Fungal and enzymatic treatment of mature municipal landfill leachate

Landfill leachate treatment using fungi and fungal enzymes: a review

Landfill leachate raises a huge risk to human health and the environment as it contains a high concentration of organic and inorganic contaminants, heavy metals, ammonia, and refractory substances. Among leachate treatment techniques, the biological methods are more environmentally benign and less expensive than the physical-chemical treatment methods. Over the last few years, fungal-based treatment processes have become popular due to their ability to produce powerful oxidative enzymes like peroxidases and laccases. Fungi have shown better removal efficiency in terms of color, ammonia, and COD. However, their use in the treatment of leachate is relatively recent and still needs to be investigated. This review article assesses the potential of fungi and fungal-derived enzymes in treating landfill leachate. The review also compares different enzymes involved in the fungal catabolism of organic pollutants and the enzyme degradation mechanisms. The effect of parameters like pH, temperature, contact time, dosage variation, heavy metals and ammonia are discussed. The paper also explores the reactor configuration used in the fungal treatment and the techniques used to improve leachate treatment efficacy, like pretreatment and fungi immobilisation. Finally, the review summarises the limitations and the future direction of work required to adapt the fungal application for leachate treatment on a large scale.

Process of landfill leachate pretreatment using coagulation and hydrodynamic cavitation oxidation

Landfill leachate poses a threat to the environment and human health, and its complex composition made it difficult to treat. Among the methods for treating landfill leachate, the physicochemical combination method is considered to have significant effectiveness, low cost, and application potential. In this study, we propose a new method of coagulation and hydrodynamic cavitation/chlorine dioxide (HC/ClO2) for treating landfill leachate. The optimal conditions for coagulation and HC/ClO2 treatment were investigated experimentally. Under the optimal conditions for coagulation, the COD removal rate was 60.14%. Under the optimal HC/ClO2 treatment conditions, the COD removal rate was 58.82%. In the combined coagulation and HC/ClO2 process, the COD removal rate was 83.58%. Thus, the proposed method can significantly reduce the organic load before subsequent biological treatment processes, thereby reducing the operation cycles and cost of biological treatment.

High-throughput bioamphiphile production by ethyl methane sulphonate induced mutant of hydrocarbonoclastic Enterobacter xiangfangensis STP-3: In depth structural elucidation and application to petroleum refinery oil sludge bioremediation

The environmental release of noxious petroleum hydrocarbons (PHCs) from the petroleum refining industries is an intractable global challenge. Indigenous PHCs degrading microbes produce insufficient yield of amphiphilic biomolecules with trivial efficiency makes the bioremediation process ineffective. In this concern, the present study is focused on the production of high yield multi-functional amphiphilic biomolecule through the genetic modification of Enterobacter xiangfangensis STP-3 strain using Ethyl methane sulphonate (EMS) induced mutagenesis. Mutant M9_{E.xiangfangensis} showed 2.32-fold increased yield of bioamphiphile than wild-type strain. Novel bioamphiphile produced by M9_{E.xiangfangensis} exhibited improved surface and emulsification activities which ensure the maximum degradation of petroleum oil sludge (POS) by 86% than wild-type (72%). SARA, FT-IR, and GC-MS analyses confirmed the expedited degradation of POS and ICP-MS analysis indicated the enhanced removal of heavy metals in connection with the ample production of functionally improved bioamphiphile. FT-IR NMR, MALDI-TOF, GC-MS and LC-MS/MS analyses portrayed the lipoprotein nature of bioamphiphile comprising pentameric fatty acid moiety conjugated with the catalytic esterase moiety. Further, homology modelling and molecular docking revealed the stronger interaction of hydrophobic amino acids, leucine and isoleucine with the PHCs in the case of wild-type esterase moiety, whereas in the mutant, aromatic amino acids were majorly interacted with the long chain and branched chain alkanes, thereby exhibited better efficiency. This is the first report on the adoption of EMS induced mutagenesis strategy to ameliorate the amphiphilic biomolecules for their sustainable applications in diverse biotechnological, environmental and industrial arenas.

