CFD simulation of anaerobic digester with variable sewage sludge rheology

A computational fluid dynamics (CFD) model that evaluates mechanical mixing in a full-scale anaerobic digester was developed to investigate the influence of sewage sludge rheology on the steady-state digester performance. Mechanical mixing is provided through an impeller located in a draft tube. Use is made of the Multiple Reference Frame model to incorporate the rotating impeller. The non-Newtonian sludge is modeled using the Hershel–Bulkley law because of the yield stress present in the fluid. Water is also used as modeling fluid to illustrate the significant non-Newtonian effects of sewage sludge on mixing patterns. The variation of the sewage sludge rheology as a result of the digestion process is considered to determine its influence on both the required impeller torque and digester mixing patterns. It was found that when modeling the fluid with the Hershel–Bulkley law, the high slope of the sewage stress-strain curve at high shear rates causes significant viscous torque on the impeller surface. Although the overall fluid shear stress property is reduced during digestion, this slope is increased with sludge age, causing an increase in impeller torque for digested sludge due to the high strain rates caused by the pumping impeller. Consideration should be given to using the Bingham law to deal with high strain rates. The overall mixing flow patterns of the digested sludge do however improve slightly.     

Experimental study of stress wave propagation across a filled rock joint

Dynamic properties of rock joints are of great interest to mining engineers, seismologists and geoscientists in characterizing the dynamic mechanical behavior of discontinuous rock mass. An experimental study of stress wave propagation across filled rock joints has been carried out using a modified Split Hopkinson Pressure Bar (SHPB) apparatus. Two granitic bars cored from a rock site were used as the incident and transmitter pressure bars in the SHPB tests, while a sand layer of different widths and water contents sandwiched between the two bars was adopted to simulate the filled joint. Each pressure bar was mounted with two strain gauges with a specific spacing. A wave separation method was used to process the test data. The dynamic stress–strain relation of the filled rock joints was derived from the separated strain waves. Finally, the dynamic stress–strain relations from the tests were curve-fitted by using the least square regression method and compared with a traditional joint model. It was found that the wave separation method is very effective for the SHPB tests using short granitic pressure bars. It was also concluded that the joint width and water content had significant effects on the dynamic stress–strain relation of the filled rock joints. Existing joint models were not able to sufficiently describe such dynamic properties of the filled rock joints.     

基于EXCEL的城镇污水规划模型研究

利用EXCEL对污水规划进行数据处理和计算,在EXCEL中建立"块面积"表、"块水量"表、"管段水量"表和"水力计算"表,编写函数将这些表的数据连接引用。输入地块面积、不同用地性质的污水量指标以得到地块污水量,将地块污水量合计起来即得到总预测污水量,也可将用其他方法预测的总污水量分配给各地块;根据污水管网布置图,在"管段水量"表中输入各地块的相关管段号,通过编写水力计算程序计算"块线比"可得到各管段的流量;由管段连接关系和管段流量以及"水力计算"表完成规划污水管网的水力计算,以得到各设计管段的管径、坡度、流速、充满度和管内底标高等参数。     

Properties of compressed lateritic soil stabilized with a burnt clay–lime binder: Effect of mixture components

In this study, a pozzolanic binder containing lime and a common thermally activated kaolinitic clay, at 750 °C, was formulated. The chemical, mineralogical and pozzolanic properties of raw materials were determined. The percentage of lime in the binder varies between 20% and 30%. The binder was used as a stabilizer in compressed lateritic soil in which water–solid (laterite and binder) and laterite–binder ratios vary, respectively, from 0.12 to 0.20 and 4 to 9. Sodium hydroxide (NaOH) was added as a chemical activator in the mixture. The NaOH–binder ratio varies from 0.02 to 0.04. The average effect of each component of the mixture on compressive strength, water absorption and apparent density of compressed laterite after 7 or 28 days of conservation at 40 ± 1 °C in an atmosphere saturated with water vapour was evaluated in a screening design of the “design in graeco – latin squares” type. It was observed that water–solid and laterite–binder ratios are the factors that influence more the properties of the products. Compressive strength increases up to a water–solid ratio of 0.16 then decreases for higher ratios. Compressive strength decreases with the increase of laterite–binder ratio. Water absorption decreases with the increase of water–solid ratio up to 0.16 then sharply increases for higher ratios. However, water absorption decreases slightly with the increase in the lime content of the binder and sodium hydroxide–binder ratio. The maximum apparent density is observed at water–solid ratio of 0.16. It increases when sodium hydroxide–binder and laterite–binder ratios increase.     

