ELECTROOSMOTIC DEWATERING PROCESS AND DESIGN EQUATIONS

This paper deals with electroosmotic dewatering that can be very effective for sludge which is difficult to dewater by conventional mechanical techniques. First, the dewatering mechanism of sludge due to electroosmosis is analyzed theoretically based on an electroosmotic flow through a compressible packed bed of particles, and then its processes under the conditions of both constant electric current and constant voltage are discussed both theoretically and experimentally. Further theoretical expressions for the dewatering rate and the electric power consumption are proposed using a simple model in which the sludge bed consists of two parts: a dewatering bed and a dewatered bed. The equations obtained theoretically are demonstrated to be applicable to the design of electroosmotic dewatering equipment.     

ELECTROOSMOTIC DEWATERING PROCESS AND DESIGN EQUATIONS

This paper deals with electroosmotic dewatering that can be very effective for sludge which is difficult to dewater by conventional mechanical techniques. First, the dewatering mechanism of sludge due to electroosmosis is analyzed theoretically based on an electroosmotic flow through a compressible packed bed of particles, and then its processes under the conditions of both constant electric current and constant voltage are discussed both theoretically and experimentally. Further theoretical expressions for the dewatering rate and the electric power consumption are proposed using a simple model in which the sludge bed consists of two parts: a dewatering bed and a dewatered bed. The equations obtained theoretically are demonstrated to be applicable to the design of electroosmotic dewatering equipment.     

ELECTROOSMOT1C DEWATERING UNDER A. C. ELECTRIC FIELD WITH PERIODIC REVERSALS OF ELECTRODE POLARITY

D.C. electric field has been usually used for electroosmotic dewatering. Under the condition of D.C., however, electrical contact resistance between the electrode and dewatering material is increased considerably with the process of dewalering. Such a circumstance hinders continuation of effective electroosmotic dewatering. To reduce the hindrance, application of A.C. electric field with periodic reversals of die electrode polarity can be expected as an improvement of electroosmotic dewatering.

Electroosmotic dewatering under the condition of A.C. was experimentally investigated mainly in the region of low frequency below Hz for the electrode polarity reversals. In the dewatering process, the A.C. electric field could reduce the hindrance caused by the D.C, and final dewalered amount was increased more than that under the D.C. electric field. For constant applied voltage, the frequency condition, at which electric current passing through the material was almost not changed with time, gave the maximum of the final dewatered amount     

ELECTROOSMOT1C DEWATERING UNDER A. C. ELECTRIC FIELD WITH PERIODIC REVERSALS OF ELECTRODE POLARITY

ABSTRACT

D.C. electric field has been usually used for electroosmotic dewatering. Under the condition of D.C., however, electrical contact resistance between the electrode and dewatering material is increased considerably with the process of dewalering. Such a circumstance hinders continuation of effective electroosmotic dewatering. To reduce the hindrance, application of A.C. electric field with periodic reversals of die electrode polarity can be expected as an improvement of electroosmotic dewatering.

Electroosmotic dewatering under the condition of A.C. was experimentally investigated mainly in the region of low frequency below Hz for the electrode polarity reversals. In the dewatering process, the A.C. electric field could reduce the hindrance caused by the D.C, and final dewalered amount was increased more than that under the D.C. electric field. For constant applied voltage, the frequency condition, at which electric current passing through the material was almost not changed with time, gave the maximum of the final dewatered amount     

高盐高有机制药废水污泥电渗透高干脱水

为研究高盐高有机制药废水污泥的电渗透脱水效果,深入认识化学污泥的电脱水过程,本文采用电渗透高干脱水技术对经抽滤脱水的高盐高有机制药废水化学污泥进行深度脱水,考察了泥饼初始pH的改变对污泥电渗透高干脱水过程中阴阳极污泥的含水率、电流、电导率、pH、zeta电位与能耗的影响,验证了对高盐高有机制药废水污泥实行电渗透高干脱水的可行性,解析了化学污泥电渗透脱水过程的机制。结果表明,泥饼pH为2、3、4时,zeta电位为正值,电渗流反向流动,无法脱水;pH增至5时,zeta电位为负值,电渗流从阴极脱除,污泥含水率从53.2%降至44.8%,脱水效果最好;但pH增至6时,脱水量有所降低。污泥电导率随pH的增加而降低。pH为5时初始电流最大。脱水15min时,即污泥含水率降至45.5%时,能源利用率最高。     

Influence of Electric Field Application with Decreasing One Sided Area of Electrodes on Electro-Osmotic Dewatering

Electro-osmotic dewatering is typically operated under an electric field of direct current condition. In the process of electro-osmotic dewatering, water content in part of the material near the electrode opposite to the drainage surface is locally reduced, resulting in an increase of electrical contact resistance between the electrode and the material being dewatered. Then the efficiency of the electro-osmotic dewatering process is reduced remarkably.

