[Pollutant Removal Efficiency of Different Units Along a Mature Landfill Leachate Treatment Process in a Membrane Biological Reactor-Nanofiltration Combined Facility].

Properties of landfill leachate are complex. Therefore, leachate should be treated by combined processes with both biological and advanced methods. Due to the shortage of engineering-scale assessment data about the pollutant treatment contribution of individual process units, existing optimization methods still lack theoretical support. Here, a membrane biological reactor (MBR)+nanofiltration (NF) system with a capacity of 800 m3·d-1 was examined. Conventional physiochemical parameters and fluorescent parameters were examined to analyze the contribution of each process unit to treating mature landfill leachate. Furthermore, the transformation of dissolved organic matter (DOM) was evaluated using excitation emission matrix fluorescence spectroscopy-parallel factor (EEMs-PARAFAC). Results showed that the biological treatment removed soluble nitrogen (dissolved nitrogen, DN) by 74.7%, 54.6% occurred in the first-stage denitrification unit. The external ultrafiltration unit reduced dissolved chemical oxygen demand (COD) and dissolved organic carbon (DOC) by 92.2% and 93.3%, respectively. The nanofiltration unit effectively removed heavy metals and salts. Based on the tracking of DOM using fluorescent parameters, the first-stage denitrification unit was found to remove 75.4% of protein-like substances. The ultrafiltration unit mainly retained DOM with high hydrophilicity, while humus with high aromaticity was mainly retained by nanofiltration. The higher the degree of humification, the better the interception effect that was obtained. This indicates that biological treatment using the MBR process can be simplified, and ultrafiltration should prove reliable at preventing clogging during the treatment of mature landfill leachate.

DOM chemodiversity pierced performance of each tandem unit along a full-scale "MBR+NF" process for mature landfill leachate treatment.

Mature landfill leachate contains a substantial fraction of recalcitrant dissolved organic matters (DOM) that is a challenging for conventional wastewater treatment that is typically focused on the removal of biodegradable organic matter. "Biological treatment + membrane treatment" has been widely employed to treat complex leachate. However, the performance of each unit based on both conventional bulk indicators and molecular information has not been well understood. Therefore, the fate of DOM chemodiversity along the full-scale treatment process across ten sampling points over three different seasons were analyzed to determine the efficiency of every unit process with the assistance of ultra-performance liquid chromatography coupled with hybrid quadrupole Orbitrap mass spectrometry. Results showed that the process performance, visualized through the molecular signals, were relatively stable in the temporal dimension. The process removed 83.2%-92.2% of DOM molecules in terms of richness, where lignin/carboxyl-rich alicyclic compounds (CRAM)-likes with relatively high saturation was preferentially removed, while newly generated bio-derived N-containing compounds (N/Cwa 0.15-0.17) became resistant. The relationship between conventional bulk physicochemical indicators and molecular indexes suggested that soluble chemical oxygen demand (sCOD) and dissolved organic carbon (DOC) were contributed by the refractory DOM with high weighted average double bond equivalents (DBEwa), which was distributed in the region of O/C 0.2-0.5 and H/C 1.2-1.8. This refractory DOM required ultrafiltration and nanofiltration for removal. DOM molecules were positively correlated with five-day biochemical oxygen demand (BOD5) and revealed that approximately 96.9%-98.4% of the DOM could be removed or transformed in the primary anoxic zone. In addition, the bio-derived aliphatic/proteins, lipids and lignin/CRAM-likes (O/C > 0.2) with condensed aromatization were the sources of dissolved organic nitrogen (DON) and still remained in the final effluent. The present study suggests that the design and operation of the combination process with biological and membrane treatment could be specifically optimized based on the DOM molecular characteristics of the wastewater.

Improvement criteria for different advanced technologies towards bio-stabilized leachate based on molecular subcategories of DOM.

Considering dissolved organic matter (DOM) molecules, the present study is an attempt to unravel the individual removal targets of nine advanced treatment technologies for bio-stabilized landfill leachate. For the eight DOM molecular subcategories, preferable technologies and removal rates were as follows: lipids ‒ powdered activated carbon (PAC) adsorption (97%) and Fenton (97%); proteins ‒ extended electrolysis (92%) and Fenton (92%); and lignins/carboxylic rich alicyclic molecules (CRAM)-like organics ‒ Fenton (90%) and extended electrolysis (75%). As to individual technologies, Fenton, PAC adsorption, extended electrolysis, and reverse osmosis (RO) had the highest removal rates based on the intensity and abundance of DOM. As to the improved technology combinations, "Fenton with PAC adsorption" and "PAC adsorption with reverse osmosis" were then recommended according to the target complementarity in compound intensity and abundance. The study suggested that the treatment strategy of an unknown recalcitrantly biodegraded wastewater could be designed in a tailored way based on the subcategorized DOM characteristics of the refractory wastewater.

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.