硫酸铝作为混凝剂时絮体破碎与再絮凝的研究

以硫酸铝为混凝剂,采用智能光散射分析仪(IPDA)对絮体破碎与再絮凝过程进行连续在线监测,考察了pH值和硫酸铝投量对絮体形成及破碎后再絮凝的影响.结果表明:当电性中和作用占主导时(硫酸铝投量为O.12 mmol/L,以Al计),絮体破碎后能继续再絮凝,高岭土-铝体系中产生的絮体恢复因子高达117%,高岭土-腐殖酸-铝体系中产生的絮体恢复因子高达110%;当网捕卷扫作用占主导时(硫酸铝投量≥0.2 mmoL/L),絮体破碎后不能完全恢复,恢复效果不如电性中和作用下的;腐殖酸的存在明显影响絮体形成和破碎后再絮凝过程的絮凝指数.     

水中单宁酸对PAC混凝过程的影响

配制浊度为(50.0±0.50)NTU的粘土悬浊液作为试验原水,以聚合氯化铝(PAC)为混凝剂,探讨在投加植物多酚单宁酸前、后混凝沉后水的剩余浊度、pH、Zeta电位、溶解性有机物浓度、残余铝的变化规律;同时借助光学显微镜和原子力显微镜对不同混凝条件下的絮体进行了形态观测分析,进而阐述水体中天然有机物对混凝过程的影响。结果表明,水中存在有机物单宁酸会使PAC的混凝效能变差,而且这种影响与单宁酸的浓度呈正相关,不仅增加了所需混凝剂的量,而且改变了水中颗粒物的带电特性、降低了颗粒的Zeta电位、增加了胶体颗粒的稳定性。单宁酸对PAC混凝过程中生成絮体的宏观形态和微观形貌都有一定的影响。若原水中含有单宁酸,当PAC投量不足时难以形成絮体,而投加足量的PAC时,单宁酸能起到吸附架桥的作用,吸附、包裹无机颗粒一起凝聚,生成大而密实的絮体,絮体显微结构上呈现出明显的亲水层。     

碳纳米管改性聚合氯化铝处理腐殖酸溶液研究

碳纳米管由于其特殊的吸附性能,对在天然水体中广泛存在的腐殖酸(HA)具有良好的吸附性,可用于腐殖酸的去除。对不同DOC含量和p H值条件下碳纳米管吸附去除腐殖酸以及使用碳纳米管改性聚合氯化铝(PACl)作混凝剂时混凝过程中絮体的形成与破碎进行了研究。结果表明:当水样DOC为4 mg/L、p H值为7.5时,使用不加碳纳米管的PACl作混凝剂,投加量为0.1 mmol/L时沉后水DOC浓度达到最低。碳纳米管对腐殖酸的吸附去除率随p H值的升高而下降,随碳纳米管含量的增加而增加,吸附主要发生在前60 min内。随着DOC含量的升高,混凝过程对DOC的去除率下降。当p H值为7.5、DOC为2 mg/L时,碳纳米管含量对于平衡时絮体的粒径无明显影响,但可以增加再生长后絮体粒径,改善絮体的沉降性,提高混凝效果。     

水源水质对混凝过程的影响及无机复合絮凝剂应用

混凝是水处理过程的常用工艺,良好的混凝效果对于保证优质的饮用水供应具有重要的意义。由于受研究手段的制约,目前有关原水水质、混凝剂的形态与组成对混凝过程影响的研究较为缺乏。采用南方某市水厂水源水进行了一系列的混凝试验,并针对混凝效果不佳的情况进行了新型复合药剂的制备与应用,结果表明:相比于水厂目前使用的聚合氯化铝(PACl),Al_(13)在去除浊度方面有显著优势,但水体中有机物浓度过高会在一定程度上限制Al_(13)的混凝效果。相比于浊度的去除,混凝对水体中有机物的去除需要更大的投药量。HCA作为一种阳离子有机絮凝剂,在被引入无机混凝剂之后可以显著增强复合药剂的电中和能力,在保证低投药量的同时,还能有效地提高对有机物的去除率,增大平衡时絮体的粒径,改善絮体的沉降性。     

复合混凝剂的强化混凝效果及絮体分形结构变化

将聚合氯化铝(PAC)分别与高锰酸钾、水合二氧化锰进行复配而得到复合混凝剂,研究了两种复合混凝剂对微污染水源水的处理效果,并考察了投药量、投药方式对混凝效果的影响,同时还对混凝过程中絮体结构的变化进行了研究。结果表明,两种复合混凝剂均具有良好的去除浊度和有机污染物的能力,当PAC投量为15 mg/L时,两种复合混凝剂分别在KMnO4投量为0.1 mg/L、水合MnO2投量为0.15 mg/L时达到最佳混凝效果。絮体分维值能很好地描述絮体结构的变化规律,在混凝过程中,两种复合混凝剂的絮体分维值均表现出先增(均在360 s时达到最大值)后逐渐减小的规律,可见絮体经历了从小到大、从松散到密实再到松散的过程。     

