Treatment of Landfill Leachate Using Activated Sludge Technology: A Review

Fenton-conditioning of landfill leachate biological sludge enables biochar for efficient Cr(Ⅵ)removal: Occurrence of oxygen-centered free radicals

Fenton-conditioning is commonly used to improve dewatering ability for municipal biological sludge, however, its application in industries is scarce. In this study, biochar (FT-BC) was successfully synthesized from a Fenton-conditioned landfill leachate biological sludge under oxygen-limited. As compared to the corresponding blank and poly ferric-pretreated biochars (BC and PF-BC), moderate Fenton conditioning of the sludge could enable good removal performance for Cr (Ⅵ) by FT-BC. It was found that the oxygen central free radicals (OCFRs) on the biochar surface was intensively promoted due to Fenton electrophilic addition of ·OH onto the oxygen-containing functional groups in biomass. The amounts of OCFRs correlated positively well with the removal efficiency, indicating these persistent free radicals (PFRs)would mainly responsible for the reductive immobilization of Cr(VI)on the FT-BC surface. This study is expected to provide a new method for reclamation of industrial biological sludges with poor agglomeration by introducing simple Fenton pre-conditioning.

Effect of hydrothermal pretreatment on leachate fed Scenedesmus sp. biomass solubilization and biogas production

The aim of the present study was to assess the effect of hydrothermal pretreatment on the solubilization and anaerobic digestion (AD) of Scenedesmus sp. biomass. At first, the microalgae was cultivated in 5% fresh leachate (FL) to recover nutrients such as nitrogen and phosphorus. Scenedesmus sp. grown in 5% FL obtained 100%, 77% and 97% removal efficiency of ammonium nitrogen (NH4+ - N), total Kjeldahl nitrogen (TKN) and phosphate phosphorous (PO43- -P), respectively. In the following step, the hydrothermal pretreatment of Scenedesmus sp. biomass was carried out at 120, 150 and 170 °C and retention time of 0, 30 and 60 min to evaluate its solubilization and biogas production through AD in batch test. Soluble chemical oxygen demand (sCOD) increased by 260% compared to untreated microalgae at 170 °C for 60 min. In comparison to untreated microalgae, the highest increase in biogas (70%) and methane yield (100%) was observed for 150 °C and 60 min pretreated microalgae as a consequence of hydrothermal pretreatment. Hydrothermal pretreatment has shown effectiveness in enhancing biomass solubilization and increasing biogas yield. Nevertheless, further research at the pilot scale is necessary to thoroughly evaluate the potential and feasibility of hydrothermal pretreatment for full-scale implementation.

Integrating advanced techniques and machine learning for landfill leachate treatment: Addressing limitations and environmental concerns

This review article explores the challenges associated with landfill leachate resulting from the increasing disposal of municipal solid waste in landfills and open areas. The composition of landfill leachate includes antibiotics (0.001-100 μg), heavy metals (0.001-1.4 g/L), dissolved organic and inorganic components, and xenobiotics including polyaromatic hydrocarbons (10-25 μg/L). Conventional treatment methods, such as biological (microbial and phytoremediation) and physicochemical (electrochemical and membrane-based) techniques, are available but face limitations in terms of cost, accuracy, and environmental risks. To surmount these challenges, this study advocates for the integration of artificial intelligence (AI) and machine learning (ML) to strengthen treatment efficacy through predictive analytics and optimized operational parameters. It critically evaluates the risks posed by recalcitrant leachate components and appraises the performance of various treatment modalities, both independently and in tandem with biological and physicochemical processes. Notably, physicochemical treatments have demonstrated pollutant removal rates of up to 90% for various contaminants, while integrated biological approaches have achieved over 95% removal efficiency. However, the heterogeneous nature of solid waste composition further complicates treatment methodologies. Consequently, the integration of advanced ML algorithms such as Support Vector Regression, Artificial Neural Networks, and Genetic Algorithms is proposed to refine leachate treatment processes. This review provides valuable insights for different stakeholders specifically researchers, policymakers and practitioners, seeking to fortify waste disposal infrastructure and foster sustainable landfill leachate management practices. By leveraging AI and ML tools in conjunction with a nuanced understanding of leachate complexities, a promising pathway emerges towards effectively addressing this environmental challenge while mitigating potential adverse impacts.

