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A novel titanium dioxide/activated carbon (TiO₂/AC) composite where AC derived from oil palm empty fruit bunch (EFB) was synthesised by using sol–gel method. All the samples were characterised by using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Fourier transformed infrared (FTIR), thermogravimetric analysis (TGA) and surface analyser. SEM analysis showed that TiO₂ particles were successfully embedded and well distributed on the AC surface. The elemental composition analysis found that the TiO₂/AC composite contained titanium (Ti), oxygen (O) and carbon (C) atoms. Meanwhile, the appearance of new band at about 960 cm⁻¹ which assigned to the Ti–O stretching was observed in the FTIR spectra when the AC was incorporated into TiO₂. TGA analysis showed that the weight loss of 32 wt.% from 150 to 550 °C was due to the decomposition of amorphous carbon layers and loss of hydroxyl groups on TiO₂. It was found that the TiO₂/AC composite had better performance in the sonocatalytic degradation of malachite green as compared to the individual AC and TiO₂ because the TiO₂/AC composite had dual functionality and huge number of active sites which could promote the mass transfer of dye molecules towards catalyst surface. By using 1.5 g/L of TiO₂/AC composite which calcined at 700 °C on 100 mL of 200 mg/L of malachite green at solution pH of 7, a degradation efficiency of 87.11% had been achieved after 30 min of ultrasonic irradiation. A lower chemical oxygen demand (COD) removal (81.75%) was observed because the structured dye molecules underwent mineralisation process during the sonocatalytic degradation to generate intermediate compounds. The TiO₂/AC composite was able to be recycled and still achieved a high degradation efficiency of 76.78% after second catalytic cycle as compared to the fresh TiO₂/AC composite with degradation efficiency of 87.11%. In conclusion, the TiO₂/AC composite had high reusability and promising for practical applications in textile industry.

The occurrence of titanium dioxide nanoparticles (nTiO₂), in the effluents released from wastewater treatment plants, has raised concerns. The fate of nTiO₂ and their potential impact on organisms from different ecosystems are widely investigated. For the first time, in this work, we report the responses of an oleaginous bacteria Rhodococcus opacus PD630, belonging to an ecologically important genus Rhodococcus to environmentally relevant concentrations of nTiO₂, under dark and UV light conditions. We observed a dose-dependent increase in nTiO₂ uptake by the bacteria that reached a maximum of 1.4 mg nTiO₂ (g cell)⁻¹ under mid-log UV exposure, corresponding to 97% uptake. The nTiO₂ induced oxidative stress in bacteria that increased from 25.1 to a maximum of 100.3, 44.1, and 51.7 μmol .OH (g cell)⁻¹ under dark, continuous, and mid-log UV, respectively. However, nTiO₂ did not affect bacterial viability. Further, due to oxidative stress, the triacylglycerol (biodiesel) content from bacteria increased from 30% to a maximum of 54% CDW. Based on our findings, we propose an application of R. opacus PD 630 in nTiO₂ remediation due to their high nTiO₂ uptake and resistance.

For plant growth, cadmium (Cd) is a toxic and easily accumulated element but silicon (Si) is beneficial. To explore the alleviating effect of Si on Cd toxicity to plants in Cd-contaminated calcareous soil, the effect of Si on Cd absorption was investigated for cucumber organs in pot experiments. The Cd concentration of cucumber organs using an atomic absorption spectrophotometer. The Si significantly inhibited Cd uptake by cucumber organs and was most effective for Si application of 100–200 mg kg⁻¹. On the whole, the translocation factors of stems and leaves did not vary significantly, but substantially varied in fruit. The distribution pattern of Cd content in different cucumber organs follows: root > stem > leaf > > fruit. For Cd content in soil ≤ 3 mg kg⁻¹, the Cd content in cucumber fruit was lower than the maximum limit of Cd content in fresh vegetables in China (GB2762-2017) for Si application of 100–300 mg kg⁻¹. However, with the Cd treatment of 5 mg kg⁻¹, the content of Cd in cucumber fruit exceeded this limit, even though Si alleviated Cd toxicity to some extent. Therefore, Si had a substantial alleviating effect on Cd uptake in cucumber, effectively reduced Cd toxicity to cucumber in calcareous soil. The study may help us understand the mechanism for silicon-mediated Cd tolerance in calcareous soil and provide theoretical basis for the application of silicon in the production of crops in alkaline soil polluted by Cd.

The response of soil microbiota to hydrocarbon contamination has been studied normally several months after the event. However, as those studies represent a “long-term” context for microbial processes, since protozoa succession can be achieved after 28 days, we wonder how fast does trophic structure of ciliates and flagellates recover from a strong pulse of petroleum contamination under the influence of Medicago sativa. We hypothesized that the root effect of M. sativa would promote faster recovery of the protozoan trophic structure, in comparison with the level reached in unplanted microcosms. The abundances of individuals, species, and trophic groups of ciliates and flagellates were determined at 1, 7, 14, and 30 days after a single pulse of 50,000 ppm of light petroleum on soil microcosms unplanted and planted with M. sativa, and their respective controls. Protozoan diversity and trophic groups were strongly reduced immediately after the pulse of contamination. Ciliates and flagellate trophic diversity increased steadily in all microcosms after 7 days. However, unplanted contaminated and planted contaminated microcosms remained the poorest communities and reached full recovery of trophic groups after 30 days. Also, the protozoan communities were segregated into 2 groups: the first from petroleum and the second formed by non-polluted microcosms. These results suggest that petroleum is a strong selection factor leading to an alternative protozoan community composition and the root effect of M. sativa promotes faster recovery of ciliate and flagellate communities after a devastation produced by a strong pulse of petroleum contamination.

