Evaluation of the biodegradability and toxicity of landfill leachates after pretreatment using advanced oxidative processes

Ecotoxicological impacts of landfill sites: Towards risk assessment, mitigation policies and the role of artificial intelligence

Waste disposal in landfills remains a global concern. Despite technological developments, landfill leachate poses a hazard to ecosystems and human health since it acts as a secondary reservoir for legacy and emerging pollutants. This study provides a systematic and scientometric review of the nature and toxicity of pollutants generated by landfills and means of assessing their potential risks. Regarding human health, unregulated waste disposal and pathogens in leachate are the leading causes of diseases reported in local populations. Both in vitro and in vivo approaches have been employed in the ecotoxicological risk assessment of landfill leachate, with model organisms ranging from bacteria to birds. These studies demonstrate a wide range of toxic effects that reflect the complex composition of leachate and geographical variations in climate, resource availability and management practices. Based on bioassay (and other) evidence, categories of persistent chemicals of most concern include brominated flame retardants, per- and polyfluorinated chemicals, pharmaceuticals and alkyl phenol ethoxylates. However, the emerging and more general literature on microplastic toxicity suggests that these particles might also be problematic in leachate. Various mitigation strategies have been identified, with most focussing on improving landfill design or leachate treatment, developing alternative disposal methods and reducing waste volume through recycling or using more sustainable materials. The success of these efforts will rely on policies and practices and their enforcement, which is seen as a particular challenge in developing nations and at the international (and transboundary) level. Artificial intelligence and machine learning afford a wide range of options for evaluating and reducing the risks associated with leachates and gaseous emissions from landfills, and various approaches tested or having potential are discussed. However, addressing the limitations in data collection, model accuracy, real-time monitoring and our understanding of environmental impacts will be critical for realising this potential.

The nematode Caenorhabditis elegans enhances tolerance to landfill leachate stress by increasing trehalose synthesis

The burgeoning issue of landfill leachate, exacerbated by urbanization, necessitates evaluating its biological impact, traditionally overshadowed by physical and chemical assessments. This study harnesses Caenorhabditis elegans, a model organism, to elucidate the physiological toxicity of landfill leachate subjected to different treatment processes: nanofiltration reverse osmosis tail water (NFRO), membrane bioreactor (MBR), and raw leachate (RAW). Our investigation focuses on the modulation of sugar metabolism, particularly trehalose-a disaccharide serving dual functions as an energy source and an anti-adversity molecule in invertebrates. Upon exposure, C. elegans showcased a 60-70% reduction in glucose and glycogen levels alongside a significant trehalose increase, highlighting an adaptive response to environmental stress by augmenting trehalose synthesis. Notably, trehalose-related genes in the NFRO group were up-regulated, contrasting with the MBR and RAW groups, where trehalose synthesis genes outpaced decomposition genes by 20-30 times. These findings suggest that C. elegans predominantly counters landfill leachate-induced stress through trehalose accumulation. This research not only provides insights into the differential impact of leachate treatment methods on C. elegans but also proposes a molecular framework for assessing the environmental repercussions of landfill leachate, contributing to the development of novel strategies for pollution mitigation and environmental preservation.

Landfill leachate a potential challenge towards sustainable environmental management

The increasing amount of waste globally has led to a rise in the use of landfills, causing more pollutants to be released through landfill leachate. This leachate is a harmful mix formed from various types of waste at a specific site, and careful disposal is crucial to prevent harm to the environment. Understanding the physical and chemical properties, age differences, and types of landfills is essential to grasp how landfill leachate behaves in the environment. The use of Sustainable Development Goals (SDGs) in managing leachate is noticeable, as applying these goals directly is crucial in reducing the negative effects of landfill leachate. This detailed review explores the origin of landfill leachate, its characteristics, global classification by age, composition analysis, consequences of mismanagement, and the important role of SDGs in achieving sustainable landfill leachate management. The aim is to provide a perspective on the various aspects of landfill leachate, covering its origin, key features, global distribution, environmental impacts from poor management, and importance of SDGs which can guide for sustainable mitigation within a concise framework.

Solar photo-Fenton and persulphate-based processes for landfill leachate treatment: A critical review

Landfilling is the most usual solid waste management strategy for solid residues disposal. However, it entails several drawbacks such as the generation of landfill leachate that seriously threaten human life and the environment due to their toxicity and carcinogenic character. Among various technologies, solar photo-Fenton and sulphate-based processes have proven to be suitable for the treatment of these polluted streams. This review critically summarises the last three decades of studies in this field. It is found that the solar homogeneous photo-Fenton process should be preferably used as a pre- and post-treatment of biological technologies and as a standalone treatment for young, medium, and mature leachates, respectively. Studies on heterogeneous solar photo-Fenton process are lacking so that this technology may be scaled-up for industrial applications. Sulphate radicals are attractive for removing both COD and ammonia. However, no study has been reported on solar sulphate activation for landfill leachate treatment. This review discusses the main advances and challenges on treating landfill leachate through solar AOPs, it compares solar photo-Fenton and solar persulphate-based treatments, indicates the future research directions and contributes for a better understanding of these technologies towards sustainable treatment of landfill leachate in sunny and not-so-sunny regions.

Effect of free ammonia on partial denitrification: Long-term performance, mechanism, and feasibility of PD/Anammox-FBBR for mature landfill leachate treatment

As a stable and effective approach for NO2--N accumulation, partial denitrification (PD) could significantly cut down operation cost, and PD/Anammox (PD/A) is a promising nitrogen removal process in wastewater treatment. The biotoxicity of free ammonia (FA) to nitrifying bacteria and anammox bacteria has been demonstrated, while whether FA affects PD bacteria is an open question. Here, long-term operation of PD-fixed bed biofilm reactor (PD-FBBR) treating synthetic wastewater and mature landfill leachate was conducted to reveal the mechanism concerning the effect of FA on PD bacteria. Stable NO2--N accumulation was achieved with NO3--N to NO2--N transformation ratio (NTR) of 60-70% during 280-day operation with FA ranged from 0 to 20.71 ± 0.23 mg/L, while NTR decreased and maintained at ∼30% when FA reached 40.59 ± 0.19 mg/L. Specific NOx--N reduction rate improved at low FA concentration (< 12 mg/L), while high FA level (> 25 mg/L) had inhibitory effect on PD bacteria. Under FA stress, more extracellular polymeric substances (EPS) were secreted, and the glnA gene abundance, glutamine synthase concentration, and glutamine concentration in cell and EPS significantly increased, indicating the enhancement of glutamine biosynthesis in PD bacteria for ammonia assimilation played an important role in response to FA stress. Metagenomic sequencing showed that FA stimulated the upregulation of narK (NO3--N/NO2--N antiporter) gene abundance and enhanced uptake of NO3--N and extrusion of NO2--N. Comamonas, unclassified_f__Comamonadaceae and Thauera were highly enriched in biofilm, which played a key role in the stable NO2--N accumulation. Furthermore, a novel two stage PD/A-FBBR was applied to mature landfill leachate treatment, and satisfactory total inorganic nitrogen removal efficiency ranged from 81.38 ± 3.56% to 89.16 ± 1.57% was obtained at relatively low COD/NO3--N of 2.57-2.84. Overall, these findings demonstrated how PD bacteria respond to FA stress and confirmed the feasibility of PD/A process in high FA wastewater treatment.