In order to improve the performance of electro-osmotic dewatering, it is supposed that a porous plate-type electrode used generally opposite to the drainage surface may be replaced to several rod-type electrodes, which are inserted into the material with dewatering. Using rod-type electrodes, the area of those electrodes becomes smaller than the plate-type electrode.

From this point of view, electro-osmotic dewatering was experimentally investigated by decreasing one-sided area of electrodes, namely the area of the plate-type electrode opposite to the drainage surface, and the influence of such an electric field application on improvement of the dewatering process is discussed in this article.     

Influence of Electric Field Application with Decreasing One Sided Area of Electrodes on Electro-Osmotic Dewatering

Electro-osmotic dewatering is typically operated under an electric field of direct current condition. In the process of electro-osmotic dewatering, water content in part of the material near the electrode opposite to the drainage surface is locally reduced, resulting in an increase of electrical contact resistance between the electrode and the material being dewatered. Then the efficiency of the electro-osmotic dewatering process is reduced remarkably.

In order to improve the performance of electro-osmotic dewatering, it is supposed that a porous plate-type electrode used generally opposite to the drainage surface may be replaced to several rod-type electrodes, which are inserted into the material with dewatering. Using rod-type electrodes, the area of those electrodes becomes smaller than the plate-type electrode.

From this point of view, electro-osmotic dewatering was experimentally investigated by decreasing one-sided area of electrodes, namely the area of the plate-type electrode opposite to the drainage surface, and the influence of such an electric field application on improvement of the dewatering process is discussed in this article.     

Electroosmotic Dewatering of Tomato Paste Suspension Under AC Electric Field

Laboratory tests have demonstrated electroosmosis under an alternate current (AC) to be effective for dewatering tomato paste suspension. Application of an alternate current (AC) field provided more promising results than those of direct current (DC) electrical field. The results show that the electroosmotic dewatering is influenced by the wave form (sine, rectangular, triangular). The decrease in the wave frequency resulted in an increase in the dewatering rate, whereas increasing the initial bed height increased the dewatering rate.     

Effects of current density and electrode material on the dewaterability of the thickened activated sludge by electro‐flotation

BACKGROUND: Electro‐flotation (EF) could improve thickening and subsequent dewatering characteristics of activated sludge although the settling characteristics of the sludge were very poor. The objectives of this study were to evaluate the performance of EF in the thickening and dewatering of activated sludge and the effects of current density and electrode material on the dewaterability of the sludge. RESULTS: The specific resistance to filtration (SRF) of the sludges thickened by EF was much lower than that by gravity sedimentation. The SRF of the thickened sludge decreased exponentially with increase of gas generation rate of the EF system. Gas generation rate could be controlled by varying the current density of the electrode. Degassing of the microbubbles by moderate mixing of the thickened sludge layer deteriorated the dewaterability of the sludge. Therefore, it is obvious that the gas bubbles entrapped in the thickened sludge play a key role in the observed dewaterability improvement. The effect of electrode material on the thickening and dewatering efficiency was trivial compared with the effect of current density of the electrode. CONCLUSION: The EF system was quite promising as an alternative to gravity sedimentation for thickening of activated sludge and the dewaterability was also improved by microbubbles generated in the system. Copyright © 2009 Society of Chemical Industry     

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.     

Performance evaluation of electrocoagulation and electrodewatering system for reduction of water content in sewage sludge

Electrocoagulation is applied to sewage sludge as a pretreatment process of an electrodewatering system to reduce the water content of sludge generated in wastewater treatment. The electrodewatering system, by incorporating an electric field as an additional driving force to the conventional pressure dewatering, has been evaluated as a function of an electrode material, applied voltage and filtration time. Experiments were carried out using sewage sludge with a pressure up to 392.4 kPa and applied electrical field ranging up to 120 V/cm. Mass median diameter of the sewage sludge by the effect of electrocoagulation increases from 34.7 μm to the 41.3 μm. The final water content of sewage sludge in the combination of both electrocoagulation and electrodewatering system can be reduced to 55 wt%, as compared to 78 wt% achieved with pressure dewatering alone. The combination of electrocoagulation and electrodewatering system shows a potential to be an effective method for reducing the water content in sludge.     

