Measurement of water content and moisture distribution in sludge by 1H nuclear magnetic resonance spectroscopy

Moisture distribution in sludge is essential for the examination of dewatering problems; however, sufficiently rapid and accurate methods of sludge moisture measurement are currently lacking. Hence, this study investigated a low-field ¹H nuclear magnetic resonance (NMR) method for measuring water content and moisture distribution in sludge. Moisture content measured by NMR was closely correlated with the thermal drying method (R² = 0.999). The loss of mechanical bound water from sludge was the primary cause of the decrease in water content from 96 to 37% during thermal drying at 40°C. NMR is more accurate, rapid, and nondestructive than other water distribution measurement methods.     

Correlation between dewatering and hydro-textural characteristics of sewage sludge during drying

The aim of this work consists in analysing the dewatering and the shrinkage of a residual urban sludge during convective drying with the objective to find correlations between dewatering and hydro-textural characteristics of the sludge. Laboratory drying experiments are performed in immobile atmosphere, at a temperature of 30 °C, with various relative humidities. Kinetics curves of dewatering and deformation are obtained. A coupled analysis of dewatering and induced volume shrinkage is proposed. This analysis allows: (i) to distinguish the respective parts played by the intrinsic characteristics of the sludge and the process parameter and (ii) to find correlations between the hydro-textural characteristics of the sludge, and its drying and shrinkage aptitudes. Attention is given to the fact that the process parameter, i.e. relative humidity, controls the first constant rate period of the dewatering and that the hydro-textural state of the sludge determine the transitions between the different dewatering periods. The relationships between the hydro-textural characteristics and the dewatering and shrinkage aptitude allow predicting the sludge behaviour during drying according to its characteristics, which is essential information in the choice of the drying strategy.     

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。     

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.     

干燥技术在制备纳米粉体中的应用

由于纳米粒子的表面效应,用湿法制备出的纳米粉体的前躯体在干燥过程中极易形成团聚,已经不能采用传统的干燥方法。根据粉体干燥的理论,阐述了纳米粉体干燥过程的团聚机理,综述了微波干燥法、超临界干燥法、冷冻干燥法、共沸蒸馏法、喷雾干燥法等在制备纳米粉体中的应用,并指出了各种方法的优缺点。     

A REPORT ON THE COURSE "DRYING TECHNOLOGY IN THE PROCESS INDUSTRIES"

Interesting results have been observed in applying acoustic energy to dewatering and drying materials. However, drying by acoustic energy alone is expensive, energy intensive, and at best can be justified only in applications where rapid drying is necessary to preserve a product, the product is heat sensitive and its value justified the cost. However, synergistic effects have been observed when acoustic energy has been used with electrophoresis and electro-osmosis to dewater materials. An electroacoustic dewatering (EAD) technology has been developed in recent years that indicates good economic potential and an effectiveness that exceeds most conventional methods of dewatering. Very good results have been obtained from laboratory studies using the techniques with fine coal slurries, food products, municipal sewage sludges, and many other products.     

ACOUSTIC AND ELECTROACOUSTIC METHODS OF DEWATERING AND DRYING

Interesting results have been observed in applying acoustic energy to dewatering and drying materials. However, drying by acoustic energy alone is expensive, energy intensive, and at best can be justified only in applications where rapid drying is necessary to preserve a product, the product is heat sensitive and its value justified the cost. However, synergistic effects have been observed when acoustic energy has been used with electrophoresis and electro-osmosis to dewater materials. An electroacoustic dewatering (EAD) technology has been developed in recent years that indicates good economic potential and an effectiveness that exceeds most conventional methods of dewatering. Very good results have been obtained from laboratory studies using the techniques with fine coal slurries, food products, municipal sewage sludges, and many other products.     

