水中絮体颗粒粒径分布规律的研究

在Friedlande颗粒粒径分布函数的基础上进行理论分析,提出絮凝过程中絮体颗粒粒径的累积分布函数.以水中高岭土和腐殖酸为去除对象,在烧杯搅拌实验确定的最佳混凝条件下,采用颗粒计数仪对絮凝慢速搅拌过程进行监测和分析,利用粒径的累积分布函数对不同慢搅历时的颗粒粒径分布进行研究.通过实验表明:水中高岭土颗粒和腐殖酸为主要污染物时,絮凝过程中絮体颗粒的粒径分布函数不能很好的遵循经验公式得出的幂函数的形式,但是其分布规律能较好的符合对数正态分布.     

絮凝体沉速在线测量方法及其应用研究

提出了在絮凝池在线测量絮凝体沉速的方法,通过连续采集絮凝体图像和计算机数据处理,跟踪絮凝体运动轨迹,从而计算每一个絮凝体的沉速,同时介绍了数据处理的过程和基本算法。将基于该方法的絮凝体沉速测量设备(FVD)应用于临江水厂,对试验结果进行的分析表明,絮凝体沉速既可作为评价絮凝效果的指标,又可作为控制混凝剂加注量的依据。     

吸附架桥机理主导下APAM的多级絮凝效能

对吸附架桥机理主导下阴离子聚丙烯酰胺(APAM)的絮凝过程进行了研究,通过改变絮凝剂投加工况,对比分析常规絮凝与多级絮凝在污染物去除效果、絮体性能、絮体生长动力学与污泥调理能耗等方面的差异。结果表明,相同投药量下,两级絮凝的出水浊度低于三级絮凝和常规絮凝,两级絮凝在最少的APAM投加量(2 mg/L)下达到最低的出水浊度(19.53 NTU);与常规絮凝相比,两级絮凝的絮体成长速率、平均粒径和沉降速率分别增加12.67%、30μm、36.74%。两级絮凝在投加间隔为240 s、投配比为1∶1条件下絮凝效能最优,出水浊度为15.34 NTU,絮体沉降速率为1.1 NTU/s,絮体密度达到1.123 4 g/cm³。絮体破碎再絮凝过程中,两级絮凝与常规絮凝破碎后均能恢复至破碎前水平,但破碎后均出现不可逆的絮体结构破损,粒径在0~100μm的絮体颗粒增多,粒径>400μm的絮体减少,破碎后两级絮凝的絮体强度因子(68.15%)高于常规絮凝(41.63%),两级絮凝的絮体强度和抗破碎剪切能力更高。在剩余污泥调理方面,两级絮凝产生的污泥只需要投加40mg/L的APAM就可以达到最低的滤饼含水率(75.5%)。因此,两级絮凝可以显著提升除浊效能与絮体性能,是强化絮凝的发展方向。     

机械破碎强度对絮体破碎再絮凝过程的影响

采用连续流混凝沉淀反应器,研究了絮凝过程中机械搅拌强度对絮体破碎再絮凝过程以及出水水质的影响。结果发现,絮体破碎再絮凝的平均粒径无法恢复至破碎前的水平,同时絮体内部结构发生了变化。当破碎阶段的搅拌转速为250 r/min时,破碎后的絮体再絮凝程度较高,絮凝结束阶段絮体平均粒径为72.9μm,接近破碎前的水平(76.1μm),同时几何分形维数由未破碎时的1.80降至1.75,说明絮体的内部结构变得更加紧实;近球态絮体的比例升至58.7%,长链态絮体比例则降至41.3%,说明机械破碎可以改变絮体形态;对于浊度为100 NTU的原水,沉淀出水浊度由未破碎时的6.69 NTU降至破碎再絮凝后的5.85 NTU,说明适当地进行机械破碎可以提高絮凝处理效果。     

