混凝预处理对超滤膜通量的影响

为探讨混凝预处理对改善超滤膜过滤通量的效果.试验采用了4种具有不同亲疏水性的水样,着重探讨混凝对有机物的疏水性和亲水性组分的去除效果以及所带来的通量改善.试验结果表明,超滤膜直接过滤原水时,4种水样的有机物截留率在12%～20%,但其中的疏水性组分均超过了50%,说明膜倾向于截留疏水性有机物.投加25 mg/L的混凝剂,4种水样的有机物去除率在12%～28%,投加量增加至100 mg/L,去除率也相应增加至25%～38%,但其中的疏水性组分均占50%以上.混凝预处理均可有效提高通量.对有机物各组分的分析表明,膜处理混凝预处理水时,主要截留亲水性组分,这是由于混凝可有效去除疏水性组分的缘故.由此也可得出结论.超滤膜的通量下降主要是由疏水性有机物引起的,亲水性组分对通量的影响较小.     

有机物对UF膜过滤通量的影响

采用截留分子量为30000的聚醚砜超滤膜进行膜过滤试验,研究有机物的特性,如亲疏水性以及相对分子质量对超滤膜通量的影响.试验结果表明,过滤亲水性组分时膜通量明显高于过滤疏水性组分.对2种不同水源的试验表明,尽管有机物含量相同,但由于亲疏水性的比例不同,造成的膜通量下降不同.疏水性越大的原水,其膜通量下降也越大.因此,疏水性组分是造成通量下降的主要因素.试验还表明,相对分子质量较大的有机物并非通量下降的主要因素,有机物的分散性可能是影响通量的主要因素.     

粉末活性炭预吸附改善超滤膜通量试验研究

研究了粉末活性炭(PAC)预处理长江原水对改善超滤膜通量的效果.试验采用截留相对分子质量分别为30000 Da和10 000 Da的2种超滤膜,着重探讨了PAC对长江水中不同分子量有机物的吸附去除效果以及其所带来的膜通量改善.试验结果表明,超滤膜直接过滤原水时,膜通量下降严重;采用PAC预吸附后,2种膜的通量在一定程度上均得到提高.对PAC预吸附和膜后水样进行不同相对分子质量有机物的测定,结果表明:PAC吸附小于1000Da相对分子质量有机物高于其他相对分子质量区间有机物总和;膜表观截留孔径越小,PAC预吸附改善膜通量效果越显著.     

不同组分的有机物对膜过滤通量下降的影响

采用DAX-8、XAD-4、IRA-958型树脂将自来水中有机物分离成强疏水性、弱疏水性、极性亲水性、中性亲水性有机物,以聚偏氟乙烯、聚醚砜、醋酸纤维3种材质的膜对各组分水样进行膜过滤试验,研究不同组分的有机物对膜过滤通量的影响.结果表明,过滤原水时,PES膜、PVDF膜和CA膜的通量分别比初始通量下降了67%、 59%和19%,表明疏水性越强的膜,越容易造成污染.就各种组分对通量的影响而言,过滤中性亲水性组分的通量下降为初始通量的41%～75%,而弱疏水性组分为6%～33%,表明中性亲水性组分对膜过滤通量的影响最大.3种膜中,CA膜对中性亲水性组分的截留率最高,达14.69%,但通量下降程度却最小,说明膜通量下降的程度并不与有机物截留总量正相关.对膜污染机制进行探讨后发现,对于截留分子量较大的超滤或微滤膜,相对分子质量>3×10⁴的中性亲水性组分通过堵塞膜孔内部,从而造成严重的膜污染;而对于截留分子量较小的超滤膜,中性亲水性组分由于无法进入膜孔,主要在膜表面形成滤饼层,从而对膜通量的影响较小.     

不同相对分子质量的有机物对膜通量的影响

采用截留分子量分别为10、30kDa的聚醚砜膜和100kDa的聚偏氟乙烯膜对原水进行分级处理,并采用截留分子量分别为150kDa的聚偏氟乙烯膜和0.1μm的醋酸纤维素膜对出水进行膜过滤试验,研究不同相对分子质量的有机物对膜通量的影响.结果表明,虽然相对分子质量>30kDa的大分子有机物仅为总有机物的15%,但它分别引起微滤膜的通量下降86%和超滤膜通量下降54%.混凝处理可以去除相对分子质量>100kDa的有机物,这部分有机物导致通量下降40%以上.因此,尽管混凝处理仅去除10%的有机物,但改善通量的效果显著.粉末活性炭可以去除相对分子量<30kDa的小分子有机物,这部分有机物对通量下降的贡献程度甚低.因此,尽管粉末活性炭去除76%的有机物,但改善通量的效果甚微.预处理改善通量的效果并不取决于去除有机物的多少,而是取决于所去除的有机物对通量的影响大小.     

