Dewatering of Sewage Sludge

Dewatering of sewage sludges is usually carried out using belt filter presses or centrifuges. The ability to remove water from sludges by mechanical dewatering is a property of both the sludge and the equipment used for dewatering. Newer high-solids centrifuges can remove more water than a belt press but require a higher chemical conditioning dose. The Gt value, the product of the mean velocity gradient and the shear time, has been found to be a useful parameter for characterizing the shear in mechanical dewatering equipment. Dewatering can be considered a two-step process, filtration followed by expression. The expression step is the most important of these and the benefits of various sludge processing techniques and conditioning chemical types remains a fruitful area of research.     

用于城市污水处理用浓缩脱水一体机

机械浓缩脱水已被广泛用于城市及工业污水的污泥脱水中,目前被广泛采用的脱水设备有带式压榨过滤机、卧式螺旋卸料沉降离心机、板框厢式压滤机等,由于脱水工艺的要求,为了减少因浓缩过程时间较长,结合在污泥中的氮磷重新释放后进入水体,造成藻类的繁殖和对水系的进一步污染,要求机械脱水设备能够对沉淀池中底流进行直接处理,即浓缩脱水一体化处理。     

PRACTICAL ASPECTS OF DEWATERING ENHANCED BY ELECTRO-OSMOSIS

Dewatering mechanism due to electro-osmosis is fairly different from that of mechanical dewataine which has been used conventionally. and electro-osmotic dewatering has Several advantages compared with the mechanical dewatering and it can be remarkably effective for hardly dewaterable sludges such as very fine Particles and gelatinous materials. In electro-osmotically enhanced dewatering, however, it would be a great problem that the achievement of complete water removal within the sludge could not be possible in principle. Because. when a liauid state in the sludge becomes to be not continuous gradually with proceeding of dewatering, the sludge does not lead electricity and and then electro-osmosis is no longer caused.

Applying electro-osmosis to sludge dewatering practically, methods for improvement of the electro-osmotic dewatering must be investigated taking account ofapos;such a situation for the performance of high dewatering efficiency. Some practical applications of the dewatering which can be considered to be available are described in this paper.     

PRACTICAL ASPECTS OF DEWATERING ENHANCED BY ELECTRO-OSMOSIS

ABSTRACT

Dewatering mechanism due to electro-osmosis is fairly different from that of mechanical dewataine which has been used conventionally. and electro-osmotic dewatering has Several advantages compared with the mechanical dewatering and it can be remarkably effective for hardly dewaterable sludges such as very fine Particles and gelatinous materials. In electro-osmotically enhanced dewatering, however, it would be a great problem that the achievement of complete water removal within the sludge could not be possible in principle. Because. when a liauid state in the sludge becomes to be not continuous gradually with proceeding of dewatering, the sludge does not lead electricity and and then electro-osmosis is no longer caused.

Applying electro-osmosis to sludge dewatering practically, methods for improvement of the electro-osmotic dewatering must be investigated taking account ofapos;such a situation for the performance of high dewatering efficiency. Some practical applications of the dewatering which can be considered to be available are described in this paper.     

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.     

SLUDGE DEWATERING AND DRYING

The production of wastewater treatment sludge, the basic characteristics of the sludge and the state of the water in the sludge are described in this paper. The methods for the determination of bound water content are discussed. The literature (including patents) on sludge dewatering and drying is reviewed, including vacuum filters, belt presses, centrifuges, direct dryers, indirect dryers and combined mode drying systems. The issues related to drying are briefly discussed. Photographs or schematics of typical dewatering and drying systems are also included.     

ULTRASOUND IN THE SUSPENSION SEPARATION METHODS

Investigations were carried out on the effect of the ultrasonic field and some selected chemical compounds on the process of preparing sludges to be dewatered by mechanical devices.

The tests; were performed in a laboratory on real sludges. The processes occurring in sludges due to presence of ultrasonic field and applied chemical reagents were determined on the basis of a commonly used method of determining the sludge dewatering, in both filtration and sedimentation.

The interdependences of value changes of the above mentioned factors and the possibilities of applying ultrasonic waves to intensifying sludge dewatering process were examined. The obtained results confirm the applicability of ultrasonic waves to the process of sludge treatment and prove that the initial assumptions concerning the use of ultrasonic field in the suspension separation methods to be valid.     

ULTRASOUND IN THE SUSPENSION SEPARATION METHODS

Investigations were carried out on the effect of the ultrasonic field and some selected chemical compounds on the process of preparing sludges to be dewatered by mechanical devices.

The tests; were performed in a laboratory on real sludges. The processes occurring in sludges due to presence of ultrasonic field and applied chemical reagents were determined on the basis of a commonly used method of determining the sludge dewatering, in both filtration and sedimentation.