Recent Developments in the Biological Filtration of Sewage to Produce High-Quality Nitrified Effluents

The biological filtration of sewage remains the process which is most commonly used for small works in rural areas throughout the UK. In many cases, the need to produce an effluent of high quality with full nitrification is essential in order to comply with the standards set by the Environment Agency. Traditionally, design loading rates of biological filters have been based on historical experience of performance, and on relatively short-term statistical evaluation of the performance of a large number of treatment works, using average and maximum values for flow and loading rates. Many works which were designed on such information have failed to nitrify consistently, particularly during the winter and spring months.
This paper describes the detailed evaluation of six full-scale, biological-filtration sewage-treatment works over a period of two years, in which there were significant changes in sewage flow rate, composition and temperature, from summer to winter. The key parameters which influence the production of high-quality nitrified effluents were determined. The conclusions are used to provide a detailed guide on the design of conventional-media biological filters to produce, consistently, fully-nitrified effluents.     

上向流与下向流BAF串联处理生活污水的特性研究

将上向流与下向流曝气生物滤池(BAF)串联处理生活污水,研究了组合工艺对COD和NH3-N的去除效能及生物膜上微生物的特性。试验发现,这种组合便于为碳化过程和硝化过程提供不同的反应条件,使对COD和氨氮的去除率得到提高;上向流BAF运行时的水头损失增加较快,运行周期较短;下向流BAF的水流阻力较小,运行周期较长,出水浊度很低;串联运行可以节省反冲洗用水;滤料表面的生物膜和滤料颗粒间隙中的生物絮体都有较高的生物活性,且絮体所起的降解作用和生物膜的一样重要。     

Ground copper slag as a supplementary cementing material and its influence on the fresh properties of self-consolidating concrete

This paper reports on an experimental programme to investigate the effect of using ground copper slag (GCS) as a replacement of cement on the fresh properties of self-consolidating concrete (SCC). Totally, seven self-compacting ground copper slag concrete (SCGCSC) mixtures were made with a fixed water–powder ratio of 0.51 in which a portion of the cement was replaced by GCS in weight ratios of 0%, 5%, 10%, 15%, 20%, 25% and 30%. The fresh properties were investigated by slump-flow, visual stability index, V-funnel, J-ring, L-box, air content, screen stability and setting time tests. The SCGCSCs were designed to give a constant slump flow of 680 ± 30 mm which was achieved by using the super-plasticiser at varying amounts. This allowed us to have a reasonable comparison of the obtained results. Totally, it has been concluded that using GCS significantly increased the workability of SCC mixtures. As the GCS increased, the slump flow is also increased at a constant amount of water and super-plasticiser, but the time required to flow is decreased. The results showed that it is possible to successfully produce SCC with GCS as cement replacement.     

The behaviour of polychlorinated biphenyls in the primary sedimentation process of sewage treatment: A pilot plant study

The behaviour of polychlorinated biphenyls (PCB) in the primary sedimentation stage of sewage treatment has been studied using a pilot scale primary sedimentation plant. The plant was operated at different hydraulic loadings, selected to cover the range expected during normal operation of a sewage treatment works. Concentrations of PCB in raw sewage were found to be in the low ng l^?1 range and in the high ng l^?1 range in primary sludges. A relationship between raw sewage PCB concentrations and variations in the raw sewage flow to the full-scale sewage treatment works was evident. Removal efficiencies of PCB were found to be highest at dry weather flow and lowest at three times dry weather flow, their removals being comparable to those of suspended solids. Mass balances of PCB and suspended solids in the treatment process have been calculated and the possible sources of error considered. Comparisons of the results have been made with those of previous studies. The implications of the presence of PCB in waste waters and sewage sludges for water re-use and sewage sludge disposal are discussed.     

Full-Scale Testing of Mechanically Raked Bar Screens

Combined sewer overflows are a known source of aesthetic pollution in urban watercourses, and screens have traditionally been used as a means of preventing such pollution. The authors have established the effectiveness of combined-sewer overflow bar screens in preventing the visual pollution of rivers and have determined the factors which influence screen efficiency so that guidance can be given on improving the performance of future installations. A field study has been undertaken to monitor existing bar screens with different bar spacings. The hydraulic performance of the overflow chambers has been established, and the sources and type of visual pollutants have been identified. Analysis of the field data has established that screen performance (for the main polluting solids) depends on (a) screen bar spacing, (b) mean rate of flow through the screens, and (c) frequency of raking. Overall, mechanically raked bar screens are likely to achieve retention efficiencies of less than 50%.     

