Soil pollution by microplastics (MPs) is an escalating environmental crisis with far-reaching consequences. However, current research on the degradation and/or remediation of MPs has mainly focused on water-simulated environments, with little attention given to soil MPs. Therefore, the review explores such terrestrial territory, exploring the potential of biodegradation and novel photocatalytic technologies for MPs degradation/remediation in soil. This review comprehensively investigates the potential of biological and photocatalytic approaches for soil MPs degradation and remediation. A temporal analysis of research from 2004 to 2024 highlights the increasing focus on this critical issue. The review explores the biocatalytic roles of diverse enzymes, including cutinase, PETase, MHETase, hydrolase, lipase, laccase, lignin peroxidase, and Mn-peroxidase, in MPs degradation. Strategies for enzyme engineering, such as protein engineering and immobilization, are explored to enhance catalytic efficiency. The potential for developing enzyme consortia for optimized MP degradation is also discussed. Photocatalytic remediation using TiO2, ZnO, clay, hydrogel, and other photocatalysts is examined, emphasizing their mechanisms and effectiveness. Computational modeling is proposed to deepen understanding of soil MPs-catalyst interactions, primarily aiming to develop novel catalysts tailored for soil environments for environmental safety and sustainable restoration. A comparative analysis of biological and photocatalytic approaches evaluates their environmental implications and the potential for synergistic combinations, with emphasis on soil quality protection, restoration and impact on soil ecosystems. Hence, this review accentuates the urgent need for innovative solutions to address MPs pollution in soil and provides a foundational understanding of the current knowledge gaps, as well as paves the way for future research and development.
The manufacture and potential application of biodegradable films for food application has gained increased interest as alternatives to conventional food packaging polymers due to the sustainable nature associated with their availability, broad and abundant source range, compostability, environmentally-friendly image, compatibility with foodstuffs and food application, etc. Gelatin is one such material and is a unique and popularly used hydrocolloid by the food industry today due to its inherent characteristics, thereby potentially offering a wide range of further and unique industrial applications. Gelatin from different sources have different physical and chemical properties as they contain different amino acid contents which are responsible for the varying characteristics observed upon utilization in food systems and when being utilized more specifically, in the manufacture of films. Packaging films can be successfully produced from all gelatin sources and the behaviour and characteristics of gelatin-based films can be altered through the incorporation of other food ingredients to produce composite films possessing enhanced physical and mechanical properties. This review will present the current situation with respect to gelatin usage as a packaging source material and the challenges that remain in order to move the manufacture of gelatin-based films nearer to commercial reality.
This study explores an innovative integrated system for removing the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from aquatic environments, utilizing a combination by modified biochar derived from waste biomass of palm kernel shells (PKS-BM) and water hyacinth (Eichhornia crassipes). The characterization of the biochar revealed significant surface functional groups, a substantial surface area, and a mesoporous structure conducive to adsorption application. Biochar-assisted phytoremediation demonstrated markedly higher removal efficiencies of 2,4-D as compared to phytoremediation alone, achieving up to 98.7%, 96.9%, and 90.3% removal efficiency for 2,4-D concentrations of 50 mg/L, 100 mg/L, and 150 mg/L, respectively. Additionally, the presence of biochar significantly enhanced the morphological growth of Eichhornia crassipes, particularly under higher concentrations of 2,4-D, by mitigating toxic effects and supporting healthier plant development. These findings suggest that integrating biochar into phytoremediation system offers a promising, sustainable approach for effectively removing herbicides from contaminated water bodies while also promoting plant health and growth.