A new microalgal negative carbon technology for landfill leachate treatment: Simultaneous removal of nitrogen and phosphorus

Replete with ammonia nitrogen and organic pollutants, landfill leachate typically undergoes treatment employing expensive and carbon-intensive integrated techniques. We propose a novel microalgae technology for efficient, low-carbon simultaneous treatment of carbon, nitrogen, and phosphorus in landfill leachate (LL). The microbial composition comprises a mixed microalgae culture with Chlorella accounting for 82.58%. After seven days, the process with an N/P ratio of approximately 14:1 removed 98.81% of NH4+-N, 88.62 % of TN, and 99.55% of TP. Notably, the concentrations of NH4+-N and TP met the discharge standards, while the removal rate of NH4+-N was nearly three times higher than previously reported in relevant studies. The microalgae achieved a removal efficiency of 64.27% for Total Organic Carbon (TOC) and 99.26% for Inorganic Carbon (IC) under mixotrophic cultivation, yielding a biomass of 1.18 g/L. The treatment process employed in this study results in a carbon emissions equivalent of -8.25 kgCO2/kgNremoved, representing a reduction of 33.56 kgCO2 compared to the 2AO + MBR process. In addition, shake flask experiments were conducted to evaluate the biodegradability of leachate after microalgae treatment. After microalgae treatment, the TOCB (Biodegradable Total Organic Carbon)/TOC ratio decreased from 56.54% to 27.71%, with no significant improvement in biodegradability. It establishes a fundamental foundation for further applied research in microalgae treatment of leachate.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Optimal pre-treatment of moderately old landfill leachate at the pilot-scale treatment plant using the combined aerobic biochemical and reagent method

Landfill leachates contain highly concentrated pollutants, and their uncontrolled discharge poses significant risks to the public health and environment. This study validated a pilot-scale two-stage aerobic biochemical and reagent method for the pre-treatment of moderately old landfill leachate at a pilot-scale treatment plant with a capacity of 400 L per day. The kinetic curves of key pollutants were described using two-factor dimensionless exponential equations, allowing for predicting maximally achievable treatment effects during the first aerobic biochemical stage. The optimal duration of aerobic biochemical pre-treatment was determined based on the concept of limiting pollutant content and minimizing operating costs for the two-stage process. Reagent-based leachate pre-treatment using the modified Fenton method was verified in a batch reactor. Optimal concentrations and dosages of reagent solutions, including polyacrylamide, aluminium sulphate, ferrous sulphate, and hydrogen peroxide, were found to comply with Ukrainian regulations for wastewater discharge into sewerage networks. Key pollution indicators of pre-treated leachate, such as NH₄⁺-N (13.4-15.5 mg × L^-1), TKN (25.7-30.2 mg × L^-1), BOD_tot (71.8-76.9 mg × L^-1), and COD (390-459 mg × L^-1), meet the required standards.

Insights into sustainable resource and energy recovery from leachate towards emission mitigation for environmental management: A critical approach

The exponential generation of municipal solid waste (MSW) and landfill disposal without any treatment has increased the continuous generation of landfill leachate. Improper MSW and leachate management are contributing to environmental degradation and water and soil pollution, which must be treated. Numerous works have been conducted on leachate treatments for energy and resource recovery. This review presents a comprehensive study of leachate management in which different treatment methods are discussed to analyze the suitability of processes that can be employed to treat leachate efficiently. Further, the characteristics of leachate are examined as properties of leachate may be varied depending upon the region. Still, several challenges related to leachate management and its treatments are discussed in this study. An integrated system could be a better option for treating leachate because it contains large amounts of organic and inorganic compounds. Proper leachate management would help to recover energy and value-added products (metals).

