The present study was designed to screen 20 fungi for their potential to degrade the chlorinated organic pesticides endosulfan and chlorpyrifos. Fungi were first screened for their tolerance to various concentrations of target pesticides using soil extract agar and subsequent degradation studies were performed in soil extract broth containing 25 mg/L of the individual pesticide. Pesticide degradation was evaluated using gas chromatography. Other parameters, such as pH and mycelial weight, were also determined. Based on percent growth inhibition of test fungi and subsequent analysis of EC50 values, the overall results revealed that chlorpyrifos showed significantly more growth inhibition in all tested fungi compared with endosulfan. Trametes hirsuta showed complete degradation of both α‐ and β‐endosulfan isomers and Cladosporium cladosporioides displayed maximum degradation of chlorpyrifos. All test fungi degraded endosulfan more efficiently than chlorpyrifos, except Phanerochaete chrysosporium, Trichoderma harzianum, and Trichoderma virens which showed higher degradation of chlorpyrifos than endosulfan. It was also found that all tested fungi degraded α‐endosulfan more efficiently than β‐endosulfan. Endosulfan sulfate was found to be the major degradation product with all tested fungi. Fungi which showed more endosulfan degradation also produced more endosulfan sulfate. However, less endosulfan sulfate was detected with T. hirsuta and Trametes versicolor, although they degraded endosulfan more efficiently. 相似文献
This study analyzes the driving factors behind regional income inequality to provide an important reference for China and other developing countries and to support the formulation of more effective regional development policies. The study used data from 625 county-level administrative units in China in 2017 and conducted a total factor analysis of China's regional income based on 10 economic dimensions using spatially explicit regression methods. The results show that commerce, population footprint, industrialization, and investment are the main factors that affected a Chinese region’s income, but different factors have different degrees of influence in different regions. The impact of economic institutions (developing an institutionally diverse market economy) on income cannot be ignored. Based on our findings, China should give local governments more autonomy, so they can formulate strategies that account for local constraints and opportunities, thereby increasing their chances of decreasing regional income inequality.
Glaciers have a very obvious feedback effect on the global water cycle and environmental change. The Qinghai–Tibetan Plateau, also known as the “Water Towers of Asia,” provides an important source of freshwater resources derived from glacial meltwater. Changes in glaciers on the Qinghai–Tibetan Plateau are the most important aspect of the research related to global climate change. Because only a few input parameters are available, the degree–day factor model of glacier mass balance has been widely used on the Qinghai–Tibetan Plateau. Study of the spatial distribution pattern of degree–day factors for glaciers on the Qinghai–Tibetan Plateau and the factors that influence glaciers is important scientifically. The study of degree–day factors is important to the calculation of the glacial grid mass balance on the Qinghai–Tibetan Plateau, and this data can be used in the analysis of the response of glaciers experiencing climate change and for predicting future glacial trends. Through an analysis of the degree–day factors related to 24 glaciers on the Qinghai–Tibetan Plateau, one can conclude that the mean value of glacial degree–day factors on the Qinghai–Tibetan Plateau is 8.14 mm day?1 °C?1. The glacial degree–day factor shows a longitudinal zonality with values ranging from high to low from east to west, a latitudinal zonality with values ranging from high to low from south to north, and a vertical zonal regularity along with the change of elevation. The spatial distribution pattern of glacial degree–day factors in the Tibetan Plateau is related to the fact that the climate environment across the Qinghai–Tibetan Plateau is mainly affected by the Indian monsoon, the eastern monsoon, and the westerly winds. The climate gradually changes from cold-humid to warm-humid from northwest to southeast. The single-unit glacier of Qinghai–Tibetan Plateau—the Renlongba Glacier—is located in the southeastern portion of the Qinghai–Tibetan Plateau in a warm and humid climate; its degree–day factor is slightly large, averaging at 6.12 mm day?1 °C?1. Mountainous barriers exist in the eastern and western parts of the Renlongba Glacier. On the east side, the degree–day factor is small (5.63 mm day?1 °C?1) because of large mountains block weather systems. The glacial tongue is affected by valley wind, contributing to glacial ablation, so the degree–day factor is large on the tongue, averaging at 6.56 mm day?1 °C?1. The degree–day factor on the west side of the Renlongba Glacier increases gradually increasing radiation and elevation, presenting a vertical zonal feature. In general, the climate of the Qinghai–Tibetan Plateau is mainly affected by the Indian and eastern monsoons and by westerly winds. In dry and cold climatic conditions, the glacial degree–day factor in the Tibetan Plateau is small, while at warm and humid climate conditions, it is large, with latitudinal, longitudinal, and vertical zonality. In addition, the degree–day factor is also affected by blocking, topography, and other local microclimatic conditions. 相似文献
The immobilization agent was the key factor that determined the success of remediation of heavy metal polluted soil. In this study, mercapto-grafted palygorskite (MP) as a novel and efficient immobilization agent was utilized for the remediation of Cd-polluted paddy soil in pot trials, and the remediation mechanisms were investigated in the aspect of soil chemistry and plant physiology with different rice cultivars as model plants. Mercapto-grafted palygorskite at applied doses of 0.1–0.3% could reduce Cd contents of brown rice and straws of different cultivars significantly. Both reduced DTPA-extractable Cd contents in rhizosphere and non-rhizosphere soil and decreasing Cd contents in iron plaques on rice root surfaces confirmed that MP was an efficient immobilization agent for Cd pollutant in paddy soil. In the aspect of soil chemistry, the pH values of rhizosphere and non-rhizosphere soils had no statistical changes in the MP treatment groups, but their zeta potentials decreased obviously, indicating that MP could enhance the fixation or sorption of Cd on soil compositions. In the aspect of antioxidant system, MP could increase POD activity of rice roots significantly to alleviate the stress of Cd to roots, and resulted in the decrease of T-AOC, SOD, and CAT activities of rice roots of the selected cultivars. MP had no inhabitation or enhancement effects on TSH of rice roots but enhance the contents of MTs and NPT to binding Cd to complete detoxification process. MP as a novel and efficient immobilization agent could complete the remediation effects through soil chemistry and plant physiological mechanisms.