Tricks and tracks in waste management with a special focus on municipal landfill leachate: Leads and obstacles

Landfilling is the most widely used disposal method for municipal solid waste around the world. The main disadvantage of this strategy is formation of leachate, among other aspects. Landfill leachate contains highly toxic and bio-refractory substances that are detrimental to the environment and human health. Hence, the risk(s) of discharging potentially harmful landfill leachate into the environment need to be assessed and measured in order to make effective choices about landfill leachate management and treatment. In view of this, the present review aims to investigate (a) how landfill leachate is perceived as an emerging concern, and (b) the stakeholders' mid- to long-term policy priorities for implementing technological and integrative solutions to reduce the harmful effects of landfill leachate. Because traditional methods alone have been reported ineffective, and in response to emerging contaminants and stringent regulations, new effective and integrated leachate treatments have been developed. This study gives a forward-thinking of the accomplishments and challenges in landfill leachate treatment during the last decade. It also provides a comprehensive compilation of the formation and characterization of landfill leachate, the geo-environmental challenges that it raises, as well as the resource recovery and industrial linkage associated with it in order to provide an insight into its sustainable management.

Activation of periodate using ultrasonic waves and UV radiation for landfill leachate treatment

In the present work, saline leachate of the Bushehr coastal city (Iran) was purified using the ultraviolet/ultrasonication wave/periodate process. The initial TDS and TOC values of the leachate studied were 7390 mg/L and 975 mg/L, respectively. During the effect of various parameters on leachate purification, the experiments were optimized at pH 3, oxidizer concentration of 4 mM, and treatment time of 120 min. The initial BOD₅/COD ratio of 0.66 was reduced to 0.42 at the end of the purification time (120 min). After leachate treatment under optimal conditions, the amount of BOD₅, COD, and UV₂₅₄ were 451.5 mg/L, 1072 mg/L, and 12.69 cm^-1, respectively. Concentrations of heavy metals in crude leachate by ICP-OES were checked. Also, the concentration of organic compounds before and after purification was determined using GC-Mass. The leachate purification kinetics followed the first-order model using the designed method. Based on the COD factor, the system energy consumption for leachate treatment was calculated to be 11.4 kWh/m³. The results showed that the system explored (UV/US/IO₄^-) can effectively purify high salinity waste leachate.

Leachate decontamination through biological processes coupled to advanced oxidation: A review

The landfill leachate is considered a toxic effluent composed of recalcitrant contaminants that requires innovative alternatives for its decontamination. Coupling between advanced oxidation processes (AOPs) and aerobic biological treatments are highlighted in this research. Therefore, a bibliographic review of the research made from 2010 to 2021 was developed. These combined alternatives were applied in leachates, and it is oriented toward the analysis of knowledge gaps, trends, and future proposals of the treatment combined that contribute to researchers who wish to work on the subject. These kinds of treatments were chosen due to a bibliometric analysis made. Also, the information was searched in several scientific database. This work was found to be unpublished, as no reviews were found so far that agglomerate studies of coupling between photocatalytic and aerobic biological processes to treat leachates. Besides, AOPs are ideal for treating wastewater of complex composition, however, when it is used as the only treatment, they are usually unprofitable, which justifies their coupling with biological treatments. Subsequently, it was determined that the knowledge main gap is the lack of documentation of treatment costs, which makes it difficult to implement on a real scale. In addition to this, the couplings trends are toward doping with metallic and nonmetallic ions of the catalyst used in the photocatalytic process to improve the efficiency of these. Finally, future research should work on finding alternatives that allow the optimization of the resources used in the combined systems and on promoting the recovery of existing products in the leachate.Implications: Leachates generate several environmental impacts due to their toxic composition. Even when coupling between heterogeneous photocatalysis and biologic treatment can solve them, issues like cost analysis and the scaling-up factor have not been developed, and futures researchers should work on that. Besides, the trend founded in almost all investigations was the catalyst doping with metals and nonmetals ions, particularly when they use TiO2 because it gives the possibility of improving efficiencies just with a structural variation. Finally, these treatment combinations require more analyses and comparison of their remotion over emerging pollutants and their performance with new designs.

Simultaneous removal of organics and ammonia using a novel composite magnetic anode in the electro-hybrid ozonation-coagulation (E-HOC) process toward leachate treatment

To achieve simultaneous organics and ammonia (NH₄⁺-N) removal toward leachate treatment, this study designed a composite anode (CA⁺), in which iron powders were attracted to RuO₂-IrO₂/Ti tube surface by an inserted magnet and utilized in electro-hybrid ozonation-coagulation (E-HOC). The E-HOC (CA⁺) resulted in higher chemical oxygen demand (COD) and NH₄⁺-N removal with most content of CO₂/H₂O and gaseous N in product compared with E-HOC (Fe⁺), electrolysis ozonation and single ozonation. Reactive chlorine species (RCS) and coagulants were co-produced by compositing RuO₂-IrO₂/Ti and Fe powders, resulting in multiple reactions including electrocoagulation, ozone oxidation, synergistic between ozone and coagulants (SOC), electrolytic chloride and synergistic oxidation between active chlorine and ozone (SCO) occurred. Hydroxyl radical (•OH) generated through SOC reaction was promoted due the RCS generation in E-HOC. The interaction between •OH and Cl^-/ClO^- also contributed to enhanced Cl•/ClO• production. Consequently, synergy of chlorine, coagulants and ozone enhanced reactive species generation which contributed to favorable organics and NH₄⁺-N removal. Enhanced •OH and RCS are also attributed to conversion of bio-refractory organics like polyphenol, polycyclic aromatics and S-containing to biodegradable ones, e.g., aliphatic compounds and CHO. This study provides an easily operating strategy for leachate treatment with high content organics and NH₄⁺-N.

Future trends and patterns in leachate biological treatment research from a bibliometric perspective

Leachate has become a great deal of concern due to its complex properties which are primarily caused by the high concentrations of organics and ammonia. Thus, proper leachate treatment is required prior to its discharge. Leachate can be treated in various ways, and biological treatment is one of the approaches. This treatment has been shown to be both effective and cost-efficient while offering the possibility of resource recovery in the form of bioenergy. In this study, the underlying patterns in publications related to leachate biological treatment were uncovered through bibliometric analysis. This study also lays the groundwork for a deeper understanding of the past, current, and future trends of the leachate biological treatment. Research publications from 1974 to 2021 were retrieved from the Scopus database, and it was identified that 2013 articles were published in the span of 47 years. From the analyzed publications, China played a leading role in publishing leachate biological treatment research articles as well as having the most productive institutions and authors. Meanwhile, the USA was found to be the most active country in initiating international collaborations with 33 countries. The research hotspots were also successfully identified using keyword co-occurrences analysis. Anaerobic digestion and constructed wetland were revealed to be the research hotspots. The critical role of biological treatment in removing nitrogen from leachate was also highlighted. Besides, numerous research gaps were identified in the application of aerobic granular sludge (AGS) for leachate treatment. This can be a potential area for research in the future. Finally, future research should be encouraged to focus on the use of sustainable treatment systems in which energy recovery in the form of biogases is promoted.

Effect of ozone pretreatment on biogranulation with partial nitritation - Anammox two stages for nitrogen removal from mature landfill leachate

Due to the extremely low C/N ratio, high concentration of ammonia nitrogen and refractory organic matter of mature landfill leachate (MLL), appropriate processes should be selected to effectively remove nitrogen and reduce disposal costs. Partial nitritation (PN) and anaerobic ammonia oxidation (AMX) have been used as the main nitrogen removal processes for MLL, and the sludge granulation in PN and AMX processes could contribute to high biological activity, good sedimentation performance, and stable resistance to toxicity. In this study, the O₃-PN-AMX biogranules process was selected to effectively remove nitrogen from MLL without carbon addition and pH adjustment. Without uneconomical NH₄⁺-N oxidation and wasting the alkalinity of MLL, ozone pretreatment achieved color removal, decreased humic- and fulvic-like acid substances, and alleviated the MLL toxicity on ammonia oxidizers. In addition, the ozonation of MLL could shorten the start-up time and improve the treatment efficiency and biogranules stability of PN and AMX processes. Efficient and stable nitritation was achieved in PN reactor without strict dissolved oxygen (DO) control, which was attributed to the unique structure of granular sludge, ozone pretreatment, and alternating inhibition of free ammonia and free nitric acid on nitrite oxidizers. Through the application of ozone pretreatment and granular sludge, the nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) of the O₃-PN-AMX biogranules process reached 0.39 kg/m³/day and 85%, respectively, for the undiluted MLL treatment. This study might provide a novel and effective operation strategy of combined process for the efficient, economical, and stable nitrogen removal from MLL.

