Forecasting of dissolved oxygen in the Guanting reservoir using an optimized NGBM (1,1) model

An optimized nonlinear grey Bernoulli model was proposed by using a particle swarm optimization algorithm to solve the parameter optimization problem. In addition, each item in the first-order accumulated generating sequence was set in turn as an initial condition to determine which alternative would yield the highest forecasting accuracy. To test the forecasting performance, the optimized models with different initial conditions were then used to simulate dissolved oxygen concentrations in the Guanting reservoir inlet and outlet (China). The empirical results show that the optimized model can remarkably improve forecasting accuracy, and the particle swarm optimization technique is a good tool to solve parameter optimization problems. What's more, the optimized model with an initial condition that performs well in in-sample simulation may not do as well as in out-of-sample forecasting.     

稳定同位素追踪水体中的氮来源的研究现状

氮是水体中的主要污染物之一。近几十年来,随着工农业的发展,使得水体中氮的污染呈上升趋势,并在今后可能会持续,最根本的解决方法是找到源头,从根本上切断污染途径以达到消除氮源的污染。在查阅相关文献的基础上,阐述了水中用同位素追踪研究氮的来源的研究进展和存在的问题,对于评价氮的污染现状、污染控制和环境管理具有十分重要的意义。     

可燃性气体含氧量安全限值的探讨

焦炉煤气的安全含氧量目前存在一些异议。由此,提出如何确定可燃性气体含氧量安全限值的问题。笔者提出了惰性气体对含氧量安全限值的影响,探讨了采用化学计算法和作图法能对可燃性气体含氧量作简单确定,用此方法确定焦炉煤气的含氧量安全限值为４％ 。笔者认为,焦炉煤气的安全氧含量可适当放宽,以２％ 为参考值。     

Uncertainty Analysis In Dissolved Oxygen Modeling in Streams

Uncertainty analysis in surface water quality modeling is an important issue. This paper presents a method based on the first-order reliability method (FORM) to assess the exceedance probability of a target dissolved oxygen concentration in a stream, using a Streeter–Phelps prototype model. Basic uncertainty in the input parameters is considered by representing them as random variables with prescribed probability distributions. Results obtained from FORM analysis compared well with those of the Monte Carlo simulation method. The analysis also presents the stochastic sensitivity of the probabilistic outcome in the form of uncertainty importance factors, and shows how they change with changing simulation time. Furthermore, a parametric sensitivity analysis was conducted to show the effect of selection of different probability distribution functions for the three most important parameters on the design point, exceedance probability, and importance factors. Note: This version was published online in June 2005 with the cover date of August 2004.     

Contributions of advective and diffusive oxygen transport through multilayer composite caps over mine waste

The relative contributions of four mechanisms of oxygen transport in multilayer composite (MLC) caps placed over oxygen-consuming mine waste were evaluated using numerical and analytical methods. MLC caps are defined here as caps consisting of earthen and geosynthetic (polymeric) components where a composite barrier layer consisting of a geomembrane (1-2 mm thick polymeric sheet) overlying a clay layer is the primary barrier to transport. The transport mechanisms that were considered are gas-phase advective transport, gas-phase diffusive transport, liquid-phase advective transport via infiltrating precipitation and liquid-phase diffusive transport. A numerical model was developed to simulate gas-phase advective-diffusive transport of oxygen through a multilayer cap containing seven layers. This model was also used to simulate oxygen diffusion in the liquid phase. An approximate analytical method was used to compute the advective flux of oxygen in the liquid phase. The numerical model was verified for limiting cases using an analytical solution. Comparisons were also made between model predictions and field data for earthen caps reported by others. Results of the analysis show that the dominant mechanism for oxygen transport through MLC caps is gas-phase diffusion. For the cases that were considered, the gas-phase diffusive flux typically comprises at least 99% of the total oxygen flux. Thus, designers of MLC caps should focus on design elements and features that will limit diffusion of gas-phase oxygen.     

A numerical study of soil cover performance

In the investigation of soil cover design options for final decommissioning of reactive mine waste, it is often necessary to analyze or predict the anticipated cover performance as a function of the cost of implementation, which is governed by the type, number and thickness of the layers in the cover system. An example of such investigation is presented in this study where one-dimensional evaporation from hypothetical moisture-retaining cover systems is simulated to assess the influence of several cover properties and hydrogeologic parameters on performance. The commercially available transient flow model, SoilCover, was used to compute suction and water content profiles for different cover design scenarios. The predicted water content profile and porosity of layers were then used to estimate the oxygen diffusion coefficients of the various layers. The oxygen diffusion coefficients were used to estimate oxygen flux through the cover systems. The oxygen flux was, in turn, related to the maximum acid flux. The studied cover and hydrogeologic parameters included soil type, thickness of barriers, and water table elevation. Two types of infiltration and oxygen barrier and two types of capillary layer with different thicknesses were studied. The water table was either kept constant at the base of the waste (tailings) or dropped by 0.5, 1, 2, and 3m over 120 days. The results showed that the relationship between water table depression and the thickness of capillary layers, on one hand, and desaturation of the infiltration and oxygen barrier, on the other, is not linear. Relationships between oxygen flux and barrier thickness and between cost increase and performance improvement of the studied cover systems are presented. Finally, a method that outlines steps for site-specific and economically feasible design of multi-layer cover systems is introduced.     

