【作者】 王辉；

【导师】 李圭白； 梁恒；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2017， 博士

【摘要】 超滤技术是水处理领域中前景广阔的绿色工艺,其具有高效稳定去除颗粒物和微生物特点,保证了饮用水的生物安全性。然而,超滤对溶解性有机物去除效能较低和运行过程中产生的膜污染问题是两大瓶颈性难题。因此,采用吸附和氧化等预处理来提高有机物的去除效能和对膜污染进行有效的控制。本论文采用粉末活性炭(Powdered activated carbon,PAC)吸附和臭氧预氧化单独或联合预处理,系统地研究了其对超滤工艺的影响。采用地表水作为超滤原水,考察了PAC粒径对膜污染的影响。粒径越小PAC对有机物的吸附效能越高(如腐殖酸,Humic acid,HA),因此粒径越小PAC对膜污染的控制效果越显著。PAC吸附后不去除PAC颗粒时,会导致膜表面形成有机物和PAC的复合污染层,增加了过滤阻力。因此采用预过滤去除吸附后的PAC颗粒,会使得PAC吸附具有更好的控制污染效果。超滤地表天然水时,增加钙离子浓度会强化天然有机物(Natural organic matter,NOM)对膜表面的粘附作用,导致其产生更加严重的水力不可逆污染。采用天然地表水进行的短期和长期PAC吸附超滤实验发现,HA吸附污染造成的膜孔堵塞是超滤初期主要的污染机制,超滤后期的污染机制为蛋白类有机物浓缩作用产生的污染和以蛋白为主滤饼层污染。由于椰壳PAC可以吸附混凝出水中的蛋白类有机物和HA类有机物,所以可以控制超滤膜长期运行的浓差极化污染和水力不可逆污染。采用两种不同的超滤亲水性再生纤维素膜(Regenerated cellulose,RC)和疏水性的聚醚砜(Polyethersulfone,PES),来评价臭氧预氧化对超滤二级出水膜污染的影响。系统地考察了臭氧预氧化对二级出水有机物(Effluent organic matter,Ef OM)组分及其物化特性的影响。臭氧预氧化对膜通量降低具有显著的缓解效果,随臭氧投加量增大效果越显著。膜污染阻力分析结构表明臭氧预氧化对RC膜和PES膜的可逆污染具有较好的缓解作用,然而臭氧预氧化能够缓解RC膜水力不可逆污染,对PES膜水力不可逆污染缓解作用不显著。通过结合表面自由能分析和静电膜孔堵塞滤饼形成模型分析,来阐释臭氧缓解亲水性膜和疏水性膜的污染机制。结合实验数据,臭氧对膜污染的缓解机制可以总结为以下三点:(1)臭氧预氧化降解了Ef OM中的大分子组分,例如多糖蛋白,同时增加了Ef OM的亲水性。(2)臭氧预氧化增加了污染物与膜之间的粘附自由能,导致两者之间的吸引作用减少或者排斥作用增大。(3)臭氧预氧化推迟了膜孔堵塞向滤饼过滤机制的转变,因此缓解了滤饼层形成的速度,降低了污染。采用了两种水源污水厂二级出水(Secondary effluent,SE)和萨旺尼河天然有机物(Suwannee River natural organic matter,SRNOM),系统地考察了臭氧预氧化和PAC吸附单独或联合预处理对超滤工艺净水效能和膜污染的影响。联合预处理比较了先PAC吸附后臭氧预氧化和先臭氧预氧化后PAC吸附两种方式。详尽地调查了联合预处理对两种水源中有机物物化特性的影响,联合预处理尤其臭氧预氧化后PAC吸附(简写为O3-PAC)对SE中大分子量有机物(如多糖)、色氨酸类有机物去除效能。模型分析结果表明联合预处理SE时,增加了超滤从膜孔堵塞向滤饼层机制转变的过滤体积,因此缓解了超滤膜滤饼层的形成。表面自由能分析表明,联合预处理尤其O3-PAC处理SE后,污染物自身从吸引作用变为排斥作用,污染物与膜之间吸引作用降低,导致污染物不易团聚同时不易粘附在膜表面。更多还原

