Evaluation of Cajanus cajan (pigeon pea) for phytoremediation of landfill leachate containing chromium and lead

Global perspective of municipal solid waste and landfill leachate: generation, composition, eco-toxicity, and sustainable management strategies

Globally, more than 2 billion tonnes of municipal solid waste (MSW) are generated each year, with that amount anticipated to reach around 3.5 billion tonnes by 2050. On a worldwide scale, food and green waste contribute the major proportion of MSW, which accounts for 44% of global waste, followed by recycling waste (38%), which includes plastic, glass, cardboard, and paper, and 18% of other materials. Population growth, urbanization, and industrial expansion are the principal drivers of the ever-increasing production of MSW across the world. Among the different practices employed for the management of waste, landfill disposal has been the most popular and easiest method across the world. Waste management practices differ significantly depending on the income level. In high-income nations, only 2% of waste is dumped, whereas in low-income nations, approximately 93% of waste is burned or dumped. However, the unscientific disposal of waste in landfills causes the generation of gases, heat, and leachate and results in a variety of ecotoxicological problems, including global warming, water pollution, fire hazards, and health effects that are hazardous to both the environment and public health. Therefore, sustainable management of MSW and landfill leachate is critical, necessitating the use of more advanced techniques to lessen waste production and maximize recycling to assure environmental sustainability. The present review provides an updated overview of the global perspective of municipal waste generation, composition, landfill heat and leachate formation, and ecotoxicological effects, and also discusses integrated-waste management approaches for the sustainable management of municipal waste and landfill leachate.

Assessment of PGP traits of Bacillus cereus NDRMN001 and its influence on Cajanus cajan (L.) Millsp. phytoremediation potential on metal-polluted soil under controlled conditions

The current study looked at the plant growth-promoting (PGP) traits of the pre-isolated and metal-tolerant Bacillus cereus NDRMN001 as well as their stimulatory effect on the physiology, biomolecule content, and phytoremediation potential of Cajanus cajan (L.) Millsp. on metal-polluted soil. The bauxite mine, which is surrounded by farmland (1 km away), has been severely polluted by metals such as Cd (31.24 ± 1.68), Zn (769.57 ± 3.46), Pb (326.85 ± 3.43), Mn (2519.6 ± 5.71), and Cr (302.34 ± 1.62 mg kg^-1) that exceeded Indian standards. The metal-tolerant B. cereus NDRMN001 had excellent PGP activities such as synthesis of hydrogen cyanide (HCN), siderophore, indole acetic acid (IAA), N₂ fixation, and P solubilization. Furthermore, the optimal growth conditions (temperature of 30°C, pH 6.5, 6% glucose, 9% tryptophan, and 1.5% tricalcium phosphate) for effective synthesis and expression of PGP traits in B. cereus NDRMN001 were determined. Such metal-tolerant B. cereus NDRMN001 traits can significantly reduce metals in polluted soil, and their PGP traits significantly improve plant growth in polluted soil. Hence, this strain (B. cereus NDRMN001) significantly improved the growth and phytoremediation potential of C. cajan (L.) Millsp on metal-polluted soil without [study I: 2 kg of sieved and autoclaved metal-polluted soil seeded with bacterium-free C. cajan (L.) Millsp. seeds] and with [study II: 2 kg of sieved and autoclaved metal-polluted soil seeded with B. cereus NDRMN001-coated C. cajan (L.) Millsp. seeds] B. cereus NDRMN001 amalgamation. Fertile soil was used as control. The physiological parameters, biomolecule contents, and the phytoremediation (Cr: 7.74, Cd: 12.15, Zn: 16.72, Pb: 11.47, and Mn: 14.52 mg g^-1) potential of C. cajan (L.) Millsp. were significantly effective in study II due to the metal-solubilizing and PGP traits of B. cereus NDRMN001. These results conclude that the test bacteria B. cereus NDRMN001 considerably improved the phytoremediation competence of C. cajan (L.) Millsp. on metal-polluted soil in a greenhouse study.