氧化塘中溶解氧浓度与光照强度关系的试验研究

通过室内实验,主要研究了氧化塘中不同表面照度下光照强度沿深度的分布,溶解氧浓度沿深度的分布,以及光照强度与溶解氧浓度的相互关系,并且对试验柱中藻类密度和溶解氧浓度的分布曲线进行了分析,目的是为氧化塘室内模型试验的照度选择和池深设计提供科学依据。      

内循环式生物反应器氧传质及流态特性研究

通过气-液两相普通流化床和内循环式生物反应器(DTBR)的对比研究,发现DTBR具有更好的氧传质能力和氧转移效率。本试验条件下,当表面气速为0.29cm/s时,DTBR的(KLα)20和E4值分别为普通流化床反应器的1.2倍和1.3倍。通过研究影响DTBR混合特性的主要因素,发现表面气速的影响最大,表面液速的影响最小。其它条件相同,表面气速分别为0.29和0.074cm/s时,DTBR的循环时间分别为12s和16s,混合时间分别为76.2s和91.8s。      

Dibutyl phthalate adsorption characteristics using three common substrates in aqueous solutions

• DBP adsorption was tested using three kinds of substrates in constructed wetlands. • The DBP adsorption capacity followed the order: steel slag>gravel>shell sand. • High temperatures increased the DBP adsorption capacity in the substrates. • DOM consistently inhibited the DBP adsorption onto steel slag and gravel. In recent years, the presence and adverse impacts of phthalic acid esters in aquatic environments have gained increasing attention. This work investigated the adsorption behavior of a typical phthalic acid ester, dibutyl phthalate (DBP), onto steel slag, gravel, and shell sand (substrates commonly used in constructed wetlands). The influence of dissolved organic matter (DOM) on DBP adsorption was investigated using humic acid as a proxy for DOM. The results demonstrated that the adsorption of DBP to three substrates reached equilibrium within 96 h, and the adsorption kinetics were well fitted by a pseudo-second-order model. The DBP adsorption isotherms were best fitted by the Langmuir adsorption model. The DBP adsorption capacity decreased in the order of steel slag>gravel>shell sand, with values of 656 mg/kg, 598 mg/kg, and 6.62 mg/kg at 25°C, respectively. DBP adsorbed to the surface of all substrates in a monolayer via an endothermic process. The DBP adsorption capacities of steel slag and gravel decreased as the DOM content increased. The DBP adsorption mechanisms to steel slag and gravel mainly involved the surface coordination of DBP with –OH or –COOH groups and electrostatic interactions. The results of this work suggest that steel slag and gravel may be ideal substrates for use in constructed wetlands to treat wastewater polluted with DBP.     

Phosphorus transformation under the influence of aluminum,organic carbon,and dissolved oxygen at the water-sediment interface: A simulative study

• The three simulation factors caused various changes in both water and sediment. • Responses to simulations differed with the reported natural lakes and wetlands. • Al has dominant effects on sediment P release control among the three factors. • Adding sediment Al can be effective and safe under the simulated conditions. • Polyphosphates were not generated, while added phytate was rather stable. The effects of sediment aluminum (Al), organic carbon (OC), and dissolved oxygen (DO) on phosphorus (P) transformation, at the water-sediment interface of a eutrophic constructed lake, were investigated via a series of simulative experiments. The above three factors had various influences on dissolved P concentration, water pH, water and surface sediment appearance, and P fractions. Additions of Al had the greatest effect on suppressing P release, and the water pH remained alkaline in the water-sediment system under various OC and DO conditions. No dissolution of the added Al was detected. ³¹P-NMR characterization suggested that OC addition did not promote biological P uptake to polyphosphates under oxic conditions. The simulation result on the added phytate indicated the absence of phytate in the original lake sediment. As compared to the reported natural lakes and wetland, the water-sediment system of the constructed lake responded differently to some simulative conditions. Since Al, OC, and DO can be controlled with engineering methods, the results of this study provide insights for the practical site restorations.