Assessing Settleability of Dry and Wet Weather Flows in an Urban Area Serviced by Combined Sewers

Settleability of dry and wet weather flow samples from a combined sewer system was examined by settling column tests, in order to improve understanding of settling processes and obtain information for design of settling tanks. In fact, these tests mimic the actual settling processes and allow evaluating total suspended solids (TSS) removal by settling. Therefore, it is also possible to assess, indirectly, removals of other pollutants, such as heavy metals, which are generally transported by solid particles in sewage. Towards this end, dry and wet weather flow samples were collected in the Liguori Channel catchment and analyzed in the laboratory for Water Supply and Sewerage (Acquedotti e Fognature) of the University of Calabria for TSS concentrations according to the Standard Methods. The settleability study revealed that removals of TSS in dry weather samples (i.e., sanitary sewage) were greater than in wet weather samples (WW), using the same experimental procedures. In particular, 65% of TSS was removed in dry weather samples at a depth of 3?m for a detention time of 40?min; while in wet weather samples the comparable removal efficiency was less than 60%.     

Separation of Fiber from Distillers Dried Grains with Solubles (DDGS) Using Sieving and Elutriation

A process was developed to separate fiber from distillers dried grains with solubles (DDGS) in a dry‐grind corn process. Separation of fiber from DDGS would provide two valuable coproducts: 1) DDGS with reduced fiber, increased fat, and increased protein contents; and 2) fiber. The process, called elusieve process, used two separation methods, sieving and elutriation, to separate the fiber. Material carried by air to the top of the elutriation column was called the lighter fraction and material that settled to the bottom of the column was called the heavier fraction. We evaluated the compositions of fractions produced from sieving and elutriation. Two commercial samples of DDGS were obtained from two dry‐grind corn plants. Sieving over four screens (869, 582, 447, and 234 μm openings) created five size categories. The two smallest size categories contained >40% (w/w) of the original DDGS and had reduced fiber and increased protein and fat contents relative to the original DDGS. Elutriation of the remaining three size categories increased protein and fat contents and reduced fiber contents in the heavier fractions. Elutriation at air velocities of 1.59–5.24 m/sec increased the protein content of the heavier fraction by 13–41% and increased the fat content of the heavier fraction by 4–127% compared with the bulk fractions of each size category. This process was effective in separating fiber from both DDGS samples evaluated. Elusieve process does not require changes in the existing dry‐grind process and can be implemented at the end of the dry‐grind process.     

Size Distribution of Wet Weather and Dry Weather Particulate Matter Entrained in Combined Flows from an Urbanizing Sewershed

Urban drainage transports a complex and heterogeneous mixture of aqueous-phase chemicals and also solid-phase particulate matter (PM). In this study, event-scale particle size distribution (PSD) of wet and dry weather flows are measured, modeled, and compared. The flows are generated from a complex urbanizing sewershed (Liguori catchment) in Cosenza, Italy. Results indicate PSDs are heterodisperse, ranging from colloidal to sand-size PM. On an event scale, dry weather PSDs are coarser than wet weather flows, yet within each flow class results indicate flow-limited behavior and only nominal variability during and between events. PSDs from each event and flow category are modeled with a cumulative gamma distribution. Results produced nonparametric distributions of shape (γ) and scaling (α) parameters as well as a d ₅₀ index. Wet weather flows generated statistically significantly higher distributions of γ and α and statistically significantly lower d ₅₀. Nonparametric parameter distributions illustrate greater, yet still nominal variability for wet weather flows.     

WGDWS天气发生器在中国五大气候区的适用性

为了检验基于干湿期的天气发生器(Weather Generator based on Dry and Wet Spells,WGDWS)在中国不同气候区的应用效果,该研究利用中国五大主要气候区16个站点57 a的逐日天气数据,通过对比生成与实测气象要素统计值,及比较WGDWS与随机天气模拟器(Daily Weather...     

Solids removal efficiency of primary settling tanks in municipal wastewater treatment plants

Solids removal efficiency of circular primary settling tanks was correlated, on the basis of several literature data, with overflow velocity, solids concentration in incoming flow and the ratio between settling tank diameter and height. Also the reliability of other correlations proposed in the literature was checked by the available data.     

