Leachate Research Articles

A Comparative Performance Assessment of the Integrated Upflow and Surface Flow-Based Constructed Wetlands Dosed with Landfill Leachate: Electrode Coupling and Input Load Variation

This study reports organic, nutrient, and coliform removal performances of two integrated wetlands designed to treat landfill leachate. Each integrated system included two components: a normal or electrode-integrated upflow-based wetland and a surface flow wetland (with internal baffle walls). The components were fully or partially filled with stone dust media and planted with Canna indica. Two hydraulic loading rates, i.e., 15 L and 60 L (per day), were applied. The integrated wetlands achieved a mean biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and coliform removal efficiency ranges of 89–94%, 95–97%, 85–91%, 91–98%, and 70–88%, respectively, within the applied loading ranges. The electrode-dependent system achieved better pollutant removal performances due to the influence of electrochemical-based bioreactions that fostered microbial decomposition. Nitrogen accumulation percentage (with respect to observed removal) in plant tissues ranged between 0.6 and 25%; phosphorus accumulation percentage was negligible, i.e., ≤0.009%. The chemical composition of the stone dust media supported nutrient adsorption. Stable nutrient removal performance was observed with both systems despite variable loading ranges due to pollutant removal in the upflow-based wetlands followed by controlled flow direction (induced by baffle walls) in the surface flow wetlands that triggered chemical and biological removals. Mean power density production ranged between 235 and 946 mW/m3 with the electrode-based integrated wetland system. In summary, this study demonstrates the application of integrated wetland systems to treat landfill leachate and the associated factors to achieve stable removal under variable loading ranges.

Denitrificimonas halotolerans sp. nov., a novel species isolated from UASB sludge treating landfill leachate.

A Gram-stain-negative, facultative anaerobe, rod-shaped strain JX-1T was isolated from UASB sludge treating landfill leachate in Wuhan, China. The isolate is capable of growing under conditions of pH 6.0-11.0 (optimum, pH 7.0-8.0), temperature 4-42℃ (optimum, 20-30℃), 0-8.0% (w/v) NaCl (optimum, 5.0%), and ammonia nitrogen concentration of 200-5000mg/L (optimum, 500mg/L) on LB plates. The microorganism can utilize malic acid, D-galactose, L-rhamnose, inosine, and L-glutamic acid as carbon sources, but does not reduce nitrates and nitrites. The major fatty acids are C18:1ω7c/C18:1ω6c, iso-C15:0, and anteiso-C15:0. The respiratory quinones are Q9 (91.92%) and Q8 (8.08%). Polar lipids include aminolipid, aminophospholipid, diphosphatidylglycerol, glycolipid, phosphatidylethanolamine, phosphatidylglycerol, and phospholipid. Compared with other strains, strain JX-1T and Denitrificimonas caeni HY-14T have the highest values in terms of 16S rRNA gene sequence similarity (96.79%), average nucleotide identity (ANI; 76.06%), and average amino acid identity (AAI; 78.89%). Its digital DNA-DNA hybridization (dDDH) result is 20.3%. The genome of strain JX-1T, with a size of 2.78Mb and 46.12mol% G + C content, lacks genes for denitrification and dissimilatory nitrate reduction to ammonium (DNRA), but contains genes for ectoine synthesis as a secondary metabolite. The results of this polyphasic study allow genotypic and phenotypic differentiation of the analysed strain from the closest related species and confirm that the strain represents a novel species within the genus Denitrificimonas, for which the name Denitrificimonas halotolerans sp. nov. is proposed with JX-1T (= MCCC 1K08958T = KCTC 8395T) as the type strain.