Degradation of refractory organic matter in MBR effluent from treating landfill leachate by the UV-nZVI-H2O2 system

In this study, nano zero-valent iron (nZVI) was used as the Fe²⁺ source in the Fenton reaction, and a UV-nZVI-H₂O₂ system was constructed to efficiently degrade and mineralize refractory organic matter in landfill leachate. The results showed that under the optimal conditions (initial pH = 3, UV = 14 W, nZVI = 0.5 g/L, and [H₂O₂] = 30 mM), the removal efficiencies of total organic carbon, absorbance at 254 nm, and color number were 61.38%, 83.89%, and 85.79%, respectively. Control experiments show that the UV-nZVI-H₂O₂ system has the highest removal rate and mineralization rate of refractory organic matter. The excellent performance of the UV-nZVI-H₂O₂ system is related to a higher H₂O₂ utilization rate. The H₂O₂ residue in the UV-nZVI-H₂O₂ system was the lowest, and the effective utilization rate of H₂O₂ was as high as 98.80%. Alcohol quenching experiments and hydroxyl radical quantitative experiments showed that the dominant reactive oxygen species in the UV-nZVI-H₂O₂ system was HO^• and the yield of HO^• was as high as 2007.80 μM, which was much higher than that in other systems. The results of spectra analysis showed that the low molecular weight, high fluorescence frequency organic matter, and relatively stable aromatic organic matter were significantly degraded after treatment with the UV-nZVI-H₂O₂ system and the aromatic degree, humification degree, molecular weight, and molecular polymerization degree of refractory organic matter were also significantly decreased. The mechanism of the UV-nZVI-H₂O₂ reaction includes homogeneous and heterogeneous Fenton reactions and adsorption and precipitation of organic matter by iron-based colloids. This study can provide theoretical and technical support for the advanced treatment of refractory organic matter in landfill leachate.

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.

Integrated membrane electrochemical reactor-membrane distillation process for enhanced landfill leachate treatment

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

The effect of activated sludge treatment and catalytic ozonation on high concentration of ammonia nitrogen removal from landfill leachate

This study adopted the combination of activated sludge treatment and catalytic ozonation technology to efficiently remove the high concentration of ammonia nitrogen from landfill leachate. Through optimizing the parameters continuously, the COD, NH₄⁺-N, UV₂₅₄ and colority respectively descended to 417.75 ± 6.72 mg/L, 9.77 mg/L, 1.98 ± 0.04 and 40 times, and 3D fluorescence also reduced significantly within 14 days. Target genes of AOB-amoA, nxrA, napA, nirS and nosZ analysis indicated that ammonia-oxidizing bacteria, nitrated bacteria, and denitrifying bacteria played a key role on nitrogen removal, aerobic denitrifying bacteria was dominated especially. The nitrogen removal process was as follows: catalytic ozonation converted nitrogen-containing organic matter into NH₄⁺-N, then NH₄⁺-N was converted into NO₂^--N and NO₃^--N with the action of ammonia oxidation, nitrification and catalytic ozonation. Finally, the denitrification microorganisms transformed NO₃^--N or NO₂^--N to N₂. Therefore, this coupled process realized the nitrogen removal effectively from landfill leachate.

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.

Co-Treatment of Landfill Leachate and Liquid Fractions of Anaerobic Digestate in an Industrial-Scale Membrane Bioreactor System

The management of the liquid fraction of digestate produced from the anaerobic digestion of biodegradable municipal solid waste is a difficult affair, as its land application is limited due to high ammonium concentrations and the municipal waste that water treatment plants struggle to treat due to high pollutant loads. The amount of leachate and the pollutant load in the leachate produced by landfills usually decreases with the time, which increases the capacity of landfill leachate treatment plants (LLTPs) to treat additional wastewater. In order to solve the above two challenges, the co-treatment of landfill leachate and the liquid fraction of anaerobic digestate in an industrial-scale LLTP was investigated along with the long-term impacts of the liquid fraction of anaerobic digestate on biocoenosis and its impact on LLTP operational expenses. The co-treatment of landfill leachate and liquid fraction of anaerobic digestate was compared to conventional leachate treatment in an industrial-scale LLTP, which included the use of two parallel lanes (Lane-1 and Lane-2). The average nitrogen removal efficiencies in Lane-1 (co-treatment) were 93.4%, 95%, and 92%, respectively, for C/N ratios of 8.7, 8.9, and 9.4. The average nitrogen removal efficiency in Lane-2 (conventional landfill leachate treatment), meanwhile, was 88%, with a C/N ratio of 6.5. The LLTP’s average chemical oxygen demand (COD) removal efficiencies were 63.5%, 81%, and 78% during phases one, two, and three, respectively. As the volume ratios of the liquid fraction of anaerobic digestate increased, selective oxygen uptake rate experiments demonstrated the dominance of heterotrophic bacteria over ammonium and nitrite-oxidising organisms. The inclusion of the liquid fraction of anaerobic digestate during co-treatment did not cause a significant increase in operational resources, i.e., oxygen, the external carbon source, activated carbon, and energy.

