Mammalian cell line-based bioassays for toxicological evaluation of landfill leachate treated by Pseudomonas sp. ISTDF1

A comprehensive review on the use of conductive materials to improve anaerobic digestion: Focusing on landfill leachate treatment

Globally, around 70% of waste is disposed of in open dumps or landfill sites, with the leachate generated from these sites containing high concentrations of organic and inorganic compounds, which will adversely affect aquatic environments if discharged without proper treatment. Anaerobic digestion of landfill leachate is an environmentally-friendly method that efficiently converts organic compounds into methane-rich biogas. However, the widespread application of anaerobic digestion has been hindered by poor system stability, low methanogenic activity and a high level of volatile fatty acids (VFAs) accumulation, increasing the operational costs of treatment. Conductive materials can be added to the digester to improve the performance of anaerobic digestion in landfill leachate treatment systems and studies reporting the use of conductive materials for this purpose are hereby thoroughly reviewed. The mechanism of microbial growth and enrichment by conductive materials is discussed, as well as the subsequent effect on waste metabolism, methane production, syntrophic relationships and interspecies electron transfer. The porous structure, specific surface area and conductivity of conductive materials play vital roles in the facilitation of syntrophic relationships between fermentative bacteria and methanogenic archaea. In addition, the mediation of direct interspecies electron transfer (DIET) by conductive materials increases the methane content of biogas from 16% to 60% as compared to indirect interspecies electron transfer (IIET) in conventional anaerobic digestion systems. This review identifies research gaps in the field of material-amended anaerobic systems, suggesting future research directions including investigations into combined chemical-biological treatments for landfill leachate, microbial management using conductive materials for efficient pollutant removal and the capacity for material reuse. Moreover, findings of this review provide a reference for the efficient and large-scale treatment of landfill leachate by anaerobic digestion with conductive materials.

Biogeochemical profiling and taxonomic characterization of municipal landfill site by metagenomic sequencing

Most of the discarded waste material paves their way to the utmost common dumping grounds, Landfills. Despite their widespread use, the landfill microbiomes are still not well characterized. Metagenomics approach provides insight into the identification of operational parameters influencing the microbiome composition and their biodegradation competencies. The metagenomic DNA was prepared to explore taxonomical community structure, phylogenetic relationships, and functional profile at the same time. A total of 100,021,052 high-quality filtered reads were acquired with a GC abundance of 62.59%. Taxonomical abundance revealed the dominance of phylum Proteobacteria and genes involved in biomolecules metabolism, aromatic compound degradation, stress tolerance, xenobiotic biodegradation etc. were revealed functionally. The intricate heterogeneous environment of landfill revealed well flourished biogeochemical metabolic profiles including nitrogen metabolism. This is the first study for the generated metagenome of Ghazipur landfill and the obtained results propose that microbial communities in landfill settings are far more intricate than expected. It remain mostly unexplored which demands the usage of multiple platforms for a better understanding.

Environmental persistence, hazard, and mitigation challenges of nitroaromatic compounds

Nitroaromatic compounds (NACs) are extensively used in different industries and are synthesized in large quantity due to their heavy demand worldwide. The broad use of NACs poses a serious pollution threat. The treatment processes used for the removal of NACs are not effective and sustainable, leading to their release into the environment. The nitro group attached to benzene ring makes the compounds recalcitrant due to which they persist in the environment. Being hazardous to human as well as other living organisms, NACs are listed in the USEPA's priority pollutant group. This review provides updated information on the sources of NACs, prevalence in different environmental matrices, and recent developments in methods of their detection, with emphasis on current trends as well as future prospects. The harmful effects of NACs due to exposure through different routes are also highlighted. Further, the technologies reported for the treatment of NACs, including physico-chemical and biological methods, and the challenges faced for their effective implementation are discussed. Thus, the review discusses relevant issues in detail making suitable recommendations, which can be helpful in guiding further research in this subject.

A comprehensive review on enzymatic degradation of the organophosphate pesticide malathion in the environment

A comprehensive review of available bioremediation technologies for the pesticide malathion is presented. This review article describes the usage and consequences of malathion in the environment, along with a critical discussion on modes of metabolism of malathion as a sole source of carbon, phosphorus, and sulfur for bacteria, and fungi along with the biochemical and molecular aspects involved in its biodegradation. Additionally, the recent approaches of genetic engineering are discussed for the manipulation of important enzymes and microorganisms for enhanced malathion degradation along with the challenges that lie ahead.

