Microwave co-pyrolysis was examined as an approach for simultaneous reduction and treatment of environmentally hazardous hospital plastic waste (HPW), lignocellulosic (palm kernel shell, PKS) and triglycerides (waste vegetable oil, WVO) biowaste as co-feedstock. The co-pyrolysis demonstrated faster heating rate (16-43 °C/min) compared to microwave pyrolysis of single feedstock (9-17 °C/min). Microwave co-pyrolysis of HPW/WVO performed at 1:1 ratio produced a higher yield (80.5 wt%) of hydrocarbon liquid fuel compared to HPW/PKS (78.2 wt%). The liquid oil possessed a low nitrogen content (< 4 wt%) and free of sulfur that could reduce the release of hazardous pollutants during its use as fuel in combustion. In particular, the liquid oil obtained from co-pyrolysis of HPW/WVO has low oxygenated compounds (< 16%) leading to reduction in generation of potentially hazardous sludge or problematic acidic tar during oil storage. Insignificant amount of benzene derivatives (< 1%) was also found in the liquid oil, indicating the desirable feature of this pyrolysis approach to suppress the formation of toxic polycyclic aromatic hydrocarbons (PAHs). Microwave co-pyrolysis of HPW/WVO improved the yield and properties of liquid oil for potential use as a cleaner fuel, whereas the liquid oil from co-pyrolysis of HPW/PKS is applicable in the synthesis of phenolic resin.
Colourants, micropollutants and heavy metals are regarded as the most notorious hazardous contaminants found in rivers, oceans and sewage treatment plants, with detrimental impacts on human health and environment. In recent development, algal biomass showed great potential for the synthesis of engineered algal adsorbents suitable for the adsorptive management of various pollutants. This review presents comprehensive investigations on the engineered synthesis routes focusing mainly on mechanical, thermochemical and activation processes to produce algal adsorbents. The adsorptive performances of engineered algal adsorbents are assessed in accordance with different categories of hazardous pollutants as well as in terms of their experimental and modelled adsorption capacities. Due to the unique physicochemical properties of macroalgae and microalgae in their adsorbent forms, the adsorption of hazardous pollutants was found to be highly effective, which involved different mechanisms such as physisorption, chemisorption, ion-exchange, complexation and others depending on the types of pollutants. Overall, both macroalgae and microalgae not only can be tailored into different forms of adsorbents based on the applications, their adsorption capacities are also far more superior compared to the conventional adsorbents.
Over the past few years, photocatalysis is one of the most promising approaches for removing organic pollutants. Zirconium dioxide (ZrO2) has been shown to be effective in the photodegradation of organic pollutants. However, low photoresponse and fast electron-hole recombination of ZrO2 affected the efficiency of catalytic performance. Modifying the photocatalyst itself (self-modification) is a prominent way to enhance the photoactivity of ZrO2. Moreover, as ZrO2-like photocatalysts have a large bandgap, improving the spectral response via self-modification could extend the visible light region and reduce the chance of recombination. Here, we review the self-modification of ZrO2 for enhanced the degradation of organic pollutants. The approaches of the ZrO2 self-modification, including the type of synthetic route and synthesis parameter variation, are discussed in the review. This will be followed by a brief section on the effect of ZrO2 self-modification in terms of morphology, crystal structure, and surface defects for enhanced photodegradation efficiency. It also covers the discussion on the photocatalytic mechanism of ZrO2 self-modification. Finally, some challenges with ZrO2 catalysts are also discussed to promote new ideas to improve photocatalytic performance.
While sulphur dioxide (SO2) is known for its toxicity, numerous effective countermeasures were innovated to alleviate its hazards towards the environment. In particular, catalytic reduction is favoured for its potential in converting SO2 into harmless, yet marketable product, such as elemental sulphur. Therefore, current review summarises the critical findings in catalytic SO2 reduction, emphasising on both dry- and wet-based technology. As for the dry-based technology, knowledge related to SO2 reduction over metal-, rare earth- and carbon-based catalysts are summarised. Significantly, both the reduction mechanisms and important criteria for efficient SO2 reduction are elucidated too. Meanwhile, the wet-based SO2 reduction are typically conducted in reactive liquid medium, such as metal complexes, ionic liquids and organic solvents. Therefore, the applications of the aforesaid liquid mediums are discussed thoroughly in the similar manner to dry-technology. Additionally, the pros and cons of each type of catalyst are also presented to provide valuable insights to the pertinent researchers. Finally, some overlooked aspects in both dry- and wet-based SO2 reduction are identified, with potential solutions given too. With these insights, current review is anticipated to contribute towards practicality improvement of catalytic SO2 reduction, which in turn, protects the environment from SO2 pollution.