DRYING OF WASTE SLUDGES IN A FLUIDIZED BED DRYER WITH A MIXER

Sludge wastes are a very attractive source of many valuable compounds such as nitrogen, phosphorus and organic matter. One of the interesting methods of sludge utilization is dewatering and drying. In this paper some problems of drying of two types of sludge wastes of different form and origin are presented. One of the sludges—a brewery by-product— contains spent grain suspension of brewer's yeast and diatomaceous earth. The second one is a by-product of a biotechnological process which contains mainly lime, protein, many microelements and some microorganisms. Moisture content of both sludges is about 65-70% w/w. The laboratory experiments of sludge drying in the fluidized bed dryer with a mixer, fluidized bed hydrodynamics, and the effects and advantages of sludge drying are shown.     

A Review of Dehydration of Various Industrial Sludges

Wastewater characteristics and sludge generation potential of point source categories are reviewed critically. Novel industry-specific sludge dewatering/drying solutions necessary to establish a sustainable model are examined through a detailed literature survey. Knowledge of sludge properties is one of the most critical issues needed to design dewatering/drying equipment. This study focuses on industrial wastewater/sludge characterization. In addition, a comprehensive review of current drying models and technologies is also presented. A summary of the results derived from a novel thin-film-based photonic sludge dewatering/drying study is outlined as an alternative approach for industrial sludge control. Sludge was dried in a tubular quartz reactor (TQR), the inner surface of which was coated with a TiO₂ thin film. The TQR was irradiated with UV A, UV B, and UV C lamps. The consumed and generated energy fluxes through endergonic and exergonic reactions driven by photolysis and photocatalysis were investigated. In addition, the variations in sludge dewatering/drying characteristics were also examined and compared with conventional methods to evaluate the energy requirements.     

Dewatering and Drying Methods for Microalgae

Microalgae can efficiently fix carbon dioxide through their phototropic metabolism, and have been recognized as a promising bioresource for animal feed, health food, fuel, cosmetic, and pharmaceutical products. However, since microalgae in cultivated medium have a low biomass concentration (0.1–1% w/w), both harvesting and concentration of microalgal biomass are often required prior to the production of commercial products. Efficient and cost-effective dewatering and drying methods for microalgae heavily affect the overall energy consumption and production cost of microalgal products. This review describes the characteristics of commonly used dewatering and drying technologies, and critically evaluates the feasibility for their use to treat microalgal biomass. No single dewatering or drying method can satisfactorily handle all types of microalgae. The suitability of each method depends on the properties of the microalgae suspension, the required process design, the quality of the end product, and the related capital and production costs.     

褐煤深度脱水的实验研究

针对褐煤低温烟气干燥技术脱水幅度难以提高,发热量增加不多等问题,提出了低温干燥与深度脱水的联合工艺。研究了不同干燥温度、干燥时间和煤样粒度对褐煤深度脱水效果的影响,结果表明:褐煤深度脱水适宜的干燥温度为500～800℃,较为适宜的干燥时间为80 s左右,当粒度小于50 mm时,干燥产物发热量随粒度变化不大。最后提出了褐煤深度脱水最佳工艺条件和参数,即当预干燥煤的Mar约为18%,煤样粒度为-50 mm,干燥温度为700℃,干燥时间为80 s时,深度脱水产物的Mar为8%,Vdaf在46%左右,折算Qnet,ar约为21 kJ/g。褐煤深度脱水促进了褐煤发热量的进一步提高,实现了褐煤资源的增值,研究结果为褐煤低温干燥与深度脱水联合工艺技术方案的确定奠定了基础。     

DRYING OF WASTE SLUDGES IN A FLUIDIZED BED DRYER WITH A MIXER

ABSTRACT

Sludge wastes are a very attractive source of many valuable compounds such as nitrogen, phosphorus and organic matter. One of the interesting methods of sludge utilization is dewatering and drying. In this paper some problems of drying of two types of sludge wastes of different form and origin are presented. One of the sludges—a brewery by-product— contains spent grain suspension of brewer's yeast and diatomaceous earth. The second one is a by-product of a biotechnological process which contains mainly lime, protein, many microelements and some microorganisms. Moisture content of both sludges is about 65–70% w/w. The laboratory experiments of sludge drying in the fluidized bed dryer with a mixer, fluidized bed hydrodynamics, and the effects and advantages of sludge drying are shown.     

