Structure of Crack in Thermally Dried Sludge Cake

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50-60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

Skin Layer on Thermally Dried Sludge Cake

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated.     

Skin Layer on Thermally Dried Sludge Cake

This work utilized an X-ray micro-computerized tomography scanner (micro-CT) to investigate how skin layers—hard and relatively impermeable layers that hinder mass transfer—form and develop on wastewater sludge cake with (cake-O) or without artificial cracks (cake-N). A novel scheme that applies Otsu's algorithm twice was employed to determine the solid phase and skin layers in the scanned cake images. Initial cracks in a cake had significant impact on how the skin layer would form on the cake. A unique correlation between effective surface area to drying (not covered by a skin layer) and moisture content was identified. The advancement velocities of skin layers on drying cake were evaluated.     

干污泥表面形貌及孔隙分布规律

污泥干燥焚烧以回收其热能的资源化利用正受到越来越多的关注。污泥干燥过程中,孔隙的大小及其分布直接影响污泥中液体及气体的传递过程．进而影响干燥速率。为研究干污泥表面形貌及孔隙分布规律,采用扫描电子显微镜观测了干污泥表面形貌。利用动态氮吸附法测量了干污泥的孔隙大小。利用数理统计方法研究了孔隙分布规律,研究结果表明干污泥的孔隙分布服从对数正态分布。建立了孔隙分布模型,求解了5种干污泥的孔隙分布特征参数,模型计算值与实际测量值吻合较好,均方根误差小于18．2％,所建立的干污泥孔隙分布模型具有一定的通用性及准确性。     

气孔结构对焦炭深层反应影响的初探

研究了气孔结构对焦炭深层反应的影响,并将分开可理论引入到气孔结构的研究中。     

Numerical Study on Moisture Transfer in Ultrasound-Assisted Convective Drying Process of Sludge

A coupled heat and moisture transfer model for ultrasound-assisted convective drying process of sludge was established. In this model, the permeable flow caused by acoustic pressure gradient in sludge was considered. The pore structure variety in sludge with ultrasonic irradiation was microscopically studied, and the pore size distribution of sludge was described by fractal geometry. Based on the fractal characterization, the physical properties of sludge including permeability, porosity, and tortuosity factor were determined, and the effective moisture diffusion coefficient of sludge under ultrasonic irradiation was also derived considering the effects of ultrasonic excitation energy and thermal effect on migration rate of water molecule. The effects of ultrasonic energy density and convective air temperature on convective drying process of sludge were numerically analyzed. The results showed that the ultrasonic irradiation changes the pore size distribution in sludge, the sludge flocs are dispersed, and the connectivity of pore structure is improved. Ultrasonic treatment is favorable to accelerating the moisture transport in the convective drying process of sludge, and the ultrasonic influence on moisture transport in sludge intensifies gradually with the increase of acoustic energy density from 0.2 to 0.6 W/ml. Furthermore, it can be also found that the enhancement effect of ultrasound on the average drying rate of sludge is more obvious at the connective air temperature of 65°C than that at 40°C under the uniform acoustic energy density and air velocity of 1.5 m/s.     

Effect of Hydraulic Retention Time on Sludge Properties,Cake Layer Structure,and Membrane Fouling in a Thermophilic Submerged Aerobic Membrane Bioreactor

Sludge properties, cake layer structure, and membrane fouling in a membrane bioreactor were studied under various hydraulic retention times (HRT). A decrease in HRT resulted in an increase in extracellular polymeric substance production in bulk sludge and changes in cake layer structure from gel layer to one or two cake layers. Particle size distribution in cake sludge changed with respect to HRT. An evolution in cake layer thickness and porosity was observed with trans-membrane pressure (TMP) jump. The change in cake layer structure might bear more responsibility for the TMP jump than the quantity of cake layer.     