Heavy metal contamination is a global issue, where the prevalent contaminants are arsenic (As), cadmium (Cd), chromium (Cr)(VI), mercury (Hg), and lead (Pb). More often, they are collectively known as “most problematic heavy metals” and “toxic heavy metals” (THMs). Their treatment through a variety of biological processes is one of the prime interests in remediation studies, where heavy metal-microbe interaction approaches receive high interest for their cost effective and ecofriendly solutions. In this review, we provide an up to date information on different microbial processes (bioremediation) for the removal of THMs. For the same, emphasis is put on oxidation-reduction, biomineralization, bioprecipitation, bioleaching, biosurfactant technology, biovolatilization, biosorption, bioaccumulation, and microbe-assisted phytoremediation with their selective advantages and disadvantages. Further, the literature briefly discusses about the various setups of cleaning processes of THMs in environment under ex situ and in situ applications. Lately, the study sheds light on the manipulation of microorganisms through genetic engineering and nanotechnology for their advanced treatment approaches.

Landfill is a public and environmental health problem; establishing and understanding methodologies to decrease its toxicity are thus necessary. Leachate samples were collected, at a sanitary landfill, immediately after the exit from the landfill, i.e. raw leachate (collection point A), after conventional treatment (point B) and after treatment by wetlands (point C). D. parodizi specimens were exposed to 3%, 10% and control (0%) dilutions of leachate from these collection points for 7 days. Markers of antioxidant defences and cell damage were analysed. At point B, the gills of D. parodizi showed higher glutathione-S-transferase (GST) and glutathione reductase (GR) activity; the latter is a supplier of glutathione reductase (GSH). The low GST activity at point A was associated with the hormesis effect. Higher levels of superoxide dismutase (SOD), ethoxyresorufin-O-deethylase (EROD) and glutathione peroxidase (GPx) occurred at point A. Glucose-6-phosphate dehydrogenase (G6PDH) was inhibited at the points with the highest pollutant load and at the highest leachate dilutions. Higher levels of markers at point A may be related to the high pollutant charge and specific compounds present in the untreated leachate. The multi-xenobiotic resistance mechanism (MXR), metallothionein-like proteins (MT) and lipid peroxidation (LPO) did not vary among treatments. The biomarker responses showed negative effects of the leachate on the freshwater bivalve and simultaneously showed that the wetland treatment employed at the Caximba sanitary landfill is effective.

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar–iron oxides, namely biochar–magnetite (BC-M), biochar–ferrihydrite (BC-F), biochar–goethite (BC-G), and biochar–hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar–iron oxides had huge surface areas of 691–864 m²/g and average pore diameters of 3.4–4.0 nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar–iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar–iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.

Simulation of groundwater quality is important for managing water resources and mitigating water shortages, especially in arid and semiarid areas. Geostatistical models have been used for spatial prediction and interpolation of groundwater parameters. Recently, hybrid intelligent models have been employed for the simulation of dynamic systems. In this study, hybrid intelligent models, based on a neuro-fuzzy system integrated with fuzzy c-means data clustering (FCM) and grid partition (GP) models as well as artificial neural networks integrated with particle swarm optimization algorithm, were used to predict the spatial distribution of chlorine (Cl), electrical conductivity (EC), and sodium absorption ratio (SAR) parameters of groundwater. Results of the hybrid models were compared with geostatistical methods, including kriging, inverse distance weighting (IDW), and radial basis function (RBF). The latitude and longitude values of observation wells and qualitative parameters in three states of maximum, average, and minimum were introduced as input and output to the models, respectively. To evaluate the models, the root mean squared error (RMSE), the mean absolute error (MAE), and CC statistical criteria were used. Results showed that in the hybrid models, NF-GP with the lowest RMSE and MAE and highest CC was the most suitable model for the prediction of water quality parameters. The RMSE, MAE, and CC values were 107.175 (mg/L), 79.804 (mg/L), and 0.924 in the average state for Cl; were 518.544 (μmho/cm), 444.152 (μmho/cm), and 0.882 for electrical conductivity; and were 1.596, 1.350, and 0.582 for sodium absorption ratio, respectively. Among the geostatistical models, the kriging was found more accurate. Using the coordinates of wells will eventually allow the NF-GP to be used for more sampling and replace the visual techniques that require more time, cost, and facilities.

The objective of this study is to examine the relationship between corporate social performance (CSP) as proxy of corporate social responsibility (CSR) and corporate firm’s performance (CFP) in the context of Pakistani financial and non-financial firms sectors. This study comprises two main firm’s performance indicators such as market base (excess stock returns) and accounting base (returns on assets and returns on capital). The data set starts from 2011 to 2017 and consists of three hundred and fifty (350) firms on equal numbers of financial and non-financial firms. This study uses a non-linear and disaggregated approach for data analysis. The results of the linear model indicate that CSP and returns on capital have a negative relationship, while the non-linear model of CSP and accounting base performance as CFP have positive association in the domain of long run. There is a significant relationship that exist among environmental social governance (ESG) disclosure score, government sub-components score, and social performance. However, a U-shaped association found between CFP and government sub-components, which further suggest that governance has a vital role toward CSP and CFP components.