不同混凝剂作用下的污泥性能研究

污泥脱水是依靠过滤介质（多孔性物质）两面的压力差作为推动力,强制水分通过过滤介质,固体颗粒被截留在介质上,以达到脱水的目的。污泥比阻是表示污泥脱水性能的综合性指标,比阻愈大,其脱水性能愈差,反之愈好。添加混凝剂可以使污泥的比阻减小,改善污泥的脱水性质。采用用布氏漏斗试验,以FeCl3和Al（2SO4）3为混凝剂,通过测定污泥滤液滤过介质的速度快慢来确定污泥比阻的大小,并确定混凝剂的最佳添加量。     

A Study for Development of Real-Scale Thermal Filter Press Dewatering (TFPD)

Real-scale thermal filter press dewatering equipment (plate size: 630 mm × 630 mm) was installed and operated at a waterworks for one year in an attempt to achieve sludge reduction. During the period, the dewaterability was evaluated according to the seasonal sludge properties in order to compare the dewaterability of thermal dewatering and mechanical dewatering, as well as to determine the economics of thermal dewatering. According to the results, the winter season sludge showed a 36% decrease in water content and a two-thirds reduction in dewatering velocity compared to the summertime sludge. In addition, the dewatered cakes of the thermal filter press dewatering equipment showed a lower specific cake resistance and water content in the dewatered cakes than the mechanical filter press dewatering equipment, indicating superior dewaterability. This was attributed to the easier removal of the filtrate remaining in the capillary tubes due to thermal dewatering. The energy consumption for thermal dewatering was 300 kJ/dry solids (DS) kg. A comparison of the sludge dryers indicated that it is possible to produce dewatered cakes that consume less energy and can be recycled. According to the performance evaluation results, the real-scale thermal filter press dewatering equipment had high adaptability to the changes in seasonal sludge, showing excellent dewaterability compared to the mechanical filter press dewatering equipment, and was economical due to the lower energy consumption.     

模拟人工湿地芦苇床中城市污泥脱水和稳定化的试验研究

人工湿地芦苇床污泥脱水和稳定化技术因其能耗、运行篱理费用低得到更多的研究。试验污泥为厌氧池加氧化沟工艺二沉池污泥,模拟人工湿地进泥负荷为0．658kgTS／m2．d．进泥中TS和VS平均含擐分别为19．68和6．93g／L,pH为6．78。试验期为1年,对第一个进混周期后的渗滤液中COD、NH4-N及Ts的含最进行了测定。试验结束后,湿地中表层和底部污泥TS含量分别达到51．5％和56．8％,底部污泥中VS含量降至12．3％。结果表明,人工湿地芦苇床对城市污泥有较好的脱水和稳定化效果。     

Characterization of synthetic and activated sludge and conditioning with cationic polyelectrolytes

This study investigates the effect of cationic polyelectrolytes on the final properties of synthetic and activated sludge. Synthetic sludge was prepared according to established procedures. Activated sludge was produced in a labscale, continuous-flow reactor which was fed with live activated sludge from a waste-water treatment plant. Capillary suction time (CST) was used to evaluate the sludge dewatering behaviour. The results from experiments indicated that the cationic polyelectrolytes had a critical effect on sludge dewatering, and made an improvement in the final properties of sludge. The two types of sludge have very similar dewatering characteristics after cationic polymer conditioning. The development of synthetic sludge is suggested also to be a possible surrogate for studying the final properties of activated sludge.     

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.     

Thermal Dewatering (TDW) to Reduce the Water Content of Sludge

Thermal dewatering describes the process whereby a heating plate and heat supply unit are incorporated into a filter press system to improve separation of water from sludge. The performance of our thermal dewatering system for both wastewater and waterworks sludge was measured and compared with mechanical dewatering in terms of water content, dewatering velocity, cake specific resistance, and energy consumption. Dewatering velocity was improved by a factor of two, cake water content was lower, and specific cake resistance was improved. However, energy consumption was higher. Thermal dewatering systems may be economical and have practical application to improving dewaterability.     

城市污水处理厂污泥脱水药剂选型研究

针对某城市污水处理厂的污泥脱水处理,进行了一系列污泥脱水药剂的烧杯倾倒实验、CST实验、污泥比阻实验。实验结果表明：在阳离子、阴离子、非离子PAM中,阳离子PAM污泥脱水效果最优;所实验药剂都有一个最佳投加量,处于4.14～5.52 kg/t绝干污泥之间;在所实验药剂中,分子量对于污泥脱水性能的影响不明显,离子度影响较大,最优离子度为50%。     

Electrode Kinetic and Electro-Kinetic Effects in Electroosmotic Dewatering of Clay Suspensions

Lockhart's remarks (1) on our previous interpretation (2) of the electrochemical aspects of the electroosmotic dewatering (EOD) of clay suspensions are analyzed to provide some further clarification. Based on Lockhan's excellent work (1, 3-8), we put forward here novel electrochemical interpretations of some features of the following experimental observations:

(i) Galvani dewatering;

(ii) The dewatering efficiency:

(iii) High voltage needed for dewatering Al-kaolinite and aluminium electrode effect.