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• DBD/Fenton process was used to treat landfill leachate and mitigate membrane fouling. • DBD/Fenton system overcame the pH limitation of the Fenton reaction. • 1O 2 , •OH, and O 2 •− were mainly involved in contaminant degradation by DBD/Fenton. • The degradation mechanism of PFOA entailed the cyclic elimination of CF 2 groups. • DBD/Fenton system promoted the formation of a loose and porous cake layer. This study investigated a sustainable approach through dielectric barrier discharge (DBD) enhanced Fenton technology coupling nanofiltration (NF) process for landfill leachate treatment. The DBD/Fe(II)/H 2 O 2 system exhibited significant synergistic effects, removing 55.07 % of TOC and 53.79 % of UV 254 within 60 min, respectively. Additionally, the DBD/Fe(II)/H 2 O 2 system demonstrated exceptional performance in removing fluorescent substances and large molecular organic compounds, thereby reducing the formation of cake layer on the nanofiltration membrane. Moreover, membrane flux increased by 2.34 times, with reversible and irreversible resistances decreasing by 75.79 % and 81.55 %, respectively. Quenching experiments revealed ·OH as the primary active species for perfluorooctanoic acid (PFOA) degradation in the DBD/Fe(II)/H 2 O 2 process. The degradation pathway of PFOA was also elucidated via capillary electrophoresis-quadrupole time-of-flight mass spectrometry analysis. Correlation analysis indicated that TOC and EEM were the primary fouling factors. Lastly, through an assessment of energy consumption, economic costs, and carbon dioxide emissions, the advantages and practical application potential of the DBD/Fe(II)/H 2 O 2 system were demonstrated. In summary, the DBD/Fe(II)/H 2 O 2 system emerges as a feasible strategy for NF pretreatment, holding immense potential for treating landfill leachate. [Display omitted] [ABSTRACT FROM AUTHOR]

• Over 89 % nitrogen in raw landfill leachate was removed through ESdAD system. • The effluent TN concentration is less than 25 mg-N/L in ESdAD system. • Superior pH modulation and system stability were obtained in ESdAD than SdAD system. • Nitrogen metabolic activity and electron transfer capacity were enhanced under current stimulation. • The coexistence of heterotrophic and autotrophic bacteria contributed to nitrogen removal improvement. The cost-effective and environment-friendly sulfur-driven autotrophic denitrification (SdAD) process has drawn significant attention for advanced nitrogen removal from low carbon-to-nitrogen (C/N) ratio wastewater in recent years. However, achieving efficient nitrogen removal and maintaining system stability of SdAD process in treating low C/N landfill leachate treatment have been a major challenge. In this study, a novel electrochemical-coupled sulfur-driven autotrophic denitrification (ESdAD) system was developed and compared with SdAD system through a long-term continuous study. Superior nitrogen removal performance (removal efficiency of 89.1 ± 2.5 %) was achieved in ESdAD system compared to SdAD process when treating raw landfill leachate (influent total nitrogen (TN) concentration of 241.7 ± 36.3 mg-N/L), and the effluent TN concentration of ESdAD bioreactor was as low as 24.8 ± 5.1 mg-N/L, which meets the discharge standard of China (< 40 mg N/L). Moreover, less sulfate production rate (1.3 ± 0.2 mg SO 4 2 − − S / mg NO x − − N vs 1.7 ± 0.2 mg SO 4 2 − − S / mg NO x − − N) and excellent pH modulation (pH of 6.9 ± 0.2 vs 5.8 ± 0.4) were also achieved in the ESdAD system compared to SdAD system. The improvement of ESdAD system performance was contributed to coexistence and interaction of heterotrophic bacteria (e.g., Rhodanobacter, Thermomonas , etc.), sulfur autotrophic bacteria (e.g., Thiobacillus, Sulfurimonas, Ignavibacterium etc.) and hydrogen autotrophic bacteria (e.g., Thauera, Comamonas, etc.) under current stimulation. In addition, microbial nitrogen metabolic activity, including functional enzyme (e.g., Nar and Nir) activities and electron transfer capacity of extracellular polymeric substances (EPS) and cytochrome c (Cyt-C), were also enhanced during current stimulation, which facilitated the nitrogen removal and maintained system stability. These findings suggested that ESdAD is an effective and eco-friendly process for advanced nitrogen removal for low C/N wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

• MP occurrence in MSW treatment and disposal systems was summarized using a size rescaling method. • Regional differences in MP pollution are related to economic and population status. • Factors influencing MPs in three MSW treatment and disposal systems were extensively discussed. • Risks of MPs in the surrounding environment of MSW treatment and disposal systems were assessed. Microplastic (MP) pollution is a significant worldwide environmental and health challenge. Municipal solid waste (MSW) can be an important source of MPs in the environment if treated and disposed of inappropriately, causing potential ecological risks. MSW treatment and disposal methods have been gradually shifting from landfilling/dumping to more sustainable approaches, such as incineration or composting. However, previous studies on MP characteristics in different MSW treatment and disposal systems have mainly focused either on landfills/dumpsites or composts. The lack of knowledge of multiple MSW treatment and disposal systems makes it difficult to ensure effective MP pollution control during MSW treatment and disposal. Therefore, this study systematically summarizes the occurrence of MPs in different MSW treatment and disposal systems (landfill/dumpsite, compost, and incineration) on the Eurasian scale, and discusses the factors that influence MPs in individual MSW treatment and disposal systems. In addition, the paper assesses the occurrence of MPs in the surrounding environment of MSW treatment and disposal systems and their ecological risks using the species sensitivity distribution approach. The study also highlights recommendations for future research, to more comprehensively describe the occurrence and fate of MPs during MSW treatment and disposal processes, and to develop appropriate pollution control measures to minimize MP pollution. [Display omitted] [ABSTRACT FROM AUTHOR]

• SBR achieved up to 93 % above partial nitrification of municipal wastewater. • SBR effluent and mature landfill leachate in UASB had an 89.4 % anammox contribution. • UASB achieved simultaneous anammox and partial denitrification with an HRT of 3.8 h. • The PN-SAPD process achieved an Eff.TIN of 3.4 mg/L and a removal efficiency of 95 %. • Ca. Brocadia had the highest abundance and was the only AnAOB for nitrogen removal. Anaerobic ammonia oxidation (anammox) of municipal wastewater is a research focus, especially the combined treatment with mature landfill leachate is a current research hotspot. In this study, municipal wastewater was treated by partial nitrification via sequencing batch reactor (SBR), and its effluent and mature landfill leachate were then mixed into an up-flow anaerobic sludge blanket (UASB) for simultaneous anammox and partial denitrification reaction. Through partial nitrification, a high nitrite accumulation rate (93.0 ± 3.8 %) was achieved by low dissolved oxygen (0.5–1.6 mg/L) and controlled aerobic time (3.5 h) in SBR. The UASB system was responsible for 78.8 ± 2.1 % nitrogen removal of the entire system with a hydraulic reaction time (HRT) of 3.8 h, accompanied by the anammox contribution up to 89.4 ± 6.0 %. The overall partial nitrification-simultaneous anammox and partial denitrification (PN-SAPD) system was controlled at a total COD/TIN of 2.8 ± 0.3 and a total HRT of only 10.2 h, achieving the nitrogen removal efficiency and effluent TIN were 95.2 ± 2.2 % and 3.4 ± 1.5 mg/L, respectively. The qPCR results showed functional genes (hzsA(B), hdh) associated with anaerobic ammonia-oxidizing bacteria (AnAOB), whose high gene copy abundance and transcription expression ensured the removal of major nitrogen from municipal wastewater and mature landfill leachate. 16S amplicon sequencing showed that the Ca. Brocadia (9.72–12.6 %) was further enrichment after sodium acetate was added, and the transcription expression of Thauera (0.5–7.0 %) caused nitrate to nitrite. The high abundance of related enzymes (hao, hzs, hdh, narGHI) involved in anammox and partial denitrification processes were found in the macrogenomic sequencing, and only Ca. Brocadia was involved in multi-pathway nitrogen metabolism in AnAOB. Based on the efficient nitrogen removal by AnAOB and denitrifying bacteria, this modified PN-SAPD process provides a new option for the co-treatment of mature landfill leachate in municipal wastewater treatment plants. [Display omitted] [ABSTRACT FROM AUTHOR]

• This study is the first one to present the integration of adsorption processes with the MD system. • The molecular-level insight into landfill leachate organic foulants is firstly presented for MD system. • Adsorption processes preferentially remove the responsible foulants fractions from the leachate. • Integration of BC adsorption with conventional MD system substantially increased the system performance. Membrane fouling and high-strength membrane concentrate production are two limitations of membrane distillation (MD) for landfill leachate treatment. In this study, activated carbon- and biochar-based adsorption processes were integrated into a conventional MD system to overcome these limitations. The organic matter fractionations of the leachate were thoroughly investigated during the treatment. Membrane-reversible and irreversible foulants differed remarkably from the inlet leachate in the non-assisted MD system. Specifically, reversible foulants were characterized by a high abundance of humic-like fluorescent components, high-molecular-weight humic-size constituents, peptides, and unsaturated compounds. In contrast, irreversible foulants were enriched with fulvic-like fluorescent components, low-molecular-weight neutrals, unsaturated compounds, and polyphenols. The adsorption-based pre-treatment effectively removed foulant precursors from landfill leachate, with a relatively higher (20%) adsorption performance for specific biochar used in this study than for activated carbon. Compared with the non-assisted MD system, the biochar-assisted MD system showed improved performance, achieving 40% overall membrane flux recovery, 42% higher filtration fluxes, and 53% lower concentrate production. In addition, a 15% higher removal of irreversible foulants was observed as compared to the reversible foulants, which can potentially increase the membrane lifespan. This study demonstrates the effectiveness of an adsorption-assisted MD system supported by increased filtration, membrane fouling alleviation, and low-strength leachate concentrate generation. [Display omitted] [ABSTRACT FROM AUTHOR]

