Channel flow and trichloroethylene treatment in a partly iron-filled fracture: experimental and model results

Technical developments have now made it possible to emplace granular zero-valent iron (Fe(0)) in fractured media to create a Fe(0) fracture reactive barrier (Fe(0) FRB) for the treatment of contaminated groundwater. To evaluate this concept, we conducted a laboratory experiment in which trichloroethylene (TCE) contaminated water was flushed through a single uniform fracture created between two sandstone blocks. This fracture was partly filled with what was intended to be a uniform thickness of iron. Partial treatment of TCE by iron demonstrated that the concept of a Fe(0) FRB is practical, but was less than anticipated for an iron layer of uniform thickness. When the experiment was disassembled, evidence of discrete channelised flow was noted and attributed to imperfect placement of the iron. To evaluate the effect of the channel flow, an explicit Channel Model was developed that simplifies this complex flow regime into a conceptualised set of uniform and parallel channels. The mathematical representation of this conceptualisation directly accounts for (i) flow channels and immobile fluid arising from the non-uniform iron placement, (ii) mass transfer from the open fracture to iron and immobile fluid regions, and (iii) degradation in the iron regions. A favourable comparison between laboratory data and the results from the developed mathematical model suggests that the model is capable of representing TCE degradation in fractures with non-uniform iron placement. In order to apply this Channel Model concept to a Fe(0) FRB system, a simplified, or implicit, Lumped Channel Model was developed where the physical and chemical processes in the iron layer and immobile fluid regions are captured by a first-order lumped rate parameter. The performance of this Lumped Channel Model was compared to laboratory data, and benchmarked against the Channel Model. The advantages of the Lumped Channel Model are that the degradation of TCE in the system is represented by a first-order parameter that can be used directly in readily available numerical simulators.     

Hot water flushing for immiscible displacement of a viscous NAPL

Thermal remediation techniques, such as hot water flooding, are emerging technologies that have been proposed for the removal of nonaqueous phase liquids (NAPLs) from the subsurface. In this study a combined laboratory and modeling investigation was conducted to determine if hot water flooding techniques would improve NAPL mass removal compared to ambient temperature water flushing. Two experiments were conducted in a bench scale two-dimensional sandbox (55 cmx45 cmx1.3 cm) and NAPL saturations were quantified using a light transmission apparatus. In these immiscible displacement experiments the aqueous phase, at 22 degrees C and 50 degrees C, displaced a zone with initial NAPL saturations on the order of 85%. The interfacial tension and viscosity of the selected light NAPL, Voltesso 35, are strongly temperature-dependent. Experimental results suggest that hot water flooding reduced the size of the high NAPL saturation zone, in comparison to the cold water flood, and yielded greater NAPL mass recovery (75% NAPL removal vs. 64%). Hot water flooding did not, however, result in lower residual NAPL saturations. A numerical simulator was modified to include simultaneous flow of water and organic phases, energy transport, temperature and pressure. Model predictions of mass removal and NAPL saturation profiles compared well with observed behavior. A sensitivity analysis indicates that the utility of hot water flooding improves with the increasing temperature dependence of NAPL hydraulic properties.     

新型侧向流曝气生物滤池处理生活污水

采用以沸石为填料的新型侧向流曝气生物滤池处理生活污水,考察了水力负荷和气水比的影响.结果表明,LBAF在最佳工况气水比10∶1,A、B段曝气量比1∶1,水力负荷0.43 m3/m2·h下,COD、SS、氨氮、总氮和总磷的去除率分别为88.01%、95.18%、78.97%、52.58%和21.02%;COD去除率随COD容积负荷的增加缓慢下降.氨氮、总氮去除率随COD容积负荷的增大明显下降,氨氮去除率随氨氮容积负荷的增大而明显降低.滤池纳污能力强,不易堵塞,可适当延长反冲周期.     

SMBR内气液两相流三维CFD模拟

应用CFD软件Fluent对浸没式膜生物反应器(submerged membrane bioreactor,SMBR)内气液两相流进行数值模拟研究,重点考查曝气系统的改变对气液两相流态的影响,并结合PIV实验验证模拟结果,从而为反应器的优化设计及膜污染的控制提供理论依据。模拟结果表明,SMBR内曝气强化了气液两相紊动,膜表面液相速度沿反应器高度增加且形成循环流动,有利于膜面污染物的脱落;反应器内气含率分布不均匀,出现死区,不利于微生物的生长;经实验验证,模拟结果吻合良好。     

内循环厌氧反应器多相流流场的三维数值分析简

利用数值模拟的方法,引入欧拉双流体多相流模型及标准k-ε紊流模型,模拟计算内循环厌氧反应器的三相流三维流场,并通过改变污泥颗粒密度及进水流量,针对固相流速及固含率的变化情况,分析条件的改变对流场的影响。研究结果表明,应用数值模拟方法可以获得内循环厌氧反应器内的流场特征;污泥颗粒密度及进水流量的改变对于反应器内污泥颗粒的流速及分布的均匀性有较为明显的影响。模拟结果对反应器的应用及优化设计具有一定的参考价值。     

