Heavy metal pollution remains a global environmental challenge that poses a significant threat to human life. Various methods have been explored to eliminate heavy metal pollutants from the environment. However, most methods are constrained by high expenses, processing duration, geological problems, and political issues. The immobilization of metals, phytoextraction, and biological methods have proven practical in treating metal contaminants from the soil. This review focuses on the general status of heavy metal contamination of soils, including the excessive heavy metal concentrations in crops. The assessment of the recent advanced technologies and future challenges were reviewed. Molecular and genetic mechanisms that allow microbes and plants to collect and tolerate heavy metals were elaborated. Tremendous efforts to remediate contaminated soils have generated several challenges, including the need for remediation methodologies, degrees of soil contamination, site conditions, widespread adoptions and various possibilities occurring at different stages of remediation are discussed in detail.
The decolorization and degradation of Direct Blue 71 were investigated using a mono culture of Pseudomonas aeruginosa. The bacterium was able to decolorize the dye medium to 70.43 % within 48 h under microaerophilic conditions. The medium was then aerated for 24 h to promote the biodegradation of the aromatic amines generated from azo bond cleavage. Reduction in total organic carbon in dye medium was 42.58 % in the microaerophilic stage and 78.39 % in the aerobic stage. The degradation metabolites formed were studied using UV-vis techniques, high performance liquid chromatography, Fourier transform infra red spectroscopy and nuclear magnetic resonance spectroscopy analysis. Data obtained provide evidence for the formation of aromatic amines and their subsequent oxidative biodegradation by a single strain of P. aeruginosa during successive microaerophilic/aerobic stages in the same flask. The influence of incubation temperature (20-45 °C), medium pH (5-10) and initial dye concentration (25-150 mg/L) on decolorization was evaluated to greatly influence decolorization extent. The optimal decolorization conditions were determined by response surface methodology based on three-variable central composite design to obtain maximum decolorization and to determine the significance and interaction effect of the variables on decolorization. The optimal conditions of response were found to be 35.15 °C, pH 8.01 and 49.95 mg/L dye concentration giving an experimental decolorization value of 84.80 %. Very high regression coefficient between the variables and the response (R(2) = 0.9624) indicated a good evaluation of experimental data by polynomial regression model.
The herbicide glyphosate is often used to control weeds in agricultural lands. However, despite its ability to effectively kill weeds at low cost, health problems are still reported due to its toxicity level. The removal of glyphosate from the environment is usually done by microbiological process since chemical process of degradation is ineffective due to the presence of highly stable bonds. Therefore, finding glyphosate-degrading microorganisms in the soil of interest is crucial to remediate this glyphosate.Burkholderia vietnamiensisstrain AQ5-12 was found to have glyphosate-degrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time (OFAT) and response surface methodology (RSM). Five parameters including carbon and nitrogen source, pH, temperature and glyphosate concentration were optimised. Based on OFAT result, glyphosate degradation was observed to be optimum at fructose concentration of 6, 0.5 g/L ammonia sulphate, pH 6.5, temperature of 32 °C and glyphosate concentration at 100 ppm. Meanwhile, RSM resulted in a better degradation with 92.32% of 100 ppm glyphosate compared to OFAT. The bacterium was seen to tolerate up to 500 ppm glyphosate while increasing concentration results in reduced degradation and bacterial growth rate.
The isolate Coriolopsis sp. (1c3) was cultured on muslin cloth to induce formation of filamentous biofilm. The biofilm and the free-mycelium forms (control) were then used to treat two triphenylmethane dyes; Cotton Blue (CB) and Crystal Violet (CV). The biofilm comprised primarily of a compact mass of mycelium while sparse mycelium network was detected in free-mycelium forms. Results revealed significant decolourization activities by filamentous biofilm of 1c3 for CB (79.6%) and CV (85.1%), compared to free-mycelium forms (72.6 and 58.3%, for CB and CV, respectively). Biodegradation occurred in both biofilm and free-mycelium forms. FTIR spectra revealed that biofilm formation (stacking of mycelium), did not have severe implications to the number and types of functional groups available for dye biosorption. The findings here suggested that formation of biofilm in 1c3 was induced effectively on muslin cloth, leading to enhanced decolourization activities. This technology is simple, feasible and can be adopted and further improved to obtain biofilm to enhance their dye removal efficiency in aqueous solutions.