褐煤干燥水分回收利用及其研究进展

褐煤干燥提质过程中的水资源化回收利用工艺技术可以提高煤阶并回收宝贵的水资源,降低干燥提质单元能耗。本文从介绍褐煤中水的存在形态出发,围绕烟气直接干燥、蒸汽流化床干燥、微波干燥、机械热压脱水干燥等工艺综述了近年来干燥水回收利用的研究现状和最新进展,讨论分析了褐煤干燥与水回收利用工艺的选择原则。在回收褐煤中丰富的水资源时,除了单纯考虑回收褐煤中的水资源,还应权衡褐煤干燥工艺、干燥温度和干燥介质、干燥水蒸气的余热利用方式以及干燥工艺上下游间的衔接等因素。基于目前褐煤资源的主要用途,将干燥尾气采用换热技术回收低温余热和干燥冷凝水直接净化处理后的二次回用技术将是以后的重要研究和应用方向。     

Experimental analysis on a novel low-temperature vacuum drying with induced nucleation technique for dewatering stingless bees honey

Honey spoilage is a major problem in storing stingless bee honey. A new method of honey dewatering was developed using a low-temperature vacuum drying with induced nucleation technique. The research’s objective is to investigate the performance of this method in reducing honey’s water content. Two different dewatering temperatures were applied until honey’s water content reached below 20%. The honey’s chemical compound before–after dewatering from one of the samples was tested using nuclear magnetic resonance (NMR) analysis. The dewatering rate improves significantly with higher temperature. The NMR analysis result found no changes in chemical compound before–after experiment except for ethanol.     

Steam Dewatering of Filter Cakes in a Vertical Filter Press

Steam dewatering of filter cakes is recognized as a competitive alternative to conventional air drying and thermally assisted mechanical dewatering (TAMD). The main benefit of cake dewatering with high-pressure steam is that mechanical and thermal dewatering can be efficiently performed in a single process step. The target of this study was to determine the potential of a steam-dewatering technique for two industrial mineral suspensions. The first mineral, kaolin, was very difficult to dewater using conventional mechanical dewatering techniques, whereas the second one, ground calcium carbonate (GCC), represented only moderate resistance to filtration. The secondary objective was to compare the filterability of the original kaolin slurry with the same slurry treated with a coagulant (aluminum sulphate, Al₂(SO₄)₃ · 16H₂O). Four different kinds of experiments were performed: tests without any kind of cake dewatering, tests with air drying, tests with steam drying, and tests with both coagulation and steam drying. The obtained results show that steam dewatering is an efficient technique for achieving lower cake-moisture contents. Also, the positive influence of coagulation on the filtration capacity was found to be considerable in the case of kaolin. An approximate energy balance was created for the steam-drying process and the determined energy efficiencies were compared with those obtainable with an ideal thermal drier. The main conclusion from these comparisons is that steam drying can be effectively used instead of traditional thermal drying if the large energy losses can be reduced by proper insulation and heat recovery systems.     

Functionalized Cellulose Fibers for Dewatering and Energy Efficiency Improvement

Paper drying accounts for nearly 80% of the energy used in the papermaking process. This is due to the high energy requirements for the process of drying by vaporization. Because the cost-effectiveness of the various physical means of dewatering far exceeds that of thermal drying, significant energy savings can be expected if the physical dewatering effectiveness is improved. To that end, a novel method of enhancing the physical dewatering process that involves the addition of hydrophobic fibers to the pulp furnish is described and evaluated. Freeness and water retention measurements indicate that the addition of hydrophobic fibers at even a few weight percent may have a significant impact on the freeness and water retention properties of the furnish and therefore a significant improvement in the effectiveness of the physical dewatering of webs made using the hydrophobically tailored furnish material.     

