一种改进的聚合模型在污泥絮凝-沉降模拟中的应用

鉴于在试验中难以观测到污泥絮团的粒径分布情况,且以往类似模拟中鲜有考虑絮团分形特征及絮团黏结效率的问题,通过一种改进的聚合模型来模拟污泥颗粒间的分形聚合机理,并在群体平衡模型(PBM)和两相流Mixture模型基础上对污泥的絮凝-沉降进行三维数值模拟。模拟结果表明:建立的数学模型能较好地反映黏性污泥分形絮凝-沉降规律,具预测絮团粒径分布的能力;在同一时刻絮团的粒径分布范围随着分形维数的降低逐渐变宽,大粒径絮团数量迅速增加,小粒径絮团数量逐渐减少;初始颗粒数量的衰减速率随分形维数的增大而增大;絮团数量总体呈先增加后减少的趋势,但当分形维数不同时,其最大值随分形维数的增大而增大,出现时间随着分形维数的增大而有所缩短。     

纳米SiO2与聚氯化铝对含表面活性剂原水的絮凝效果研究

借助图像分析技术与分形理论,对含十二烷基硫酸钠(SDS)高岭土颗粒的动态絮凝过程、絮体分形结构的形态学特征、纳米SiO2与聚氯化铝(PAC)对剩余浊度与SDS的去除效果进行了研究分析。结果表明:①SDS存在时,高岭土颗粒表面ζ电位绝对值增加,且高岭土原始粒径略有增大;②投加PAC,剩余浊度降低明显,但SDS的表观去除率较低;③升高水温对浊度与SDS去除效果有改善;④纳米SiO2能显著提高PAC对浊度与SDS的去除效果,悬浊液中絮体粒径增大,絮团内部孔隙率较高,沉速加快,分维值下降。     

PAC为混凝剂时高岭土悬浊液的混凝条件及絮凝体形态学特征

通过显微摄像仪对絮凝体的形成过程及其形态学特性进行了系统的研究.试验结果表明,高岭土悬浊液的最佳混凝pH为7～8,在低投药量时,压缩双电层和吸附电中和是主要的混凝机理,在高投药量条件下,则是卷扫絮凝起主导作用.絮凝体平均粒径和分形维数都随搅拌时间的延长而增大,并最终趋于稳定.在pH=7和以PAC作为混凝剂的条件下,形成的絮凝体最大粒径为0.45 mm,对应的分形维数约为1.68.随着投药量的增大,絮凝体分形维数的变化较小,但絮凝体平均粒径显著增加.当投药量过高时,网扫絮凝作用下的絮体结构松散,抗剪切能力差,絮凝体分形维数略有下降(1.60),但絮凝体平均粒径减小明显,降至0.25 mm左右.     

PDMDAAC复合PAC用于冬季低温低浊黄河水研究

阐述用有机阳离子高分子聚二甲基二烯丙基氯化铵(PDMDAAC)与无机混凝剂复合物对冬季低温低浊黄河水的脱浊处理研究过程。通过混凝烧杯实验,考察了药剂投加量及PAC与PDMDAAC的复合配比对低温低浊黄河水脱浊效果的影响。结果表明,对温度为8℃左右,浊度在50NTU以下的黄河水,PDMDAAC对PAC强化混凝脱浊效果明显,PAC与PDM-DAAC的复合配比越低,复合混凝剂脱浊效果越好。要达到6NTU的水厂沉淀出水余浊标准,PAC需1.3 mg/L左右的投加量,而脱浊效果较好的低复合配比药剂PAC投加量在1.0 mg/L左右,减少残余铝含量20%左右。     

大坝下游河道剖面分形与水力因素的关系研究

基于一维、二维非恒定流分形计算分析模型,对长江某段河道进行横纵剖面的分形维数分析,并建立了与水力因素的相关关系。研究结果表明:该段河道纵剖面分形维数呈二阶分维特征,整体的分形维数小于分段分形维数;流量越大,河道越短,纵剖面的分形维数越小;分析得到的横剖面分形维数呈一阶分维特征,水越深,横剖面的分形维数越大;通过综合分析得到了剖面分形维数与通航水力指标的关系,认为该段的最大水流速度不应大于3.5m/s。     