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 FeIIFeIII 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 (pH 0 = 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 Ti 4 O 7 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 (ClO 3 −, NH 4 + and NO 3 −) 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 NH 4 + from mineralization of refractory organic nitrogen during EAOPs. Image 1 • NF concentrate of landfill leachate pre-treated in a membrane bioreactor was treated. • Ti 4 O 7 anode and FeII/FeIII LDH-CF cathode was used for the first time for a real effluent. • 96% removal of dissolved organic carbon was achieved by heterogeneous electro-Fenton. • Optimal conditions for biodegradability enhancement were identified. • Optimal conditions for minimization of toxic by-products were identified. [ABSTRACT FROM AUTHOR]

Abstract Sulfate radical (SO 4 -) -based advanced oxidation processes (SR-AOPs) have proven effective for simultaneously removing refractory dissolved organic matter (DOM) and ammonia in municipal landfill leachates. However, the knowledge on the competition of leachate DOM and ammonia for SO 4 -, the utilization efficiency of persulfate, as well as the reaction pathways and final products of ammonia oxidation during the SR-AOP treatment remains little known, thereby leading to a lack of a comprehensive evaluation of the emerging leachate treatment technology. The objective of this study was to further investigate the performance of a thermally activated persulfate system for treatment of a mature landfill leachate and re-evaluate the benefits and restrictions of SR-AOPs for leachate treatment. The laboratory experimental results showed that removal patterns of chemical oxygen demand (COD) and ammonia relied heavily upon the dose of persulfate that could be thermally activated to produce reactive sulfate radicals, reflecting the competition of leachate DOM, ammonia, and non-target leachate constituents for SO 4 -. The utilization efficiency of the added persulfate could be more efficiently utilized for removing the two target leachate pollutants at a lower persulfate dose, whereas more persulfate was wasted due to the reactions with non-target leachate constituents (e.g. Cl− and CO 3 2−) and/or self-decomposition with the increasing persulfate dose. During the treatment, ammonia was oxidized, via the direct attack of SO 4 - and/or by molecular chlorine produced from the reactions of chloride and sulfate radicals, into nitrate and nitrogen gas, while nitrite was not detected. Of importance, this study highlighted three potentially negative impacts of SR-AOPs on the quality of treated leachate, including accumulation of total dissolved solids, the production of undesirable nitrate, and the pH decrease due to the continuous formation of hydrochloric acid. Therefore, the three issues should be carefully evaluated when a SR-AOP is selected for leachate treatment. Because these impacts become less pronounced with a decreasing persulfate dose, SR-AOPs as a pre-treatment, which is achieved at a relatively low persulfate dose, may be an appropriate option for the SR-AOP application to leachate treatment. Graphical abstract Image 1 Highlights • Sulfate radicals are competed among organics, NH 3 , and other leachate constituents. • Utilization efficiency of sulfate radicals is decreased with an increasing persulfate dose. • Oxidation products of NH 3 after SR-AOP treatment include nitrate and nitrogen gas. • Cl− inhibits COD removal but improves the abatement of NH 3 -N during SR-AOP treatments. • TDS increase, nitrate formation, and pH decrease may restrict SR-AOPs for leachate treatment. [ABSTRACT FROM AUTHOR]

Abstract Applications of Fenton's oxidation of landfill leachate is limited by both high reagent requirements and a large amount of sludge generation. To address those issues, forward osmosis (FO) and humic acid (HA) recovery were incorporated with Fenton's treatment. In the FO, leachate was concentrated by 3.2 times in 10 hours using a 5-M NaCl draw solution. The HA recovery increased from 1.86 to 2.45 g L−1 at pH 2 after FO concentration, mainly because of the replacement of O in the HA structure by other inorganics (i.e., Cl, Na, K) with higher molecular weights. Due to the movement of alkalinity causing species (i.e., HCO 3 −, CO 3 2-) to the draw side driven by a concentration gradient, the H 2 SO 4 requirement per g of recovered HA and per g of removed COD decreased by 46.4% and 17.1%, respectively. The HA recovery also decreased sludge generation by 30%. At a dimensionless oxidant dose of 0.5, the proposed system reduced the overall requirement of H 2 SO 4 by 25.2%, NaOH by 34.6%, and both FeSO 4.7H 2 O and H 2 O 2 by 35%, compared to the standalone Fenton's treatment of raw leachate. Those results have demonstrated that the proposed system could greatly decrease the leachate volume, lower the reagent requirements, and reduce the sludge production towards sustainable leachate treatment. Graphical abstract Image 1 Highlights • Leachate is effectively treated by a cooperative system for reduced reagent input. • Forward osmosis decreases leachate volume and benefits humic acid recovery. • Recovery of potentially useful humic acids greatly reduces organic contents. • Both use of Fenton reagents and sludge production have been significantly reduced. [ABSTRACT FROM AUTHOR]

• Simultaneous methanogenesis and denitrification was successfully achieved in AnMBBR. • Carbon and nitrogen in the landfill leachate were efficiently removed. • Methane yield and methanogenic bacteria were greatly promoted by rhamnolipids. • Rhamnolipids played an ameliorative effect by resisting the inhibition of landfill leachate. • XDLVO theatrically revealed rhamnolipids enhanced the interaction of pollutants and biofilms. In this study, an anaerobic moving bed biofilm reactor (AnMBBR) was developed for simultaneous methanogenesis and denitrification (SMD) to treat high-strength landfill leachate for the first time. A novel strategy using biosurfactant to ameliorate the inhibition of landfill leachate on the SMD performance was proposed and the underlying mechanisms were explored comprehensively. With the help of rhamnolipids, the chemical oxygen demand (COD) removal efficiency of landfill leachate was improved from 86.0% ± 2.9% to 97.5% ± 1.6%, while methane yields increased from 50.1 mL/g-COD to 69.6 mL/g-COD, and the removal efficiency of NO 3 −-N was also slightly increased from 92.5% ± 1.9% to 95.6% ± 1.0%. The addition of rhamnolipids increased the number of live cells and enhanced the secretion of extracellular polymeric substances (EPS) and key enzyme activity, indicating that the inhibitory effect was significantly ameliorated. Methanogenic and denitrifying bacteria were enhanced by 1.6 and 1.1 times, respectively. Analysis of the microbial metabolic pathways demonstrated that landfill leachate inhibited the expression of genes involved in methanogenesis and denitrification, and that their relative abundance could be upregulated with the assistance of rhamnolipids addition. Moreover, extended Deraguin - Landau - Verwery - Oxerbeek (XDLVO) theory analysis indicated that rhamnolipids reduced the repulsive interaction between biofilms and pollutants with a 57.0% decrease in the energy barrier, and thus accelerated the adsorption and uptake of pollutants onto biofilm biomass. This finding provides a low-carbon biological treatment protocol for landfill leachate and a reliable and effective strategy for its sustainable application. [Display omitted] [ABSTRACT FROM AUTHOR]

• Semi-volatile organic matter was the most frequently detected in leachate. • Toluene, ethylbenzene, xylenes and benzene were frequently detected in leachate. • Solubility was the key factor driving the entry of organic matter into leachate. • Volatile and hydrophilic matter was easier to remove by the A/O and SBR processes. • Hydrophobic contaminants were more likely to be removed by the MBR and UF process. Volatile and semi-volatile organic compounds (VOCs and SVOCs) carried by landfilled wastes may enter leachate, and require appropriate treatment before discharge. However, the driving factors of the entry of VOCs and SOVCs into leachate, their removal characteristics during leachate treatment and the dominant factors remain unclear. A global survey of the VOCs and SOVCs in leachate from 103 landfill sites combined with 27 articles on leachate treatment was conducted to clarify the abovementioned question. The results showed that SVOCs such as polycyclic aromatic hydrocarbons (PAHs), phthalate acid esters (PAEs) and phenols were the most frequently detected in leachate on a global scale. However, four kinds of VOCs, i.e., toluene, ethylbenzene, xylenes and benzene, were frequently detected at high concentrations in landfill leachate as well. The concentrations of VOCs and SVOCs in leachate ranged from 1 × 10° to 1 × 108 ng/L. Solubility was a key factor driving the entry of VOCs and SOVCs into leachate, and higher solubility enables higher detectable concentrations in leachate (P <0.05). It was easiest to remove monocyclic aromatic hydrocarbons (MAHs) from leachate, followed by phenols and PAHs, and it was most difficult to remove PAEs. In terms of removing MAHs, the anoxic/oxic (A/O) process and the sequential batch reactor (SBR) process were comparable to the advanced oxidization process and far superior to the ultrafiltration and nanofiltration processes, and the removal rate increased with an increase in the Henry's constant and/or the hydrophilicity of the contaminants during the A/O and SBR processes (P <0.05). There were no significant differences among biological, advanced oxidation and reverse osmosis processes in the removal of phenolic. In terms of removing PAHs, the A/O process was comparable to the advanced oxidization process and more efficient than the other treatment processes. As to removing PAEs, the membrane bioreactor process was almost the same efficient as the advanced oxidization process and far more efficient than the other biological treatment processes. Future research should focus on the pollution of atmospheric VOCs and SVOCs near aeration units in leachate treatment plants, as well as the health risk assessment of VOCs and SVOCs in the treated leachate effluent. To the best of our knowledge, this is the first review regarding the occurrence and removal of VOCs and SVOCs from landfill leachates worldwide. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Image 1 Highlights • Co-treatment of landfill leachate with municipal wastewater is a common approach. • Recalcitrant organic compounds in leachate can decrease UV disinfection efficiency. • UVQS consist of three major fractions, humic acids, fulvic acids and hydrophilics. • Combination of different treatments can reduce UVQS concentrations in leachate. • The importance of UVQS to wastewater treatment should be better recognized. [ABSTRACT FROM AUTHOR]

