一般污泥和含油污泥的处理方法外文翻译.doc

The ways of regular sludge and oily sludge treatingGenerally speaking， there is a procedure for treating sludge after secondary treatment of wastewater if we want to prevent our living environment from second polluting. Wastewater treatment objectives are accomplished by concentrating impurities into solid form and then separating these solids from the bulk liquid. This concentration of solids， referred to as sludge， contains many objectionable materials and must be disposed of properly. Sludge disposal facilities usually represent 40 to 60 percent of disposed of the construction cost wastewater-treatment plants， account for as much as 50 percent of the operating cost， and are the cause of a disproportionate share of operating difficulties.First of all， the initial sludge is separated from the clean water lying upon it in the secondary clarifier by pumping it to a tank. Because the initial sludge have a high water content that usually can up to 99.5 percent in volume， sludge thickening is a necessary procedure， and there are several techniques are available foe volume reduction. Mechanical methods such as vacuum filtration and centrifugation may be used where the sludge is subsequently to be handled in a semisolid state. There methods are commonly used preceding sludge incineration. Where further biological treatment is intend，volume reduction by gravity thickening or flotation is common practice. In both cases， the sludge remains in a liquid state.Gravity thickeners are very similar in design and operation to the secondary clarifiers used in wastewater treating systems. The thickening function is the major design parameter， and tanks are generally deeper than secondary clarifiers to provide greater thickening capacity. A well-designed， well-operated gravity thickener should be able to， at least double the solids content of the sludge. In another word， the water content ratio of sludge can be reduced from 99.5 percent in volume to 98 percent or ever much more reduction. It should be noted that the design of gravity thickeners should be based on the results of pilot plant analysis wherever possible， since successful loading rates are highly dependent on the nature of the sludge.In dissolved air flotation， a small quantity of water， usually secondary effluent is subjected to aeration under a pressure of about 400kPa. This supersaturated liquid is then release near the bottom of a tank through which the sludge is passed at atmospheric pressure. The air is release in the form of very small bubbles that attach them selves to， or become entrapped in， the sludge solids， floating the solids to the surface. The thickened sludge is skimmed off at the top of the tank while the liquid is removed near the bottom and is returned to the aerator.After volume reducing， sludge represents a considerable hazard to the environment and must be rendered inert prior to disposal. The most common means of stabilizing is by biological degradation. Because this process is intended to convert solids to unicellular end products， the term digestion is commonly applied to this process. Sludge digestion serves both to reduce the volume of the thickened sludge still further and to render the remaining solids inert and relatively pathogen-free. These goals can be accomplished by either anaerobic or aerobic digestion.Sludge contains a wide variety of organisms， and thus requires a wide variety of organisms for its decomposition. The literature relating to anaerobic sludge digestion often divides the organisms into two kinds， the acid formers and the methane formers. So we can divide the anaerobic sludge digestion into two steps too. On the first step， the acid formers consist of facultative and anaerobic bacteria that solubilize the organic solids through hydrolysis. The soluble products are then fermented to acids and alcohols of low molecular weight. The second step， the methane formers consist of strict anaerobic bacteria that convert the acids and alcohols， along with hydrogen and carbon dioxides to methane. Because this two kings bacteria can keep themselves living in oxygen-less surroundings， reactor for anaerobic digesters must be closed. Other parameter such as reacting temperature， pH value and turbulence of the mixture should be considered to design the tank.Sludge can also be stabilized by aerobic digestion. Generally restricted to biological sludge in the absence of primary sludge， this process is essentially a continuation of the aeration process， with the volume being