【Abstract】 Ultrafiltration(UF)is the most promising “green” technoloogy in water treatreament field.UF can efficiently remove particulate matter and microorganism,which ensures the biological security of drinking water.However,two inevitable impediments limiting for UF are low removal of soluble organic matter and the development of membrane fouling in the process progress.To this end,pre-treatment before UF is often applied to improve the performance of organic matter abatement and control membrane fouling.The effects of individual or combined pre-treatment of powdered activated carbon(PAC)adsorption and pre-ozonation on the UF process were systematically studied in this dissertation.Effect of PAC size on membrane fouling was investigated using surface water as feed water of UF.PAC of smaller size adsorbed more organic matter(such as humic acid,HA),resulting in better control efficiency of membrane fouling.When PAC particles after adsorption were not removed from the feed water of UF,a combined PAC and organic matter of cake layer developed,leading to the increase of fitration resistance.Therefore,the elimination of organic-adsorbed PAC particles before UF benefited the alleivation of membrane fouling.During UF of surface water,the increase of calcium ion enhanced the attachment of natural organic matter(NOM)on the membrane surface,resulting in the deterioration of hydraulically irreversible fouling.By comparing the short term and long run of PAC adsoption UF process,the fouling mechanism of UF initial period is pore block caused by HA,moreover,the fouling mechanisms of long term run are the concentration effect fouling resulting from protein-like organic matter concentration and the formation of proteindominating cake layer.Coconut-based PAC could adsorb protein-like and HA organic matter in the pre-coagulated water,therefore,the fouling of concentration effect and hydralically irreversible fouling were ameliorated by coconut-based PAC.Two types of UF membranes,hydrophilic regenerated cellulose(RC)and hydrophobic polyethersulfone(PES)were used to evaluate the effect of pre-ozonation on the membrane fouling in the UF of secondary effluent.The physicochemical property changes of effluent organic matter(Ef OM)matrix including biopolymer fractions by pre-ozonation were systemically investigated.The increase of ozone dosage led to greater alleviation of flux decline for these two types of membranes.In terms of fouling resistance analysis,the reversible fouling resistances of RC and PES membranes were improved by pre-ozonation.The irreversible fouling resistances of RC membranes were enhanced by pre-ozonation,however,preozonation exhibited no significant impact on those of PES membranes.Additionally,the classical pore blocking model and the extended Derjaguin-Landau-Verwey-Overbeek(XDLVO)theory were employed to scrutinize the fouling alleviation mechanism caused by pre-ozonation.As a result,the overarching mechanisms of fouling reduction were attributed to the following key reasons:(1)Ozone degraded biopolymers of Ef OM including proteins and polysaccharides into smaller fractions,thereby increasing free energy of cohesion of Ef OM and rendering them more hydrophilic and more stable;(2)pre-ozonation augmented the interfacial free energy of adhesion between foulants and the RC/PES membranes,leading to the increase of repulsions and/or the decrease of attractions;and(3)pre-ozonation prolonged the transition from pore blocking to cake filtration that was a dominant fouling mechanism,thereby reducing fouling.The effects of individual or combined pre-ozonation and PAC adsorption pretreatment on the purification performance and membrane fouling,using secondary effluent and Suwannee River natural organic matter(SRNOM).In the combined pretreatment,PAC adsorption followed by pre-ozonation and pre-ozonation followed by PAC adsorption were compared.The physicochemical characteristic changes of organic matter caused by combined pretreatment were detailly investigated.The macromolecular of organic matter(such as polysaccharide)and tryptophan-like matters were better removed by the combined pretreatment,especially by preozonation followed by PAC adsorption(abbreviation: O3-PAC)pretreatment.The model analysis showed that the transitive volume,that altered the fouling mechanism from pore blocking to cake layer filtration,was increased by the combined pretreatment.This resulted in the postponement of cake layer formation.The interfacial free energy results indicated that the cohesion interactions of foulant-foulant was altered from attractive interaction to repulsive interaction,and attractive interaction between foulant and membrane was decreased by combined pretreatment especially by O3-PAC pretreatment.These results implied that foulant had lower potential to aggregate and attach on the membrane surface.更多还原