外文翻译---用膜过滤和混凝相结合增强天然有机物的去除.docx

附录1 文献翻译用膜过滤和混凝相结合增强天然有机物的去除维克斯.詹姆士c 汤普森.马克a 凯兰.尤得g美国弗吉尼亚纽波特纽斯沿河路400马尔科姆纺织公司11832电话：804-8738700 传真：804-8738723摘要：随着水质标准的调整及消毒消毒副产物(d/dbp)条例的实施，必然要求相应饮用水处理设备能够达到对水中颗粒和耐消毒的微生物以及天然有机物（nom）的更多去除。对于传统的水处理装置，混凝技术要求颗粒和浊度的最大去除效率要达到地表水处理规1(swtr)和地表水深度处理规则(eswtr)的要求，而强化混凝技术则要求达到 d/dbp条例的要求。对于生活饮用水，通过膜滤法比如微滤和超滤(mf/uf)，浊度、颗粒和微生物的除去可以达到swtr2,3的要求。而不经过预处理、mf/uf只能除去10%的消毒副产物的前体物质。然而，这种工艺与传统的化学混凝5作用或粉状活性炭(pac)6相结合去除天然有机物，它们有相同的去除效果。为了满足今后的水质要求，mf/uf在水处理技术中越来越被人们重视。关键词：混凝 膜过滤 天然有机物 浊度 消毒消毒副产物1 常规混凝对悬浮颗粒的去除以地表水为水源水供给的饮用水，一般采用用常规工艺处理。这种工艺的原理是物理/化学分离，通过投药/混合，絮凝，沉淀和过滤等一系列过程使水中的悬浮颗粒得到有效去除。常规处理工艺要求投加混凝剂使颗粒凝聚成团从而可通过过滤去除。混凝剂能通过电荷中和促进颗粒聚合，从而有利于在随后的沉淀和过滤中去除原水水质随时间和季节的不同会影响混凝剂的最佳投加量，这些因素包括ph值、碱度、总有机碳(toc)浓度及水温。混凝剂投加量通常根据烧杯试验的经验来进行调节，通过检测原水水质来相应的按比例调整投加量，原水水质改变混凝剂的投加量也要随之改变。因此，这种工艺本身的缺点就是人为确定的投加量变化可能超过或达不到实际的变化。混凝经沉淀后的出水浊度是评价整个工艺过程对有机物去除效果的主要指标，同时出水浊度的高低对滤池的正常运行也有重要意义。控制浊度对后续操作工艺有以下好处：降低水力停留时间，改善滤后水质，减少滤池反冲洗和间歇次数。ph对絮凝作用有很大的影响，它会影响澄清液的浊度。一般说来，ph在6.5和6.5之间时，絮凝效果最好，有最佳的的去浊率7。2 常规混凝对nom的去除类似d/dbp条例这类新的饮用水处理标准越来越趋向于控制水中nom的多少。nom是植物和动物的有机物质经过降解而成的，它是构成消毒副产物的前体物的主要部分，toc是衡量其多少的一个参数。新的条例实施后，自来水厂的在保证浊度去除的基础上还要减少消毒副产物的形成。这就要严密检测进水的物理化学性质的变化并进行必要调整，以使水质稳定。此外还要进行工艺上的调整以达到d/dbp条例的要求，例如废止预氯化工艺，用臭氧消毒代替氯胺和二氧化氯消毒。为了进一步减少消毒副产物的前体物，人们提出了强化混凝工艺。强化混凝可以使水中nom的去除达到一定的要求。强化混凝是一个要经过两个阶段调整的概念。根据d/dbp条例第一阶段的要求，自来水厂应根据原水的碱度使toc去除达到相应的水准。在加入化学消毒剂之前，比如加入氯，先要去除水中的toc。对于工艺流程采用常规工艺的水厂来说，为了满足toc去除水平，就要重新调整混凝剂投加量并优化混凝过程。如果采用常规工艺的水厂可以通过增加混凝剂投量就能满足所要求的toc去除率，那么就可以说它达到了强化混凝的要求。d/dbp条例第一实施阶段对不同的toc浓度和不同碱度的原水所要求的toc去除率见表1。表格1：强化混凝去除toc的百分比原水toc(mg/l)原水碱度0-6060-1201200-44030204-84535258504030如果原有工艺不能满足上述标准，那么就在一定的ph下用锥型瓶做强化混凝实验确定混凝剂量。强化混凝剂量为每增加10mg/1混凝剂时，相应的toc减少量不得少于0.3mg/1。强化混凝除了能满足近期的水质处理要求外，增加絮凝剂量可以处理那些不受d/dbp规则限制的水体。例如：原水toc含量高的水体（如美国东南方的水）用超剂量的絮凝剂可以大大地减少dbp的前体物质。一般而言，在最佳ph值5.0-6.0的条件下8每mgtoc约消耗金属絮凝剂5-20mg。而nom的性质和浓度限制采用的处理工艺，特别是絮凝剂、助凝剂和氧化剂的种类和剂量会随着nom的性质和浓度的不同而相差很远。人们认识到用强化混凝工艺可以达到去除nom/toc的要求,并把它已归入到swtr的技术要求中，强化混凝特别适于对dbp有要求的情况下。为了满足swtr的过滤技术要求，在混凝工艺后还要进一步强化滤池的处理效果。本部分主要是强调以下两个方面：强化混凝可以通过测量还原的toc得到nom和dbp的去除量；过滤必须进一步除去浊度和颗粒物，从而达到swtr和eswtr的要求。3 d/dbp条例对常规过滤设备的影响常规过滤法需要改进处理装置使其去除后浊度和颗粒物低于swtr规定的值。象eswtr这样的新规则打算增加过滤技术要求和引入其它微生物除去要求，比如复合子囊孢子卵囊。影响单个处理厂的原因不一，但是，下列陈述指示该装置将要发生的变化：混凝剂除去nom最佳的ph值要低于使浊度减少到最低时的ph值；d/dpb条例显著影响常规媒介过滤器的使用特性，因为增加助凝剂的剂量会使滤膜上的颗粒负荷增加；常规的过滤装置将产生大量的滤渣；在许多过程中用ph调节水是必需的，它是为了调节平衡和满足技术要求。4 微滤和超滤法微滤和超滤法是一种物理分离（筛子）法。它不同与常规的过滤法，物理和化学的之间的参数不能影响过滤器的滞留效率。滤膜基本上充当表面型过滤器，俘获在过滤器表面的颗粒物可以用反冲洗的方法去除。这种处理方法有如下基本优点：4.1浊度和微生物的去除微滤/超滤对水中的颗粒物去除率高。而经它过滤处理后的水质的浊度一般小于0.1ntu。过滤后的水浊度相对进水浊度而言变化是最小的。膜滤法可以使浊度超过100ntu的原水达到出水水质。研究证明膜过滤对贾第鞭毛虫胞囊虫和其它记录的6种之多的微生物有很高的去除效果。4.2滤后出水水质稳定与常规过滤相比，膜滤法的一个重要因素是处理装置易失常。如果常规过滤可以很快的调整化学药剂和处理条件的一致性。然而，经过膜过滤后，无论原水水质怎么变化，其出水水质的微生物和颗粒物同样能降到一定的水平内。膜滤法原理不是用靠增加膜两侧的压差和缩短清洗时间来达到出水水质要求。从操作技术要求来看，膜操作系统要求提供的原水水质稳定，变化很小。微滤后滤液的水质取决于膜控制系统膜的直径和操作方法。这种优点特别适合于那些小型的处理系统，而且操作简单，便于控制。5 微滤和超滤同混凝相结合微法/超滤法作为独立的处理系统时，大约能去除10%的dbp的前体物。研究表明：这是由于膜能截住分子量为400至5000的dbp前体物9。它远远小于能截止分子量超过5000的超滤和能截止分子量超过1000000的微滤和常规的过滤法一样，利用絮凝剂改变水的外观，如色度，浊度等. 由于dbp的出现，试行条例要求增加附加处理设施和方法来提高水质。象常规过滤器一样，用合适的絮凝剂使其附着在微滤器上从而降低dbp由于原水水质的变化性，这种方法的dbp除去率在5%到70%范围内变化。膜滤是利用物理方法使颗粒和微生物除去，因此并不需要通过投加絮凝剂来达到过滤作用。这种工艺可以尽可能完善的除去nom。用絮凝剂与微滤/超滤工艺相结合并不是一种新工艺。在早期工业废水中，人们已用絮凝剂如明矾、铁盐和聚合氯化物等来沉淀去除那些不能溶解的金属。一般用助凝剂的用量，水中色度的减少和含磷量的降低来评价这种处理工艺的效果。使用絮凝剂时要合理，它要能改变水的过滤性，使无机物能很好的去除，为此，要改进操作和反冲洗体制。絮凝剂也因除去有机物从而使膜上的污垢增厚，影响过滤。这种工艺技术优点有如下：去除nom高，因为过滤膜对粒子的去除率高；絮凝剂缔结很低因为在过滤之前还未产生大的可沉淀的絮凝体；可以根据颗粒的去除而优化絮凝剂的化学和凝聚作用，且絮凝剂也可被当作颗粒物去除，因此nom去除率高。