reduced by thickening in the secondary clarifier and sludge thickener. The most common application of aeration digestion involves stabilizing sludge wasted from extended aerobic systems. Then， aerobic digestion is not as sensitive to environmental factors as is its anaerobic counterpart and is not as subject to upsets.After sludge digestion， the organics can be removed and the volume of sludge can be reduced by further. Then， the sludge needs disposed. Several potions are available for the ultimate disposal of sludge. These include incineration， placement in a sanitary landfill， and incorporation into as a fertilizer or soil conditioner. Raw sludge can be incinerated， provided the water content is sufficiently reduced. Supplement fuel is necessary to initiate and maintain combustion and municipal solid waste may be used for this purpose. Raw or digestion sludge can be also be disposed of in sanitary landfills. Land application of sludge has been practiced for many years， modern application being limited to digested sludge. The nutrient value of the sludge is beneficial to vegetation， and its granular nature may serve as a soil conditioner. Its application has been limited to ground used for forage crops for nonhuman consumption， although the possibility of its use on ground used to grow edible produce is still being investigated. Metal toxicity in plants and water pollution from excess nitrates appear to be the limiting factors in land application of sludge. Sludge may be applied in a liquid state by spraying， ridge and furrow， or by direct injection beneath the soil. Dewatered sludge may be spread on the land and cultivated into the soil by conventional agricultural equipment.We see the treatment of sludge as a regular treating what have been mentioned in the front of this writings. The sludge will contribute to the environment polluting， so we should be do our best to make the sludge hazardless. Now， some sludge of more different characteristics which leading different kinds of environment polluting are investigated. In this writings， I will talk something about oily sludge which can be saw as a topic sludge produced from our oil production and processing activities. A huge amount of oily sludge is produced， and this sludge usually contains a considerable quantity of oil， which should be removed before its finally disposal. Generated in a vast amount in petroleum refinery plants oily sludge cannot be safely disposed unless its oil content is reduced below a certain limit. In addition， the vast amounts if oil sludge generated in refineries from water-oil separation systems and accumulation of waste oily materials in crude oil storage tanks poses great problem because of the expensive disposal and its large harmfulness of environment. Petroleum is a complex mixture of non-aqueous and hydrophobic components like n-alkane， aromatics， resins and asphalt. Many of these components are toxic， mutagenic and carcinogenic. Therefore， their release to the environment is strictly controlled and they are classified as priority environmental pollutants by the US Environmental Protection Agency due to their adverse impact on human health and environment. A variety of methods have been suggested to treat oily sludge. There are physical or chemical methods such as incineration， chlorination， ozonation， and combustion， biological treatment such as bioremediation， conventional composting and so on. Nowadays， with the technology of oily sludge treatment developing， separation of oil from oily sludge by freezing and thawing and the oily sludge bioremediation could be more attractive waysFreeze/thaw treatment is generally accepted as a physical sludge conditioning method that can significantly improve certain sludge dewatering characteristics， change the floc structure into a more compact form and reduce the sludge bound water content .Once the so-called gross-migration“ of flocs occurs， freezing front would reject impurities in the solution to the far-ends of the vessel， thereby achieving concentration purposes recently discussed the benefit obtainable from freeze/thaw treatment. To our best knowledge， there is no work appearing in literature having discussed the feasibility of employment of freeze/thaw treatment for separating oil from the oily sludge. But as natural freezing is easily accessible in many countries， if feasible， freeze/thaw treatment may provide an alternative for oily sludge treatment and disposal. Comparing the result from freeze/thaw treatment to regular treatment， we can