Plastic biodegradation has emerged as a sustainable approach and green alternative in handling the ever-increasing accumulation of plastic wastes in the environment. The complete biodegradation of polyethylene terephthalate is one of the most recent breakthroughs in the field of plastic biodegradation. Despite the success, the effective and complete biodegradation of a wide variety of plastics is still far from the practical implementation, and an on-going effort has been mainly devoted to the exploration of novel microorganisms and enzymes for plastic biodegradation. However, alternative strategies which enhance the existing biodegradation process should not be neglected in the continuous advancement of this field. Thus, this review highlights various strategies which have shown to improve the biodegradation of plastics, which include the pretreatment of plastics using UV irradiation, thermal, or chemical treatments to increase the susceptibility of plastics toward microbial action. Alternative pretreatment strategies are also suggested and compared with the existing techniques. Besides, the effects of additives such as pro-oxidants, natural polymers, and surfactants on plastic biodegradation are discussed. In addition, considerations governing the biodegradation performance, such as the formulation of biodegradation medium, cell-free biocatalysis, and physico-chemical properties of plastics, are addressed. Lastly, the challenges and future prospects for the advancement of plastic biodegradation are also highlighted.
Thiocyanate (SCN-) is a contaminant requiring remediation in gold mine tailings and wastewaters globally. Seepage of SCN--contaminated waters into aquifers can occur from unlined or structurally compromised mine tailings storage facilities. A wide variety of microorganisms are known to be capable of biodegrading SCN-; however, little is known regarding the potential of native microbes for in situ SCN- biodegradation, a remediation option that is less costly than engineered approaches. Here we experimentally characterize the principal biogeochemical barrier to SCN- biodegradation for an autotrophic microbial consortium enriched from mine tailings, to arrive at an environmentally realistic assessment of in situ SCN- biodegradation potential. Upon amendment with phosphate, the consortium completely degraded up to ∼10 mM SCN- to ammonium and sulfate, with some evidence of nitrification of the ammonium to nitrate. Although similarly enriched in known SCN--degrading strains of thiobacilli, this consortium differed in its source (mine tailings) and metabolism (autotrophy) from those of previous studies. Our results provide a proof of concept that phosphate limitation may be the principal barrier to in situ SCN- biodegradation in mine tailing waters and also yield new insights into the microbial ecology of in situ SCN- bioremediation involving autotrophic sulfur-oxidizing bacteria.
The use of pesticides and the subsequent accumulation of residues in the soil has become a worldwide problem. Organochlorine (OC) pesticides have spread widely in the environment and caused contamination from past agricultural activities. This article reviews the bioremediation of pesticide compounds in soil using microbial enzymes, including the enzymatic degradation pathway and the recent development of enzyme-mediated bioremediation. Enzyme-mediated bioremediation is divided into phase I and phase II, where the former increases the solubility of pesticide compounds through oxidation-reduction and hydrolysis reactions, while the latter transforms toxic pollutants into less toxic or nontoxic products through conjugation reactions. The identified enzymes that can degrade OC insecticides include dehalogenases, phenol hydroxylase, and laccases. Recent developments to improve enzyme-mediated bioremediation include immobilization, encapsulation, and protein engineering, which ensure its stability, recyclability, handling and storage, and better control of the reaction.
Amidst the increasing significance of innovative solutions for bioremediation of heavy metal removal, this paper offers a thorough bibliometric analysis of microbial-induced carbonate precipitation (MICP) for heavy metal removal, as a promising technology to tackle this urgent environmental issue. This study focused on articles published from 1999 to 2022 in the Scopus database. It assesses trends, participation, and key players within the MICP for heavy metal sequestration. Among the 930 identified articles, 74 countries participated in the field, with China being the most productive. Varenyam Achal, the Chinese Academy of Sciences, and Chemosphere are leaders in the research landscape. Using VOSviewer and R-Studio, keyword hotspots like "MICP", "urease", and "heavy metals" underscore the interdisciplinary nature of MICP research and its focus on addressing a wide array of environmental and soil-related challenges. VOSviewer emphasises essential terms like "calcium carbonate crystal", while R-Studio highlights ongoing themes such as "soil" and "organic" aspects. These analyses further showcase the interdisciplinary nature of MICP research, addressing a wide range of environmental challenges and indicating evolving trends in the field. This review also discusses the literature concerning the potential of MICP to immobilise contaminants, the evolution of the research outcome in the last two decades, MICP treatment techniques for heavy metal removal, and critical challenges when scaling from laboratory to field. Readers will find this analysis beneficial in gaining valuable insights into the evolving field and providing a solid foundation for future research and practical implementation.