高浓度悬浊液架桥絮凝分形体的形态学研究

对85kg／m^3的黄河泥沙水进行了高浓度悬浊液架桥絮凝沉降试验，考察了架桥絮凝分形体的形态学特性，并用电镜观察了絮体构造。结果表明，絮体结构及其形成过程具有分形特征；参数“分维D”可用于定量表征分形絮凝体的形态学特性：①絮体生长机制以DLCA与RLCA模式为主，其生长模式从快速混合阶段的分枝状DLCA结构逐步向慢速絮凝阶段的密实RLCA构型演变；②粒径分布在3个区域，其曲线形状类似广义的正态分布，“分维”能定量确定絮体密实性与沉降特性达最佳时的粒径范围；③分形结构的不断演变引起絮体内部渗透性显著不同，分形絮体自由沉降规律不能用Stokes定律进行合理解释；④在一定粒径范围内，絮体有效质量密度与Stokes粒径存在双对数线性关系，絮体的孔隙率是影响其密实性的主要原因；⑤对相同含沙量的泥沙水絮凝时，Al2（SO4）3形成的无机混凝剂絮体结构与高分子架桥絮体分形结构相比，具有絮体粒径小、结构脆弱，能承受的剪切强度G值低等特点。     

聚丙烯酰胺对水泥浆体流动度的影响机理研究

研究了聚丙烯酰胺(PAM)对水泥浆体流动度的影响规律,测试了水泥颗粒的粒径分布、水泥浆体的流变参数和水泥颗粒对减水剂的吸附率,分析了PAM影响机理。结果表明：微量的PAM可使水泥浆体的流动度显著下降;PAM促进了水泥浆体絮凝、提升了水泥浆体的黏度是造成水泥浆体流动度不良的主要原因。     

砂在砂浆中的堆积密度的计算方法

本文将砂浆体中的砂颗粒及其表面包裹着的一层水泥浆膜看作为复合颗粒,从而通过理论计算推导了砂在砂浆体中的堆积密度的计算方法。通过试验确定了公式的参数,并验证了该方法的有效性。通过该方法可以找出在相同流动度下砂在砂浆体中的最佳粒径分布;当给定砂的粒径分布与砂灰比时,可以推算其流动度。     

基于图像处理的烟雾颗粒粒径计算方法研究

介绍了一种基于扫描电镜采集烟雾粒子图像,通过计算机图像处理计算出烟雾粒径的方法.该方法能够准确、实时地测量烟雾粒径,是扫描电子迁移粒径谱仪等仪器测量烟雾粒径的有效补充,也可以作为其测量结果的标定.     

新型聚铝硅絮凝剂用于微污染原水的直接过滤研究

以TEOS为硅源制备了新型聚铝硅絮凝剂(TEOS-PAC),并将其应用于处理微污染原水的直接过滤工艺,研究了滤前水中絮体的粒径分布以及絮凝时间、投药量对处理效果的影响,分析了滤床各层的截污情况,并与硫酸铝、聚合氯化铝、聚硅酸铝等絮凝剂作了比较.结果表明:TEOS-PAC具有形成絮体快、絮体小且密实、投药量少、过滤周期长、所需床层浅、处理效果好等优点,是采用直接过滤工艺处理该类原水的适宜絮凝剂.     

超塑化剂对新拌水泥浆体多级絮凝结构的影响

在运用光学显微镜观察絮凝结构的基础上,构建了新拌水泥浆体多级絮凝结构模型.应用旋转黏度计测试了掺不同类型超塑化剂新拌水泥浆体的流变参数,探讨了不同类型超塑化剂对新拌水泥浆体多级絮凝结构的作用.结果表明:掺加不同类型的超塑化剂后,新拌水泥浆体的回滞圈面积大小不一,这是由于不同类型超塑化剂可以分散不同水泥颗粒结合力形成的不同级次新拌水泥浆体絮凝结构的缘故;超塑化剂的分散能力越强,新拌水泥浆体中絮凝结构越小、分散越均匀,新拌水泥浆体流动性就越好.     