絮凝剂的投加量则要根据絮凝剂和溶液中的成分之间的反应关系来确定。絮凝剂的反应动力很快，在絮凝剂刚刚加入的几秒内就会反应完全。絮凝剂可在泵的吸入管处投加，然后快速混合。絮凝剂的投加速度要略少于常规过滤，这是因为它所形成的絮凝物并不是所要除去的目标。水的化学因素,包括ph的范围可以调到最佳值，使有机物能通过物理分离的方法过滤而被去除。6 结论净水处理的实际操作要根技术规章要求做适当的调整。规章规定为了确保人民的身体健康，消费者从自家水龙头下取得的水必须要达到水质标准。水处理厂(wtp)的处理效率严格规定从配水系统出来的水质要稳定且质量要好。这就意味着水处理厂需要更多的综合的净水处理装置设备，而且也要保护原水水质和确保净化了的水在输送系统中不变质。规章要求如swtr和eswtr对常规过滤中水的颗粒物和微生物去除率要求很高，而用过滤性能好的mf/uf可以完成上述要求。mf/uf和常规混凝相结合对去除dbp的前体物的效果跟常规过滤装置的效果差不多。这种处理方法的好处就是对浊度和颗粒物以及微生物的去除效果好且不会影响nom的去除。所以，可用强化混凝来提高nom的去除率，也可使在后期处理中的形成的dbp减少。因此，经这样处理过的水出水水质就很好。膜处理法作为处理工艺的一种，越来越被重视，特别是常规工艺出现问题或是处理结果答不到要求时，膜处理就很重要了。 文献原文the use of membrane filtration in conjunction with coagulationprocesses for improved nom removaljames c. vickers*, mark a. thompson, and uday g. kelkarmalcolrn pirnie inc., 11832 rock landing drive, ste. 440, newport news, ua 23606-4206, us.4tel:804-8738700, fax: 804-8738723abstractchanges in regulatory requirements and the forthcoming disinfectant/disinfection by-products (d/dbp) rule will require that drinking water treatment facilities be operated to achieve maximum removals of particles and disinfectant tolerant microorganisms as well as natural organic matter (nom). for the conventional water treatment plant, this may require balancing coagulation requirements for maximum particle and turbidity removal efficiency, as required by the surface water treatment rule (swtr) 1 and enhanced surface water treatment rule (eswtr), with the enhanced coagulation requirements as required by the d/dbp rule. for drinking water production, the use of membrane filtration processes such as microfiltration and ultrafiltration (mf/uf) to satisfy the turbidity, particle and microorganism removal requirements of the swtr is well established 2,3.without pretreatment, mf/uf treatment processes can achieve only nominal(10 percent) removal of disinfection by-products (dbp) precursors 4. however, these processes can be used in combination with conventional coagulation chemistry 5 or powdered activated carbon (pac) 6 to achieve similar removals of nom. the role of mf/l1f as a treatment technique will evolve as more information is developed on how to apply the processes to meet current and future water quality objectives.1 .conventional coagulation for particle removaldrinking water from surface water supplies is typically produced using the conventional treatment process.this process is characterised as a physio-chemical separation process.the conventional treatment process consists of a multiple step sequence of coagulant addition/mixing,flocculation,sedimentation and media filtration to achieve the desired particle removals. conventional treatment processes require the use of a coagulant to achieve the filtration objective.coagulant use is necessary to achieve charge neutralization and facilitate particle aggregation necessary for the sedimentation and filtration processes to work properly. variations in the daily and seasonal raw water quality and chemistry issues such as ph, alkalinity, total organic carbon (toc), and temperature determine the optimum coagulant dose.control of coagulant addition is often developed empirically using jar testing and is only achievable by monitoring the raw water quality and performing proportional adjustments of chemical dosings. the changein coagulant dose must be made at the time ofthe raw water change and to the proper level.his process has