环境工程专业英语unit14.doc

3 Biological Wastewater TreatmentApplication of microbial degradation and removal of undesirable constituents in industrial and municipal wastes is not a new concept. It is commonly used process for general wastewater treatment activities and has been for many years. As the awareness of chemical contamination of the environment, much research on biological degradation of toxic chemicals has occurred. Among the range of treatment technologies, biological degradation ranks among the most effective. Its management and application is enhanced by the potential to apply biological treatment in sequence with other chemical and thermal processes.Activated sludgeThe activated sludge process is s typical type of suspended growth biological treatment system and probably the most widely used biological process for the treatment of organic and industrial wastewaters. However, it can only treat aqueous organic wastestreams having less than 1% suspended solid content, and can not tolerate shock loading of concentrated organics. Therefore, the wastestream entering this process will usually have passed through a pretreatment process which includes a clarifier (primary clarifier) and an equalization basin. The primary clarifier is used for removal of grit, oily and fatty material and gross solid material, while the equalization basin is used to dampen wastewater flow variations and to provide more uniform organic loading to the activated sludge system.Activated sludge process are used to treat municipal and industrial wastes since they are versatile, flexible, and can be used to produce an effluent of desired quality by varying process parameters. The process was so-named because it produces an active mass of microorganisms capable of aerobically stabilizing a waste. Many versions of the basic process exist but all are fundamentally similar.The term activated sludge is applied to both the process and to the biological solids in the treatment unit. The mixed liquor suspended solids or activated sludge contains a variety of heterotrophic microorganisms such as bacteria, protozoa, fungi, and larger microorganisms. The predominance of a particular microbial species depends upon the waste that is treated and the way in which the process is operated.The activated sludge process is currently the most widely used biological treatment process. This is partly the result of the fact that recirculation of the biomass, which is an integral part of the process, allows microorganisms to adapt to changes in wastewater composition with a relatively short acclimation time and also allows a greater degree of control over the acclimated bacterial population.An activated sludge system consists of an equalization basin, a settling tank, an aeration basin, a clarifier, and a sludge recycle line. Wastewater is homogenized in an equalized basin to reduce variations in the feed, which may cause process upsets of the microorganisms and diminish treatment efficiency. Settleable solids are then removed in a settling tank.Next, wastewater enters an aeration basin, where an aerobic bacterial population is maintained in suspension and oxygen, as well as nutrients, are provide. The contents of the basin are referred to as the mixed liquor. Oxygen is supplied to the aeration basin by mechanical or diffused aeration, which also aids in keeping the microbial population in suspension. The mixed liquor is continuously discharged from the aeration basin into a clarifier, where the biomass is separated from the treated wastewater. A portion of the biomass is recycled to the aeration basin to maintain an optimum concentration of acclimated microorganisms in the aeration basin. The remainder of the separated biomass is discharged or “wasted”, The biomass may be further dewatered on sludge drying beds or by sludge filtration to disposal. The