High throughput sequencing-based metagenomic analysis and network analysis were applied to investigate the broad-spectrum profiles of ARGs in landfill leachate from 12 cities in China. In total, 526 ARG subtypes belonging to 21 ARG types were detected with abundances ranging from 1.1 × 10 −6 to 2.09 × 10 −1 copy of ARG/copy of 16S rRNA gene. 68 ARG subtypes that accounted for 73.4%–93.4% of the total ARG abundances were shared by all leachate samples. The four most abundant ARGs, sul 1, sul 2, aad A and bac A can be served as ARG indicators to quantitatively predict the total abundances by linear functions (r 2  = 0.577–0.819, P  < 0.001). No distinct regional distribution pattern of the ARGs was observed among different cities in China, while the ARG compositions of the leachate were clearly distinct from those of other environmental sample types. Nearly 90% ARG subtypes in the anaerobic digestion sludge from sewage treatment plants (STPADS) were shared by the leachate and the abundances of leachate and STPADS ARGs generalists accounted for 84.5% and 87.7% of total abundances in these two types of anaerobic samples, respectively. Furthermore, Procrustes analysis suggested that microbial community composition might be the determining factor of ARG compositions in landfill leachate. ARGs within the same type or among the different types showed higher incidences of non-random co-occurrence and 17 genera might be potential hosts of multiple ARGs. This study highlighted that landfill leachate is an important reservoir of various ARGs and provided a useful reference for the surveillance and risk management of ARGs in landfill environments. [ABSTRACT FROM AUTHOR]

• Molecular selectivity of sorbents and ionization modes effect DOM analysis. • Landfill leachate DOM showed unprecedented molecular diversity. • N/S containing molecules formed 83% of all molecules observed in landfill leachate. • More than 55% of molecules detected in LDOM were bio-recalcitrant. Molecular characterization of landfill leachate dissolved organic matter (LDOM) is essential for developing effective processing techniques. However, the molecular selectivity of extraction method and ionization modes often leads to the bias of molecular characterization of LDOM. Here, seven representative sorbents were selected and electrospray ionization negative ion mode (ESI (−)) and positive ion mode (ESI (+)) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to investigate the molecular composition of different LDOM samples. Obvious sorbent selectivity during extraction procedure was observed, resulting in the underestimation of molecular diversity of LDOM from 32.7% to 69.3%. Totally, 14,000−18,000 unique molecules were obtained in a single sample, indicating the unprecedented molecular diversity of LDOM. Lignins, proteins and lipids are three major molecular groups in LDOM, and N or S containing molecules occupied 83%. Although much of total organic carbon was removed during biochemical treatment process, the molecular diversity of LDOM was not reduced because a considerable of bio-recalcitrant molecules was produced. The results uncover the sorbents selectivity and ionization modes selectivity in LDOM analysis and provided a comprehensive change of LDOM molecular composition during biochemical treatment, which benefits the development of accurate methods to remove organic carbon in landfill leachate. [Display omitted] [ABSTRACT FROM AUTHOR]

• ITMD achieved simultaneous ammonium recovery and water purification. • ITMD obtained a COD rejection rate of 99.5% at various pH values. • Elevating the feed pH to 12 increased ammonia capture to 75%. • Feed pH elevation exacerbated the complex fouling of organics and inorganics. • ITMD provides a highly economical LFL treatment cost of $2–3/m3. Resources recovery from landfill leachate (LFL) has been attracting growing attention instead of merely purifying the wastewater. An integrated two-stage membrane distillation (ITMD) was proposed to simultaneously purify LFL and recover ammonia in this study. The results showed that organics could be always effectively rejected by the ITMD regardless of varying feed pH, with COD removal higher than 99%. With feed pH increased from 8.64 to 12, the ammonia migration (50–100%) and capture (36–75%) in LFL were considerably enhanced, boosting the separated ammonia enrichment to 1.3–1.7 times due to the improved ammonium diffusion. However, the corresponding membrane flux of the first MD stage decreased from 13.7 to 10.5 L/m2·h. Elevating feed pH caused the deprotonation of NOM and its binding with inorganic ions, constituting a complex fouling layer on the membrane surface in the first MD stage. In contrast, the membrane permeability and fouling of the second MD were not affected by feed pH adjustment because only volatiles passed through the first MD. More importantly, it was estimated that ITMD could obtain high-quality water and recover high-purity ammonium from LFL with relatively low ammonium concentration at an input cost of $ 2–3/m3, which was very competitive with existing techniques. These results demonstrated that the ITMD can be a valuable candidate strategy for simultaneous water purification and nutrient recovery from landfill leachate. [Display omitted] [ABSTRACT FROM AUTHOR]

Landfill leachate is often an important source of emerging organic contaminants including perfluoroalkyl and polyfluoroalkyl substances (PFASs) requiring proper treatment to protect surface water and groundwater resources. This study investigated the occurrence of PFASs in the leachate of a capped landfill site in Singapore and the efficacy of PFASs removal during flow through a constructed wetland (CW) treatment system. The CW treatment system consists of equalization tank, aeration lagoons, sedimentation tank, reed beds and polishing ponds. Target compounds included 11 perfluoroalkyl acids (PFAAs) (7 perfluoroalkyl carboxylic acids (PFCAs) and 4 perfluoroalkane sulfonates (PFSAs)) and 7 PFAA precursors. Although total PFASs concentrations in the leachate varied widely (1269 to 7661 ng/L) over the one-year sampling period, the PFASs composition remained relatively stable with PFCAs consistently being predominant (64.0 ± 3.8%). Perfluorobutane sulfonate (PFBS) concentrations were highly correlated with total PFASs concentrations and could be an indicator for the release of PFASs from this landfill. The release of short-chain PFAAs strongly depended on precipitation whereas concentrations of the other PFASs appeared to be controlled by partitioning. Overall, the CW treatment system removed 61% of total PFASs and 50–96% of individual PFASs. PFAAs were removed most efficiently in the reed bed (42–49%), likely due to the combination of sorption to soils and sediments and plant uptake, whereas most of the PFAA precursors (i.e. 5:3 fluorotelomer carboxylate (5:3 acid), N-substituted perfluorooctane sulfonamides (N-MeFOSAA and N-EtFOSAA)) were removed in the aeration lagoon (>55%) by biodegradation. The sedimentation tank and polishing ponds were relatively inefficient, with only 7% PFASs removal. [ABSTRACT FROM AUTHOR]

Landfill leachate could be a significant source of emerging contaminants (ECs) and antibiotic resistance genes (ARGs) into the environment. This study provides the first information on the occurrence of selected ECs and ARGs in raw leachate from 16-year old closed landfill site in Singapore. Among the investigated ECs, acetaminophen (ACT), bisphenol A (BPA), clofibric acid (CA), caffeine (CF), crotamiton (CTMT), diclofenac (DCF), N , N -diethyl-m-toluamide (DEET), gemfibrozil (GFZ), lincomycin (LIN), salicylic acid (SA), and sulfamethazine (SMZ) were the most frequently detected compounds in raw landfill leachate. The concentrations of detected ECs in raw landfill leachate varied significantly, from below quantification limit to 473,977 ng/L, depending on the compound. In this study, Class I integron ( intl1 ) gene and ten ARGs were detected in raw landfill leachate. Sulfonamide resistance ( sul1, sul2, and dfrA ), aminoglycoside resistance ( aac6 ), tetracycline resistance ( tetO ), quinolone resistance ( qnrA ), and intl1 were ubiquitously present in raw landfill leachate. Other resistance genes, such as beta-lactam resistance ( blaNMD1 , blaKPC , and blaCTX ) and macrolide-lincosamide resistance ( ermB ) were also detected, detection frequency of <50%. The removal of target ECs and ARGs by a full-scale hybrid constructed wetland (CW) was also evaluated. The vast majority of ECs exhibited excellent removal efficiencies (>90%) in the investigated hybrid CW system. This hybrid CW system was also found to be effective in the reduction of several ARGs ( intl1 , sul1 , sul2 , and qnrA ). Aeration lagoons and reed beds appeared to be the most important treatment units of the hybrid CW for removing the majority of ECs from the leachate. [ABSTRACT FROM AUTHOR]