The greenhouse phytotoxicity experiment was conducted to analyse and assess the capability of Scirpus mucronatus (L.) in tolerating and removing petrol in contaminated soil. This research was conducted for 72 days by using 5, 10 and 30 g/kg petrol as soil contaminants. Results showed that the system planted with S. mucronatus (L.) had high potential to treat the 10 g/kg petrol-contaminated soil and had an average Total Petroleum Hydrocarbon (TPH) removal of 82.1%. At 5 and 30 g/kg petrol, the planted system removed 74.9% and 75.8% TPH, respectively. The petrol (10 g/kg) affected the plant growth positively, which was indicated by the increase in dry and wet weights throughout the research period. The removal of the TPH in the system was performed because of the interaction of plants and rhizobacteria. SEM showed that a high concentration of petrol (30 g/kg) affected the plant tissue negatively, as indicated by the altered structures of the root and stem cells. EDX results also confirmed that petrol was absorbed by the plant, as shown by the increased carbon content in the plant's root and stem after the treatment.
Soil and water contaminated with radionuclides threaten the environment and public health during leaks from nuclear power plants. Remediation of radionuclides at the contaminated sites uses mainly physical and chemical methods such as vitrification, chemical immobilization, electro-kinetic remediation and soil excavation, capping and washing being among the preferred methods. These traditional technologies are however costly and less suitable for dealing with large-area pollution. In contrast to this, cost-effective and environment-friendly alternatives such as phytoremediation using plants to remove radionuclides from polluted sites in situ represent promising alternatives for environmental cleanup. Understanding the physiology and molecular mechanisms of radionuclides accumulation in plants is essential to optimize and improve this new remediation technology. Here, we give an overview of radionuclide contamination in the environment and biochemical characteristics for uptake, transport, and compartmentation of radionuclides in plants that characterize phytoextraction and its efficiency. Phytoextraction is an eco-friendly and efficient method for environmental removal of radionuclides at contaminated sites such as mine tailings. Selecting the most proper plant for the specific purpose, however, is important to obtain the best result together with, for example, applying soil amendments such as citric acid. In addition, using genetic engineering and optimizing agronomic management practices including regulation of atmospheric CO2 concentration, reasonable measures of fertilization and rational water management are important as well. For future application, the technique needs commercialization in order to fully exploit the technique at mining activities and nuclear industries.
Oil pollution which results from industrial activities, especially oil and gas industry, has become a serious issue. Cinder beats (CB), coconut fiber (CF) and polyurethane foam (PUF) are promising immobilization carriers for crude oil biodegradation because they are inexpensive, nontoxic, and non-polluting. The present investigation was aimed to evaluate this advanced technology and compare the efficiency of these immobilization carriers on supporting purple phototrophic bacterial (PPB) strains in hydrocarbon biodegradation of crude oil contaminated seawater. The surface of these biocarriers was supplemented with crude oil polluted seawater and immobilized by PPB strains, Rhodopseudomonas sp. DD4, DQ41 and FO2. Through scanning electron microscopy (SEM), the bacterial cells were shown to colonize and attach strongly to these biocarriers. The bacteria-driven carrier systems degraded over 84.2% supplemented single polycyclic aromatic hydrocarbons (PAHs). The aliphatic and aromatic components in crude oil that treated with carrier-immobilized consortia were degraded remarkably after 14 day-incubation. Among the three biocarriers, removal of the crude oil by CF-bacteria system was the highest (nearly 100%), followed by PUF-bacteria (89.5%) and CB-bacteria (86.3%) with the initial crude oil concentration was 20 g/L. Efficiency of crude oil removal by CB-bacteria and PUF-bacteria were 86.3 and 89.5%, respectively. Till now, the studies on crude oil degradation by mixture species biofilms formed by PPB on different carriers are limited. The present study showed that the biocarriers of an oil-degrading consortium could be made up of waste materials that are cheap and eco-friendly as well as augment the biodegradation of oil-contaminated seawater.