Development of a Laboratory Method for the Comparison of Settling Processes of Road-Deposited Sediments with Artificial Test Material

Sediments deposited on road surfaces are contaminated with pollutants; the load of pollution increases from coarse to fine particles. When it rains, different fractions of the road-deposited sediments are washed off depending on the rain intensity, the slope of the catchment, and other site-specific factors. This road runoff is often treated using settling processes implemented in different types of manufactured treatment devices. These devices can be tested with well-defined artificial test materials to determine the removal efficiencies of particulate matter in a reproducible manner. However, the suitability of the currently deployed artificial test materials to represent the settling behavior of real runoff particle collectives is largely unknown. In this study, a laboratory method to measure and compare the settling behavior of artificial and real particle collectives with a reproducible particle size composition was developed. The particle collectives were obtained from different road surfaces, fractionated into sieve classes, and then recomposed into a defined particle size distribution that represented the road runoff. The settling velocity was analyzed in a modified settling column setup under constant conditions. The resulting data form a cumulative curve of the settling velocities for both artificial and real particle collectives. The main result from this work is that the tested artificial material and the recomposed real particle collectives have comparable settling behaviors despite different losses on ignition and densities.     

Effects of Ground Corn Particle Size on Ethanol Yield and Thin Stillage Soluble Solids

The effects of ground corn particle size on ethanol yield and soluble solids in thin stillage was evaluated using a 2‐L laboratory dry‐grind procedure. The procedure was optimized for grinding, liquefaction, sacchari‐fication, and fermentation parameters. The optimized procedure was reproducible with a coefficient of variation of 3.6% in ethanol yield. Five particle size distributions of ground corn were obtained using a cross‐beater mill equipped with five screens (0.5, 2, 3, 4, and 5 mm). Particle size had an effect on ethanol yield and on soluble solids concentration in thin stillage. The highest ethanol yield of 12.6 mL/100 mL of beer was achieved using a 0.5‐mm screen in the cross‐beater mill. Treatment using the 0.5‐mm mill screen resulted in soluble solids concentration of 25.1 g/L and was higher than soluble solids concentrations obtained with other screens. No differences in soluble solid concentrations were observed in samples of thin stillage obtained from 2, 3, 4, and 5‐mm screens which had a mean yield of 16.2 g/L. By optimizing particle size for maximum ethanol yield and minimum solids in thin stillage, dry‐grind corn plants could realize reduced capital and operating costs.     

Urban Runoff Impacts on Particulate Metal Concentrations in River Seine

Metallic contents (Cd, Cu, Pb, Zn) of suspended solids (SS) were measured in two sites (Suresnes and Chatou) in the river Seine, downstream Paris, during three summer periods. These two sites, which are respectively located downstream and upstream two of the most important combined sewer overflows (CSO's) of the Parisian sewer system (Clichy and La Briche), allow us to assess these CSO immediate impacts. Samples were collected using sediment traps, weekly during dry weather and daily during the week following the major CSO's events. The heavy metal concentrations, relatively large but stable during summer periods, were shown to further increase downstream Paris after main rain discharges occurred. Metal concentrations measured within the Seine SS during rain events, allowed us to establish that the observable immediate impact of Clichy overflows is only 5% of what it could be. The general principle demonstrated through this work is that most SS originating from CSO's rapidly settle once they reach the river. These polluted particles greatly contribute to the SS chronic pollution downstream Paris during dry weather, through a slow resuspension mechanism of the deposited sediments.     

Measuring dry deposition: A re-assessment of the state of the art

The exchange process known as dry deposition encompasses the dynamic exchange of trace gases and aerosol particles, and the gravitational settling of large particles. Except for particles large enough that their sedimentation velocity exceeds turbulent velocities, the rate of deposition is mostly determined by surface properties, such as roughness, stickiness, and wetness, and by atmospheric stability. Thus, it is difficult to interpret results obtained using collection devices having surfaces different from those of nature. Other methods for measuring dry deposition exist, mostly micrometeorological, but these are sufficiently complicated that routine application as in a monitoring network is not yet feasible. For some chemical species and in some locations, inferential methods offer considerable promise. These methods measure atmospheric concentrations (C) of the relevant chemical species, and derive relevant deposition velocities (v_d) on a site-specific, species-dependent, and time-evolving basis. The dry deposition rates of interest are then evaluated as the product v_d.C. A major goal of current research programs is to provide the knowledge necessary to evaluate v_d. Experimental methods are reviewed, and potential sources of error are examined, for both the research methods and the “concentration monitoring” methodologies presently being advocated for use in numerical models as well as for routine monitoring.     