Advanced leachate treatment at Mascara landfill (Algeria): A hybrid pilot approach with activated sludge and ferric chloride

This study investigates a hybrid treatment approach, that combines a Sequencing Batch Reactor (SBR) with a coagulation-flocculation process, to reduce the contaminants in Landfill Leachate (LL), targeting Chemical Oxygen Demand (COD), Turbidity, and Total Suspended Solids (TSS). The experimental set-up incorporated a batch reactor at room temperature and a pH between 7.7 and 8.7, with an Arduino monitoring system for heightened precision. The SBR was operated continuously over a 24-hour cycle, with a Hydraulic Retention Time (HRT) set at 5 days and variable sludge retention times (SRT) of 5, 10, and 15 days. The Aluminum sulfate (Al2 (SO4)3), Ferric Chloride (FeCl3), and Lime (CaO) were assessed for the coagulation-flocculation process. The results indicate a promising removal efficiency of 40 % for COD, 31 % for turbidity, and 47 % for TSS using the SBR process. FeCl3 showed higher findings, achieving removal yields of 87 % for COD and 86 % for turbidity, at an optimized dose of 10 g/L and pH 5.5. Furthermore, adding 0.25 g/L of CaO significantly improved the removal efficiency to 94.14 % for COD, 98.22 % for turbidity and 99.78 % of the TSS. Therefore, this study's results underline the effectiveness of combining SBR with coagulation-flocculation, particularly using FeCl3 and CaO, in treating landfill leachate.

Metagenomic analysis of bacterial communities in heavy metal leachate-contaminated soils at Jalan Lipis Sanitary Landfill, Pahang, Malaysia

A variety of bacterial communities can be found in heavy metal leachate-contaminated soil. These bacteria might have molecular defenses that allow them to endure a high heavy metal concentration. However, there aren't enough datasets on bacterial populations to be exploited for bioremediation, especially the biotreatment of leachate contaminated with heavy metals. This research examined the diversity of the bacterial population in heavy metal leachate-contaminated soil from the Jalan Lipis Sanitary Landfill in Pahang, Malaysia. The soil samples were taken from three (3) different locations. pH analysis showed that the heavy metal leachate-contaminated soil possesses alkaline pH. ICPMS analysis showed high concentration of nickel (112.96 mg/kg) followed by manganase (89.83 mg/kg), arsenic (43.84 mg/kg), and lead (3.62 mg/kg). The three most prevalent bacteria in the heavy metal leachate-contaminated soil from the site were Pseudomonas C (Proteobacteria), Flavobacterium (Bacteroidota), and Proteiniclasticum (Firmicutes), according to metagenomic sequencing of the 16 s rRNA gene. The alpha and beta bacterial diversity analysis indicate that each location with different heavy metal concentration differs significantly on its bacterial diversity providing a valuable information to be applied in heavy metal bioremediation exclusively from landfill leachate.

Sustainable H2O2 production in a floating dual-cathode electro-Fenton system for efficient decontamination of organic pollutants

Electrochemical advanced oxidation processes (EAOPs) based on natural air diffusion electrode (NADE) promise efficient and affordable advanced oxidation water purification, but the sustainable operation of such reaction systems remains challenging due to severe cathode electrowetting. Herein, a novel floating cathode (FC) composed of a stable hydrophobic three-phase interface was established by designing a flexible catalytic layer of FC. This innovative electrode configuration could effectively prolong the service life of the cathode by mitigating the interference of H2 bubbles from the hydrogen evolution reaction (HER), and the H2O2 production rate reached 37.59 mg h−1·cm−2 and realize a long-term stable operation for 10 h. Additionally, an FC/carbon felt (CF) dual-cathode electro-Fenton system was constructed for in situ sulfamethoxazole (SMX) degradation. Efficient H2O2 production on FC and Fe(III) reduction on CF were synchronously achieved, attaining excellent degradation efficiency for both SMX (ca. 100%) with 2.5 mg L−1 of Fe(Ⅱ) injection. For real wastewater, the COD removal of the FC/CF dual-cathode electro-Fenton system was stabilized at exceeding 75%. The practical application potential of the FC/CF dual-cathode electro-Fenton system was also demonstrated for the treatment of actual landfill leachate in continuous flow mode. This work provides a valuable path for constructing a sustainable dual-cathode electro-Fenton system for actual wastewater treatment.

