DEWATERING OF WASTE ACTIVATED SLUDGE VIA CENTRIFUGAL FIELD

ABSTRACT

While conducting centrifugal dewatering tests on waste activated sludge, this work considered how the rotational speed and the application of cationic polyelectrolyte flocculation affected the sludge. Increased rotational speed and/or conditioning the sludge to a charge neutralization point could enhance dewatering efficiency. A model was proposed to estimate the disruption energy exerted on the sludge body using centrifugation. Experimental results indicate that the disruption energy level provided by the centrifuge increases with rotational speed and decreasing water content in the filter cake. Moreover, polyelectrolyte flocculation may significantly reduce the disruption energy level of the water from sludge particles and the residual water contents at the end of the test.     

Consolidation dewatering and centrifugal sedimentation of flocculated activated sludge

This study investigated experimentally the consolidation dewatering and centrifugal-settling processes for activated sludge subjected to cationic polyelectrolyte flocculation. The results were reported for the dynamic response of sediment cake thickness (an index for cake compaction) under various doses of polyelectrolyte conditioning, compression-permeability cell configuration and mode of operation (batch and continuous) in a centrifugal-settling cell. The reduction in sediment thickness of sludge by consolidation and centrifugation was found to correspond mostly well with the optimal dose of polyelectrolyte based on the capillary suction time. The relaxation/rebound of cake thickness was observed in both consolidation dewatering and centrifugal dewatering with comparable compaction/relaxation time scale ratios. The equilibrium sediment consolidation ratio increases with the effective solid pressure characterized by P_m and P_s, for the consolidation dewatering and centrifugal sedimentation, respectively. The experimentally determined time scales of the cake consolidation dewatering/centrifugal sedimentation processes agree reasonably well with the theory by Landman and Russel (Phys. Fluids A 5 (1993) 550).     

Flockung und Entwässerung von Klärschlamm mit Hilfe von Polyelektrolyten

An investigation was performed with the aim of ascertaining how a digested sewage sludge could be converted into mechanically stable flocs through the addition of a flocculating agent, while achieving the best possible dewatering efficiency with the lowest possible dosage of flocculation agent. In order to obtain conclusive results which can be transferred to large-scale plants, the effectiveness of the flocculating agents and the various flocculation procedures were tested in a patented, mobile, computer-assisted flocculation and dewatering apparatus. The sewage sludge was conditioned with flocculating agents which had previously been thoroughly characterized in terms of their chemical structure, charge density and molar mass. The cationic flocculating agents had charge densities ranging from 25–55 mol-% and molar masses from 1.5 · 10⁶–12.9 · 10⁶ g mol^?, whereas the anionic flocculating agent had a charge density of 36 mol-% and a molar mass of 7.6 · lo6 g mol^?. In contrast to other suspensions already investigated, for sewage sludge it was found that no improvement can be achieved in the already very high dewatering level when cationic monoflocculation is used (laboratory trial: 95% filtrate yield by mass after 4 s). Nor was it possible to reduce the optimum dosage by using the dual procedure. In addition, it was possible to show that the chemical structure, i.e. the nature of the polyelectrolyte, and the molar mass of the cationic polyelectrolytes investigated exert a by far larger influence on the dewatering efficiency than the charge density in a range between 25 and 55 mol-%. Furthermore, it has also been observed that the conditioning efficiency of the polyelectrolytes increases as the molar mass rises and the chemical structure influences the dewatering result primarily through the position of the charge-bearing group.     

基于介观尺度模拟的污泥絮凝形态及机理

用介观动力学的方法对胶体颗粒与高分子链的絮凝过程进行了模型研究,并根据模型结果对污泥和阳离子聚丙烯酰胺的絮凝过程和污泥脱水机理进行有针对性的探讨。通过建立粗粒化模型和经验势函数力场有效模拟了负电性的胶体颗粒与阳离子型高分子链的絮凝过程;模拟得出了絮凝的外观形态,证明了高分子链对胶体颗粒的桥接作用以及表面电荷的中和作用对絮凝的影响;并对絮凝反应过程的体系势能变化进行了研究。对实际污泥胶体颗粒和阳离子聚丙烯酰胺溶液拍摄了电镜图片并观察了其吸附过程;最后研究了高分子链离子度对溶液体系絮凝的影响,验证了离子度的增加有利于絮凝体的形成,但同时也由于絮凝体结构的复杂而对污泥脱水造成了一定的不利影响。     

高分子絮凝剂特性对污泥调理和脱水效果的影响及在线絮凝检测技术应用研究

高分子絮凝剂品种及特性对污泥调理及脱水效果有很大影响,试验结果表明絮凝剂的相对分子质量是决定性因素,电荷特性影响较小。利用一种在线絮凝检测技术可连续检测污泥调理工艺中污泥颗粒絮凝过程,从而形成了一种全新的污泥絮凝检测方法,为污泥调理和脱水工艺的过程控制提供了可能性。     

Effects of polyacrylamide on microbial density levels and biodegradability in waste‐activated sludge

