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.     

Mechanical Dewatering and Thermal Drying of Sludge in a Single Apparatus

This article describes the Centridry® technology (marketed in the UK by Euroby Ltd.) used at the Monsanto wastewater treatment plant in Antwerp, Belgium, for handling excess wastewater-activated sludge. In one single enclosed machine, sludge with an initial solids concentration of 1.5 to 4% w/w dry substance is mechanically dewatered with a high-solids decanter centrifuge and thermally dried in a flash dryer, yielding a final product with a concentration of solids ranging from 80 to 95% w/w dry substance. Operational experience with varying sludge characteristics affecting the fouling sensitivity of the system is presented for the Centridry technology at the Monsanto plant in Antwerp.     

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.     

Conditioning and Dewatering of Phosphorus-Rich Biological Sludge

The conditioning and dewatering of phosphorus-rich biological sludge, obtained from a pilot-scale biological phosphorus removal plant, was investigated. Dual conditioning utilizing a polyampholyte (AC4601) in combination with aluminum chloride (AlCl₃), ferric chloride (FeCl₃), and calcium chloride (CaCl₂) was studied. Capillary suction time (CST) and specific resistance to filtration (SRF) were utilized to assess sludge dewaterability. The dewaterability and removal of dissolved phosphorus from the phosphorus-rich sludge were examined. Compared with conditioning with only AC 4601, dual conditioning by adding 49 kg/ton of AlCl₃ prior to addition of AC4601 resulted in formation of large flocs, better dewaterability, and removal of 50% of soluble phosphorus. Better dewaterability, even larger flocs (> 1 cm), and 75% removal of soluble phosphorus were found when dosage of AlCl₃ increased to 189.2 kg/ton. The use of alumina (Al₂O₃) in combination with AC4601 could achieve equivalent dewaterability. However, only insignificant removal of soluble phosphorus (ca. 10%) was found. Sludge conditioning utilizing FeCl₃ and AC4601 was also very effective. A higher dosage of AC4601 was required and insignificant removal of soluble phosphorus was found when CaCl₂ was used in combination with AC4601. The interactions between hydrolyzed species of trivalent metal ions and polyampholyte contributed to enhanced dewaterability. Precipitates acted as skeleton builder and assisted in dewaterability as well. In addition, the removal of phosphorus was due to its precipitation reactions with metal ions. This study demonstrated an alternative way to condition phosphorus-rich sludge that could control the release of phosphorus from sludge to aqueous phase under anaerobic environment and achieve enhanced dewaterability simultaneously.     

Sewage Sludge Dewatering Process Using Liquefied Dimethyl Ether as Solid Fuel

This article describes the dewatering of sewage sludge using liquefied dimethyl ether (DME), which clarified the effect of sludge type and its particle size. Changes in the heating value of the dewatered sludge were also examined. In addition, the change in dewaterability upon reuse of the liquefied DME was investigated experimentally.

Regardless of the nature of the sludge, its dewatering behavior was similar. The amount of dewatered water could be increased by decreasing the diameter of the sludge cake. Complete drying of the sludge cake via DME dewatering resulted in retention of approximately 96% of the heating value (17.7 MJ/kg-sludge) of the original sludge cake dry base (18.4 MJ/kg db). The DME could be recovered after extraction, and reuse experiments showed that liquefied DME dewatering performance was unchanged after five reuses.     

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。     

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.     