Use of lyophilized and acclimated digestate dominated by Methanobrevibacter as a start-up inoculum in anaerobic digester led to higher methane production in biochemical methane potential assays

Transporting wet inoculum for full-scale anaerobic digester (AD) start-up is usually infeasible and costly, especially, for remote locations. To overcome these burdens lyophilized AD inoculum is thought to be used after on-site acclimation. For this reason, in this study, the impact of three different acclimated lyophilized AD inoculums collected from full-scale mesophilic AD installations treating different feedstocks was tested for 20 days to monitor AD start-up and methane production by using biochemical methane potential (BMP) assays. The lyophilized inoculums after acclimation were fed to corresponding triplicate digesters treating similar feedstocks as digestate (DG), waste activated sludge (WAS) plus landfill leachate (LL) and WAS, LL plus food waste from municipal solid waste (FWMSW). As a control, no inoculum added digesters with three different feedstocks collected freshly from full-scale mesophilic AD installations treating DG, WAS + LL and WAS + LL + FWMSW were also run in triplicates. All the digesters displayed enhanced methane production in two days of the incubation, the digesters fed with DG as an inoculum displayed shortened start-up and the highest methane production with 42.77 % comparing to control. BMP assays of the other two inoculums tested also displayed 4.73 % enhanced methane production for WAS plus LL and 4.51 % enhanced methane production for WAS, LL plus FWMSW comparing to their corresponding controls. Metagenome analyses of the inoculums used revealed that the dominant methanogens were Methanobacteriaceae (100 % Methanobrevibacter) for DG, %33 Methanosaetaceae (%100 Methanothrix) and %27 Methanobacteriaceae (%71 Methanobrevibacter and %29 Methanosphaera) for WAS + LL, %35 Methanosaetaceae (%100 Methanothrix) and %30 Methanobacteriaceae (%91 Methanobrevibacter and %9 Methanosphaera) for WAS + LL + FWMSW. The lyophilized DG dominated by hydrogenotrophic genus Methanobrevibacter seems to be promising inoculum after acclimation, however, its efficiency needs to be further analysed for the ADs treating various feedstocks.

Optimization of ultrasonication and alkalinization as pretreatment methods for leachate co-digested with food waste toward maximum synergistic effects

Anaerobic co-digestion (AcoD) of food waste (FW) and landfill leachate has shown promising results in enhancing the methane yield. However, leachate includes toxic and refractory compounds that may impact the decomposition process. In this research, co-digested leachate was pretreated using ultrasonication and alkalinization to manipulate its characteristics toward improved synergism with FW. Experimental optimization was conducted through biochemical methane potential (BMP) assays to identify the optimum operating conditions of the pretreatment methods. The study evaluated the synergistic effects of co-digestion with raw and pretreated leachate on enhancing the performance in terms of feedstock solubilization and methane production. The BMP test demonstrated that alkalinization and ultrasonication improved the total methane generation by 35% and 27%, respectively, yielding around 397 and 375 mL CH4 per g of volatile solids. Moreover, ultrasonication and alkalinization enhanced the synergistic effects by 28% and 36%, respectively, compared to co-digestion with untreated leachate. Optimization by response surface methodology revealed that maximum performance could be achieved with leachate sonication at 212 W for 37.5 min or augmenting 788 g NaOH per kg of volatile solids. Kinetic and statistical models were derived to simulate and assess the impacts of the pretreatment parameters on the AcoD process. The results indicated that the ultrasonication energy had a higher influence on total solubility and methane production than alkaline dosage. Additionally, energy efficiency analyses were performed to examine the overall viability of the examined management approach and found that alkalinization increased the net energy efficiency by 23%, whereas ultrasonication was inefficient within the examined laboratory conditions despite the improved performance. The findings support an integrated organic waste management system where separated FW is co-treated with landfill leachate.

