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• Landfill leachate was effectively treated by SAARB combined Fenton method. • Fulvic- and humic-like substances were identified in SAARB effluent. • Two fluorescent substances were tracked with parameters varying in Fenton method. Semi-aerobic aged-refuse biofilter (SAARB) can achieve good treatment efficiency for organics and nitrogen ammonia, but the effluent of SAARB from treating landfill leachate (SAARB leachate) has high chemical oxygen demand (COD), compared to the discharge standard (100 mg/L), and high humification degree. In this study, the conventional Fenton method was used in the advanced treatment of SAARB leachate. Fluorescent components in SAARB leachate were identified and tracked with parallel factor (PARAFAC) analysis, and the influencing factors, i.e., Fe2+ dosage, n(H 2 O 2 /FeSO 4) ratio, initial pH, and reaction time, on the removal of fluorescent components were systematically investigated. UV–Vis spectra show the structural transformation of dissolved organic matter (DOM) in SAARB leachate. Results show that SAARB leachate mainly contains two fluorescent components: fulvic-like substances [C1; excitation (Ex)/emission (Em) (nm), (245)280/405] and humic-like substances [C2; Ex/Em (nm), (260)360/435]. A higher Fe2+ dosage, longer reaction time, and acidic conditions increased the degradation efficiency of organics, but excess H 2 O 2 inhibited the treatment process. Under optimum Fenton parameters (Fe2+ dosage of 5 mmol/L, n(H 2 O 2 /FeSO 4) ratio of 8, initial pH of 4, and reaction time of 60 min), removal rates of C1 and C2 were 52.97% and 77.81%, respectively. UV–Vis spectra indicate that the Fenton reaction can destroy unsaturated conjugated bonds, decreasing the humification degree, hydrophobicity, molecular weight, and condensation degree. Finally, the biodegradability (represented by BOD 5 (biochemical oxygen demand for 5-days)/COD) greatly increased (from 0.05 to 0.36), thus benefiting further biological treatment. The results provide suggestions and guidance for practical applications in landfill leachate treatment. [ABSTRACT FROM AUTHOR]

Refractory organic matter in membrane bioreactor effluent resulting from landfill leachate treatment has a complex composition. This paper identified the transformation mechanism of organic matter in a flocculation-ultraviolet (UV)/peroxymonosulfate (PMS) system at the molecular level using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. The results showed that the flocculation system was able to remove a large amount of dissolved organic matter (DOM) with high oxidation and unsaturation/saturation. UV radiation displayed a relatively strong reactivity for DOM with an electron-rich structure, which it can transform into DOM with lower aromaticity through photolysis and photosensitivity, although the effectiveness of the transformation was poor. In comparison, due to the action of reactive oxygen species, the UV/PMS system can enable reactions such as demethylation, dehydrogenation, decarboxylation, dehydroxylation, ring cleavage, and decarbonylation. It can remove approximately 60% quantity of the total DOM and produce DOM featuring a higher degree of oxidation and saturation than that of the UV system alone. The results showed that the UV/PMS system was a complementary of flocculation in DOM removal from the membrane bioreactor effluent, while the system also resulted in a large number of sulfuric compounds; thus, requiring further evaluation of its ecological effects. [Display omitted] • Flocculation removed most oxidized DOM and newly-produced sulfuric and aliphatic DOM. • UV radiation decreased the aromaticity of electron-rich DOM. • The combination of UV/PMS and flocculation ahieved effective DOM removal. • Sulfuric compounds were produced in the treated leachate, needing further evaluation. [ABSTRACT FROM AUTHOR]

During leachate treatment, molecular information regarding the completely removed, partially removed, less-reactive, increased, and produced parts of dissolved organic matter (DOM) remains unknown. This study applied ESI FT-ICR MS to investigate the transformation characteristics of leachate nanofiltration concentrate (NFC) DOM during a combined flocculation–O 3 /H 2 O 2 process. The NFC contained 5069 compounds in four main classes (CHO, CHON, CHOS, and CHONS compounds). The DOM number decreased to 4489 during flocculation and to 2903 after the O 3 /H 2 O 2 process. During flocculation, the completely and partially removed DOM was mainly low-oxygen unsaturated and phenolic compounds. Saturated DOM was produced and remained in the flocculated effluent. During the O 3 /H 2 O 2 process, the completely and partially removed DOM were mainly low-oxygen unsaturated and phenolic compounds that were mainly in a reduced state. Flocculation can remove many (condensed) aromatic compounds, and methylation and hydrogenation reactions occurred during flocculation. In the O 3 /H 2 O 2 process, dearomatization, demethylation, carboxylation, and carbonylation reactions further achieved the degradation of DOM that was resistant to flocculation. Overall, the combined flocculation-O 3 /H 2 O 2 process collectively eliminated a broader range of DOM than the single processes could achieve. The results of this study provide an in-depth understanding of DOM transformation in an NFC treatment. [Display omitted] • Transformation of NFC DOM in flocculation-O 3 /H 2 O 2 process was studied by FT-ICR MS. • Removed, less-resistant, and produced parts of NFC DOM in flocculation-O 3 /H 2 O 2 were determined. • A Kendrick mass defect theory was used to study DOM transformation of NFC. • Flocculation-O 3 /H 2 O 2 collectively eliminated a broader range of DOM. [ABSTRACT FROM AUTHOR]