Phytoremediation is considered as a cost-effective and environmentally friendly
technique for decontaminating environments that have been contaminated with
heavy metal ions. The technique describes the use of plants and their concomitant
microbes to mitigate environmental contaminations. However, conventional
remediation techniques like chemical, thermal and physical treatment methods are
too costly, and may end of causing more contamination to the environment.
Phytoremediation practice provides a major information on the utilization of plants
and their materials in decontaminating polluted environments. Heavy metals and
other organic contaminants are among the most precarious substances released into
the environment which have an eminent level of toxicity and sturdiness of both
aquatic and terrestrial organisms. The review aimed at providing a broad
understanding of utilizing various plants and their materials in decontaminating
polluted environments with heavy metals and other organic contaminants. It also
provided the general methods used in treating the aforementioned contaminants in
an environment. The review further discussed the classes of phytoremediation like
phytoextraction, phytovolatilisation, phytostabilization, phytotransformation,
phytodegradation and phytofiltration. The generalized advantages and disadvantages
of phytoremediation were ultimately highlighted.
The evaluation of degradation and growth kinetics of Serratia marcescens strain AQ07 was carried out using three half-order models at all the initial concentrations of cyanide with the values of regression exceeding 0.97. The presence of varying cyanide concentrations reveals that the growth and degradation of bacteria were affected by the increase in cyanide concentration with a total halt at 700 ppm KCN after 72 h incubation. In this study, specific growth and degradation rates were found to trail the substrate inhibition kinetics. These two rates fitted well to the kinetic models of Teissier, Luong, Aiba and Heldane, while the performance of Monod model was found to be unsatisfactory. These models were used to clarify the substrate inhibition on the bacteria growth. The analyses of these models have shown that Luong model has fitted the experimental data with the highest coefficient of determination (R2) value of 0.9794 and 0.9582 with the lowest root mean square error (RMSE) value of 0.000204 and 0.001, respectively, for the specific rate of degradation and growth. It is the only model that illustrates the maximum substrate concentration (Sm) of 713.4 and empirical constant (n) of 1.516. Tessier and Aiba fitted the experimental data with a R2 value of 0.8002 and 0.7661 with low RMSE of 0.0006, respectively, for specific biodegradation rate, while having a R2 value of 0.9 and RMSE of 0.001, respectively, for specific growth rate. Haldane has the lowest R2 value of 0.67 and 0.78 for specific biodegradation and growth rate with RMSE of 0.0006 and 0.002, respectively. This indicates the level of the bacteria stability in varying concentrations of cyanide and the maximum cyanide concentration it can tolerate within a specific time period. The biokinetic constant predicted from this model demonstrates a good ability of the locally isolated bacteria in cyanide remediation in industrial effluents.
