Comments on “Two-dimensional concentration distribution for mixing-controlled bioreactive transport in steady-state” by O.A. Cirpka and A.J. Valocchi     

Haibing Shao  Florian Centler  Cecilia De Biase  Martin Thullner  Olaf Kolditz 《Advances in water resources》2009

In this comment we present a re-analysis of the analytical solution presented by Cirpka and Valocchi for steady-state concentrations of dissolved bioreactive compounds and bacterial biomass in porous media. We discuss the validity range of the analytical solution. In particular, the criterion used to determine the sustainability of biomass is revisited. This re-analysis shows that the ω$\omega$ criterion used by Cirpka and Valocchi is only a necessary but not a sufficient criterion to determine the bioreactive zones. As a consequence, the analytical solution does not provide the exact distribution of compounds throughout the domain, but can serve as upper or lower boundaries for species concentrations at a given location. These conclusions are supported by the simulation results obtained from an established reactive transport model.  相似文献   

Performance of A Combination Process of UV/H2O2/Micro‐Aeration for Oxidation of Dichloroacetic Acid in Drinking Water     

WenHai Chu  N. Y. Gao  Y. Deng 《洁净——土壤、空气、水》2009,37(3):233-238

The decomposition of dichloroacetic acid (DCAA) in water using a UV/H₂O₂/micro‐aeration process was investigated in this paper. DCAA cannot be removed by UV radiation, H₂O₂ oxidation or micro‐aeration alone, while UV/H₂O₂/micro‐aeration combination processes have proved effective and can degrade this compound completely. With initial concentrations of about 110 μg/L, more than 95.1% of DCAA can be removed in 180 min under UV intensity of 1048.7 μW/cm², H₂O₂ dosage of 30 mg/L and micro‐aeration flow rate of 2 L/min. However, more than 30 μg/L of DCAA was left after 180 min by UV/H₂O₂ combination process without micro‐aeration with the same UV intensity and H₂O₂ dosage. The effects of applied UV radiation intensity, H₂O₂ dose, initial DCAA concentration and pH on the degradation of DCAA have been examined in this study. Degradation mechanisms of DCAA with hydroxyl radical oxidation have been discussed. The removal rate of DCAA was sensitive to operational parameters. There was a linear relationship between rate constant k and UV intensity and initial H₂O₂ concentration, which indicated that a higher removal capacity can be achieved by improvement of both factors. A newly found nitrogenous disinfection by‐product (N‐DBP)‐DCAcAm, which has the potential to form DCAA, was easier to remove than DCAA by UV/H₂O₂ and UV/H₂O₂/micro‐aeration processes. Finally, a preliminary cost comparison revealed that the UV/H₂O₂/micro‐aeration process was more cost‐effective than the UV/H₂O₂ process in the removal of DCAA from drinking water.  相似文献   

Rice Husk Ash as a Low Cost Adsorbent for the Removal of Methylene Blue and Congo Red in Aqueous Phases     

Anirban K. Chowdhury  Anupam D. Sarkar  Amitava Bandyopadhyay 《洁净——土壤、空气、水》2009,37(7):581-591

Adsorption is of significant importance for effluent treatment, especially for the treatment of colored effluent generated from the dyeing and bleaching industries. Low cost adsorbents have gained attention over the decades as a means of achieving very high removal efficiencies to meet effluent discharge standards. The present article reports on batch investigations for color removal from aqueous solutions of Methylene Blue (MB) and Congo Red (CR) using Rice Husk Ash (RHA) as an alternative low cost adsorbent. The performance analysis was carried out as a function of various operating parameters, such as initial concentration of dye, adsorbent dose, contact time, shaker speed, interruption of shaking and ionic concentration. Performance studies revealed that a very high percentage removal of color was achievable for both dyes. The maximum percentage removal of MB was 99.939%, while 98.835% removal was observed for CR. These percentage removals were better than existing systems. Detailed data analysis indicated that adsorption of MB followed the Temkin isotherm, while CR followed the Freundlich isotherm. These isotherms were feasible within the framework of experimentation. Batch kinetic data, on the other hand, indicated that pseudo second order kinetics governed adsorption in both cases. Sensitivity analysis further indicated that the effects of initial dye concentration, shaker speed, pH and ionic strength had no noticeable effect on the percentage dye removal at equilibrium. Batch desorption studies revealed that 50% acetone solution was optimum for CR, while desorption of MB varied directly with acetone concentration.  相似文献   

A Study of the Thermodynamics and Kinetics of Copper Adsorption Using Chemically Modified Rice Husk     

Hasanur Jaman  Debarati Chakraborty  Papita Saha 《洁净——土壤、空气、水》2009,37(9):704-711

The use of rice husk as a low cost adsorbent for the removal of copper from wastewater has been explored in a laboratory scale experiment. The rice husk used for the study was treated with alkali to increase the sorption properties. The influence of metal ion concentration, weight of biosorbent, stirring rates, temperature and pH were also evaluated, and the results are fitted using adsorption isotherm models. From the experimental results it was observed that almost 90–98% of the copper could be removed using treated rice husk. The Langmuir adsorption isotherm, Freundlich isotherm and Tempkin isotherm models were used to describe the distribution of copper between the liquid and solid phases in batch studies, and it was observed that the Langmuir isotherm better represented the adsorption phenomenon. The experimental rate constant, activation energy, Gibbs free energy, enthalpy and entropy of the reaction were calculated in order to determine the mechanism of the sorption process.  相似文献   

Heating rate dependency of petroleum-forming reactions: implications for compositional kinetic predictions     