UV-quenching substance (UVQS), as an emerging municipal solid waste (MSW)-derived leachate contaminant, has a potential to interfere with UV disinfection when leachate is disposed of at publicly owned treatment works (POTWs). The objective of this study was to evaluate and compare two chemical oxidation processes under different operational conditions, i.e. Fenton process and ozonation, for alleviation of UV 254 absorbance of a biologically pre-treated landfill leachate. Results showed that leachate UV 254 absorbance was reduced due to the UVQS decomposition by hydroxyl radicals (·OH) during Fenton treatment, or by ozone (O 3 ) and ·OH during ozonation. Fenton process exhibited a better treatment performance than ozonation under their respective optimal conditions, because ·OH could effectively decompose both hydrophobic and hydrophilic dissolved organic matter (DOM), but O 3 tended to selectively oxidize hydrophobic compounds alone. Different analytical techniques, including molecular weight (MW) fractionation, hydrophobic/hydrophilic isolation, UV spectra scanning, parallel factor (PARAFAC) analysis, and fluorescence excitation-emission matrix spectrophotometry, were used to characterize UVQS. After either oxidation treatment, residual UVQS was more hydrophilic with a higher fraction of low MW molecules. It should be noted that the removed UV 254 absorbance (ΔUV 254 ) was directly proportional to the removed COD (ΔCOD) for the both treatments (Fenton process: ΔUV 254 = 0.011ΔCOD; ozonation: ΔUV 254 = 0.016ΔCOD). A greater ΔUV 254 /ΔCOD was observed for ozonation, suggesting that oxidant was more efficiently utilized during ozonation than in Fenton treatment for mitigation of the UV absorbance. [ABSTRACT FROM AUTHOR]

• Degradation kinetics of DOM fractions were compared among EO with different anodes. • The emergence of the 290 nm absorbance band was attributed to formation of chlorine. • Abs420 indicated the shift of the oxidation of DOM from HA fraction to BP fraction. • Abs420 indicated the shift from oxidation of DOM to formation of ClO 3 − and ClO 4 −. • It can achieve a trade-off between DOM degradation and ClO 3 − and ClO 4 − formation. Electrochemical oxidation (EO) is an attractive option for treatment of dissolved organic matter (DOM) in landfill leachate but concerns remain over the energy efficiency and formation of oxidation byproducts ClO 3 − and ClO 4 −. In this study, EO treatment of landfill leachates was carried out using representative active and nonactive anode materials, cell configurations and current densities. Size exclusion chromatograms coupled with 2D synchronous and asynchronous correlation analysis showed that the sensitivity of DOM fractions to EO degradation was dependent on the anode material. The nonactive boron-doped diamond (BDD) anode demonstrated the best performance for DOM oxidation. The humic acid-like fraction (HA, 2.5–20 kDa) predominated the visible absorbance of landfill leachates at λ ≥400 nm, and it generally had the highest reaction rates except the occurrence of the pH-induced denaturation and precipitation of the proteinaceous biopolymer fraction (BP, >20 kDa). During the EO treatment of landfill leachate with BDD anode, the UV absorbance spectra of landfill leachates at wavelengths <400 nm were affected by the formation of free chlorine. Instead, the decrease of Abs420 was found to be a good indicator of the shift of the oxidation from predominantly HA fraction to the proteinaceous BP fraction. The behavior of the Abs420 parameter was also indicative of the transition from the energy-efficient oxidation of DOM to the dominance of side reactions of chlorine evolution and the subsequent formation of ClO 3 − and ClO 4 −. These findings suggest that the EO treatment of landfill leachate can be optimized by adjusting the current density with feedback signals from the online monitoring of Abs420, to achieve a trade-off between degradation of DOM and control of ClO 3 − and ClO 4 −. [Display omitted] [ABSTRACT FROM AUTHOR]

• Energy recovery from LL was intensified by linking light and dark bio-reactions. • EPS contributed largely to synergistic mechanisms of dual microalgae system. • More EPS in mixed microalgae system was conducive to nutrients assimilation. • Microalgae photosynthesis cooperate dark fermentation well for energy conversion. • 10.80 kJ/L of energy (7.75% conversion efficiency) was output under SO:CV of 1:1. Bioconversion of nutrients and energy from landfill leachate (LL) to biohydrogen and volatile fatty acids (VFAs) using dark fermentation (DF) is a promising technique for developing a sustainable ecosystem. However, poor performance of DF caused by vulnerable fermentative bacteria vitality and strong LL toxicity significantly hinder its commercialization. Herein, an integrated technique linking microalgae photosynthesis and DF was proposed, in which mixed microalgae were applied to robustly reclaim nutrients and chemical oxygen demand (COD) from LL. Then, microalgae biomass was fermented into biohydrogen and VFAs using the DF process. Underlying synergistic mechanisms of the interaction of Scenedesmus obliquus and Chlorella vulgaris resulting from the functioning of extracellular polymeric substances (EPS) were discussed in detail. For better absorption of nutrients from LL, the mixed microalgae secreted obviously more EPS than pure microalgae, which played vital roles in the assimilation of cellular nutrients by forming more negative zeta potential and secreting more tyrosine-/tryptophan-family proteins in EPS. Besides, mixed microalgae produced more intracellular proteins and carbohydrates than the pure microalgae, thereby providing more feedstock for DF and achieving higher energy yield of 10.80 kJ/L than 6.64 kJ/L that was obtained when pure microalgae were used. Moreover, the energy conversion efficiency of 7.75% was higher for mixed microalgae than 4.77% that was obtained for pure microalgae. This work may inspire efficient disposal of LL and production of bioenergy, together with filling the knowledge gaps of synergistic mechanisms of dual microalgal interactions. [Display omitted] [ABSTRACT FROM AUTHOR]

• Hybrid MER and MD was firstly developed for LFL treatment. • MER removed 61% hardness and recovered 31 % of ammonia nitrogen and 48% of HA in LFL. • MD membrane fouling reversibility was significantly improved with MER pretreatment. • MER pretreatment reduce ∼20% energy consumption and carbon emission in the MD treatment. Treatment of recalcitrant landfill leachate (LFL) induces huge energy consumption and carbon emissions due to its complex composition. Although membrane distillation (MD) exhibits good potential in LFL treatment with waste heat utilization, membrane fouling and ammonia rejection are still the major problems encountered that hinder its application. Herein, membrane electrochemical reactor (MER) was coupled with MD for simultaneous membrane fouling control and resource recovery. LFL pretreatment with membrane-less electrochemical reactor (EO) and without pretreatment were also purified by MD for comparison. Results showed that the MER-MD system rejected almost all COD Cr , total phosphorus, metal salts, and ammonia nitrogen (increased by 33.5%–43.5% without chemical addition), and recovered 31% of ammonia nitrogen and 48% of humic acid in the raw LFL. Owing to the effective removal of hardness (61%) and organics (77%) using MER, the MER-MD system showed higher resistance to the membrane wetting and fouling, with about 61% and 14% higher final vapor flux than those of the MD and EO-MD systems, respectively, and the pure water flux could be fully recovered by alkaline solution cleaning. Moreover, SEM-EDS, ATR-FTIR and XRD characterization further demonstrated the superiority of the MD membrane fouling reversibility of the MER-MD system. Energy consumption and carbon emissions analysis showed that the MER-MD system reduced the total energy consumption/carbon emissions by ∼20% and ∼8% compared to the MD and EO-MD systems, respectively, and the ammonia nitrogen recovered by MER could offset 8.25 kg carbon dioxide equivalent. Therefore, the introduction of MER pretreatment in MD process would be an option to decrease energy consumption and reduce carbon emissions for MD treatment of LFL. [Display omitted] [ABSTRACT FROM AUTHOR]

Glycogen accumulating organisms (GAOs) capable of storing organic compounds as polyhydroxyalkanoate (PHA) have been used for endogenous denitritation (ED), but the effect of carbon sources type on nitrogen removal performance of GAOs treating landfill leachate is unclear. In this study, a successful ED system treating landfill leachate (COD/NH 4 + -N (C/N): 4) without external carbon source addition was applied. The mature leachate with C/N of 1 was used as the feeding base solution, with acetate, propionate, and glucose examined as the carbon sources, and their effects on yields and compositions of PHA produced by GAOs were determined and associated with nitrogen removal performance. In the case of sole carbon source, acetate was much easier to be stored than propionate and glucose, which led to a higher nitrogen removal efficiency. Glucose had the lowest amount of PHA storage and led to the lowest performance. In the case of composite carbon sources (two scenarios: acetate + propionate; acetate + propionate + glucose), GAOs stored sufficient PHA and exhibited similar nitrogen removal efficiencies. Moreover, type of carbon source influenced the compositions of PHA. The polyhydroxybutyrate (PHB) fraction in PHA was far more than polyhydroxyvalerate (PHV) in all tests. PHV was synthesized only when acetate existed in carbon source. The microbial diversity analysis revealed that Proteobacteria was the most abundant phylum. Among the 108 genera detected in this ED system, the genera responsible for denitritation were Thauera , Paracoccus , Ottowia and Comamonadaceae_unclassified , accounting for 46.21% of total bacteria. Especially, Paracoccus and Comamonadaceae_unclassified transformed the carbon source into PHA for denitritation, and carried out endogenous denitritation. [ABSTRACT FROM AUTHOR]

The potential of microalgae to bioremediate wastewater has been reported in numerous studies but has not been investigated as extensively for landfill leachate, which may be attributed to its complex nature and toxicity. In this study we explored if microalgal phycoremediation could constitute an alternative biological treatment option for landfill leachate management in regions with temperate climatic conditions. The aim of this study was to assess the performance of microalgae species at relatively low temperature (15 °C) and light intensity (14:10 h, light: dark, 22 μmol m −2 s −1 ) for reduction in energy inputs. Four chlorophyte strains originating from the North-West of Ireland were selected and used in batch experiments in order to evaluate their ability to reduce total ammonia nitrogen, oxidised nitrogen and orthophosphate in landfill leachate. The Chlamydomonas sp. strain SW15aRL isolated from raw leachate achieved the highest level of pollutant reduction whereby a decrease of 51.7% of ammonia nitrogen was observed in 10% raw leachate (∼100 mg l −1 NH 4 + -N) by day 24 in experiments without culture agitation. However, in the experiment conducted with 10% raw leachate supplemented with phosphate, a decrease of 90.7% of ammonia nitrogen was obtained by day 24 while also achieving higher biomass production. This series of experiments pointed to phosphorus being a limiting factor in the microalgae based phycoremediation of the landfill leachate. The effective reduction of ammonia nitrogen in landfill leachate can be achieved at lower temperature and light conditions. This was attained by employing native species adapted to such conditions and by improving nutrient balance. [ABSTRACT FROM AUTHOR]