连续流砂过滤器深度处理市政污水的中试研究

采用好氧/缺氧连续流砂过滤器中试实验研究深度处理北京某污水处理厂二级出水。实验结果表明,当连续流砂过滤器好氧段聚合氯化铝投量为20 mg/L,缺氧段碳源投量为32 mg/L时,COD、NH+4-N、TN和TP的平均去除率分别为34.77%、86.54%、66.94%和84.10%,最终出水均达到北京市新(改、扩)建城镇污水处理厂排放A标准(DB11/890-2012)。克隆文库法分析石英砂表面生物膜中的细菌群落结构表明,其优势菌群为β-proteobacteria,其中大部分能以废水中碳源为电子供体还原硝酸盐。     

潜流人工湿地去除毒死蜱、双酚A、4-壬基酚

为研究潜流人工湿地对毒死蜱、BPA及4-NP的去除效果,选取宽叶香蒲、芦苇、花叶香蒲及小香蒲4种湿地植物,通过SPE-HPLC测定进出水中3种污染物的浓度,计算4种植物潜流人工湿地对3种污染物的去除效率。结果表明,水力停留时间3 d,4组植物对毒死蜱、BPA和4-NP去除率均高于60%,各植物组对毒死蜱和4-NP的去除效果之间无显著性差异,宽叶香蒲对BPA的去除率为82.66%,显著高于其余3种植物组62.96%~69.63%。在静态条件下,毒死蜱、BPA和4-NP在模拟系统内降解过程符合一级降解动力学方程,降解方程分别为：c=124.63exp（-t/25.393）+3.7618 ①,c=316.61exp（-t/34.955）+0.56475 ②,c=168.91exp（-t/17.061）+12.133 ③（c,剩余浓度,μg/L;t,停留时间,h）,半衰期分别为18、21和11 h。     

侧流化学除磷对AO连续流生物除磷系统的影响

为解决城市污水高效除磷和磷回收的问题,开发厌氧释磷上清液侧流除磷工艺(anaerobic supernatant phosphate strip process,简称ASPS工艺),在侧流比为33%下运行,发现该工艺对生物除磷系统的影响主要表现在以下几个方面:(1)系统磷和有机物的去除性能不受影响,出水可溶性磷和COD浓度分别为(0.53±0.12)mg/L、(42.00±5.69)mg/L;(2)活性污泥分布松散并与大量丝状菌结合成难沉降的絮状结构,沉降性能变差,粒径变小;(3)从系统内微生物能量代谢角度分析知,胞内PHA和糖原含量水平无明显变化;但胞内聚磷颗粒含量减少,厌氧释磷受阻,侧流厌氧释磷浓度从22.17 mg/L下降至5.20 mg/L,最终导致侧流部分失去高浓度磷化学沉淀的优势;(4)化学磷回收量占进水磷量比由133.02%下降至31.20%,可实现磷的有效去除和回收利用;(5)对微生物种群变化的影响还有待进一步探究。     

Computational Fluid Dynamics (CFD) Simulations on the Effect of Rough Surface on Atmospheric Turbulence Flow Above Hilly Terrain Shapes

The behavioral distribution of the atmospheric turbulence flow over the terrain with changes in a rough surface has become one of the most important topics of air pollution research, among such other topics as transportation and dispersion pollutants. In this study, a computational model on atmospheric turbulence flow over a terrain hill shaped with rough surface was investigated under neutral atmospheric conditions. The flow was assumed to be 2D and modeled using computational fluid dynamics (CFD) models, which were numerically solved using Reynolds-averaged Navier-Stokes equations. Rough surface conditions were modeled using a number of windbreak fences regularly spaced on the hill. The mean velocity and turbulent structures such as turbulence intensity and turbulent kinetic energy were investigated in the upwind and downwind regions over the hill, and the numerical models were validated against the wind-tunnel results to optimize the turbulence model. The computational results agreed well with the results obtained from the wind tunnel experiments. The computational results indicate that the mean velocity was observed to increase dramatically around the crest of the upwind slope of the hill. A thick internal boundary layer was observed with a fence on the crest and downwind region of the hill. The reversed flow and recirculation zone were formed in the wake region behind the hill. It was thus determined that turbulent kinetic energy decreases as the mean velocity increases.     

流动注射——薄层安培检测法测定水中亚硝酸盐和硝酸盐

将流动注射分析与薄层安培检测法相结合,以碳糊为工作电极,测定了水中ＮＯ－２－Ｎ和ＮＯ－３－Ｎ。研究结果表明,该方法与标准方法相比,具有简单、快速、准确,不受水体颜色干扰的优点。