Nowadays, a growing number of microplastics are released into the environment due to the extensive use and inappropriate management of plastic products. With the increasing body of evidence about the pollution and hazards of microplastics, microplastics have drawn major attention from governments and the scientific community. As a kind of emerging and persistent environmental pollutants, microplastics have recently been detected on a variety of substrates in the world. Therefore, this paper reviews the recent progress in identifying the sources of microplastics in soil, water, and atmosphere and describing the transport and fate of microplastics in the terrestrial, aquatic and atmospheric ecosystems for revealing the circulation of microplastics in the ecosystem. In addition, considering the persistence of microplastics, this study elucidates the interactions of microplastics with other pollutants in the environment (i.e., organic pollutants, heavy metals) with emphasis on toxicity and accumulation, providing a novel insight into the ecological risks of microplastics in the environment. The negative impacts of microplastics on organisms and environmental health are also reviewed to reveal the environmental hazards of microplastics. The knowledge gaps and key research priorities of microplastics are identified to better understand and mitigate the environmental risks of microplastics.
Improper healthcare waste (HCW) management poses significant risks to the environment, human health, and socio-economic sustainability due to the infectious and hazardous nature of HCW. This research aims at rendering a comprehensive landscape of the body of research on HCW management by (i) mapping the scientific development of HCW research, (ii) identifying the prominent HCW research themes and trends, and (iii) providing a research agenda for HCW management towards a circular economy (CE) transition and sustainable environment. The analysis revealed four dominant HCW research themes: (1) HCW minimization, sustainable management, and policy-making; (2) HCW incineration and its associated environmental impacts; (3) hazardous HCW management practices; and (4) HCW handling and occupational safety and training. The results showed that the healthcare industry, despite its potential to contribute to the CE transition, has been overlooked in the CE discourse due to the single-use mindset of the healthcare industry in the wake of the infectious, toxic, and hazardous nature of HCW streams. The findings shed light on the HCW management domain by uncovering the current status of HCW research, highlighting the existing gaps and challenges, and providing potential avenues for further research towards a CE transition in the healthcare industry and HCW management.
Waste furniture boards (WFBs) contain hazardous formaldehyde and volatile organic compounds when left unmanaged or improperly disposed through landfilling and open burning. In this study, pyrolysis was examined as a disposal and recovery approach to convert three types of WFBs (i.e., particleboard, plywood, and fiberboard) into value-added chemicals using thermogravimetric analysis coupled with Fourier-transform infrared spectrometry (TG-FTIR) and pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS). TG-FTIR analysis shows that pyrolysis performed at an optimum temperature of 250-550 °C produced volatile products mainly consisting of carbon dioxide, carbon monoxide, and light hydrocarbons, such as methane. Py-GC/MS shows that pyrolysis at different final temperatures and heating rates recovered mainly phenols (25.9-54.7%) for potential use as additives in gasoline, colorants, and food. The calorific value of WFBs ranged from 16 to 18 MJ/kg but the WFBs showed high H/C (1.7-1.8) and O/C (0.8-1.0) ratios that provide low chemical energy during combustion. This result indicates that WFBs are not recommended to be burned directly as fuel, however, they can be pyrolyzed and converted into solid pyrolytic products such as biochar with improved properties for fuel application. Hazardous components, such as cyclopropylmethanol, were removed and converted into value-added compounds, such as 1,4:3,6-dianhydro-d-glucopyranose, for use in pharmaceuticals. These results show that the pyrolysis of WFBs at high temperature and low heating rate is a promising feature to produce value-added chemicals and reduce the formation of harmful chemical species. Thus, the release of hazardous formaldehyde and greenhouse gases into the environment is redirected.
In agriculture, the convenience and efficacy of chemical pesticides have become inevitable to manage cultivated crop production. Here, we review the worldwide use of pesticides based on their categories, mode of actions and toxicity. Excessive use of pesticides may lead to hazardous pesticide residues in crops, causing adverse effects on human health and the environment. A wide range of high-tech-analytical methods are available to analyse pesticide residues. However, they are mostly time-consuming and inconvenient for on-site detection, calling for the development of biosensors that detect cellular changes in crops. Such new detection methods that combine biological and physicochemical knowledge may overcome the shortage in current farming to develop sustainable systems that support environmental and human health. This review also comprehensively compiles domestic pesticide residues removal tips from vegetables and fruits. Synthetic pesticide alternatives such as biopesticide and nanopesticide are greener to the environment. However, its safety assessment for large-scale application needs careful evaluation. Lastly, we strongly call for reversions of pesticide application trends based on the changing climate, which is lacking in the current scenario.
