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Utilization of urban sewage sludge: Chinese perspectives Purpose Urbanization and industrialization in China has resulted in a dramatic increase in the volume of wastewater and sewage sludge produced from wastewater treatment plants. Problems associated with sewage sludge have attracted increasing attention from the public and urban planners. How to manage sludge in an economically and environmentally acceptable manner is one of the critical issues that modern societies are facing.

Methods Sludge treatment systems consist of thickening, dewatering，and several different alternative main treatments(anaerobic digestion, aerobic digestion, drying, composting, and incineration). Agricultural application, landfill, and incineration are the principal disposal methods for sewage sludge in China. However, sewage sludge disposal in the future should focus on resource recovery, reducing environmental impacts and saving economic costs.

Results The reuse of biosolids in all scenarios can be environmentally beneficial and cost-effective. Anaerobic digestion followed by land application is the preferable options due to low economic and energy costs and material reuse.

Conclusion It is necessary to formulate a standard suitable for the utilization of sewage sludge in China.

1 Introduction

In 2008, it is estimated that 57 billion tons of municipal wastewater was discharged in China, 58% of which came from municipal domestic sewage, while the production of municipal wastewater and dewatered sewage in China increased approximately 5% per year on average from 1998 to 2009 as shown in Fig.1.Sewage sludge as an inevitable by-product of wastewater treatment process presents a number of environmental concerns.

Wastewater treatment processes concentrate various pollutants such as heavy metals, organic micro-pollutants, and pathogens into sludge. Sludge disposal can thereby result in the release of toxins into the environment and subsequently into the food chain. On the other hand, it has been estimated that depending on technology choice, approximately 30～60% of sewage treatment plant operating costs are related to sludge treatment activities. Therefore, the management of sewage sludge in an economically and environmentally acceptable way is a matter of increasing importance.

Fig. 1 Production of municipal wastewater and dewatered sewage sludge in China

An ideal way to solve the issue of sludge waste is to minimize its production in biological wastewater treatment processes, rather than rely on post-treatment. When mechanical wastewater treatment is used, a diversity of approaches for sewage sludge treatment processes and end use exists, each with different associated costs and environmental impacts. Strategies on end uses of biosolids have traditionally been based on cost, regulatory, environmental, and public acceptance considerations. In recent years, several methods have been used to evaluate their economic and environmental acceptability. Hospido et al considered land application as an acceptable option for anaerobic digested sludge by evaluating environmental and economic costs of three

scenarios (land application, incineration, and pyrolysis of dried sludge), but the environmental impact of construction was ignored. Also little detailed economic analysis information is available for other alternative scenarios. Barber used a model comparing the environmental impacts and economic costs of different alternative treatment and disposal scenarios. Nevertheless, the transport costs associated with the full range of biosolids management options were not discussed, which may be one of the limiting factors of sludge land application in China. Few investigations have been reported on the environmental and economic impacts of pyrolysis and gasification scenario, partly due to their high cost and scarce application in practice. Therefore, more detailed papers should be investigated for an overall comparison of different treatment and end use of urban sewage sludge, to determine which combinations are more sustainable.

There are 1,258 municipal wastewater treatment plants(WWTPs) in China. The method of sewage sludge disposal is carried out using four processes: 45% of the sludge produced is being utilized in agriculture, 3.5% is being incinerated, 34.5% is landfilled including 3.5% with domestic waste, while 3.5% is used in some other areas (Fig. 2). There are political and economic incentives to increase the agriculture application of sludge since it contains large amounts of organic matter and nutrients, such as N and P. However, the reduced availability of land, increased public comprehension of pathogen risk, the potential for food chain contamination by heavy metals, and the risk of uncertainty surrounding organic micropollutants act to limit sludge land application. Landfill is also decreasing because of technology, economic capacity, and new legislation. Incineration due to significant dry solid volume reduction and energy recovery from the sludge can contribute to a sustainable biosolids strategy, but environmental pollution and the cost should be

carefully treated. Other disposal options such as pyrolysis, gasification,combustion,and co-combustion of sewage sludge with other materials and use as an energy source in the production of cement or building materials have been intensively investigated. These processes which can recover energy from sewage sludge will probably become the future trends of development.

Fig. 2 Ways of sludge disposal and utilization in China (2010)

Based on the above considerations, it can be expected that studies for the treatment of sewage sludge shall focus on the following aspects: safe handling, resource recovery, and low economic costs. In all these respects, the recovery of sustainable energy from sewage sludge will be of obvious importance. Another issue of concern is to reduce toxins in sewage sludge before the final treatment and minimize the negative impacts on human and ecosystem health. The aim of this paper is to discuss the current situation and future outlook for sewage sludge treatment and disposal and estimate the environmental and economic impacts of various options from sewage sludge. It also provides some reference for decision makers to better manage sewage sludge.