Supramolecular bioamphiphile facilitated bioemulsification and concomitant treatment of recalcitrant hydrocarbons in petroleum refining industry oily waste

Bioremediation of real-time petroleum refining industry oily waste (PRIOW) is a major challenge due to the poor emulsification potential and oil sludge disintegration efficiency of conventional bioamphiphile molecules. The present study was focused on the design of a covalently engineered supramolecular bioamphiphile complex (SUBC) rich in hydrophobic amino acids for proficient emulsification of hydrocarbons followed by the concomitant degradation of total petroleum hydrocarbons (TPH) in PRIOW using the hydrocarbonoclastic microbial bio-formulation system. The synthesis of SUBC was carried out by pH regulated microbial biosynthesis process and the yield was obtained to be 450.8 mg/g of petroleum oil sludge. The FT-IR and XPS analyses of SUBC revealed the anchoring of hydrophilic moieties of monomeric bioamphiphilic molecules, resulting in the formation of SUBC via covalent interaction. The SUBC was found to be lipoprotein in nature. The maximum loading capacity of SUBC onto surface modified rice hull (SMRH) was achieved to be 45.25 mg/g SMRH at the optimized conditions using RSM-CCD design. The SUBC anchored SMRH was confirmed using SEM, FT-IR, XRD and TGA analyses. The adsorption isotherm models of SUBC onto SMRH were performed. The integrated approach of SUBC-SMRH and hydrocarbonoclastic microbial bio-formulation system, emulsified oil from PRIOW by 92.86 ± 2.26% within 24 h and degraded TPH by 89.25 ± 1.75% within 4 days at the optimum dosage ratio of SUBC-SMRH (0.25 g): PRIOW (1 g): mass of microbial-assisted biocarrier material (0.05 g). The TPH degradation was confirmed by SARA fractional analysis, FT-IR, ¹H NMR and GC-MS analyses. The study suggested that the application of covalently engineered SUBC has resulted in the accelerated degradation of real-time PRIOW in a very short duration without any secondary sludge generation. Thus, the SUBC integrated approach can be considered to effectively manage the hydrocarbon contaminants from petroleum refining industries under optimal conditions.

Approach to a fungal treatment of a biologically treated landfill leachate

White-rot fungi (WRF) have the ability to synthetize extracellular enzymes that could degrade recalcitrant pollutants. The aim of this work was to evaluate the use of P. chrysosporium to treat a biologically and physically pre-treated landfill leachate which high load of refractory compounds (COD>1000 mg/L, BOD₅<50 mg/L) in order to reduce COD and colour. Batch tests were carried out at 26 °C and 135 rpm for 15 days. The soluble chemical oxygen demand (sCOD), soluble biological oxygen demand (sBOD₅) and colour, as well as the lignin peroxidase (LiP) and manganese peroxidase (MnP) enzymatic activities were analysed. Besides, the effects of different operating conditions, i.e., pH control, permeate dilution and supplementation, on treatment efficacy were investigated. The control of pH was shown to be key for fungal treatment. In addition, it was found that the addition of carbon and nitrogen sources improved the enzymatic synthesis and the removals of sCOD and colour. Data here obtained open the possibility of using fungi for reducing the amount of recalcitrant pollutants still present in treated landfill leachates or similar effluents.

A critical review on microbes-based treatment strategies for mitigation of toxic pollutants

Contamination of the environment through toxic pollutants poses a key risk to the environment due to irreversible environmental damage(s). Industrialization and urbanization produced harmful elements such as petrochemicals, agrochemicals, pharmaceuticals, nanomaterials, and herbicides that are intentionally or unintentionally released into the water system, threatening biodiversity, the health of animals, and humans. Heavy metals (HMs) in water, for example, can exist in a variety of forms that are inclined by climate features like the presence of various types of organic matter, pH, water system hardness, transformation, and bioavailability. Biological treatment is an important tool for removing toxic contaminants from the ecosystem, and it has piqued the concern of investigators over the centuries. In situ bioremediation such as biosparging, bioventing, biostimulation, bioaugmentation, and phytoremediation and ex-situ bioremediation includes composting, land farming, biopiles, and bioreactors. In the last few years, scientific understanding of microbial relations with particular chemicals has aided in the protection of the environment. Despite intensive studies being carried out on the mitigation of toxic pollutants, there have been limited efforts performed to discuss the solutions to tackle the limitations and approaches for the remediation of heavy metals holistically. This paper summarizes the risk assessment of HMs on aquatic creatures, the environment, humans, and animals. The content of this paper highlights the principles and limitations of microbial remediation to address the technological challenges. The coming prospect and tasks of evaluating the impact of different treatment skills for pollutant remediation have been reviewed in detail. Moreover, genetically engineered microbes have emerged as powerful bioremediation capabilities with significant potential for expelling toxic elements. With appropriate examples, current challenging issues and boundaries related to the deployment of genetically engineered microbes as bioremediation on polluted soils are emphasized.