Municipal solid waste management: Dynamics, risk assessment, ecological influence, advancements, constraints and perspectives

Global energy consumption has been increasing in tandem with economic growth, putting pressure on the world's supply of renewable energy sources. Municipal Solid waste (MSW) has been reported contributing immensely to the improvement of a secure environment and renewable sources. Energy scarcity and conventional MSW disposal methods in developing countries lead towards many environmental and economic issues. Scientists have been able to experiment with various waste-to-energy conversion technologies in light of this situation. This communication highlights and reviews WtE technologies to convert MSW and other feedstocks into electricity, hydrogen gas, bioethanol along with other value added products like fertilizer(s), platform chemicals as an environmentally friendly products. This review comprehensively summarized the dynamics, risk assessment, ecological influence, advancements, constraints and perspectives altogether in field of municipal solid waste management and treatment. Stare-of-the-art information on ecological influence and risk assessment in handling and transportation of municipal solid waste has been provided. Advanced trends involved in remediation of emerging pollutants and resources obtained from municipal solid wastes have been uncovered. Lastly, this paper comprises constraints and perspectives for uncovering MSW based circular bioeconomy aspects.

Fulvic acid degradation in Fenton-like system with bimetallic magnetic carbon aerogel Cu-Fe@CS as catalyst: Response surface optimization, kinetic and mechanism

In this study, Cu-Fe bimetallic magnetic chitosan carbon aerogel catalyst (Cu-Fe@CS) was prepared by the sol-gel method to degrade Fulvic acid (FA) in Fenton-like system. Degradation experiment results showed bimetallic catalyst Cu-Fe@CS can degrade more FA than monometallic catalysts (Cu@CS and Fe@CS) due to the synergistic effect between the copper and iron. Plackett Buiman (PB) design showed that pH and temperature exhibited significant influence on FA degradation. The significant factors were optimized by Central Composite Design (CCD), the results revealed that the maximum FA removal reached 96.59% under the conditions of pH 4.07 and temperature 93.77 °C, the corresponding TOC removal reached 77.7%. The kinetic analysis implied that the reaction followed pseudo-first order kinetic with correlation coefficient (R²) = 0.9939. The Arrhenius fitting analysis revealed that Cu-Fe@CS had a lower activation energy (Ea) than Cu@CS and Fe@CS, meaning that reaction was easier to occur in Fenten-like system with Cu-Fe@CS. Catalyst still remained the higher FA and TOC removals of 96.28% and 77.33% after six runs, respectively. The FA removal was reduced by 65.53% with 12 mmol tertiary butanol (TBA) as scavenger, indicating that •OH played an important role in FA degradation. Finally, the catalytic degradation mechanism was proposed.

Advanced catalytic oxidation coupled to biological systems to treat pesticide-contaminated water: A review on technological trends and future challenges

This article had the one and only objective of consolidating the couplings of advanced oxidation processes and biological systems in the decontamination of wastewater with pesticide content reported in the Scopus and Web of Science databases, through a critical analysis of which have been the most used, what methodologies have been implemented to develop them, identifying the objectives of each work, determining the success of the research and where the main niches of knowledge are, which can lead to the generation of new scientific knowledge as well as future trends. A co-occurrence analysis was carried out through the VOSViewer software to determine the most associated key words with the treatment configurations described above. Fenton and Photo-Fenton processes, heterogeneous photocatalysis TiO₂/UV, electrocatalysis, ozonization and a particular case of hydrodynamic cavitation-ozone as main advanced oxidation processes, together with advanced biological processes such as sequential batch bioreactor (SBR), membrane bioreactor (MBR), mobile bed biofilm reactor (MBBR); biodegradability and toxicity tests with bacterial strains and surface wetlands, whose treatment philosophy is activated sludge. The main future trends are the reuse of treated wastewater, the analysis and control of costs towards the efficient use of resources and the primary study of the byproducts generated in advanced oxidation to improve the efficiencies in the coupling.

Comparison between Aliivibrio fischeri and activated sludge microorganisms in the evaluation of the toxic pollutants of leachates from Brazilian landfills

Ecotoxicological assessment of landfill leachate has become a priority to determine its impacts on the ecosystem. Toxicity assays with microorganisms stand out due to their quick response, low cost and ease of testing. In this context, the present study evaluated the acute toxic effects of leachates from two landfills of different ages and modes of operation to bacterium Aliivibrio fischeri and activated sludge microorganisms and the ammonia nitrogen and humic substances (HS) sensitivity to these organisms. Reductions greater than 30% in leachate toxicity were observed after ammonia removal for A. fischeri and activated sludge microorganisms. After 97% removal of HS, the greater reductions in toxicity (44.28 to 79.82%) were verified for microbial species studied, indicating that the organic compounds (measured as chemical oxygen demand, total organic carbon and humic substances) were the primary pollutants responsible for the toxicity of the leachates. Concerning the organisms studied, A. fischeri showed greater sensitivity to the leachates' pollutants compared to the activated sludge microorganisms. Nevertheless, a strong correlation was observed between A. fischeri and activated sludge microorganisms' toxicity responses, suggesting that respirometry assay can be used to determine leachate toxicity.

A review on integrated approaches for municipal solid waste for environmental and economical relevance: Monitoring tools, technologies, and strategic innovations

Rapid population growth, combined with increased industrialization, has exacerbated the issue of solid waste management. Poor management of municipal solid waste (MSW) not only has detrimental environmental consequences but also puts public health at risk and introduces several other socioeconomic problems. Many developing countries are grappling with the problem of safe disposing of large amounts of produced municipal solid waste. Unmanaged municipal solid waste pollutes the environment, so its use as a potential renewable energy source would aid in meeting both increased energy needs and waste management. This review investigates emerging strategies and monitoring tools for municipal solid waste management. Waste monitoring using high-end technologies and energy recovery from MSW has been discussed. It comprehensively covers environmental and economic relevance of waste management technologies based on innovations achieved through the integration of approaches.

Chemical safety assessment of transformation products of landfill leachate formed during the Fenton process

Organic chemicals identified in raw landfill leachate (LL) and their transformation products (TPs), formed during Fenton treatment, were analyzed for chemical safety following REACH guidelines. The raw LL was located in the metropolitan region of Campina Grande, in northeast Brazil. We elucidated 197 unique chemical structures, including 154 compounds that were present in raw LL and 82 compounds that were detected in the treated LL, totaling 39 persistent compounds and 43 TPs. In silico models were developed to identify and prioritize the potential level of hazard/risk these compounds pose to the environment and society. The models revealed that the Fenton process improved the biodegradability of TPs. Still, a slight increase in ecotoxicological effects was observed among the compounds in treated LL compared with those present in raw LL. No differences were observed for aryl hydrocarbon receptor (AhR) and antioxidant response element (ARE) mutagenicity. Similar behavior among both raw and treated LL samples was observed for biodegradability; Tetrahymena pyriformis, Daphnia magna, Pimephales promelas and ARE, AhR, and Ames mutagenicity. Overall, our results suggest that raw and treated LL samples have similar activity profiles for all endpoints other than biodegradability.