The potential of Phragmites australis to bioaccumulation and translocate heavy metals from landfill leachate

Constructed wetlands serve as an eco-friendly solution for treating landfill leachate, leading to reduced energy use, economic savings, and less environmental harm. A novel study in the cold climate of western Iran has examined the effectiveness of Phragmites australis, also known as common reed, in a pilot-scale project. The study focused on the reed's capacity to bioaccumulate and translocate heavy metals within a horizontal subsurface flow constructed wetland. The findings revealed significant removal rates for heavy metals such as Fe, Mn, Cd, Cr, Ni, and Pb, with efficiencies of 81.23 %, 76.02 %, 26.92 %, 44.73 %, 20.13 %, and 28.24 % respectively. The bioaccumulation factor for these metals was above 1.0, signifying effective uptake by the plant. However, the translocation factor for all metals, except for Mn, did not exceed 1.0. This indicates that although Phragmites australis is an effective phytostabilizer, effectively sequestering heavy metals in its root system, it is not adept at moving these metals to its aboveground tissues. Rather, it tends to concentrate them within its roots and rhizomes.

Integration of two-stage membrane distillation and fenton-based process for landfill leachate treatment: Ammonia and water recovery and advancement towards zero liquid discharge

The recovery of resources from landfill leachate (LL) represents a more sustainable approach, as it combines meeting release standards with the valorization of raw materials and contributing to the circular economy. Therefore, this study aims to evaluate the performance of a two-stage Direct Contact Membrane Distillation (2S-DCMD) for the recovery of water and ammonia from LFL integrated with the Fenton-based process for the treatment of the membrane concentrate generated in the second stage, aiming to obtain zero effluent discharge. In the first stage, the hot LFL flows through the shell side of the polypropylene hollow fiber membrane module, while the sulfuric acid solution passes through the lumen side·NH3 is recovered in the form of ammonium sulfate. In the second stage, the hot effluent from the first stage flows through the hot channel of the poly(tetrafluoroethylene) sheet membrane module, while the cooled distilled water flows through the other side in countercurrent. Despite the high efficiency of MD, disposing of the concentrate presents challenges, as pollutant concentrations can escalate by an additional 25 % to 50 % compared to the original contaminants in the raw feed. To address this issue, an advanced oxidative process of Fenton (AOP/Fenton) was optimized for treating the concentrate. In the first stage, NH3 removal reached 97.84 %, accompanied by a recovery rate of 79 %. In the second stage, a permeate with high quality was produced. Substantial removal rates were observed in this stage: colour (99.96 %), turbidity (99.89 %), COD (99.33 %), and Sulfates (90.08 %). The AOP/Fenton under optimal conditions (21.50 g/L of Fe2+ and 80 mL of H2O2) the removal of COD was 88.69 %. Thus, this route emerges as a viable alternative for landfill leachate treatment with the recovery of important resources.

The fate of various organic compounds including pharmaceuticals in the treatment of landfill leachate and anaerobic digestate using deammonification

Studies focusing on the fate of organic compounds specifically recalcitrant organics and pharmaceuticals in a deammonification plant are scarce. This study downscaled a full-scale deammonification plant, which was being operated with the same wastewater streams of this study and evaluated for the first time the fate of different fractions of organic compounds in deammonification process along with the removal of nitrogenous compounds. Organic compounds in the feed and effluent were analyzed and their changes in the deammonification process were characterized. The results demonstrate that deammonification achieved over 90% of ammonium removal. COD monitoring revealed that around 11% of COD was reduced during the process mainly due to aerobic COD degradation and heterotrophic denitrifying bacteria. Analysis of the organic fractions revealed that high molecular weight components (around 11 kDa) are susceptible to removal and their concentrations tend to decrease in the reactor. Concentrations of humic substances, specifically fulvic acid-like substances, were reduced. Tracking nine different pharmaceutical residues revealed that morphine and cotinine were completely removed, while pregabalin and oxazepam which are known to be highly recalcitrant were more than 60% removed. The research finding can help in optimizing treatment processes by revealing the fate of different organic compounds, especially pharmaceuticals, within the deammonification process, thereby contributing to better effluent quality, regulatory compliance, and environmental protection.