For decades, most of the developing nations have relied on chlorpyrifos for insecticidal activity in the agriculture sector. It is a common chlorinated organophosphorus pesticide that has been widely used to control insects to protect plants. This study aimed to investigate the effects of environmental characteristics such as salinity, pH, temperature, and surfactant on Hortaea sp. B15 mediated degradation of chlorpyrifos as well as enzyme activity and metabolic pathway. The highest bacterial growth (4.6 × 1016 CFU/mL) was achieved after 20 h of incubation in a 100 mg/L chlorpyrifos amended culture. The fit model and feasible way to express the chlorpyrifos biodegradation kinetics in normal condition and optimized was a first-order rate equation, with an R2 value of 0.95-0.98. The optimum pH for chlorpyrifos biodegradation was pH 9, which resulted in a high removal rate (91.1%) and a maximum total count of 3.8 × 1016 CFU/mL. Increasing the temperature over 40 °C may inhibit microbial development and biodegradation. There was no significant effect of culture salinity on degradation and bacterial growth. In the presence of non-ionic surfactant Tween 80, the maximum chlorpyrifos degradation (89.5%) and bacterial growth (3.8 × 1016 CFU/mL) was achieved. Metabolites such as 3,5,6-trichloropyridin-2-ol and 2-pyridinol were identified in the Hortaea sp. B15 mediated degradation of chlorpyrifos. According to the findings, Hortaea sp. B15 should be recommended for use in the investigation of in situ biodegradation of pesticides.
Microplastics are the small fragments of the plastic molecules which find their applications in various routine products such as beauty products. Later, it was realized that it has several toxic effects on marine and terrestrial organisms. This review is an approach in understanding the microplastics, their origin, dispersal in the aquatic system, their biodegradation and factors affecting biodegradation. In addition, the paper discusses the major engineering approaches applied in microbial biotechnology. Specifically, it reviews microbial genetic engineering, such as PET-ase engineering, MHET-ase engineering, and immobilization approaches. Moreover, the major challenges associated with the plastic removal are presented by evaluating the recent reports available.
Versatility and desirable attributes of synthetic plastics have greatly contributed towards their wide applications. However, vast accumulation of plastic wastes in environment as a result of their highly recalcitrant nature has given rise to plastic pollution. Existing strategies in alleviating plastic wastes accumulation are inadequate, and there is a pressing need for alternative sustainable approaches in tackling plastic pollution. In this context, plastic biodegradation has emerged as a sustainable and environmental-friendly approach in handling plastic wastes accumulation, due to its milder and less energy-intensive conditions. In recent years, extensive research effort has focused on the identification of microorganisms and enzymes with plastic-degrading abilities. This review aims to provide a timely and holistic view on the current status of plastic biodegradation, focusing on recent breakthroughs and discoveries in this field. Furthermore, current challenges associated to plastic biodegradation are discussed, and the future perspectives for continuous advancement of plastic biodegradation are highlighted.
Surfactants have always been a prominent chemical that is useful in various sectors (e.g., cleaning agent production industry, textile industry and painting industry). This is due to the special ability of surfactants to reduce surface tension between two fluid surfaces (e.g., water and oil). However, the current society has long omitted the harmful effects of petroleum-based surfactants (e.g., health issues towards humans and reducing cleaning ability of water bodies) due to their usefulness in reducing surface tension. These harmful effects will significantly damage the environment and negatively affect human health. As such, there is an urgency to secure environmentally friendly alternatives such as glycolipids to reduce the effects of these synthetic surfactants. Glycolipids is a biomolecule that shares similar properties with surfactants that are naturally synthesized in the cell of living organisms, glycolipids are amphiphilic in nature and can form micelles when glycolipid molecules clump together, reducing surface tension between two surfaces as how a surfactant molecule is able to achieve. This review paper aims to provide a comprehensive study on the recent advances in bacteria cultivation for glycolipids production and current lab scale applications of glycolipids (e.g., medical and waste bioremediation). Studies have proven that glycolipids are effective anti-microbial agents, subsequently leading to an excellent anti-biofilm forming agent. Heavy metal and hydrocarbon contaminated soil can also be bioremediated via the use of glycolipids. The major hurdle in the commercialization of glycolipid production is that the cultivation stage and downstream extraction stage of the glycolipid production process induces a very high operating cost. This review provides several solutions to overcome this issue for glycolipid production for the commercialization of glycolipids (e.g., developing new cultivating and extraction techniques, using waste as cultivation medium for microbes and identifying new strains for glycolipid production). The contribution of this review aims to serve as a future guideline for researchers that are dealing with glycolipid biosurfactants by providing an in-depth review on the recent advances of glycolipid biosurfactants. By summarizing the points discussed as above, it is recommended that glycolipids can substitute synthetic surfactants as an environmentally friendly alternative.