紊动对黏性细颗粒泥沙絮凝沉降影响的试验研究

利用室内环形水槽及高倍摄像设备,定量研究了不同悬沙浓度及紊动剪切对黏性细颗粒泥沙絮凝沉降特性的影响。试验中观测到的絮团粒径为分散颗粒的几倍到几十倍,絮团中值粒径随着水体紊动剪切的增大呈先增大后减小的变化趋势,最大的中值粒径约为150μm,出现在紊动剪切为30 1/s条件下。悬沙浓度的增大促进絮团的发育,在350 mg/L条件下形成的絮团整体粒径比150 mg/L条件下的更大。絮团中值沉降速度在0.7～3.4 mm/s之间,絮团最大的中值沉速出现在紊动强度最大时65 1/s,此时所形成的絮团结构密实,有效密度较大。絮团有效密度随着粒径的增大而减小,研究表明,采用变分形维数方法,对有效密度随粒径变化的模拟结果与试验结果吻合较好。     

河道形态特征的随机分形模拟

应用随机分形理论中的一维和二维RMD模型,在给定平面区域上生成了不同分形维数、粗糙程度及分辨率的河道剖面轮廓及床面形态。结果表明:不同分形维数的河道剖面轮廓或床面形态具有相似的微观粗糙结构,且随着分形维数的增大,结构复杂程度提高,粗糙度的峰谷位置不变,但各点的幅值将发生不同程度的变化。     

黄河原水絮体分形及分形维数研究

水的混凝处理过程中,絮凝体的结构具有分形构造特征,直接影响着水处理的固液分离效果,若絮凝体较为密实,形态结构紧凑,则易于沉降.依据分形理论,以郑州段黄河原水为研究对象,借助电子显微镜和图像分析系统,考察了絮凝体分形维数与混凝剂投量、沉后水浊度、UV254、CODMn之间的关系.结果表明,絮体分形维数的变化能够很好地反映絮凝程度及处理效果,可作为自来水厂进行混凝控制的参数.     

基于耗散粒子动力学的剪切流中黏性沙絮凝机理研究

基于介观尺度下的耗散粒子动力学方法,建立了包含力场势函数的均匀各向同性紊流模型,对不同剪切率条件下黏性泥沙的絮凝过程及絮团形态进行了模拟计算。结果表明:随着剪切率的增大,体系中絮团初始出现的时间先急剧减小,后经短暂平稳过渡,又迅速增大,最后基本保持不变;水体剪切率较小时,非键能减小速度较快,随着剪切率进一步增大,非键能减小速度逐渐变缓,体系稳定性逐渐降低;当剪切率较小时,絮团形态更为致密,分形维数逐渐增大;随着剪切率的进一步增大,伴随有多个小絮团出现,分形维数逐渐减小,最终保持在1.12左右;在紊动剪切条件下,体系中絮团一直处于碰撞、絮凝、破碎的动态过程。     

四氯化锆与硫酸铝处理微污染水的絮体形态及强度

以某微污染水库水为研究对象,采用激光粒度仪对四氯化锆(Zr Cl4)和酸铝(Alum)的絮凝、破碎及再絮凝过程絮体粒径进行了在线监测,对比考察了不同PH条件下,2种混凝剂形成的絮体的粒径、生长速率、分形维数及强度。     

Effects of flocculent aggregates on microfiltration with coagulation pretreatment of high turbidity waters.

Immersed membrane systems, and those with in-line coagulation, have been extensively applied in drinking water systems. Sedimentation is usually replaced by membrane processes in both systems. In these systems, voluminous flocculent aggregates formed during coagulation could be potential foulants. When raw waters with high turbidity are introduced, particle loadings to membrane due to coagulation pretreatment are enormous and thus could increase fouling. In general, during the rainy season, the turbidity of the Han River water, which supplies drinking water for the City of Seoul, Korea, is more than a hundred times higher than usual. Therefore, effects of floc on membrane fouling were investigated with highly turbid waters. Two turbidity concentrations, 40 and 200 NTU, were formulated by the addition of kaolin (used as a natural particle surrogate) to the Han River raw water. The results showed that the flux decline behaviours of the highly turbid waters were different from those of natural raw water. Coagulation pretreatment was very effective at reducing membrane fouling. Flocculent aggregates showed a negative effect on the flux decline but a positive effect on the membrane cleaning efficiency.     