Abstract: Landfill leachates are an important pool of organotin compounds (OTCs). Several studies have been performed on the occurrence of OTCs in landfill leachates, but only a few of them report degradation and biomethylation processes by bacteria. In the present study transformation of OTCs in landfill leachate was investigated under simulated landfill conditions over a time span of six months. The degradation and biomethylation processes of OTCs were followed by the use of isotopically enriched tin tracers, namely 117Sn-enriched tributyltin (TBT), 119Sn-enriched dibutyltin (DBT), 117Sn-enriched SnCl2, 117Sn-enriched SnCl4 and a 119Sn-enriched butyltin mix containing TBT, DBT and monobutyltin (MBT). Transformation of OTCs in spiked leachates was followed at m/z of the enriched spikes and at m/z 120, which allowed simultaneous observation of the transformation of OTCs in the leachate itself and of the added spike. In parallel, these processes were also monitored in a non-spiked leachate sample at m/z 120. Quantification of OTCs was performed by gas chromatography – inductively coupled plasma mass spectrometry (GC-ICP-MS). To discriminate the biotic and abiotic transformations of OTCs and inorganic tin species, sterilization of leachate was also performed and data compared to non-sterilized samples. During the course of the experiment the microbial degradation of TBT was clearly manifested in Sn-enriched spiked leachate samples, while abiotic pathway of degradation was observed for DBT. Biomethylation process was also observed in the leachate spiked with Sn-enriched Sn2+ or Sn4+, in concentrations close to those found for total tin in landfill leachates. Monomethyltin (MMeT) was formed first. Stepwise alkylation resulted in dimethyltin (DMeT) and trimethyltin (TMeT) species formation. Hydrolysis of Sn2+ and Sn4+ species was found to be a limiting factor which controlled the extent of methyltin formation. The results of the present investigation importantly contribute to a better understanding of the processes that OTCs undergo in leachates, and provide useful information to managers of landfills in taking measures necessary to prevent the release of toxic methyltin species to the nearby environment. [Copyright &y& Elsevier]

Abstract: Partitioning of organic pollutants is essential to their fate, mobility and removal from water and soil. To study the partitioning behavior of selected alkylphenols, bisphenol A, phthalates and polycyclic aromatic hydrocarbons (PAHs), a method for separating the truly dissolved and colloidal phase of organic pollutants was developed, verified and applied to samples of landfill leachate and stormwater from urban areas and waste-sorting sites. Alkylphenols, bisphenol A, phthalates and PAHs were detected in all the untreated samples (total concentrations), most of the filtered samples and frequently in the colloid-bound phase. Concentrations of alkylphenols and PAHs in urban stormwater were one order of magnitude lower than in the landfill leachates and stormwater from waste-sorting sites. The difference between total, dissolved and colloid-bound concentrations in the water samples was not statistically significant for any phenols or phthalates, but for three of the PAHs; naphthalene (mostly dissolved), phenanthrene and fluoranthene (mostly particulate). These results indicate that in landfill leachates and stormwaters, organic pollutants are predominantly attached to colloids and/or truly dissolved in contrast to their expected strong sorption to particulate matter. Occurrence and concentrations of pollutants in dissolved and colloid-bound phases correlated negatively with the K OW. However, even highly hydrophobic compounds were frequently detected in filtered samples, i.e. the dissolved phases, and it is suggested that the organic content in the colloids decreases the compounds'' partition to particles. The results confirm that the K OW values of specific organic pollutants well describe the compounds partition-binding process to dissolved organic carbon (DOC) colloids. Our findings call for a re-assessment of the organic pollutants'' mobility and associated risks. This knowledge can also serve as a base for selecting efficient treatment methods for stormwater and landfill leachates. [Copyright &y& Elsevier]

Abstract: A cost effective and widely applied approach for landfill leachate disposal is to discharge it to a municipal wastewater treatment plant (WWTP). The recalcitrant nature of leachate organics and the impact on the downstream WWTPs were comprehensively investigated in this study. Size fractionation by ultrafiltration (UF) and microfiltration (MF) was employed in conjunction with various analyses (TOC, COD, nitrogen species and UV254 absorbance) on raw and biologically treated landfill leachates to provide insight into biological treatability. Overall, landfill leachate organics showed bio-refractory properties. Less than half of the organic matter, measured as total organic carbon (TOC), could be removed in the biological processes examined. Size distribution data showed that the <1 thousand Daltons (kDa) fraction is dominant in most untreated and treated landfill leachates, indicating difficulties for membrane treatment. Also, most removal occurred for the <1 kDa fraction in the biological processes, while the intermediate size fractions increased slightly. This may be caused by bio-flocculation and/or partial degradation of larger molecular weight fractions. Organic nitrogen was investigated in this study as one of the first explorations for landfill leachates. Organic nitrogen in landfill leachates was more bio-refractory than other organic matter. UV quenching by landfill leachates was also investigated since it interferes with the UV disinfection at WWTPs. The combination of activated carbon and activated sludge (PACT) showed some effectiveness for reducing UV quenching, indicating that carbon adsorption is a potential method for removal of UV quenching substances. Fourier transform Infrared (FT/IR) data showed that aromatic groups are responsible for the UV quenching phenomenon. [Copyright &y& Elsevier]

Abstract: Stabilized landfill leachate has previously been treated with activated carbon (AC); however, information on the selectivity of AC depending upon the pore size is minimal. Isotherm and kinetic experiments were conducted using three commercially available AC products, one micro-porous and two meso-porous. Equilibrium adsorption and intra-particle diffusion of organic matter from stabilized leachate was studied. Isotherm experimental data were fitted to Langmuir, Freundlich, and Redlich–Peterson isotherm models in non-linear forms. Of the three isotherm models, the Redlich–Peterson model provided the best fit to the experimental data and showed a similar organic matter adsorption capacity (approximately 0.2 g total organic carbon (TOC) g−1 AC) for both micro-porous and meso-porous AC. The organic matter effective intra-particle diffusion coefficients (De ) in both AC types were on the order of 10−10 m2 s−1 for AC particle sizes greater than 0.5 mm. Meso-porous ACs showed slightly higher De compared to micro-porous AC. Rapid small-scale tests showed a maximum of 80% TOC removal from leachate by each AC investigated. Fluorescence spectroscopy showed a preferential adsorption of fulvic-type organic matter with an increase in empty bed contact time by each AC. [Copyright &y& Elsevier]

Abstract: Typically, a mature landfill leachate contains high levels of non-biodegradable organics and ammonia nitrogen. Simultaneous removal of the both persistent leachate pollutants is a significant challenge. This paper reports the first scientific study to apply a sulfate radical () – based advanced oxidation process (SR-AOP) to treat a mature leachate, with an emphasis of concurrent removal of refractory organics and ammonia. In this study, all the experiments were run in a batch reactor with temperature control. In the thermal persulfate oxidation (TPO) process, persulfate (S2O8 2-) was activated by heat to produce powerful oxidants, (Eo = 2.6 V). Three factors affecting the removal efficiencies of chemical oxygen demand (COD) and ammonia nitrogen were investigated, including initial solution pH (3–8.3), temperature (27–50 °C), and chemical dose (:12COD0 = 0.25–2.0). Typically, acidic pH (3–4), higher temperature, and higher dose favored the removal of COD and ammonia. At :12COD0 = 2 and 50 °C, the COD removal rates were 79% and 91% at pH 8.3 (no pH adjustment) and 4, respectively; and the ammonia nitrogen removal reached 100% at pH 8.3 or 4. SR-AOP appears to be more advantageous over hydroxyl radical (OH∙)-based advanced oxidation processes (HR-AOPs) because OH∙ almost does not oxidize ammonia. Furthermore, compared with Fenton treatment of the same batch leachate sample, the TPO could achieve a higher COD removal at an identical chemical dose. For example, COD removal was 40% at H2O2:2.125COD0 = 2 during Fenton treatment (pH 3), but 91% at :12COD0 = 2 during TPO (pH 4). These findings demonstrate that SR-AOP is a promising landfill leachate treatment method. [Copyright &y& Elsevier]