The application of microorganisms in azo dye remediation has gained significant attention, leading to various published studies reporting different methods for obtaining the best dye decolouriser. This paper investigates and compares the role of methods and media used in obtaining a bacterial consortium capable of decolourising azo dye as the sole carbon source, which is extremely rare to find. It was demonstrated that a prolonged acclimation under low substrate availability successfully isolated a novel consortium capable of utilising Reactive Red 120 dye as a sole carbon source in aerobic conditions. This consortium, known as JR3, consists of Pseudomonas aeruginosa strain MM01, Enterobacter sp. strain MM05 and Serratia marcescens strain MM06. Decolourised metabolites of consortium JR3 showed an improvement in mung bean's seed germination and shoot and root length. One-factor-at-time optimisation characterisation showed maximal of 82.9% decolourisation at 0.7 g/L ammonium sulphate, pH 8, 35 °C, and RR120 concentrations of 200 ppm. Decolourisation modelling utilising response surface methodology (RSM) successfully improved decolourisation even more. RSM resulted in maximal decolourisation of 92.79% using 0.645 g/L ammonium sulphate, pH 8.29, 34.5 °C and 200 ppm RR120.
Metal remediation is important considering the environmental pressure due to soil pollution from landfill leachate. Hence, identifying potential plant-based option for remediation, especially the use of bio-/hyper-accumulators, is inevitable. Contamination of soil with heavy metals has been a decades-long concern. This study is therefore aimed to evaluating the metal-remediation potentials of four ornamental plant species-Cordyline fruticosa, Duranta variegated, Tradescantia spathacea, and Chlorophylum comosum-on leachate-contaminated soil. Details of the study involved leachate analysis, soil characterization, and metal-accumulation test on selected plants. Characterization of both landfill soil and leachate has indicated that Pb, Cu, As, Mn, Cr, Zn, Fe, and Ni were higher than the prescribed limits. The high metal reduction efficiency of C. fruticosa on all the studied metals was about 63%, 85%, 77.88%, 77.55%, and 75% for Pb, As, Mn, Zn, and Cr concentrations. The metal removal by the plants was significantly higher as compared to control soil (P
Application of urea manufacturing wastewater to teak (Tectona grandis) trees, a fast growing tropical timber plants, is an environmentally-friendly and cost-effective alternative for treatment of nitrogen-rich wastewater. However, the plant growth is strongly limited by lack of phosphorus (P) and potassium (K) elements when the plants are irrigated with wastewater containing high concentration of nitrogen (N). A greenhouse experiment was conducted to optimize the efficiency of teak-based remediation systems in terms of nutrient balance. Twelve test solutions consisted of 4 levels of P (95, 190, 570, 1140 mgL-1) and 3 levels of K (95, 190, 570 mgL-1) with a constant level of N (190 mgL-1) were applied to teak seedlings every four days during the study period. Evapotranspiration rate, nutrient removal percentage, leaf surface area, dry weight and nutrient contents of experimental plants were determined and compared with those grown in control solution containing only N (N:P:K = 1:0:0). Teak seedlings grown in units with 1:0.5:1 N:P:K ratio were highly effective at nutrient removal upto 47%, 48% and 49% for N, P and K, respectively. Removal efficiency of teak plants grown in other experimental units decreased with increasing P and K concentrations in test solutions. The lowest nutrient removal and plant growth were recorded in units with 1:6:0.5 N:P:K ratio which received the highest ratio of P to K. The findings indicated that teak seedlings functioned effectively as phytoremediation plants for N-rich wastewater treatment when they were being supplied with proper concentrations of P and K.