inherent disadvantages inthat the actual rate required may be over orunder what is necessary.turbidity of the water from the sedimentation basin has been historically used as the primary indicator of overall process efficiency and is key to maintaining the operational performance of media filters.using turbidity as the process indicator has the following operational benefits:一reduces particle loading rates on the mediafilters一improves filtered water turbidity一minimizes filter backwashing and downtime.the ph of coagulation has a significant effect upon settled water turbidity. in general,for optimum turbidily reduction, the ph of coagulation should be between 6.5 and 7.07.2.conventional coagulation for nom removalnew regulations such as the d/dbp rule arc being developed to in order to address the presence of nom. nom occurs as a result of the degradation of plant and animal matter and is an important contributing factor to the formation of dbps. nom can be measured indirectly through toc analysis.operation of the water plant will focus on removal of turbidity while minimizing the formation of dbps. this will require that physical and chemical parameters be closely monitored and adjusted to compensate for variances in incoming raw water quality process changes such as discontinuing prechlorination and the use of alternative disinfectants such as chloramine, chlorine dioxide and ozone have been implemented to address the d/dbp issues.further reductions in dbp formation is being sought through the process ofenhanced coagulation. enhanced coagulation will require that a water supply achieve a certain level of nom removal.enhanced coagulation is regulatory concept defined by a two step process. stage 1 of the d/dbp rule may require that water utilities meet a level of toc removal dependent on raw water alkalinity.the toc removal must be achieved prior to the addition of achemical disinfectant,such as chlorine.for utilitieswhich practice conventional treatment,meeting the required toc removal level may likely require reevaluation of existing coagulant strategies anc optimizing coagulation.if the system can meet the applicable toc removal percentage by increasing coagulant dose, it has met the enhanced coagulation requirement.the proposed regulatory requirements for toc removal are shown in table 1.table 1 required percent removal of toc for enhanced coagulationif the system cannot meet the above criteria, the system determines the coagulant dose for enhanced coagulation by conducting jar tests, at prescribed ph conditions.the enhanced coagulation dose is defined as the dose at which an additional 10mg/1 of coagulant does not produce a corresponding 0.3 mg/1 reduction in toc.in addition to the future requirements forenhanced coagulation, some systems may benefit from increasing coagulant dose beyond that required by the d/dbp rule. for example, systems with high raw water toc levels (e.g. southeastern united states) may further reduce dbp formation potential byincreasing coagulant dose beyond future requirements. in general, the optimal ph for toc removal is in the range of 5.0 to 6.0 8 with metal coagulant dosages ranging from 5 to 20mg metal coagulant/mg of toc. the nature and concentration of nom will dictate the treatment process adopted, especially the coagulant type and dose, polymer type and dose, and oxidant type and dose.it should