混凝沉淀法去除富营养化景观水体中磷和藻类的试验研究

考察了采用硫酸铝(Al2(SO4)3·18H2O)和三氯化铁(FeCl3·6H2O)为混凝剂对富营养化景观水中磷和藻类的去除效果,并通过正交试验确定了最佳反应时间、混凝剂投加量和pH值.试验结果表明,两种混凝剂单独使用均可有效去除水中藻类和磷酸盐.Al2(SO4)3比FeCl3更适用于混凝沉淀去除富营养化景观水体中的藻类和磷.     

微气泡水力空化强化混凝除藻的试验研究

利用微气泡水力空化装置强化混凝沉淀去除水体中的藻类。结果表明,微气泡水力空化可以有效地提高混凝除藻效果,减少混凝剂用量。当混凝剂投加量为1 mg/L时,水力空化预处理5 min,对藻类的去除率较空白样提高13%,而空化预处理20 min则藻类去除率提高30%。对藻类的去除率均为65%时,1 h的水力空化可以减少50%的混凝剂投加量。微气泡水力空化时间和空气流量对强化混凝效果有很大的影响,在空化处理时间为10~20 min、空气流量为0.5~0.8L/min的条件下,可以达到最优的除藻效果。p H值的变化也直接影响除藻率,在p H值=8的弱碱性条件下,对藻类的去除效果最为理想。水力空化也可以提高混凝对UV254和浊度的去除效果。     

聚苯乙烯微塑料对自来水厂混凝絮体的影响

混凝是净水工艺中不可或缺的环节,而微塑料在原水中客观存在。以聚苯乙烯（PS）为例,分析了微塑料对混凝过程中浊度去除效果、絮体大小和分形维数的影响。结果表明,当混凝剂投加量为14 mg/L时,微塑料的存在导致浊度去除率降低了7.1%,絮体大小与分形维数也相应降低;当投加量增加至26 mg/L时,微塑料可使浊度去除率提高0.8%,达到95.2%,分形维数增大至1.587,絮体粒径无明显变化。说明在混凝剂投加量较低时,微塑料的存在对浊度去除效果、絮体粒径及分形维数有负面影响,但随着混凝剂投加量的继续提高,负面影响减弱,微塑料的存在甚至还可以促进浊度去除和分形维数的提高。     

具有氧化性能混凝剂的研发及对有机物的去除效果

通过将零价纳米铁(nZVI)与Al_(13)进行复配,研发了兼具原位氧化功能的高电荷聚合态混凝剂nZVI@Al_(13),考察了nZVI、Al_(13)不同配比和pH值等因素对有机物去除效果、分子质量分布及结构组成的影响。结果表明,混凝剂复配后,Al_(13)中高聚合态铝含量增加,提高了混凝剂的混凝效率。中性条件下,腐殖酸(HA)去除率随Al_(13)投量的增加先增大后趋于平缓,Al_(13)的最佳投量为0. 03 mmol/L,此时HA去除率约为70%;单独nZVI对HA的最大吸附去除率仅为10%; nZVI和Al_(13)复配后对HA的去除效果好于单独两种方式的加和,nZVI对Al_(13)的强化混凝起到协同作用。当pH值 7. 0时,过多的OH~-使得Al_(13)解聚,影响混凝效果,nZVI和Al_(13)对HA的去除效果均有所下降。当pH值7. 0时,复配混凝剂对HA的去除率均优于单独Al_(13),最大去除率达到84%。复配混凝剂对分子质量2 000 u的有机物的去除效果较单独Al_(13)提高了约8%。     

悬浮澄清池中高密度絮体的特性分析

阐述了混凝剂与助凝剂联合投加形成的高密度絮体对悬浮澄清池中水流微观流态、絮凝反应颗粒之间的凝结力和碰撞的或然率等的影响,解释了其去除浊度和有机物效果良好的试验事实,并对高密度絮体形成的条件进行了分析。     

Enhanced coagulation for high alkalinity and micro-polluted water: the third way through coagulant optimization

Conventional coagulation is not an effective treatment option to remove natural organic matter (NOM) in water with high alkalinity/pH. For this type of water, enhanced coagulation is currently proposed as one of the available treatment options and is implemented by acidifying the raw water and applying increased doses of hydrolyzing coagulants. Both of these methods have some disadvantages such as increasing the corrosive tendency of water and increasing cost of treatment. In this paper, an improved version of enhanced coagulation through coagulant optimization to treat this kind of water is demonstrated. A novel coagulant, a composite polyaluminum chloride (HPAC), was developed with both the advantages of polyaluminum chloride (PACl) and the additive coagulant aids: PACl contains significant amounts of highly charged and stable polynuclear aluminum hydrolysis products, which is less affected by the pH of the raw water than traditional coagulants (alum and ferric salts); the additives can enhance both the charge neutralization and bridging abilities of PACl. HPAC exhibited 30% more efficiency than alum and ferric salts in dissolved organic carbon (DOC) removal and was very effective in turbidity removal. This result was confirmed by pilot-scale testing, where particles and organic matter were removed synergistically with HPAC as coagulant by sequential water treatment steps including pre-ozonation, coagulation, flotation and sand filtration.     