Vast amounts of plastic waste are causing serious environmental issues and urge to develop of new remediation methods. The aim of the study is to determine the role of inorganic (nitric acid), organic (starch addition), and biological (Pseudomonas aeruginosa) soil amendments on the degradation of Polyethylene (PE) and phytotoxic assessment for the growth of lettuce plant. The PE-degrading bacteria were isolated from the plastic-contaminated soil. The strain was identified as Pseudomonas aeruginosa (OP007126) and showed the highest degradation percentage for PE. PE was pre-treated with nitric acid as well as starch and incubated in the soil, whereas P. aeruginosa was also inoculated in PE-contaminated soils. Different combinations were also tested. FTIR analysis and weight reduction showed that though nitric acid was efficient in degradation, the combined application of starch and bacteria also showed effective degradation of PE. Phytotoxicity was assessed using morphological, physiological, and biochemical parameters of plant. Untreated PE significantly affected plants' physiology, resulting in a 45% reduction in leaf chlorophyll and a 40% reduction in relative water content. It also had adverse effects on the biochemical parameters of lettuce. Bacterial inoculation and starch treatment mitigated the harmful impact of stress and improved plants' growth as well as physiological and biochemical parameters; however, the nitric treatment proved phytotoxic. The observed results revealed that bacteria and starch could be effectively used for the degradation of pre-treated PE.
Greenhouse experiments were carried out to determine the phytotoxic effects on the plant Ludwigia octovalvis in order to assess its applicability for phytoremediation gasoline-contaminated soils. Using plants to degrade hydrocarbons is a challenging task. In this study, different spiked concentrations of hydrocarbons in soil (1, 2, and 3 g/kg) were tested. The results showed that the mean efficiency of total petroleum hydrocarbon (TPH) removal over a 72-day culture period was rather high. The maximum removal of 79.8 % occurred for the 2 g/kg concentration, while the removal rate by the corresponding unplanted controls was only (48.6 %). The impact of gasoline on plants included visual symptoms of stress, yellowing, growth reduction, and perturbations in the developmental parameters. The dry weight and wet weight of the plant slightly increased upon exposure to gasoline until day 42. Scanning electron microscopy (SEM) indicated change to the root and stem structure in plant tissue due to the direct attachment with gasoline contaminated compared to the control sample. The population of living microorganisms in the contaminated soil was found to be able to adapt to different gasoline concentrations. The results showed that L. octovalvis and rhizobacteria in gasoline-contaminated soil have the potential to degrade organic pollutants.
A novel kinetic model has been developed to explain the degradation of total petroleum hydrocarbons. Microbiome engineered biochar amendment may result in a synergistic impact on degradation of total petroleum hydrocarbons (TPHs). Therefore, the present study analyzed the potential of hydrocarbon-degrading bacteria A designated as Aeromonas hydrophila YL17 and B as Shewanella putrefaciens Pdp11 morphological characterized as rod shaped, anaerobic and gram-negative immobilized on biochar, and the degradation efficiency was measured by gravimetric analysis and gas chromatography-mass spectrometry (GC-MS). Whole genome sequencing of both strains revealed the existence of genes responsible for hydrocarbon degradation. In 60 days remediation setup, the treatment consisting of immobilization of both strains on biochar proved more efficient with less half-life and better biodegradation potentials compared to biochar without strains for decreasing the content of TPHs and n-alkanes (C12-C18). Enzymatic content and microbiological respiration showed that biochar acted as a soil fertilizer and carbon reservoir and enhanced microbial activities. The removal efficiency of hydrocarbons was found to be a maximum of 67% in soil samples treated with biochar immobilized with both strains (A + B), followed by biochar immobilized with strain B 34%, biochar immobilized with strain A 29% and with biochar 24%, respectively. A 39%, 36%, and 41% increase was observed in fluorescein diacetate (FDA) hydrolysis, polyphenol oxidase and dehydrogenase activities in immobilized biochar with both strains as compared to control and individual treatment of biochar and strains. An increase of 35% was observed in the respiration rate with the immobilization of both strains on biochar. While a maximum colony forming unit (CFU/g) was found 9.25 with immobilization of both strains on biochar at 40 days of remediation. The degradation efficiency was due to synergistic effect of both biochar and bacteria based amendment on the soil enzymatic activity and microbial respiration.
