Effect of frequency on ultrasound-assisted centrifugal dewatering of petroleum sludge

In this work, petroleum sludge has been treated with ultrasound at 20, 25, 30, 35, and 40?kHz to study the effects of frequency on dewatering during pretreatment process. Various parameters, including water content, droplet size distribution, viscosity, and temperature, were analyzed to quantify the improvement of dewaterability which will affect the subsequent centrifugal dehydration. The results showed that 25 and 30?kHz ultrasound could directly remove water by 26.3 and 28.1?wt%, respectively, but resulted in decrease in droplet diameter in remaining water. Although there is little or no separation of water by high-frequency ultrasounds, 35 and 40?kHz strongly affected the emulsified water and increased the mean droplet size. These differences could be primarily explained by acoustic resonance and cavitation effects. In addition, the centrifugal results showed that dewatering ratio up to 78.5?wt% was achieved for sludge with viscosity of 6?Pa?·?s after treated at 40?kHz. Through analysis and comparison of different-frequency ultrasonic treatments, a unified characterization method is developed to provide quantitative evaluation for selecting the proper pretreatment.     

Measurement of bound water in waste activated sludge: Use of the centrifugal settling method

The feasibility of employing a centrifugal settling method for measuring the bound water content in waste activated sludge was investigated. The results demonstrated that, for such highly compressible sludge, the centrifugal settling test can only provide information about the cake compressibility and the method proposed by Matsuda and colleagues fails. A method combining vacuum filtration tests and centrifugal settling tests for estimating the bound water content is proposed and compared with expression tests. The agreement was close.     

A unified theory on solid-liquid separation: Filtration, expression, sedimentation, filtration by centrifugal force, and cross flow filtration

Based upon a new conception that the solid compressive pressure on a cake surface is not null, almost of all solid-liquid separation operations have been re-examined. For cake filtration, the phenomenon caused by the solid compressive pressure on a cake surface is discussed for thin cake. New expression and hindered sed-imentation theories are developed by above new conception using Darcy’s equation. Application of the new conception to centrifugal filtration and tangential filtration is also discussed. Above results lead to the conclusion that cake filtration, expression, hindered sedimentation, centrifugal filtration and tangential filtration can be described with a unified theory, and the main difference between the operations is only the boundary condition of cake.     

Modelling the electro-osmotically enhanced pressure dewatering of activated sludge

The mechanical dewatering of biological materials, such as activated sludge, is troublesome due to their high compressibility. The dewatering can be improved drastically by the use of electro-osmosis, a technique in which a direct current electric field is applied to the filter cake, inducing an electro-kinetic displacement of the liquid phase. In this article, a model is presented which describes this process for a one-dimensional, one-sided filter press. The model starts from two existing models, each describing a part of the process [Iwata, M., Igami, H., Murase, T., 1991. Analysis of electroosmotic dewatering. Journal of Chemical Engineering of Japan 24(1), 45-50; Sørensen, P.B., Moldrup, P., Hansem, J.A., 1996. Filtration and expression of compressible cakes. Chemical Engineering Science 51(6), 967-979]. A robust solution scheme for the basic flux and continuity equations is used to describe filtration and expression. Regarding the electro-osmosis, an adapted form of the Darcy equation, expressing electro-osmotic induced flow as well as pressure induced flow, is integrated into the former solution scheme. This permits the simulation of the overall process using a single model. Validation of the model revealed that the experimental piston height during dewatering can be described accurately provided that temperature effects are taken into account.     

离心沉降法粒度分析──固液分离设备选型依据之一

应用离心沉降粒度分析仪进行粒度分析时，准确、合理地选择沉降介质及圆盘转速等测试条件是获得正确测试结果的关键。粒度分析结果为固液分离设备及分离介质的选型提供了依据。     

酸及磁化处理对污泥沉降与脱水性能影响研究

研究酸处理及磁化对污水处理厂活性污泥沉降性能的影响。通过对不同pH值下污泥沉降性能曲线的分析、微观照片的观察、离心脱水性能的考察,得出pH值为4时污泥沉降性能最佳、2000r/min下10min的离心效果最好;比较两组不同MLSS污泥在不同磁感应强度、不同磁场位型下污泥沉降曲线和磁化前后的颗粒微观照片,得出磁场的确能够改善污泥的沉降性能。     

离心脱水与溶气气浮组合工艺处理含油污泥

针对在污泥脱水生产过程中,带式压滤机不能处理油泥并且滤液悬浮物较高的问题,采用离心脱水机与溶气气浮机组合的工艺,在获得较高含固率的同时有效去除了滤液中的油和悬浮物,满足了后续污水处理工艺的要求,提高了污泥处理效率,在保证装置平稳运行的同时实现了离心脱水机对脱水泥浆的最大减量化。     

