污泥脱水性能指标的比较分析

研究了评价污泥脱水性能的4个指标:毛细吸水时间(CST)、污泥比阻(SRF)、结合水(BW)、含固率(DS)之间的相关性,发现DS与标准化CST、SRF、BW显著相关。标准化CST与SRF极显著相关,与BW的相关性较弱,SRF与BW的相关性更弱。研究结果表明,在衡量污泥的脱水性能时没必要同时测定CST和SRF,CST测定简单,重现性好,是衡量污泥脱水性能的较好指标,但同时,也应当与衡量污泥脱水程度的指标,如含固率等,一起综合考虑污泥的脱水性能。     

Solar drying of wastewater sludge: A review

Drying constitutes an important process for wastewater sludge management, as it can reduce the mass and the volume of the product and consequently the cost of storage, handling and transport. During constant operating conditions, the drying kinetic of the sludge has shown mainly: a constant drying rate, one or two falling rate periods and a final short period with variations along the process of the physical properties of the product with the appearance of shrinkage and cracks phenomena. Solar drying was benefit as using free solar energy can reduce the cost of the operation. On the other hand, it plays an important role for the pathogen reduction until Environmental protection Agency (EPA) recommendations. In some studied cases, the value of 1000 CFU g⁻¹ DS, which represents the EPA Class A pathogen requirement, for fecal coliform was attained. The general design of used solar dryers was constituted of: a greenhouse made with transparent material and a floor, where the product is speared in thick layers. Furthermore, fans and ventilations can be used in order to have homogeneous distribution of the air inside the greenhouse with replacement of humidified air with fresh one. Automatic or handle mix of the product was used once or for several times a day. In order to increase the performances of the drying system, other ways such as heating the floor using solar water heater, infrared lamps, using heat pumps or adding thermal energy storage systems were also tested. Covered solar drying has given better results than open solar drying. However, the origin of the wastewater sludge affects the obtained results. Alternatively, modeling drying systems was effectuated using heat and mass balances, applied for the air and the dried product. Solar drying of wastewater sludge has given satisfactory results.     

规模化猪场厌氧消化污泥脱水工艺研究

规模化猪场厌氧消化污泥堆肥是消化污泥处置的最重要途径之一,而作为污泥堆肥的重要预处理环节,消化污泥脱水却一直是道难题,文章就如何选择合理的污泥脱水工艺展开深入探讨.研究表明,规模化猪场消化污泥具有相对密度小、比阻大、有机养分含量高等特点,运用机械方法脱水不但费用高,而且技术上难度大,还会破坏消化污泥原本的有机养分组成,降低其堆肥后的农用的价值;和机械脱水方法相比,自然脱水方法在经济上具有明显的优势,而且技术上也可行.最后,文章认为污泥干化床工艺是自然脱水方法中较为理想的厌氧消化污泥脱水工艺.     

污泥的太阳能干燥实验研究

采用自行设计制造的混合型污泥太阳能干燥装置对污水处理厂机械脱水后含水率在80％左右的污泥进行干燥。通过实验研究探索了利用混合型太阳能干燥器干燥污泥的可行性及污泥的干燥特性，并对污泥在干燥过程中外形发生变化的规律及其与干燥过程的关系作了描述，研究结果表明污泥形变、空气参数及太阳辐射强度是影响污泥干燥过程的主要因素，对太阳能污泥干燥的工业化生产具有参考价值。     

基于CFD技术的太阳能污泥干燥室内热湿环境研究

基于传热传质理论,建立一种太阳能污泥干燥室内热湿耦合传递的数学模型。综合考虑空气流动以及对流和辐射传热,利用CFD软件Fluent的k~ε湍流模型、组分输运模型及辐射模型,初步分析了在太阳辐射条件下不同干燥室结构、排风形式以及通风量对太阳能污泥干燥室内干燥区域的温度、相对湿度以及速度分布的影响。模拟结果表明:干燥室内温、湿度模拟值与实测值吻合较好,平均相对误差分别为3.55%和5.39%。对比分析不同结构下干燥室内的流场分布,两出口排风形式的太阳能污泥干燥室可以形成良好的干燥微环境。当两出口排风风速≥5 m/s时,室内干燥区域温度高于室外环境温度,同时相对湿度低于室外环境相对湿度,且增大出流风速,在干燥区域内空气扰流强度增强,有利于干燥室内污泥水分的蒸发。     

Enhancement of hydrogen production in steam gasification of sewage sludge by reusing the calcium in lime-conditioned sludge