Technologies applicable to the removal of heavy metals from landfill leachate

This article presents a review of the main physical, chemical, electrochemical, and biological technologies used for treating heavy metals in the wastewater of industrial processes and in synthetic aqueous solutions which could be applied to leachate from landfills. This paper outlines the generalities, operating principles, and modifications made to the technologies described. It discusses and assesses which of these have better removal rates and higher levels of efficiency in minimizing the heavy metal concentrations contained in leachates, such as mercury, chromium, lead, nickel, and copper among others. The first part of the document presents the so-called conventional technologies, such as chemical, physical, and electrochemical treatment. These have been used to treat different wastewater, especially industrial waste, operating adequately from the technical topic, but with high costs and the secondary products' production. The second part exposes biological treatments tend to be most widely used due to their versatility, effectiveness, and low cost, when compared with traditional technologies. It is important to note that there is no single treatment and that each of the technologies reviewed has different heavy metal decontamination rates. All technologies search to reduce concentrations of heavy metals to values that are safe for the natural resources where they are discharged or disposed, thereby complying with the regulatory limits regulated in each of the regions.

Investigating landfill leachate toxicity in vitro: A review of cell models and endpoints

Landfill leachate is a complex mixture characterized by high toxicity and able to contaminate soils and waters surrounding the dumpsite, especially in developing countries where engineered landfills are still rare. Leachate pollution can severely damage natural ecosystems and harm human health. Traditionally, the hazard assessment of leachate is based on physicochemical characterization but the toxicity is not considered. In the last few decades, different bioassays have been used to assess the toxicity of this complex matrix, including human-related in vitro models. This article reviews the cell bioassays successfully used for the risk assessment of leachate and to evaluate the efficiency of toxicity removal of several processes for detoxification of this wastewater. Articles from 2003 to 2018 are covered, focusing mainly on studies that used human cell lines, highlighting the usefulness and adequacy of in vitro models for assessing the hazard involved with exposure to leachate, particularly as an integrative supporting tool for chemical-based risk assessment. Leachate is generally toxic, mutagenic, genotoxic and estrogenic in vitro, and these effects can be measured in the cells exposed to already low concentrations, confirming the serious hazard of this wastewater for human health.

Denitrification of landfill leachate under different hydraulic retention time in a two-stage anoxic/oxic combined membrane bioreactor process: Performances and bacterial community

Two-stage anoxic/oxic combined membrane bioreactor (A/O-A/O-MBR) process was used to treat leachate generated from Shenyang Laohuchong landfill, and the effect of hydraulic retention time (HRT) was studied. A long HRT of 9 d and a short HRT of 5 d showed negative effect on the stability of process, resulting in a higher organic concentration of effluent than that with a HRT of 7 d, while the highest removal of chemical oxygen demand (COD), ammonia (NH₄⁺-N) and total nitrogen (TN) were achieved with a HRT of 7 d, which was 82.4%, 99.1% and 75.3% respectively. The analysis of microbial communities by high-throughput sequencing showed that phyla Proteobacteria and Bacteroidetes were the dominant bacteria, which accounted for 36.63-42.39%, 29.21-38.66%, respectively. For genus classification, the most representative of Ferruginibacter, unclassified-Saprospiraceae and Nitrosomonas accounted for 20.76-35.11% totally. The other communities, including Nitrobacter, Planctomyces, Rhodobacteraceae and Nitrospirae, were also developed for organic degradation and denitrification.

Advanced treatment of landfill leachate membrane concentrates: performance comparison, biosafety and toxic residue analysis

With the improvement of people's consciousness about health, more attention has been paid to the biosafety of effluent reaching conventional discharge standard. In this contribution, removal efficiency of chemical oxygen demand (COD), acute toxicity, genotoxicity and estrogenicity in landfill leachate membrane concentrates (MCs) among UV-Fenton, Fenton and activated carbon adsorption process were compared. Daphnia magna acute toxicity assay, comet assay, cytokinesis-block micronucleus and E-screen assay were performed to assess whether the effluent reaching the main parameters of Chinese Discharge Standard (GB 16889-2008) still had toxic residues. Under the conditions that COD of effluents treated by the three processes were up to the discharge standard, no obvious toxic residue was found in the effluent of UV-Fenton treatment, but effluent from Fenton or activated carbon adsorption process showed genotoxicity or estrogenicity to some extent. Dynamic analysis of UV-Fenton degradation process for estrogen simulation solutions was also conducted, and the formation of intermediates was detected by gas chromatography-mass spectrometry (GC/MS). Toxic residues might be caused by the lack of treatment duration and the formation of more toxic intermediates. UV-Fenton was found to be efficient for the treatment of MCs. Biosafety should be concerned when a new wastewater discharge standard is being established.