基于图像处理的混凝控制方法研究

根据絮体等效直径与沉淀出水浊度具有很好的相关性这一特征,采用计算机实时采集和图像处理的方法对絮体图像进行定量分析得到等效直径,并将其作为控制混凝剂加注量的目标值,实现水处理过程中混凝剂添加的自动控制。     

混凝剂加注量的自动控制新方法

报导了净水过程中使用计算机实时采集和定量分析絮凝池絮体图像,算出絮体沉淀“等效直径”作为控制混凝剂加注率的目标值,并用进水流量和沉淀水浊度信号自动修正目标设定植,加注量为进水流量与加注率之积。实验数据表明,该方法能适应水质和其他因素的变化自动调整加注量,达到了稳定沉淀水浊度的目的。     

混凝剂中的铝形态对藻类混凝过程的影响

为了考察混凝剂中的铝形态对藻类混凝过程的影响,使用3种具有不同铝形态分布的混凝剂对含藻水进行了混凝试验。结果表明,硫酸铝由于具有较低含量的Alb,电中和能力较差,故需要较大的投量才能去除藻类,形成絮体;含藻水体系中的有机物主要是腐殖酸及富里酸类物质,微生物代谢产物(SMP)在硫酸铝作混凝剂时得到较好的去除,而腐殖酸及富里酸的去除率较低可能是造成硫酸铝混凝效果较差的原因;Alc(Al(30))在混凝中的作用机理主要是吸附架桥作用,可有效去除水体中的有机物,Al₁₃的主要作用机理是电中和作用,可以有效去除水体中的颗粒物;Al₁₃与Al₃₀由于具有形态的稳定性,其混凝过程受pH值的影响较小。絮体强度因子随着pH值的升高先增大后减小,Al₁₃作混凝剂时絮体恢复因子随pH值的升高先增大后减小,而其他两种混凝剂所形成絮体的恢复因子随pH值的升高而增大。     

Floc structural characteristics using conventional coagulation for a high doc, low alkalinity surface water source

Removal of natural organic matter (NOM) is well established using metal salt coagulants. In addition, flocculant aids are also commonly used to improve solid removal. The objectives of this paper is to describe the impacts of both NOM and polymer on floc structure. The study offers a comparison of floc physical characteristics for coagulant precipitate flocs, organic-coagulant flocs and organic-coagulant-polymer flocs for optimum coagulant and polymer doses. A ferric sulphate-based coagulant was used as the primary coagulant and the polymer selected was a high molecular weight (MW) cationic polydiallyldimethylammonium chloride (polyDADMAC). Floc size, breakage, re-growth and settling characteristics were measured. Precipitate flocs were larger than organic flocs and had better settling characteristics when compared to NOM-coagulant flocs. When polymer was added, floc size and compaction was seen to further reduce. An explanation was offered in terms of the mode of flocculation involved. Floc breakage behaviour showed that polymer reduced the rate of floc degradation but did not greatly improve floc re-growth potential after breakage, which was generally poor for all of the suspensions.     

A study of titanium sulfate flocculation for water treatment

There are limited studies available on titanium salt flocculation. In this research, coagulation experiments of titanium sulfate were conducted using both distilled water and kaolin clay suspension. Results showed that titanium sulfate flocculation was most effective in the pH range 4-6, and negligible concentrations of titanium were found in the well-flocculated water. The floc isoelectric point (IEP) was found to be near pH 5. Measurements showed that the titanium flocs possessed greater density, diameter and settling velocity than the aluminum flocs. The titanium flocs were composed of TiO(OH)₂, which would change from the amorphous phase into anatase titanium dioxide under elevated temperatures. Floc images showed the structural similarity of titanium and aluminum flocs. Laboratory results and a pilot experiment showed that titanium sulfate could be an alternative coagulant for water and wastewater treatment.     

The impact of pH on floc structure characteristic of polyferric chloride in a low DOC and high alkalinity surface water treatment

The adjustment of pH is an important way to enhance removal efficiency in coagulation units, and in this process, the floc size, strength and structure can be changed, influencing the subsequent solid/liquid separation effect. In this study, an inorganic polymer coagulant, polyferric chloride (PFC) was used in a low dissolved organic carbon (DOC) and high alkalinity surface water treatment. The influence of coagulation pH on removal efficiency, floc growth, strength, re-growth capability and fractal dimension was examined. The optimum dosage was predetermined as 0.150 mmol/L, and excellent particle and organic matter removal appeared in the pH range of 5.50-5.75. The structure characteristics of flocs formed under four pH conditions were investigated through the analysis of floc size, effect of shear and particle scattering properties by a laser scattering instrument. The results indicated that flocs formed at neutral pH condition gave the largest floc size and the highest growth rate. During the coagulation period, the fractal dimension of floc aggregates increased in the first minutes and then decreased and larger flocs generally had smaller fractal dimensions. The floc strength, which was assessed by the relationship of floc diameter and velocity gradient, decreased with the increase of coagulation pH. Flocs formed at pH 4.00 had better recovery capability when exposed to lower shear forces, while flocs formed at neutral and alkaline conditions had better performance under higher shear forces.     