Biocatalytic lipoprotein bioamphiphile induced treatment of recalcitrant hydrocarbons in petroleum refinery oil sludge through transposon technology

The present investigation employed transposon technology to enhance the degradation of recalcitrant petroleum hydrocarbons present in petroleum oil sludge by using biosurfactant hyper-producing strain Enterobacter xiangfangensis STP-3. Out of 2500 transposon induced mutants, mutants M_{257E.xiangfangensis} and M_{916E.xiangfangensis} hyper-produce biocatalytic lipoprotein biosurfactant by1.98 and 2.34 fold higher than wild-type strain. Transposon induced mutation also modified the amino acid composition which improved the hydrophobicity and thermal stability of the biosurfactants produced by mutants, compared to the wild-type biosurfactant. GC-MS and LC-MS-MS revealed that biosurfactants have pentameric lipid moiety and esterase as protein moiety. Increased biosurfactant hydrophobicity and yield by the mutants resulted in the enhanced bioavailability of petroleum hydrocarbons, thereby mutants M_{257E.xiangfangensis} and M_{916E.xiangfangensis} demonstrated better petroleum oil sludge degradation by 82% and 88% respectively, than wild-type (72%). Disrupted genes vgr G and pgm M in M257_{E.xiangfangensis} and M916_{E.xiangfangensis} respectively hyper-produce biosurfactant by competitive pathway inhibition and increased precursor availability mechanism. Hyper-production of biosurfactant was also validated by comparing the expression of biosynthetic genes ent E, ent F and est using qPCR. This is the first report on the application of transposon technology to hyper-produce biosurfactant for the effective bioremediation of hydrocarbon contaminated environments.

Leachate treatment potential of nanomaterial based assemblies: a systematic review on recent development

Rapid development of the population has brought about a serious problem of waste generation and management. Open dumping and land filling are two of the preferred options for waste management and treatment. As a consequence of this, the accumulation of leachates has become one of the concerns for environmental sustainability. In this regard, various treatment methodologies have been developed in recent decades. Among them, the nanomaterial-based approaches are the emerging ones in the current scenario due to their various unique properties. Furthermore, nanomaterial-based assemblies (i.e., nanomaterials combined with microbes, chemical catalysts, enzymes, and so on) have been introduced as a novel modification for leachate treatment. This work, therefore, has been dedicated to comprehensively reviewing all nanomaterial based leachate treatment techniques. In this regard, the first part of this review will discuss the nano catalyst, nano adsorbent along with their synthesis and mechanistic view of pollutant removal potential. In the second part, the nanomaterial-based microbial conjugates applied in the leachate treatments have been discussed. Apart from this, various other nanomaterial-based methods have been discussed in the third part of the review. Hence this review is providing an insight of all the recent developments pertaining to the nano material based leachate treatment techniques.

Ecotoxicological Estimation of 4-Cumylphenol, 4-t-Octylphenol, Nonylphenol, and Volatile Leachate Phenol Degradation by the Microscopic Fungus Umbelopsis isabellina Using a Battery of Biotests

