Predicting pollutant removal in constructed wetlands using artificial neural networks(ANNs)

Growth in urban population,urbanisation,and economic development has increased the demand for water,especially in water-scarce regions.Therefore,sustainable approaches to water management are needed to cope with the effects of the urbanisation on the water environment.This study aimed to design novel configurations of tidal-flow vertical subsurface flow constructed wetlands(VFCWs) for treating urban stormwater.A series of laboratory experiments were conducted with semi-synthetic influent stormwater to examine the effects of the design and operation variables on the performance of the VFCWs and to identify optimal design and operational strategies,as well as maintenance requirements.The results show that the VFCWs can significantly reduce pollutants in urban stormwater,and that pollutant removal was related to specific VFCW designs.Models based on the artificial neural network(ANN) method were built using inputs derived from data exploratory techniques,such as analysis of variance(ANOVA) and principal component analysis(PCA).It was found that PCA reduced the dimensionality of input variables obtained from different experimental design conditions.The results show a satisfactory generalisation for predicting nitrogen and phosphorus removal with fewer variable inputs,indicating that monitoring costs and time can be reduced.     

Carrier lifetime regulation strategy to improve the sewage purification capacity of superhydrophobic silver phosphate fabric

Sewage contains a variety of components including oil slick and water-soluble pollutants. How to remove different types of pollutants at the same time is a challenge. In this paper, superhydrophobic fabric (SH fabric) was prepared by the combination of silver phosphate photocatalyst with fabric substrate. Surface oil slick and rhodamine B contaminants can be removed simultaneously by SH fabric. The degradation efficiency after three cycles is still maintained above 90% under outdoor light source conditions. In order to improve the degradation efficiency of silver phosphate photocatalyst, ethanol/water mixed solvent was used. And the reasons for the improvement of catalyst performance were studied systematically. It is found that the charge transfer resistance of the silver phosphate catalyst prepared by addition of ethanol (S-3) decreases, while the carrier concentration and lifetime increase. The VB and CB of silver phosphate with the best degradation performance (S-3) are 2.425 eV and 0.135 eV, respectively. It is hoped that this SH fabric could provide a new solution to the improvement of catalyst performance and comprehensive treatment of sewage.     

Modeling of dibenzothiophene oxidative desulfurization using response surface methodology

The effect of reaction temperature, mixing speed and oxidant to catalyst volume ratio, including their interactions on the oxidative desulfurization of dibenzothiophene by using response surface methodology was studied. Hydrogen peroxide was used as oxidant and acetic acid as catalyst. The obtained model accurately predicts conversion of dibenzothiophene and the best conversion of 98.7% was observed at temperature 70°C, mixing speed of 1250 rpm and oxidant to catalyst volume ratio of 1:1. At high temperatures, a major limitation of the desulfurization process is the mass transfer and the high mixing speed is needed to achieve an efficient process.     

Droplet dynamics in a proton exchange membrane fuel cell flow field design with 3D geometry

Water management is crucial to achieve both high-performance and durability of proton exchange membrane fuel cell (PEMFC). Therefore, it is necessary to investigate the dynamic behavior of droplets in PEMFC channel for water management. In this paper, we explore the kinetics of droplets in a 3D flow field by experimental and theoretical analysis. More specifically, we examine the following four perspectives: 1) the movement and falling of droplets, and their force and deformation, 2) the superiority of 3D flow field drainage, 3) the pressure and viscous force under different scenarios including varying droplet sizes and velocities, and 4) the expression describing the shape change of droplets. The results show that the 3D flow field has a greater driving force on droplets and that their deformation affects the discharge of liquid water. Throughout the study, we provide better understanding of droplet dynamic in PEMFC gas channels. It enables to optimize the design and working conditions of these channels.     

