Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

Raw water from the Songhua River was treated by four types of coagulants, ferric chloride(FeCl3), aluminum sulfate(Al2(SO4)3),polyaluminum chloride(PACl) and composite polyaluminum(HPAC), in order to remove dissolved organic matter(DOM). Considering the disinfection byproduct(DBP) precursor treatability, DOM was divided into five chemical fractions based on resin adsorption.Trihalomethane formation potential(THMFP) and haloacetic acid formation potential(HAAFP) were measured for each fraction. The results showed that hydrophobic acids(HoA), hydrophilic matter(HiM) and hydrophobic neutral(HoN) were the dominant fractions.Although both HoN and HoA were the main THM precursors, the contribution for THMFP changed after coagulation. Additionally,HoA and HiM were the main HAA precursors, while the contribution of HoN to HAAFP significantly increased after coagulation.HoM was more easily removed than HiM, no matter which coagulant was used, especially under enhanced coagulation conditions.DOC removal was highest for enhanced coagulation using FeCl3 while DBPFP was lowest using PACl. This could indicate that not all DOC fractions contained the precursors of DBPs. Reduction of THMFP and HAAFP by PACl under enhanced coagulation could reach51% and 59% respectively.     

Al13形态在混凝中的作用机制

从铝的水解形态转化角度考察了铝盐在高碱度和高有机物浓度水体中的混凝行为.结果表明,铝盐的混凝效能是与混凝过程中的Al₁₃含量成正比.高投药量时氯化铝(AlCl₃)既可以有效调节水体pH值又能在混凝过程中原位水解产生较多的Al₁₃形态,因而混凝效能要高于聚合氯化铝(PACl).在铝盐混凝中,调节pH值到6～7之间可以控制铝形态分布从而达到提高混凝效能和减少残留铝的目的.在调节pH值强化混凝的方法中使用传统铝盐的效果要好于无机高分子絮凝剂.     

柠檬酸对不同混凝剂混凝效果的影响

通过对不同混凝剂(Al2(SO4)3、Fe2(SO4)3、PACl25)混凝过程中絮体粒径大小的测定,研究了在不同pH条件下柠檬酸浓度对3种混凝剂混凝效果的影响.结果发现,随着柠檬酸浓度的增加,3种混凝剂混凝过程中生成絮体的速率和粒径大小都在逐渐降低,但3种混凝剂受到抑制的程度不同:对于硫酸铝,当n(柠檬酸)/n(Al) =0.1时,混凝20 min内没有絮体生成;对于硫酸铁,仅当n(柠檬酸)/n(Fe)=0.05时,絮体就不再生成;而当n(柠檬酸)/n(Al) =0.5时,PACl25絮体仍能很快地形成.不同的pH值下柠檬酸对混凝效果的抑制程度也不同:对于硫酸铝,pH =6时生成絮体最大,pH =8时没有絮体生成;对于硫酸铁,pH =5时产生絮体的情况和pH =6时相似,而pH =7时絮体消失;而对于PACl25,絮体大小随着pH值的升高而增大(pH在7～9之间).另外,通过对Zeta电位的测定可知,随着柠檬酸浓度的增加,3种混凝剂的Zeta电位都在降低,但降低的速率不同:硫酸铁＞硫酸铝＞ PACl25,这与絮体粒径大小的变化规律一致.     

混凝-吸附处理黄河水及对氯消毒中氯衰减的影响

选用2种无机高分子混凝剂聚合氯化铁(PFC)和聚合氯化铝(PAC)处理黄河水,考察了混凝剂的投加量对浊度、UV254、DOC和高锰酸盐指数的去除效果,并结合混凝出水的Zeta电位分析其混凝机制.选择粉末活性炭与混凝联用,研究了混凝剂和吸附剂投加量以及二者的投加顺序对有机物去除效果的影响,并对混凝吸附后出水进行加氯消毒,考察水中残余氯随时间的变化.结果表明,2种混凝剂均有较高的浊度去除率(﹥90%).PAC对UV254、高锰酸盐指数和DOC的去除率分别为29.2%、26.1%和27.9%;PFC对三者的去除率分别为32.3%、23.3%和32.9%.PAC在混凝过程中,电中和作用占主导地位;PFC在混凝过程中,吸附架桥和电中和同时发挥作用.混凝-吸附联用处理黄河水样时,有机物的去除率随混凝剂和吸附剂投加量的增加而升高.先混凝后吸附工艺对UV254和DOC的去除效果优于先吸附后混凝工艺.先使用PAC混凝后吸附对UV254和DOC的去除率分别为95.2%和99.9%;对于PFC,先混凝后吸附对UV254和DOC的去除率分别为90.1%和99.9%.但是先投加粉末活性炭能提高矾花的沉降性能,且处理出水在保持持续消毒效果方面优于前者.     