Two-stage anoxic/oxic combined membrane bioreactor system for landfill leachate treatment: Pollutant removal performances and microbial community

In this study, a laboratory-scale two-stage anoxic/oxic (A/O) combined membrane bioreactor (MBR) was operated for 113d for the treatment of landfill leachate. The average removal of chemical oxygen demand (COD), ammonia (NH₄⁺-N) and total nitrogen (TN) achieved 80.60%, 99.04% and 74.87%, respectively. A mass balance evaluation suggested that the removal of COD, NH₄⁺-N and TN occurred mainly in the second A/O process, and the total removal capacity of COD, NH₄⁺-N and TN were 125.60g/d, 24.35g/d and 22.40g/d, respectively. High-throughput sequencing analysis indicated that the Proteobacteria (44.57-50.36%), Bacteroidetes (22.09-27.25%), Planctomycetes (6.94-8.47%), Firmicutes (3.31-4.53%) and Chloroflexi (3.13-4.80%) were the dominated phyla in the bacterial community during the operation period. At the genus level, Nitrosomonas, Nitrobacter, Planctomyces, Saprospiraceae and Pseudomonas showed relatively high abundance, which played an important role in the removal of pollutants.

An integrated approach to study the risk from landfill soil of Delhi: Chemical analyses, in vitro assays and human risk assessment

In the present study, landfill soil of three municipal solid waste landfill sites of Delhi, India were toxico-chemically analyzed for human risk assessment as inadequate information is available on the possible health effects of the contaminants present in landfill soil. The landfill soil samples were prepared for analyzing heavy metal concentration, organic contaminants and toxicity analysis separately. Composite soil sample collected from three landfill sites were analyzed for heavy metal by ICP-AES. Metal concentration so obtained was below the permissible limit of soil but higher than the set limits for effluent. Some of the persistent organic contaminants like phthalates, benzene derivatives, halogenated aliphatic compounds and PAHs derivatives were detected by scan mode GC-MS. Further, concentration of 17 polycyclic aromatic hydrocarbons (PAHs) in landfill soil of Delhi was evaluated by selective ion monitoring GC-MS in order to ascertain their contamination levels and potential health risk. The concentration of total PAHs in the samples ranged from 192 to 348µg/kg. The maximum concentrations of PAHs were found in Ghazipur landfill site followed by Okhla and Bhalswa landfills. Cancer risk (CR) values of sampling sites were within the acceptable range for adults, adolescents and children (both male and female) suggesting that PAHs present in landfill soil are unlikely to pose any cancer risk for population based on dermal contact, ingestion and inhalation exposure pathways. However, landfill soil organic extract showed significant cytotoxic and genotoxic effects on HepG2 cell line as revealed by MTT and Comet assays respectively. The observed MTT EC₅₀ values ranged from 7.58 to 12.9g SedEq/Lalong with statistically significant DNA damage. Thus, although the soil organic extract contained low concentrations of PAHs with negligible carcinogenic potential, but the mixture of organic pollutants present in soil were found to be toxic enough to affect human health due to their synergistic or additive actions.

Biosorption of landfill leachate by Phanerochaete sp. ISTL01: isotherms, kinetics and toxicological assessment

The study investigates the ability of fungus Phanerochaete sp. ISTL01 for biosorption of color from landfill leachate. Batch mode experiments were conducted to study the effects of pH, temperature, adsorbent dose, contact time and initial leachate concentration on biosorption. Maximum biosorption capacity was determined as 17.73 mg g^-1 of biomass. Equilibrium isotherms and kinetics were further studied. The biosorption data were found to fit well to the Freundlich isotherm and pseudo-second-order kinetic model. The value of activation energy suggested that chemisorption mechanism was involved. Biosorption efficiency was also evaluated by the Methyltetrazolium (MTT) assay for cytotoxicity and alkaline comet assay in HepG2 human hepato-carcinoma cells. The fungus reduced toxicity as shown by 1.3-fold increase in MTT EC₅₀ and 1.5- and 1.1-fold reduction in Tail moment and Olive tail moment, respectively, after 12 h biosorption. The fungus showed good biosorption characteristics in terms of contaminant-level reduction per unit mass of adsorbent, process kinetics and toxicity reduction, envisaging its application in leachate treatment.