This study addressed the possible role of polyelectrolyte flocculation on microbial density levels in a waste‐activated sludge. Such an effect is commonly ignored. Applying polyelectrolyte reduced the density level of coliform bacteria in the flocculated sludge. Polyelectrolyte also reduced the 5‐day biochemical oxygen demand of sludge, possibly retarding the subsequent biodegradation processes. © 2001 Society of Chemical Industry     

Sludge Dewatering and Aggregate Formation Effects through Taylor Vortex Assisted Flocculation

Abstract

For polymer induced flocculation processes, the effects of flow patterns in a gap of a conical stirrer on aggregate formation and subsequent sludge dewatering efficiency were analysed. Different flow regimes were identified by lab scale investigations with model substances and summarized in a Ta and Re number plane. An enhancement of sludge dewaterability for polymer induced flocculation processes was identified through post‐treatment of flocculated sludge aggregates by the specific flow pattern of stable and wavy Taylor vortices. Photo‐optical image analysis of flocculated aggregates shows a clear change of aggregate size distribution with less small particles during aggregate forming by Taylor vortices compared to classical flocculation procedure by stirrer. Results from technical scale dewatering analyses confirmed enhancement of sludge dewatering efficiency for six different dewatering machines using the identified wavy and stable Taylor vortex flow pattern regime.     

Anwendung von Polyelektrolyten bei der mechanischen Fest/Flüssig-Trennung

Use of Polyelectrolytes in Mechanical Solids/Liquid Separation. This article shows how optimisation tasks for the dewatering of sludge can be solved by starting from studies of chemical structure and steric properties of polyelectrolytes and laboratory experiments based thereon with a trans-portable computer-aided flocculation and dewatering apparatus. The optimum polyelectrolyte dosage lies in the range of the critical concentration c* (viscosimetric measurements) of the dissolved polyelectrolytes. On optimisation of the flocculant regime for mechanical solids/liquid separation by combined addition of anionic and cationic polyelectrolytes (dual process), it is necessary to consider the overall system of sedimentation and filtration. In an industrial scale plant, the consumption of flocculant could be reduced by up to 10% compared to laboratory studies. At the same time, the dewatering behaviour could be improved by up to 60%, a shearing strength of the sludge in excess of 20 kN/m² reliably established, and plant operating reliability achieved for changing sedimentation properties.     

WATER REMOVAL FROM SLUDGE IN A HORIZONTAL ELECTRIC FIELD

A new method for sludge dewatering was proposed, in which a horizontal electric field was applied in order to facilitate the dissipation of gases produced at electrodes and to keep the anode soaked in water during the dewatering process. The effects of operation conditions such as the magnitude of electric field strength, pH of aqueous phase, the pretreatment procedures including flocculation, freezing and heating on the water removal were examined, respectively. The morphological difference between the concentrated sludge produced by electrodewatering and by vacuum filtration was revealed with scanning electron microscopy, which shown that electrodewatering was effective in removing the capillary water in the sludge floc. At electric field strength of 1200 V/m, the sludge concentration could be increased from 3 to 8%(w/w), indicating that over 60% of water was removed from the sludge. Compared to those operated in a vertical electric field, the method described in the present study has the advantages in terms of high eficiency, simple structure and ease of operation.     

WATER REMOVAL FROM SLUDGE IN A HORIZONTAL ELECTRIC FIELD

A new method for sludge dewatering was proposed, in which a horizontal electric field was applied in order to facilitate the dissipation of gases produced at electrodes and to keep the anode soaked in water during the dewatering process. The effects of operation conditions such as the magnitude of electric field strength, pH of aqueous phase, the pretreatment procedures including flocculation, freezing and heating on the water removal were examined, respectively. The morphological difference between the concentrated sludge produced by electrodewatering and by vacuum filtration was revealed with scanning electron microscopy, which shown that electrodewatering was effective in removing the capillary water in the sludge floc. At electric field strength of 1200 V/m, the sludge concentration could be increased from 3 to 8%(w/w), indicating that over 60% of water was removed from the sludge. Compared to those operated in a vertical electric field, the method described in the present study has the advantages in terms of high eficiency, simple structure and ease of operation.     

超声能量密度对污泥脱水性能的影响

<正>引言近年来,生物法在城市污水处理中得到广泛的应用,然而在处理过程中产生了大量的污泥,污泥中含有50%～70%的有机物和较多的氮、磷等营养成分以及致病菌、寄生虫卵等有害物质。其化学     

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.     