Breakage and re-growth of flocs: effect of additional doses of coagulant species

Several polyaluminum chloride (PACl) coagulants were prepared, with different OH/Al ratios (B values), and characterized by Ferron assay. These were used in studies of floc formation, breakage and re-growth with kaolin suspensions under controlled shear conditions, using a continuous optical monitoring method. Particular attention was paid to the effect of small additional coagulant dosages, added during the floc breakage period, on the re-growth of broken flocs. The results showed that the re-growth ability was greatly dependent on the nature of the PACl species added as second coagulant. The re-growth ability of broken flocs was greatest when the second coagulant was PACl₀ (i.e. AlCl₃, with B = 0) and least with PACl₂₅ (B = 2.5). In the latter case there was no effect on floc re-growth, irrespective of the initial coagulant used. PACls with intermediate B values gave some improvement in floc re-growth, but less than that with PACl₀. Additional dosage of PACl₀ gave re-grown flocs about the same size or even larger than those before breakage. The re-growth of broken flocs is significantly correlated with the species Al_a (monomeric) and Al_b (polymeric), as determined by Ferron assay. The amorphous hydroxide precipitate formed from PACl₀, (mainly Al_a) can greatly improve the adhesion between broken flocs and give complete re-growth. However, for PACl₂₅, mostly composed of Al_b, the nature of the precipitate is different and there is no effect on floc re-growth.     

Effect of two-stage coagulant addition on coagulation-ultrafiltration process for treatment of humic-rich water

A novel two-stage coagulant addition strategy applied in a coagulation-ultrafiltration (UF) process for treatment of humic-rich water at neutral pH was investigated in this study. When aluminum sulfate (alum) doses were set at a ratio of 3:1 added during rapid mix stage and half way through flocculation stage, the integrated process of two-stage alum addition achieved almost the same organic matter removal as that of conventional one-stage alum addition at the same overall dose. Whereas membrane fouling could be effectively mitigated by the two-stage addition exhibited by trans-membrane pressure (TMP) developments. The TMP developments were found to be primarily attributed to external fouling on membrane surface, which was closely associated with floc characteristics. The results of jar tests indicated that the average size of flocs formed in two-stage addition mode roughly reached one half larger than that in one-stage addition mode, which implied a beneficial effect on membrane fouling reduction. Moreover, the flocs with more irregular structure and lower effective density resulted from the two-stage alum addition, which caused higher porosity of cake layer formed by such flocs on membrane surface. Microscopic observations of membrane surface demonstrated that internal fouling in membrane pores could be also remarkably limited by two-stage alum addition. It is likely that the freshly formed hydroxide precipitates were distinct in surface characteristics from the aged precipitates due to formation of more active groups or adsorption of more labile aluminum species. Consequently, the flocs could further connect and aggregate to contribute to preferable properties for filtration performance of the coagulation-UF process. As a simple and efficient approach, two-stage coagulant addition strategy could have great practical significance in coagulation-membrane processes.     

混凝沉淀工艺深度处理污水厂二级出水的混凝剂优化

通过烧杯试验，确定了采用混凝、沉淀工艺深度处理城市污水处理厂二级出水时，最佳的混凝剂组合及投量。结果表明，铝盐混凝剂与PAM组合使用时比铁盐混凝剂与PAM组合使用时的处理效果更好，当PAC＋PAM的组合投量为20mg／L＋5mg／L或30mg／L＋1mg／L、硫酸铝＋PAM的组合投量为30mg／L＋5mg／L时，混凝、沉淀出水浊度为2．5～3．5NTU，COD为25-40mg／L，TP为0．06-0．12mg／L。由于混凝后水中所形成的絮体较小，难于沉淀，因此混凝沉淀工艺对SS的去除效果较差，实际工程中可考虑增设过滤单元。