Abstract: In this study, As leaching from five arsenic bearing solid residuals (ABSRs) comprised of the iron hydroxide adsorbent Bayoxide E33 used in long-term operations was evaluated in leaching trials using California Waste Extraction Test (CalWET) and Toxicity Characteristic Leaching Protocol (TCLP) leachate solutions, a landfill leachate (LL), and synthetic leachate (SL). The initial As loading of the media, which reflects the influence of source water chemistry and varying treatment conditions at the point of removal, strongly influenced the magnitude of As release. The chemical composition of the leachate also influenced As release and demonstrated the relative importance of different release mechanisms, namely media dissolution, pH-dependent sorption/desorption, and ion exchange. The CalWET solution, which partially dissolved the iron-based media, resulted in 100 times more As release than did the TCLP solution, which did not dissolve the media. The LL had a higher pH than the TCLP solution, and even though its organic carbon content was lower it tended to release more As. Tests with the SL were conducted to determine the influence of variations in leachate pH, phosphate, bicarbonate, sulfate, silicate, and natural organic matter (NOM). Release increased at high pH, in the presence of high concentrations of phosphate and bicarbonate, and in the presence of high NOM concentrations. For pH, this reflects the pH-dependence of sorption reactions, whereas for the anions and NOM, direct competition appeared important. Similar to the CalWET solution, excess NOM dissolved portions of the media thereby facilitating As release. In general, our results suggest that estimating As release into landfills will remain a challenge as it depends upon As loading, which reflects site-specific properties, and the composition of the leachate, which varies from landfill to landfill. [Copyright &y& Elsevier]

Abstract: In this study, the adsorption of bisphenol A (BPA) and 17α-ethinyl estradiol (EE2) from landfill leachate onto single-walled carbon nanotubes (SWCNTs) was investigated. Different leachate solutions were prepared by altering the pH, ionic strength, and dissolved organic carbon (DOC) in the solutions to mimic the varying water conditions that occur in leachate during the various stages of waste decomposition. The youngest and oldest leachate solutions contained varying DOC and background chemistry and were represented by leachate Type A (pH = 5.0; DOC = 2500 mg/L; conductivity = 12,500 μS/cm; [Ca2+] = 1200 mg/L; [Mg2+] = 470 mg/L) and Type E (pH = 7.5; DOC = 250 mg/L; conductivity = 3250 μS/cm; [Ca2+] = 60 mg/L; [Mg2+] = 180 mg/L). These solutions were subsequently combined in different ratios to produce intermediate solutions, labeled B–D, to replicate time-dependent changes in leachate composition. Overall, a larger fraction of EE2 was removed as compared to BPA, consistent with its higher log KOW value. The total removal of BPA and EE2 decreased in older leachate solutions, with the adsorptive capacity of SWCNTs decreasing in the order of leachate Type A > Type B > Type C > Type D > Type E. An increase in the pH from 3.5 to 11 decreased the adsorption of BPA by 22% in young leachate and by 10% in old leachate. The changes in pH did not affect the adsorption of EE2 in the young leachate, but did reduce adsorption by 32% in the old leachate. Adjusting the ionic strength using Na+ did not significantly impact adsorption, while increasing the concentration of Ca2+ resulted in a 12% increase in the adsorption of BPA and a 19% increase in the adsorption of EE2. DOC was revealed to be the most influential parameter in this study. In the presence of hydrophilic DOC, represented by glucose in this study, adsorption of the endocrine disrupting compounds (EDCs) onto the SWCNTs was not affected. In the absence of SWCNTs, hydrophobic DOC (i.e., humic acid) adsorbed 15–20% of BPA and EE2. However, when the humic acid and SWCNTs were both present, the overall adsorptive capacity of the SWCNTs was reduced. Hydrophobic (π-π electron donor-acceptor) interactions between the EDCs and the constituents in the leachate, as well as interactions between the SWCNTs and the EDCs, are proposed as potential adsorption mechanisms for BPA and EE2 onto SWCNTs. [Copyright &y& Elsevier]

Abstract: We studied the phosphorus (P) binding capacity of Ca-rich alkaline filter material – hydrated oil shale ash (i.e. hydrated ash) in two onsite pilot-scale experiments (with subsurface flow filters) in Estonia: one using pre-treated municipal wastewater with total phosphorus (TP) concentration of 0.13–17.0 mg L−1 over a period of 6 months, another using pre-treated landfill leachate (median TP 3.4 mg L−1) for a total of 12 months. The results show efficient P removal (median removal of phosphates 99%) in horizontal flow (HF) filters at both sites regardless of variable concentrations of several inhibitors. The P removal efficiency of the hydrated ash increases with increasing P loading, suggesting direct precipitation of Ca-phosphate phases rather than an adsorption mechanism. Changes in the composition of the hydrated ash suggest a significant increase in P concentration in all filters (e.g. from 489.5 mg kg−1 in initial ash to 664.9 mg kg−1 in the HF filter after one year in operation), whereas almost all TP was removed from the inflow leachate (R 2 = 0.99). Efficiency was high throughout the experiments (median outflow from HF hydrated ash filters 0.05–0.50 mg L−1), and P accumulation did not show any signs of saturation. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the application of Fenton and Oxone/Co2+ oxidation processes for landfill leachate treatment was investigated. The removal of the chemical oxygen demand (COD), suspended substances (SS) and the color of the landfill leachate by Fenton oxidation to that by Oxone/Co2+ oxidation were compared under optimal operational conditions. For Fenton oxidation process, the optimal conditions were determined as: [H2O2]=80mmol L−1, [H2O2]/[Fe2+]=2.0, initial pH=2.5, reaction temperature=37.5±1°C, reaction time=160min, number of stepwise addition=3. Under the given conditions, 56.9% of the COD removal efficiency was achieved, but the SS and the color of the treated landfill leachate increased due to the generation of a large quantity of ferric hydroxide sludge. In reference to Oxone/Co2+ oxidation process, the optimal conditions were determined as: [Oxone]=4.5mmol L−1, [Oxone]/[Co2+]=104, pH=6.5, reaction temperature=30±1°C, reaction time=300min, number of stepwise addition=7, the COD, SS and the color removal efficiencies were 57.5, 53.3 and 83.3%, respectively. From this work, it can be concluded that Oxone/Co2+ oxidation process demonstrated higher degradation efficiencies of the COD, SS and color for landfill leachate treatment than that by Fenton oxidation process. It also suggested that Oxone/Co2+ oxidation process could be considered as one of the most promising technologies for practical applicability to treat landfill leachate in large scale. For further improving the efficiency of Oxone/Co2+ oxidation process, we proposed that combination of it with other technologies in future such as ultraviolet, ultrasound and biological methods. [Copyright &y& Elsevier]

Abstract: The issue of domestic waste is recognised as one of the most serious environmental problems facing the nation. With the UK producing 35 million tonnes of municipal solid waste per annum, an understanding of the ranges of toxicity of landfill emissions is crucial to determine the degree of concern we should have about the potential effects these waste sites could have upon nearby populations and the surrounding environment. The aim of this study was to evaluate the bioreactivity of landfill leachates in terms of their capacity to damage ROS-sensitive bacteriophage plasmid DNA and induce toxicity in a commercial photobacterium toxicity assay, based on the light emission of Vibrio fischeri bacteria (ROTAS™). The bacterial assay revealed widespread biostimulation and a hormesis response in the bacteria, with α-, β- and γ-response curves observed following exposure to the different landfill leachates. Different biological mechanisms lead to variations in bioreactivity, as seen in the plasmid DNA scission and ROTAS assays. [Copyright &y& Elsevier]

A system consisting of a two-stage UASB and anoxic–oxic reactor was used to enhance COD and nitrogen removal from landfill leachate. To improve denitrification efficiency, the raw leachate with recycled final effluent was pumped into the first-stage UASB (UASB1) to carry out simultaneous denitrification and methanogenesis. The results over 180d show that the maximum organic removal rate in UASB1 and UASB2 was 12.5 and 8.5kgCODm−3 d−1 in the oxic zone of the A/O reactor, respectively. The COD and biochemical oxygen demand (BOD5) removal efficiency of the system was 80–92% and about 99%, respectively. Without controlling temperature (17–30°C) and dissolved oxygen (0.5–4.0mgL−1), the maximum NH4 +-N removal rate was 0.68kg NH4 +-Nm−3 d−1, and about 99% of NH4 +-N removal was obtained by nearly complete nitritation. The 81–93% total nitrogen removal was obtained by complete denitrification in the UASB1 and in the anoxic zone of the A/O reactor. Fluorescence in situ hybridization (FISH) analysis of the sludge samples from A/O reactor showed that ammonia oxidizing bacteria (AOB) consisted 4% of the eubacterium, while nitrite oxidizing bacteria (NOB) counted less than 0.2% of that. The study shows that the main factors achieving and maintaining nitritation are a proper range of free ammonia concentration obtained by dilution recycled final effluent that inhibits NOB but not AOB; effective control on aeration time by indication of “ammonia valley” on pH profile; and highly efficient denitrification and its reproducing alkalinity to result in pH above 8.5. [Copyright &y& Elsevier]

Ozonation combined with electrolysis (ozone–electrolysis) is a new advanced oxidation process for water treatment. The advantages of ozone–electrolysis are (1) that reagents such as hydrogen peroxide or ferrous salts are unnecessary, (2) there is less influence from chromaticity, and (3) electric power is only required for operation. However, electrolysis has a serious limitation, in that it requires electrical conductivity (EC). This research is aimed at developing an ozone–electrolysis reactor that is applicable to wastewater with low EC using a cation exchange membrane as solid electrolyte. Moreover, experimental evidence of hydroxyl radical (·OH) generation via the cathodic reduction of ozone was obtained. Competitive kinetics analysis, based on the experimental data from the ozone–electrolysis of a mixed solution of 1,4-dioxane and tert-butyl alcohol, revealed that ·OH contributed to 1,4-dioxane degradation. The ozone–electrolysis reactor was successfully applicable to degradation of 1,4-dioxane in both 1,4-dioxane solution (EC: less than 0.30μS/cm) and a landfill leachate treated by a low-pressure reverse osmosis membrane (EC: 0.06mS/cm). The use of a solid electrolyte was also very effective in reducing the electric power required for electrolysis. [Copyright &y& Elsevier]