Analysis of the Bacterial Biocenosis of Activated Sludge Treated with Leachate from Municipal Landfills

The influx of toxic pollutants into wastewater treatment plants can negatively affect the quality of the activated sludge (AS). One source is landfill leachate. The identification of microorganisms present in AS is very important, e.g., while improving wastewater treatment technology. Therefore, the aim of the study was to investigate the effect of raw leachate and after purification of Phragmites australis and Ceratophyllum demersum on the composition of the AS bacterial biocenosis. In addition, AS status was assessed by LIVE/DEAD BacLight ™ fluorescent staining. The obtained results showed that the leachate did not significantly affect the cell membranes of AS bacteria, and even a slight improvement was noted. The research carried out using the next-generation sequencing method shows that the origin of the samples (active and closed storage) and the method of processing do not significantly affect the composition of the AS bacterial biocenosis at higher taxonomic levels. However, at the species level, the appearance of bacteria not previously present in AS was observed, namely: Flavobacterium luticocti, Candidimonas nitroreducens and Nitrobacter hamburgensis. The obtained results suggest that the leachate may be a source of microorganisms positively influencing the condition of AS bacteria.

Landfill leachate treatment by persulphate related advanced oxidation technologies

Landfill leachate is produced from garbage decomposition with highly toxic and bio-refractory compounds, which poses serious harm to environmental security and human health. Thus, it is urgent to treat landfill leachate properly. Persulfate (PS) oxidation has attracted extensive attentions in terms of fast reaction speed, non-selectivity to target pollutants and thorough oxidation. In recent years, PS oxidation has been widely adopted for landfill leachate purification. However, the related results have been rarely summarized. In this review, the treatment of landfill leachate by PS oxidation system is discussed systematically including oxidants, activation modes and oxidation mechanisms. In addition, the current situation of PS oxidation system and other coupled systems for landfill leachate treatment is also summarized. Finally, the challenges and future research directions of landfill leachate treatment based on PS oxidation process are proposed. Meaningfully, this review will provide valuable references for the development of landfill leachate treatment process, promoting the application of advanced oxidation technology in landfill leachate treatment.

Critical review of advanced oxidation processes in organic wastewater treatment

With the development of industrial society, organic wastewater produced by industrial manufacturing has caused many environmental problems. The vast majority of organic pollutants in water bodies are persistent in the environment, posing a threat to human and animal health. Therefore, efficient treatment methods for highly concentrated organic wastewater are urgently needed. Advanced oxidation processes (AOPs) are widely noticed in the area of treating organic wastewater. Compared with other chemical methods, AOPs have the characteristics of high oxidation efficiency and no secondary pollution. In this paper, the mechanisms, advantages, and limitations of AOPs are comprehensively reviewed. Besides, the basic principles of combining different AOPs to enhance the treatment efficiency are described. Furthermore, the applications of AOPs in various wastewater treatments, such as oily wastewater, dyeing wastewater, pharmaceutical wastewater, and landfill leachate, are also presented. Finally, we conclude that the main direction in the future of AOPs are the modification of catalysts and the optimization of operating parameters, with the challenges focusing on industrial applications.

UVA-LED Technology’s Treatment Efficiency and Cost in a Competitive Trial Applied to the Photo-Fenton Treatment of Landfill Leachate

The objective of this trial was to assess the application of UVA-LED technology as an alternative source of irradiation for photo-Fenton processes, aiming to reduce treatment costs and provide a feasible treatment for landfill leachate. An optimized combination of coagulation with ferric chloride followed by photo-Fenton treatment of landfill leachate was optimized. Three different radiation sources were tested, namely, two conventional high-pressure mercury-vapor immersion lamps (100 W and 450 W) and a custom-designed 8 W 365 nm UVA-LED lamp. The proposed treatment combination resulted in very efficient degradation of landfill leachate (COD removal = 90%). The coagulation pre-treatment removed about 70% of the COD and provided the necessary amount of iron for the subsequent photo-Fenton treatment, and it further favored this process by acidifying the solution to an optimum initial pH of 2.8. The 90% removal of color improved the penetration of radiation into the medium and by extension improved treatment efficiency. The faster the Fenton reactions were, as determined by the stoichiometric optimum set-up reaction condition of [H2O2]0/COD0 = 2.125, the better were the treatment results in terms of COD removal and biodegradability enhancement because the chances to scavenge oxidant agents were limited. The 100 W lamp was the least efficient one in terms of final effluent quality and operational cost figures. UVA-LED technology, assessed as the application of an 8 W 365 nm lamp, provided competitive results in terms of COD removal, biodegradability enhancement, and operational costs (35–55%) when compared to the performance of the 450 W conventional lamp.