be noted that the process for achieving the required nom/toc removals is by the use of enhanced coagulation.this is in addition to the requirements of the swtr the process of enhanced coagulation is used specifically to only address dbp issues.the requirements for meeting the filtration requirements of the swtr may require modification within the filtration process after changes with the coagulation process are made.these points can be stated as follows:一enhanced coagulation addresses only nom and dbp removal as measured through the reduction of toc,一filtration must still accomplish the turbidity and particle removal requirements of the swtr and forthcoming eswtr.3. lmpact of d/dbp rule on conventional filter plantsthe conventional filtration process will need to be modified to address treatment changes in order to maintain the turbidity and particle removal requirement under the swtr. proposed new regulations such as the eswtr will increase the filtration requirements and incorporate additional microorganism removal requirements, such as cryptosporidicm oocysts. the impact upon individual treatment plants will vary, however,the following statements provide an indicationof the changes that will occur:一the ph of coagulation for optimum nom removal is lower than ph used to minimize settled water turbidity.the d/dpb rule may significantly effect(reduce) the operational performance on conventional media filters as increased coagulant dosages will increase particle loading.一more residuals will be produced from aconventional filter plant.一a number of in process ph adjustments tothe water may be necessary in order tobalance regulatory and operationalrequirements.4.microfiltration and ultrafiltration as atreatment techniquemf/uf are physical separation (sieving)processes.unlike conventional filtration processes, the interrelationship between physical and chemical parameters are not critical to the retention efficiencies the filter.membrane filters primarily act as surface filters, with particles trapped on the filter surface being removed by backwash techniques.the primary benefit of this treatment approach are as follows:4.1. turbidity and microorganism removalmf/uf are highly effective treatment processes for the removal of particles inwater. finished water quality is a primary factor in the evaluation of the system as filtered water turbidities are normally less than 0.1 ntu. variations in filtered water quality are minimal with respect to incoming turbidity levels.membrane filters have been shown to effectively reduce raw waterturbidity levels in excess of 100 ntu without compromising the finished water quality.studies have demonstrated consistently high removal of giardia, cryptosporidium and other microorganisms in excess of 6-log.4.2. consistent finished water qualityan important factor when comparing membrane fihration to conventional filters is what happens when treatment is upset.conventional filters can have breakthrough if chemical additions and treatment conditions are not quickly and properly adjusted however, the filtered water quality from a membrane filter is very consistent despite raw water changes and will continue to produce the same level of microbial and particle removal. membrane filtration systems lose operational performancc such as increasing pressure differentials across the membrane and shortening of the cleaning