The electrodes in industrial precipitators collect many tons of dust daily, and the efficient transfer of this dust burden to the hoppers is a challenging problem in mechanical engineering. Many varieties of devices have been tried; hammers, vibrators, scrapers, water flushing, gas blasting, etc. Impact devices for this purpose are usually called “rappers.” Laboratory experiments described in this paper show that normal (perpendicular) rapping is more effective than shear rapping; that thick dust layers are more easily removed by rapping than thin ones; that rapping becomes easier with increasing temperature, within limits; and that the electrostatic forces acting upon the precipitated dust layer play an important role. Quantitative data are shown graphically. The relation of these results to previous studies by other investigators is discussed. 相似文献
Due to concerns about ecotoxicological effects of pharmaceuticals and other micropollutants released from wastewater treatment plants, activated carbon adsorption is one of the few processes to effectively reduce the concentrations of micropollutants in wastewater. Although aimed mainly at apolar compounds, polar compounds are also simultaneously removed to a certain extent, which has rarely been studied before. In this study, adsorption isotherm and batch kinetic data were collected with two powdered activated carbons (PACs) to assess the removal of the polar pharmaceuticals 5-fluorouracil (5-Fu) and cytarabine (CytR) from ultrapure water and wastewater treatment plant effluent. At pH?7.8, single-solute adsorption isotherm data for the weak acid 5-Fu and the weak base CytR showed that their adsorption capacities were about 1 order of magnitude lower than those of the less polar endocrine disrupting chemicals bisphenol A (BPA) and 17-α-ethinylestradiol (EE2). To remove 90 % of the adsorbate from a single-solute solution 14, 18, 70, and 87 mg?L?1 of HOK Super is required for EE2, BPA, CytR, and 5-Fu, respectively. Effects of solution pH, ionic strength, temperature, and effluent organic matter (EfOM) on 5-Fu and CytR adsorption were evaluated for one PAC. Among the studied factors, the presence of EfOM had the highest effect, due to a strong competition on 5-Fu and CytR adsorption. Adsorption isotherm and kinetic data and their modeling with a homogeneous surface diffusion model showed that removal percentage in the presence of EfOM was independent on the initial concentration of the ionizable compounds 5-Fu and CytR. These results are similar to neutral organic compounds in the presence of natural organic matter. Overall, results showed that PAC doses sufficient to remove >90 % of apolar adsorbates were able to remove no more than 50 % of the polar adsorbates 5-Fu and CytR and that the contact time is a critical parameter. 相似文献
An assessment of the risk to human health and the environment associated with the presence of organic contaminants (OCs) in landfills necessitates reliable predictive models. The overall objectives of this study were to (1) conduct column experiments to measure the fate and transport of an OC in a simulated solid waste mixture, (2) compare the results of column experiments to model predictions using HYDRUS-1D (version 4.13), a contaminant fate and transport model that can be parameterized to simulate the laboratory experimental system, and (3) determine model input parameters from independently conducted batch experiments. Experiments were conducted in which sorption only and sorption plus biodegradation influenced OC transport. HYDRUS-1D can reasonably simulate the fate and transport of phenol in an anaerobic and fully saturated waste column in which biodegradation and sorption are the prevailing fate processes. The agreement between model predictions and column data was imperfect (i.e., within a factor of two) for the sorption plus biodegradation test and the error almost certainly lies in the difficulty of measuring a biodegradation rate that is applicable to the column conditions. Nevertheless, a biodegradation rate estimate that is within a factor of two or even five may be adequate in the context of a landfill, given the extended retention time and the fact that leachate release will be controlled by the infiltration rate which can be minimized by engineering controls. 相似文献
Surface water from rivers or lakes, infiltrating through porous media, is increasingly used as a source of public water supply. During bank filtration the water chemistry is substantially changed by various processes such as biodegradation, sorption and mixing with ambient groundwater, but the details of this natural attenuation are not yet entirely understood. In order to gain a better understanding, the degradation of an organic substance (DTPA) is examined here using various model approaches for steady state conditions. Models are fitted on data from an experimental study under near-field conditions. The results show advantages and disadvantages of the different model approaches and provide a guideline for the modelling of other organic substances under different but similar conditions. 相似文献