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• Application of membrane separation process in China is comprehensively investigated. • Leachate treatment capacity of NF is the highest in landfill and incineration plant. • A combination of NF and RO exhibits the best efficiency for leachates treatment. • Membrane processes are more likely to be adopted in economically developed regions. • Operation costs of membrane process mainly depends on the pre-treatment process. 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. [ABSTRACT FROM AUTHOR]

• Solidification and stabilization effect of Pb in MSWI fly ash was compared. • Pb leaching concentration, volume change ratio, and treatment cost were evaluated. • Combined solidification-stabilization process yielded the best treatment effect. • Optimal parameters are obtained through response surface methodology. Fly ash is a hazardous material that is produced from municipal solid waste incineration. It contains heavy metals and should be properly treated to meet landfill entry requirements. In this study, under the precondition that the leachable concentration of lead (Pb) exceeded the limit value for landfill disposal, the effects of cement solidification, chemical stabilization, and their combination on the leachable Pb concentration and the chemical state of Pb were systematically investigated. In addition, the reaction conditions were optimized by response surface methodology (RSM) in terms of leachable Pb concentration, volume change ratio, and treatment cost. The results indicated that the leachable Pb concentration decreased at lower cement or sodium dihydrogen phosphate (NaH 2 PO 4) dosages in cement solidification or NaH 2 PO 4 stabilization, and the liquid-to-solid ratio had a significant influence on cement solidification. The leachable Pb concentration met the limit value for landfill disposal in the individual processes with 20% cement or 5% NaH 2 PO 4 , and in the combined process with 10% cement + 2% NaH 2 PO 4. The combined process achieved the best treatment efficiency by enabling Pb to transform to a stable residual state. According to the RSM, a combined cement content of 11.64%, NaH 2 PO 4 content of 2.79%, and liquid-to-solid ratio of 0.48 were the optimal parameters, resulting in substantial decreases in the volume change ratio and treatment costs, while satisfying the preconditions for landfill disposal. In conclusion, the combined process can reduce the pollution risk to the environment, and is an efficient and cost-effective pre-treatment method for incinerator fly ash. [ABSTRACT FROM AUTHOR]

• The performance differences of three pilot-scale landfills were investigated. • MSW stabilization in the SABL was greatly accelerated. • NH 4 +–N in SABL leachate was substantially lower than that from the other landfills. • SABL leachate exhibited the least chloride pollution risk. Many studies have sought to optimize operation parameters and enhance the treatment capacity of bioreactor landfills (BL) under ideal laboratory conditions. At pilot scale, conclusions drawn from laboratory-scale experiments will be different due to variations in actual landfill composition and changes in environmental conditions. However, comparative pilot-scale studies of traditional anaerobic landfills (AnL) and BLs are rare. In this study, three pilot-scale landfills, including an AnL, anaerobic BL (AnBL) and semi-aerobic BL (SABL), were monitored to examine the difference in performance at different scales and among types of landfills. Settlement amount followed the order SABL (25.45 cm) > AnBL (18.67 cm) > AnL (14.38 cm). Decomposition of organic matter (i.e., volatile fatty acids) was more rapid in SABL than in the other landfills and no hydrolytic acidification period was observed. Therefore, among the three landfills, SABL entered the methanogenic stage in a much shorter time and MSW stabilization was accelerated due to this landfill's unique combination of aerobic-anoxic-anaerobic ambient. In addition, NH 4 +–N concentration in leachate from the SABL (~19.96 mg/L) was substantially lower than from AnL (338.28 mg/L) and AnBL (233.22 mg/L), and SABL leachate exhibited the least chloride pollution risk. This study provides theoretical support and strong evidence for using SABLs to treat MSW in practical applications. [ABSTRACT FROM AUTHOR]

• 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]

Highlights • Coupling SAARB and ozonation was firstly applied to the treatment of leachates. • DOM in mature leachate is significantly different from that in young leachate. • Degradation and transformation mechanism were studied using 3D-EEM-PARAFAC model. • The combined process may provide suggestions and guidance for practical project. Abstract Dissolved organic matter (DOM) in mature landfill leachate is significantly different from that in young landfill leachate; the composition of DOM greatly influences both biological treatment and advanced treatment processes. In the present study, the transformation and degradation mechanisms of landfill leachates in a combined semi-aerobic aged refuse biofilter (SAARB) and ozonation process was investigated using organic removal analysis, molecular weight distribution (MWD), 3D-EEM-PARAFAC analysis, UV–Vis spectroscopy, and linear regression. Results revealed that the DOM in mature landfill leachate contained a greater amount of aromatic substances and had higher molecular weight than DOM in young landfill leachate. After the SAARB process, humus contained in the SAARB was discharged with effluent from both mature and young landfill leachate. Due to the differences in composition and structure of organic matter, the COD removal efficiency (17.89%) of SAARB effluent from treating mature landfill leachate (mature SAARB effluent) was much lower than that (45.91%) of SAARB effluent from treating young landfill leachate (young SAARB effluent) under the same operational parameters of the ozonation process. As indicated by PARAFAC analysis, better chemical stability of DOM in mature SAARB effluent resulted in inferior ozone treatment efficiency. Furthermore, the hydrophobicity and the concentration of benzene ring compounds in the mature and young SAARB effluent were reduced significantly by the ozonation process. Therefore, great improvements in the biodegradability of SAARB effluents were achieved in the ozonation process. Overall, the results of this study provide suggestions and guidance for practical applications of these technologies. [ABSTRACT FROM AUTHOR]