The phenolic xenobiotics nonylphenol (NP), 4-tert-octylphenol (4-t-OP), and 4-cumylphenol (4-CP) have the potential to seriously disrupt the endocrine system. Volatile phenols (VPs), especially those present in landfill leachate, also adversely affect the health of numerous organisms. Microbial degradation of xenobiotics can result in the formation of intermediates with higher toxicity than the precursor substrates. Therefore, the main aim of this study was to assess the changes in environmental ecotoxicity during the biotransformation of nonylphenol, 4-tert-octylphenol, 4-cumylphenol and volatile phenols by Umbelopsis isabellina using a battery of biotests. The application of bioindicators belonging to different taxonomic groups and diverse trophic levels (producers, consumers, and reducers) indicated a significant reduction in toxicity during the cultivation of fungus cultures both for nonylphenol, 4-tert-octylphenol, 4-cumylphenol and volatile phenols. The rate of toxicity decline was correlated with the degree of xenobiotic biotransformation. Removal of 4-cumylphenol and 4-tert-octylphenol also led to a decrease in the anti-androgenic potential. Moreover, this is the first report demonstrating the anti-androgenic properties of 4-cumylphenol. The results showed that U. isabellina is an attractive tool for the bioremediation and detoxification of contaminated environments.

Sinapis alba L. and Triticum aestivum L. as biotest model species for evaluating municipal solid waste leachate toxicity

The volume of municipal solid waste (MSW) inputs is rapidly increasing with a growing human population, and its composition is changing due an increased diversity of materials being deposited. There is an associated increase in leachate, a common toxic byproduct of MSW facilities that must be collected and treated prior to its release into the environment. There is growing interest in plant-based methods that are economical and efficient for leachate toxicity assessment such as biological tests that use indicator species. In the present study, the tolerance thresholds of two herbaceous species, Sinapis alba L. (mustard) and Triticum aestivum L. (wheat) to increasing shares of leachate sourced from an MSW facility in the Czech Republic were assessed through a variety of physiological parameters. Soil-based biotests showed a stimulation in the shoot biomass, leaf expansion, primary root elongation and carbon assimilation rate of the selected plant species to leachate concentrations between 20 and 50 %. Higher leachate concentrations led to reductions in most physiological parameters, especially the elongation of seedling roots when growth solutions with >50 % leachate were applied. While S. alba was more sensitive to increasing proportions of leachate in terms of growth parameters of the shoot tissues, photosystem II efficiency and chlorophyll pigment concentrations were more responsive in T. aestivum, indicating species-dependent differences. The present biotests provide further support for the use of both Sinapis alba L and Triticum aestivum L. as indicator species of phytotoxicity.

Genomic characterization of Enterobacter xiangfangensis STP-3: Application to real time petroleum oil sludge bioremediation

Sustainable treatment of petroleum oil sludge still remains as a major challenge to petroleum refineries. Bioremediation is the promising technology involving bacteria for simultaneous production of biosurfactant and followed by degradation of petroleum compounds. Complete genomic knowledge on such potential microbes could accentuate its successful exploitation. The present study discusses the genomic characteristics of novel biosurfactant producing petrophilic/ petroleum hydrocarbon degrading strain, Enterobacter xiangfangensis STP-3, isolated from petroleum refinery oil sludge contaminated soil. The genome has 4,584,462 bp and 4372 protein coding sequences. Functional analysis using the RAST and KEGG databases revealed the presence of biosynthetic gene clusters linked to glycolipid and lipopeptide production and multiple key candidate genes linked with the degradation pathway of petroleum hydrocarbons. Orthology study revealed diversity in gene clusters associated to membrane transport, carbohydrate, amino acid metabolism, virulence and defence mechanisms, and nucleoside and nucleotide synthesis. The comparative analysis with 27 other genomes predicted that the core genome contributes to its inherent bioremediation potential, whereas the accessory genome influences its environmental adaptability in unconventional environmental conditions. Further, experimental results showed that E. xiangfangensis STP-3 was able to degrade PHCs by 82 % in 14 days during the bioremediation of real time petroleum oil sludge with the concomitant production of biosurfactant and metabolic enzymes, To the best of our knowledge, no comprehensive genomic study has been previously reported on the biotechnological prospective of this species.