Response of Cajanus cajan to excess copper in the soil: tolerance and biomass production

Soil contamination by excess heavy metals or trace elements is a global concern, as these elements are highly bioaccumulated in living organisms, migrating throughout the food chain, and causing health problems. Sustainable technologies, using plants, have been increasingly studied and used to contain, reduce, or extract these elements from the soil. In this sense, it is essential to identify plant species that tolerate certain elements, present high biomass production and are resistant to adverse soil conditions. For this reason, we evaluated the biomass production and tolerance of Cajanus cajan in response to different concentrations of copper (30, 60, 120, and 240 mg/dm³, in addition to the control treatment) in the soil, as well as the effect of this metal on photosynthetic pigments and gas exchange. C. cajan was sown in soil previously contaminated with copper sulfate and cultivated in a greenhouse for 60 days after emergence. C. cajan is copper tolerant, approximately 88% copper is accumulated in the roots and therefore there is low copper translocation to the shoot, consequently, the chlorophyll content, the net photosynthesis rate, carbon assimilation, dry biomass, the root system development, and nodulation were not affected by copper. C. cajan can be explored in strategies to improve soil conditions and is a promising species in soil phytoremediation studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01203-6.

Adsorption and enrichment of U in a cellulase-producing Trichoderma sp. and its physiological response mechanism

The cellulase produced by Trichoderma sp. was characterized by investigating the adsorption and enrichment of U and the physiological response to U exposure. The effects of U exposure (0 and 400 μM) on the growth, morphological characteristics, cellulase production, U adsorption, and U enrichment capacity of the Trichoderma strain were assessed. The effects of U exposure on the basic metabolism of this fungus were also analyzed by non-targeted metabolomics. Exposure to U (400 μM) for 24 h resulted in OD₆₀₀ turbidity of 0.278, and activities of carboxymethyl cellulase (CMC), filter paper enzyme (FPA), and β-glucosidase of 12834 U·mL^-1, 9285 U·mL^-1, and 12574 U·mL^-1, respectively. The measurement of the background α and β radioactivity showed an α activity concentration of 3.35 × 10⁶ Bq·kg^-1 in the fungus, a β activity concentration of 6.28 × 10⁵ Bq·kg^-1, and a U enrichment rate of 70.4 ± 4.5%. GC-MS metabolomics analysis identified a total of 319 metabolites (34 up-regulated and 30 down-regulated), which mainly caused the metabolic imbalance of organic acids and derivatives. The alanine, aspartate, and glutamate metabolic pathways were the most significantly enriched. Trichoderma sp. therefore has a strong ability to tolerate/accumulate U and continues to produce cellulase under U (400 μM) exposure. However, U interferes with the basic metabolism of this fungus.

Overview of Approaches to Improve Rhizoremediation of Petroleum Hydrocarbon-Contaminated Soils

Soil contamination with petroleum hydrocarbons (PHCs) has become a global concern and has resulted from the intensification of industrial activities. This has created a serious environmental issue; therefore, there is a need to find solutions, including application of efficient remediation technologies or improvement of current techniques. Rhizoremediation is a green technology that has received global attention as a cost-effective and possibly efficient remediation technique for PHC-polluted soil. Rhizoremediation refers to the use of plants and their associated microbiota to clean up contaminated soils, where plant roots stimulate soil microbes to mineralize organic contaminants to H2O and CO2. However, this multipartite interaction is complicated because many biotic and abiotic factors can influence microbial processes in the soil, making the efficiency of rhizoremediation unpredictable. This review reports the current knowledge of rhizoremediation approaches that can accelerate the remediation of PHC-contaminated soil. Recent approaches discussed in this review include (1) selecting plants with desired characteristics suitable for rhizoremediation; (2) exploiting and manipulating the plant microbiome by using inoculants containing plant growth-promoting rhizobacteria (PGPR) or hydrocarbon-degrading microbes, or a combination of both types of organisms; (3) enhancing the understanding of how the host–plant assembles a beneficial microbiome, and how it functions, under pollutant stress. A better understanding of plant–microbiome interactions could lead to successful use of rhizoremediation for PHC-contaminated soil in the future.