V. Dieckmann  B. Horsfield  H. J. Schenk 《Organic Geochemistry》2000,31(12)

The generation of bulk petroleum, liquid and gaseous hydrocarbons from the Duvernay Formation was simulated by heating immature kerogens in a closed system (MSSV pyrolysis) at four different heating rates (0.013, 0.1, 0.7 and 5.0 K/min). Using the established parallel reaction kinetic model, temperature and compositional predictions were tested to be suitable for geological conditions by comparing the laboratory results with natural changes in source bitumens and reservoir oil maturity sequences from the Duvernay Formation. In the case of bulk liquid and gaseous hydrocarbons, the above kinetic calculations can be considered valid because their maximum yields are independent of laboratory heating rates. In contrast, the contents of paraffins, aromatics and sulfur compounds show a pronounced heating rate dependence. Extrapolated to geological heating rates, the compositional predictions are consistent with the bulk composition of natural products in the Duvernay-petroleum system showing an increase of paraffinicity and hydrogen content. In contrast to that, the “hump” decreases with decreasing heating rate, a trend which is confirmed by the low amounts of unresolved compounds in natural high maturity products. Because of these heating-rate dependent compositional changes, geological predictions of natural molecular composition by the commonly used kinetic models are not suitable.  相似文献   

煤中有机质二次生烃迟滞性及其反应动力学机制   总被引：25，自引：1，他引：24       下载免费PDF全文

秦勇  张有生 《地球科学》2000,25(3):278-282

采用自然成熟度系列与其预热残渣系列样品相结合方式, 通过热解模拟方法, 对煤中有机质二次生烃迟滞性显现特征和化学反应动力学机制进行了探讨.结果表明: 二次生烃起始成熟度增高, 二次生烃峰位成熟度呈规律性后移, 二次生烃作用“死线”位于R_o=4.0 %左右; 二次生烃峰位成熟度与起始成熟度之差随起始成熟度的增高呈抛物线式演化, 二次生烃的绝对迟滞性和相对迟滞性均呈阶段性演化, 由此可对二次生烃迟滞深度进行预测; 二次生烃半峰宽随起始成熟度呈阶段性演化, 暗示二次生烃起始成熟度位于生油高峰附近的烃源岩, 其生烃量可能相对较大.同时, 原始样品平均活化能的演化经历了4个阶段, 它们与热解生烃量及二次生烃迟滞性的阶段性演化特征高度吻合, 揭示出二次生烃作用严格受控于反应动力学的地球化学机制.   相似文献   

塔里木盆地熟化有机质成烃动力学模型原始参数的恢复及意义   总被引：12，自引：2，他引：10  

卢双舫  李启明 《地质论评》2000,46(5):556-560

针对塔里木盆地主力源岩层大多埋深较大、成熟度较高,对这些源岩所进行的模拟实验不能反映或描述样品在达到现今埋深这前所经历的成烃演化过程的难题,本文先由模拟实验数据出发,建立和标定各样品的化学动力模型,在此基础上,推导和建立了恢复化学动力的始参数的方法并利用塔里木盆地的样品进行了应用。结果表明,深埋样品有机质中有相当部分的低活化能组分已在其前期演化过程中被成烃反应所消耗。因此,要客观描述样品的全部成烃  相似文献   

吸附对土壤水环境中有机污染物生物降解过程的影响研究   总被引：11，自引：1，他引：10       下载免费PDF全文

刘凌  崔广柏 《水科学进展》2000,11(4):401-407

在土壤水环境系统中,吸附作用是影响有机污染物生物降解过程的主要制约因素。污染物的吸附性越强,则其存在于土壤水溶液的重量百分比就越小,生物降解可能性也就越低。本文建立了定量描述吸附作用对有机污染物在土壤颗粒内部传输过程影响的数学模型。通过模型计算发现,有机污染物的土壤-水吸附分配系数Kd越大,则其从土壤颗粒内部传输到外部水溶液的速率就越小,总的降解速率也就越低。  相似文献   

Study of Pyrolysis Kinetics of Asphaltenes in Silurian Oilsands in the Tarim Basin   总被引：3，自引：0，他引：3  

LIAO Zewen  GENG AnsongThe State Key Laboratory of Organic Geochemistry  Guangzhou Institute of Geochemistry  Chinese Academy of Sciences  Guangzhou  Guangdong 《《地质学报》英文版》2000,74(3):680-684

It is a special petroleum geological phenomenon that Silurian oilsands are extensively distributed in the central and northeast Tarim basin. Some geochemical studies of the oilsands have been carried out, but there is still great controversy over the hydrocarbon-regenerating potential of oilsands and the possibility of Silurian oilsands as hydrocarbon source rocks. In this study, the kinetics of asphaltenes pyrolysis was directly used to simulate the potential of Silurian oilsands for regenerating hydrocarbons. According to the experimental results, combined with other related organic geochemical analysis, it is considered that Silurian oilsands in the Tarim basin have a high hydrocarbon-regenerating potential and are latent hydrocarbon source rocks.  相似文献   

煤生烃动力学研究进展     

吴保祥  段毅  郑朝阳  王传远 《煤田地质与勘探》2006,34(2):33-37

化学反应动力学是评价煤的生烃过程和生烃特性行之有效的方法。目前,煤生烃动力学模型理论研究和标定得到了不断的深化,煤生烃动力学研究在认识煤源岩成烃规律方面也有长足发展,并在煤源岩评价中初见成效。但是在压力条件下,关于生烃动力学在煤源岩定量和动态评价方面的研究则报道较少。另外,对单体化合物形成动力学的研究还处于探索之中。这些研究将代表煤源岩生烃动力学领域未来发展的重要方向。   相似文献