Methylene blue (MB) is a dye used in the textile industry and a potential wastewater pollutant. Adsorption of MB onto the chitosan is a promising method for MB removal. Upon contact with chitosan, MB molecules can aggregate leading to the appearance of additional bands in the MB absorption spectrum. This phenomenon is called metachromasy. In this paper the kinetics and thermodynamic parameters related to the removal of MB as single molecules (Sng-MB) and aggregates (Agg-MB) species by chitosan from simulated wastewater were studied. Additionally, it was investigated means to suppress metachromasy and improve the efficiency of the removal process. For both MB species, the adsorption process followed the pseudo-second-order adsorption kinetics model. For each temperature studied, Agg-MB always presented higher rate constant than Sng-MB, indicating faster adsorption of Agg-MB in comparison with Sng-MB, whereas the highest removal percentage (around 65%) for both species was obtained at 323 K. A lower activation energy was obtained for the adsorption of Agg-MB (28 kJ/mol) than for Sng-MB (65 kJ/mol), indicating Agg-MB adsorption is favored in relation to Sng-MB. The thermodynamic studies indicated the adsorption process for both MB species is endothermic and spontaneous from 298 to 348 K. The metachromasy could be suppressed by performing the experiments at pH 3, leading to a removal percentage around 70% in comparison with 20 and 60%, for experiments at pH 7 and 12, respectively, at 298 K. Analysis of chitosan before and after adsorption process, by using X-ray diffraction, infrared spectroscopy, scanning and transmission electron microscopies, indicated that no structural changes happened to chitosan throughout the process.
In this work, we formulate a predator–prey–pathogen model in which the predator is specialist in nature and infected prey can undergo refugia of constant size to avoid predator attack. To investigate the predation effect on the epidemics, we take a situation where the predator eats infected prey only. This is in accordance with the fact that the infected individuals are less active and can be caught more easily. Though it is a well-known fact that consumption of infected prey may harm predator population, the opposite holds in few cases. This leads to a controlled measure of disease prevalence. As predator consumes a particular type of prey species, Holling type II functional response is appropriate. This corroborates to the specialist type of predator. For biological validity of the model, boundedness of the system is studied. The dynamical behavior of the model has been analyzed throughly. Model analysis shows that all the population remains in coexistence when predator consumes the infected prey rather than the susceptible one. The results establish the fact that the effects of refuge used by prey decrease the equilibrium density of susceptible prey population, whereas the opposite holds for infected prey population. However, equilibrium density of predator may decrease or increase by increasing the amount of prey refuge. Global stability of the coexistence equilibrium point is developed by using Li and Muldowney’s high-dimensional Bendixson’s criterion. Numerical simulations are performed to validate our theoretical results.
Waste cooking oil (WCO) is one of the most promising feedstocks for biodiesel production as it is environment friendly, has energy supply potential, impacts edible oil safety, and enables competitive recycling costs. However, one central roadblock to the development of WCO-based biodiesel in China is its fairly low collection rate in the formal WCO supply chain. Most waste cooking oil is still collected by informal collectors with some flowing back to “table.” The aim of our paper is to identify the most effective incentive conditions and targets in the WCO supply chain to offer recommendations that address this WCO roadblock. Accordingly, we designed a Stackelberg game model among restaurants, recyclers, and biodiesel production enterprises. The results show that restaurants are the best targets for incentives in this WCO supply chain. With a certain amount of monetary incentives, the WCO supply for biofuel production can be improved significantly. If the restaurant subsidy is 4000 yuan/ton, the amount of WCO recycled would increase by 47%, which is far more efficient than incenting recyclers or biofuel producers. We also set up four scenarios and found that compared with a single policy approach (mandatory only or economic incentive only), a combined policy (mandatory with economic incentive) would be the most effective means to incent restaurants to submit WCO for biofuel. There was also a correlation between policy incentive effectiveness and restaurant sensitivity to WCO submission profits. When the price sensitivity was larger than 17.98, the best policy for the government would be to offer economic incentives to restaurants. To guarantee the effectiveness of such policy incentives, supporting laws, policy guidelines, and routine supervision should be provided as well.
The green coconut (Cocus nucifera) is widely consumed in the world; however, its processing generates a large amount of waste, which presents a high energetic potential. The coconut waste is composed of skin, husk, and shell, where each part can be showing different physicochemical and thermal characteristics. Thus, this study presents the physicochemical and thermal characteristics of skin, husk, and shell of green coconut waste. The physicochemical behavior was evaluated by proximate analysis and ultimate analysis, while the thermal behavior was evaluated by thermogravimetric analysis under five different heating rates (5, 10, 15, 20, and 30 °C min−1). In addition, from the thermogravimetric data was evaluated the activation energy (E a) by using Friedman and Ozawa–Flynn–Wall (OFW) methods. The physicochemical and thermal characteristics presented by each part of the coconut indicate that the material can be used completely due to the great similarity between the heating value of each part of the coconut (HHVskin = 18.98 MJ kg−1, HHVhusk = 18.15 MJ kg−1, and HHVshell = 18.64 MJ kg−1), although they different contents of moisture and ash. A different thermal behavior of each part of the coconut was also observed, being associated with the possibility of different components in its structures, which directly influences the E a value. Based on the E a values, the husk shows a better applicability for pyrolysis process, due to lower energy required per mol of biomass.
In this paper, we attempted to map out the research activities in ‘environmental health and toxicology’ through a ‘scientometric analysis’ of the world research outputs. The aim was to identify the historical and current research trajectories in the subject and locate the possible gap in the existing literature. Considering the fact that in the absence of an in-depth analysis of the trends in research, it is utterly possible that some areas of research get more than adequate attention from the global research and policy community, while some equally important areas of the subject remain completely unaddressed or neglected. Our motive is to provide the scientific community, policymakers and academicians a clear picture of ‘where environmental health and toxicology research is heading today and where is the gap in existing studies’. The results of our study show that the publication interest on the topic has observed a constant development during the past 21 years. Nevertheless, considering the intense growth of researches on medical sciences, we argue that environmental health and toxicology research needs further attention in a pollution-laden global environment. We observe a lack of representation from countries and institutes from the global south and thus argue that the current research trends on the topic calls for more research focus on environmental health and toxicology from the institutes and universities present in the developing world. This could be achieved by exploring more collaborative opportunities by the research organizations in both the global north and global south, more research infrastructure and funding in the developing countries, creating adequate human resources through capacity building and training exercises, etc. We further argue that the pioneering journals in the field may contribute or encourage participation of the researchers from the developing world in environmental health and toxicology research by calling for ‘special issues’, especially on the topics of significance of those countries and ensure adequate representation of diverse topics across the globe. Finally, we would like to conclude that it is indispensable for the international research community to appositely recognize the gap in research on environmental health and toxicology and holistically attend to the concerns of significance. It is up to them and the policymakers to ensure that no significant aspect of research is left behind due to inadequate research and policy attention.