Effect of hexavalent chromium on the environment and removal techniques: A review

Despite the importance of chromium (Cr) in most anthropogenic activities, the subsequent environmental adulteration is now a source of major concern. Cr occurs in numerous oxidation states, with the furthermost stable and frequently occur states being Cr(0), Cr(III) and Cr(VI). Cr(0) and Cr(III) are vital trace elements while Cr(VI) is dispensable and noxious to living organisms. Predominantly in plants, Cr at low concentrations of about 0.05-1 mg/L assist to boost growth as well as increase productivity. However, accumulation of Cr could represent a potential threat to living organisms. Cr absorption, displacement and accretion depend on its speciation, which also determines its toxicity which is often diverse. Indications of its toxicity include; reduction of seed germination, retardation of growth, reduction of yield, inhibition of enzymatic activities, weakening of photosynthesis, nutrient, oxidative disparities and genetic mutation in plants as well as several injurious diseases in animals and humans. In this study, we have presented a comprehensive review as well as an informative account of the influence of Cr on the environment drawn from researches carried out over the years following an analytical approach. Uniquely, this work presents a review of the effects and remediation of Cr from soil and wastewater drawn from several evidence and meta-data-based articles and other publications. Accordingly, the write-up is intended to appeal to the consciousness of the general public that the significance of Cr notwithstanding, its environmental toxicity should not be taken for granted.

Bioremediation potential of new cadmium, chromium, and nickel-resistant bacteria isolated from tropical agricultural soil

Soil management using fertilizers can modify soil chemical, biochemical and biological properties, including the concentration of trace-elements as cadmium (Cd), chromium (Cd) and nickel (Ni). Bacterial isolates from Cd, Cr, and Ni-contaminated soil were evaluated for some characteristics for their use in bioremediation. Isolates (592) were obtained from soil samples (19) of three areas used in three maize cultivation systems: no-tillage and conventional tillage with the application of mineral fertilizers; minimum tillage with the application of sewage sludge. Four isolates were resistant to Cr³⁺ (3.06 mmol dm^-3) and Cd²⁺ (2.92 mmol dm^-3). One isolate was resistant to the three metals at 0.95 mmol dm^-3. All isolates developed in a medium of Cd²⁺, Cr³⁺ and Ni²⁺ at 0.5 mmol dm^-3, and removed Cd²⁺ (17-33%) and Cr⁶⁺ (60-70%). They were identified by sequencing of the gene 16S rRNA, as bacteria of the genera Paenibacillus, Burkholderia, Ensifer, and two Cupriavidus. One of the Cupriavidus isolate was able to remove 60% of Cr⁶⁺ from the culture medium and showed high indole acetic acid production capacity. We evaluated it in a microbe-plant system that could potentially be deployed in bioremediation by removing toxic metals from contaminated soil.

Heavy metal intake and health risk implications from consumption of dried pulses in Trinidad and Tobago, W.I

The increase in urbanisation and industrialisation have contributed significantly to elevated concentrations of heavy metals in soils. The eventual uptake of heavy metals by agronomic crops could potentially affect human health based on consumption patterns in various regions of the globe. This study investigated the potential health risks to consumers of dried legumes in a small island developing state that rely primarily on the importation of those crops from major producers. Several varieties were analysed for selected heavy metals in which Cd and Pb were not detected and Cr was only present in certain legumes. The concentrations of Cu, Mn, Ni, and Zn were all below the established World Health Organisation (WHO) maximum permissible limit (MPL) and the target hazard quotient (THQ) and hazard index (HI) values were below one for all samples, suggesting no non-carcinogenic risk to consumers.

Phytoremediatory efficiency of Chrysopogon zizanioides in the treatment of landfill leachate: a case study

A common approach for waste management is their disposal in landfills, which is usually associated with the production of dangerous gases and of liquid leachate. Due to its toxicity, polluted liquid negatively impacts on the environment with the possible contamination of large volumes of soil, groundwater, and surface water. Leachate remediation is therefore subject of intensive research, and phytoremediation has been achieving increasing interest in recent decades. We describe here the suitability of vetiver grass for the remediation of two leachates collected in urban landfills of northern Italy, characterized by different composition. Our objective was measuring the accumulation/tolerance potential of this species and the evapotranspiration ability in a pot experiment, to evaluate applicability of vetiver plants for the reduction and decontamination of landfill leachate. Plants were grown for 4 months in pots with a zeolite growth bed and watered with either tap water (control) or undiluted landfill leachate. Plant growth and fitness and elemental content in shoots and roots were evaluated at the end of the experiment. In these experimental conditions, the high bioaccumulation of metals highlights the suitability of this species for its employment in phytoremediation; however, vetiver growth under leachate treatment was strongly dependent on leachate composition, making a case-to-case evaluation of plant tolerance necessary before large-scale application.