New insights into co-treatment of mature landfill leachate with municipal sewage via integrated partial nitrification, Anammox and denitratation

As a low consumption and high efficiency process, Partial Nitrification-Anammox/denitratation (PNAD) was applied to co-treat mature landfill leachate with municipal sewage for 300 days. Specifically, ammonia (670.2 ± 63.7 mg N/L) contained in mature landfill leachate was firstly oxidized to nitrite (611.5 ± 28.1 mg N/L) in sequence batch reactor (SBR_PN); meanwhile, organic matter in municipal sewage was partially removed in another reactor (SBR_OMR); finally, nitrite produced (611.5 ± 28.1 mg N/L) in SBR_PN and ammonia (53.1 ± 6.4 mg N/L) residing in pretreated municipal sewage were simultaneously degraded through combined Anammox-denitratation process in an up-flow anaerobic sludge bed (UASB_AD). A satisfactory effluent quality of 10.3 mg/L TN was obtained after long-term operation, with Anammox and denitrification contributing to 86.2% and 5.8% nitrogen removal efficiency, respectively. Mass balance confirmed 67.2% nitrate generated from Anammox could be reduced to nitrite and in-situ reused. Anammox bacteria genes and nitrate reductase/nitrite reductase ratio were highly detected, accelerating combined Anammox-denitratation. Further, Ca. Brocadia triumph among various Anammox bacteria groups, increasing from 1.2% (day 120) to 3.6% (day 280).

Combining yeast MBR, Fenton and nanofiltration for landfill leachate reclamation

This study investigated the best way to combine nanofiltration (NF) and Fenton with membrane bioreactor inoculated with Saccharomyces cerevisiae (MBRy) for the treatment of landfill leachate, aiming at compliance with legislation and water reuse. Firstly, the permeate from MBRy was treated by Fenton process followed by NF (MBRy - Fenton - NF). Another alternative evaluated was the polishment of MBRy permeate by NF and treatment of NF concentrate by Fenton process (MBRy - NF - Fenton_{(concentrate)}). COD removal in the Fenton step was optimized according to central composite design (CCD) and 85.5% removal was obtained at pH = 3, Fe²⁺:H₂O₂ molar ratio = 1:9.81 and C:H₂O₂ molar ratio = 1:1.14. Increased toxicity was observed with the Fenton application (EC₅₀ = 2.45%). The NF showed the best performance treating the MBRy permeate. High permeate flux (8.9 ± 1.6 L h^-1 m^-2) and ion rejection (82 ± 4.2%), and low membrane fouling was observed in this condition. Although both NF permeate presented potential for reuse, the final COD concentration was lower in the MBRy - Fenton effluent (88 mg L^-1). The Fenton application for the NF concentrate was able to remove 87.24% of COD. With a preliminary economic analysis, it was verified that the MBRy - NF - Fenton_{(concentrate)} combination is the most advantageous due to the lower chemical reagent and membrane area requirements. Thus, this route presents itself as an alternative for landfill leachate reclamation.

Coupling chemical oxidation processes and Leptosphaerulina sp. myco-remediation to enhance the removal of recalcitrant organic pollutants in aqueous systems

This research evaluated for the first time, the coupling of chemical oxidation processes with Leptosphaerulina sp. (a Colombian fungus), to degrade a refractory pollutant. For such purpose, a model contaminant (crystal violet, CV) was considered. Initially, the pollutant, at high concentrations (i.e., 200 and 50 mg L^-1), was submitted to the fungus action. However, the CV inhibited the growth and enzymatic production of the fungus. Then, three chemical oxidation processes: TiO₂-photocatalysis, sonochemistry, or electrochemistry (with a Ti/IrO₂ anode in sodium chloride) were used as treatments previous to the myco-remediation. These oxidative treatments led to the pollutant degradation (~100%) by the action of radicals or active chlorine species, but they showed low mineralization. Indeed, the total organic carbon removal (TOC) was 54, ~15, and 31% to TiO₂-photocatalysis (after 12 h), sonochemistry (after 12 h), and electrochemistry (after 1.33 h), respectively. Thus, the resultant solutions from the chemical oxidations were submitted to the action of Leptosphaerulina sp. (this time effective fungus growth and enzymes production were observed). It was found that the TOC removals by the fungus were 87, 84, and 83% for solutions pre-treated by TiO₂-photocatalysis (12 h), sonochemical (12 h), and electrochemical (1.33 h) treatments, respectively. Regarding the enzymatic production, TiO₂-photocatalysis/Leptosphaerulina sp., ultrasonication/Leptosphaerulina sp., and electrochemical oxidation/Leptosphaerulina sp. combinations reached the highest activities of laccase (0.6 U mg^-1, at day 15), manganese peroxidase (1.35 U mg^-1, at day 7) and versatile peroxidase (1.72 U mg^-1, at day 15), respectively. The results from this work evidence feasibility of the pre-treatment with chemical oxidation processes as a strategy to enhance Leptosphaerulina sp. action toward recalcitrant organic pollutants (as CV) in water.

Significant improvement in biodegradability of a real Optical Brightening Agent (OBA) wastewater using small doses of Fenton's reagent

Optical Brightening Agent (OBA) wastewater (OBAW) has been reported to be highly resistant to biodegradation. In this study, a real OBAW from an industry which was already treated using primary and secondary treatments (residual COD of secondary clarifier overflow (SCO): 3400-3700 mgL^-1) was further treated by Fenton's treatment (FT). Zahn-Wellens biodegradability test revealed that using small doses of H₂O₂ and Fe⁺², the biodegradability of SCO improved to 90% as compared to ∼18% without FT. UV-Vis analysis revealed that ca. 80% of initially present OBAs were removed by treatment sequence outlined in this study. Biodegradability study on individual raw wastewaters from four types of OBAs (designated OBA-TS, OBA-DS-U, OBA-HS, and OBA-DS-D) being manufactured at the time of this study, revealed that OBA-TS wastewater was the most biodegradable (>95% biodegradability) followed by OBA-DS-U (∼60%), OBA-HS (∼20%), and OBA-DS-D (<5%). Application of FT improved the biodegradability of these streams as: OBA-DS-U (∼70%), OBA-HS (∼60%), and OBA-DS-D (∼50%). A treatment sequence consisting of waste coal dust (WCD) pretreatment-FT-biodegradation is a novel, economical, and sustainable approach to treating highly recalcitrant OBA wastewater.