Chemical aspects of coagulation using aluminum salts—II. coagulation of fulvic acid using alum and polyaluminum chloride

This is the second of a two-part series investigating chemical aspects of coagulation using AI salts. Part I of the series examined the hydrolytic reactions of AI. In this paper, the coagulation of fulvic acid (FA) by alum and polyaluminum chloride (PACI) is examined. An Al speciation methodology was used to examine complexation reactions between Al and FA for water treatment conditions. From pH 5 to 7 and at typical coagulant doses, hydrolysis and complexation of Al is described by a simple model based on the reaction stoichiometry between AI, FA and OH⁻. Model results show that when alum is used as a coagulant, Al complexed with FA is hydrolyzed to a ligand number, This is similar to the ligand number for the prehydrolyzed PACI and explains similarities in dose requirements for these coagulants. Effects of temperature on coagulation performance are shown to be largely chemical in nature. Chemical aspects of coagulation are discussed and the importance of complex formation in coagulation is examined.     

Effects of raw water conditions on solution-state aluminum speciation during coagulant dilution

The speciation of aluminum in solutions of alum and various prehydrolyzed, aluminum-based water treatment coagulants was investigated by 27Al NMR at 5 degrees C and 25 degrees C. Alum solutions were seen to contain only mononuclear species including an AlSO4(+) complex, while the prehydrolyzed coagulant solutions contained polynuclear aluminum species, as well. The relative proportions of both polynuclear species and AlSO4(+) complex decreased in cold water. The presence of organic matter had little effect on the speciation of aluminum in diluted alum, but markedly reduced the relative proportion of the tridecamer species in the prehydrolyzed coagulant solutions. The relationship between Al speciation in the coagulants and organic matter removal during jar tests was considered, and the possible role of sulfate in both the formation of the tridecamer species and the effect of organic matter on coagulation efficiency was discussed.     

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.     

Mechanism of natural organic matter removal by polyaluminum chloride: effect of coagulant particle size and hydrolysis kinetics

The mechanism of natural organic matter (NOM) removal by AlCl(3) and polyaluminum chloride (PACl) was investigated through bench-scale tests. The fraction distributions of NOM and residual Al after coagulation in solution, colloid and sediment were analyzed as changes of coagulant dosage and pH. The influence of NOM, coagulant dose and pH on coagulation kinetics of AlCl(3) was investigated using photometric dispersion analyzer compared with PACl. Monomeric Al species (Al(a)) shows high ability to satisfy some unsaturated coordinate bonds of NOM to facilitate particle and NOM removal, while most of the flocs formed by Al(a) are small and difficult to settle. Medium polymerized Al species (Al(b)) can destabilize particle and NOM efficiently, while some flocs formed by Al(b) are not large and not easy to precipitate as compared to those formed by colloidal or solid Al species (Al(c)). Thus, Al(c) could adsorb and remove NOM efficiently. The removal of contaminant by species of Al(a), Al(b) and Al(c) follows mechanisms of complexation, neutralization and adsorption, respectively. Unlike preformed Al(b) in PACl, in-situ-formed Al(b) can remove NOM and particle more efficiently via the mechanism of further hydrolysis and transfer into Al(c) during coagulation. While the presence of NOM would reduce Al(b) formed in-situ due to the complexation of NOM and Al(a).     

Effect of shear force and solution pH on flocs breakage and re-growth formed by nano-Al13 polymer

The breakage and re-growth of flocs formed by polyaluminum chloride (PAC) and the Al₁₃O₄ (OH)₂₄⁷⁺ (Al₁₃ for short) polymer were comparatively evaluated for the coagulation of humic acid (HA). A series of jar experiments were conducted to investigate the impacts of shear rate and solution pH on flocs breakage and re-aggregation potential. Results indicated that the responses of flocs to the increasing shear force and solution pH depend on the coagulant used. The ability of flocs to resist breakage decreased with the increasing shear rate. For all levels of shear force investigated in this study, the flocs formed by Al₁₃ polymer were weaker than those of PAC, whereas Al₁₃ polymer displayed a better recoverability than PAC. The similar results were obtained when pH of solution was changed. The flocs generated in acidic conditions were stronger and more recoverable than those generated in alkaline conditions no matter which coagulant was used.     