用分形理论研究低渗储层孔隙结构

储集层岩石的孔隙结构非均质性对于油气的渗流规律以及水驱油效率都具有重要的影响。利用分形理论对孔隙结构的非均质性进行研究。结果表明,分形维数不同孔隙结构不同,所研究的储集层具有单一分形（分形维数2.690 7～2.814 0）和分段分形特征（分形维数2.414 8～2.995 2）;以分形维数为基础,可以根据孔喉渗透率贡献判断孔隙结构的非均质性和复杂程度。     

分形几何学在钽电容界面形貌图像处理中的应用

利用无规分形对钽电容中ＭｎＯ２／Ｔａ２Ｏ５和Ｔａ／Ｔａ２Ｏ５界面的ＳＥＭ形貌进行了图像处理．根据得出的分形维数值,验证了被膜过程为化学反应控速,阳极氧化击穿过程为扩散控速．     

Effect of Immersion Time in Osmosis and Ultrasound on Papaya Cell Structure during Dehydration

The effect of ultrasound-assisted osmotic dehydration applied at atmospheric pressure for different lengths of time on papaya tissue structure was evaluated. Ultrasound induced the loss of cellular adhesion, formation of large cell interspaces, and light rupture of the cell walls. The changes in the tissue structure caused by ultrasound application increased sugar loss, water loss, and effective water diffusivity. Ultrasound-assisted osmotic dehydration induced a gradual distortion in the shape of the cells, loss of cellular adhesion, and the formation of large channels caused by rupture of the cell walls. The changes caused by the application of osmotic dehydration resulted in high water loss and sugar gain.     

污水处理厂剩余污泥热处理发酵产氢的影响因素

研究了影响污水处理厂剩余污泥热处理厌氧发酵产氢的4个因素：热处理时间、污泥浓度、起始pH和反应瓶顶隙率. 结果表明,热处理时间会影响污泥热处理的效果,导致发酵产氢的底物?污泥不同,从而影响热处理污泥的发酵产氢,121℃下热处理5 min为最佳处理时间. 中性起始pH值(6.5~8.0)下,热处理污泥的氢产率相对稳定,低于6.5不利于发酵产氢. 当反应瓶的顶隙率为51.61%时,热处理污泥的氢产率最大. 7.81 g/L为最佳污泥浓度,该浓度下污泥的氢产率最大,高于或低于该浓度时,污泥的发酵氢产率均下降. 在最佳条件下,热处理污泥的氢产率达19.57 mL/g VSS.     

Structural Analysis and Dewatering Characteristics of Waste Sludge from WWTP MBR

Abstract

A pilot‐scale UF membrane bioreactor (MBR) of 1 m³/day capacity was set up in an industrial wastewater treatment plant to evaluate its performance. This study mainly focused on testing the dewaterability and structural analysis of MBR sludge. MBR had 14% reduction of excess sludge production in relative to the conventional activated sludge process (CAS sludge). For dewatering, MBR sludge had comparable dewaterability with the CAS sludge but required nearly 20% less flocculant to reach the highest filterability χ and lowest specific filtration resistance (SRF). This could reduce the cost for running the dewatering facilities and final disposal. Meanwhile the chemical and morphological analyses on MBR sludge exhibited lower EPS (exocellular polymeric substances) content, slightly smaller flocs and more compact morphology. Additionally, to estimate the appropriate polyelectrolyte dose prior to dewatering, we measured the hysteresis loop area of the sludge rheogram (shear stress vs. shear rate) using a co‐axial cylinder viscometer. For both sludges, the area dramatically increased at some critical flocculant dosage and then plateaued off. The critical dosage, though not optimal, still led to an acceptable dewatering performance for the sludge.     

对竹园第-污水处理厂污泥产率的分析

根据上海市竹园第一污水处理厂的运行数据,研究了该厂的污泥产率。结果表明竹园第一污水处理厂每万吨水产泥率的变化范围为0．38—1．44tSS／万M2;剩余污泥的表观产率系数（Lobs）和合成产率系数（y）分别为0．56和0．58kgVSS／kgBOD,均在正常范围以内;衰减系数（虬）为0．006d-1;惰性ss产泥率的变化范围为0．20～0．50tSS／万M2。     