Temperature and velocity properties of a ceiling jet impinging on an unconfined inclined ceiling

Understanding the characteristics of ceiling jet flow is important because most fire detectors and suppression devices are designed to operate within the ceiling jet; the increases in temperature and smoke concentration within the ceiling jet become trigger occupants to begin fire-fighting action or to evacuation. A series of pool fire tests was conducted using a flat, unconfined model ceiling with dimensions of 2.5 m (D)×3.0 m (L) and changing the ceiling inclination angle of up to 40°. A single ceiling height is used. Two fire heat release rates were used to evaluate the effects: one with and the other without the flame tip touching the inclined ceiling under a steady-state condition. Maximum temperature and its position were determined based on the measurement using a rake consisting of 0.2-mm-diameter chromel–alumel thermocouples. The maximum velocity and its position were obtained by the particle image velocimetry method. These data were compared with the velocities obtained using a bi-directional flow probe and the relationship between them was clarified. Empirical formulae for the temperature rise and velocity versus the radial distance from the plume impingement point along the steepest run in the upward direction were developed considering the effect of the inclination angle. Variations in the Froude number and the Richardson number with radial distance were clarified with and without the flame tip touching the inclined ceiling.     

Influence of forced air volume on water evaporation during sewage sludge bio-drying

Mechanical aeration is critical to sewage sludge bio-drying, and the actual water loss caused by aeration can be better understood from investigations of the relationship between aeration and water evaporation from the sewage sludge bio-drying pile based on in situ measurements. This study was conducted to investigate the effects of forced air volume on the evaporation of water from a sewage sludge bio-drying pile. Dewatered sewage sludge was bio-dried using control technology for bio-drying, during which time the temperature, superficial air velocity and water evaporation were measured and calculated. The results indicated that the peak air velocity and water evaporation occurred in the thermophilic phase and second temperature-increasing phase, with the highest values of 0.063 ± 0.027 m s^?1 and 28.9 kg ton^?1 matrix d^?1, respectively, being observed on day 4. Air velocity above the pile during aeration was 43–100% higher than when there was no aeration, and there was a significantly positive correlation between air volume and water evaporation from day 1 to 15. The order of daily means of water evaporation was thermophilic phase > second temperature-increasing phase > temperature-increasing phase > cooling phase. Forced aeration controlled the pile temperature and improved evaporation, making it the key factor influencing water loss during the process of sewage sludge bio-drying.     

大开洞异形板屋盖的力学分析与结构设计

结合某教学楼工程,介绍了其大开洞异形板屋盖的力学分析方法和结构设计过程,对整体结构采用了空间杆件结构有限元分析方法,对异形板采用了实体单元建模的有限元分析方法,指出该文的计算方法是正确的,能够保证结构的安全和适用。     

姜堰市城区污水处理厂的设计与运行

详细介绍了姜堰市城区污水处理厂一期工程采用CAST污水脱氮除磷处理工艺的工艺流程,各处理单元的设计参数及主要处理构筑物、设备等,并分析了运行效果,提出建议,为相关水处理工程提供经验。     

高平整度要求的钢筋混凝土结构板施工

洁净电子业厂房要求楼地面表面平整、坚实、光滑。北京某工程结构混凝土采用原浆找平压光工艺,施工中在钢筋马凳上焊MIO螺母并拧入调节螺杆,解决标高控制点施工过程中易受扰动的问题;采用可调节、可拆卸式的钢筋导轨作为混凝土找平的主要措施,使表面平整度控制更精确;使用加长刮杠和大型磨光机,保证了混凝土结构板内实外光,表面平整度满足严格的要求。     

纵向非均匀锈蚀钢筋拉拔过程的有限元分析

混凝土中的钢筋锈蚀问题日益突出,针对非均匀锈蚀混凝土构件的试验研究,从粘结本构关系入手,对锈蚀钢筋构件结构性能退化和破坏特征进行数值计算分析。混凝土和钢筋均采用8节点实体单元建模;钢筋与混凝土之间的粘结单元采用非线性弹簧单元Combine 39,同时,实常数赋值考虑位置函数影响,从而建立了纵向非均匀锈蚀钢筋构件的计算模型。通过计算获得了非均匀锈蚀钢筋拉拔位移与拉拔力之间关系,拉拔过程中混凝土应力变化和破坏发展过程,以及锈蚀钢筋与混凝土之间粘结应力的演化规律。     

污水源热泵制热模型及外在参数影响

分别建立了污水源热泵四大部件(蒸发器、压缩机、冷凝器、膨胀阀)模型,并进行耦合。采用MATLAB软件进行编程模拟,分别计算了污垢热阻、污水流量、污水进口温度变化对热泵冬季制热性能的影响。结果显示:当污垢热阻在0~1(m2·K)/kW范围内变化,系统制热量由353kW降低到301kW,降低了14.8%;当污水入口温度由8℃升高到20℃时,系统制热量由320kW升高到423kW,升高了32.1%;当污水流量由10kg/s升到20kg/s时,系统制热量由339kW增加到364kW等。过程中热泵COP在3.6~4.8范围内变化,说明污水源热泵具有较好的热性能。     