Factors affecting aerobic granule sludge formation in leachate treatment - a systematic review

The biological treatment of landfill leachate due to high concentration of Chemical Oxygen Demand (COD), ammonia, and other toxic compounds is so difficult. One of the leachate treatment technology is the sludge biogranulation, that containing the two aerobic and anaerobic process. The aim of this study was conducted for determining the main factors affecting aerobic granule sludge formation in leachate treatment. In this study, all related papers in international databases were evaluated including Google Scholar, Science Direct, and PubMed, Also Open Access Journal Directory from 1990 until 2020 were investigated. The keywords used included Aerobic Granule Sludge (AGS), leachate treatment, Wastewater treatment, Granular Sequential Batch Reactors (GSBR), Formation Extracellular polymeric substance (EPS). Overall, 2,658 articles were retrieved of which 71 were selected after revising the titles and abstracts. Aerobic granulation has been only lately studied and a limited number of studies have been devoted to identification aspects of the process such as the organic source, and other factor affecting on formation granules. Some factors as shear stress, settling time, and the effluent discharge site have direct effect on the efficiency of aerobic granules reactor and other factors such as divalent metal ions, dissolved oxygen concentration, the ratio of height to diameter of the reactor, temperature affecting on the granulation process. If suitable conditions provide, the aerobic granule sludge process can be useful for leachate treatment.

Population dynamics of microbial species under high and low ammonia nitrogen in the alternate layer bioreactor landfill (ALBL) approach

Anaerobic landfill process is still believed to be a complex ecosystem due to the lack of knowledge on the functional activities of microbial species. This research sought to introduce a novel landfill bioreactor, named here as the alternate layer bioreactor landfill (ALBL) of fresh MSW (FW) and stabilized waste (CT) to avoid inhibitory conditions for the microbial species in anaerobic landfill. The stabilized waste layer in the bottom of landfill cell significantly changed microbial ecology of fresh MSW which in turn reduced the concentrations of NH₄-N (29-31%) and VFAs (33-38%) in the ALBL approach, compared to fresh MSW disposal in sanitary landfill. The reduction of NH₄-N favored early onset of methanogenesis within 6 weeks and methane (CH₄) content of landfill gas increased from 11% to 40-50% (v/v), owing to the coexistence of Methanosarcinales (36-50%) and Methanomicrobiales (26-28%) archaea. The acetoclastic methanogenesis was achieved by reducing NH₄-N toxicity in the ALBL.

Landfill leachate treatment through the combination of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO and membrane filtration processes

This study developed a process of genetically engineered bacteria Rhodococcus erythropolis expressing Nirs and AMO combined with membrane bioreactor (MBR), nanofiltration (NF) and reverse osmosis (RO) membrane (pRho-NA-MNR) for advanced treatment of landfill leachate. Results demonstrated that pRho-NA-MNR presented higher removal rate of chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia nitrogen (N-NH₄), total nitrogen (TN) and total organic carbon (TOC) than activated sludge (AS-MNR) system. Administration of pRho-NA increased nitrification by converting N-NH₄ to nitrite (N-NO₂) and Nitrate (N-NO₃), and promoting denitrification by converting N-NO₂ to nitrogen (N₂) in the landfill leachate treatment, promoted the pH control, increased sludge activity and effluent yield, shortened phase length adaptation under alternating aerobic-anoxic conditions. pRho-NA increased the nitration and denitrifying rate in the aerobic and anaerobic stage in the system by increasing Cyt cd1 and Cyt c expression in the activated sludge. Nitrogen removal by nitrification and denitrification was positively correlated to the concentration of Nirs and AMO expression. Treatment with pRho-NA promoted pollutant removal efficiency of membrane bioreactor, nanofiltration and reverse osmosis membrane processes in landfill leachate. In conclusion, data suggest that pRho-NA-MNR facilitates the formation of granular sludge and enhances comparable removal of nitrogen and organic compounds, indicating the practice of this process should be considered in landfill leachate treatment system.