• DOM composition in landfill and incineration leachate was systematically compared. • Transformations of the DOM molecular compositions by MBR/NF were investigated. • Phenolic compounds, polyphenols and polycyclic aromatics enriched in MBR leachate. • NF lowered the DOM abundances but with more complex DOM in the NF concentrate. • Coagulation in conjunction with an advanced O 3 /H 2 O 2 process was used to treat NF concentrate. Transformations of the molecular compositions of dissolved organic matter (DOM) in incineration leachate (IL) were investigated. Results revealed that DOM in IL had a lower oxidation degree than that in mature MSW landfill leachate (LL). Moreover, aliphatic compounds (2.0 ≥ H/C ≥ 1.5) having the highest bioavailability were the most abundant type of DOM in IL, making IL significantly more biodegradable than LL. Under microbial actions, etc., DOM composed of phenolic compounds (aromaticity index (AI) ≤ 0.50 and H/C < 1.5), polyphenols (0.66 ≥ AI > 0.50) and polycyclic aromatics (AI > 0.66) in MBR-treated effluents were enriched and more diverse than in the untreated leachates. Nanofiltration (NF) dramatically lowered the relative abundances of phenolic compounds, polyphenols and polycyclic aromatics in effluent generated by treatment of IL in a MBR. Although the concentration of DOM in NF effluent was comparatively low, the DOM compositions in the resulting NF concentrate were nearly identical to those in MBR effluent, but were more complex than those in an international standard DOM due to a higher content of CHOS and CHONS heteroatomic compounds. Particularly, coagulation in conjunction with ozone/hydrogen peroxide oxidation process were dramatically reduced most polyphenols and polycyclic aromatics from the NF concentrate. [ABSTRACT FROM AUTHOR]

• Refractory organics are degraded by the synergistic effects of MW with PS and H 2 O 2. • The MW/PS process degrades organics better than the MW/H 2 O 2 process. • Differences in DOM degradation mechanisms were revealed at the molecular level. • Humus is better degraded in the MW/PS process due to the major contribution of SO 4 -. This study investigated the degradation of organics in mature leachate treated by microwave radiation-activated persulfate (MW/PS) and hydrogen peroxide (MW/H 2 O 2) processes. Obvious synergistic effects existed in both the MW/PS and MW/H 2 O 2 processes, but were significantly higher in the MW/PS process. Refractory organics were better degraded by the MW/PS process than the MW/H 2 O 2 process due to the major contribution of SO 4 –. 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/H 2 O 2 and MW/PS processes, but the MW/PS process degraded dissolved organic matter (DOM) over a wider range than the MW/H 2 O 2 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. [ABSTRACT FROM AUTHOR]

• A combined process to treated landfill leachate was studied at the molecular level. • Mature landfill leachate contained a variety of organics with low bioavailability. • A membrane bioreactor can remove some organics from mature landfill leachate. • A reverse osmosis system can almost completely remove organics from mature leachate. This study investigated the effectiveness of a combined membrane bioreactor (MBR) and reverse osmosis (RO) process for treating leachate produced by a large-scale anaerobic landfill. The MBR process had limited treatment efficiency for removing organic pollutants, but when combined with RO, the integrated system completely removed macromolecular compounds (i.e., humic- and fulvic-like substances) and produced effluent that satisfied the applicable discharge standard. The landfill leachate contained many types of DOM that had high molecular weight and were highly unsaturated. Although the MBR process removed some DOM that had a relatively low saturated degree (mainly aliphatic compounds (2.0 ≥ H/C ≥ 1.5) with relatively high bioavailability), many bio-refractory compounds were not removed. The RO system greatly reduced the content of residual DOM in MBR effluent and was effective for removing heteroatom DOM, especially polycyclic aromatics (AI > 0.66) and polyphenols (0.66 ≥ AI > 0.50). The effluent from the combined process of MBR and RO treatment mainly contained a small number of aliphatic compounds and phenolic compounds (AI ≤ 0.50 and H/C < 1.5) that had higher bioavailability than DOM in the raw leachate and posed little environmental risk. [ABSTRACT FROM AUTHOR]