Bioassays for toxicological risk assessment of landfill leachate: A review

Landfilling is the most common solid waste management practice. However, there exist a potential environmental risk to the surface and ground waters due to the possible leaching of contaminants from the landfill leachates. Current municipal solid waste landfill regulatory approaches consider physicochemical characterization of the leachate and do not assess their potential toxicity. However, assessment of toxic effects of the leachates using rapid, sensitive and cost-effective biological assays is more useful in assessing the risks as they measure the overall toxicity of the chemicals in the leachate. Nevertheless, more research is needed to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants in order to evaluate leachate toxicity. There is a need for a multispecies approach using organisms representing different trophic levels so as to understand the potential impacts of leachate on different trophic organisms. The article reviews different bioassays available for assessing the hazard posed by landfill leachates. From the review it appears that there is a need for a multispecies approach to evaluate leachate toxicity.

Evaluation of toxicity and estrogenicity of the landfill-concentrated leachate during advanced oxidation treatment: chemical analyses and bioanalytical tools

Landfill-concentrated leachate from membrane separation processes is a potential pollution source for the surroundings. In this study, the toxicity and estrogenicity potentials of concentrated leachate prior to and during UV-Fenton and Fenton treatments were assessed by a combination of chemical (di (2-ethylhexyl) phthalate and dibutyl phthalate were chosen as targets) and biological (Daphnia magna, Chlorella vulgaris, and E-screen assay) analyses. Removal efficiencies of measured di (2-ethylhexyl) phthalate and dibutyl phthalate were more than 97 % after treatment with the two methods. Biological tests showed acute toxicity effects on D. magna tests in untreated concentrated leachate samples, whereas acute toxicity on C. vulgaris tests was not observed. Both treatment methods were found to be efficient in reducing acute toxicity effects on D. magna tests. The E-screen test showed concentrated leachate had significant estrogenicity, UV-Fenton and Fenton treatment, especially the former, were effective methods for reducing estrogenicity of concentrated leachate. The EEQchem (estradiol equivalent concentration) of all samples could only explain 0.218-5.31 % range of the EEQbio. These results showed that UV-Fenton reagent could be considered as a suitable method for treatment of concentrated leachate, and the importance of the application of an integrated (biological + chemical) analytical approach for a comprehensive evaluation of treatment suitability.

Landfill leachate treatment using bacto-algal co-culture: An integrated approach using chemical analyses and toxicological assessment

The present study aims to evaluate the feasibility of leachate treatment using a synergistic approach by microalgae and bacteria. Leachate from one of the landfill of Northern India showed the presence of various toxic organic contaminants like naphthalene, benzene, phenol and their derivatives, napthols, pesticides, epoxides, phthalates and halogenated organic compounds. ICP-AES analysis revealed high concentrations of Zn, Cr, Fe, Ni, and Pb beyond the maximum permissible limit of discharge. Bacto-algal co-culture was found to be the most efficient in removal of toxic organic contaminants and heavy metals. Further, detoxification efficiency of bacto-algal treatment was evaluated by Methyl tetrazolium (MTT) assay for cytotoxicity and alkaline comet assay for genotoxicity using hepatoma HepG2 cells. Reduction in toxicity was confirmed by an increase in LC50 by 1.9 fold and reduction in Olive Tail Moment by 40.6 fold after 10 days of treatment. Results of the study indicate bioremediation and detoxification potency of bacto-algal co-culture for leachate treatment.

Ipomoea hederifolia rooted soil bed and Ipomoea aquatica rhizofiltration coupled phytoreactors for efficient treatment of textile wastewater

Ipomoea aquatica, a macrophyte was found to degrade a highly sulfonated and diazo textile dye Brown 5R up to 94% within 72 h at a concentration of 200 mg L(-1). Induction in the activities of enzymes such as azoreductase, lignin peroxidase, laccase, DCIP reductase, tyrosinase, veratryl alcohol oxidase, catalase and superoxide dismutase was observed in leaf and root tissue in response to Brown 5R exposure. There was significant reduction in contents of chlorophyll a (25%), chlorophyll b (17%) and carotenoids (30%) in the leaves of plants. HPLC, FTIR, UV-vis spectrophotometric and HPTLC analyses confirmed the biotransformation and removal of parent dye from solution. Enzymes activities and GC-MS analysis of degradation products lead to the proposal of a possible pathway of phytotransformation of dye. The proposed pathway of dye metabolism revealed the formation of Napthalene-1,2-diamine and methylbenzene. Toxicity study on HepG2 cell lines showed a 3 fold decrease in toxicity of Brown 5R after phytoremediation by I. aquatica. Hydrophytic nature of I. aquatica leads to its exploration in a combinatorial phytoreactor with Ipomoea hederifolia soil bed system. Rhizofiltration with I. aquatica and soil bed treatment by I. hederifolia treated 510 L of effluent effectively within 72 h. I. aquatica along with I. hederifolia could decolorize textile industry effluent within 72 h of treatment as evident from the significant reductions in the values of COD, BOD, solids and ADMI. Further on field trials of treatment of textile wastewater was successfully carried out in a constructed lagoon.