The interdependences of value changes of the above mentioned factors and the possibilities of applying ultrasonic waves to intensifying sludge dewatering process were examined. The obtained results confirm the applicability of ultrasonic waves to the process of sludge treatment and prove that the initial assumptions concerning the use of ultrasonic field in the suspension separation methods to be valid.     

污泥深度脱水技术研究进展

随着经济的发展和国民生活水平的提高,污水污泥的排放量逐年增加,环境问题愈发严重,污泥的处理处置成为焦点问题,污泥脱水是制约污泥处置处理进一步发展的关键。本文针对目前污泥深度脱水技术开展,首先简述了不同来源污泥的分类及其基本特性,然后重点阐述了不同污泥预处理技术,分析了各污泥深度脱水技术作用机理,并对各自脱水效果及优缺点进行比较分析。结果表明,物理法中水热预处理对污泥的可脱水程度提升最大。较低声强、短时间的超声波处理对污泥脱水性能有着明显的改善。化学法在污泥过滤性能以及脱水速率方面有很大优势,酸碱处理后污泥zeta电位上升,污泥过滤性能及脱水速率得到改善。高级氧化法处理后污泥脱水效果高于酸碱处理,微生物细胞被溶解释放出有机物,可脱水程度改善。生物法处理污泥除改善污泥脱水性能外,还有对环境污染小等特点,但耗时较长。最后对污泥的后续脱水工艺进行综述,介绍了现存的主流脱水工艺,包括机械脱水、热干化技术、水热脱水工艺等;并针对不同的污泥后续利用方法,选取合适的预处理技术,提出相应优化的污泥处理工艺流程。     

Conditioning for Municipal Sludge Dewatering. From Filtration Compression Cell Tests to Belt Press

Belt presses are commonly used to achieve sewage sludge dewatering. As this process essentially works by squeezing, it was interesting to better understand how the sludge conditioning affects cake expression. Experiments were carried out with conditioned municipal activated sludge on both a filtration compression cell (FCC) and a laboratory-scale belt press. Two cationic polyelectrolytes with a high charge density (80%) but different molecular weights were used. A significant impact of the conditioning was observed for FCC tests. The higher molecular weight polyelectrolyte led to much shorter filtration phases than with the medium molecular weight one. However, it produced wetter filter cakes. It also led to more elastic filter cakes but less susceptibility to creep. Higher final dryness was observed for sludge conditioned by the medium molecular weight polymer. Experiments carried out on the belt press device did not exhibit such impact. Consequently, the FCC test is not suitable to analyze the sludge dewatering by belt press, although it enables characterization of the expression phase. Indeed, some additional features involved in belt press, such as shear forces or progressive pressurization of the cake, are not characterized by classical FCC tests.     

Conditioning for Municipal Sludge Dewatering. From Filtration Compression Cell Tests to Belt Press

Belt presses are commonly used to achieve sewage sludge dewatering. As this process essentially works by squeezing, it was interesting to better understand how the sludge conditioning affects cake expression. Experiments were carried out with conditioned municipal activated sludge on both a filtration compression cell (FCC) and a laboratory-scale belt press. Two cationic polyelectrolytes with a high charge density (80%) but different molecular weights were used. A significant impact of the conditioning was observed for FCC tests. The higher molecular weight polyelectrolyte led to much shorter filtration phases than with the medium molecular weight one. However, it produced wetter filter cakes. It also led to more elastic filter cakes but less susceptibility to creep. Higher final dryness was observed for sludge conditioned by the medium molecular weight polymer. Experiments carried out on the belt press device did not exhibit such impact. Consequently, the FCC test is not suitable to analyze the sludge dewatering by belt press, although it enables characterization of the expression phase. Indeed, some additional features involved in belt press, such as shear forces or progressive pressurization of the cake, are not characterized by classical FCC tests.     

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.     

污泥深度脱水技术在城市污泥处理处置中的应用

深度脱水工艺是指脱水后污泥含水率达到55％～65％,特殊条件下污泥含水率还可以更低。该文介绍了污泥深度脱水技术在我国的发展现状和应用前景。通过分析目前上海在污泥处理处置中遇到的问题和解决对策,并结合上海白龙港污泥深度脱水项目实例,总结该工艺在工程设计、污泥调理、设备选型和运行管理中的一些经验。     

ANALYSIS OF THE DRYING OF RESIDUAL SLUDGE: FROM THE EXPERIMENT TO THE SIMULATION OF A BELT DRYER

The drying of residual sludge is a current environmental problem not sufficiently described in the literature, hence research investigations on this dewatering process are required. This paper proposes a modelling of a conveyor dryer belt. However the study of residual sludges dewatering in order to design or simulate drying equipment requires some experimental investigations. An analysis in terms of drying kinetics is proposed in this paper. Specific experiments were also needed in order to better describe some particular aspects such as crusting, shrinkage, and particle size impact. According to these data some analytical expressions have been derived and integrated in a belt dryer model. The set of air operating conditions (T, RH, v) was reduced to a single parameter, the drying potential. The results of the simulations show that a conveyor belt dryer is not well adapted to activated sludge. This is essentially due to a crust phenomenon. For a PVC industrial sludge this kind of dryer is more efficient and allows drying with reasonable residence times. Several simulations were run in order to point out the relevant parameters of the process.     