Herein, tropical fruit biomass wastes including durian seeds (DS) and rambutan peels (RP) were used as sustainable precursors for preparing activated carbon (DSRPAC) using microwave-induced H3PO4 activation. The textural and physicochemical characteristics of DSRPAC were investigated by N2 adsorption-desorption isotherms, X-ray diffraction, Fourier transform infrared, point of zero charge, and scanning electron microscope analyses. These findings reveal that the DSRPAC has a mean pore diameter of 3.79 nm and a specific surface area of 104.2 m2/g. DSRPAC was applied as a green adsorbent to extensively investigate the removal of an organic dye (methylene blue, MB) from aqueous solutions. The response surface methodology Box-Behnken design (RSM-BBD) was used to evaluate the vital adsorption characteristics, which included (A) DSRPAC dosage (0.02-0.12 g/L), (B) pH (4-10), and (C) time (10-70 min). The BBD model specified that the DSRPAC dosage (0.12 g/L), pH (10), and time (40 min) parameters caused the largest removal of MB (82.1%). The adsorption isotherm findings reveal that MB adsorption pursues the Freundlich model, whereas the kinetic data can be well described by the pseudo-first-order and pseudo-second-order models. DSRPAC exhibited good MB adsorption capability (118.5 mg/g). Several mechanisms control MB adsorption by the DSRPAC, including electrostatic forces, π-π stacking, and H-bonding. This work shows that DSRPAC derived from DS and RP could serve as a viable adsorbent for the treatment of industrial effluents containing organic dye.
This study evaluated the characteristics of zinc chloride modified vitex doniana seed activated carbon (VDZnCl2) for the removal of methylene blue. VDZnCl2 was characterized for textural properties, surface morphology and surface chemistry. Batch adsorption of methylene blue by VDZnCl2 was evaluated for the effects of concentration, contact time, adsorbent dosage, and solution pH. The surface area increased from 14 to 933 m2/g with porous texture to facilitate adsorption. The SEM micrograph showed varieties of pores with widened cavities. The FTIR spectra showed the characteristics of O-H and C=C groups commonly found in carbonaceous materials. The maximum methylene blue adsorption was recorded as 238 mg/g at concentration range of 1-800 mg/L and VDZnCl2 dosage of 50 mg. Sips isotherm fitted well with the equilibrium data, suggesting that the adsorption by VDZnCl2 was a physical process onto its heterogeneous surface, while the applicability of pseudo-first-order kinetics implies that external diffusion was the rate controlling mechanism. The performance put up by VDZnCl2 suggested that it is a potential adsorbent substitute for dye wastewater treatment.
Heavy metal pollution is one of the most pervasive environmental problems globally. Novel finely tuned algae have been proposed as a means to improve the efficacy and selectivity of heavy metal biosorption. This article reviews current research on selective algal heavy metal adsorption and critically discusses the performance of novel biosorbents. We emphasize emerging state-of-the-art techniques that customize algae for enhanced performance and selectivity, particularly molecular and chemical extraction techniques as well as nanoparticle (NP) synthesis approaches. The mechanisms and processes for developing novel algal biosorbents are also presented. Finally, we discuss the applications, challenges, and future prospects for modified algae in heavy metal biosorption.