Spatial and Temporal Variance of Metal and Suspended Solids Relationships in Urban Stormwater—Implications for Monitoring

Relationships between total suspended solids (TSS) and metals (Cu, Pb and Zn) were tested and compared amongst base and high flows of three urbanised catchments in Sydney Estuary, Australia. Significant relationships between TSS and Cu, Pb and Zn were detected for high flows within each catchment; however, no significant relationship was detected for TSS/Zn and TSS/Cu in one of the creeks (Whites Creek) and for TSS/Zn in another (Hawthorne Canal) in 2010 during base flow. Relationships between metals and TSS also varied significantly in locations of intercept and slope between high and base flow and amongst catchments. Spatial variance in TSS/metal relationships were likely caused by specific anthropogenic activities because land uses, meteorology and geology within the study catchments were similar. Results suggest TSS may be used as a surrogate for estimating metal loading in real time for urban catchments, once relationships between metals and TSS were established for individual catchments and for base and high flow conditions. Moreover, no differences in TSS/metal relationships were detected between 2009 and 2010 in Hawthorne Canal during high flow conditions, suggesting that this method of real-time monitoring may be reliable for assessing Cu, Pb and Zn loads during high flows over inter-annual periods. However, long-term consistency of TSS/metal relationships for base flow may need testing since changes in TSS/Zn and TSS/Cu relationships were detected between 2009 and 2010 in Hawthorne Canal. Although irregular discharges to stormwater did not conform to TSS/metal relationships, irregular discharges may be detected in real time by increased flow during dry weather conditions, which may facilitate regulation of these conditions that currently result in potential environmental harm to aquatic biota in Sydney Estuary.     

Water retention characteristics of soils over the whole moisture range: a comparison of laboratory methods

The exact characterization of soil hydraulic properties is essential for various purposes, such as agricultural and groundwater management. Various laboratory methods for the determination of soil water retention characteristics are frequently applied. Standard methods comprise: (i) the hanging‐water column and (ii) the simplified evaporation method (HYPROP^©) for wet to moderate moisture ranges; and (iii) the pressure plate and (iv) the dew point method (WP4C PotentiaMeter®) for moderate to dry moisture ranges. These four methods were evaluated and compared, with the aim of demonstrating their compatibility. The hanging‐water column method and the evaporation method provided comparable retention data in the wet to moderate moisture range. The dew point method provided corresponding results over the dry range, while retention data obtained from the pressure plate method sometimes had a tendency to over‐estimate water contents. Hysteresis was observed for retention data in the dry range when applying the dew point method to previously wetted or dried samples.     

Comparison of three methods for determining the particle density of soil with liquid pycnometers

Abstract

Three liquid pycnometer methods for determining the particle density of a sand and peat soil were assessed. The determinations were made on samples at two initial water contents, air dry and slightly moistened. Water was used as the filling liquid in methods 1 and 2, and ethanol in method 3. In method 1, a water bath was used to wet the samples while a 70 kPa vacuum was used in methods 2 and 3. The mean values determined with the methods tested differed by less than 0.15 g/cm³. It was concluded that the most precise and accurate values can be achieved using water as the filling liquid and a water bath to wet the samples.     

Wet and Dry Deposition Fluxes of Polychlorinated Biphenyls (PCBs) in an Urban Area of Turkey

Atmospheric polychlorinated bihenyls (PCBs) deposit by dry and wet deposition mechanisms, and therefore they constitute a significant polluting source for lands and surface waters. Various samplers have been used to determine the PCB pollution level resulting from deposition. In the presented study, a modified wet deposition sampler (WDS) was used for sampling both wet and dry deposition samples with the same instrument by which wet deposition reservoir of the WDS is opened and dry deposition reservoir is closed when rain starts. Wet and dry deposition samples were collected between June 2008 and June 2009. In the samples taken from BUTAL which is known as an urban area with heavy traffic, ??PCB dry deposition fluxes were determined as 18?±?10 ng/m²??day, and wet deposition fluxes for dissolved and particle phase were measured as 480?±?1,185 and 475?±?1,000 ng/m²??day, respectively. The dissolved and particle-phase PCB concentrations in rain were 10?±?13 and 13?±?14 ng/l, respectively. The contribution of wet deposition to total PCB deposition was determined as 52%. PCB concentrations in the ambient air were measured to be 370?±?200 and 20?±?20 pg/m³ for gas and particle phases, respectively. Washout ratio was determined by proportioning rain concentration to concentration in air. The washout ratios of the samples were between 1,675?C311,800 and 12,775?C2,511,120 for dissolved and particulate phases, respectively.     