3D mechanical modeling of soil orthogonal cutting under a single reamer cutter based on Drucker–Prager criterion

Reamers have been the major implement used to enlarge the hole size in reaming stage of horizontal directional drilling (HDD). The choice of its available structural design becomes critical to maximize the rate of penetration and minimize the tripping time, thereby decreasing the cost of operations and the risk of experiencing stability problems. Moreover, because the duration period of a HDD project is largely dependent on the reaming stage, it is crucial to study the reaming efficiency by use of the appropriate operating conditions (cutting angle and depth). In the paper, the reaming efficiency of reamer is analyzed based on the development of a 3D analytical cutting force model of soil orthogonal cutting under a single reamer cutter. Focusing on the soil orthogonal cutting mechanism under a single reamer cutter, the interaction and friction between soil and cutter and the shear action of 3D shear zone are comprehensively considered, consequently the mechanical properties are given. Based on these analyses and using the Drucker–Prager criterion given a weight to the intermediate principal stress, the analytical models are proposed. In addition, this paper presents 3D FEM simulations for the analysis of soil orthogonal cutting under a single reamer cutter. The subject has been covered in two parts. Part one deals with the verification of the analytical cutting force model, the other focuses on the assessment and selection of the criterions of shear angle. The analytical cutting force model presented provides the capability to evaluate cutter loading for utilization of a single cutter with different rake angles to cut soils, and to plot the effect of change in the rake angle. Finally, the optimum rake angle of single reamer cutter was obtained. The results of this analysis can be integrated to study reamer performance. It can also provide a guideline to the application and design of the reamer assembly for various soils.     

Analysis of coupled gas flow and deformation process with desorption and Klinkenberg effects in coal seams

Coupled gas flow and solid deformation in porous media has received considerable attention because of its importance in pneumatic test analysis, contaminant transport, and gas outbursts during coal mining. Gas flow in porous media is quite different from liquid flow due to the large gas compressibility and pressure-dependent effective permeability. The dependence of gas pressure and gas desorption on gas permeability has a significant effect on gas flow, but has been ignored in most previous studies. Moreover, solid deformation has a direct impact on the porosity, which also leads to desorption or sorption of methane in the coal seam. In this study, a coupled mathematical model for solid deformation and gas flow is proposed and is implemented using a finite element method. The numerical code is used to solve the gas flow equation with Klinkenberg effect, and is validated by comparison with available analytical solutions. Then, it is used to simulate the coupled process during gas migration in a deformable coal seam. The numerical results indicate that the desorption and Klinkenberg effects and mechanical process effect make a significant contribution to gas flow in the coal seam. Without considering the desorption and Klinkenberg effects and the coupling action of mechanical process, the gas pressure in the coal seam would be underestimated.     

Estimation of sewer leakage to urban groundwater using depth-specific hydrochemistry

The contribution of sewer leakage to urban groundwater recharge remains poorly characterised. There has been a tendency to focus on estimating leakage from pipe network characteristics rather than its impact on the receiving environment. Indeed, pipeline leakage simulation models are frequently used to analyse sewage systems and optimise maintenance efforts. Here a mass balance approach employing groundwater geochemistry is presented to estimate sewer leakage rates; this is done using depth-specific groundwater quality measurements from multilevel monitoring piezometers, specially installed in the Sherwood Sandstone aquifer underlying Doncaster (UK). The results show that leakage rates from the foul sewage system are up to 10% of flow per annum (30–40% of urban recharge) and highlight the utility of groundwater quality monitoring (in particular depth-specific sampling) as an alternative means to assess sewage ingress to urban groundwater.     

Utilization of Mn–Fe solid wastes from electrolytic MnO2 production in the manufacture of ceramic building products

The aim of this work is to evaluate the utilization of Mn–Fe solid wastes, originating from electrolytic manganese oxide production plants, as raw materials in the manufacturing process and on the properties of traditional ceramic building products such as bricks, roof or floor tiles. The Mn–Fe solid wastes are chemically and morphologically characterized. Subsequently, ceramic test specimens incorporating 2.5, 5, 7.5 and 10 wt.% solid wastes are made. Two different shaping technologies are used, namely compaction and extrusion. The green specimens are finally fired to different peak temperatures ranging from 950 to 1100 °C. The final products are characterized concerning important properties such as modulus of rupture, water absorption, weight loss and color. It appears that Mn–Fe solid wastes when used up to a percentage of 7.5 wt.% improve the basic properties of traditional building ceramic products. The results of this study are demonstrated by the successful pilot production of real size ceramic products.