壳聚糖絮凝剂的投加量对污泥脱水性能的影响

通过污泥比阻的测定,分析絮凝剂剂量对污泥脱水性能的影响。同时对三氯化铝、阳离子聚丙烯酰胺、壳聚糖以及复合絮凝剂的絮凝效果进行比较。结果表明,无论是无机絮凝剂和有机絮凝剂都存在最佳剂量,小于或大于最佳投加量,絮凝效果都不好。阳离子聚丙烯酰胺(CPAM)、壳聚糖、三氯化铝的最佳投加质量浓度分别为0．2g/L、10g/L、35g/L。与三氯化铝相比,阳离子聚丙烯酰胺的药剂消耗量要低得多。壳聚糖与CPAM相比,在达到相同的絮凝效果时,壳聚糖的用量大于CPAM的用量。将壳聚糖与氯化铝复合,用两段法应用于污泥调理,研究这种复合絮凝剂的脱水性能,实验表明壳聚糖和三氯化铝复合,能大大提高污泥的脱水性能。     

New cationic polyelectrolytes for flocculation processes of baker's yeast waste water

Summary New cationic polyelectrolytes synthesized by homopolymerization or copolymerization of allyl-acrylate quaternary ammonium salts with acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) were tested as flocculants in a baker's yeast waste water. The effect of polymer structure, molecular weight and charge density on the flocculation properties were investigated with respect to total organic content, optical density and volume of sludge. The results were compared with that of a commercial polyelectrolyte Zetag 7557 (acryloxyethyltrimethylammoniumchloride-acrylamide copolymer) (Allied Colloids). The flocculation results indicated that the efficiency of the new copolymers was similar to commercial polyelectrolyte Zetag 7557 and both polymer bridging and charge patch models are effective. Received: 2 April 2002 / Revised version: 13 May 2002 / Accepted: 13 May 2002     

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.     

超声辅助絮凝强化污染底泥土工管袋脱水减容

将超声处理结合絮凝剂用于土工管袋脱水减容.以滤饼含水质量分数为优化指标,考察超声处理与添加絮凝剂的顺序对脱水性能的影响,并考察了超声处理的最优操作条件.结果表明:先添加絮凝剂再进行超声作用可取得较好的脱水效果,当絮凝剂的投加量(质量分数)为5‰(以干基计),超声波的能量密度为0.5 W/mL,作用时间为10 s,脱水效...     

Comparison of initiation methods in the structure of CPAM and sludge flocs properties

Cationic polyacrylamides (CPAMs) synthesized by thermal, ultrasonic, microwave, and UV initiation were characterized through magnetic resonance hydrogen spectroscopy (¹H NMR), Fourier transform infrared spectra, scanning electron microscopy, and thermal gravimetric analysis. The CPAMs for flocculation and dewatering of alum sludge produced through drinking water treatment were evaluated based on the residual turbidity of the supernatant, dry solid content, mean volume diameter and floc size distribution, fractal dimension of the flocs, and zeta potential as a function of flocculant dosage. Comparisons of the characteristics and performance of CPAMs synthesized through different initiation methods were systematically conducted. Flocculation and dewatering test results demonstrated that CPAMs synthesized through microwave and UV initiation had better flocculation performance and dewatering capability than those synthesized through thermal and ultrasonic initiation. All four CPAMs exhibited a similar final floc size distribution but different mean volume diameters and floc structures. The fractal dimension of the flocs and the zeta potential were in the following order: CPAM3 (microwave initiation) > CPAM4 (UV initiation) > CPAM1 (thermal initiation) > CPAM2 (ultrasonic initiation). Discussions on fractal dimension and zeta potential indicated that the electrostatic patches model and adsorption/bridging effect mechanisms played the main role in the formation of sludge flocs. Lastly, microwave and UV initiation were found to be alternative and recommendable initiation methods for the synthesis of CPAMs with improved flocculation performance and sludge dewatering capability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44071.     

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。     

Fenton试剂对剩余污泥脱水性能的改善

研究了利用Fenton试剂调理城市污水处理厂剩余污泥,通过测定污泥毛细吸水时间(CST)、污泥比阻(SRF)和泥饼含水率来表征污泥脱水性能的变化,分别考察了污泥初始pH、H2O2投加量、H2O2/Fe2+、反应温度和反应时间对污泥调理效果的影响。综合考虑,确定Fenton调理污泥的最佳条件为:pH=3、抽滤脱水和离心脱水H2O2最佳投加量分别为3 g/L和9 g/L、H2O2/Fe2(+质量比)最佳范围为8～12、反应温度50℃、反应时间60 min。对污泥离心上清液中胞外聚合物(EPS)含量的研究表明,Fenton调理后污泥上清液中蛋白质和多糖含量有大幅升高,说明Fenton试剂能有效氧化破解EPS,从而提高污泥的絮凝性,改善污泥的脱水性能。Fenton氧化后污泥颗粒粒径变小,比表面积增大。     

火力发电厂烟气脱硫废水处理工艺

石灰石-石膏湿法脱硫所产废水,由于水质较为特殊,不能直接排入电厂工业废水处理系统,需设置单独的处理装置.采用物化法对脱硫废水进行处理,经过中和、沉淀、混凝以及污泥脱水等步骤,脱硫废水主要水质指标均显著降低,出水水质达到污水综合排放标准GB 8978--1996的二级新建排放标准的要求.实际运行表明,该处理工艺处理脱硫废水有效,运行稳定,运行费用较低,效益显著.但该工艺Cl~-脱除能力有效,有待进一步研究.