叠螺脱水机与离心脱水机在污泥处理中的应用比较

阐述了炼油厂污泥的来源及特性,从工作原理、工艺流程和运行成本3方面对叠螺脱水机与离心脱水机进行了比较分析。2种污泥脱水机均适用于含油污泥(主要成分是浮渣)、剩余活性污泥的脱水处理;离心脱水机主要是依靠转鼓高转速产生的离心力使具有一定密度差的泥水分离,而叠螺脱水机主要是依靠螺杆的挤压来实现污泥脱水;离心脱水机必须配套污泥输送泵、比重剂加药设备;叠螺脱水机在运行成本上占有明显优势,还可以显著改善运行中对工作环境的污染。基于叠螺脱水机运用螺杆挤压原理实现污泥脱水,该设备不适用于含较大硬度颗粒的污泥脱水。     

阴极滤布对活性污泥电渗透脱水的影响(英文)

The mechanical dewatering of activated sludge is troublesome due to its high compressibility of solids. The dewatering can be enhanced dramatically by the use of electroosmosis,in which an electric field is applied to the sludge cake.In this study,the influence of filter cloth on the cathode on the dewatering of activated sludge was investigated.It was found that thicker filter cloth led to lower water removal from the sludge cake,so a stainless steel cathode net with small pore size instead of filter cloth was applied,which improves the dewatering efficiency and reduces the electric power consumption.Moreover,water absorbent materials were helpful to remove the water from the sludge cake.For the electroosmotic dewatering at 7 kPa and 24 V·cm-1,the water content in the sludge cake decreased to 60%(by mass) with the average 0.075 kW·h·kg-1of water removed by using the cathode net.     

Study of saline wastewater influence on activated sludge flocs through automated image analysis

BACKGROUND: In activated sludge systems, sludge settling ability is considered a critical step in effluent quality and determinant of solid–liquid separation processes. However, few studies have reported the influence of saline wastewater on activated sludge. This work aims the evaluation of settling ability properties of microbial aggregates in a sequencing batch reactor treating saline wastewaters of up to 60 g L^?1 NaCl, by image analysis procedures. RESULTS: It was found that the sludge volume index (SVI) decreased with salt content up to 20 g L^?1, remaining somewhat stable above this value. Furthermore, it was found that between the first salt concentration (5 g L^?1) and 20 g L^?1 aggregates suffered a strong deflocculation phenomenon, leading to a heavy loss of aggregated biomass. Regarding SVI prediction ability, a good correlation coefficient of 0.991 between observed and predicted SVI values was attained. CONCLUSION: From this work the deflocculation of aggregated biomass with salt addition due to pinpoint floc formation, dispersed bacteria growth and protozoa absence could be established. With respect to SVI estimation, and despite the good correlation obtained, caution is advisable given the low number of SVI data points. Copyright © 2008 Society of Chemical Industry     

Numerical modelling of filtration with and without sedimentation runs

From experimental batch runs of filtration with sedimentation above the cake formed, a procedure is proposed and applied to experimental data for obtaining the relationships between the settling solids velocity in the hindered settling zone, the local specific resistance and the effective pressure and the solids concentration. Considering the material and momentum balances in the hindered settling zone above the cake, in the cake and in the filter membrane, a simulation program was obtained that satisfactorily reproduces the experimental runs of filtration with sedimentation runs. This simulation work confirms the hypothesis considered in the theory of filtration with sedimentation runs, e.g. the fact that the characteristic lines arise tangently from the cake surface. In addition, the method developed for obtaining the different relationships considered has been demonstrated as correct. The simulation of filtration without sedimentation runs (stirring the suspension above the cake) has also been studied.     

Effect of sludge retention time in sludge holding tank on excess sludge production in the oxic‐settling‐anoxic (OSA) activated sludge process

The activated sludge process is a core technology in wastewater treatment plants. Excess sludge produced in the process must be treated and disposed of properly and may account for up to 60% of total plant operating cost. Therefore, it is necessary to develop new biological concepts to minimize excess sludge production. The oxic‐settling‐anoxic process (OSA process), a modified activated sludge process, may produce less excess sludge than the conventional activated sludge process. The effect of sludge retention time in the sludge holding tank of the OSA process on excess sludge yield has been studied. Four pilot‐scale activated sludge systems were employed, one of which was a conventional activated sludge process, and was used as the control system. The other three were OSA systems operated with different sludge retention times (5.5 h, 7.6 h, and 11.5 h) in the sludge holding tank. All systems were operated with synthetic wastewater for 7 months. Results showed that the three OSA processes with 5.5 h, 7.6 h, and 11.5 h sludge retention time reduced the excess sludge by 33%, 23% and 14%, respectively. Compared to the control process, chemical oxygen demand (COD) removal efficiency and effluent NH₃–N concentration were not significantly influenced, but total nitrogen (TN) removal efficiency decreased by 0–9%. Total phosphorus (TP) removal efficiency of OSA processes with 7.6 h and 11.5 h sludge retention time increased by 19%. Sludge settleability was excellent in the three OSA processes. No distinct shift in the diversity of the predominant species was found in microbial populations. We conclude that the OSA system could reduce excess sludge production. Results suggest 6–7 h sludge retention time would be optimal. Copyright © 2007 Society of Chemical Industry     