Xylene, a recalcitrant compound present in wastewater from activities of petrochemical and chemical industries causes chronic problems for living organisms and the environment. Xylene contaminated wastewater may be biodegraded through a benthic microbial fuel cell (BMFC) as seen in this study. Xylene was oxidized into intermediate 3-methyl benzoic acid and entirely converted into non-toxic carbon dioxide. The highest voltage of the BMFC reactor was generated at 410 mV between 23 and 90 days when cell potential was 1 kΩ. The reactor achieved a maximum power density of about 63 mW/m2, and a current of 0.4 mA which was optimized from variable resistance (20 Ω - 1 kΩ). However, the maximum biodegradation efficiency of the BMFC was at 87.8%. The cyclic voltammetry curve helped to determine that the specific capacitance was 0.124 F/g after 30 days of the BMFC operation. Furthermore, the fitting equivalent circuit was observed with the help of Nyquist plot for calculating overall internal resistance of 65.82 Ω on 30th day and 124.5 Ω on 80th day. Staphylococcus edaphicus and Staphylococcus sparophiticus were identified by 16S rRNA sequencing as the dominant species in the control and BMFC electrode, presumably associated with xylene biodegradation.
The present study aimed to investigate the removal efficiency of cephalexin (CFX) by a novel Cu-Zn bionanocomposite biosynthesized in the secondary metabolic products of Aspergillus arenarioides EAN603 with pumpkin peels medium (CZ-BNC-APP). The optimization study was performed based on CFX concentrations (1, 10.5 and 20 ppm); CZ-BNC-APP dosage (10, 55 and 100 mg/L); time (10, 55 and 100 min), temperature (20, 32.5 and 45 °C). The artificial neural network (ANN) model was used to understand the CFX behavior for the factors affecting removal process. The CZ-BNC-APP showed an irregular shape with porous structure and size between 20 and 80 nm. The FTIR detected CC, C-O and OH groups. ANN model revealed that CZ-BNC-APP dosage exhibited the vital role in the removal process, while the removal process having a thermodynamic nature. The CFX removal was optimized with 12.41 ppm CFX, 60.60 mg/L of CZ-BNC-APP, after 97.55 min and at 35 °C, the real maximum removal was 95.53% with 100.52 mg g-1 of the maximum adsorption capacity and 99.5% of the coefficient. The adsorption of CFX on CZ-BNC-APP was fitted with pseudo-second-order model and both Langmuir and Freundlich isotherms models. These findings revealed that CZ-BNC-APP exhibited high potential to remove CFX.
The current review highlighted the quantitative microbiological risk assessment of Vibrio parahaemolyticus in Prawn farm wastewaters (PFWWs) and the applicability of nanoparticles for eliminating antibiotic-resistant bacteria (ARB). The high availability of the antibiotics in the environment and their transmission into human through the food-chain might cause unknown health effects. The aquaculture environments are considered as a reservoir for the antibiotic resistance genes (ARGs) and contributed effectively in the increasing of ABR. The metagenomic analysis is used to explore ARGs in the non-clinical environment. V. parahaemolyticus is among the pathogenic bacteria which are transmitted through sea food causing human acute gastroenteritis due to available thermostable direct hemolysin (tdh), adhesins, TDH related hemolysin (trh). The inactivation of pathogenic bacteria using nanoparticles act by disturbing the cell membrane, interrupting the transport system, DNA and mitochondria damage, and oxidizing the cellular component by reactive oxygen species (ROS). The chloramphenicol, nitrofurans, and nitroimidazole are among the prohibited drugs in fish and fishery product. The utilization of probiotics is the most effective and safe alternative for antibiotics in Prawn aquaculture. This review will ensure public understanding among the readers on how they can decrease the risk of the antimicrobial resistance distribution in the environment.