不同水体溶解性有机物的混凝去除特性

采用硫酸铝、工业氯化铁、无机高分子絮凝剂(PAC)3种无机混凝剂,对广州珠江、北京密云、天津滦河不同原水进行了混凝实验,分析了不同混凝剂去除水体有机物的特性以及不同水体溶解性有机物(DOM)的内在分级特征与其混凝去除率的关系.实验结果表明,①珠江水体由于碱度低,pH较易下降,高投药浓度下此水体DOM更易被氯化铁去除;中低投药下,在南方水体中,PAC与盐类絮凝剂对去除DOM的混凝性能差别不如在北方水体中明显,表明南北方水体DOM的内在特性存在一定差异,即北方水体DOM中可混凝去除部分的有机物易发生电中和作用,带有较多负电基团,南方珠江水体DOM含带电基团的有机物相对较少,而中性有机物含量相对较高,这与进一步分级结果一致.②所有水体从混凝收敛点看,总溶解性有机碳(DOC)去除率都是工业PAC最高,显示电中和(憎水化)-沉淀(吸附)可能为这些水体DOM的主要去除机理.③从不同水体的DOC平均去除率看,珠江水体高于密云水体,它们又明显高于滦河水体.对水体DOM进一步的化学分级研究结果表明,DOC去除率越高的水体,其中的憎水中性物质(HoN)含量也越高.这表明,除了碱度、总有机碳(TOC)外,原水DOM的内在化学分级特征也是影响水体DOC混凝去除率的重要因素.     

Application of a green coagulant with PACl in efficient purification of turbid water and its mechanism study

The applications of natural polymeric flocculants due to their green feature has been recently received much more attention. In this work, the combined usages of a cationic starch-based coagulant and polyaluminum chloride (PACl) were extensively evaluated for various addition sequences in the coagulation of both raw (surface water from the Jiuxiang River) and synthetic turbid water (two kaolin suspensions with different initial turbidities). Two typical cationic starch-based coagulants with different structures (St-G and St-E) were tried. In comparison to St-G, St-E and PACl used individually as well as St-G and St-E dosed after PACl, the combination of the starch-based coagulants fed before PACl showed higher turbidity removal efficiency, which featured not only less optimal doses of both inorganic and organic coagulants but also lower residual turbidity. On the basis of a detailed analysis of the particle size and its distribution in solution supernatants before and after coagulation by two starch-based coagulants and PACl, polymeric coagulants preferentially coagulate the small-sized colloids due to their distinct long-chain structures, but PACl preferentially coagulates the medium-sized ones. Thus, the medium-sized particles that were previously formed by the starch-based coagulants would be collectively and effectively removed by the subsequent addition of PACl. The addition sequence of the inorganic and organic coagulants in their combined usage is an important factor for improvement of the turbidity removal efficiency in practice.     

Synchronous removal of CuO nanoparticles and Cu2+ by polyaluminum chloride-Enteromorpha polysaccharides: Effect of Al species and pH