clarified effluent is discharged.The recycled biomass is referred to as activated sludge. The term “activated” is used because the biomass contains living and acclimated microorganisms that metabolize and assimilate organic material at a higher rate when returned to the aeration basin. This occurs because of the low food-to-microorganism ratio in the sludge from the clarifier.For the treatment of industrial wastewater, supplemental nutrient sources are often needed to provide sufficient nitrogen and phosphorus. In most cases, nitrogen is added as ammonia and phosphorus as phosphoric acid. A proper pH range (6 to 8) and s sufficient dissolved oxygen concentration (a minimum of I to 2mg/L) must also be maintained in the aeration basin to support a healthy and active system.The aeration basin hydraulic retention time (HRT) and sludge residence time (SRT) are important operational factors. HRT is defined as the ratio of the volume of aeration tank to the influent liquid flow rate, and SRT is the total amount of sludge in the system divided by the rate of sludge leaving the system as waste. Sufficient time must be provided to allow the bacteria to assimilate the organic material in the wastewater. The HRT is usually from 6 to 24 hours and SRT is from 4 to 10 days for the activated sludge process. The optimum operating temperature is in the range of 25C to 32C.Although organisms present in activated sludge systems range from viruses to multicellular organisms, the predominant and most active are heterotrophic, and to lesser extent, autotrophic bacteria, which are both aggregated in the sludge flocs and dispersed in the liquid. Heterotrophic bacteria utilize organic material as a source of carbon and energy, while autotrophic bacteria generally depend on the oxidation of mineral compounds for energy requirements and utilize carbon dioxide as a carbon source. These bacteria are capable of performing hydrolysis and oxidation reactions.Complex hydrocarbons are oxidized to lower molecular weights by oxygenase enzymes which incorporate oxygen directed into the long chain or cyclic hydrocarbon molecule. Polysaccharides, fats, and proteins are degraded from their polymeric state to units via hydrolysis. The end-products, i. e., alcohols and acids, from those reactions will enter the microorganism and be metabolized by oxidation reactions catalyzed by endo-enzymes. The oxidation follows the chemical sequence of: alcohols oxidized to aldehydes and then to acids. A portion of the acids are oxidized to carbon dioxide and water to obtain the necessary energy to use remaining acids for cell growth.Generally, the activated sludge process is readily capable of decomposing alcohols, aldehydes, fatty acids, alkanes, alkenes, cyclo alkenes and aromatics. Other compounds such as isoalkanes and halogenated hydrocarbons are more resistant to microbial decomposition. Therefore, the degree of treatment and the rate of decomposition are dependent upon the acclimated biomass in the activated sludge system. However, only dilute aqueous wastes can normally be treated, and most hazardous organic wastes are toxic or inhibitory to the process except at very low concentrations. Therefore, treatment of hazardous wastes by this process is often most practical where the aqueous waste can be mixed with a more readily biodegradable wastewater stream.Dissolved metal ions and fine metal particles produce so adverse effect on microbial metabolism by binding at the enzyme active site or causing conformational changes in the enzyme with activated sludge process. Normally, microorganisms can tolerate only a few milligrams per liter or less of heavy metals. Heavy metals may be kept insoluble by the addition of ferrous sulfate to encourage sulfide precipitation and light metal cations may be detoxified by encouraging formation of carbonates and bicarbonates. In addition to biodegradation, organic materials may be removed by air-stripping, and/or sorption to the sludge.