含油污泥脱水设备与技术

分析了含油污泥的性质 ,介绍了国内外含油污泥处理技术与脱水设备的现状 ,并比较各方法及设备的优缺点。提出了含油污泥脱水设备与技术的发展趋势和几点建议。     

污泥板框压滤脱水给料的研究

在污泥板框压滤脱水的过程中,对泵给料和贮料罐给料两种给料方式进行了试验研究,从能耗方面对两种给料方式进行了比较,得出贮料罐给料优于泵给料。     

Compression Dewatering of Particulate Suspensions and Sludge: Effect of Shear

Experiments were carried out at the lab-scale to study the effect of a shearing action in a compression dewatering process. The impact of different process parameters, such as shear rate, filter-cake thickness, and pressure, on the final dry solid fraction was analyzed. Also, materials with different degrees of compressibility have been used. For slightly and moderately compressible materials (talc and kaolin, respectively), significantly higher final dry solid fractions (up to 0.79 wt/wt with talc and 0.75 wt/wt with kaolin) were obtained in the presence of a torsion shear. This behavior may mainly be explained by a rearrangement of the solid particles within the cake induced by the radial forces. A low shear rate (around 0.7 s^?1) was generally sufficient to cause a quite significant increase in the cake dryness (a 12.8% increase was observed with 11-mm-thick talc cakes). A further increase in the shear did not lead to noticeable changes in the final dry solid fraction in the cakes. Otherwise, reducing the filter-cake thickness was beneficial for the dewatering. For talc cakes, the dry solid fraction was increased by 21% for a 3 mm thickness against 7% for a 25 mm thickness. With a highly compressible material, such as activated sludge, the filter-cake dryness did not change with the application of a shearing action. This behavior may be mainly attributed to the fact that biological sludge dewatering is markedly influenced by a low permeability skin at the cake/medium interface, which is very thin and not perturbed by shear forces, due to the cake thickness. The low rigidity of the solid matter in this particular case may also limit the reorientation of the particles.     

Laboratory Experiments on Electroosmotic Dewatering of Vegetable Sludge and Mine Tailings

ABSTRACT

Vegetable wastes in the food industry are costly lo handle because of their high moisture content. while mill plant tailings in the mining industry contain large quantities of ultralines which are difficult io dewater.This paper describes the results of small scale electmosmotic dewatering (EOD) and combined field dewatering (CFD) measurements with model vegetable sludges and mine tailings.     

转炉脱水设备的选择与应用

转炉炼钢工艺过程中将产生大量的除尘污泥 ,外排会造成的环境污染和资源浪费 ,对马钢第三炼钢厂现有污泥脱水系统进行改造 ,通过选择更新污泥脱水设备 ,转炉污泥完全回收 ,取得了很好的经济效益和环境效益。     

带式压滤机化学污泥脱水在生产中的应用

为配合中国石油吉林石化公司30万t／a乙烯工程A／O工艺废水处理工程化学污泥脱水的需要,进行了DY(12000-XB型带式压滤机应用于化学污泥脱水生产性能力考核测试。确定了最佳带速、带张紧压力、投泥量、投药量和产泥量等指标,具有显著的经济和环境效益。在相同产泥量务件下．该带式压滤机比WL(F)-600Ⅱ型离心机年运行费用可节约58．86万元。     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

叠氏污泥脱水技术处理炼油厂“三泥”

分析了炼油厂“三泥”性质和脱水预处理对策,介绍了叠氏污泥脱水机特点原理及处理炼油企业“三泥”的典型应用实例.当处理罐底泥时,进料含水率在86.7％～90.2％时,经叠氏污泥脱水机脱水后泥饼含水率降为54.2％～55.9％;当处理剩余活性污泥时,进料含水率在95.5％～97.5％时,经叠氏污泥脱水机脱水后泥饼含水率降为78.0％～79.0％;当处理浮渣时,进料含水率在90.5％～92.0％时,经叠氏污泥脱水机脱水后泥饼含水率降为67.9％～68.7％.所处理物料的脱水泥饼的含水率均低于80％,满足污泥迸一步处理前的脱水需求,与离心机相比节电在1/10以上.     

Effect of Digested Sludge Properties on Mechanical Dewatering Efficiency: An Experimental Approach

To optimize the anaerobic digestion process of residual sludge, co-substrates addition and pre-treatments are increasingly being employed. Nevertheless, if these processes allow the optimization of biogas production, they can significantly impact the efficiency of mechanical dewatering processes for digested sludge. In this article, the impact of co-substrate addition (oily sludge) and thermal pre-treatment on the efficiency of mechanical dewatering of digested sludge was investigated. To this purpose, mechanical dewatering experiments were conducted at lab-scale by using a filtration-compression cell to determine the limit dryness of various digestates. In addition, control factors of the mechanical dewatering efficiency of digested sludge were investigated. Results highlight that 67% of the variance of the limit dryness of digestates is due to the variable “volatile solid/total solid ratio.”