The effect of polymeric flocculants on floc strength and filter performance.

Polymeric flocculants are widely used throughout the water industry as flocculant aids, they are known to increase floc density and aid settlement in the clarification stage of the water treatment process. In this research, polymeric flocculants were used to improve floc strength prior to filtration on a dissolved air flotation (DAF) plant in an attempt to prevent filter breakthrough. A modified jar test procedure using a PDA (photometric dispersion analyser) optical flocculation monitor was developed in order to evaluate the system floc strength. Filtration trials were carried out on a pilot filter rig situated on a surface water treatment works in Yorkshire. The filter feed originated from the main plant filter channel. Filter performance was assessed by continuous online monitoring of effluent particle counts, turbidity and headloss over the period of the filter run. Results indicated that low doses of polymeric flocculants had a beneficial effect on filtered water quality, as measured by particle counts, turbidity, UV254 absorption and dissolved organic carbon (DOC). Polymeric flocculants also had the effect of extending filter run length. The modified jar test results indicated that the flocculants used improved the floc strength and enhanced reflocculation of the micro flocs present after the flotation process.     

利用溶气气浮工艺强化处理低浊高色富含有机物地表水

低浊高色富含有机物地表水难于混凝,试验采用“混凝-溶气气浮”(“混凝-DAF”)工艺处理此类水,并与常规“混凝-沉淀”工艺进行了比较。结果表明,“混凝-DAF”工艺在较低投药量时能取得更好的处理效果;对于“混凝-DAF”工艺,增大混凝剂投量后出水浊度基本不变,但出水色度及CODMn可进一步降低;“混凝-DAF”工艺去除水中有机物的能力优于“混凝-沉淀”工艺。最后,对“混凝-DAF”工艺去除水中有机污染物的机理进行了探讨。     

Optimizing the coagulation process in a drinking water treatment plant -- comparison between traditional and statistical experimental design jar tests

In this study of coagulation operation, a comparison was made between the optimum jar test values for pH, coagulant and coagulant aid obtained from traditional methods (an adjusted one-factor-at-a-time (OFAT) method) and with central composite design (the standard design of response surface methodology (RSM)). Alum (coagulant) and polymer (coagulant aid) were used to treat a water source with very low pH and high aluminium concentration at Sri-Gading water treatment plant (WTP) Malaysia. The optimum conditions for these factors were chosen when the final turbidity, pH after coagulation and residual aluminium were within 0-5 NTU, 6.5-7.5 and 0-0.20 mg/l respectively. Traditional and RSM jar tests were conducted to find their respective optimum coagulation conditions. It was observed that the optimum dose for alum obtained through the traditional method was 12 mg/l, while the value for polymer was set constant at 0.020 mg/l. Through RSM optimization, the optimum dose for alum was 7 mg/l and for polymer was 0.004 mg/l. Optimum pH for the coagulation operation obtained through traditional methods and RSM was 7.6. The final turbidity, pH after coagulation and residual aluminium recorded were all within acceptable limits. The RSM method was demonstrated to be an appropriate approach for the optimization and was validated by a further test.     

九龙江流域水厂生产废水回用条件的初步研究

以九龙江原水为研究对象,从改善低浊水混凝条件优化净水工艺角度,对生产废水的回用条件和作用规律进行了研究。研究认为:回用具有适当含固率的生产废水可以改善水处理过程的混凝条件,节省投药量,节药率一般为10%～40%;存在改善混凝条件、节省投药量的最佳含固率和最佳混合水浊度范围,最佳含固率为0.1%～0.7%,最佳混合水浊度为60～400NTU;原水浊度是显著影响最佳含固率的因素。当原水浊度小于60NTU时,最佳含固率随原水浊度的升高而增加,当原水浊度大于60NTU时.最佳含固率随原水浊度的升高而降低,最佳混合水浊度表现出相同的规律;在生产过程中,建议以最佳混合水浊度控制生产废水的回用。     