2 Composition of sewage sludge in China

The composition and characteristics of sewage sludge depend on several factors, such as the origin of the wastewater, the purification treatment of the wastewater, stabilization treatment, time and storage conditions, or the coagulant agents used. Generally, sewage sludge is composed of organic compounds, macronutrients, and a wide range of micronutrients, non-essential trace metals, organic micropollutants, and microorganisms. It should be stated that some parameters are important when considering the ultimate disposal of the processed sludge and energy reuse from the sludge during treatment. Dry matter has an effect on fuel requirements, exhaust gas production at the incineration process, and the cost of sludge transportation. V olatile matter, a measure of the sludge organic content, is the most important parameter regarding the energetic use of sewage sludge. Other factors, such as harmful organic compounds, micropollutants, nutrients, and heavy metal, cannot be neglected. According to Hua et al., polynuclear aromatic hydrocarbons have become one of the primary pollutants in sludge of Zhejiang WWTPs instead of heavy metals, which has a great influence on agriculture application of sewage sludge. Emerging contaminants such as pharmaceuticals, personal care products, illicit drugs, flame retardants, and perfluorinated compounds should be focused on, due to their endocrine-disrupting properties. N and P are essential resources especially with respect to P. Natural P deposits of sufficient quality are becoming scare, prompting rapid price increase. As a result, large quantities of sludge are applied to farmland. Heavy metal content which is very sensitive to the wastewater source decides whether sewage sludge can be applied to land or not. The threshold value of heavy metal for sludge end use should meet the Pollutants Control Standard of Sludge.

3 Sewage sludge treatment process and anaerobic digestion

Sludge treatment process Biosolids management was divided into categories for sludge treatment and end use, which are likely to be realized by different entities—the wastewater treatment plant and the recipient of treated sludge. Sludge treatment systems generally consist of thickening, dewatering, and several alternative main treatments, such as anaerobic digestion, aerobic digestion, drying, composting, and incineration, which are critical in determining biosolids quality and post-treatment options. Anaerobic digestion or composting is used to meet regulatory requirement for pathogen and remnant organic materials reduction prior to land application. Although incineration can significantly decrease dry solid volume and effectively attain a 100% reduction of pathogens and viruses, it produces dioxins, furans, and fly ash, as incurring as higher running/operational costs. Drying is a necessary process prior to thermal utilization of sewage sludge. The moisture content should meet standards regulated by Chinese legislation after sludge treatment.

Life cycle assessment as an environmental information analysis tool to aid planners in the wastewater treatment plant has been extensively applied to sludge treatment. Hong et al carried out a quantified environmental and economic analysis of six alternative scenarios: dewatering, dewatered sludge composting, dewatered sludge drying, dewatered sludge incineration, incinerated ash melting, and dewatered sludge melting, each with and without digestion. The results show that sewage sludge digestion leads to the lower economic and environmental impacts, while dewatered sludge melting is an environmentally optimal and economically affordable method. Murry et al. did an integrated study, comparing nine alternative treatment schemes and arranged them in order of environmental and economic impacts. They proposed that anaerobic digestion (no lime) is overall the most preferable sludge treatment option whereas incineration, particularly coal-fired, is the most costly. A

common feature of these methods was the utilization of the resource embodied in sludge; for example, heat drying with compost takes advantage of embodied nutrients, anaerobic digestion, and incineration of sewage sludge takes advantage of embodied energy. Overall, in order to decrease the environmental and economic impacts during sludge treatment, maximizing potential offsets, including the efficiency of the thickening process, energy capture from anaerobic digestion, and the electricity production rate generated from biogas, is required.

Anaerobic digestion Anaerobic digestion is considered an essential process in a modern WWTP due to reduction of sludge volume, generation of energy-rich biogas, and production of a nutrient-rich final product. Compared with other technologies, it is the most efficient method to capture energy from biosolids with high water content. Barber reported that the conversion of methane produced from anaerobic digestion to electricity and heat is the main contributor to renewable energy within the WWTP. In the EU, 50% of sewage treatment plants have anaerobic digestion, 18% incorporate aerobic digestion, and 4% lime stabilization, whereas 24% of the plants undertake no sludge stabilization. The same tendency is observed in China, but no detailed available information was reported. However, its application has often been limited by very long retention times and low overall degradation efficiency. In order to increase biodegradability and enhance anaerobic digestion with lower retention time and higher biogas production, various sludge pretreatment techniques have been applied in sludge digestion. These processes include biological (largely thermal phased anaerobic), thermal hydrolysis, mechanical (such as ultrasound, high pressure and lysis), chemical with oxidation (mainly ozonation), alkali, and combined pretreatment.