Gasification is a promising alternative process for sewage sludge energy utilization. CaO has been identified as an effective additive which can increase H₂ content of syngas produced by coal, biomass, and sludge gasification. Considering that lime (CaO) is a widely applied conditioner for sewage sludge dewatering in filter press, this study investigated the enhanced efficiency of syngas, especially regarding H₂ yield, in the catalytic steam gasification of dry dewatered sludge with physically mixed CaO and dry sludge dewatered with CaO as conditioner. The experiments were conducted in an electrically heated reactor at 873 K, 973 K and 1073 K, respectively. According to the results, conditioner CaO improved the H₂ and syngas production more remarkably than additive CaO. It was identified by XRD and SEM-EDX that conditioner CaO was completely converted into Ca(OH)₂ while additive CaO was still presented mainly as CaO. Furthermore, the Ca species of conditioner CaO was evenly distributed over the sludge matrix while Ca species of additive CaO maintained the original state with uneven distribution, both of which could increase the formation of H₂ through interacting with produced gas and catalyzing thermal cracking of tar to some extent. In addition, the pore structure tests and XPS analyses revealed that, comparing to additive CaO, conditioner CaO was more favorable for the formation of pores, and it had a greater potential to encourage partial cleavages of C–C bonds and C–H bonds, resulting in the decomposition of organic macromolecules into relative small molecules, which might be more easily converted to the gaseous products. These indicate that it is valuable to reuse the Ca in lime-conditioned sludge during gasification process.     

Response surface optimization of a novel pilot dryer for processing mixed forest industry biosludge

As a promising sludge handling alternative capable of utilizing the secondary energies in industrial environments, we investigated the use of a novel pilot‐scale cyclone dryer for processing industrial mixed sludge from the forest industry. Attainable sludge dry solids contents (%) and respective specific energy consumption of drying (kWh kg^?1 H₂O) were successfully modelled by response surface methodology based on a constructed design of experiments. Predicted sludge dry solids and the specific energy consumption of drying varied between <30–65% and <0.4–1.8 kWh kg^?1 H₂O depending on controlled inlet air temperature, sludge feeding rate and humid air recirculation levels. The response models were further optimized for efficient combustion of processed sludge with inlet air temperatures corresponding to potentially available secondary heat. According to the results, energy efficient drying of mixed sludge with a specific energy consumption <0.7 kWh kg^?1 H₂O can be performed with inlet air temperatures ≥60 °C corresponding with pilot‐scale feeding capacities between 300–350 and 550 kg h^?1 depending on inlet air temperature. These findings suggest that the introduction of novel drying systems capable of utilizing the available secondary energies of industrial environments could significantly improve the energy efficiency of sludge drying and potentially allow considerable cost savings for industrial operators. Copyright © 2015 John Wiley & Sons, Ltd.     

Solar sludge drying — Based on the IST process

Sludges containing water can only be dewatered to a certain extent mechanically. Beyond this level, moisture must be expelled by means of thermal processes. In the municipal sewage treatment plant in Kandern-Hammerstein, IST Anlagenbau GmbH has operated its own development, a solar dryer for sewage sludges, since December 1994. The result reveals that about 700 - 800 kg water/m² ground space and year are evaporated in southern Germany. Recycling of waste heat enabled a heating of the ground plate thus doubling or tripling the drying performance. The unit operates fully automatically with a PLC control system. Although considerably more ground space is required than in comparison to an industrial drying unit, operating costs of the solar drying system are competitive, frequently even considerably lower. In the mean time, a second drying plant has been in operation since August 1997 in Iffezheim near Baden-Baden. Many improvements were made in details of design. In principle, the process can be applied for all bulk materials containing water.     

An Application of Solar Energy Storage in the Gas: Solar Heated Biogas Plants

Abstract

Temperature is an important factor that may affect the performance of anaerobic digestion. Therefore, biogas plants without heating system work only in warmer regions for the whole year. In regions with extreme temperature variations, for instance in Turkey, the biogas plant should be built with heating system. One of the methods is to use solar energy to increase the reactor temperature. In this study, solar heated biogas plants were reviewed. Furthermore, the optimization of insulation thicknesses and solar energy systems for 5 m³ biogas reactor were carried out for two different cities for three different climatic zones in Turkey. Based on the obtained results, the ratio of annually produced biogas used for reactor heating was calculated for each city, with and without solar heating system. Obtained results indicate that the biogas consumption for reactor heating is decreased by approximately 19% for average of six cities when solar heating system is used. This means that available biogas potential would be increased.     