An Extensive Analysis of Combined Processes for Landfill Leachate Treatment

Sanitary landfilling is the predominant process for solid urban waste disposal, but it generates leachate that poses environmental, economic, and social concerns. Landfill leachate (LL) contains complex and refractory pollutants and toxic compounds that can vary depending on landfill maturity, age, and biochemical reactions, making its treatment challenging. Due to its unique characteristics and occurrence in remote locations, LL requires separate treatment from wastewater. Various conventional treatment processes involving biological, chemical, and physical processes have been used for LL treatment, but a single treatment process is insufficient to meet environmental standards. This review demonstrates that combined treatment processes are more effective and efficient for LL treatment compared to single processes. Among the various combinations, chemical–chemical and chemical–biological treatments are the most commonly used. Specifically, the integration of Fenton with adsorption and a membrane bioreactor (MBR) with nanofiltration (NF) processes shows promising results. The combined processes of MBR with NF, Fenton with adsorption, and PF with biological treatment show maximum removal efficiencies for COD, reaching 99 ± 1%, 99%, 98%, and 97%, respectively. Additionally, the combined Fenton with adsorption process and EC with SPF process enhance biodegradability as indicated by increased BOD5/COD ratios, from 0.084 to 0.82 and 0.35 to 0.75, respectively. The findings emphasize the importance of developing and implementing enhanced combined treatment processes for LL, with the aim of achieving efficient and comprehensive pollutant mineralization. Such processes have the potential to address the environmental concerns associated with LL and contribute to sustainable waste management practices.

Electrochemically regulating COD/TN ratio of aged landfill leachate via rapid chlorine-mediated ammonia oxidation with RuO2-IrO2/Ti anode

Electrochemical oxidation process was employed to regulate the ratio of chemical oxygen demand to total nitrogen (COD/TN ratio) of aged landfill leachate, aiming to meet the requirement of biological treatment. The results indicate that the ammonia nitrogen can be rapidly removed through electrogenerated chlorine radicals over a typical chlorine evolution RuO2-IrO2/Ti anode. The increased input current and decreased flow rate are beneficial to COD/TN ratio improvement, and COD/TN ratio can be increased to more than 16 at 1000 mA (input current) and 0.3 L/h (flow rate). According to the obtained experimental data, we present a strategy for COD/TN ratio increase: (i) determining the COD/TN ratio balance coefficient (B) of aged landfill leachate, and selecting the anode with COD/TN ratio adjustment coefficient (TN) >B, where TN represents the ability to regulate COD/TN ratio, and B represents the specific TN to keep the same COD/TN ratio; (ii) performing the wastewater treatment experiments at different control parameters during electrochemical process; (iii) calculating the k of control parameter sensitivity curves to achieve different tolerance abilities, and further preferentially regulating the reaction process to high average current efficiency (ACE) of ammonia nitrogen and low ACE of COD. This work validates that the electrochemical process can increase the COD/TN ratio together with enhancing the biodegradability of such refractory wastewater, and also provides an effective tool for regulation of the COD/TN ratio via complete ammonia oxidation.

Importance of pyrolysis temperature and particle size on physicochemical and adsorptive properties of urban wood-derived biochar

Physicochemical properties of biochars made from urban wood waste at different pyrolysis temperatures (400-700 °C) and particle sizes (1-2 mm and 63-75 μm) were compared to their ability for heavy metals adsorption at various contact times (30-300 min) and adsorbent dosages (0.1-5 g L-1) in real landfill leachate. The yield, volatile matter, hydrogen and oxygen contents, and functional groups of biochars decreased with increasing pyrolysis temperature; while pH, electrical conductivity, ash, fixed carbon, and specific surface area (SSA) increased. FE-SEM images showed that the creation of pores on the surface of biochars increased significantly with increasing pyrolysis temperature. Moreover, particle size exhibited no significant effect on the properties of biochars (p>0.05), except for the SSA. The SSA of biochars with a particle size of 63-75 μm was significantly higher than that measured in 1-2 mm biochars. The adsorption efficiency of heavy metals from landfill leachate increases with increasing pyrolysis temperature, contact time and adsorbent dosage. Conversely, reducing the particle size increases the adsorption efficiency. The highest adsorption efficiency for Pb, Zn, Ni, Cd, and Mn was obtained as a result of using biochar pyrolyzed at 700 °C with a particle size of 63-75 μm (i.e., BC700/63-75) by 60.39%, 75.01, 64.36, 58.87%, and 71.15%, respectively. Pseudo second-order kinetic and the Langmuir isotherm were recognized as the most appropriate models to describe the adsorption process. The chemical adsorption was identified as the main mechanism for the adsorption of metal ions onto BC700/63-75.