In this study, various HCl-supported hydrochar made from root powder of long-root Eichhornia crassipes were applied to adsorb aqueous sulfachloropyridazine (SCP). Adsorption capacity (qe μg g-1) was positively correlated with combined severity-CS. With CS increasing, carbonization degree, hydrophobicity, porosity and isoelectric point of hydrochar increased, but content of polar functional groups decreased. Hydrophobic interaction was important for SCP adsorption. A 24 × 36 peak area table was generated from 24 FT-IR absorbance spectra computed by peak detection algorithm. Afterwards, correlation analysis between qe μg g-1 and FT-IR peak area were conducted, indicating that wavenumbers at 555.4, 1227.47, 1374.51, 1604.5, 2901.4/2919.2 and 3514.63 cm-1 were helpful for SCP adsorption. Further, multivariate linear regression analyses showed that aromatic skeleton and phenolic hydroxyl were the two biggest contributors. Electrostatic attraction did not exist during the SCP adsorption process. Under strong acid condition, protonated amino groups in cationic SCP acting as a hydrogen donator interacted with electron-rich functional groups onto hydrochar by Hydrogen interaction. Under weak acid condition, neutral SCP served as an π electron donor to bond with hydrochar by π-π electron donator-acceptor interaction. This work could guide the functional groups modification strategy of hydrochar to make better use of it in water purification field.
Waste cooking oil (WCO) is considered as one of the hazardous wastes because improper disposal of WCO can cause significant environmental problems such as blockages of drains and sewers as well as water or soil pollution. In this review, the physical and chemical properties of WCO are evaluated along with its regulations and policies in different countries to promote WCO refined biofuels. Blended WCO can be an auxiliary fuel for municipal solid waste incinerators while the heat produced is able to form superheated steam and subsequently generate electricity via combined heat and power system. Also, WCO contains high ratio of hydrogen atoms compared to carbon and oxygen atoms, making it able to be catalytically cracked, synthesizing hydrogen gas. WCO-based biodiesel has been traditionally produced by transesterification in order to substitute petroleum-based diesel which has non-degradability as well as non-renewable features. Hence, the potentials of hazardous WCO as a green alternative energy source for electricity generation, hydrogen gas as well as biofuels production (e.g. biodiesel, biogas, biojet fuel) are critically discussed due to its attractive psychochemical properties as well as its economic feasibility. Challenges of the WCO utilization as a source of energy are also reported while highlighting its future prospects.
Sulfur hexafluoride (SF6) is the most potent greenhouse gas contributed by the power and semiconductor industries. The global emissions of gas in the past 10 years have increased tremendously due to lack of disposal routes. This was brought to 190 nations' attention in the Kyoto Protocol for the need of emission control measures to reduce its impacts of climate change and global warming. Various novel techniques have surfaced to tackle this issue, such as non-thermal plasma (NTP) which includes radio frequency plasma, microwave plasma, dielectric barrier discharge, and electron beam. The main by-products resulting from the decomposition of SF6 by these techniques are sulfur oxyfluorides, sulfur dioxide, hydrofluoric acid, and fluorine gas. This environmental and health effects as well as global emission of SF6 gas are considered a threat to humans and the climate, where modern disposal methods of contaminated SF6 gas and its by-products should replace the conventional approaches. Relevant government policies on the safety and disposal concern of SF6 gas are reviewed and challenges and further research directions for the disposal of SF6 gas are highlighted in this review article.
Chinese liquor distillers' grain (CLDG) is an abundant industrial organic waste showing high potential as feedstock for biofuel conversion. In this study, CLDG was used as substrate by microbial community in pit mud to produce medium-chain fatty acids (especially caproate). Simulated and real fermentation were used to evaluate the effect of ethanol and lactic acid being the electronic donors (EDs) during the anaerobic chain elongation (CE). The caproate concentration was achieved at 449 mg COD/g VS, with the corresponding high carbon selectivity at 37.1%. Microbial analysis revealed that the domestication of pit mud increased the abundance of Caproiciproducens (converting lactic acid into caproate) and Lactobacillus (producing lactic acid), leading to enhanced caproate production. The lactic acid conversion facilitated in full utilization of ethanol through CE consumption. The coexistence of EDs benefited the CE system and that this green energy production can be a promising high-performance biofuel donor for sustainable industrial production development.