From biogas-to hydrogen – Based integrated urban water,energy and waste solids system - Quest towards decarbonization

Three integrated systems of water and municipal solid waste (MSW) management were evaluated regarding their energy use, production and CO_2eq emissions:(1) Biogas based aerobic treatment of wastewater and waste solids disposal by landfilling wherein codigesting sludge with MSW and landfill gas capture produce electricity by a turbine and generator.(2) Biogas based wastewater treatment with codigestion of sludge with biodegradable solids combined with incineration of combustible sludge and other solids.(3) Hydrogen-based system replacing landfilling by indirect gasification of organic solids followed by hydrogen fuel cells.There are great differences between CO_2eq emissions of biogas and hydrogen-based systems. The first two systems are positive CO₂ and methane emitters. Achieving net zero carbon emissions is unlikely. The H₂ based system is fully decarbonized and in addition to clean water, energy and negative carbon dioxide emissions it produces valuable commodities such as energy, concentrated hydrogen, fertilizers, oxygen/ozone, and concentrated carbon dioxide.     

Dewatering of wastewater sludge through a solar still

Wastewater sludge was passed through a laboratory solar still in order to determine the dewatering process. A number of parameters describing the distillate and the sludge were measured at the end of each day in order to determine the process behavior under conditions of relatively high solar radiation and temperature levels. It was realized that dewatering is accelerated and further analysis is needed in order to determine optimum conditions and design parameters for a demonstration plant that will operate towards reducing the sludge volume.     

Influence of sludge properties on the direct gasification of dewatered sewage sludge in supercritical water

In the present study, ten different types of dewatered sewage sludges were treated in supercritical water in a high-pressure autoclave under a given condition (at 400 °C, 60 min and 23 MPa). The feasibility of direct gasification and the effect of sludge properties on the gasification of dewatered sewage sludge with various properties in supercritical water were investigated. The results showed that dewatered sewage sludge with various water contents (73.48–88.51 wt%), organic matter contents (29.25–73.02 wt%, on dry basis) and inorganics can be directly gasified in supercritical water. The total gas and phenol production increased linearly with the increment of organic matter content in dewatered sewage sludge. The difference in hydrogen content in the gaseous product may be related to the content of water and inorganic as well as pH value of the sludge. The char/coke formed in the solid residue increased with decrement of water content, which inhibited the gasification reaction and resulted in the carbonization reaction.     

Application of a thermally assisted mechanical dewatering process to biomass

Thermally assisted mechanical dewatering (TAMD) is a new process for energy-efficient liquid/solids separation which enhances conventional-device efficiency. The main idea of this process is to supply a flow of heat in mechanical dewatering processes to favour the reduction of the liquid content. This is not a new idea but the proposed combination, especially the chosen operating conditions (T < 100 °C and P < 3000 kPa) constitutes an original approach and a significant energy saving since the liquid is kept in liquid state. Response surface methodology was used to evaluate the effects of the processing parameters of TAMD on the final dry solids content, which is a fundamental dewatering parameter and an excellent indicator of the extent of TAMD. In this study, a two-factor central composite design was used to establish the optimum conditions for the TAMD of alfalfa biomass. Experiments were carried out on a laboratory compression cell. Experiments showed that the dewatering enhancement results only from thermal effects. With a moderate heat supply (T_piston = 80 °C), the dry solid content of the press cake can reach 66%, compared to 36% at ambient temperature. A significant regression model, describing changes on final dry solids content with respect to independent variables, was established with determination coefficient, R², greater than 88%. With an energy consumption of less than 150 kWh/m³, the use of the TAMD process before a thermal drying process leads to an energy saving of at least 30% on the overall separation chain.     

Performance studies of solar tunnel dryer for drying aonla (embilica officinalis) pulp

A solar tunnel dyer was constructed and evaluated the performance for drying aonla pulp. The dryer consists of a transparent UV stabilized plastic covered solar collector cum drying unit. Evaluation parameters are air temperature, solar insolation, moisture content, relative humidity and airflow rate. A minimum of 111.18 m² solar collector area is required to dry a batch 1000 kg aonla pulp in 16 hours (two days drying period). The initial and final moisture content considered were 424.93 and 10.08% dry basis, respectively. It was observed that on an average 43 per cent of higher temperature was obtained in solar tunnel dryer over the ambient temperature. The results obtained during the test period denoted that the maximum gained energy occurred at 13 o’clock hour and then gradually declined since the maximum solar radiation occurred at this time.     