Currently, combined sludge digestion with other processes to achieve maximum utilization has attracted more and more attention. Using energy released by microbial decomposition to complete water evaporation in the process of biological drying is a promising method for dewatering sludge. There are some advantages in this process such as low-cost and energy consumption since no fossil fuel is depleted in such systems. Moreover, CO2 emission can also be significantly reduced, while the remaining sludge can be converted into amino acid salt with a content of 90% amino acid after acidification. An effective project like this has already been applied in Qinhuangdao City, China.

4 Ways of sludge disposal and utilization

4.1 Main disposal methods in China

Landfill Landfill is economical and low energy consumption due to its low-technology processes. However, it is a significant source of CH4and N2O, which are greenhouse gases with a high global warming potential. Leachate containing P and heavy metal can threaten surface and ground waters, and none of the nutrient or energy content is recovered from landfill. Biosolid management technologies for very small towns, with limited technical and financial resources, may justifiably consider investing in biofiltration or methane trapping and flaring at their local landfill.

Land application Land application of sewage sludge has a great incentive in view of its fertility and soil conditioning properties. It has been shown that the use of sewage sludge derived soil amendments can improve soil physical properties, such as porosity, aggregate stability, bulk density, water retention and movement, and sequester carbon in the soil, thereby reducing atmospheric CO2content and global warming potential. The environmental offset in electricity and fuel consumption is also great when sludge is used

in place of synthetic fertilizers.

Land application of sewage sludge is convenient and low requirements. Various stabilized biosolids such as slurry, dewatered cake, and dried pellets can be applied to land. However, sludge utilization can be limited due to its heavy metal, organic micropollutants, and pathogen content. Heavy metal concentrations depending on the relative contributor of industrial wastewaters to the overall flow can be decreased from sludge via source control. Pathogens are removed by pretreatment such as thermophilic anaerobic digestion, or composting.

Land application is available only when the sludge quality meets the local criteria with respect to pathogens and heavy metal content. In addition, the doses and rates of sludge application should also be carefully considered. Reports show that excessive application of sludge has increased the bioavailability of heavy metals, which might pose a serious risk to human health. While long-term application of sewage sludge can result in leaching of P and heavy metals, the risks of which are greater than the transfer of heavy metals into plant tissue and the food chain in the case of crops.

In addition, recovery of N and P should also be taken seriously. It is generally accepted that with the rapid urbanization in China, increasing amounts of N and P are entering the cities through food consumption. It is estimated that N and P contained in urban sewage sludge were 31,500 and 23,600 tons, respectively, in 2009. With increasing urbanization, the improvement of sewage treatment systems and nutrient use efficiency in food production systems, it is anticipated that nutrients contained in the urban waste stream are likely to increase dramatically in China in the next 10–20 years. Although the absolute amounts of N and P in sewage sludge are not great as compared to chemical fertilizers

applied to agricultural land in China, their emission to the environment will have serious impacts on water quality and ecosystem health. P, as a nonrenewable resource, is becoming depleted, and production of P fertilizer is increasingly more expensive, thus threatening food security globally. Therefore, recovery of nutrients from sewage sludge in a sustainable way is becoming an important challenge for environmental engineers.

4.2 Thermochemical processes for sludge

Incineration Incineration of sewage sludge is a process in which its organic matter is completely transformed into CO2 and H2O under high-temperature and aerobic conditions, while inorganic compounds remain in the ash. It is an effective way to dispose of sludge with advantages such as large reduction of sludge volume, thermal destruction of toxic organic compounds, and minimization of odor generation. The final sludge volume after incineration is approximately 10% of that after mechanical dewatering. The energy produced in the incineration process can be used for drying the mechanically dewatered sludge cake prior to the incineration process or can be used for the production of electricity. The amount of energy produced strongly depends upon the water content of the sludge and performance of the incineration.