微孔陶瓷在陶瓷颜料脱水中的应用

对微孔陶瓷脱水的原理进行了研究。在陶瓷颜料生产中 ,采用微孔陶瓷脱水再烘干的方法与传统的电烘干方法进行了较深入的比较 ,并阐述了本方法具有比传统的干燥方法能耗低、产量高、污染少 ,操作方便等优点 ,尤其可节能80%以上 ,能够显著地提高经济效益 ,有着较好的推广应用前景     

Production of highly-sinterable rare-earth oxide powders by controlled humidity dewatering of precursors

The sintering behavior of rare-earth oxide powders produced from reverse strike hydroxide, oxalate and carbonate precursors was studied. The influences of controlled humidity dewatering of precursors on powder morphology and sintering behavior were extensively studied, and were compared with those produced by oven drying or dewatering by using organic washes (ATA method). Significant differences in behavior were observed for hydroxide- and carbonate-derived powders dewatered in different ways; oxalate-derived powders showed little behavioral dependence on dewatering method. In general, controlled humidity dewatering proved effective in leading to highly-sinterable powders from any of the three precursors investigated, ATA treatment was effective for hydroxide and oxalate precursors, and oven drying generally led to good sinterability only for oxalate-derived powders. Compaction behavior and surface area of the powders were also determined and attempts were made to correlate these characteristics with sintering behavior.     

市政污泥热力干化过程中黏滞特性研究进展

黏滞现象是城镇污泥脱水干化过程中面临的主要问题之一,污泥在干化设备中的黏附和结团,导致干化设备运行效率大幅降低,给污泥干化系统的经济性和安全性带来显著的负面影响。本文从污泥黏附力和结团力入手,简要介绍了污泥黏滞现象的形成机理以及低含水率条件下污泥黏滞性的主要测量方法,包括搅拌法、平板法、黏附-结团失效特性法、阻抗法、黏附量法和滑板黏度法等,并对比分析了各种分析方法的优缺点。综述了包括胞外聚合物（EPS）、温度和污泥含水率等主要因素对污泥黏滞特性的影响规律,并简要探讨了各因素的影响机理。概述了国内外污泥降黏方法的研究进展,讨论了各种降黏方法的工业应用前景,同时探讨了污泥黏滞特性研究领域未来值得深入研究的方向。     

MEASUREMENT ERRORS PROCESSING BY COVARIANCE ANALYSIS FOR AN IMPROVED ESTIMATION OF DRYING CHARACTERISTIC CURVE PARAMETERS

ABSTRACT

The aim of this paper is to show the interest of the covariance analysis applied to measurement error in the particular case of the identification of a drying characteristic curve from experimental drying data. The modelisation of drying by use of the Drying Characteristic Curve (DCC) method is first presented with usual specifications (power function, critical moisture content …). The experimental procedure used to obtain drying curves and the data processing are detailled and analysed. Measurements errors are identified at the first step of the procedure and their effects on the estimation error of the exponent α of the power function are estimated. Three different methods for estimating α are presented under their matrix form: the least square method and two methods based on the «Gauss–Markov» or «Maximum likelihood» theorem, firstly under a simplified form suited if the estimation errors are uncorrelated and secondly under a complete form suited even if the estimation errors are correlated. These three methods are applied to experimental results obtained with ginger roots drying. The value of the exponent α of the power function and then the distances between the three corresponding theoretical drying curves (representing product water content vs. time) and the experimental points are studied. It is shown that in this particular application, the complete Gauss–Markov method leads to the better fitting and that the simplified Gauss–Markov method, since it is a priori non appliable in this case where errors are correlated, gives quite better results than the oridnary least squares method. The covariance matrices of the estimation errors of reduced water content, reduced drying rate and exponent α are also presented in order to show the correlations existing between the measurement errors of each variable during a drying cycle.