Experimental and modelling performances of a roof-integrated solar drying system for drying herbs and spices

This paper presents experimental performance of solar drying of rosella flower and chili using roof-integrated solar dryer and also presents modelling of the roof-integrated solar dryer for drying of chili. Field-level tests for deep bed drying of rosella flower and chili demonstrated that drying in the roof-integrated solar dryer results in significant reduction in drying time compared to the traditional sun drying method and the dry product is a quality dry product compared to the quality products in the markets. The payback period of the roof-integrated solar dryer is about 5 years. To simulate the performance of the roof-integrated solar dryer for drying herbs and spices using hot air from roof-integrated solar collectors, two sets of equations were developed. The first set of equations was solved implicitly and the second set of equations was solved explicitly using finite difference technique. The simulated air temperatures at the collector outlet agreed well with the observed air temperatures. Good agreement was also found between experimental and simulated moisture contents.     

Evaluation and establishment of diffuse solar radiation models for Bursa,Turkey

The main objective of the present study is to evaluate the applicability of the diffuse solar radiation models from previous studies and establish new models for Bursa. Therefore, 35 regression models from previous studies in the literature are used and categorized as follows: (1) cloudness index is the function of clearness index; (2) cloudness index is the function of relative sunshine duration; (3) the diffuse coefficient is the function of the clearness index; and (4) the diffuse coefficient is the function of the relative sunshine duration. Also, new four diffuse solar radiation models were developed using 1968–2015 long-term global solar radiation and sunshine duration data. The new models are then compared with 35 empirical equations available in previous studies in terms of different statistical tests. Consequently, Models 6 and 8 are found as the most accurate and high-performance empirical models for estimation of the monthly mean diffuse solar radiation on a horizontal surface for Bursa, Turkey.     

市政污泥干燥特性的实验研究和模拟分析

采用薄层干燥的方式对嘉兴市某污水处理厂的脱水市政污泥在不同厚度和温度下的干燥特性进行实验研究,并通过引入薄层干燥模型,对薄层市政污泥干燥过程进行模拟分析.结果表明:厚度越小或干燥温度越高,污泥干燥速率越快.当温度从70?℃上升到130?℃时,最大干燥速率从0.02587?g·(g·min)-1上升到0.08158?g·...     

Solar drying of pineapple using solar tunnel drier

Field level experiments on solar drying of pineapple using solar tunnel drier were conducted at Bangladesh Agricultural University, Mymensingh, Bangladesh. The drier consists of a transparent plastic covered flat plate collector and a drying tunnel connected in a series to supply hot air directly into the drying tunnel using two dc fans operated by a solar module. This drier has a loading capacity of 120–150 kg of pineapple and a total of eight drying runs were conducted. In all the cases the use of the solar tunnel drier leads to considerable reduction of drying time in comparison to sun drying. The pineapple being dried in the solar tunnel drier were completely protected from rain, insects and dust, and the quality of the pineapple dried in the tunnel drier was of quality dried products as compared to sun dried products. Proximate analysis also indicates that the pineapple dried in the solar tunnel drier is a good quality dried product for human consumption.     

污泥热干化技术适应性分析及未来发展趋势

污泥干化是污泥处理、处置和资源化利用的前提。文章概述了几种常用的污泥热干化技术,并从能耗、安全性、环境友好性、灵活性4个方面分析其适应性。污泥干化在我国起步较晚,通过适应性对比,推荐转盘式干化技术作为污泥热干化的主导工艺,未来仍将以主流干化技术为主导,并不断完善、优化,而新兴的干化技术则是对主流干化技术有效的补充。     

A review of the properties of biosludge and its relevance to enhanced dewatering processes

Difficulties in dewatering of biosludge result in economical and environmental issues for wastewater treatment plants. Various attempts have been made to overcome this problem by achieving some pretreatment on biosludge. The main purpose of all pretreatment methods is to modify the biosludge characteristics in such a way to boost settling of cells and solid particles of sludge, and to ease the release of water molecules from extracellular polymeric substances and cells and to facilitate flow of water through forming filter cake. The present work presents an overview of different properties of sludge and their measurement, the main reasons of sludge dewatering difficulty, the fundamentals of sludge dewatering and various proposed methods for sludge pretreatment. The advantages and drawbacks of different methods are described and the dominance of one over the others is discussed mostly with respect to energy requirement and environmental impacts. Some recommendations have been made for optimal application of each method.