利用图像分析法测定焦炭气孔结构的研究

通过Optimas6．5图像处理与分析软件，对不同厂家焦炭的气孔结构图像进行分割和统计，实现了用图像分析法对焦炭气孔结构参数的测定。与传统方法相比，图像分析法具有准确性更高、数据代表性更好等优点。     

污泥中重金属形态分析及其生物可利用性研究

通过对白龙港污水处理厂的污泥源、污泥中重金属含量、污泥浸出液中重金属含量的分析,从污泥中重金属形态分析数据的角度对其生物可利用份额作了探讨。     

污泥干燥机在污泥干化焚烧工艺中的应用

污泥干化焚烧工艺综合考虑了污泥处置的可靠性、先进性、适用性、安全性与经济性等原则,将是现阶段我国一线城市污泥治理的主流工艺路线。本文通过对不同种类的污泥干燥机进行综合性能比较,推荐了作为污泥干化焚烧工艺的主流干燥机。国产干燥机在经过对国外同类设备的消化吸收后,今后将在国内污泥干化领域占据一席之地。     

Experimental and Theoretical Study of Agitated Contact Drying of Sewage Sludge under Partial Vacuum Conditions

Agitated contact drying experiments were carried out in a cylindrical lab-scale paddle dryer to study the drying kinetics of sewage sludge under partial vacuum conditions. To explore the drying mechanisms, the penetration model for vacuum contact drying of agitated particulate materials, developed by Schlünder and Mollekopf, was applied to simulate the experimental results. The influence of the drying parameters (system pressure, heating temperature, stirrer speed, and dryer load) on the drying kinetics was studied both experimentally and theoretically. The results indicate that pressure and temperature significantly influence the drying rates of sewage sludge, whereas stirring speed and dryer load have no obvious effects on drying rates in the examined range. The experimental and simulated drying rates were in acceptable agreement as long as the temperature difference between dryer and sludge was small. A crust is likely to form on the dryer surface, however, when the temperature difference becomes large; this crust leads to markedly lower drying rates than the calculated ones. Furthermore, a comparison between partial vacuum contact drying and atmospheric contact drying is presented. The results indicate that the mass transfer resistance increases with rising drying potential in the examined experimental range.     

Sewage Sludge Solar Drying: Experiences from the First Pilot-Scale Application in Greece

Increasingly strict regulations governing sludge management have raised interest in drying technologies. The feasibility of sewage sludge solar drying was experimentally evaluated in a 66-m² pilot-scale greenhouse plant under typical weather conditions in Greece. The greenhouse was equipped with ventilation fans to maximize the drying process efficiency and a turning drum for efficient sludge mixing. The obtained results proved the applicability and the high performance of the solar drying technology. The time necessary to achieve a dry product with a dry solids content up to 95% ranged between 8 and 31 days, depending on the weather conditions. During drying, sludge organic matter was reduced by 5–21%, and total and fecal coliform content was also decreased up to three orders of magnitude. By taking into consideration the sludge content in heavy metals, the final product can partially or totally replace commercially available inorganic fertilizers in agricultural applications, in accordance with the restrictions imposed by national and European regulations. Based on a preliminary cost analysis concerning the construction of a solar drying facility covering a sum of 80,000 population equivalent (PE), a corresponding capital cost of 24 €/PE is anticipated.     

Application of Fractal Theory for Prediction of Shrinkage of Dried Kiwifruit Using Artificial Neural Network and Genetic Algorithm

In current research, fractal theory has been applied for estimation of shrinkage of osmotically dehydrated and air-dried kiwifruit using a combination of neural network and genetic algorithm. Kiwifruits were dehydrated at different conditions and digital images of final dried products were taken. Kiwifruit-background interface lines were detected using a threshold combined with an edge detection approach and their corresponding fractal dimensions were calculated based on a box counting method. A neural network was constructed using fractal dimension and moisture content as inputs to predict shrinkage of dried kiwifruit and a genetic algorithm was applied for optimization of the neural network's parameters. The results indicated good accuracy of optimal model (correlation coefficient of 0.95) and high potential application of fractal theory and described intelligent model for shrinkage estimation of dried kiwifruit.