COMPOSITE MODELING APPROACH AND EXPERIMENTAL STUDY FOR SUBSURFACE TRANSPORT OF CONTAMINANTS FROM LAND-DISPOSAL SITES

1 .　INTRODUCTIONThecontaminationofsoiland groundwatersystemsandtheadverseeffectsofthecontamina tionoftheseresourceshavebecomeamatterofconsiderableconcern .Thetransportofcontami nantsinsoilandgroundwaterisacompositionofcomplexchemicalandhydraulicphenomena .Dur ingthepastdecadesmuchattentionhasbeengiventothetheoryandmodelingofcontaminanttrans portinsaturatedsoil (Davidetal.1996 ;Bouchard1988;Brusseauetal .1989) .Thisdevelopmenthasbeenacceleratedandincreasedduetothedifficultyandhighcostsof…     

畦灌施肥地表水流与非饱和土壤水流-溶质运移集成模拟：Ⅰ模型

本文基于零惯性量方程和一维对流-弥散方程建立起畦灌溉施肥地表水流溶质运移模型,并利用HYDRUS-2D软件模拟二维非饱和土壤水流溶质运移过程,以一维地表水流溶质运移模拟得到的通量条件作为二维非饱和土壤水流溶质运移模拟的上边界,利用编制的程序将两个模型进行集成,构建起畦灌施肥地表与非饱和土壤水流溶质运移集成模型。基于多时段分步迭代计算方法,实现沿畦长地表入渗溶质通量动态变化条件下的二维非饱和土壤水流溶质运移模拟。     

Optimising the performance of a lab-scale tidal flow reed bed system treating agricultural wastewater.

A gravel-based tidal flow reed bed system was operated with three different strategies in order to investigate its optimal performance for the treatment of a high strength agricultural wastewater. According to the three strategies, individual reed beds were saturated and unsaturated with the wastewater for different periods while reasonably stable hydraulic and organic loadings were maintained. Experimental results demonstrated that the system produced the highest pollutant removal efficiencies with a relatively short saturated period and long unsaturated period, highlighting the importance of oxygen transfer into reed bed matrices during the treatment. Significant removals of some major organic and inorganic pollutants were achieved under all three operational conditions. Nitrification was not the major route of ammoniacal-nitrogen removal when the system was under high organic loading. Due to the filtration of suspended solids and the accumulation of biomass, gradual clogging of the reed bed matrices took place, which caused concerns over the long-term efficiency of the tidal flow system.     

Organic carbon biodegradability and heterotrophic bacteria along a combined sewer catchment during rain events

The aim of this study was the evaluation of fluxes of organic carbon and biodegradability of waste waters during rain events in order to better predict the impacts of combined sewer overflows (CSO). The combined sewer system studied was located in a densely populated urban catchment adjacent to Paris. Five subcatchments of different size, have been monitored during several rain events for suspended solids, conductivity, ammonium, chemical and biological oxygen demand. In addition, two of these subcathments have been evaluated for dissolved and particulate organic carbon, their biodegradable fractions, and the total bacterial biomass. Several indexes, indicate a lower degradability of waste water during dry weather at the downstream stations, accompanied by an increase of bacterial size and bacterial biomass. A further decrease of biodegradable organic carbon related to rain intensity can be seen at all stations. Our results show a higher proportion of refractory organic carbon during rain events than during dry weather with a possible contribution of the in-sewer sediments to the bacterial wet weather flux.     

CSO treatment strategy based on constituent index relationships in a highly urbanised catchment.

In urbanising catchments the variability of particulate matter (solids) and oxygen demanding constituents of wet weather and dry weather characteristics result in variable treatment effectiveness from physical unit operations and biological unit processes. Higher organic concentrations during dry weather flow are more amenable to biological unit processes while the higher inorganic loads generated largely by urban wet weather constituents and much larger flows can be more effectively treated or conditioned by physical unit operations, including ideally preceded by hydrologic controls. This study examines the relationships between total chemical oxygen demand (COD)(t), dissolved chemical oxygen demand (COD)(d), particulate chemical oxygen demand (COD)(p) and solids, measured as total suspended solids (TSS). Results also provide an index for selection and optimisation of treatment operations for combined sewer overflow (CSO) loads.     

Comparison of measured and simulated distribution of microbial biomass in subsurface vertical flow constructed wetlands.

