Effects of biomass accumulation on microbially enhanced dissolution of a PCE pool: a numerical simulation

Recent studies have shown that dechlorinating bacteria can accelerate the dissolution rate of dense, nonaqueous phase liquids (DNAPLs) containing tetrachloroethene (PCE). We present an advection-dispersion-reaction model for a two-dimensional domain, with groundwater flowing over a pool of free-product PCE. PCE is converted to cis-1,2-dichloroethene (cDCE) and toxicity due to PCE or cDCE is neglected. We adopt previously published correlations relating biomass concentrations and hydraulic conductivity, accounting for biofilm growth and plug-like growth. The system of coupled equations is solved numerically. The high biotransformation rate of PCE increases the concentration gradient of PCE at the water-DNAPL interface, enhancing dissolution. The higher the electron donor (ED) concentration, the larger the dissolution enhancement. Based on the values of maximum specific rate we used, when the electron donor is unlimited, the active biomass accumulates adjacent to the water-NAPL interface and microbial reactions can significantly enhance the pool dissolution. The resulting steady-state dissolution rate can be approximated by a half-order solution when zero-order kinetics are suitable for representing the microbial reaction. However, bioclogging may significantly reduce local hydraulic conductivity; thus, it decreases the flow near the water-DNAPL interface, decreasing dissolution. When the ED is the limiting factor, active biomass accumulates away from the interface. This creates a no-flow zone between the active biomass and the interface. The enlargement of the no-flow zone, due to the donor limitation, diminishes the concentration gradient and the flushing around the water-DNAPL interface. Such adverse impacts may significantly decrease the enhancement predicted by models that do not consider the effects of bioclogging.     

Absorption and reaction kinetics of amines and ammonia solutions with carbon dioxide in flue gas

The removal system for the absorption of CO2 with amines and NH3 is an advanced air pollution control device to reduce greenhouse gas emissions. Absorption of CO2 by amines and NH3 solutions was performed in this study to derive the reaction kinetics. The absorption of CO2 as encountered in flue gases into aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), and NH3 was carried out using a stirred vessel with a plane gas-liquid interface at 50 degrees C. Various operating parameters were tested to determine the effect of these variables on the absorption kinetics of the reactants in both gas and liquid phases and the effect of competitions between various reactants on the mass-transfer rate. The observed absorption rate increases with increasing gas-liquid concentration, solvent concentration, temperature, and gas flow rate, but changes with the O2 concentration and pH value. The absorption efficiency of MEA is better than that of NH3 and DEA, but the absorption capacity of NH3 is the best. The active energies of the MEA and NH3 with CO2 are 33.19 and 40.09 kJ/mol, respectively.     

Organic contamination in the greenhouse soils from Beijing suburbs, China

Selected persistent organic pollutants including HCHs, DDTs and PAHs together with PAEs were determined in the greenhouse soils from Beijing suburbs. The total concentrations were 11.64-29.80 ng g(-1) for HCHs, 18.04-101.33 ng g(-1) for DDTs, 1.34-3.15 microg g(-1) for PAEs and 1.92-7.84 microg g(-1) for PAHs, respectively. Predominance of beta-HCH in all samples was obviously observed, suggesting a lack of new HCHs sources. High concentrations of DDE and DDD in comparison to their parents in the samples indicated that most of the DDT had been transformed into its metabolites. The contamination of PAHs was relatively serious and the most abundant compounds were 4-, 5- and 6-ring unsubstituted PAHs. The profiles reflect the important effect of traffic on the PAHs remaining in greenhouse soils. Three phthalate esters (DIBP, DnBP and DEHP) accounted for more than 97% of the phthalates studied. Analysis of n-alkanes was also performed in order to trace the natural or anthropogenic sources of hydrocarbons. Characterization and identification of these compounds in greenhouse soil may help in development of strategies to be used in monitoring organic pollutants in this region.     

冷拔无缝钢管爆裂分析

在无缝钢管的冷拔过程中,存在着冷作硬化和氢脆现象,它们是造成钢管爆裂的主要原因。此文对两个现象进行了分析,提出了一些防止钢管爆裂的措施。     

地球化学动力学反应器原理和速率方程测定

主要介绍了地球化学动力学实验研究中的三种反应器类型，即间歇反应器、活塞流反应器和混合流反应器，概述了它们的工作原理和速率方程测定方法，最后对比了三类反应器的性能，指出混合流反应器最适合于测定矿物－水反应速率。     

农用化学品对农产品的污染及其对策

由于农业大量使用化学品 ,使农产品的农药残留量及其衍生物增加 ,从而对人体健康造成具大的危害性。本文的主要目的就是让人们进一步认识在农产品生产中使用农用化学品的危害 ,倡导我国农业走绿色农产品生产的道路     

环保型煤炭开采与利用技术--煤炭地下气化

介绍了煤炭地下气化技术的开发与应用，相比传统煤炭开采燃用技术，煤炭地下气化实现了煤炭清洁开采与利用，指出煤炭地下气化技术是环保型开采与利用技术，应用积极推广利用。     

含油污水乳化液微波分离实验研究

针对油气田乳化含油污水难分离的特点,利用微波技术进行的实验室研究结果表明,微波辐照温度与其后的静置时间都是影响其破乳率的重要因素,其分离效果随微波辐照后温度的增高而加强,而且在相同温度下乳液破乳率随静置时间加长而迅速增高。研究结果证实,微波辐射技术具有时间短、能耗少、效率高等特点,且经过微波处理后的含油污水易于进行油品回收再利用,有良好的应用前景。     

Saltcedar control and water salvage on the Pecos river, Texas, 1999-2003

A large scale ecosystem restoration program was initiated in 1997 on the Pecos River in Western Texas. Saltcedar (Tamarix spp.), a non-native invasive tree, had created a near monoculture along the banks of the river by replacing most native vegetation. Local irrigation districts, private landowners, federal and state agencies, and private industry worked together to formulate and implement a restoration plan, with a goal of reducing the effects of saltcedar and restoring the native ecosystem of the river. An initial management phase utilizing state-of-the-art aerial application of herbicide began in 1999 and continued through 2003. Initial mortality of saltcedar averaged about 85-90%. Monitoring efforts were initiated at the onset of the project to include evaluating the effects of saltcedar control on salinity of the river water, efficiency of water delivery down the river as an irrigation water source, and estimates of water salvage. To date, no effect on salinity can be measured and irrigation delivery was suspended in 2002-2003 due to drought conditions. Water salvage estimates show a significant reduction in system water loss after saltcedar treatment. However, a flow increase in the river is not yet evident. Monitoring efforts will continue in subsequent years.     

污水深度处理系统在油田污水处理中的应用分析

乐安油田是通过蒸汽吞吐减轻原油粘度进行开采的稠油油田。针对其特点,借鉴美国、加拿大污水回用的成功经验和先进技术,建成投产了国内第一座也是最大的一座油井采出水回用于湿蒸汽发生器的大型泵站 ── 乐安污水深度处理站。文章详细介绍了污水深度处理系统以及运行2年来所取得的成果,证明油田采出水深度处理后回用于湿蒸汽发生器技术是完全可行并易于操作的。