Current trends and advances in analytical techniques for the characterization and quantification of biologically recalcitrant organic species in sludge and wastewater: A review

The study of organic matter in wastewater is a major regulatory and environmental issue and requires new developments to identify non-biodegradable refractory compounds, produced mainly by thermal treatments. Recent advances linking physicochemical properties to spectroscopic analyzes (UV, Fluorescence, IR) have shown that the refractory property is favored by several physicochemical parameters: weight, hydrophobicity, aromaticity and chemical functions. Currently, the most effective developments for the quantification of refractory compounds are obtained with hyphenated methods, based on steric separation of the macromolecular species by steric exclusion chromatography (SEC)/PDA/Fluorescence systems. Hyphenated techniques using High Resolution Mass Spectrometry (HRMS), ultra-high-resolution mass spectrometry with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and NMR have been developed to analyze macromolecules in wastewater with minor sample preparation procedures. A particular class has been identified, the melanoidins, generated by Maillard reactions between sugars, amino acids, peptides and proteins present in wastewater and sludge, but low molecular weight compounds formed as intermediates, such as ketones, aldehydes, pyrazines, pyridines or furans, are also recalcitrant and are complex to identify in the complex matrices. The lack of available standards for the study of these compounds requires the use of specific techniques and data processing. Advances in chemometrics are obtained in the development of molecular or physicochemical indices resulting from the data generated by the analytical detectors, such as aromaticity calculated by SUVA₂₅₄ and determined by UV, fluorescence, molar mass, H/C ratio or structural studies (measuring the amount of unsaturated carbon) given by hyphenated techniques with SEC. It is clear that nitrogen compounds are widely involved in refractoriness. New trends in nitrogen containing compounds characterization follow two axes: through SEC/PDA/Fluorescence and HRMS/NMR techniques with or without separation. Other techniques widely used in food or marine science are also being imported to this study, as it can be seen in the use of "omics" methods, high-performance thin layer chromatography (HPTLC) and chromatography at the critical condition, rounding out the important developments around SEC. While improving the performance of stationary phases is one of the challenges, it results in a fundamental understanding of the retention mechanisms that today provide us with more information on the structures identified. The main objective of this review is to present the spectroscopic and physicochemical techniques used to qualify and characterize refractoriness with a specific focus on chemometric approaches.

Effective photochemical treatment of a municipal solid waste landfill leachate

This work aimed at studying the photochemical treatment of a landfill leachate using ultraviolet light, hydrogen peroxide, and ferrous or ferric ions, in a batch recycle photoreactor. The effect of inorganic carbon presence, pH, initial H2O2 amount (0-9990 mg L-1) as well as Fe(II) (200-600 ppm) and Fe(III) (300-700 ppm) concentrations on the total carbon removal and color change was studied. Prior to the photochemical treatment, a pretreatment process was applied; inorganic nitrogen and inorganic carbon were removed by means of air stripping and initial pH regulation, respectively. The leachate sent subsequently for photochemical treatment was free of inorganic carbon and contained only organic carbon with concentration 1200±100 mg L-1 at pH 5.1-5.3. The most favorable concentrations of H2O2 and ferric ions for carbon removal were 6660 mg L-1 and 400 ppm, respectively. Adjusting the initial pH value in the range of 2.2-5.3 had a significant effect on the organic carbon removal. The photo-Fenton-like process was more advantageous than the photo-Fenton one for leachate treatment. By applying the most favorable operating conditions, 88.7% removal of total organic carbon, 100% removal of total inorganic carbon, 96.5% removal of total nitrogen, and 98.2% color removal were achieved.

Applicability of conventional and non-conventional parameters for municipal landfill leachate characterization

The disposal of municipal solid waste (MSW) in landfills generates leachate, a highly polluting liquid to the aquatic environment. Leachate composition become a challenge to choose the best treatment process. Then, detailed techniques to determine the organic content, in terms of refractability, composition, sources and biodegradability in landfill leachate can help to choose the appropriate treatment and improve landfill management. In this sense, the aim of this study is to apply conventional and non-conventional parameters through inert chemical oxygen demand (COD) analyses and spectroscopic techniques of fluorescence and UV-vis absorbance for the characterization of municipal landfill leachate. Results indicated that physicochemical characterization cannot provided enough detailed information about leachate composition, which becomes the treatment process fragile. Inert COD, besides have high time to execution (∼30 days), presented additional information on potential of biological treatability in anaerobic conditions. Dissolved organic matter (DOM) characterization showed transitions between labile and refractory organic matter compounds. Moreover, the cost estimated showed that non-conventional parameters analysis have lower investment than conventional, being their implementation feasible. In conclusion, the synergy between conventional and non-conventional parameters, and the detailed information provided by inert COD and DOM characterization, shown a useful tool to the landfill management and, consequently, improving treatment process and its efficiency.

Alternative method of composting on a reclaimed municipal waste landfill in accordance with the circular economy: Benefits and risks

Waste composting is becoming a key element of integrated waste management. Composting has a number of advantages, including economic benefits, improvement of soil properties through the use of compost, reduction in the use of chemical fertilisers, and minimization of environmental pollution. Composting on a landfill surface appears to be an economical solution that can help close the waste loop and material cycle. In this study, a composting plant located on a landfill surface was analysed. The main objective of the research was to identify the species of plants growing in the organic fraction of municipal solid waste in temporary storage, in the composting plant, and in maturing compost located in a reclaimed plot at the landfill site. During monitoring, 88 plant species were identified altogether. It was observed that compost can become a source of weed infestation. To control the presence of weeds in the compost, basic principles of composting are to be followed to reduce the quantity of weed seeds. The thermophilic phase must occur to reduce the viability of seeds in the input materials and sufficient moisture must be ensured during the composting process. When these principles are strictly observed and the stored compost is maintained without vegetation, the supply of seeds in the compost will be low, and the undesirable spread of plant species to adjacent areas will be controlled. The results showed that the use of the obtained compost did not result in the propagation of weed species. This study demonstrates that composting on a reclaimed landfill offers various advantages such as a closed waste management cycle, coverage of the active landfill body, and fertilisation of the reclaimed part of the landfill.

Ozonation Pretreatment for Reduction of Landfill Leachate Fouling on Membranes: A Response Surface Methodology Analysis

Batch ozonation was performed to assess its efficacy as a pretreatment for reverse osmosis (RO) membranes for treating leachate with high concentrations of recalcitrant organic compounds. Leachate samples from two different landfills were collected and characterized. The modified fouling index (MFI) was used to estimate the fouling potential of raw and ozonized leachates. A response surface experimental design was applied to optimize operational pH and ozone dose. The results demonstrate that the best operational conditions are 1.5 g/L of O3 at pH 12.0 and 1.5 g/L of O3 at pH 9.0 for Landfills 1 and 2, which reduce MFI by 96.22% and 94.08%, respectively. Additionally, they show toxicity factor decays of 98.44% for Landfill 1 and 93.75% for Landfill 2. These results, along with the similar behavior shown by leachate samples from distinct landfills, suggest that ozonation is a promising technology to fit this kind of wastewater into the requirements of RO membranes, enabling their use in such treatment.

Speciation and conversion of carbon and nitrogen in young landfill leachate during anaerobic biological pretreatment

There is an increasing need for landfill leachate pretreatment prior to discharge to wastewater treatment plants due to increasingly stringent sewer discharge limits. Lab-scale tests have shown that the anaerobic biological processes can effectively remove chemical oxygen demand and dissolved organic carbon from landfill leachate. Our work expands the knowledge in anaerobic leachate pretreatment by systematically studying the conversion of carbon and nitrogen species, particularly their recalcitrant fractions in a submerged anaerobic biofilm reactor using real-world leachate from a typical young municipal solid waste landfill. After reaching steady state, the reactor removed 41.7% of the fulvic acids (i.e., 1290 mg C/L). While compounds with a low degree of oxidation (O:C < 0.2) and compounds with a low degree of saturation (H:C < 1) were removed, compounds that were more oxidized (O:C > 0.2) and more saturated (H:C > 1) were produced. At steady state, 98% of recalcitrant dissolved organic nitrogen (i.e., rDON = 222 mg N/L) was removed. Compared to the DON in the raw leachate, the produced DON in the pre-treated leachate were more oxidized (O:C > 0.35) and more bioavailable (N:C > 0.07). The submerged anaerobic biofilm reactor may be an efficient leachate pretreatment method if rDON removal is needed.

