a type of non-biodegradable wastewater intercepted by the membrane filtration of the landfill leachate membrane bioreactor (MBR) effluent. The concentrations of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) in the LLMC collected from a landfill in Beijing were determined to be 4700 mg/L and 487 mg/L, 2–5 times higher than those in the MBR effluent. The photoelectro oxidation (PEO) followed with the NaClO enhanced Fe²⁺ coagulation were more effective for the removal of COD than the Fenton oxidation followed with the enhanced coagulation. The final removal efficiencies of COD, UV₂₅₄, NH₄⁺-N and color degree were 86%, 95%, 93% and 95% with Fe²⁺ (90 mmol/L) and NaClO (60 mmol/L, Fe²⁺:NaClO = 1.5:1), and PEO for 3 hours with a current density of 400 A/m². Due to the existence of Cl⁻, the chlorinated intermediates, which would be more toxic, were detected in the PEO treatment. However, the intermediates could be eliminated finally. As a result, the NaClO enhanced Fe²⁺ coagulation treatment combined with PEO treatment was efficient for the treatment of LLMC.

Raw hematite based Fe(III) bio-reduction process for humified landfill leachate treatment

Microorganisms from paddy soils and raw hematite are used for enhancing natural Fe(III) bio-reduction, in order to remove macromolecular organic pollutants from humified landfill leachate. Based on batch experiments, 60% of refractory organics can be adsorbed by hematite in 12 days. In the presence of Fe(III)-reducing bacteria, 489.60 ± 0.14 mg L^-1 of dissolved organic matters can be degraded to 51.90 ± 3.96 mg L^-1 within 50 days; twelve types of semi volatile organic compounds can be degraded; hereby, the reaction follows a first-order kinetics. Crystalline Fe(III) is transformed into the amorphous form and reduced to Fe(II), hydroquinone functional groups in the humic acid (HA) are transformed to quinone ones, and the formation of HA-hematite ligands is promoted. Comparing with most of the studies about electron shuttling of HA, the transformation of quinone in the HA to hydroquinone could not be observed in the present bio-system. Based on column evaluations, more than 93% of chemical oxygen demand (influent concentration of 658 ± 19 mg L^-1) could be removed microbially under flow conditions, when the hydraulic retention time was 45 h. Raw hematite-based Fe(III) bio-reduction has a promising potential for the removal of humic and benzene series in humified landfill leachate.

Effect of the structure of stacked electro-Fenton reactor on treating nanofiltration concentrate of landfill leachate

The membrane concentrate from landfill leachate has great potential risks of the environmental pollution. The aim of this study was to investigate the structure effect of stacked electro-Fenton (EF) reactor on the nanofiltration (NF) concentrate treatment from landfill leachate. The stacked EF reactor was constructed with a carbon-PTFE gas diffusion cathode and an IrO₂-Ta₂O₅ anode with different electrode spacings (i.e., 2, 5, 10, and 40 mm) and electrode pairs (i.e., 1, 3, 6, and 9). Results showed that smaller electrode spacing and more electrode pairs in the stacked EF reactor improved the COD removal in the NF concentrate treatment. The specific energy consumption decreased with smaller electrode spacing but increased with more electrode pairs. Under the current density of 15 mA cm^-2, Fe²⁺ dosage of 560 mg L^-1, the stacked EF reactor with 9 electrode pairs and the electrode spacing of 2 mm removed 71 ± 6% of the total COD in the NF concentrate within 6 h and the specific energy consumption was 207 ± 20 kWh∙kg COD^-1. The COD removal was kept stable in the stacked EF reactor within 3 cycles of operation. Three-dimensional fluorescence spectroscopic and gas chromatographic mass spectrometric analysis showed that humic acids and aromatic proteins were efficiently degraded in the EF process and large amount of aromatic hydrocarbons was detected in the treated NF concentrate. Our stacked EF reactor could be used to treat leachate concentrates with effectively degradation of the refractory organic pollutants.