A review of the characteristics of Fenton and ozonation systems in landfill leachate treatment

The development and application of Fenton and ozonation systems in landfill leachate treatment over the last 20 years, and the current research status are reviewed in this paper, with an emphasis on the technical and economic characteristics of Fenton and ozonation systems used to treat different types of landfill leachate. To date, a total of 101 and 78 articles have been published regarding leachate treatment by Fenton and ozonation systems, respectively. These articles considered the use of two systems to treat aged leachate, biologically treated leachate and leachate comprising the concentrated solution resulting from reverse osmosis (RO). The oxidization mechanisms of the two systems used to treat landfill leachate significantly differed in terms of their optimal process parameters (e.g., initial pH value, reagent dosage, and reaction time) and removal efficiency. The Fenton and ozonation systems outperformed persulfate-based advanced oxidation technology in terms of their improved biodegradability of landfill leachate and engineering practicability. The cost of the reagents required to treat landfill leachate by Fenton and ozonation systems accounted for at least 85% of the total operating cost. In contrast to the ozonation system, the Fenton system was more cost-effective when both systems were used to treat the same type of landfill leachate. This study provides a theoretical basis for the operation of Fenton and ozonation systems and also offers technical support for landfill leachate disposal companies that opt to use these technologies.

Biodegradation of petroleum refining industry oil sludge by microbial-assisted biocarrier matrix: process optimization using response surface methodology

Safe disposal of petroleum oil sludge generated from crude oil storage tank bottom is a major challenge for petroleum refineries across the globe. The presence of long chain hydrocarbons in petroleum oil sludge are known to have effects on the environment through bioaccumulation or biosorption. The present study was focused to develop a modified bioremediation process using hydrocarbonoclastic microbial-assisted biocarrier matrix (MABC) mediated through biosurfactants and biocatalysts for the efficient treatment of petroleum industrial oily sludge. The development of hydrocarbonoclastic microbial-assisted biocarrier matrix was confirmed by scanning electron microscopy analysis. The biocatalysts such as lipase, laccase, esterase and biosurfactant produced by MABC system were found to be 40 U/mg, 18 U/mg, 36 U/mg and 220 mg/g of oil sludge respectively using one variable at a time approach. Further, the response surface methodology was used to determine the optimum treatment conditions (Time, pH, Mass of biocarrier matrix and Amount of oil sludge) for the enhanced removal of total petroleum hydrocarbons (TPH) present in the oil sludge and TPH was degraded by 88.78% at Hydraulic Retention Time of 7 days. The biodegradation of oil sludge was confirmed using Gas Chromatography-Mass Spectrometry analysis.

Occurrence of methylisothiazolinone in water and soil samples in Poland and its biodegradation by Phanerochaete chrysosporium

Methylisothiazolinone is a commonly used biocide that is released into natural environments. In this work, the ability of the fungal strain Phanerochaete chrysosporium DSM 1556 to biotransform this compound was evaluated. The tested strain was able to remove MIT (at concentrations 50 μg L^-1 and 30 mg L^-1) from the growth medium with the efficiency 90% after the first 6 h and 100% after 12 h of incubation. Moreover, for the first time, qualitative LC-MS/MS and GC-MS analysis showed monohydroxylated and dihydroxylated methylisothiazolinone and N-methylmalonamic acid as the main products of fungal biodegradation. The ecological toxicity of the tested biocide and its derivatives was also evaluated by using an acute toxicity test with Daphnia magna. An approximately 90% decrease in the toxicity of metabolites formed in the P. chrysosporium culture was noticed. The concentration of MIT in soil and water samples collected in Poland was assessed for the first time. The analysis showed that the selected locations in Poland are contaminated by MIT in the range from 1.04-10.08 μg L^-1.

Chemical Composition and Hazardous Effects of Leachate from the Active Municipal Solid Waste Landfill Surrounded by Farmlands

Landfill leachates are potentially harmful to the environment and to human health. The objective of this study was to characterize leachates in order to analyze whether a relationship exists between the stored waste and the composition of leachates, and to detect possible leakages of pollutants into the environment. To achieve these objectives, field data, Global Positioning System data and physico-chemical data were used. Biological tests are becoming increasingly popular in determining leachate toxicity; therefore, two toxicity tests were performed with the seeds of white mustard (Sinapis alba L.) and duckweed (Lemna minor L.). Leachates were sampled from the leachate pond. Groundwater quality was monitored by using drill holes. The research and analysis carried out are important to determine their potential impact on agricultural areas located near the landfill. Demonstrably increased (P < 0.05) concentrations of heavy metals were detected only in the leachate pond which closes the landfill body, where it links up with the landfill insulation layer. Water sampled from drill holes reaching into groundwater was not contaminated. The results showed that the leachates did not leak outside the landfill. Nevertheless, they were found to be phytotoxic. Both toxicity tests showed that the increasing amount of leachates resulted in the increasing growth inhibition of the tested plants. The proper handling of leachates should have been ensured.

