Modeling water and sediment contamination of Lake Pontchartrain following pump-out of Hurricane Katrina floodwater

Levee failure and overtopping as a result of Hurricane Katrina caused major flooding of New Orleans, Louisiana. Floodwaters, which were contaminated with heavy metals, organic chemicals, and fecal coliform bacteria (FCB), were pumped into neighboring Lake Pontchartrain during dewatering. The impact of levee failure on water and benthic sediment concentrations in the lake was investigated by applying a numerical water quality model coupled to a three-dimensional, numerical hydrodynamic model. The model was used to compute water and benthic sediment concentrations throughout the lake for lead, arsenic, benzo(a)pyrene (BaP), and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), and water concentrations for FCB. Computed concentrations resulting from actual pumped discharges with levee failure and overtopping were compared to computed concentrations resulting from pumped discharges without levee failure or overtopping, and concentrations from both sets of conditions were compared to ecological water and sediment quality screening guideline values. The model indicated that incremental increases above pre-Katrina benthic sediment concentrations are about a factor of 10 greater with dewatering of the floodwaters than with dewatering of storm water without flooding. However, these increases for the metals are small relative to pre-Katrina concentrations. The results showed that the ecological screening-level sediment quality guideline values were exceeded for BaP and DDE in areas near the south shoreline of the lake as a result of floodwater pump-out, whereas, this was not the case for storm water removal without flooding. The model showed that lake water column concentrations should be about the same during both dewatering conditions regardless of whether there is flooding or not.     

Influence of aeration modes on leachate characteristic of landfills that adopt the aerobic–anaerobic landfill method

As far as the optimal design, operation, and field application of the Aerobic–Anaerobic Landfill Method (AALM) are concerned, it is very important to understand how aeration modes (different combinations of aeration depth and air injection rate) affect the biodegradation of organic carbon and the transformation of nitrogen in landfill solid waste. Pilot-scale lysimeter experiments were carried out under different aeration modes to obtain detailed information regarding the influence of aeration modes on leachate characteristics. Results from these lysimeter experiments revealed that aeration at the bottom layer was the most effective for decomposition of organic carbon when compared with aeration at the surface or middle layers. Moreover, the air injection rate led to different nitrogen transformation patterns, unlike the lesser influence it has on organic carbon decomposition. Effective simultaneous nitrification and denitrification were observed for the aeration mode with a higher air injection rate (=1.0 L/min). On the other hand, the phenomenon of sequenced nitrification and denitrification could be observed when a low air injection rate (=0.5 L/min.) was employed. Finally, it is concluded that, for AALM, air injection with a higher air injection rate at the deepest layer near the leachate collection pipe tends to accelerate the stabilization of landfill waste as defined in terms of the enhancement of denitrification as well as organic carbon decomposition.     

大通湖主要污染物浓度空间分布及其污染来源解析

为了解大通湖主要污染物TN、TP和NH3-N的空间分布特征及污染来源,于2017年9月对大通湖及周边河流进行采样分析。结果表明,大通湖周边入湖河流的ρ(TN)为0. 74～2. 18 mg/L,ρ(NH3-N)为0. 094～0. 874 mg/L,ρ(TP)为0. 02～0. 243 mg/L;湖体ρ(TN)为0. 82～1. 47 mg/L,呈现湖体中间低、四周高的特征,ρ(NH3-N)为0. 14～0. 42 mg/L,但整体差异较大,高值区主要在大通湖西南及东部,ρ(TP)为0. 160～0. 289 mg/L,水质为Ⅴ类或劣Ⅴ类,TP为湖体的主要污染物,湖体的ρ(TP)变化呈现出从四周向中部增加的趋势,高值区主要集中在大通湖正南及湖心处;根据2016年大通湖区域污染源统计及入湖污染物计算,大通湖水环境的TP污染负荷大小排序为农田径流畜禽养殖生活污水工业污染网箱养鱼旅游服务。     

Co-solvent selection and recovery

The selection and recovery of two or more solvents (i.e. co-solvents) are studied because of their importance in environmentally responsible processing. A particularly challenging problem arises when the contaminants (or solutes) are comprised of a mixture of volatile and nonvolatile compounds. The nonvolatile components present difficulties in solvent selection while the volatile components give rise to solvent recovery challenges. Traditional approaches such as the Kauri-Butanol test and predictions based on solubility parameters from regular solution theory can result in poor solvent selection when some of the contaminants are nonvolatile. A simple, graphical and rigorous procedure based on Gibbs energies of mixing for all binary mixtures of solvents and contaminants is proposed for choosing solvent/contaminant pairs. This selection procedure is based on the choice of solvent resulting in the lowest solvent/contaminant Gibbs free energy of mixing for a given contaminant. Nonvolatile contaminants are often easily separated in a single-stage flash vessel. Volatile contaminants, on the other hand, can form homogeneous or heterogeneous azeotropes with commonly used solvents, give rise to distillation boundaries and result in a challenging co-solvent recovery problem. A systematic procedure for the synthesis, design and economic analysis for co-solvent recovery is presented. Residue curve maps are used to identify distillation boundaries and to generate a conceptual process flow sheet for co-solvent recovery. Equipment sizes for the separators and auxiliaries (i.e. condensers, reboilers, decanters, etc.) are determined and capital investment, installation and operating costs are calculated. The removal of oil-water emulsions from the surface of machined metal parts using n-propyl bromide (NPB) and isopropyl alcohol (IPA) in a closed-loop degreaser is used to illustrate the proposed methodology of co-solvent selection and recovery. Analysis shows that the Kauri-Butanol test and the use of solubility parameters can result in poor solvent selection. In contrast, the proposed methodology shows that NPB is competitive with banned solvents like chlorodifluoro, fluorodichloroethane and trichloroethane and highly regulated solvents such as perchloroethylene, trichloroethylene and is a good solvent for the removal of machining oils while IPA is a good solvent for removing water. Separation of mixtures of NPB/IPA/water is difficult because of the presence of three binary and one ternary azeotrope that create three distinct distillation regions as well as regions of vapor-liquid-liquid behavior. It is shown that these distillation boundaries preclude direct water separation and that a two-distillation sequence with decantation is required to cross boundaries and recover both solvents. A variety of geometric illustrations are presented to elucidate key concepts.     