frequency instead of compromising finished water quality.from the operational perspective,there quirements necessary to operate a membrane system under normal and varying feed water conditions are minimal.filtrate quality of the microfiltration system is achieved without the direct interaction of a control system or intcrvention of an operator.this advantage is of particular importance for small systems where operator involvement is minimal.5. microfiltration and ultrafiltration with coagulants for a combined treatment approachmf/uf as a stand alone treatment process can achieve approximately 10 percent removal of dbp precursors. studies indicate that this matter which contributes to the formation of dbp is in excess of 400 daltons molecular weight yet below a 5,000 dalton molecular weight cut off (mwco) 9.this is significantly less than the approximate mwco of a ultrafilter which is above 5,000 daltons or a microfilter which is in excess of 1,000,000 daltons. as with conventional filtration processes,the use of a coagulant may improve water quality aspects.proposed regulations which address the presence of dbp may necessitate the use of additional treatment techniques or procedures to improve water quality. as with the operation of a conventional filter, the ability of a microfiltration system to achieve dbp reduction using coagulants is site specific and must be optimized for the location.there can be significant variability in dbp removal due to inherent water quality.typical toc removal range from 5 percent to 70 percent. membrane filters utilize a physical barrier to achieve particle and microorganism removal, and therefore do not require the use of a coagulant to achieve the filtration objective. this allows the process chemistry to be specifically optimized for the removal of nom.the use of coagulants in conjunction with mf/uf processes is not new. the use of a coagulants such as alum, ferric salts and polyaluminum chlorides have been previously applied in industrial wastewater applications as part of the precipitation chemistry necessary to remove insoluble metals.the treatment approach has also been evaluated as a flux enhancing agent, to reduce color, or to address phosphorous reduction in astewaters.the concept of using a coagulant follows a rational that coagulant use will alter the filterability of the water, therefore facilitating the operation and backwashing ofa system. coagulant use may also provide additional removal of organic matter which may also contribute to membrane fouling.the possible advantages of this treatment techniauc are as follows:higher nom removals are possible because a membrane filter has higher particle removal efficiency.lower coagulant closings are. possible because a full and settleable floc is not developed prior to filtration.higher nom removals because organic removal coagulation chemistry and coagulant selection can be optimized specifically for nom removal as particle removal is assured.the methodology for coagulant addition is determined by the rate at which the reaction occurs between the coagulant and the solubleconstituent.kinetics of coagulant reactions are very fast and are normally complete within the first few seconds after coagulant addition.coagulant addition may be as simple as flash mixing which may occur atthe pump suction.coagulant addition rates may be less than what i