挤出式污泥脱水装置在大牛地气田含醇含油污泥处理中的应用

在大牛地气田天然气开发过程中,产生大量含有甲醇、凝析油的污泥,为避免污泥污染环境,需使用专门的脱水设备处理污泥,降低污泥含水率,然后将污泥焚烧。经传统板框式脱水机、带式脱水机等脱水设备处理后的泥饼含水率在75%-85%之间,需要进行二次干化处理,而新型的挤出式污泥脱水装置处理后的泥饼含水率最低可降低到65%,无需进行二次干化处理,大大提高了污泥处理效率,同时也取得了较好的安全效益和经济效益。     

Effect of Polyelectrolyte Conditioning and Voltages on Fractionation of Macro and Trace Metals due to Sludge Electro-Dewatering

The purpose of this laboratory study was to investigate the simultaneous impacts of the electro-dewatering process on dry solids (DS) content and mobilization of metals in sewage sludge. The results suggested that the use of polyelectrolytes is necessary in mechanical pressure-driven dewatering and also in electro-dewatering. With polyelectrolyte conditioning, the DS content in the final sludge cake could be increased to 39%. Dewatering with slightly cationic polymer was not effective, but medium, strongly and very strongly cationic polymers performed equally. During electro-dewatering, an increase of voltage from 10 to 40 V resulted in a dryer sludge cake. Polyelectrolyte addition reduced the content of exchangeable metal species and increased less mobile, reducible species in the sludge. Furthermore, the more stable or immobile metal fractions were more likely to remain intact in dewatered sludge. Among heavy metals, Cu and Pb were immobile but Cr, Co, Ni, and Zn could more easily be mobilized during electro-dewatering. The application of high voltage had a direct effect on the migration of metal fractions, whereas, the sludge conditioning by a different cationic polymer had an indirect effect on the migration of these metals during electro-dewatering.     

ANALYSIS OF THE DRYING OF RESIDUAL SLUDGE: FROM THE EXPERIMENT TO THE SIMULATION OF A BELT DRYER

ABSTRACT

The drying of residual sludge is a current environmental problem not sufficiently described in the literature, hence research investigations on this dewatering process are required. This paper proposes a modelling of a conveyor dryer belt. However the study of residual sludges dewatering in order to design or simulate drying equipment requires some experimental investigations. An analysis in terms of drying kinetics is proposed in this paper. Specific experiments were also needed in order to better describe some particular aspects such as crusting, shrinkage, and particle size impact. According to these data some analytical expressions have been derived and integrated in a belt dryer model. The set of air operating conditions (T, RH, v) was reduced to a single parameter, the drying potential. The results of the simulations show that a conveyor belt dryer is not well adapted to activated sludge. This is essentially due to a crust phenomenon. For a PVC industrial sludge this kind of dryer is more efficient and allows drying with reasonable residence times. Several simulations were run in order to point out the relevant parameters of the process.     

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.     

无机调理剂与表面活性剂联合调理对污泥脱水性能的影响

研究了CaO、PAFC联合表面活性剂预处理对污泥脱水性能的影响。以污泥滤饼含水率和比阻（SRF）作为评价污泥脱水性能的指标,通过测定污泥调理过程中胞外聚合物（EPS）含量、Zeta电位的变化来阐明污泥脱水性能的变化。实验结果表明,十二烷基二甲基苄基氯化铵（1227）的加入导致上清液中EPS含量发生变化,有效降低了SRF和滤饼含水率,提高污泥脱水性能。CaO、PAFC和表面活性剂的联合调理污泥比单独使用表面活性剂的效果更好,CaO、PAFC的投加不仅改善污泥脱水性能,并有助于减少表面活性剂的用量。污泥上清液中EPS及其各组分含量与污泥滤饼含水率、SRF均有较高的相关性,对污泥的脱水性能有重要贡献。实验中确定的最佳污泥调理条件是CaO投加量为66.67 mg·（g DS）^-1、PAFC投加量为33.33 mg·（g DS）^-1和表面活性剂投加量为56.25 mg·（g DS）^-1,污泥滤饼含水率和SRF分别降至69.41%、0.294×10¹³ m·kg^-1。     

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.