Abstract: The distribution of phthalic acid esters (PAEs) (including diisobutylphthalate (DIBP), di-n-butylphthalate (DnBP) and bis(2-ethyl)hexylphthalate (DEHP)) in dissolved organic matter (DOM) fractions of leachates from sanitary or bioreactor landfills was evaluated. The leachate DOM was fractionated into humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fractions. Measurements showed that the PAEs were bound mostly to the HA fraction in leachate, regardless of their landfill age or the presence of leachate recirculation. The PAEs affinity for HA and FA differed considerably relative to the sorption coefficients reported for model compounds. Molecular weight of DOM correlated with PAEs partition in collected leachate samples fractions while aromaticity was a poor predictor. Based on the presence of phenolic, carboxyl or amide groups in DOM fractions, hydrogen bonding is likely to be involved in interactions between PAEs and leachate DOM. The peptide groups, particularly presented in HA fracion, might explain the strong affinity of PAEs for HA. The fluorescence excitation emission matrix contour plots showed that the HyI fractions shared certain similarities with humic substances in terms of molecular structure, which may be one reason why PAEs exhibited a clear sorption to the HyI fractions. [Copyright &y& Elsevier]

In an effort to treat N-rich streams in a more sustainable way, recent years have seen the development of new technologies, most of which are based on autotrophic denitrification via nitrite (anammox). In order to attain a suitable influent for that process, the wastewater must be treated by partially oxidising the ammonium to nitrite. In that aspect, this article presents the start-up and operation of a Partial Nitritation Sequencing Batch Reactor (PN-SBR) treating urban landfill leachates. Stable partial nitritation has been reached treating high ammonium loads (1–1.5kgNm−3 d−1), demonstrating the feasibility of this technology as a previous step of anammox process. This study has also given away the importance of pH influence over ammonium oxidising bacteria (AOB) activity, thus it has been possible to determine the values of the half inhibition constants for free ammonia (k I,FA=605.48±87.18mg N–NH3 L−1) and free nitrous acid (k I,FNA=0.49±0.09mg N–HNO2 L−1), as well as the half-saturation constant for bicarbonate ( CL−1). [Copyright &y& Elsevier]

Two-stage aged-refuse bioreactor (ARB) was applied to treat landfill leachate in Shanghai Waste Laogang Disposal Plant. The removal efficiencies of chemical oxygen demand (COD), biological oxygen demand (BOD), total organic carbon (TOC), total nitrogen (TN) and ammonia nitrogen (NH3–N) of landfill leachate treated by the two-stage bioreactor system were 98.5%, 99.9%, 98.0%, 64.2% and 99.9%, respectively. The COD and BOD in the second stage effluent were 239 and 7mgl−1, respectively. Thus three types of electrolysis were employed to further treat the second effluent, undivided electrolysis (UDE), divided electrolysis (DE) with Ti/PbO2 cathode and DE with gas diffusion cathode. All electrolysis processes possessed good color removal effect, while the DE with gas diffusion cathode had the best TOC removal effect. The optimum electrolysis time of leachate was 30min. The TOC removal efficiencies were 51.4% and 39.7% in anolyte and catholyte, respectively, after 30min electrolysis at 5V. In addition, the DE with gas diffusion cathode showed the least energy consumption of 9.8kWhm−3 at 30min. The organic pollutants in the leachate were analyzed through a gas chromatography coupled with mass spectrometry (GC–MS) system. Through the two-stage ARB, the species and concentrations of organic pollutants in landfill leachate reduced greatly. Several chlorinated organic compounds were detected in the effluent after the UDE and the anolyte of the DE. In addition, the concentration of absorbable organic halogens (AOX) increased greatly during the electrolysis. Hence, careful consideration should be given in the application of electro-oxidation into the treatment of chloride-containing wastewater. [Copyright &y& Elsevier]

Abstract: Municipal solid waste landfill leachates from 9 Norwegian sites were size charge fractionated in the field, to obtain three fractions: particulate and colloidal matter >0.45μm, free anions/non-labile complexes <0.45μm and free cations/labile complexes <0.45μm. The fractionation showed that Cd and Zn, and especially Cu and Pb, were present to a large degree (63–98%) as particulate and colloidal matter >0.45μm. Cr, Co and Ni were on the contrary present mostly as non-labile complexes (69–79%) <0.45μm. The major cations Ca, Mg, K, and Mn were present mainly as free cations/labile complexes <0.45μm, while As and Mo were present to a large degree (70–90%) as free anions/non-labile complexes <0.45μm. Aluminium was present mainly as particulate and colloidal matter >0.45μm. The particulate and colloidal matter >0.45μm was mainly inorganic; indicating that the metals present in this fraction were bound as inorganic compounds. The fractionation gives important information on the mobility and potential bioavailability of the metals investigated, in contrast to the total metal concentrations usually reported. To study possible changes in respective metal species in leachate in aerated sedimentation tanks, freshly sampled leachate was stored for 48h, and subsequently fractionated. This showed that the free heavy metals are partly immobilized during storage of leachate with oxygen available. The largest effects were found for Cd and Zn. The proportion of As and Cr present as particulate matter or colloids >0.45μm also increased. [Copyright &y& Elsevier]

Abstract: In recent years, studies of leachate treatment by conventional Fenton, photo-Fenton and electro-Fenton processes have indicated that these methods can effectively reduce concentrations of organic contaminants and color. In addition, the process can increase the biodegradable fraction of organic constituents in leachate, particularly in mature or biologically recalcitrant leachate. Oxidation and coagulation both play important roles in the removal of organics. Initial pH, dosages of Fenton reagents, aeration, final pH, reagent addition mode, temperature, and UV irradiation may influence final treatment efficiency. In this paper, current knowledge of performance and economics of Fenton processes for treatment of landfill leachate as reported for laboratory, pilot and full-scale studies is reviewed, with the conclusion that the Fenton process is an important and competitive technology for the treatment or pretreatment of landfill leachate. [Copyright &y& Elsevier]

Abstract: Large molecular refractory organic compounds (i.e., humic substances) were the major chemical oxygen demand (COD) components of aged raw landfill leachate. To investigate the behaviours of the large molecular refractory organic compounds when they were subjected to oxidation with ozone only (O3 only) and ozone combined with hydrogen peroxide (O3/H2O2), the aged raw landfill leachate first was filtered with 0.8 and 0.45μm pore size filters in series, then was sequentially fractionated with 10,000 MWCO; 5000 MWCO; and 1000 MWCO membranes, and four samples were formed: 0.45μm–10,000Da; 10,000–5000Da; 5000–1000Da; and <1000Da. Mass distribution profiles of COD, 5-day biochemical oxygen demand (BOD5), colour and metals in the aged raw leachate were developed through mass balance. After membrane fractionation of the aged raw leachate, the metals were fractionated with the humic substances. Each fractionated sample as well as the aged raw leachate was oxidised with O3 only and O3/H2O2. The H2O2 enhanced the reduction of COD and colour; while, the BOD5 after O3 only was always higher than that of O3/H2O2. The addition of H2O2 improved the peak reduction of large molecules, but the effects of H2O2 on the fractions of 10,000–5000Da and 5000–1000Da were likely insignificant, which is in accordance with the COD results. No correlation was found between the BOD5 increase and the area of new peak formed after oxidation. However, the BOD5 of each sample after oxidation with O3 only was the logarithmic function of its total peak area. [Copyright &y& Elsevier]

A worst-case simulation of the mass-balance for metals in the waste deposited during 1 year and the levels of cadmium (Cd), lead (Pb), mercury (Hg), chromium (Cr) and iron (Fe) in the leachate was calculated for four sanitary landfills in Western Norway. Estimates of the levels of metal content in mixed municipal solid waste (MSW) were found by using recent literature values calculated in a mass-balance study at a Norwegian waste incinerator plant. Leachate from the landfills were sampled and analyzed monthly during 1 year, and from these measurements the total annual discharge of the selected metals through the leachate was determined. The levels of the measured heavy metals in the leachate were low. For Cd less than 0.06%, for Pb less than 0.01% and for Hg less than 0.02% of the estimated year''s deposited mass of metals were leached from the landfills during the year of investigation. The high retention of these metals are most likely due to sulfide precipitation, but also due to the immobile condition of the metals in their original deposited solid state (plastics, ceramics, etc.). The percentage of Cr leached was relatively higher, but less than 1.0% per year. The mass balance of Fe suggests that this element is more mobile under the prevailing conditions. The percentage of Fe leached varied and was estimated to be between 1.9% and 18%. The present study clearly supports the theory that MSW only to a small extent will lead to discharge of metals if deposited at well-constructed sanitary landfills with top layers. [Copyright &y& Elsevier]

Landfill leachates are composed of a complex mixture of degradation products including dissolved organic matter, which includes a wide range of potentially fluorescent organic molecules and compounds. Here we investigate the excitation–emission matrix fluorescence of landfill leachates from three contrasting landfill sites. Landfill fluorescence properties are all characterized by intense fluorescence at λex=220–230 nm, and λem=340–370 nm which we suggest derives from fluorescent components of the Xenobiotic Organic Matter fraction such as naphthalene, as well as at λex=320–360 nm, and λem=400–470 nm from a higher molecular weight fulvic-like fraction. Landfill leachates are characterized by intense fluorescence, with ∼102 intensity units of fluorescence at λex=220–230 nm, and λem=340–370 nm mg-1 of total organic carbon, demonstrating leachate detection limits of <0.1 mg l-1 total organic carbon. We demonstrate that for all landfill sites, leachate fluorescence intensity has a strong correlation with ground water quality determinants ammonia, total organic carbon and biochemical oxygen demand. We investigate both within-site and between-site leachate fluorescence properties, and demonstrate that although there is significant within-site variability, leachates from all 3 sites can be statistically discriminated using just fluorescence properties (65% success rate) or with a combination of fluorescence and basic geochemical parameters (85%). Our findings suggest that fluorescence can be used as a rapid and sensitive tracer of leachate contamination of ground water, as well as help discriminate, together with geochemical determinants, leachates from different landfill sources. [Copyright &y& Elsevier]