Simultaneous bioelectricity generation and pollutants removal of sediment microbial fuel cell combined with submerged macrophyte

A submerged macrophyte sediment microbial fuel cell (SP-SMFC) was constructed in this study. Ceratophyllum demersum L., Vallisneria natans, Hydrilla verticillate were chosen as the submerged plants to form cer-SMFC, val-SMFC, hyd-SMFC systems. Plant groups showed the advantage of bioelectricity generation and pollutants removal compared with the unplanted system. The cer-SMFC group stood out with the maximum power density as 24.56 mW m^?2 and the average pollutants removal in overlying water (COD: 81.16%, TN: 65.27%, TP: 79.10%) and in sediments (TN: 26.40%, TP: 21.79%). The determination of root exudates and radial oxygen loss (ROL) demonstrated that C. demersum L. was superior to other studied submerged macrophytes. More root exudates may contribute to an increase in available substrates for electrochemically active bacteria and other microorganisms. Higher enzyme activities were obtained in three SP-SMFCs (especially in cer-SMFC). ATPase and APA activities in cer-SMFC group were increased by over 40% compared with the control. The results indicated that the presence of plants enhanced the microorganism activities, thereby improving bioelectricity generation and pollutants removal. This study will facilitate the application of SP-SMFC technology as an alternative for in situ remediation of polluted sediments.     

Physicochemical properties of pine-derived bio-chars modified by metal oxides and their performance in the removal of NO

Pine-derived bio-chars have been prepared at different temperatures with and without KOH chemical activation. Three metal oxides (V₂O₅, MnO and CuO) were loaded on this chars by incipient-wetness impregnation method respectively. Pine wood pellets were characterized by thermogravimetric, and pine-chars samples were characterized by SEM-EDS, XRD, N₂ physisorption and FTIR. Activity test for the selective catalytic reduction of NO with NH₃ was also carried out in dry simulated flue gas at fixed temperature 160 °C. The results show that pretreatment with KOH and carbonization at 600 °C seems to be the best method for pine-chars preparation. Active metal oxides are well distributed on the surface of carbon support and are partly reduced by carbon during preparation. The mesopores disappear in V- and Mn-containing samples, and V-addition could decrease the amount of micropores as well. At the fixed temperature 160 °C, the active metal oxides have an order of CuO > V₂O₅ >> MnO_x >> Non-modified sample on the NO reduction activity. Pine-chars modified by CuO seems to be the best option in this research.     

Turbidity removal of fine coal–water suspension by flocculation using Taguchi (L16) experimental design

Taguchi method is rather practical way for setting the best combination of different variables for various parameters in such phenomenon requiring excessive number of experiments. In this study, a series of flocculation experiments were performed using Taguchi (L₁₆) experimental design to determine the optimum conditions for the turbidity removal from fine coal suspensions. The effects of some controllable factors on the turbidity removal were evaluated by effective flocculation recovery via analysis of mean statistical approach and the percentage contributions of each parameters were also defined using analysis of variance statistical approach. The most influential factor was determined as the polymer concentration with a contribution of 47.831%. The optimum conditions were ascertained as pH?=?7, stirring speed of 500?rpm, polymer concentration of 2?mg/L, flocculation time of 3?min, and polymer type of 934SH.     

有色冶炼二次含砷物料碱法脱砷工艺现状

分析了典型二次含砷物料化学成分特点,概括了当前有色冶炼工业中产生的二次含砷物料碱法脱砷工艺及原理,主要包括湿法脱砷工艺和火法—湿法联合脱砷工艺。其中,碱法脱砷工艺常用NaOH单碱浸出、NaOH-Na_2S混合碱浸出和NaOH+Na_2S混合碱两段浸出三种体系,并采用双氧水、加压、曝气、微波、球磨等氧化手段强化砷的浸出;火法—湿法联合脱砷工艺主要有低温碱性熔炼—水浸、焙烧预氧化—碱性浸出以及低温碱性焙烧—热水浸出工艺,低温碱性焙烧—热水浸出工艺选择性脱砷效果好,物料普适性广。最后,结合现有研究指出了碱法脱砷工艺存在的问题及二次含砷物料无害化、资源化研究方向。