Microplastic (MP) pollution has emerged as a pressing environmental concern due to its ubiquity and longevity. Biodegradation of MPs has garnered significant attention in combatting global MP contamination. This study focused on MPs within sediments near the sewage outlet of Shenzhen Bay. The objective was to elucidate the microbial communities in sediments with varying MPs, particularly those with high MP loads, and to identify microorganisms associated with MP degradation. The results revealed varying MP abundance, ranging from 211 to 4140 items kg-1 dry weight (d. w.), with the highest concentration observed near the outfall. Metagenomic analysis confirmed the enrichment of Psychrobacter species in sediments with high MP content. Psychrobacter accounted for ∼16.71% of the total bacterial community and 41.71% of hydrocarbon degrading bacteria at the S3 site, exhibiting a higher abundance than at other sampling sites. Psychrobacter contributed significantly to bacterial function at S3, as evidenced by the Kyoto Encyclopedia of Genes and Genomes pathway and enzyme analysis. Notably, 28 enzymes involved in MP biodegradation were identified, predominantly comprising oxidoreductases, hydrolases, transferases, ligases, lyases, and isomerases. We propose a putative mechanism for MP biodegradation, involving the breakdown of long-chain plastic polymers and subsequent oxidation of short-chain oligomers, ultimately leading to thorough mineralization.
The bioremediation of polluted groundwater, wastewater aeration pond and biopond sites was investigated using bacteria isolated from these sites located at the oil refinery Terengganu Malaysia. Out of 62 isolates, only 16 isolates from groundwater (8) and wastewater aeration pond (3) and biopond (5) were chosen based on growth medium containing 1% (v/v) Tapis crude oil. Only four isolates; Acinetobacter faecalis, Staphylococcus sp., Pseudomonas putida and Neisseria elongata showed percentage biodegradation of crude oil more than 50% after 5 days using Mineral Salts Medium (MSM). The effect of physical parameters (temperature, pH and agitation) on growth by all four strains showed a maximum growth in MSM medium with 1% Tapis crude oil at 37 degrees C with pH 7 and agitation of 130 rpm.
In this study, bamboo waste (BW) was subjected to pyrolysis-assisted ZnCl2 activation to produce mesoporous activated carbon (BW-AC), which was then evaluated for its ability to remove cationic dyes, specifically methylene blue (MB) and crystal violet (CV), from aqueous environments. The properties of BW-AC were characterized using various techniques, including potentiometric-based point of zero charge (pHpzc), scanning electron microscopy with energy dispersive X-rays (SEM-EDX), X-ray diffraction (XRD), gas adsorption with Brunauer-Emmett-Teller (BET) analysis, infrared (IR) spectroscopy. To optimize the adsorption characteristics (BW-AC dosage, pH, and contact time) of PBW, a Box-Behnken design (BBD) was employed. The BW-AC dose of 0.05 g, solution pH of 10, and time of 8 min are identified as optimal operational conditions for achieving maximum CV (89.8%) and MB (96.3%) adsorption according to the BBD model. The dye removal kinetics for CV and MB are described by the pseudo-second-order model. The dye adsorption isotherms revealed that adsorption of CV and MB onto BW-AC follow the Freundlich model. The maximum dye adsorption capacities (qmax) of BW-AC for CV (530 mg/g) and MB (520 mg/g) are favorable, along with the thermodynamics of the adsorption process, which is characterized as endothermic and spontaneous. The adsorption mechanism of CV and MB dyes by BW-AC was attributed to multiple contributions: hydrogen bonding, electrostatic forces, π-π attraction, and pore filling. The findings of this study highlight the potential of BW-AC as an effective adsorbent in wastewater treatment applications, contributing to the overall goal of mitigating the environmental impact of cationic dyes and ensuring the quality of water resources.