Incineration as an attractive disposal method has been applied worldwide. For example, the amount of sludge being incinerated in Denmark has already reached 24% of the sludge produced, 20% in France, 15% in Belgium, and 14% in Germany, while in USA and Japan the percentage has increased to 25% and 55%, respectively. The main problems for combustion of sludge are high running cost and environmental impacts. Environmental problems relate to the accumulation of heavy metals in ashes and exhaust gases to the atmosphere. The former can be solved by using incineration ash as raw materials in cement

manufacturing, during which process heavy metals are immobilized in cement. Exhaust gases consist of dioxins, furans, and other pollutants (CO2, NO x, N2O, and SO x). Emissions of dioxins and furans are not generally a problem if temperatures above 600°C are kept and flue gases are rapidly cooled below 400°C. N2O can effectively be eliminated by increasing the combustion temperature to 880°C. Addition facilities such as electrostatic precipitators, wet scrubber system, etc. are also needed to comply with the strict exhaust gas emission standards. Large investment for the purification of flue gases may raise social objections.

Co-combustion of sewage sludge with other natural resources (coal, lignite, or wood) or municipal solid waste is also an alternative method for the management of sewage sludge. Environmentally and economically, technology scenarios for co-combusting of biosolids meet Waste Incineration Directive emission criteria and provide a net energy gain, but absence of policy and legal clarity, supply chain insecurity, and market immaturity hinder the development of co-combustion.

Incineration is suitable for cities; for example, Hangzhou has switched to incineration as the preferred option in sewage management, where land is very valuable. To avoid the high operation cost for sludge incineration and also to improve the energy recovery efficiency, exploiting new types of sewage sludge incinerators, implementation of a combined heat and power production unit at incineration plants, and the use of the polluted drying gas in the incineration process are feasible. It is expected that incineration will play an increasingly important role in sewage management in China in the coming decade. Pyrolysis Pyrolysis is a thermal decomposition of organic substances in the absence of air or in an oxygen-deficient atmosphere. The products of pyrolysis are biogas (non

condensable), bio-oil (condensable volatiles), and carbonaceous bio-char residue all of which have a potential end use and can be maximized by modulating the process conditions. Compared to incineration, pyrolysis has some potential advantages. One advantage is that the conversion of the combustible gases into electrical power can be achieved more efficiently.In addition, the formation and emission of toxic organic compounds, such as dioxins, NO x, and SO x, can be avoided in pyrolysis with low oxygen concentration.

Using steam pyrolysis to treat sludge is currently a practice being conducted in China, for example, in the city of Shenzhen. After treatment, the moisture content of sludge is reduced from 80% to 50%, resulting in the final sludge volume decreasing by 60%. During this process, pathogen and odor can be thoroughly removed. The treatment sludge can be made into organic fertilizer, which can be used for horticulture and forestry cultivation. It is a proof of concept for the sustainable development of the circular economy.

Other technologies, such as production of bio-oil from the pyrolysis of sewage sludge, have attracted attention due to the non-renewable nature and the increasing price of fossil fuel. Because the mechanism of such a process is complex, many parameters such as temperature, sewage sludge types, retention time, and the catalysts used affect bio-oil production. Literature concerning the production of bio-oil from sludge has demonstrated that the temperature and volatile solid content were the primary factors affecting oil and char yields. The maximum oil yield was achieved with primary sludge at 500°C, and the optimum pyrolysis temperature for waste activated sludge was 400°C. It is also stated that the optimal pyrolysis temperature for bio-oil production is 450°C. Experimental studies on pyrolysis liquids obtained from different sewage sludge have come to very interesting

conclusions: High sewage sludge ash content favored the decrease in the char yield and the generation of nonvolatile gases, while the sewage sludge with less content of oxygen-containing compounds would favor the quality of the pyrolysis liquids. It elucidates some recommendable characteristics in order to use sewage sludge as pyrolysis feedstock. Metal oxide catalysts can have different influence on pyrolysis. The presence of Fe2O3 and ZnO probably inhibited the decomposition of organic matters in demineralized sludge samples to generate more solid residues, while Al2O3,CaO,and TiO2 promoted the degradation of organic matters to produce less solid residues. Al2O3 and TiO2 may decrease pyrolysis time, while CaO, Fe2O3, and ZnO may prolong pyrolysis time. It is therefore important to formulate optimal catalysts for such systems.

However, the acceptance of this technology may be limited by the low economic value of the product, as well as the relative complexity of the processing equipments. The economic viability of pyrolysis may be improved if the yield of oil were enhanced or if value-added products such as adsorbents could be produced from the pyrolysis chars.