The multi-component reactive transport module CW2D has been developed to model transport and reactions of the main constituents of municipal wastewater in subsurface flow constructed wetlands and is able to describe the biochemical elimination and transformation processes for organic matter, nitrogen and phosphorus. It has been shown that simulation results match the measured data when the flow model can be calibrated well. However, there is a need to develop experimental techniques for the measurement of CW2D model parameters to increase the quality of the simulation results. Over the last years methods to characterise the microbial biocoenosis in vertical subsurface flow constructed wetlands have been developed. The paper shows measured data for microbial biomass and their comparison with simulation results using different heterotrophic lysis rate constants.     

Integrated modelling of two xenobiotic organic compounds.

This paper presents a dynamic mathematical model that describes the fate and transport of two selected xenobiotic organic compounds (XOCs) in a simplified representation of an integrated urban wastewater system. A simulation study, where the xenobiotics bisphenol A and pyrene are used as reference compounds, is carried out. Sorption and specific biological degradation processes are integrated with standardised water process models to model the fate of both compounds. Simulated mass flows of the two compounds during one dry weather day and one wet weather day are compared for realistic influent flow rate and concentration profiles. The wet weather day induces resuspension of stored sediments, which increases the pollutant load on the downstream system. The potential of the model to elucidate important phenomena related to origin and fate of the model compounds is demonstrated.     

A MATHEMATICAL MODEL FOR HEAT AND MASS TRANSFER IN UNSATURATED WET POROUS MEDIA CONSIDERING EFFECT OF CAPILLARY HYSTERESIS

Based on the transport mechanism of heat and mass transfer and by using the minimum gradient theory for unsaturated flow in capillary porous media, a mathematical model is developed for heat and mass transfer in unsaturated wet porous media considering the effect of capillary hysteresis. The heat and mass transport properties in the derived differential equations are analyzed in detail. which opens new way to further develop practical methods for determining heat and mass transport properties in wet porous media.     

区域饱和-非饱和多孔介质的溶质运移简化模型

在迭代求解区域饱和非饱和拟三维渗流模型的基础上,建立区域溶质运移简化模型。该模型将溶质运动在非饱和带简化为一维垂直运动,饱和带简化为二维剖面运动,在非饱和带与饱和带分别形成对流_弥散方程,并通过维持近饱和带溶质质量守恒组成统一的系统,采用有限单元法数值处理技巧,在同一个矩阵方程中求解饱和与非饱和含水层的浓度变化。该模型无需迭代计算,大大减少工作量,为求解区域溶质运移问题提供了新方法。算例验证表明,区域溶质运移简化模型技术可行,结果可信。     

Phenol wastewater remediation: advanced oxidation processes coupled to a biological treatment.

Nowadays, there are increasingly stringent regulations requiring more and more treatment of industrial effluents to generate product waters which could be easily reused or disposed of to the environment without any harmful effects. Therefore, different advanced oxidation processes were investigated as suitable precursors for the biological treatment of industrial effluents containing phenol. Wet air oxidation and Fenton process were tested batch wise, while catalytic wet air oxidation and H2O2-promoted catalytic wet air oxidation processes were studied in a trickle bed reactor, the last two using over activated carbon as catalyst. Effluent characterisation was made by means of substrate conversion (using high liquid performance chromatography), chemical oxygen demand and total organic carbon. Biodegradation parameters (i.e. maximum oxygen uptake rate and oxygen consumption) were obtained from respirometric tests using activated sludge from an urban biological wastewater treatment plant (WWTP). The main goal was to find the proper conditions in terms of biodegradability enhancement, so that these phenolic effluents could be successfully treated in an urban biological WWTP. Results show promising research ways for the development of efficient coupled processes for the treatment of wastewater containing toxic or biologically non-degradable compounds.     