Fate of coagulant species and conformational effects during the aggregation of a model of a humic substance with Al13 polycations

A model of a humic substance (MHS) obtained from auto-oxidation of catechol and glycine, was aggregated at pH 6 and 8 with Al(13) polycations. The fate of Al(13) coagulant species upon association with MHS functional groups was studied using solid state (27)Al Magic-angle spinning (MAS) NMR and CP-MAS (13)C NMR. Electrophoretic measurements and steady-state fluorescence spectroscopy with pyrene as a fluoroprobe, were combined to investigate structural re-organization of humic material with aluminum concentration. MAS (27)Al NMR revealed that the coagulant species are Al(13) polycations or oligomers of Al(13) units at both pHs. CP MAS (13)C spectra indicated that, at low Al concentration, hydrolyzed aluminum species bind selectively to carboxylic groups at pH 6 and to phenolic moieties at pH 8. At higher coagulant concentrations, the remaining functional groups also interact with hydrolyzed Al to yield similar CP MAS (13)C spectra in the optimum concentration range. Negative values of electrophoretic mobility were obtained at optimum coagulant concentrations even though an overall charge balance was achieved between MHS anionic charge and Al(13) cationic charge at pH 6. The polarity-sensitive fluorescence of pyrene revealed that the interaction of Al(13) coagulant species with MHS functional groups induces the formation of intramolecular hydrophobic microenvironments. Such structural changes were reversed upon further addition of Al(13) polycations.     

Effects of humic acid on physical and hydrodynamic properties of kaolin flocs by particle image velocimetry

The physical and hydrodynamic properties of kaolin flocs including floc size, strength, regrowth, fractal structure and settling velocity were investigated by in situ particle image velocimetry technique at different humic acid concentration. Jar-test experimental results showed that the adsorbed humic acid had a significant influence on the coagulation process for alum and ferric chloride. Kaolin flocs formed with the ferric chloride were larger and stronger than those for alum at same humic acid concentration. Floc strength and regrowth were estimated by strength factor and recovery factor at different humic acid concentration. It was found that the increased humic acid concentration had a slight influence on the strength of kaolin flocs and resulted in much worse floc regrowth. In addition, the floc regrowth after breakage depended on the shear history and coagulants under investigation. The changes in fractal structure recorded continuously by in situ particle image velocimetry technique during the growth-breakage-regrowth processes provided a supporting information that the kaolin flocs exhibited a multilevel structure. It was proved that the increased humic acid concentration resulted in decrease in mass fractal dimension of kaolin flocs and consequently worse sedimentation performance through free-settling and microbalance techniques.     

The origin of Al(OH)3-rich and Al13-aggregate flocs composition in PACl coagulation

The composition of hydrolyzed Al species is essential for the understanding of coagulation with Al-based coagulants. Surface characteristics of flocs formed by coagulation with two distinct polyaluminum chloride (PACl) coagulants were identified. One commercial coagulant (PACl-C) with voluminous monomeric Al and colloidal Al(OH)₃ and a custom-made PACl (PACl-Al₁₃) containing high Al₁₃ content were applied to destabilize kaolin particles. The flocs formed by PACl-C and PACl-Al₁₃ at neutral and alkaline pH ranges, respectively, were observed by FE-SEM and HR-TEM. In addition, the Al composition of these flocs was characterized by XPS and HR-XRD, and the imaging of Al(OH)₃ precipitates and Al₁₃ aggregates were conducted by SEM as well as tapping mode AFM in liquid system. The observations of flocs indicate that the morphology of Al(OH)₃-rich flocs are fluffy and porous around the edge of flocs, while the Al₁₃-aggregate flocs have a glossy contour and irregular structure. Both Al(OH)₃-rich and Al₁₃-aggregate flocs do not possess well-formed crystalline structure except for the Al₁₃-like crystal exists in the Al₁₃-aggregate flocs. Among Al(OH)₃ precipitates, colloidal Al(OH)₃ is micro-scale in size, while amorphous Al(OH)₃ is nano-scale. During the formation of Al₁₃ aggregates, some coiled and clustered Al₁₃ aggregates with smoother surface were observed. The XPS study on floc surface showed that tetrahedral (Al^IV) /octahedral (Al^VI) Al ratio on the surfaces of PACl-C and PACl-Al₁₃ flocs is 1:1.6 and 1:9.9, respectively. Of the in situ formed Al₁₃, almost half of Al-hydroxide precipitates on the surface of Al(OH)₃-rich flocs possess the Al^IV center. It also found that the irregularly aggregated Al₁₃ with a similar Al₁₃ crystalline structure subsists on the surface of Al₁₃-aggregate flocs.