Copper oxide nanomaterials have been extensively applied and can have serious impacts when discharged into the aquatic environment, especially when complexed with humic acid (HA) to form composite contaminants. As an innovative recycled coagulant aid, Enteromorpha polysaccharides (Ep) were associated with polyaluminum chloride (PACl) (denoted as PACl-Ep) to simultaneously remove CuO nanoparticles, Cu²⁺ and HA in this study. The influence of different Al species coagulants (AlCl₃, PACl_b and PACl_c) and water pH on coagulation performance, floc properties and reaction mechanisms was investigated in detail. Results showed that in the three PACl-Ep systems, PACl_b-Ep gave the highest removal efficiencies for turbidity and Cu²⁺, and the best UV₂₅₄ removal effect was reached by using PACl_c-Ep. Higher contents of Al_b and Al_c contributed to great coagulation performance because of their stronger bridging and sweeping effects. For all the Al species coagulants, alkalescent conditions were more conducive to removing Cu and HA compared to acidic conditions. Additionally, smaller and more agminated flocs with great recovery ability were formed by PACl_b-Ep and PACl_c-Ep systems (bridging and enmeshment effects cooperated with the chelated reticular structure formed by the Ep and Al species). Similarly, due to the increased hydrolysis and hydroxide precipitates, flocs formed under the condition of alkalescence were smaller, denser and stronger compared with weakly acidic conditions.     

聚合氯化铝中纳米Al13电荷特性及其混凝效果

采用聚丙烯酰胺凝胶柱层析法分离纯化聚合氯化铝(PAC)中的Al₁₃形态,并采用Al-Ferron逐时络合比色法和ZATESIZER 3000HSA测定仪对分离所得纳米Al₁₃形态以及AlCl₃和PAC进行了分析表征和电荷特性的对比性研究;采用烧杯实验法对3个样品处理实际和模拟水样的混凝效果进行了对比性研究.Al-Ferron逐时络合比色法的结果表明,采用层析法分离可得到含量99%左右的纳米Al₁₃形态;电荷特性和混凝效果研究结果表明纳米Al₁₃形态较其它两者具有更好的除浊、除腐殖酸和脱色效果并且具有更强的电中和能力,因此Al₁₃形态是一种具有较高正电荷和较高的水解稳定性,在给水和废水处理中的一种较为有效的Al形态.     

复合混凝剂用于夏季太湖水混凝脱浊研究

用特征粘度系列化的聚二甲基二烯丙基氯化铵(PDM)与聚合氯化铝(PAC)复合得到稳定的复合混凝剂,用于夏季高藻太湖水强化混凝脱浊处理.通过混凝烧杯实验.考察了无机/有机复合比例、PDM特征粘度对脱浊效果及絮团沉淀性能的影响.结果表明,对浊度为30-33 NTU,温度为28～30℃,藻含量为2.6×107个儿的太湖水,在与某市水厂混凝强度相近的搅拌强度下.当达到该水厂2NTU沉淀池出水的余浊标准时,PAC需7.00 mg/L的投加量.质量复合比例为5:1、10:1、20:1的PAC(以Al2O3计)/PDM复合混凝剂所需PAC投加量随PDM特征粘度0.52、1.53、2.46 dL/g的增加分别为3.00-2.83 ms/L、3.50-3.49ms/L、5.37-4.67 mg/L,相对于PAC减少投加量57.14%-59.57%、50%-50.14%、23.29%-33.29%;作为深度处理的技术准备.当沉淀出水浊度要求提高至1NTU的情况下,复合药剂依然可发挥好的作用,PAC需10 mg/L的投加量,PAC(以Al2O3计)与PDM质量复合配比为20:1、10:1、5:1的复合混凝剂需8.33-3.91 mg/L的投加量,能比PAC减少投加量16.7%～60.9%.可见,PDM明显提高了PAC的混凝脱浊效果与沉淀性能,且PAC/PDM质量复合配比越低,PDM特征粘度越高,脱浊效果与沉淀性能越好.     

混凝沉淀过程中铝系混凝剂的形态转化规律

研究了模拟配水中硫酸铝和氯化铝2种传统铝凝聚剂和2种聚合氯化铝(PAC)絮凝剂在混凝过程中的形态转化规律以及原水浊度和溶解性有机碳(DOC)对残余铝形态分布的影响.结果表明,在低浊体系中,投加铝系混凝剂是导致出水余铝升高的主要原因;但在高浊体系中,铝系混凝剂,尤其是聚合铝具有一定的除铝功能;混凝沉淀过程中传统铝凝聚剂的残余铝总量明显高于聚合铝混凝剂的残余铝总量;聚合铝混凝剂的残余铝全部为悬浮态铝,传统铝混凝剂的残余铝中还存在着胶体态铝和溶解态铝.原水浊度和DOC浓度增加,会提高残余铝中胶体态铝和溶解态铝的含量.