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.

Prospects of integrating algae technologies into landfill leachate treatment

Landfilling of municipal waste, an environmental challenge worldwide, results in the continuous formation of significant amounts of leachate, which poses a severe contamination threat to ground and surface water resources. Landfill leachate (LL) is generated by rainwater percolating through disposed waste materials and must be treated effectively before safe discharge into the environment. LL contains numerous pollutants and toxic substances, such as dissolved organic matter, inorganic chemicals, heavy metals, and anthropogenic organic compounds. Currently, LL treatment is carried out by a combination of physical, chemical, and microbial technologies. Microalgae are now viewed as a promising sustainable addition to the repertoire of technologies for treating LL. Photosynthetic algae have been shown to grow in LL under laboratory conditions, while some species have also been employed in larger-scale LL treatments. Treating leachate with algae can contribute to sustainable waste management at existing landfills by remediating low-quality water for recycling and reuse and generating large amounts of algal biomass for cost-effective manufacturing of biofuels and bioproducts. In this review, we will examine LL composition, traditional leachate treatment technologies, LL toxicity to algae, and the potential of employing algae at LL treatment facilities. Emphasis is placed on how algae can be integrated with existing technologies for biological treatment of LL, turning leachate from an environmental liability to an asset that can produce value-added biofuels and bioproducts for the bioeconomy.

Selecting Bacteria Candidates for the Bioaugmentation of Activated Sludge to Improve the Aerobic Treatment of Landfill Leachate

In this study, a multifaceted approach for selecting the suitable candidates for bioaugmentation of activated sludge (AS) that supports leachate treatment was used. To determine the exploitation of 10 bacterial strains isolated from the various matrices for inoculating the AS contaminated with the Kalina pond leachate (KPL), their degradative potential was analyzed along with their aptitude to synthesize compounds improving remediation of pollutants in wastewater and ability to incorporate into the AS flocs. Based on their capability to degrade aromatic compounds (primarily catechol, phenol, and cresols) at a concentration of 1 mg/mL and survive in 12.5% of the KPL, Pseudomonas putida OR45a and P. putida KB3 can be considered to be the best candidates for bioaugmentation of the AS among all of the bacteria tested. Genomic analyses of these two strains revealed the presence of the genes encoding enzymes related to the metabolism of aromatic compounds. Additionally, both microorganisms exhibited a high hydrophobic propensity (above 50%) and an ability to produce biosurfactants as well as high resistance to ammonium (above 600 µg/mL) and heavy metals (especially chromium). These properties enable the exploitation of both bacterial strains in the bioremediation of the AS contaminated with the KPL.

Impact of the Biological Cotreatment of the Kalina Pond Leachate on Laboratory Sequencing Batch Reactor Operation and Activated Sludge Quality

Hauling landfill leachate to offsite urban wastewater treatment plants is a way to achieve pollutant removal. However, the implementation of biological methods for the treatment of landfill leachate can be extremely challenging. This study aims to investigate the effect of blending wastewater with 3.5% and 5.5% of the industrial leachate from the Kalina pond (KPL) on the performance of sequencing batch reactor (SBR) and capacity of activated sludge microorganisms. The results showed that the removal efficiency of the chemical oxygen demand declined in the contaminated SBR from 100% to 69% and, subsequently, to 41% after the cotreatment with 3.5% and 5.5% of the pollutant. In parallel, the activities of the dehydrogenases and nonspecific esterases declined by 58% and 39%, and 79% and 81% after 32 days of the exposure of the SBR to 3.5% and 5.5% of the leachate, respectively. Furthermore, the presence of the KPL in the sewage affected the sludge microorganisms through a reduction in their functional capacity as well as a decrease in the percentages of the marker fatty acids for different microbial groups. A multifactorial analysis of the parameters relevant for the wastewater treatment process confirmed unambiguously the negative impact of the leachate on the operation, activity, and structure of the activated sludge.