单词表microbial makrobla 微生物的diffused aeration扩散曝气 鼓风曝气degradation ,degrde()nn 降解mechanical aeration mknk()l ,eren机械曝气toxic tkska 有毒的sludge drying bed 污泥干化床aqueous ekwsa 水的 含水的 水状的 sludge filtration fltren污泥过滤tolerate tlretvt 忍受sludge disposal dspz()l污泥处置concentrated knsntretda 浓缩的 集中的assimilate smletv 同化 吸收shock loading a 冲击负荷supplemental ,splmntla 补充的 clarifier klrifain 澄清器ammonia mn氨equalization basin ,ikwlzen bes()n调节池phosphoric acid fsfrk sd磷酸dampen dmp()nvt 抑制 使沮丧multicellular mltseljla 多细胞的uniform junfma 一致的，统一的predominant prdmnnta 主要的organic loading有机负荷autotrophic ,ttrfka 自养的versatile vstala 通用的aggregate grgtv 聚集flexible fleksb()la 灵活的floc flkn 絮状物effluent eflntn 出水disperse dspsv 分散heterotrophic ,hetrtrfka 异养的mineral compoundsmn()r()l kmpandn 无机物autotrophic ,ttrfka 自养的hydrolysis hadrlssn 水解作用predominance prdmnnsn 优势 优越species spiiza 物种recirculation r,skjlenn 再循环oxygenase ksdnesn 加氧酶biomass ba()msn （单位面积或体积内）生物质enzyme enzamn 酶integral ntgr()l; ntegr()la 整体的incorporate nkpretv 包含 吸收 合并homogenize hmdnazvt 使均匀 使类同long chain hydrocarbon 长链烃diminish dmnv 减小 变少cyclic hydrocarbon saklk; sk-环烃aeration basin ,eren bes()n曝气池polysaccharide ,plskradn 多糖 多聚糖aerobic bacterial erbk bktrl好氧细菌的fat n 脂肪blast aerationblst ,eren鼓风曝气proteinn 蛋白质polymeric ,plmerka 聚合的inhibitory nhbtra 抑制的monomeric ,mnmrka 单分子的aldehyde ldhadn.乙醛endoenzyme ,enduenzaimn 内酶active site 活性部位aldehyde ldhadn 乙醛conformational ,knfmenla 构象的fatty acid ft sdn 脂肪酸ferrous sulfate fers slfet硫酸亚铁alkane lkenn 烷烃sulfide slfadn硫化物alkenen 烯烃precipitation pr,spte()nn 沉淀cyclo alkene sakln 环烯烃cation ktann 阳离子aromatic rmtkn 芳香烃detoxify ditksfavt 解毒isoalkane ,aslkenn 异烷烃air-stripping strp脱气halogenated hydrocarbonhldnet ,hadr()kb()n卤化烃sorption sp()n吸附 吸收 吸着废水生物处理利用微生物来降解和去除工业和城市废弃物中的不良成分在并不是一个新概念。这种工艺被普遍的用于一般污水处理活动已有多年。随着人们对环境化学污染认识的提高，出现了许多关于用生物降解有毒化学物质的研究。在各种处理技术中，生物降解属于最有效的（方法）。它的管理和应用被生物处理的潜在应用所增强，其他依次为化学和热过程。（？）活性污泥活性污泥法是典型的悬浮生长的生物处理系统，可能是有机和工业废水处理使用最广泛的生物工艺。然而，它只能用于处理悬浮固体含量少于1%的废水中的水溶性水有机物，并且不能承受集中有机物的冲击载荷。因此，在废水进入这个工艺过程前，通常会经过一个预处理过程，预处理包括一个沉淀池（初沉池）和一个调节池。初沉池用于去除沙砾、油和脂肪物质以及大的固体物质，而调节池是用来抑制污水流量变化和为活性污泥系统提供更加均衡的有机负荷。由于活性污泥法的通用性、灵活性和通过改变工艺参数能够获得达到水质要求的出水，因此常被用于处理市政和工业废物。这种工艺之所以被如此命名是因为它产生一个活性很高的微生物群，它能够在好氧时稳定废物。目前存在着这种基本工艺的许多版本，但根本上是相似的。活性污泥这个术语用来表示工艺和处理单元中生物固体。混合液悬浮固体或活性污泥中含有多种异养微生物，如细菌、原生动物、真菌和较大的微生物。特定的微生物优势菌种取决于处理的废物种类和工艺的运行方式。在活性污泥法是目前应用最广泛的生物处理工艺。部分原因是由于生物量再循环的事实，这也是工艺的主体部分，使微生物在相对短的适应时间内适应废水成分变化，还允许更大程度的控制适应环境的微生物数量。活性污泥系统包括调节池，初沉池，曝气池，二沉池和污泥循环系统。废水在调节池中被均质化来降低来水的变化，这可能会导致微生物过程混乱和降低处理效率。然后沉降性固体在沉淀池中被去除。接下来，污水进入曝气池，池中好氧菌群保持这悬浮状态，曝气池也提供氧气,和营养。池中的内容被称为混合液。氧气是由机械或扩散曝气提供给曝气池，这有助于保持微生物种群处于悬浮状态。混合液从曝气池中连续排出，进入沉淀池，这可以使生物从废水中分离出来。一部分的微生物循环回曝气池来维持曝气池适应环境微生物的最佳浓度。剩余污泥会在污泥干化床上被进一步脱水，或者用污泥过滤来处理。澄清的出水则被排放。循环生物质被称为活性污泥。“活性的”这个术语被应用是因为生物质包含了活跃的和适应环境的微生物，这些微生物返回至曝气池中可以以较高的速率代谢和吸收有机物质。这种现象的发生是由于来自二沉池的污泥中微生物食物的比例低。对于工业废水的治理，通常需要补充营养来源以提供充分的氮和磷。在大多数情况下，氨作为氮添，磷酸作为磷添加。曝气池中必须保持合适的pH范围(6到8)和足够的溶解氧浓度(最小量为1到2 mg / L)，用以支持一个健康和活跃的系统。曝气池的水力停留时间(HRT)和污泥停留时间(SRT)是重要的操作参数。HRT的定义是曝气池的体积和流入液体流速的比值，SRT则是系统中污泥总量除以污泥作为废物离开系统的速率。必须提供足够的时间让细菌同化污水中的有机物质。对于活性污泥法，HRT的通常是6到24小时，SRT为4到10天。最佳的操作温度介于25C到32C之间。虽然存在于活性污泥系统生物范围为病毒到多细胞生物，但是主要的和最活跃的是异养的，其次为自养细菌，这些都聚合于污泥絮体中和分散在液体中。异养细菌利用有机物质作为碳源和能量来源，而自养细菌通常依靠无机化合物的氧化满足能量需求和利用二氧化碳作为碳源。这些细菌能够完成水解和氧化反应。复杂的碳氢化合物通过加氧酶被氧化为较低的分子量，这包括将氧直接加入长链或环状烃分子。多糖、脂肪和蛋白质通过水解作用从聚合态降解为各个单元。这些反应的最终产物，即醇类和酸类，将进入微生物，并在酶的催化作用下通过氧化作用而被代谢。氧化遵循化学顺序：醇先被氧化成醛，然后是酸。一部分酸被氧化为二氧化碳和水，来获得细胞生长利用剩余酸的必要能量。通常，活性污泥法能够很容易的分解醇类、醛类、脂肪酸、烷烃、烯烃、环烯烃和芳香烃。其他的化合物如异烷烃和卤代烃更耐微生物分解。因此，处理的程度和分解的速度依赖于活性污泥系统中适应环境的生物量。然而，只有稀释的液体废物通常能被处理，大部分的有机废物除了在非常低的浓度时，是有毒的或者会抑制反应过程。因此，这个工艺处理有害废物通常是最实用的，液体废物可以与更易生物降解的废水混合。活性污泥法中，溶解的金属离子和金属微粒对微生物代谢产生如此的不利影响，是通过约束酶活性部位或引起酶构象变化。通常，微生物可以承受只有几毫克每升或更少的重金属。通过添加硫酸亚铁铵，可以促进硫化物沉淀，重金属就可以保持不溶性状态。轻金属阳离子的解毒可以通过促进其形成碳酸盐和重碳酸盐。除了生物降解外，有机物质可以通过脱气或者污泥的吸附而被去除。