This work aims to apply the use of food-grade algae (FGA) composited with chitosan-benzaldehyde Schiff base biopolymer (CHA-BD) as a new adsorbent (CHA-BA/FGA) for methyl violet 2B (MV 2B) dye removal from aqueous solutions. The effect of three processing variables, including CHA-BA/FGA dosage (0.02-0.1 g/100 mL), pH solution (4-10), and contact duration (10-120 min) on the removal of MV 2B was investigated using the Box-Behnken design (BBD) model. Kinetic and equilibrium dye adsorption profiles reveal that the uptake of MV 2B dye by CHA-BA/FGA is described by the pseudo-second kinetics and the Langmuir models. The thermodynamics of the adsorption process (ΔG°, ΔH°, and ΔS°) reveal spontaneous and favorable adsorption parameters of MV 2B dye onto the CHA-BA/FGA biocomposite at ambient conditions. The CHA-BA/FGA exhibited the maximum ability to absorb MV 2B of 126.51 mg/g (operating conditions: CHA-BA/FGA dose = 0.09 g/100 mL, solution pH = 8.68, and temperature = 25 °C). Various interactions, including H-bonding, electrostatic forces, π-π stacking, and n-π stacking provide an account of the hypothesized mechanism of MV 2B adsorption onto the surface of CHA-BA/FGA. This research reveals that CHA-BA/FGA with its unique biocomposite structure and favorable adsorption properties can be used to remove harmful cationic dyes from wastewater.
A major worldwide challenge that presents significant economic, environmental, and social concerns is the rising generation of food waste. The current work used chicken bones (CB) and rice (R) food waste as alternate precursors for the production of activated carbon (CBRAC) by microwave radiation-assisted ZnCl2 activation. The adsorption characteristics of CBRAC were investigated in depth by removing an organic dye (crystal violet, CV) from an aquatic environment. To establish ideal conditions from the significant adsorption factors (A: CBRAC dosage (0.02-0.12 g/100 mL); B: pH (4-10); and C: duration (30-420), a numerical desirability function of Box-Behnken design (BBD) was utilized. The highest CV decolorization by CBRAC was reported to be 90.06% when the following conditions were met: dose = 0.118 g/100 mL, pH = 9.0, and time = 408 min. Adsorption kinetics revealed that the pseudo-first order (PFO) model best matches the data, whereas the Langmuir model was characterized by equilibrium adsorption, where the adsorption capacity of CBRAC for CV dye was calculated to be 57.9 mg/g. CV adsorption is accomplished by several processes, including electrostatic forces, pore diffusion, π-π stacking, and H-bonding. This study demonstrates the use of CB and R as biomass precursors for the efficient creation of CBRAC and their use in wastewater treatment, resulting in a greener environment.
In this study, the focus was on utilizing tropical plant biomass waste, specifically bamboo (BB), as a sustainable precursor for the production of activated carbon (BBAC) via pyrolysis-induced K2CO3 activation. The potential application of BBAC as an effective adsorbent for the removal of methylene blue (MB) dye from aqueous solutions was investigated. Response surface methodology (RSM) was employed to evaluate key adsorption characteristics, which included BBAC dosage (A: 0.02-0.08 g/L), pH (B: 4-10), and time (C: 2-8 min). The adsorption isotherm analysis revealed that the adsorption of MB followed the Freundlich model. Moreover, the kinetic data were well-described by the pseudo-second-order model, suggesting the role of a chemisorption process. The BBAC demonstrated a notable MB adsorption capacity of 195.8 mg/g, highlighting its effectiveness as an adsorbent. Multiple mechanisms were identified as controlling factors in MB adsorption by BBAC, including electrostatic forces, π-π stacking, and H-bonding interactions. The findings of this study indicate that BBAC derived from bamboo has the potential to be a promising adsorbent for the treatment of wastewater containing organic dyes. The employment of sustainable precursors like bamboo for activated carbon production contributes to environmentally friendly waste management practices and offers a solution for the remediation of dye-contaminated wastewater.