find that after thawing， however， an oil layer gradually appeared at the top of the sample. Finally， three layers stood clearly in the tube: at the top was a clear， transparent oil layer; at the bottom， a deep-dark sediment layer， while in between， a water layer. Still settling of original sludge for 24 h leads to a clear supernatant and a deep-dark sediment. No oil phase could be visually observed. The above-mentioned results clearly reveal that， simple freezing and thawing treatment can efficiently separate oil.The physico-chemical treatments can be applied for the oily sludge， but these methods are extremely expensive. Composting and bioremediation with an introduction of oil degrading microorganisms (bio-augmentation) or activation of indigenous ones are now considered as two major economic methods for the decontamination of oil pollutions. Composting has some visible advantages including relatively low capital and maintenance costs， simple design and operation and some (but incomplete) removal of oil pollution. However， in general， the efficiency of composting is unsatisfact- ory to meet the current environmental regulations. For more content of the oil， the oily sludge is much more difficult for the bioremediation. Numerous researches have demonstrated high bioremediation efficiency for oil polluted soils， but these methods have limitations for the oily sludge mainly dealt with extremely high pollution level. Most of the experiments were carried out in the lab， while the field experiments were very few. The bioremediation treatment of the oily sludge was just beginning. These experiments were meaningful for the advance of this technology. There is a study of oily sludge treating in China during 2004.The bioremedia- tion by augmentation of biopreparation was compared with a conventional composting. The oily sludge and oil polluted soil were received from an oil production plant. The total hydrocarbon content (THC) varied from 327.7 to 371.2 g kg-1 of dry sludge and the THC in contaminated soil was 151.0 g kg-1. Before application of preparation， straw， sawdust， top sand and pure soil were added in different proportions to the sludge and soil and mixed thoroughly. Such sludge and soil composites were used for negative controls and for activation of indigenous oil degrading microorganisms with addition of fertilizer (positive controls). For composting， crude manure and straw were added to the oily sludge and the THC was 101.4 g kg-1. The biopreparation was applied every 2 weeks and experiment lasted 56 days under the ambient temperature. The sludge was mixed and watered every 3 days. After three times of biopreparation application， the THC decreased by 4653% in the oily sludge and soil， while in the positive controls (activation of indigenous microorganisms) the THC decreased by 1323%， and there was no oil degradation in negative controls After composting， the THC decreased by 31% in the oily sludge. The above-mentioned phenomenon clearly reveals that， bioremediation will be an effective way to deal with oily-sludge more efficiently as well as economically.一般污泥和含油污泥的处理方法一般来讲，为了不造成环境的二次污染，需要在污水处理的二级处理之后添加一道污泥处理工艺。污水处理的目标通过把水中杂质浓缩成固体形态再从流体中分离而实现。这种浓缩质变称为污泥，因包含了大量的有害物质，需要妥善处置。污泥处理设备大约占污水处理厂的40%-60%基建投资，污泥处理则占50%左右的处理费用，同时也造成了和其经济费用不成比例的处理难度。首先，原污泥通过污泥泵由二沉池打到另一个池子中从而和上清液分离。因为原污泥的含水率通常能达到99.5%，所以污泥必须浓缩，有多种可行的方法用于减少污泥的体积。例如真空过滤和离心等机械处理的方法通常用于将污泥以半固体形式处置之前。通常这些方法是污泥焚烧处理的准备工作。如果计划采用生物处理，则多数才用重力沉降或者是气浮的方法进行浓缩。这两种情况所对应的污泥仍然是流态的。重力浓缩池的设计和运行类似于污水处理中的二沉池。浓缩功能是主要的设计参数，为了满足更大的浓缩能力，浓缩池基本上比二沉池要深。一个设计正确，运行良好的重力浓缩池至少能提高两倍的污泥含泥量。也就是说，污泥的含水率可以有99.5%减少到98%，或者更少。这里值得一提的是，重力浓缩池的的设计要尽量基于中式结果的分析，因为合适的污泥负荷率与污泥的属性的有很大关系的。如果采用溶气气浮浓缩，需要有一小部分的水，通常是二沉池出水，在400kPa的压力下充气。这种过饱和的液体通入罐底，而污泥在大气压下通过。气体以小气泡的形式和污泥中的固体颗粒黏附，或则是被包围，从而带动固体颗粒上浮到表面。浓缩了的污泥的上部被除去，而液体由底部流回溶气罐充气。体积减少后，污泥中含有大量的有害成分，在处置之前需要将之转化为惰性成分。最常用的方法是生物降解稳定。因为这个过程目的在于将物质转化为最终无菌产物，所以常应用消化的方法。污泥消化既能进一步的减少污泥体积也能使所含固体转化为惰性物质并且大体的上没有病菌。通过厌氧消化或好养消化都能达到污泥消化目的。污泥含有多种有机物，因此需要多种微生物来分解。有关资料将厌氧消化中的微生物分为两类：产酸菌和甲烷菌。所以，我们也能把厌氧消化分为两步。第一步，由兼性厌氧菌和厌氧菌组成的产酸菌通过水解作用溶解有机固体。接着溶解质由发酵作用转化为酒精和低分子量分子。第二步，有严格厌氧菌组成的甲烷菌将乙酸、酒精、水和二氧化碳转化为甲烷。因为两种菌群只能在无氧的环境下存活，所以厌氧消化的反应器必须是密闭的。设计容器的时候同时也要考虑另外的一些因素，例如：温度、pH值和混合物搅拌。污泥也可以通过好氧消化稳定。这种消化基本上只能用于可生化污泥而不能用于初沉池污泥，伴随着二沉池和污泥浓缩池中污泥体积的减少，这个工艺需要不断的鼓气。好氧消化多应用于深度曝气系统。再者，好氧消化对环境条件不敏感，也不局限有流行变化。污泥消化以后，污泥中的有机物能被去除并且能进一步的减少污泥体积。接下来，污泥需要处置。多种方法可以用来有效的处置污泥。其中包括焚烧、卫生填埋和用作化肥以及土壤改良剂。原污泥可以用来焚烧，可以有效地减少含水率。添加燃料可以用来引起和维持燃烧，城市垃圾也可能用来达到这个目标。原污泥和消化污泥也可以用卫生填埋来处置。污泥的土地应用实践了好几年，而现在只限于处理消化污泥。污泥的营养成分有利于植物成长，而其颗粒特性可用于土地改良。这些应用局限有饲料作物和非人类消费，而运用于支持可食用植物的可能性正在研究中。污泥土地应用的主要限制