Analysis of the Bioaugmentation Potential of Pseudomonas putida OR45a and Pseudomonas putida KB3 in the Sequencing Batch Reactors Fed with the Phenolic Landfill Leachate

The treatment of landfill leachate could be challenging for the biological wastewater treatment systems due to its high toxicity and the presence of poorly biodegradable contaminants. In this study, the bioaugmentation technology was successfully applied in sequencing batch reactors (SBRs) fed with the phenolic landfill leachate by inoculation of the activated sludge (AS) with two phenol-degrading Pseudomonas putida OR45a and Pseudomonas putida KB3 strains. According to the results, the SBRs bioaugmented with Pseudomonas strains withstood the increasing concentrations of the leachate. This resulted in the higher removal efficiency of the chemical oxygen demand (COD) of 79–86%, ammonia nitrogen of 87–88% and phenolic compounds of 85–96% as compared to 45%, 64%, and 50% for the noninoculated SBR. Simultaneously, the bioaugmentation of the AS allowed to maintain the high enzymatic activity of dehydrogenases, nonspecific esterases, and catalase in this ecosystem, which contributed to the higher functional capacity of indigenous microorganisms than in the noninoculated AS. Herein, the stress level experienced by the microorganisms in the SBRs fed with the leachate computed based on the cellular ATP measurements showed that the abundance of exogenous Pseudomonas strains in the bioreactors contributed to the reduction in effluent toxicity, which was reflected by a decrease in the stress biomass index to 32–45% as compared to the nonbioaugmented AS (76%).

Mycoremediation of Old and Intermediate Landfill Leachates with an Ascomycete Fungal Isolate, Lambertella sp

In the present study, an Ascomycete fungal strain, Lambertella sp., isolated from environmental polluted matrices, was tested for the capacity to reduce the contamination and the toxicity of intermediate and old landfill leachates. Batch tests in flasks, under co-metabolic conditions, were performed with two different old leachates, with suspended and immobilized Lambertella sp. biomass, resulting in a soluble chemical oxygen demand depletion of 70% and 45%, after 13 and 30 days, respectively. An intermediate landfill leachate was treated in lab-scale reactors operating in continuous conditions for three months, inoculated with immobilized Lambertella sp. biomass, in absence of co-substrates. The Lambertella sp. depleted the corresponding total organic carbon by 90.2%. The exploitability of the Lambertella sp. strain was evaluated also in terms of reduction of phyto-, cyto-, and mutagenicity of the different Landfill Leachates at the end of the myco-based treatment, resulting in an efficient depletion of leachate clastogenicity.

Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment

Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.

Adsorption of dissolved organic matter from landfill leachate using activated carbon prepared from sewage sludge and cabbage by ZnCl2

Sewage sludge and cabbage (Brassica oleracea) were used to prepare activated carbon by high-temperature inert carbonization with the activator ZnCl₂. The physicochemical characteristics of the sludge-based activated carbon (SAC) were analyzed, and the effects on the removal of chemical oxygen demand (COD) from the landfill leachate by the adsorbent dosage, adsorption time, and the solution pH were investigated in different adsorbents. Three-dimensional fluorescence spectroscopy and gas chromatography-mass spectrometry were used to analyze the organic compounds in the leachate before and after adsorption. The results demonstrated that the average iodine content of the SAC was 535.01 mg/g. The average specific surface area was 917.72 m²/g, and the dominant pore size was in the mesoporous range. The optimum parameters for adsorption were a dosage of 3%, adsorption time of 60 min, and pH = 8, and the COD removal rate reached 85.61%. The adsorption of COD on the SAC was best fitted by the Freundlich model. Additionally, the SAC was found to have a high removal efficiency for refractory organic matter and short-chain alkanes, such as humic acid-like substances, in the leachate but was not effective for long-chain alkanes.

Sequential coagulation and Fe0-O3/H2O2 process for removing recalcitrant organics from semi-aerobic aged refuse biofilter leachate: Treatment efficiency and degradation mechanism

Landfill leachate effluent obtained after semi-aerobic aged refuse biofilter (SAARB) treatment still contains various recalcitrant organics. In this study, a sequential coagulation and Fe⁰-O₃/H₂O₂ process was developed for treating SAARB leachate. The effects in terms of degradation of recalcitrant organics and the related mechanisms due to the coagulation and Fe⁰-O₃/H₂O₂ processes were systematically explored and discussed. The results indicated that polymerized ferric sulfate was the most efficient coagulant for treating SAARB leachate where the chemical oxygen demand (COD), UV₂₅₄, and CN removal efficiencies were 59.60%, 63.22%, and 70.32%, respectively. In the Fe⁰-O₃/H₂O₂ process under the optimized conditions comprising Fe⁰ dose = 0.6 g/L, O₃ dose = 26.80 mg/min, H₂O₂ dose = 1.0 mL/L, and reaction time = 20 min, the COD, UV₂₅₄, and CN removal efficiencies with the coagulated supernatant were 43.39%, 59.47%, and 93.20%, respectively, and the biodegradability (biochemical oxygen demand/COD) improved greatly from 0.06 to 0.34. Analysis of UV-Vis and 3D-EEM spectra indicated that coagulation-resistant substances in the SAARB leachate could be effectively degraded and destroyed by the Fe⁰-O₃/H₂O₂ process. In the O₃/H₂O₂ environment, Fe⁰ generated Fe²⁺ and iron oxides (Fe₂O₃, Fe₃O₄, and FeOOH) with homogeneous and heterogeneous catalytic roles against O₃/H₂O₂ to produce reactive oxygen species. Furthermore, Fe(OH)₂ and Fe(OH)₃ colloids contributed to the removal of organics to some extent via adsorption and precipitation effects. In conclusion, the proposed sequential coagulation and Fe⁰-O₃/H₂O₂ process is an efficient method for treating recalcitrant organics in SAARB leachates.

Use of sawdust as pretreatment of photo-Fenton process in the depuration of landfill leachate

A research of the depuration of landfill leachate using sawdust as activated carbon material to be applied in adsorption process as pretreatment of solar photo-Fenton and solar photo-Fenton + O₃, was carried out. The activated sawdust shows very irregular shapes and pores, and a high capacity to remove ammonium (87.0%), iron (70.2%) and copper (61.1%). As well, it has the capacity to remove humic acid (18.3%), COD (33.7%) and colour (19.5%). Also, a removal of organic matter was obtained in terms of COD (76.4%), colour (74.9%), nitrate (50.0%), ammonium (12.8%) and humic acid (73.3%) due to the joint action of ozone and solar photo-Fenton process. The overall treatment (filtration, adsorption, photo-Fenton and photo-Fenton + ozone) carried out showed a very high removal of pollutants, with a reduction of COD, colour, ammonium and humic acid of 95.1%, 95.0%, 94.5% and 97.9%, respectively. With this enhancement in the landfill leachate (LL) quality, there is a reduction of toxicity, obtaining with the LL 50% diluted, a germination index for Lactuca sativa of 20% GI. This shows that the incorporation of sawdust is a useful pretreatment of photo-Fenton in the treatment of landfill leachate.