With the progressive increase in human activities in the Antarctic region, the possibility of domestic oil spillage also increases. Developing means for the removal of oils, such as canola oil, from the environment and waste "grey" water using biological approaches is therefore desirable, since the thermal process of oil degradation is expensive and ineffective. Thus, in this study an indigenous cold-adapted Antarctic soil bacterium, Rhodococcus erythropolis strain AQ5-07, was screened for biosurfactant production ability using the multiple approaches of blood haemolysis, surface tension, emulsification index, oil spreading, drop collapse and "MATH" assay for cellular hydrophobicity. The growth kinetics of the bacterium containing different canola oil concentration was studied. The strain showed β-haemolysis on blood agar with a high emulsification index and low surface tension value of 91.5% and 25.14 mN/m, respectively. Of the models tested, the Haldane model provided the best description of the growth kinetics, although several models were similar in performance. Parameters obtained from the modelling were the maximum specific growth rate (qmax), concentration of substrate at the half maximum specific growth rate, Ks% (v/v) and the inhibition constant Ki% (v/v), with values of 0.142 h-1, 7.743% (v/v) and 0.399% (v/v), respectively. These biological coefficients are useful in predicting growth conditions for batch studies, and also relevant to "in field" bioremediation strategies where the concentration of oil might need to be diluted to non-toxic levels prior to remediation. Biosurfactants can also have application in enhanced oil recovery (EOR) under different environmental conditions.
Increasing aquaculture cultivation produces large quantities of wastewater. If not handled properly, it can have negative impacts on the environment. Constructed wetlands (CWs) are one of the phytoremediation methods that can be applied to treat aquaculture effluent. This research was aimed at determining the performance of Cyperus rotundus in removing COD, BOD, TSS, turbidity, ammonia, nitrate, nitrite, and phosphate from the batch CW system. Treatment was carried out for 30 days with variations in the number of plants (10, 15, and 20) and variations in media height (10, 12, and 14 cm). The result showed that aquaculture effluent contains high levels of organic compounds and nutrients, and C. rotundus can grow and thrive in 100% of aquaculture effluent. Besides that, the use of C. rotundus in CWs with the effect of numbers of plants and media height showed performance of COD, BOD, TSS, turbidity, ammonia, nitrate, nitrite, and phosphate with 70, 79, 90, 96, 64, 82, 92, and 48% of removal efficacy, respectively. There was no negative impact observed on C. rotundus growth after exposure to aquaculture effluent, as indicated by the increase in wet weight, dry weight, and growth rate when compared to the control. Thus, adding aquaculture effluent to CWs planted with C. rotundus supports the growth and development of plants while also performing phytoremediation.
Certain rhizobacteria can be applied to remove arsenic in the environment through bioremediation or phytoremediation. This study determines the minimum inhibitory concentration (MIC) of arsenic on identified rhizobacteria that were isolated from the roots of Ludwigia octovalvis (Jacq.) Raven. The arsenic biosorption capability of the was also analyzed. Among the 10 isolated rhizobacteria, five were Gram-positive (Arthrobacter globiformis, Bacillus megaterium, Bacillus cereus, Bacillus pumilus, and Staphylococcus lentus), and five were Gram-negative (Enterobacter asburiae, Sphingomonas paucimobilis, Pantoea spp., Rhizobium rhizogenes, and Rhizobium radiobacter). R. radiobacter showed the highest MIC of >1,500 mg/L of arsenic. All the rhizobacteria were capable of absorbing arsenic, and S. paucimobilis showed the highest arsenic biosorption capability (146.4 ± 23.4 mg/g dry cell weight). Kinetic rate analysis showed that B. cereus followed the pore diffusion model (R2 = 0.86), E. asburiae followed the pseudo-first-order kinetic model (R2 = 0.99), and R. rhizogenes followed the pseudo-second-order kinetic model (R2 = 0.93). The identified rhizobacteria differ in their mechanism of arsenic biosorption, arsenic biosorption capability, and kinetic models in arsenic biosorption.