盐度对伊利石不等速沉降絮凝的影响

盐度是影响粘性泥沙絮凝沉降的重要因素之一。将胶体化学中的XDLVO理论引入颗粒沉降三维格子玻尔兹曼模型,模拟黏土矿物质絮凝沉降过程,研究伊利石在不同盐度条件下的不等速絮凝沉降过程。模拟结果表明,伊利石黏结概率随着盐度先增加后保持不变,最佳絮凝盐度在5左右;伊利石絮凝形成的絮团粒径呈现双峰分布,盐度对粒径分布有一定影响。盐水中双电层排斥力受到抑制,起主要作用的是范德华吸引力,使得伊利石颗粒更容易产生絮凝,三维数值模型从细观尺度揭示了盐度对伊利石不等速沉降絮凝的影响机理。     

Effects of addition sequence and rapid mixing conditions on use of dual coagulants.

The performance of dual coagulants in clay suspension was investigated in this study using aluminium chloride and the cationic polymer as coagulants. According to the study results, the performance of dual coagulants was affected by dosage of aluminium chloride. Beneficial effect by use of dual coagulants were only noted when aluminium chloride was underdosed. The addition sequence of coagulants was important for the performance of dual coagulants. Simultaneous addition resulted in the best performance, while addition of the polymer first resulted in the worst performance. Addition of aluminium chloride first resulted in the similar performance as single use of aluminium chloride. Although sulphate ion improved the floc characteristics, similar results were obtained. The effectiveness of rapid mixing depended on dosage of aluminium chloride. Extending rapid mixing (6 min) was beneficial when aluminium chloride was underdosed so that coagulation occurred at the combination region. However, such benefit was not observed at the optimum condition, which belonged to the sweep coagulation region. Different floc formation caused the difference. Extended rapid mixing would be beneficial when collision between clay particles and Al(III) was necessary. However, such benefit would disappear at the optimum condition because rapid mixing could break up the floc already formed.     

A case study of dissolved air flotation for seasonal high turbidity water in Korea.

A DAF (Dissolved-Air-Flotation) process has been designed considering raw water quality characteristics in Korea. Although direct filtration is usually operated, DAF is operated when freshwater algae blooms occur or raw water turbidity becomes high. Pre-sedimentation is operated in case when the raw water turbidity is very high due to rainstorms. A main feature of this plant is that the operation mode can be changed (controlled) based on the characteristics of the raw water to optimize the effluent quality and the operation costs. Treatment capacity (surface loading rate) and efficiency of DAF was found to be better than the conventional sedimentation process. Moreover, low-density particles (algae and alum flocs) are easily separated while the removal of them by sedimentation is more difficult. One of the main concerns for DAF operation is a high raw water turbidity. DAF is not adequate for raw water, which is more turbid than 100 NTU. In order to avoid this problem, pre-sedimentation basins are installed in the DAF plant to decrease the turbidity of the DAF inflow. For simulation of the actual operation, bench and full-scale tests were performed for highly turbid water conditions. Consequently, it is suggested that pre-sedimentation with optimum coagulation prior to DAF is the appropriate treatment scheme.     

活化硅酸助凝剂在给水处理中的应用研究

研究了活化硅酸配制和保存的合适参数,并通过试验得到了对于江苏某湖水,活化硅酸的最佳投加量和投加时间.同时进行了生产性试验,并与PAM做了助凝效果和经济效果的比较分析.结果表明活化硅酸具有良好的助凝作用,并在经济性和安全性上优于PAM.     

强化混凝在微污染水源水处理中的应用

系统分析了微污染水强化常规混凝工艺的研究进展和局限性,阐述了影响强化混凝的主要因素:混凝剂种类的影响,混凝剂投加量的影响,pH值对混凝的影响,以及碱度及原水水质的影响。说明了几种强化混凝方法,展望了强化混凝处理技术在微污染水源水处理中的应用。