Effect and mechanism of Mn2+ on urease activity during anaerobic biological treatment of landfill leachate.

As a crucial hydrolytic enzyme, urease plays a vital role in anaerobic biological treatment. It is well-known that manganese ions are abundant in landfill leachate, but their concentration fluctuates significantly. However, few studies have investigated the effect and mechanism of different concentrations of Mn2+ on urease activity during anaerobic biological treatment of landfill leachate. This paper aimed to investigate the effects and mechanisms of different concentrations of Mn2+ on urease activity. The results showed that an appropriate amount of Mn2+ could significantly enhance urease activity, while a high concentration of Mn2+ could inhibit it. Insight into the mechanisms behind this phenomenon, various methods such as Zeta potential, particle size, ultraviolet spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and statistical analysis were employed in our study. Research suggested that, on one hand, Mn2+ may form hydrogen bonds with the side chain amino or carboxyl groups of urease amino acid residues, affecting the structure of urease through hydrogen bonding. Additionally, Mn2+ also binds to urease through hydrophobic interactions. On the other hand, the C-OH and C-N functional groups in urease have a strong affinity for Mn2+, and changes in these functional groups can greatly enhance the activity of urease. Furthermore, under the action of high concentrations of Mn2+, while the structure of urease becomes more stable, there is also a steric hindrance phenomenon that affects the substrate from entering the catalytic center. Therefore, studying the mechanism of Mn2+ affecting urease activity has significant biological significance and provides a new perspective for exploring the impact of metals on anaerobic bioprocessing of landfill leachate.

Bipolar membrane assistant landfill leachate coagulation by bauxite tailings with oxalic acid

In this study, bauxite tailings were innovatively employed as the coagulant resource in the treatment of nanofiltration concentrated landfill leachate (NCLL) via bipolar membrane electrodialysis (BMED). The employment of H2C2O4 as the leaching acid, in lieu of HNO3, not only promoted the leaching of metal ions but also minimized the competitive migration of free H+, attributable to its chelating effect. The COD removal increased from about 40.4 % to about 49.9 %, while the energy consumption (EC) decreased to about 0.05 kWh/g COD when the acid is replaced by H2C2O4. An optimal dosage of bauxite tailing is crucial for effective COD removal. An increase in the initial concentration of H2C2O4 benefits metal leaching, while, an excessive concentration thereof augments the competition of H+ ions, thereby impeding the coagulation process. Furthermore, the current density exerted a notable impact on both COD removal and EC, with an optimal density identified at 5 mA/cm2. Connecting more treatment units still maintains COD removal efficiency at approximately 50 %, with a significant reduction in EC of about 24 %, necessitating only 0.038 kWh/g COD. Humic-like and fulvic-like acids are efficiently coagulated, which represent the principal biorefractory substances in NCLL. Consequently, this research delineates a novel approach for the utilization of bauxite tailings and the treatment of NCLL.

An Assessment of the Effectiveness of Using Calcium Peroxide to Purify Landfill Leachate from Contaminants

An Assessment of the Effectiveness of Using Calcium Peroxide to Purify Landfill Leachate from Contaminants

Potential application of landfill leachate as the substrate for electricity generation.

Potential application of landfill leachate as the substrate for electricity generation.

