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• O 3 /H 2 O 2 and MW/PS processes for the MBR effluent are systematically compared. • MW/PS process has a better treatment effect on refractory organics in MBR effluent. • Ozone plays a major role in the degradation of aromatic organic compounds in the O 3 /H 2 O 2 process. • Hydroxyl and sulfate radicals are the main reactive oxygen species in the MW/PS process. • Chemical oxidation (i.e. O 3 /H 2 O 2 , MW/PS) is a viable technology to eliminate organics in leachate. 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 (O 3 /H 2 O 2) 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 O 3 dosage improved the organic removal efficiency in the O 3 /H 2 O 2 process, and the use of H 2 O 2 improved the treatment efficiency, while excessive H 2 O 2 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 O 3 /H 2 O 2 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 O 3 /H 2 O 2 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 O 3 is the main selective oxidant in the O 3 /H 2 O 2 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 O 3 /H 2 O 2 process. The results of this study provide a reference for the selection of an advanced oxidation process to eliminate refractory organics in landfill leachate. [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]

• 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]

Landfill leachate contains high concentrations of complex organic matter (OM) that can severely impact the ecological environment. If landfill leachate is to be treated using a combined "biological + advanced treatment" process, the molecular information of OM must be investigated to optimize the operation parameters of the combined process and maximize the removal of organic pollutants. This study applied ultra-high resolution mass spectroscopy to investigate the degradation and transformation characteristics of refractory OM in mature landfill leachate at the molecular level (m / z = 150–800) during biological treatment (i.e., semi-aerobic aged refuse biofilter, SAARB) and subsequent chemical oxidation (i.e., the Fenton process and ozonation). After SAARB treatment, the polycyclic aromatics (aromatic index, AI > 0.66) and polyphenol (0.66 ≥ AI > 0.50) contents increased, and the highly unsaturated phenolic compounds (AI ≤ 0.50 and H/C < 1.5), which have a high bioavailability, were mostly removed. Compared with raw leachate, SAARB effluent (i.e., SAARB leachate) contained fewer organics with short carbon chains, more organics with long carbon chains, an elevated condensation degree for organics and, thus, a considerably reduced biodegradability. Although both the Fenton and ozonation processes could remove many of the polycyclic aromatics and polyphenols, ozone produced considerable amounts of aliphatic compounds with high bioavailability. Compared to ozonation, the Fenton process utilized the hydroxyl radical to non-selectively react with OM and produced better mineralization results. Unlabelled Image • The Fenton process had a better mineralization effect for leachate treatment. • The SAARB process cannot remove polycyclic aromatic and polyphenol compounds. • Transformation of DOM in Chemical treatment was characterized by ESI FT-ICR MS. • The types of OM targeted by ozonation and the Fenton process are quite different. [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]

Ultraviolet-quenching substances (UVQS), recently identified pollutants in landfill leachate, can interfere with ultraviolet disinfection when landfill leachate is co-treated with municipal sewage. This study investigated the elimination of UVQS in mature landfill leachates through a membrane bioreactor (MBR) and a semi-aerobic aged refuse biofilter (SAARB). Humus (i.e., fulvic and humic acids) was the main component of organic matter in both MBR- and SAARB-treated landfill leachates, while there was a more stable chemical structure of humus in the MBR-treated leachate. The concentration of UVQS in MBR-treated mature landfill leachate was higher than that of SAARB-treated leachate. Ozonation can degrade UVQS effectively, especially for landfill leachate containing a high concentration UVQS (i.e., MBR-treated landfill leachate). However, a large accumulation of small molecule acid might be caused by ozonation for highly concentrated UVQS in landfill leachate, leading to the delayed degradation of total organic carbon. Moreover, ozonation degraded both fulvic acid and humic acid; and degraded humic acid more effectively. For instance, 88.0% removal (MBR-CP2) and 96.0% removal (SAARB-CP2) of humic acid was higher than those (83.3% for MBR-CP1 and 92.3% for SAARB-CP1) of fulvic acid. The destruction of UV-quenching functional groups of organics (such as C C) by ozone was the main UVQS degradation mechanism of ozonation applied to MBR- and SAARB-treated landfill leachates. Therefore, the ozonation process can efficiently decrease UV absorption intensity in both MBR- and SAARB-treated landfill leachates. • More leachate UVQS can be reduced by SAARB (6.35 cm−1) than MBR (29.85 cm−1). • Humus is the main UVQS in MBR- and SAARB-treated landfill leachates. • Humic can be degraded more efficient than fulvic in ozonation process. • Ozonation process can destruct UV-quenching polar functional groups. [ABSTRACT FROM AUTHOR]