Characterization and treatment of landfill leachates by electro-Fenton process: A case study in Algeria

The feasibility of the electro-Fenton (EF) process to improve the biodegradability of Algerian leachates was examined, in order to prepare this kind of flux for conventional biological treatment. This work also included, for the first time in Algeria, the control and monitorization of a landfill-the "Hamici" landfill. Several physicochemical parameters were determined allowing its classification into an intermediate degradation phase, namely considering their alkaline pH (8.7), high ammonium concentration (3,120 mg/L), low content in heavy metals, and biodegradability (BOD₅ /COD = 0.22). The effects of important parameters such as current intensity, treatment time, and temperature on COD removal have been studied and optimized by using response surface analysis of a central composite design, where 91.1% of COD was removed with a treatment time of 285 min, a current intensity of 3 A, and a temperature of 20°C. A biodegradability test, which was performed on a solution electrolyzed with 120 min, 2 A, and 20°C, allowed to improve the leachates biodegradability from 0.2 to 0.42, with a removal rate of COD and TOC of 53.35% and 34.5%, respectively. However, the current efficiency declined from 137% to 76.6% when the current intensity was rise from 0.5 to 2 A. These results showed the relevance of EF process applied on raw intermediate leachates and its possible benefit in the Algiers leachates treatment processes. Thus, it was concluded that biological treatment can be combined with EF process for optimal mineralization of leachates with clear advantages in this studied location. PRACTITIONER POINTS: Characterization and treatment of leachates by electro-Fenton (EF) process were carried out. The leachates are intermediate type and therefore biologically recalcitrant. The operating parameter for EF process were modeled and optimized by the central composite design. Current intensity of 2 A reduces COD and TOC of 53.35% and 34.5%, respectively. The ratio BOD₅ /COD increased from 0.2 to 0.42 after 120 min of electrolysis time.

Landfill Impacts on the Environment— Review

Waste management (WM) is a demanding undertaking in all countries, with important implications for human health, environmental preservation, sustainability and circular economy. The method of sanitary landfilling for final disposal of waste remains a generally accepted and used method but the available scientific evidence on the waste-related environmental and health effects is not conclusive. Comparative studies of various WM methods (landfilling, incineration, composting etc.) show that among the municipal solid waste (MSW) treatment and disposal technological options, sanitary landfilling or open dumping is popular in most countries because of the relative low cost and low-technical requirement. The European Union (EU) Directive on waste landfills has introduced specific goals for reducing the volume of disposed waste and very strict requirements for landfilling and landfill sites. Evaluation of the impact of landfills on the environment is a crucial topic in the literature and has received increased attention recently, given growing environmental concerns. The main goal of this survey was to conduct a comprehensive assessment of possible impacts of MSW landfills on the environment. The main conclusion of the overall assessment of the literature is that the disposal of MSW in landfills entails a number of environmental risks but with respect to the current situation and rich style of living adopted in industrially developed countries, the idea of WM systems functioning without landfilling—at least in the foreseeable future within one generation—seems to be somewhat unreal. The results also provided important information of landfills as a source of environmental risk. Results of this research may have an important impact on landfill management and the disposal of waste. From the literature review, it is evident that even if high levels of waste avoidance, reuse and recycling are achieved, some waste materials will always need to be forwarded for disposal.

Evaluation of toxic potential of leachate originating from experimental landfill cells containing household waste and healthcare waste

Two experimental cells with household solid waste and healthcare solid waste were monitored in order to evaluate the pollution potential, and its toxicity effects corresponding to the chemical substances present in the leachates generated, correlating the physico-chemical composition with the ecotoxicity results (organisms Aliivibrio fischeri and Danio rerio). From the statistical evaluation of the physico-chemical analysis results, leachate generated in the household solid waste cell presented greater or equal values than to the healthcare solid waste cell, except for the turbidity parameter. The ecotoxicity results showed the same behaviour as that obtained with the physico-chemical analysis. A significant positive correlation was verified between chemical oxygen demand, alkalinity and ammonia nitrogen parameters with the leachate toxicity. This study concluded that healthcare solid waste presented less or equal polluting potential compared with household solid waste, and the co-disposal can be considered a viable alternative in sanitary landfills.

Targeted removal of organic foulants in landfill leachate in forward osmosis system integrated with biochar/activated carbon treatment

Forward osmosis (FO) has been adopted to treat complex wastewater such as landfill leachate due to its high rejection of organics. In this study, the in-line adsorptive process using biochar (BC) or powdered activated carbon (PAC) was applied to a cross flow FO system to enhance the mitigation of the FO membrane fouling from landfill leachate. The changes in the leachate composition along the treatments were tracked by excitation emission matrix-parallel factor analysis (EEM-PARAFAC) to identify tryptophan-like (C1), fulvic-like (C2), and humic-like (C3) components. After a single operation of FO, the C1 was found to be the main constituent responsible for membrane fouling irrespective of varying operation conditions regarding draw solute concentrations and flow rates. Both sorbents (i.e., BC and PAC) exhibited the preferential removal behavior towards C1 > C2 > C3, which was well supported by their individual adsorption isotherm model parameters. The addition of in-line adsorption treatment to FO resulted in substantial improvements in the filtered volume (>57%) and the flux recovery (>80%) compared to the single FO operation. Without chemical cleaning of membrane, the flux was fully recovered at a dose of 10 g/L BC or 0.3 g/L of PAC. A significant and negative correlation was found between the flux recovery and the C1 of the feed leachate or the corresponding spectral peak intensity (p < 0.05) for the integrated FO system, suggesting the potential of using on-line fluorescence monitoring for the performance of the integrated system in terms of fouling mitigation. This study provided a new insight into the effectiveness of BC or PAC adsorption as the in-line integration with an FO system for the targeted removal of FO membrane foulants in landfill leachate.

Evaluation of coagulation-flocculation and nanofiltration processes in landfill leachate treatment

Landfill leachate consists mostly of a high content of refractory organic matter, ammonia and toxic compounds. All these compounds, regardless of their nature, have a potential pollution effect on local ground and surface waters. In this context, the purpose of the present study was to evaluate a treatment process (coagulation-flocculation with lime coupled with nanofiltration) applied to landfill leachate from Seropédica, Rio de Janeiro (Brazil). Jar tests were conducted to determine the optimum dosage of lime (ranged from 0 to 10 g L^-1) and, at optimum lime dose, ammonia nitrogen was removed during coagulation-flocculation process due to high pH. The process was settled for 6 h with slow stirring (50 rpm) to promote air entrainment and NH₃-N stripping before using the final treatment step of nanofiltration at 8 bar. After ammonia stripping, NH₃-N was reduced from 1,236 mg L^-1 to 353 mg L^-1 (71% removal efficiency). At the end of the combined treatment, TOC (total organic carbon), HS (humic substances) and COD (chemical oxygen demand) removals were 89%, 80% and 94%, respectively. The results showed that the combined process was effective in the removal of recalcitrant compounds and NH₃-N.

Influence of amoxicillin after pre-treatment on the extracellular polymeric substances and microbial community of anaerobic granular sludge

A combined process coupling a Fe₃O₄ nanoparticles (Fe₃O₄ NPs) heterogeneous Fenton-like reaction and an anaerobic biological technology was investigated in order to effectively treat amoxicillin-containing wastewater. With the increase in the pretreatment degree, the average COD removal rate correspondingly increased from 84.8% to 92.4% using the anaerobic biological treatment, and the biodegradability and COD removal efficiency was improved by the pretreatment processes. During the process of amoxicillin degradation, hydroxyl free radicals tended to attack the lactamide, amide and pentacyclic rings of amoxicillin. In the excitation-emission matrix (EEM) spectra of soluble microbial products (SMPs), the absorption peak of humic acid gradually decreased with application of the pretreatment. The pretreatment products were more beneficial to the characteristics of anaerobic granular sludge. For the microbial community structure, the proportion of Methanothrix and Clostridia increased with addition the heterogeneous Fenton-like pretreatment, which favored conversion of organic contaminants to volatile fatty acids and biogas.