考虑土体非饱和特性的斜坡降雨入渗模型及边坡稳定性分析

降雨入渗是诱发滑坡的关键因素,研究斜坡降雨入渗规律对于滑坡的预测与防范具有重要意义。传统的Green-Ampt模型及改进的Green-Ampt模型均假定入渗过程为均匀饱和入渗,忽略了入渗过程中湿润锋锋面上方非饱和区的存在。针对这一不足,首先,基于达西定律分析斜坡内基质吸力的分布规律;然后,结合非饱和土VG模型得到了斜坡内湿润区含水量沿深度变化的函数关系;最后,基于改进的Green-Ampt模型推导了考虑土体非饱和特性的斜坡降雨入渗模型,并将其引入到无限斜坡稳定性分析当中。研究结果表明:与数值解和现有模型相比,考虑土体非饱和特性的降雨入渗模型能更加准确地反映降雨入渗的过程,基于改进模型计算的稳定性系数较好地揭示了恒定降雨强度下斜坡稳定性的变化规律,证明了该方法的正确性和适用性。     

Surface and subsurface water coupled ecological model in a mangrove swamp,Ishigaki Island,Japan

A surface and subsurface water coupled ecological model is presented to describe material cycling in a mangrove area, to which an ecosystem model is applied in order to account for chemical and biological reactions as well as physical processes. In this model, the nutrient transport from the groundwater to the river is estimated by the combined use of field measurements and numerical simulation of subsurface flow. The water movement and temporal variations in nutrient concentration obtained from the numerical simulation show a good agreement with the field observations, indicating that this model is valid for simulating material cycling in a mangrove area. The numerical simulation reveals that the supply of dissolved nutrients from the mangrove to the coastal area during spring tides is about 1.6 to 5.5 times larger than that during neap tides.     

湿度和密度双变化条件下的非饱和黄土渗透函数

准确确定非饱和土的渗透系数非常重要,而湿度和密度均会对非饱和土的渗透系数产生较为复杂的影响,因此对于对水敏感的非饱和黄土,如何将湿度和密度的影响综合引入渗透函数中,就值得深入研究。基于此认识,利用非饱和土水气运动联合测试方法,对1.4~1.67g/cm3之间几种干密度的非饱和黄土试样进行不同增湿级数的浸水渗透试验,结果表明试样在一定干密度范围内,增湿级数对其渗水系数测定值的影响较小,最大测定值与最小测定值的差值在2倍左右。在此基础上,将不同干密度下渗透系数比与饱和度的关系曲线进行分析,提出了考虑湿度和密度的渗透函数,并通过试验验证了该函数在一定条件下的合理性。     

Are standard wastewater treatment plant design methods suitable for any municipal wastewater?

The design and operational parameters of an activated sludge system were analyzed treating the municipal wastewaters in Istanbul. The design methods of ATV131, Metcalf & Eddy together with model simulations were compared with actual plant operational data. The activated sludge model parameters were determined using 3-month dynamic data for the biological nutrient removal plant. The ATV131 method yielded closer sludge production, total oxygen requirement and effluent nitrogen levels to the real plant after adopting correct influent chemical oxygen demand (COD) fractionation. The enhanced biological phosphorus removal (EBPR) could not easily be predicted with ATV131 method due to low volatile fatty acids (VFA) potential.     

河套平原次生盐渍化地区地下水动态调控模拟研究

在盐荒地野外水盐运移试验的基础上,建立了基于饱和-非饱和带的土壤水盐运移模型,以地下水埋深为调控关键因子,利用HYDRUS软件模拟了河套灌区荒地不同时段的不同控制地下水埋深条件下包气带水盐变化规律。通过模型反算,定量确定了不同时段防治盐渍化的地下水埋深临界值。模拟结果:在年内2~3次灌溉淋滤的条件下,3月-6月份(春融返盐期)控制地下水埋深大于2.4~2.7 m,7月初-9月初,控制地下水埋深大于1.8~2.1 m,9月中旬-11月中旬(秋浇积盐期),控制地下水埋深大于1.5~1.8 m,11月下旬-3月上旬(冬封期)控制地下水埋深大于2.0~2.3 m可使0~50 cm土层的全盐量基本小于0.2%,处于非盐渍化状态。研究结果可为河套平原次生盐渍化区水盐运移调控和盐渍化改良提供借鉴和依据,具有重要理论和应用意义。     

Anaerobic microbial metabolism in hyporheic sediment of a gravel bar in a small lowland stream