The effect of iron concentration,hindered settling,saturating cation and aggregate density of clays on the size distribution determined by gravitation X‐ray sedimentometry

X‐ray sedimentation is potentially attractive for estimating the particle‐size distribution of soil, but has been thought to overestimate clay fractions because of the iron they contain. We have examined X‐ray sedimentation for estimating the particle‐size distribution of fully dispersed and of aggregated clay. We obtained good agreement between the pipette and X‐ray sedimentation methods using two different kaolinite samples with a small iron concentration. We also studied montmorillonite saturated with Li, Na, K, Mg or Ca to investigate possible effects of hindered settling. For the Ca montmorillonite, we obtained good agreement between X‐ray sedimentation and the pipette method at concentrations up to 40 g l^?1. We also found that X‐ray sedimentation could be used at concentrations less than those recommended by the manufacturer. Hindered settling was observed at concentrations > 20 g l^?1 for Li‐ and Na‐saturated montmorillonite. Our data suggest that conducting experiments at different mass concentrations is a sensitive test to detect such problems. Finally we used a fractal model to investigate the possible errors that might result from the size dependence of aggregate density and show that the error caused by assuming a single value for particle density of solids is small.     

利用土壤颗粒的沉降粒级研究泥沙的迁移与分布规律

了解不同粒径泥沙迁移运动规律,有助于深入理解侵蚀条件下碳、氮、磷等元素的生物地球化学过程。土壤营养元素的迁移转化与泥沙颗粒的运动规律密切相关,而泥沙的运动规律由颗粒大小、性状、孔隙度和密度等因素共同决定。依据泥沙颗粒沉降速度分选的原理,针对中国两种典型侵蚀土壤(红壤和黄绵土),分别进行了土壤机械组成(矿质土粒分选)和沉降速度分选测定。结果表明,土壤颗粒的沉降粒级可有效区分红壤和黄绵土中不同粒径团聚体的沉降速度,能够更加准确地反映出同一粒径颗粒因性状、密度和孔隙度的差异而形成的不同沉降速度。相对于质地疏松的黄绵土,红壤的机械组成显示,有86.9%的有机碳与≤32μm的矿物颗粒相结合,很有可能随悬移过程汇入下游水体。但土壤颗粒沉降速度分布表明,约有90.5%的红壤有机碳与等效石英粒径≥63μm的团聚体相结合,易在经历较短的迁移过程后,快速沉积于下坡面。这表明,现有的土壤侵蚀模型大多利用土壤机械组成(即矿质粒径大小)在反映泥沙运动或元素迁移规律方面存在片面性。土壤的团聚过程可有效缩减有机碳和无机碳的迁移距离,从而使其更易沉积于陆生环境。土壤颗粒的沉降速度分级对认识泥沙颗粒和养分元素在侵蚀—迁移—沉积过程中的生物地球化学过程提供了新的途径和视角。     

OPTIMUM DESIGN OF SEDIMENTATION TANKS BASED ON SETTLING CHARACTERISTICS OF KARACHI TANNERY WASTES

A study was carried out in a specially designed settling column to investigate the settling characteristics of effluents arising from Karachi tanneries. The Jar-tests were conducted to determine the optimum dosage of coagulants such as potash alum and ferric chloride to maximize the removal of suspended solids (S.S) from the wastes. For alum, the optimum dosage was found to be 150 mg L^-1, whereas with ferric chloride it was 30 mg L^-1. Experiments carried out in the settling column with the optimum coagulant dosages showed that the coagulation with ferric chloride was much better than with alum, as it removes about 84% S.S from the wastes compared to 70% removal obtained in case of alum. Design curves in terms of percent removal of S.S. vs loading rate and detention time were constructed using data obtained from settling column. These curves can be used in designing the settling tanks employed in the tannery wastes treatment plants.     