Advanced biological sequential treatment of mature landfill leachate using aerobic activated sludge SBR and fungal bioreactor

This study utilized Penicillium spp. to treat mature landfill leachate (MLL) in a continuous bioreactor and batch experimental tests under non-sterile conditions. MLL characteristics such as chemical oxygen demand (COD), soluble COD (sCOD), total carbon (TC), total organic carbon (TOC), and color removal efficiency were determined. The lignocellulosic enzymatic activity of laccase (Lac), lignin-peroxidase (LiP), and manganese-peroxidase (MnP) was also determined. The batch experimental test was carried out with raw and pretreated MLL containing the initial NH4 +-N concentrations of 0, 105, 352, and 914 mg/L. A maximum COD reduction of 41% and maximum enzymatic activity of 193, 37, and 25 U/L for Lac, LiP and MnP was recorded for the MLL containing 352 mg/L NH4 +-N. The continuous bioreactor exhibited maximum values of 52, 54, 60, 58, and 75 percentage of COD, sCOD, TC, TOC, and color removal efficiency with MLL containing 352 mg/L NH4 +-N that was pretreated at HRT 120 h, while the maximum detected lignocellulosic enzymatic activities were 149, 27, and 16 U/L for Lac, LiP, and MnP, respectively. A total of 64% COD reduction was achieved from the raw MLL considering 12% COD and 100% NH4 +-N reduction in the aerobic activated sludge sequencing batch reactor pretreatment process. The steady and higher removal efficiency of the bioreactor over the entire study period is promising for further exploration to enhance removal of refractory contaminants from the MLL.

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.

Selective adsorption and recovery of volatile fatty acids from fermented landfill leachate by activated carbon process

An adsorption-desorption process was applied on fermented landfill leachate to adsorb and recover acetic and butyric acid, using activated carbon. In this study, the first, volatile fatty acids adsorption process from fermented leachate was optimized, by investigating various affecting factors such as pH, time, agitation speed, activated carbon dosage, and temperature. The optimum condition for maximum adsorption of 88.94% acetic acid and 98.53% butyric acid, was 19.79 %wt activated carbon dosage, 40.00 rpm of agitation speed, in 9.45 °C and contact time of 179.89 h, while the pH of the substrate was kept fixed at pH:3.0. Results of X-ray fluorescence (XRF) spectrometry, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and zeta potential revealed that carbon is the dominant component in the adsorbent with a significant effect to remove organic impurities, and it was observed that the activated carbon after the adsorption process showed an amorphous structure peak with a large internal surface area and pore volume. The results exposed that the adsorption on the surface of activated carbon was due to the chemisorption, and the chemisorption mechanism was supported by covalent bonding. The kinetic study displayed excellent fit to Pseudo-second order kinetics model. The second phase of this study was to recover the adsorbed VFAs using multistage desorption unit, in which application of deionized water and ethanol (as desorption agents) resulted in 89.1% of acetic acid and 67.8% of the butyric acid recovery.

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.

Leachates and natural organic matter. A review of their biotreatment using fungi

Leachates have different concentrations of organic matter and levels of biodegradability, depending on the age of the landfill and they must be treated using appropriate techniques, such as fungal degradation, in order to protect the environment and water resources. Natural organic matter contains the same type of organic species as old and medium age leachates, but at lower concentrations. The present study compiles and assesses all the available literature on the biotreatment of these compounds, mainly humic acids, by fungi. It was found that the efficiency of the fungal biodegradation of these wastewaters depends on the characteristics and concentration of the organic matter in the leachate, the microorganisms selected and whether they were immobilized or not, the nutrients present in the medium and their concentrations, the experimentation time, the temperature and the pH. The influence of the mode of inoculation has only been studied in natural organic matter, but similar effects are expected in the treatment of the leachates. The interactions between these parameters are complex and the optimal conditions have to be determined by laboratory and pilot testing, employing multivariate statistical techniques and experimental design.