Investigation on PFAS Sources and Removal in a Municipal Wastewater Treatment Plant

PFAS (per- and poly-fluoroalkyl substances) is a complex family of manmade highly fluorinated aliphatic organic chemicals including thousands of chemical structures identified. PFASs were first synthesized in the 1940s and their physical and chemical properties such as oil and water repellency, temperature resistance, and friction reduction were then used in a wide range of products and industrial applications. Awareness about the possible health and environmental risks related to exposure to these substances has only risen in recent years and is resulting in the inclusion of such compounds in the Proposal for the recast of the Directive of the European Parliament and of the Council concerning urban wastewater treatment.A research was carried out at a municipal wastewater treatment plant (MWWTP) in Northern Italy to define the inflowing load of PFAS, the main load sources and the removal efficiency of the treatment processes.First, the contribution of the water supplied to the local population was excluded by means of specific chemical analyses. Then, the 100 industrial settlements served by the MWWTP were examined for the raw materials used, the final products and the productive cycle and 8 of them were selected as potential sources. A sampling campaign was carried out and the specific PFAS load was calculated. The total PFAS load entering the MWWTP was calculated from the analytical results and the flow. The percent contribution of each of the selected settlements to the total PFAS load was then calculated. 40% derives from a textile dyeing industry and 32% from a waste platform receiving also landfill leachates. 89% of the total PFAS load comes from the sum of such contributions and two other activities: the processing of slaughterhouse wastes and the production of chemicals for agriculture.Specific investigations lead to attribute an important role also to fire drills and fire extinguishing, using Aqueous Film Forming Foams (AFFF) containing PFAS. So, domestic contribution can be held as negligible.The removal in the WWTP was null and, in some cases, negative. As also reported in the literature some precursors can be transformed in PFAS during the biological process and some sludge accumulated compounds can be released.

Dynamic changes in dissolved organic matter during transport of landfill leachate in porous medium.

The dynamic changes in dissolved organic matter (DOM) during the transport of landfill leachate (LL) in porous medium should be explored, considering the high levels of DOM in the LL of municipal solid waste. Column experiments were carried out at 25°C at a Darcy's flux of 0.29cm/h for 2722h to compare the transport of Cl-, ultraviolet absorbance at 254nm (UV254), chemical oxygen demand (COD), and dissolved organic carbon (DOC) in the simulated porous medium by using the CXTFIT2.1 code. Results showed that the convection-dispersion equation (CDE) could describe Cl- transport well. The high levels of λ and D could be highly correlated with the physicochemical properties of the porous medium. The transport of the studied DOM with evident aromatic character could be described appropriately by the CDE model with the first-order reaction assumption, considering the similar variation trends of UV254, COD, and DOC in the effluent during experiments. Specifically, the values of retardation factor (R) were in the following order: DOC > UV254 > COD, whereas the low values of the first-order decay coefficient (k1) for DOC and COD were still higher than that for UV254. High contents of humic-like substances in the DOM with complex toxic components resulted in the natural low removal efficiencies of COD, DOC, and UV254 (≤ 23%), which could be confirmed by the variations of fluorescence index (FI) and humification index (HIX) in the effluent. The results should be helpful in evaluating the environmental risk induced by the LL leakage in a landfill site.

Overlooked competition and promotion effects in electrochemical oxidation of humic acid and ammonia in landfill leachate

Electrochemical oxidation (EO) can effectively reduce the degree of humification and toxicity of landfill leachate by generating highly active oxidative species in situ. However, the selective and competitive oxidation of humic acid (HA) and ammonia (NH4+) and the role of different oxidative species during the EO process in complex aqueous conditions remain unclear. In this study, a nanostructured tin-antimony electrode (Ti/Sb-SnO2 NFs) was prepared and compared with three types of commercial electrodes (Ti/Ir-RuO2, Ti4O7, Ti/Sb-SnO2) in terms of electrochemical properties and electrocatalytic oxidation of HA and NH4+. The de-humification capacity, interactive effects of HA and NH4+ on each other's oxidation by different oxidative species, as well as the related oxidation byproducts were investigated. The differences in pollutant electrooxidation among the different electrodes were found to be insignificant. The presence of HA was found to be detrimental to NH4+ degradation while reducing the N2 conversion rate. Interestingly, NH4+ initially inhibited the degradation rates of HA while promoted the degradation and reduced the accumulation of organic chlorine during the later EO process. A proposed mechanism accounts for both competitive and promotional effects for simultaneous HA and NH4+ oxidation during the EO process.