Comparing storage battery and solar cell in assisting Eucalyptus Globulus to phytoremediate soil polluted by Cd, Pb, and Cu

Metal decontamination and leaching alleviation capacity of Eucalyptus globulus with and without electric field were investigated using ICP-MS. The biomass production of the chosen plant increased from 0.87 kg in planting control without electrokinetic treatment to 1.16 and 1.42 kg in experiments with electric field supplied by storage battery and solar cell, respectively. Under the influence of electric field with a voltage of 6.5 V, significantly more Cd, Pb and Cu were extracted by the species. Precipitation simulation was performed to evaluate the capacity of battery and solar panel to intercept leaching. The total volume of leachate gathered from the control decreased from 1012 mL to 299 and 336 mL in containers treated by storage battery and solar cell, respectively. In addition to reduction of leachate, the leaching mass of Cd, Pb and Cu was decreased significantly by electric fields (both battery and solar cell) treatments. The effect of remediation and environmental risk alleviation by solar cell was comparable with storage battery, at least during the 30-day experimental period. On the basis of the present study, solar cell should be a suitable substitute for conventional power supply to improve metal polluted soil when considering phytoremediation efficiency and energy consumption.

Heavy metals uptake on Malpighia emarginata D.C. seed fiber microparticles: Physicochemical characterization, modeling and application in landfill leachate

Environmental heavy-metals contamination is a worldwide concern and the treatment of their sources constitutes a sustainable and efficient alternative. This work investigated the performance of Malpighia emarginataD.C. seed fibers microparticles (Me-SFMp) as biosorption platform for heavy metal ions. Integrated physicochemical analyses (FAAS, FTIR, SEM/EDS and XRF) showed that such ability was associated with the high microstructural porosity, wide surface area and diversity of functional groups on Me-SFMp structures, which favored the high and fast uptake of the target-substances (Cd, Zn, Cr, Pb, Cu and Ni ions). In terms of reactional kinetics, the pseudo-second order model showed better data correlation (R² from 0.9992 to 0.9998) and suggested the chemisorption as limiting step of the reaction mechanisms. From the Langmuir isotherms (R² from 0.9993 to 0.9998), it was observed that these phenomena occurred non-linearly on a homogeneous biosorbent monolayer. Me-SFMp can also be reused after desorption processes conducted in acid medium and, under ideal conditions (0.8 g biosorbent dosage; 100 mL of 1.00 mg L^-1 multi-metal solution adjusted to pH = 8.0; 300 rpm stirring speed; and 60 min contact time), the following maximum removal percentages order was observed for the first cycle: Cd (100%) = Zn (100%) > Cr (95.1%) > Pb (86.8%) > Cu (84.2%) > Ni (81.0%). The procedure was successfully applied to remove the studied heavy metal ions from raw landfill leachate, even in the presence of several (in)organic interferers, reinforcing the strong biosorbent-adsorbate interaction and the viability of this proposal.

Chromium tolerance, bioaccumulation and localization in plants: An overview

In the current industrial scenario, chromium (Cr) as a metal is of great importance, but poses a major threat to the environment. Phytoremediation provides an environmentally sustainable, ecofriendly, cost effective approach for environmental cleanup of Cr. This review presents the current status of phytoremediation research with particular emphasis on cleanup of Cr contaminated soil and water systems. It gives a detailed account of the work done by different authors on the Cr bioavailability, uptake pathway, toxicity and storage in plants following the phytoextraction mechanism. This paper also describes recent findings related to Cr localization in hyperaccumulator plants. It gives an insight into the processes and mechanisms that allow plants to remove Cr from contaminated sites under varying conditions. These detailed knowledge of changes in plant metabolic pool in response to Cr stress would immensely help understand and improve the phytoextraction process. Further, this review provides a detailed understanding of Cr uptake and detoxification mechanism by plants that can be applied in developing a suitable approach for a better applicability of the process.