Delamination of plastic-coated waste paper by enzymes of the white rot fungus Dichomitus squalens

Many paper products are coated with plastic to improve their quality and stability. However, this limits recycling and recovery options and the plastic-coated waste paper is mostly disposed in landfills. Such practices are uneconomical and contrary to sustainable waste management. In this work enzymes of the white rot fungus Dichomitus squalens were investigated for possible delamination of plastic-coated waste paper. Enzymes were found capable to release the polyethylene foil from plastic-coated paper which resulted in 88.6-91.5% mass loss. The delamination rate, however, was depended on the ratio between plastic-coated paper and volume of enzyme filtrate. Results of a consequent experiment showed that enzymes are also efficient when plastic-coated paper is treated in a sequencing batch reactor resulting in 88.2-90.6% mass loss. The system was fully functional up to the 5th cycle; afterwards, the delamination rate reduced due to high thickness of the waste paper sludge. The enzyme activity, however, was still very high; with the laccase activity at the end of the experiment above 900 U/L and manganese peroxidase above 250 U/L. Our results demonstrated, that plastic-coated waste paper has the potential to be efficiently recovered instead of being disposed in landfills.

Bioremediation of Landfill Leachate with Fungi: Autochthonous vs. Allochthonous Strains

Autochthonous fungi from contaminated wastewater are potential successful agents bioremediation thanks to their adaptation to pollutant toxicity and to competition with other microorganisms present in wastewater treatment plant. Biological treatment by means of selected fungal strains could be a potential tool to integrate the leachate depuration process, thanks to their fungal extracellular enzymes with non-selective catalytical activity. In the present work, the treatability of two real samples (a crude landfill leachate and the effluent coming from a traditional wastewater treatment plant) was investigated in decolorization experiments with fungal biomasses. Five autochthonous fungi, Penicillium brevicompactum MUT 793, Pseudallescheria boydii MUT 721, P. boydii MUT 1269, Phanerochaete sanguinea MUT 1284, and Flammulina velutipes MUT 1275, were selected in a previous miniaturized decolorization screening. Their effectiveness in terms of decolorization, enzymatic activity (laccases and peroxidases), biomass growth and ecotoxicity removal was compared with that of five allochthonous fungal strains, Pleurotus ostreatus MUT 2976, Porostereum spadiceum MUT 1585, Trametespubescens MUT 2400, Bjerkanderaadusta MUT 3060 and B. adusta MUT 2295, selected for their well known capability to degrade recalcitrant pollutants. Moreover, the effect of biomass immobilization on polyurethane foam (PUF) cube was assessed. The best decolorization (60%) was achieved by P. spadiceum MUT 1585, P. boydii MUT 721 and MUT 1269. In the first case, the DP was achieved gradually, suggesting a biodegradation process with the involvement of peroxidases. On the contrary, the two autochthonous fungi seem to bioremediate the effluent mainly by biosorption, with the abatement of the toxicity (up to 100%). The biomass immobilization enhanced enzymatic activity, but not the DP. Moreover, it limited the biomass growth for the fast growing fungi, MUT 721 and MUT 1269. In conclusion, robust and versatile strains coming from well-characterized collections of microorganisms can obtain excellent results comparing and even exceeding the bioremediation yields of strains already adapted to pollutants.

Mature landfill leachate utilization using a cost-effective hybrid method

The main goal of this study was to investigate the co-digestion of sewage sludge and mature landfill leachate pretreated through hydrodynamic cavitation. The process efficiency was analyzed from the aspects of organics removal, biogas production, kinetics and digestate quality. Energy efficiency of the overall treatment was evaluated as well. A dose of hydrodynamically cavitated leachate of 5% v/v was used as a substrate for co-digestion with sewage sludge at a hydraulic retention time of 20 days. This improved the kinetics, biogas production and corresponding yields, as well as digestate quality. Fourier transform infrared photoacoustic spectroscopy analysis seemed to indicate that no new toxic compounds were formed with co-digestion. The investigated two-stage treatment is recommended as a safe and cost-effective method of utilizing mature leachate.

