Designer carbon nanotubes for contaminant removal in water and wastewater: A critical review

The search for effective materials for environmental cleanup is a scientific and technological issue of paramount importance. Among various materials, carbon nanotubes (CNTs) possess unique physicochemical, electrical, and mechanical properties that make them suitable for potential applications as environmental adsorbents, sensors, membranes, and catalysts. Depending on the intended application and the chemical nature of the target contaminants, CNTs can be designed through specific functionalization or modification processes. Designer CNTs can remarkably enhance contaminant removal efficiency and facilitate nanomaterial recovery and regeneration. An increasing number of CNT-based materials have been used to treat diverse organic, inorganic, and biological contaminants. These success stories demonstrate their strong potential in practical applications, including wastewater purification and desalination. However, CNT-based technologies have not been broadly accepted for commercial use due to their prohibitive cost and the complex interactions of CNTs with other abiotic and biotic environmental components. This paper presents a critical review of the existing literature on the interaction of various contaminants with CNTs in water and soil environments. The preparation methods of various designer CNTs (surface functionalized and/or modified) and the functional relationships between their physicochemical characteristics and environmental uses are discussed. This review will also help to identify the research gaps that must be addressed for enhancing the commercial acceptance of CNTs in the environmental remediation industry

Removal of mercury(II) and cadmium(II) ions from synthetic wastewater by a newly synthesized amino and thiolated multi-walled carbon nanotubes

Functionalization of multi-walled carbon nanotubes can be carried out by introducing amino and thiol functional groups onto the nanotube sidewalls. This functionalized multi-walled carbon nanotubes can be used as a new type of efficient metal ions adsorbent from aqueous solutions. In this study, batch and column adsorption experiments were carried to evaluate the adsorption capacities of single and binary system mercury and cadmium. In the single system, the maximum adsorption capacity of 204.64 and 61.10 mg/g were obtained for mercury and cadmium, respectively, while for binary systems, the values of 35.89 and 14.09 mg/g were achieved for mercury and cadmium, respectively. Column breakthrough curves were obtained and described by Yan and Thomas models. The bigger Thomas rate constant (kTh) (120.77 ml/min/mg for Cd(II) and 9.44 ml/min/mg for Hg(II)) indicated that the intensity of adsorption of Cd(II) onto thiolated MWCNTs was higher compared to Hg(II). However, the value of maximum adsorption capacity (qe) for Hg(II) (39.75 mg/g) was bigger than that of Cd(II) (9.72 mg/g) in continuous system.No Full Tex

Application of Ozone and Granular Activated Carbon for Distillery Effluent Treatment

The main objective of this study was to investigate the treatment of distillery vinasse through the integrated process of ozone oxidation and Granular Activated Carbon (GAC) in a continuous process. The continuous process was carried out both by each of the GAC and ozone processes alone and by the combination of the two in order to investigate the synergistic effects of the two modes on COD and color removal in the treatment of vinasse from laboratory ethanol production from cane molasses. The continuous processes were performed at an ozone generation rate of 240mg/h, GAC dose of 100g, and at room temperature (25°C). Color removal efficiency of O3 was higher than its COD removal from vinasse. The COD and color removal efficiencies of the O3 process were about 25% and 74%, respectively. Moreover, GAC/O3 process was found to negatively affect the synergy of COD and color removal efficiency from distillery vinasse. This negative effect decreased by increasing influent pH level. The results indicate that the initial pH has a considerable effect on the three processes investigated

Application of Chemical Coagulation Method for Paper-Recycling Wastewater Treatment

Paper-recycling wastewaters have high volume and high pollution and its treatment is the most difficult and complicated process because of their colored pollutants and certain rigid chemical structure. In this study, the efficiency of alum in coupled with polyaluminum chloride (PACl) coagulant on the treatment of paper recycling wastewater was investigated. The effects of initial pH, initial COD and coagulation concentration on sludge volume index (SVI), and turbidity and COD removal were studied. Set tested for coagulation process was 2-12 initial pH, 200-2000 mg/l of alum concentration, 50-1500 mg/l of PACl concentration and 250- 2250 mg/l initial COD. According to the data obtained from batch studies, maximum percentage removal of turbidity and COD 89.90% and 85.16% respectively. The SVI of 193 ml/gr was found in this study. This study showed that the alum and PACl coagulants have high ability to remove pollutants from wastewater factory

Mapping land degradation risk due to land susceptibility to dust emission and water erosion

Land degradation is a cause of many social, economic, and environmental problems. Therefore identification and monitoring of high-risk areas for land degradation are necessary. Despite the importance of land degradation due to wind and water erosion in some areas of the world, the combined study of both types of erosion in the same area receives relatively little attention. The present study aims to create a land degradation map in terms of soil erosion caused by wind and water erosion of semi-dry land. We focus on the Lut watershed in Iran, encompassing the Lut Desert that is influenced by both monsoon rainfalls and dust storms. Dust sources are identified using MODIS satellite images with the help of four different indices to quantify uncertainty. The dust source maps are assessed with three machine learning algorithms encompassing the artificial neural network (ANN), random forest (RF), and flexible discriminant analysis (FDA) to map dust sources paired with soil erosion susceptibility due to water. We assess the accuracy of the maps from the machine learning results with the area under the curve (AUC) of the receiver operating characteristic (ROC) metric. The water and aeolian soil erosion maps are used to identify different classes of land degradation risks. The results show that 43 % of the watershed is prone to land degradation in terms of both aeolian and water erosion. Most regions (45 %) have a risk of water erosion and some regions (7 %) a risk of aeolian erosion. Only a small fraction (4 %) of the total area of the region had a low to very low susceptibility for land degradation. The results of this study underline the risk of land degradation for in an inhabited region in Iran. Future work should focus on land degradation associated with soil erosion from water and storms in larger regions to evaluate the risks also elsewhere

Application of integrated ozone and granular activated carbon for decolorization and chemical oxygen demand reduction of vinasse from alcohol distilleries

This study investigates the treatment of the distilleries vinasse using a hybrid process integrating ozone oxidation and granular activated carbons (GAC) in both batch and continuous operation mode. The batch-process studies have been carried out to optimize initial influent pH, GAC doses, the effect of the ozone (O3) and hydrogen peroxide (H2O2) concentrations on chemical oxygen demand (COD) and color removal of the distilleries vinasse. The continuous process was carried out on GAC and ozone treatment alone as well as the hybrid process comb both methods to investigate the synergism effectiveness of the two methods for distilleries vinasse COD reduction and color removal. In a continuous process, the Yan model described the experimental data better than the Thomas model. The efficiency of ozonation of the distilleries vinasse was more effective for color removal (74.4%) than COD removal (25%). O3/H2O2 process was not considerably more effective on COD and color removal. Moreover, O3/GAC process affected negatively on the removal efficiency by reducing COD and color from distilleries vinasse. The negative effect decreased by increasing pH value of the influent.No Full Tex