离心式超细分级机的试验及分析

本文介绍了ＺＬＦ新型超细离心式分级机的特点和现场工艺试验情况，试验结果表明，产品粒度均匀，能适应对物料超细分级的要求。     

混凝沉淀--活性污泥法处理PVA退浆废水的研究

采用混凝--优势菌活性污泥工艺进行了处理含PVA退浆废水的小试研究,其中活性污泥中接种了PVA降解优势菌.处理后CODCr去除率达到93.52%,出水水质达到了GB 4287-1992《纺织染整工业水污染物排放标准》中的二级排放标准.     

Ca2+对序批式生物反应器活性污泥性能的影响

二价阳离子能够中和活性污泥表面负电荷,影响微生物活性和生物絮凝性能。本文采用序批式生物反应器（SBR）考察Ca²⁺对污泥活性和污泥絮体表面性质的影响,利用红外光谱和三维荧光光谱分析胞外聚合物（EPS）组分和结构的变化,揭示Ca²⁺与污泥疏水性和zeta电位之间的联系,明确Ca²⁺在生物絮凝中的作用。结果表明：在进水COD、TN和NH₄⁺-N分别为420mg/L、40mg/L和35mg/L的条件下,当Ca²⁺浓度达到160mg/L时,COD、NH₄⁺-N和TN去除率最高（分别为96.7%、90.02%和73.2%）,DHA活性和耗氧呼吸速率（OUR）达到最大,分别为124mgTF/L和3.1mg/（min·L）。Ca²⁺促进了污泥微生物EPS的生成,增大了EPS中蛋白质含量。Ca²⁺与EPS表面带负电的官能团形成架桥,吸附桥联的Ca²⁺中和EPS表面的负电荷,减少了污泥表面负电荷之间的静电斥力,使污泥絮体保持稳定;同时增大了污泥表面的疏水性,改善了污泥的絮凝性和沉降性。     

Consolidation and flow of cohesive bulk solids

The strength and the flow properties of bulk solids can be determined by performing shear tests. A shear test always consists of two parts, consolidation and measurement of strength. The measured strength depends on the way and degree of consolidation. During consolidation a stress history is impressed on the bulk solid sample which only vanishes after steady state flow. Since the consolidation is normally done nonhydrostatically, the strength will depend on the direction of stress application (anisotropy). Thus, the strength of a bulk solid sample strongly depends on its stress history and it can show anisotropic behaviour. These effects have to be considered when comparing available shear testers.     

Filterability of activated sludge in membrane bioreactors

The filterability of activated sludge is an important factor for the economical operation of membrane bioreactors (MBR). In the literature mainly investigations on sludge dewaterability in respect to further disposal are published. In this study, a procedure for determining filterability in a crossflow test cell is introduced. Its features are: no increase in sludge concentration during batch trials, crossflow conditions, and little impact on the sludge structure. The activated sludge filterability is given as the ratio of permeate flux after 40 min of operation to clear water flux. Sludge samples of eight different MBR and one conventional wastewater treatment plant (wwtp) have been examined and compared. Contrary to the literature, no impact of suspended solids (SS) concentration, sludge viscosity, or extractable extracellular polymer substances (EPS) concentration on the filterability was found. Instead, the composition of the liquid phase was found to effect most the filterability of activated sludge, a major influence being the concentration of suspended EPS: the higher the suspended EPS concentration, the lower the filtration index. Suspended EPS concentration increases with high mechanical stress in the MBR and high F/M ratios, if the treated wastewater contains considerable amounts of proteins or polysaccharides.     

离心式压缩机的能力核算及其软件开发

介绍了离心式压缩机能力核算的重要性、原理、方法、软件开发及工业应用。     

石油化工污泥调质深度脱水工艺应用研究

以某石油化工企业的污泥为研究对象,对污泥调质深度脱水技术的主要影响因素进行了一系列小试研究。实验结果表明,该技术能够有效降低化工污泥的含水率,实现污泥的减量化。通过单因素试验确定各影响因素对污泥深度脱水的影响。研究得出最佳工艺:在化工污泥中加入12%生石灰和2%ME调理剂后,混合10 min,抽滤15 min,污泥最终含水率降低到50.6%,达到污泥混合填埋对污泥含水率的要求。最佳条件下脱水污泥浸出液重金属浓度比原始污泥有所降低,调理剂不增加脱水污泥的重金属含量。