Organic matters removal from landfill leachate by immobilized Phanerochaete chrysosporium loaded with graphitic carbon nitride under visible light irradiation

This study investigated the technical applicability of a combination of Phanerochaete chrysosporium (P. chrysosporium) with photocatalyst graphitic carbon nitride (g-C₃N₄) for organic matters removal from landfill leachate under visible light irradiation. Photocatalyst g-C₃N₄ was well immobilized on the hyphae surface of P. chrysosporium by calcium alginate. The typical absorption edge in visible light region for g-C₃N₄ was at about 460 nm, and the optical absorption bandgap of g-C₃N₄ was estimated to be 2.70 eV, demonstrating the great photoresponsive ability of g-C₃N₄. An optimized g-C₃N₄ content of 0.10 g in immobilized P. chrysosporium and an optimized immobilized P. chrysosporium dosage of 1.0 g were suitable for organic matters removal. The removal efficiency of total organic carbon (TOC) reached 74.99% in 72 h with the initial TOC concentration of 100 mg L^-1. In addition, the gas chromatography coupled with mass spectrometry (GC-MS) measurements showed that immobilized P. chrysosporium presented an outstanding removal performance for almost all organic compounds in landfill leachate, especially for the volatile fatty acids and long-chain hydrocarbons. The overall results indicate that the combination P. chrysosporium with photocatalyst g-C₃N₄ for organic matters removal from landfill leachate may provide a more comprehensive potential for the landfill leachate treatment.

A new route of bioaugmentation by allochthonous and autochthonous through biofilm bacteria for soluble chemical oxygen demand removal of old leachate

Landfill leachate contains environmental pollutants that are generally resistant to biodegradation. In this study, indigenous and exogenous bacteria in leachate were acclimated in both biofilm and suspension forms to increase the removal of soluble chemical oxygen demand (SCOD). The bacteria from the leachate and sewage were acclimated to gradually increasing leachate concentration prepared using a reverse osmosis membrane over 28 days. The SCOD removal was measured aerobically or nominally anaerobically. Biofilms were prepared using different carrier media (glass, rubber, and plastic). The maximum SCOD removal in suspensions was 32% (anaerobic) and in biofilms was 39% (aerobic). In the suspension form, SCOD removal using acclimated bacteria from leachate and sewage anaerobically increased in comparison with the control (P < .05). In the biofilm form, the aerobic condition and the use of acclimated bacteria from leachate and sewage increased the removal efficiency of SCOD in comparison with other biofilm groups (P < .05). Three species of bacteria, including Bacillus cereus, Bacillus subtilis, and Pseudomonas aeruginosa were identified in the biofilm from leachate and sewage. Bioaugmentation technology using biofilms and acclimations can be an effective, inexpensive, and simple way to decrease SCOD in old landfill leachate.

Treatment of landfill leachate using immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO₂ nanoparticles

This study investigated the performance of immobilized Phanerochaete chrysosporium loaded with nitrogen-doped TiO2 nanoparticles in the treatment of raw landfill leachate with a very low biodegradability ratio (BOD5/COD) of 0.09. The effects of various operating parameters, such as initial chemical oxygen demand (COD) concentration, pH, temperature, and biosorbent dosage, were evaluated with respect to the removal efficiency of total organic carbon (TOC) and ammonia nitrogen (NH3-N). For the immobilized biosorbents, an optimum pH of 6.0 for TOC and 7.0 for NH3-N were found suitable for TOC and NH3-N removal at temperature of 37°C, respectively. The most superior removal efficiencies of TOC and NH3-N of landfill leachate were over 75% and 74% in 72 h at an initial COD concentration of 200 mg L(-1), respectively. In addition, heavy metals were partly removed by the immobilized biosorbents during the process of landfill leachate treatment. The species and mass percentage of organic compounds in landfill leachate after the treatment were found to have considerably declined according to the gas chromatography coupled with mass spectrometry (GC-MS) system. These results indicate that the immobilized P. chrysosporium loaded with nitrogen-doped TiO2 nanoparticles could be a convenient and efficient method for the treatment of landfill leachate.