Continuous flow experiments were conducted using sand-packed columns to investigate the relative significance of bacterial growth, metal precipitation, and anaerobic gas formation on biologically induced clogging of soils. Natural leachate from a local municipal landfill, amended with acetic acid, was fed to two sand-packed columns operated in upflow mode. Degradation of the influent acetic acid resulted in the production of methane and carbon dioxide, and simultaneous reduction of manganese, iron, and sulphate. Subsequent increase in the influent acetic acid concentration from 1750 to 2900 mg/l, and then to 5100 mg/l, led to rapid increase in the dissolved inorganic carbon, solution pH, and soil-attached biomass concentration at the column inlet, which promoted the precipitation of Mn2+ and Ca2+ as carbonate, and Fe2+ as sulphide. An influent acetic acid concentration of 1750 mg/l decreased the soil''s hydraulic conductivity from an initial value of 8.8×10−3 cm/s to approximately 7×10−5 cm/s in the 2–6 cm section of the column. Increasing the influent acetic acid to 5100 mg/l only further decreased the hydraulic conductivity to 3.6×10−5 cm/s; rather, the primary effect was to increase the length of the zone experiencing reduced hydraulic conductivity from 0–6 cm to the entire column. As bioaccumulation was limited to the 0–5 cm section of the column, and the effect of metal precipitation was negligible, the reduction on the deeper sections of the column is attributed to gas flow, which was up to 1440 ml/day. Mathematical modelling shows that biomass accumulation and gas formation were equally significant in reducing the hydraulic conductivity, while metal precipitation contributed only up to 4% of the observed reduction. [Copyright &y& Elsevier]

• Advances on the characterization and treatment of landfill leachate are reviewed. • The state-of-the-art innovations of spectroscopic techniques are highlighted. • Advanced oxidation techniques are promising in landfill leachate treatment. • Limitations/challenges of current characterization/treatment approaches are discussed. • Perspectives on the development of characterizing/treating approaches are envisaged. Landfill leachate is a complicated organic wastewater generated in the sanitary landfilling process. Landfill leachate must be appropriately disposed to avoid ecotoxicity and environmental damage. An in depth understanding of the physiochemical characteristics and environmental behaviors of landfill leachate is essential for its effective treatment. In this study, recent advances on the properties of landfill leachate, its characterization methods and treatment techniques are critically reviewed. Specifically, the up-to-date spectroscopic techniques for landfill leachate characterization and advanced oxidation treatment techniques are highlighted. Moreover, the drawbacks and challenges of current techniques for landfill leachate characterization and treatment are discussed, along with the future perspectives in the development of characterization and treatment approaches for landfill leachate. [Display omitted] [ABSTRACT FROM AUTHOR]

• Combined electrochemical process (CEP) reduced the COD by 96% in 3.5 hours • Electrocoagulation-electrooxidation enhanced the BOD 5 /COD from 0.015 to 0.530 • Cathodic electrocoagulation was dominant in electrooxidation-electrocoagulation • Chloride can be a surrogate to determine electrocoagulation efficiency in CEPs • Changes in CEP sequence can deter Pb dissolution from Ti/ß-PbO 2 anodes 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-PbO 2) 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-PbO 2 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 (BOD 5 /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-PbO 2 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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Efficacy of different biocides for disinfection against algae and E. coli is evaluated. • Organohalogens are quantified following disinfection of landfill leachate. • Biocides have a threshold dosage under which organohalogens form below detectability. • Disinfection mechanism partly explains biocide action with organohalogen formation. • Metabisulfite is identified as a safe, eco-friendly, and effective biocide. This study evaluates 9 biocides as disinfectants against microbiological contaminants, specifically, microalgae and E. coli , while assessing their safety and environmental impact. Specifically, the biocide effectiveness and corresponding generation of halogenated compounds is assessed in a real contaminated groundwater receiving acidic leachate from a phosphogypsum landfill. Oxidizing agents are investigated, namely, hypochlorite, peracetic acid, hydrogen peroxide, chlorine dioxide, and persulfate, together with electrophilic biocides, namely, 2,2-dibromo-2-cyanoacetamide and (chloro-) methylisothiazolinone. In addition, a novel disinfection approach is assessed by applying reducing agents, namely, sulfite and metabisulfite. The disinfection mechanism and the formation of halogenated compounds are discussed on the basis of the mode of action and of the molecular structure of each biocide. Overall, the results show that an optimal dosage of the biocides exists to minimize the formation of harmful compounds in water while maximizing disinfection, especially for hypochlorite and peracetic acid. This dosage was between 0.03 mM and 0.15 mM depending on the biocide. The safety of electrophilic biocides is found to be associated to their molecular structure rather than their mode of action. Hydrogen peroxide, MIT, and metabisulfite are the most promising disinfectants in the contaminated groundwater matrix of interest since no halogenated by-products are detected upon successful disinfection, while they are able to completely inactivate bacteria and remove over the 80% of microalgae in the selected matrix. In particular, metabisulfite represents a highly promising biocide, owing to its low environmental and health impacts, as well as economic feasibility (estimated reagent cost ~0.002 € per cubic meter of treated water). Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Three distinct AOA were enriched in a full-scale WWTP with detectable activities. • AOA outcompeted Comammox and AOB and dominated the AOM community. • Low aeration, long retention time, high NH 4 + and Cu2+ are favorable for the growth of AOA. • The dominant AOA is likely resulted from competition advantage by highly expressing Amt1. • Niche adaptation of the AOA enhancesdominance by the unique biochemical functionalities. Recent studies indicate that ammonia-oxidizing archaea (AOA) may play an important role in nitrogen removal by wastewater treatment plants (WWTPs). However, our knowledge of the mechanisms employed by AOA for growth and survival in full-scale WWTPs is still limited. Here, metagenomic and metatranscriptomic analyses combined with a laboratory cultivation experiment revealed that three active AOAs (WS9, WS192, and WS208) belonging to family Nitrososphaeraceae were active in the deep oxidation ditch (DOD) of a full-scale WWTP treating landfill leachate, which is configured with three continuous aerobic-anoxic (OA) modules with low-intensity aeration (≤ 1.5 mg/L). AOA coexisted with AOB and complete ammonia oxidizers (Comammox), while the ammonia-oxidizing microbial (AOM) community was unexpectedly dominated by the novel AOA strain WS9. The low aeration, long retention time, and relatively high inputs of ammonium and copper might be responsible for the survival of AOA over AOB and Comammox, while the dominance of WS9, specifically may be enhanced by substrate preference and uniquely encoded retention strategies. The urease-negative WS9 is specifically adapted for ammonia acquisition as evidenced by the high expression of an ammonium transporter, whereas two metabolically versatile urease-positive AOA strains (WS192 and WS208) can likely supplement ammonia needs with urea. This study provides important information for the survival and application of the eutrophic Nitrososphaeraceae AOA and advances our understanding of archaea-dominated ammonia oxidation in a full-scale wastewater treatment system. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• MPs concentration in landfill leachate were 235.4±17.1 item/L and 11.4±0.8 µg/L. • Tiny MPs (<50 µm) can account for over 50% in landfill leachate. • Low densities and irregular shapes of MPs implied the difficulty of removal by settling. • Membrane processes largely reduced MP loadings but also generated and released MPs. • Sludge dewatering liquor accumulated MPs and separated treatment may help mitigation. Due to the environmental risks caused by microplastics, understanding the sources and characteristics of microplastics and cutting off their routes into the environment are crucial. However, so far, studies on microplastics in the landfill leachate system (a major pathway of microplastics into the environment) are still limited, especially for tiny particles <50 µm that might have higher risks to the environment. This study investigated the microplastics in landfill leachate and in leachate treatment works, with a size detection limit down to 10 µm. The results showed that the microplastics particle and mass concentrations in the untreated leachate were 235.4 ± 17.1 item/L and 11.4 ± 0.8 µg/L, respectively, with tiny particles (<50 µm) accounting for over 50%. Overall, 27 polymeric materials were detected in leachate samples, with polyethylene and polypropylene being the most abundant in the untreated leachate. The neutral buoyancy of microplastics (average density: 0.94 g/cm3), together with irregular shapes, suggested they may be difficult to be removed by sedimentation. Further exploring the fate of microplastics in leachate treatment works showed that the membrane treatment effectively reduced microplastics loading to 0.14% for particle and 0.01% for mass, but the average particle density rose. The differences in polymeric materials distribution at different sampling locations and the presence of membrane-related polymer in membrane treatment effluent suggested tiny microplastics could be generated and released from membrane systems. Moreover, this study discovered that the sludge dewatering liquor could contain a high amount of microplastics, and the estimated particle loading was about 3.6 times higher than that in dewatered sludge. This suggested a new approach to microplastics mitigation through separating microplastics from the sludge dewatering liquor before its recirculation. Image, graphical abstract [ABSTRACT FROM AUTHOR]