Laboratory Yields and Process Stream Compositions from E‐Mill and Dry‐Grind Corn Processes Using a Granular Starch Hydrolyzing Enzyme

In dry‐grind corn processing, the whole kernel is fermented to produce ethanol and distillers dried grains with solubles (DDGS); the E‐Mill process was developed to generate coproducts in addition to DDGS. Compositions of thin stillage and wet grains obtained from the E‐Mill process will be different from the dry‐grind process. Knowledge of thin stillage compositions will provide information to improve coproducts from both processes. Laboratory dry‐grind and E‐Mill processes that used granular starch hydrolyzing enzymes (GSHE) were compared and process yields determined. Two methods, centrifugation and screening, were used to produce thin stillage and wet grains from the laboratory processes. Compositions of process streams were determined. In the dry‐grind process using GSHE, solids contents of beer, whole stillage, and wet grains were higher compared to the same fractions from the E‐Mill process using GSHE. Solids contents of mash for both processes were similar. Total solids, soluble solids, and ash contents of thin stillage were similar for the two processes. Fat content of thin stillage from E‐Mill was lower than that from the dry‐grind process; protein content of E‐Mill thin stillage was higher than that from dry‐grind thin stillage. Removal of germ and fiber before fermentation changed composition of thin stillage from the E‐Mill process. The screening method produced higher thin stillage and lower wet grains yields than using a centrifugation method. The screening method was less time consuming but resulted in limited wet grains material for additional analyses or processing. The centrifugation method of thin stillage separation removed more solids from thin stillage than the screening method.     

Critical state parameters from intact samples of two agricultural topsoils

The critical state parameters of intact samples of a sandy loam (Eutric Cambisol) and a clay loam (Gleysol) were estimated in a constant cell volume triaxial apparatus. Samples were taken under wet and dry conditions. The parameters describing the clay loam were the more variable. This was true of both its initial condition and its response to deformation. Under dry conditions, the sandy loam was less sensitive to increasing stress but compacted more at low stress than the clay loam. Isotropic stress compacted the wet soils until the percentage saturation reached about 85–95% and axial loading caused little further compaction. The difference in strength between soils was greater for the wet samples, whereas the corresponding compactibility differences were greater under dry conditions. The sandy loam was stiffer than the clay loam and the shear modulus decreased exponentially with increasing specific volume before deformation. The rebound slope was about one-twentieth of the compression index for the dry soils and about one-third of the compression index for the wet soils. A simple model of recompression accounted for plastic deformation below the virgin compression line, where the critical state model usually assumes elasticity. The proposed model reproduced the main observed features of repeated isotropic loading.     

土壤样品中痕量丁草胺的分析方法

本研究完善了土壤中除草剂丁草胺残留的分析测试方法。在实验室条件下,利用超声提取、弗罗里硅土柱(湿法填柱和干法填柱)进行净化和分离、毛细管气相色谱分析测试,进一步优化了弗罗里硅土柱净化分离丁草胺的条件。土壤中丁草胺的平均回收率为97.46%,检出限为0.002mgkg-1,变异系数小于10%。本方法灵敏度高、重复性好、可排除有机污染物对微量丁草胺残留物测定的干扰,同时减少了有机试剂的用量,适用于土壤样品中痕量丁草胺的分析测试。     

Soil moisture variability in a semi-arid gully catchment: implications for runoff and erosion control

Spatial patterns in surface soil moisture during dry and wet weather conditions have been recorded over a 3.68 ha gully catchment in central Spain. During dry weather conditions this spatial pattern was characterised by areas of relatively wet and dry soil, forming a mosaic of areas with contrasting hydrological response. Semi-variogram analysis has indicated that these areas are spatially isolated and unconnected, with the effect that surface runoff from source areas within the catchment may be re-absorbed by surrounding areas which act as sinks for overland flow. Consequently during dry weather conditions, variation in the soil's physical and hydrological properties, as reflected by spatial differences in soil moisture, may be advantageous in minimising widespread catchment runoff and erosion, by creating spatial isolation of runoff producing areas and by promoting discontinuity in hydrological pathways. During wet weather conditions, however, extensive saturation, exceeding a catchment wetness threshold, increased spatial continuity in hydrological pathways, regardless of the spatial variation in soil hydraulic properties, resulting in widespread runoff and erosion. Management strategies should therefore aim to raise this wetness threshold value, by improving the soils physical and hydrological properties. The creation of a mosaic pattern of areas with contrasting hydrological response may prove to be an effective management strategy in runoff and erosion control in semi-arid environments.