Genotoxicity assessment of membrane concentrates of landfill leachate treated with Fenton reagent and UV-Fenton reagent using human hepatoma cell line

Membrane concentrates of landfill leachates contain organic and inorganic contaminants that could be highly toxic and carcinogenic. In this paper, the genotoxicity of membrane concentrates before and after Fenton and UV-Fenton reagent was assessed. The cytotoxicity and genotoxicity was determined by using the methods of methyltetrazolium (MTT), cytokinesis-block micronucleus (CBMN) and comet assay in human hepatoma cells. MTT assay showed a cytotoxicity of 75% after 24h of exposure to the highest tested concentration of untreated concentrates, and no cytotoxocity for UV-Fenton and Fenton treated concentrates. Both CBMN and comet assays showed increased levels of genotoxicity in cells exposed to untreated concentrates, compared to those occurred in cells exposed to UV-Fenton and Fenton reagent treated concentrates. There was no significant difference between negative control and UV-Fenton treated concentrates for micronucleus and comet assay parameters. UV-Fenton and Fenton treatment, especially the former, were effective methods for degradation of bisphenol A and nonylphenol in concentrates. These findings showed UV-Fenton and Fenton reaction were effective methods for treatment of such complex concentrates, UV-Fenton reagent provided toxicological safety of the treated effluent, and the genotoxicity assays were found to be feasible tools for assessment of toxicity risks of complex concentrates.

Combined chemical and toxicological evaluation of leachate from municipal solid waste landfill sites of Delhi, India

In the present study, landfill leachate of three landfill sites of Delhi, India, was toxico-chemically analyzed for human risk assessment. Raw leachate samples were collected from the municipal solid waste (MSW) landfills of Delhi lacking liner systems. Samples were characterized with relatively low concentrations of heavy metals while the organic component exceeded the upper permissible limit by up to 158 times. Qualitative analysis showed the presence of numerous xenobiotics belonging to the group of halogenated aliphatic and aromatic compounds, polycyclic aromatic hydrocarbons (PAHs), phthalate esters, and other emerging contaminants. Quantitative analysis of PAHs showed that the benzo(a)pyrene-toxic equivalence quotient (BaP-TEQ) ranged from 41.22 to 285.557 ng L(-1). The human risk assessment methodology employed to evaluate the potential adverse effects of PAHs showed that the cancer risk level was lower than the designated acceptable risk of 10(-6). However, significant cytotoxic and genotoxic effects of leachates on HepG2 cell line was observed with MTT EC50 value ranging from 11.58 to 20.44 % and statistically significant DNA damage. Thus, although the leachates contained low concentrations of PAHs with proven carcinogenic potential, but the mixture of contaminants present in leachates are toxic enough to cause synergistic or additive cytotoxicity and genotoxicity and affect human health.

Enhanced removal of COD and color from landfill leachate in a sequential bioreactor

In the present study, a sequential treatment process was carried out using a fungal sp. (Phanerochaete sp.) followed by a bacterial sp. (Pseudomonas sp.) for the degradation and detoxification of contaminants in landfill leachate. The process was optimized using Box-Behnken design (BBD) and response surface methodology (RSM) for three variables (C source, N source and duration), while monitoring two responses (% COD and color removal). After treatment in a bioreactor under optimized conditions, enhanced removal of COD (76.9%) and color (45.4%) was observed. Further, GC-MS analysis of metabolites detected at different stages of treatment showed formation of degradation products of lignin and polycyclic aromatic compounds. Treatment efficiency was finally evaluated by the alkaline comet assay in HepG2 human hepato-carcinoma cells. The results indicated no statistically significant DNA damage at the end of the treatment, making the effluent suitable to be discharged conforming to the safety standards.