Thyroid status in juvenile alligators (Alligator mississippiensis) from contaminated and reference sites on Lake Okeechobee, Florida, USA

Exposure to environmental contaminants has been shown to alter normal thyroid function in various wildlife species, including the American alligator (Alligator mississippiensis). Abnormalities in circulating levels of the thyroid hormone thyroxine (T₄) have been reported in juvenile alligators from several contaminated lakes in Florida. To further elucidate these functional thyroid abnormalities, this study examines the structure of thyroids and circulating T₄ concentrations from juvenile alligators collected from three sites of varying contamination on Lake Okeechobee, Florida. The following variables were used to characterize thyroid morphology: epithelial cell height, width and area, percent colloid, and follicle area. These variables were compared among study sites and between genders. No difference was detected in epithelial cell height, epithelial cell area, or follicle area among the sites, whereas significant differences in epithelial cell width (p=0.02) and percent colloid (p=0.008) were found. Animals from the most contaminated site (Belle Glade) had significantly greater epithelial cell widths and significantly less colloid present in their follicles compared to animals from the reference site (West). Gender did not have a significant interaction with site for any variable measured. Thyroxine (T₄) concentrations were elevated in the intermediately contaminated site (Conservation Area 3A) compared to the other sites (p<0.0001). It is proposed that the disruptions seen in Lake Okeechobee alligators are due to disruptions at both the thyroid and extra-thyroidal tissues.     

人工湿地污染物去除效率稳定性分析——以沈阳市满堂河污水处理中心为例

利用沈阳市满堂河污水处理中心人工湿地8年来运行数据,对人工湿地整体系统和不同功能区的水质净化效果进行了对比分析,结果表明,潜流人工湿地对CODCr的去除效率,在50%～70%;表面流人工湿地对CODCr的去除效率,稳定在20%左右;人工湿地系统整体对悬浮物和氨氮的去除效率保持在50%以上;人工湿地系统对污染物质的去除效率,随着运行时间增加而日趋稳定。     

Strong links between metal contamination, habitat modification and estuarine larval fish distributions

Changes to larval fish assemblages may have far reaching ecological impacts. Correlations between habitat modification, contamination and marine larval fish communities have rarely been assessed in situ. We investigated links between the large-scale distribution of stressors and larval fish assemblages in estuarine environments. Larval fish communities were sampled using a benthic sled within the inner and outer zones of three heavily modified and three relatively unmodified estuaries. Larval abundances were significantly greater in modified estuaries, and there were trends towards greater diversity in these systems. Differences in larval community composition were strongly related to sediment metal levels and reduced seagrass cover. The differences observed were driven by two abundant species, Paedogobius kimurai and Ambassis jacksoniensis, which occurred in large numbers almost exclusively in highly contaminated and pristine locations respectively. These findings suggest that contamination and habitat alteration manifest in substantial differences in the composition of estuarine larval fish assemblages.     

废水自动采样器存在偏差原因分析及解决方法

简述了废水自动采样器应用现状。根据废水自动采样器性能指标要求,分析了自动采样器在验收和使用过程中应当重视的几个因素。并通过系列的比对、调查,对机器采样和手工采样可能引起监测结果有所偏差的几个方面进行了探讨,提出了解决这些偏差的一些方法和建议。     

河岸材料对河流有机污染物净化能力的影响

在河流水质号模型(RWQM1)的基础上,根据河岸材料影响河流对有机污染物净化能力的机理,建立了"简化河流水质1号模型"(S-RWQM1),并利用该模型模拟受河岸材料影响的生物化学反应过程,以及分析河岸材料及水体中微生物含量、代谢状况、有机污染物降解率与模型参数的相关性。对S-RWQM1的动力学参数进行灵敏度分析,发现对CODCr组分中易生物降解溶解性有机物Ss以及异养菌XH模拟计算结果影响较大的参数分别为异养菌好氧生长速率常数Kgro,H,aer,T0、异养菌好氧内源呼吸速率常数Kresp,H,aer,T0。相关性分析结果显示,以釉面瓷砖、透水砖、松木片为河岸材料的微生物脂磷含量、甲基萘醌与泛醌的摩尔比值MK/UQ、有机污染物降解率与模型参数中Kgro,H,aer,T0的相关系数分别为0.995、-0.904、0.988;格宾护岸的微生物脂磷含量、有机污染物降解率与Kgro,H,aer,T0的相关系数分别为0.862、0.990,与Kresp,H,aer,T0的相关系数分别为0.951、0.997。通过调整Kgro,H,aer,T0以及Kresp,H,aer,T0值,可提高CODCr模拟精度。结果表明,S-RWQM1可较好地反映河岸材料对水体中有机污染物净化能力的影响。