Evaluation of the biodegradability and toxicity of landfill leachates after pretreatment using advanced oxidative processes

Leachate from urban solid waste landfills is a complex mixture of organic and inorganic substances that cause damage to the environment, due to the high concentration of recalcitrant organic matter and toxicity. The objective of this study was to apply advanced oxidation processes (AOP), namely the dark Fenton and solar photo-Fenton processes, to young and old landfill leachates prior to biological treatment. The leachates were obtained from the Seropedica and Gramacho landfill sites, respectively, located in Rio de Janeiro State, Brazil. For the two Fenton processes, different conditions of pH (1.5, 3.0 and 5.0) and Fe²⁺: H₂O₂ ratio (1:2, 1:5 and 1:10) were evaluated. Biodegradability was evaluated using the Zahn-Wellens methodology and Aliivibrio fischeri acute toxicity tests were conducted in order to predict the toxicity in the activated sludge. The best conditions for both Fenton processes were pH of 3.0 and Fe²⁺: H₂O₂ and COD_RAW:H₂O₂ mass ratios of 1:5 and 1:1, respectively. The solar photo-Fenton process was more effective at improving the quality for both leachates, reaching COD, TOC and abs 254 nm reductions of 82%, 85% and 96.3%, respectively, for the Seropedica landfill leachate. In the case of the Gramacho landfill leachate, the corresponding reductions were 78.2, 80.7% and 91.1%, respectively. The biodegradability results for the untreated leachates from the Seropedica and Gramacho sites were 65% and 30% respectively. The biodegradability of both leachates was improved by the Fenton processes, especially the solar photo-Fenton process, which increased the leachate biodegradability to 89% (Seropedica) and 69% (Gramacho). For both leachates, a greater reduction in the acute toxicity was achieved with the solar photo-Fenton compared to the dark-Fenton process. The Seropedica landfill leachate showed high toxicity (EC50 = 33%, 15 min), after the dark Fenton and solar photo Fenton processes, with EC50 values of 81 and 91%, respectively. In the case of Gramacho landfill leachate toxicity, the EC50 value of the raw leachate was 13%, whereas after the dark Fenton and solar photo Fenton processes the corresponding values were 54% and 59%, respectively. These results indicate that the Fenton process (especially solar photo-Fenton), was efficient in terms of increasing the biodegradability and reducing the toxicity of the leachate. This is important in relation to protecting the microbiological community in the activated sludge process.

Membrane bioreactor performance in treating Algiers' landfill leachate from using indigenous bacteria and inoculating with activated sludge

This study focuses on the treatment of both organic and metallic pollution in the Staoueli landfill leachate. This leachate contains a large amount of organic and inorganic matter and it must imperatively be treated before being released into the environment. Our work presents a comparative study between two membrane sequenced batch bioreactors (B2 contains indigenous leachate bacteria and B1 contains activated sludge). The purpose is to assess the best treatment to use, one that allows the reduction of the polluting load of the leachate and a reduction of membrane fouling. Performances were evaluated by measuring the chemical oxygen demand (COD) and the metal content of the leachate (zinc, iron). The results showed a similar COD removal efficiency in B2 (95%) and B1 (93%). Coupling the bioreactors with an ultrafiltration process allowed a notable reduction in zinc and iron concentrations: Fe of 35% and Zn of 78% for B1UF, and Fe of 71% and Zn of 74% for B2UF.

Next-generation sequencing showing potential leachate influence on bacterial communities around a landfill in China

The impact of contaminated leachate on groundwater from landfills is well known, but the specific effects on bacterial consortia are less well-studied. Bacterial communities in a landfill and an urban site located in Suzhou, China, were studied using Illumina high-throughput sequencing. A total of 153 944 good-quality reads were produced and sequences assigned to 6388 operational taxonomic units. Bacterial consortia consisted of up to 16 phyla, including Proteobacteria (31.9%-94.9% at landfill, 25.1%-43.3% at urban sites), Actinobacteria (0%-28.7% at landfill, 9.9%-34.3% at urban sites), Bacteroidetes (1.4%-25.6% at landfill, 5.6%-7.8% at urban sites), Chloroflexi (0.4%-26.5% at urban sites only), and unclassified bacteria. Pseudomonas was the dominant (67%-93%) genus in landfill leachate. Arsenic concentrations in landfill raw leachate (RL) (1.11 × 10³ μg/L) and fresh leachate (FL2) (1.78 × 10³ μg/L) and mercury concentrations in RL (10.9 μg/L) and FL2 (7.37 μg/L) exceeded Chinese State Environmental Protection Administration standards for leachate in landfills. The Shannon diversity index and Chao1 richness estimate showed RL and FL2 lacked richness and diversity when compared with other samples. This is consistent with stresses imposed by elevated arsenic and mercury and has implications for ecological site remediation by bioremediation or natural attenuation.

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.