Transformation and degradation mechanism of landfill leachates in a combined process of SAARB and ozonation

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

Treatment of Landfill Leachates with Combined Acidification/Coagulation and The Fe0/H2O2 Process

One of the major environmental concerns associated with waste disposal is the large amount of generated landfill leachates (LL), which are considered a type of wastewater with a complex composition. There is an urgent need to find an effective LL treatment method. LL were subjected to pretreatment followed by the Fe0/H2O2 process. Pretreatment efficiency was coagulation at pH 6.0 >> coagulation at pH 9.0 > acidification at pH 3.0. Coagulation at pH 6.0 in an optimal Fe3+ dose of 1000 mg/L decreased total organic carbon (TOC) from the initial concentration of 1061 mg/L to 491 mg/L while acidification to pH 3.0 decreased TOC to 824 mg/L. After acidification, the Fe0/H2O2 process with 8000/9200 mg/L Fe0/H2O2 reagent doses decreased TOC to 499 mg/L after a processing time of 60 min. Performance of the Fe0/H2O2 process after coagulation at pH 6.0 for optimal Fe0/H2O2 8000/5540 mg/L reagent doses decreased TOC to 268 mg/L (75% TOC removal). Treatment of landfill leachates with combined process coagulation and Fe0/H2O2 also increased their susceptibility to biodegradation, expressed as the biochemical oxygen demand/chemical oxygen demand (BOD5/COD) ratio from 0.13 to 0.43, allowing LL to be considered as susceptible to biodegradation. Fe0/H2O2 process kinetics was described. A statistical analysis confirmed the obtained results. The proposed method can be successfully applied for LL treatment.

Ecotoxicological evaluation of electrochemical oxidation for the treatment of sanitary landfill leachates

In this study, the efficiency of electrochemical oxidation to treat a sanitary landfill leachate was evaluated by the reduction in physico-chemical parameters and in ecotoxicity. The acute toxicity of the sanitary landfill leachates, before and after treatment, was assessed with the model organism Daphnia magna. Electrochemical oxidation treatment was effective in the removal of organic load and ammonium nitrogen and in the reduction of metal ions concentrations. Furthermore, a reduction of 2.5-fold in the acute toxicity towards D. magna after 36 h of treatment was noticed. Nevertheless, the toxicity of the treated leachate is still very high, and further treatments are necessary in order to obtain a non-toxic effluent to this aquatic organism. Toxicity results were also compared with others described in the literature for different leachate treatments and test organisms.

Impairment of Mitochondrial-Nuclear Cross Talk in Lymphocytes Exposed to Landfill Leachate

Landfill leachate, a complex mixture of different solid waste compounds, is widely known to possess toxic properties. However, the fundamental molecular mechanisms engaged with landfill leachate exposure inducing cellular and sub-cellular ramifications are not well explicated. Therefore, we aim to examine the potential of leachate to impair mitochondrial machinery and its associated mechanisms in human peripheral blood lymphocytes. On assessment, the significant increase in the dichlorofluorescein (DCF) fluorescence, accumulation of 8-Oxo-2'-deoxyguanosine (8-oxo-dG), and levels of nuclear factor erythroid 2-related factor 2 (Nrf-2) strongly indicated the ability of the leachate to induce a pro-oxidant state inside the cell. The decrease in the mitochondrial membrane potential and alterations in the mitochondrial genome observed in leachate-exposed cells further suggested the disturbances in mitochondrial machinery. Moreover, these mitochondrial-associated redox imbalances were accompanied by the increased level of NF-κβ, pro-inflammatory cytokines, and DNA damage. In addition, the higher DNA fragmentation, release of nucleosomes, levels of polyadenosine diphosphate ADP-ribose polymerase (PARP), and activity of caspase-3 suggested the involvement of mitochondrial mediated apoptosis in leachate exposed cells. These observations were accompanied by the low proliferative index of the exposed cells. Conclusively, our results clearly indicate the ability of landfill leachate to disturb mitochondrial redox homeostasis, which might be a probable source for the immunotoxic consequences leading to plausible patho-physiological conditions in humans susceptible to such environmental exposures.

Evaluation of reduction estrogenic activity in the combined treatment of landfill leachate and sanitary sewage

Combined treatment of urban solid waste leachate and domestic sewage has emerged in Brazil and worldwide as an alternative to minimize the difficulties of treating landfill leachate. Landfill leachate is a complex matrix of organic and inorganic substances, recalcitrant material and xenobiotic organic compounds that are considered to be highly toxic, as well as endocrine disrupting compounds (EDC) that contribute to increased estrogenic activity. Although combined treatment is feasible for removal of organic matter, ammonia and toxicity, the efficiency of the removal of estrogenic substance is poorly investigated. In this study, the activated sludge process in batch and continuous modes was used for the combined treatment of 2% and 5% leachate/sewage mixtures. Estrogenic activity was reduced in reactors in both batch and continuous modes. The activated sludge process achieved average reductions of the estradiol equivalent (EQ-E2) values in the combined treatment of 94.5, 60.8 and 66.4% for the sanitary sewage, 2% mixture leachate in sewage and 5% mixture leachate in sewage reactors, respectively, in batch mode. For continuous reactors, 86%, 72%, and 65% of reduction of EQ-E2were achieved for sanitary sewage, 2 and 5% mixture with sanitary sewage. As for EQ-E2, the increase in the concentration of leachate in the sewage mixture was detrimental to the removal of estrogenic compounds during the biological process. Therefore, a limit on the % leachate/sewage mixtures should be established to achieve efficiency in the combined treatment of leachate in a Wastewater Treatment Plant (WWTP).

High-efficiency nutrients reclamation from landfill leachate by microalgae Chlorella vulgaris in membrane photobioreactor for bio-lipid production

Using microalgae to treat landfill leachate is a promising approach due to the effective nutrients reclamation ability and additional profit of bio-lipid production. To offset the negative effect of landfill leachate on microalgae cells, a membrane photobioreactor (m-PBR) was adopted in the study, in which microalgae biomass concentration was improved from 0.66 in traditional photobioreactor (T-PBR) to 0.95 g/L. Nutrients reclamation efficiencies of leachate were analyzed according to elemental balance, and the results showed that nitrogen reclamation efficiency was generally lower than 50% while phosphorus reclamation efficiency was higher than 70% due to elemental availability. The nitrogen and phosphorus reclamation efficiencies in the m-PBR were much higher than that in the T-PBR. Besides, lipid produced from the m-PBR had a high cetane number of 60.96% and low linolenic acid content of 8.32%, which demonstrated good combustion properties of the microalgae-based lipid when using landfill leachate as nutrients source.

Exploring the fate and oxidation behaviors of different organic constituents in landfill leachate upon Fenton oxidation processes using EEM-PARAFAC and 2D-COS-FTIR

In this work, the changes of different organic constituents in landfill leachate were tracked in Fenton oxidation processes with different operation parameters including H₂O₂ doses, pH, and the ratios of [H₂O₂]/[Fe] via fluorescence excitation emission matrix - parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2D-COS). One tryptophan-like (C1), one fulvic-like (C2), and one humic-like (C3) components were identified in the leachates. The removal behaviors of the individual fluorescent components were dependent upon the operation conditions, suggesting the existence of unique characteristics with respect to the responses to the oxidation mechanisms, which were likely altered by different operation conditions. For all tested conditions, a greater extent of removal was consistently found for C3 versus C1 and C2 except for the relatively high pH ranges (>6.0), in which C2 presented the highest removal rates. 2D-COS combined with synchronous fluorescence spectra exhibited the preferential oxidation sequence in the order of C3 > C1 > C2 with higher H₂O₂ doses. 2D-COS coupled with Fourier transform infrared (2D-COS-FTIR) showed that aromatic functional groups were initially oxidized, followed by the removal of carboxylic groups and the formation of inorganic functional groups and aldehyde or ketonic groups. Hetero 2D-COS maps further revealed the close association between the aromatic groups and C3, and between the carboxylic groups and C1. This study utilizing 2D-COS provided new insights into the dynamic behavior of heterogeneous landfill leachate in Fenton oxidation processes under varying operation conditions.