Clogging is the most significant challenge limiting the application of constructed wetlands. Application of a forced resting period is a practical way to relieve clogging, particularly bioclogging. To reveal the alleviation mechanisms behind such a resting operation, evapotranspiration and oxygen flux were studied during a resting period in a laboratory vertical-flow constructed wetland model through physical simulation and numerical model analysis. In addition, the optimum theoretical resting duration was determined based on the time required for oxygen to completely fill the pores, i.e., formation of a sufficiently thick and completely dry layer. The results indicated that (1) evapotranspiration was not the key factor, but was a driving force in the alleviation of bioclogging; (2) the rate of oxygen diffusion into the pores was sufficient to oxidize and disperse the flocculant biofilm, which was essential to alleviate bioclogging. This study provides important insights into understanding how clogging/bioclogging can be alleviated in vertical-flow constructed wetlands.
To reveal the formation mechanism of a pulse-jet airflow’s cleaning effect in a filter bag, a theoretical model is built by using the theory of the gas jet and unitary adiabatic flow according to given specifications and dimensions of the bags and resistance characteristics of the cloth and dust layer. It is about the relationship between cleaning system structure and operating parameters. The model follows the principle that the flow and kinetic energy of jet flow injected into a filter bag should be consistent with the flow of cleaning airflow in the bag and the pressure drop flowing through the filter cloth and dust layer. The purpose of the model is to achieve the peak pressure of cleaning airflow, which dominates the effect of the pulse-jet cleaning process. The cleaning system structure includes air pressure in the nozzle, structure and size of nozzle, exit velocity of nozzle, jet distance, and diameter of jet cross section. Based on the condition of the cleaning system structure and operating parameters established by using the theoretical model, Fluent software is applied to carry out a numerical simulation of the jet airflow field at the nozzle’s outlet, jet airflow field between nozzle and bag top, and cleaning airflow field in the filter bag. Experimental results are used to verify the reliability of the theoretical model. They are obtained in a pilot-scale test filter with a single bag, with length 2 m and in general full-scale dimensions of the cleaning system. The results show that when any rectification measure is not installed at the bag opening, the cross-sectional area covered by the jet gas is hardly sufficient to cover the entire area of the bag opening. A large portion of the gases injected into the filter bag will overflow reversely upward from the edge due to pressure differences between the upper area and lower area inside the bag opening. This led to a serious shortage of the cleaning airflow and ar limited increase in static pressure. When a venturi-type rectifier tube is installed at the bag opening, the jet flow is converted to funnel flow for which the cross-section velocity distribution is more uniform at the throat of the rectifier tube due to the guided effects of the upper tapered pipe. Then it is transited to stressful flow below the bag opening via rectified effects of the lower dilated pipe. The results show that the gap between the static pressure of gas in the bag and the expected value is significantly reduced. The theoretical value of the nozzle diameter is enlarged to compensate for two aspects of adverse effects of cleaning airflow and energy. This is because the flow is not a purely free-form jet from the nozzle to the entrance of the rectifier tube and because the gas suffers from local resistance while flowing through the rectifier tube. The numerical simulation and experiment show that the peak pressure of cleaning airflow in the filter bag is able to reach the expected value. The results confirm that the mechanism of the pulse-jet cleaning airflow and the calculation method of the pulse-jet cleaning system structure and operating parameters offered in this study are correct. The study results provide a scientific basis for designing the system of pulse-jet fabric filters.
Implications: Pulse-jet cleaned fabric filters are commonly used for air pollution control in many industries. Pulse-jet cleaning is widely used for this purpose as it enables frequent cleaning while the filter is operating. However, the theoretical system of the forming mechanism of the pulse-jet cleaning has not formed so far. This indicates the theoretical model plays an important role in designing effective pulse-jet cleaned fabric filters. 相似文献