Distribution of dissolved oxygen, nitrate, sulphate, carbon dioxide and dissolved organic carbon (DOC), acetate and lactate was studied in the stream and interstitial water along the subsurface flowpath in the hyporheic zone of a small lowland stream. Sediments were found to act as a source of nitrous oxide and methane. Interstitial methane concentrations were significantly much higher in comparison to those from surface water, and were significantly lower in the relatively well oxygenated downwelling zone than in the rather anoxic upwelling zone. The interstitial concentrations of O₂, NO₃^?1 and SO₄^?2 showed significant decline along the subsurface flowpath, while concentrations of CO₂, N₂O, DOC, acetate and lactate remained unchanged. In addition to field measurements, ex situ incubation of sediments was carried out in the laboratory. Maximal methane production was found in the incubation assay using acetate (mean value 380 µg CH₄ kg DW^?1 d^?1). Mean value of the denitrification potential was 1.1 mg N₂O kg DW^?1 d^?1. Nitrous oxide production potential reached 71–100% of denitrification potential. Our results demonstrate that respiration of oxygen, nitrate, sulphate and methanogenesis may coexist within the hyporheic zone and that anaerobic metabolism is an important pathway in organic carbon cycling in the Sitka stream sediments. Copyright © 2005 John Wiley & Sons, Ltd.     

三峡库区乡镇生活污水人工快渗处理中的氮素转化

以三峡库区乡镇生活污水为水源,以三峡库区特有的滤料为介质,研究了三峡库区乡镇生活污水人工快渗处理中氮素的转化行为.结果表明:人工快渗技术用于三峡库区乡镇生活污水无害化处理极为有效,其出水总氮、氨氮及硝氮的平均质量浓度分别为10.18mg/L、6.26mg/L及3.08mg/L,TN、NH+4-N的平均去除率分别为75....     

基于分形理论的非饱和土多相流相对渗透系数模型

相对渗透系数是描述非饱和土水力特性的重要参数之一,然而在传统非饱和土相对渗透系数研究中着重研究了湿润相的渗流特性,而非湿润相的渗流特性研究较少。为研究非饱和土壤多相流运移特征,将土壤孔隙简化为一簇服从分形定律的迂曲毛细管,通过建立液相与气相在多孔介质中的输运特征模型,结合Young-Laplace方程与Buckingham-Darcy定律得到了非饱和土的液相与气相的相对渗透系数模型。该模型仅包含2个参数,其物理意义明确且均可通过试验测得。最后通过8组试验数据对提出的模型进行验证,结果表明提出的模型可较好地描述非饱和土多相渗流特征,验证了其合理性与适用性。     

Hydrogen-driven denitrification of wastewater in an anaerobic submerged membrane bioreactor: potential for water reuse.

An anaerobic submerged membrane bioreactor was coupled with a novel hydrogen delivery system for hydrogenotrophic denitrification of municipal final effluent containing nitrate. The biological treatment unit and hydrogen delivery unit were proven successful in removing nitrate and delivering hydrogen, respectively. Complete hydrogen transfer resulted in reducing nitrate below detectable levels at a loading of 0.14 kg Nm(-3) d(-1). The produced water met all drinking water guidelines except for color and organic carbon. However, the organic carbon was removed by 72% mostly by membrane rejection. To reduce the organic carbon and color of the effluent, post treatment of the produced water is required.     

The Influence of Model Structure Uncertainty on Water Quality Assessment

Physically-based mathematical water quality models are known as potentially effective tools to simulate the temporal and spatial variations of water quality variables along rivers. Each model relies on specific sets of assumptions and equations to simulate the physico-biochemical processes, which influence on its simulation results. This paper aims to improve the insight in the uncertainties related to state–of–the–art river physico-biochemical water quality modelling. Sensitivity analysis is applied to the processes implemented in three most popular commercial software packages: MIKE11, InfoWorks RS and InfoWorks ICM. This is done for the Molse Neet river case study. Firstly, the physico-biochemical processes are screened to obtain a preliminary assessment on the critical processes and to determine the processes that require more detailed comparison. Then, local sensitivity analysis is carried out to specify the sensitive parameters and processes. Results show that the hydrodynamic results, heat transfer rate and reaeration simulations cause large differences in model simulation outputs for water temperature and dissolved oxygen concentrations. The ignorance of processes related to sediment transport, phytoplankton and bacteria has a significant influence on the higher values of organic matter and lower values of dissolved oxygen concentrations. The three models show consensus on the main pollutant sources explaining organic matter and nitrate concentrations, but disagree on the main factors explaining the DO concentrations.