5 Perspectives

This paper reviews present and future directions of sewage sludge management in China. Up until now, most of the sewage sludge produced in the process of wastewater treatment has been used in agriculture or disposed of in landfills, or via incineration. Sewage sludge is rich in resources including nutrients and energy. Given the vast population and rapid urbanization in China, sewage sludge represents a major issue in environment and resource management. To resolve this issue, we propose that a holistic approach should be taken to manage sewage sludge in China, and future research and commercialization should focus on the following aspects:

? Life-cycle analysis of food and water consumption in urbanized regions to provide a full account of nutrient flow within urban ecosystems and to calculate the value of sewage sludge within a given boundary/region

? Diverse resource recovery systems (for nutrients, bioenergy, and raw substances for building materials) should be developed and applied for sewage sludge management, and in many cases, these systems should be integrated and optimized depending on the quality of sewage sludge and the scale of the region producing sewage sludge. Cost–benefit analysis should also be conducted so that the best technology available can be selected for different scenarios

? Novel and environmentally friendly materials derived from sewage sludge, such as PHA, are appealing, and the potential of different bacterial species and recombinant strains should be explored further in the context of increased PHA yield and productivity

? For sustainable management of sewage sludge, frameworks for risk assessment should be developed for different options of resource recovery, and the risks should be communicated to the public

? New energy policies and regulations such as the climate change levy and enforcing source control to municipal sewers are critical in determining the sustainability of the future in sludge management

英文文献翻译

中等分辨率制备分离的 快速色谱技术 W. Clark Still,* Michael K a h n , and Abhijit Mitra Departm(7nt o/ Chemistry, Columbia Uniuersity,1Veu York, Neu; York 10027 ReceiLied January 26, 1978 我们希望找到一种简单的吸附色谱技术用于有机化合物的常规净化。这种技术是适于传统的有机物大规模制备分离，该技术需使用长柱色谱法。尽管这种技术得到的效果非常好，但是其需要消耗大量的时间，并且由于频带拖尾经常出现低复原率。当分离的样本剂量大于1或者2g时，这些问题显得更加突出。近年来，几种制备系统已经进行了改进，能将分离时间减少到1-3h，并允许各成分的分辨率ΔR f≥（使用薄层色谱分析进行分析）。在这些方法中，在我们的实验室中，媒介压力色谱法1和短柱色谱法2是最成功的。最近，我们发现一种可以将分离速度大幅度提升的技术，可用于反应产物的常规提纯，我们将这种技术称为急骤色谱法。虽然这种技术的分辨率只是中等（ΔR f≥），而且构建这个系统花费非常低，并且能在10-15min内分离重量在的样本。4 急骤色谱法是以空气压力驱动的混合介质压力以及短柱色谱法为基础，专门针对快速分离，介质压力以及短柱色谱已经进行了优化。优化实验是在一组标准条件5下进行的，优化实验使用苯甲醇作为样本，放在一个20mm*5in.的硅胶柱60内，使用Tracor 970紫外检测器监测圆柱的输出。分辨率通过持续时间（r）和峰宽（w,w/2）的比率进行测定的（Figure 1），结果如图2-4所示，图2-4分别放映分辨率随着硅胶颗粒大小、洗脱液流速和样本大小的变化。

外文翻译 - 英文

The smart grid Smart grid is the grid intelligent (electric power), also known as the "grid" 2.0, it is based on the integration, high-speed bidirectional communication network, on the basis of through the use of advanced sensor and measuring technology, advanced equipme nt technology, the advanced control method, and the application of advanced technology of decision support system, realize the power grid reliability, security, economic, efficient, environmental friendly and use the security target, its main features include self-healing, incentives and include user, against attacks, provide meet user requirements of power quality in the 21st century, allow all sorts of different power generation in the form of access, start the electric power market and asset optimizatio n run efficiently. The U.S. department of energy (doe) "the Grid of 2030" : a fully automated power transmission network, able to monitor and control each user and power Grid nodes, guarantee from power plants to end users among all the nodes in the whole process of transmission and distribution of information and energy bi-directional flow. China iot alliance between colleges: smart grid is made up of many parts, can be divided into:intelligent substation, intelligent power distribution network, intelli gent watt-hourmeter,intelligent interactive terminals, intelligent scheduling, smart appliances, intelligent building electricity, smart city power grid, smart power generation system, the new type of energy storage system.Now a part of it to do a simple i ntroduction. European technology BBS: an integration of all users connected to the power grid all the behavior of the power transmission network, to provide sustained and effective economic and security of power. Chinese academy of sciences, institute of electrical: smart grid is including all kinds of power generation equipment, power transmission and distribution network, power equipment and storage equipment, on the basis of the physical power grid will be modern advanced sensor measurement technology, network technology, communication

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(完整版)冲压类外文翻译、中英文翻译冲压模具设计

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