This study presents an extended thermodynamic and phenomenological combined model to mitigate the environmental hazardous acid gas over composite membranes. The model has been applied to an acid gas such as carbon dioxide (CO2) for its permeation through polyetherimide incorporated montmorillonite (Mt) nanoparticles hollow fiber asymmetric composite membranes. The well-established non-equilibrium lattice fluid (NELF) model for penetrating low molecular weight penetrant in a glassy polyetherimide (PEI) was extended to incorporate the other important polymer/filler system features such as tortuosity in acid gas diffusion pathways resulted from layered filler aspect ratio and concentration. The model mentioned above predicts the behavior of acid gas in PEI-Mt composite membranes based on thermodynamic characteristics of CO2 and PEI and tortuosity due to Mt. The calculated results are compared to experimentally determined values of CO2 permeability through PEI-Mt composite asymmetric hollow fiber membranes at varying transmembrane pressures and Mt concentrations. A reasonable agreement was found between the model predicted behavior and experimentally determined data in terms of CO2 solubility, Mt concentration and aspect ratio were calculated based on average absolute relative error (%AARE). The proposed modified model efficiently predicts the CO2 permeance across MMMs up to 3 wt% Mt loadings and 6 bar pressure with ± 10%AARE.
In this article, the removal of cephalexin (CFX) antibiotic from non-clinical environment is reviewed. Adsorption and photocatalytic degradation techniques are widely used to remove CFX from waters and wastewaters, the combination of these methods is becoming more common for CFX removal. The treatment methods of CFX has not been reviewed before, the present article aim is to organize the scattered available information regarding sustainable approaches for CFX removal from non-clinical environment. These include adsorption by nanoparticles, bacterial biomass, biodegradation by bacterial enzymes and the photocatalysis using different catalysts and Photo-Fenton photocatalysis. The metal-organic frameworks (MOFs) appeared to have high potential for CFX degradation. It is evident from the recently papers reviewed that the effective methods could be used in place of commercial activated carbon. The widespread uses of photocatalytic degradation for CFX remediation are strongly recommended due to their engineering applicability, technical feasibility, and high effectiveness. The adsorption capacity of the CFX is ranging from 7 mg CFX g-1 of activated carbon nanoparticles to 1667 mg CFX g-1 of Nano-zero-valent iron from Nettle. In contrast, the photo-degradation was 45% using Photo-Fenton while has increased to 100% using heterogeneous photoelectro-Fenton (HPEF) with UVA light using chalcopyrite catalyst.
Coronavirus Diseases 2019 (COVID-19) pandemic has a huge impact on the plastic waste management in many countries due to the sudden surge of medical waste which has led to a global waste management crisis. Improper management of plastic waste may lead to various negative impacts on the environment, animals, and human health. However, adopting proper waste management and the right technologies, looking in a different perception of the current crisis would be an opportunity. About 40% of the plastic waste ended up in landfill, 25% incinerated, 16% recycled and the remaining 19% are leaked into the environment. The increase of plastic wastes and demand of plastic markets serve as a good economic indicator for investor and government initiative to invest in technologies that converts plastic waste into value-added product such as fuel and construction materials. This will close the loop of the life cycle of plastic waste by achieving a sustainable circular economy. This review paper will provide insight of the state of plastic waste before and during the COVID-19 pandemic. The treatment pathway of plastic waste such as sterilisation technology, incineration, and alternative technologies available in converting plastic waste into value-added product were reviewed.
The term "Total petroleum hydrocarbons" (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research.
Neodymium-doped polyaniline supported Zn-Al layered double hydroxide (PANI@Nd-LDH) nanocomposite has been prepared via an ex-situ oxidative polymerization process. The as-prepared nanocomposite shows selective fluorescence detection and adsorption of hexavalent chromium Cr(VI) within a short period. The fluorescence intensity of PANI@Nd-LDH decreases linearly with Cr(VI) concentrations ranging from 200 ppb to 1000 ppb with a limit of detection (LOD) of 1.5 nM and a limit of quantification (LOQ) of 96 nM. The sensing mechanism can be ascribed by the inner filter effect of Cr(VI), the intercalation of Cr(VI) within the intergallery region of LDH, and the synergistic affinity of metal ions along with the polymer chain for Cr(VI). The adsorption performance of PANI@Nd-LDH nanocomposite is evaluated for Cr(VI) from wastewaters, which displayed high removal capacity towards Cr(VI) (219 mg/g) as compared on bare Nd-LDH (123 mg/g) and LDH (88 mg/g) respectively. The adsorption of Cr(VI) on PANI@Nd-LDH depends on the pH of the aqueous solution. The adsorption isotherm and kinetics are supported by the Langmuir model and pseudo-second-order model, respectively. Owing to the highly sensitive detection and adsorption of Cr(VI) from aqueous water samples demonstrated the potential application of PANI@Nd-LDH as an excellent environmental probe can be exploited.