臭氧-粉末炭联用作为预处理缓解膜污染的效果与机制

研究臭氧、粉末炭以及它们的组合作为超滤膜的预处理,控制膜污染以及去除有机物的效果和机制.结果表明,臭氧主要氧化强疏组分的大分子有机物,将其转化为中分子和亲水性的小分子.臭氧可有效控制膜污染,表明大分子的疏水有机物是主要的污染因素.粉末炭可吸附小分子有机物,也可缓解膜污染,说明小分子有机物也对膜污染有所贡献.臭氧与粉末炭的组合不仅有效控制膜污染,还可强化有机物的去除,它们之间存在协同作用.     

不同原水中膜污染物质的表征与确定

本文采用有机物的组分分析、相对分子质量分布及三维荧光等分析手段,研究了青草沙水库和滆湖原水的膜过滤通量的表现,探讨了膜污染的机理.试验结果表明,中亲组分有机物造成的微滤膜和超滤膜的通量下降最为严重,而疏水性有机物对通量的影响甚微.滆湖水对微滤膜的通量下降较青草沙水库水严重,而青草沙水库水对超滤膜的通量下降较滆湖水严重.膜污染机理的分析表明,微滤膜污染主要由膜孔堵塞造成,而超滤膜的通量主要受大分子有机物形成的滤饼层的影响.三维荧光分析表明,蛋白质类的有机物是造成膜污染的主要物质.     

预涂动态膜强化超滤去除海水中有机物及其对膜污染的影响

以粉末活性炭和硅藻土为涂膜材料,在聚醚砜超滤膜表面形成预涂动态膜,考察了预涂动态膜对海水中有机物的去除效果和作用机制,通过比较分析直接超滤和预涂动态膜过滤海水前后膜表面亲疏水性、形貌结构、粗糙度及膜阻力分布的变化,探讨了活性炭和硅藻土预涂覆对超滤膜污染的影响.结果表明,预涂动态膜可提高超滤膜对海水中溶解有机碳(DOC)和UV_(254)的去除率,活性炭预涂动态膜对海水中DOC和UV_(254)的去除率较直接超滤分别提高11.2%和11.3%.硅藻土预涂膜主要利用超滤膜表面形成的硅藻土滤饼层强化海水中蛋白质类有机物的截留,活性炭对海水中小分子有机物的额外吸附导致海水过滤过程中活性炭预涂膜对有机物的去除效果优于硅藻土预涂膜.与直接超滤相比,预涂动态膜过滤海水后膜表面亲水性更好,膜表面粗糙度更低,膜过滤阻力也更小,活性炭预涂动态膜净化海水时膜过滤总阻力较直接超滤降低50.3%.利用涂膜材料在超滤膜表面形成的滤饼层将超滤膜与有机物进行了"隔离",避免了超滤膜与有机污染物直接接触,降低了小分子有机物在膜孔内的吸附堵塞,能够有效减缓超滤膜的不可逆污染.     

藻类有机物的特性以及对超滤膜的污染

采用凝胶色谱、亲疏水性、荧光色谱等方法研究铜绿微囊藻类有机物的特性.结果表明,铜绿微囊藻类有机物(AOM)主要由亲水性组分构成,占78%,比紫外吸光度仅为1.1 L/(mg.m).超滤膜法测定结果表明,藻类有机物中相对分子质量30 000的有机物占40%以上,并且主要由中性亲水性组分构成.荧光色谱分析表明,AOM中含有蛋白质类和腐殖质类物质.膜过滤试验表明,藻类有机物对超滤膜造成严重的通量下降,这可归结为大分子的中性亲水性组分堵塞膜孔的缘故.     

城市污水二级出水有机物分子量分布和亲疏水特性对纳滤膜污染的影响

分别采用分子量分级膜和XAD-8树脂,研究了污水厂二级出水中有机物分子量分布特征及不同分子量分布区间亲疏水有机物的相对含量,考察了分子量分布及亲疏水特性对纳滤膜透水性能的影响.结果表明,二级出水有机物中,小分子亲水性有机物含量最高,小于2k的有机物占总有机物含量的45.61%,其中亲水性物质占28.07%,疏水性物质占17.54%;不同特征的原水分别经纳滤膜过滤,分子量分布对膜污染影响较大,分子量小于30k时,分子量区间越小,比通量衰减越快,分子量大于30k时,分子量区间越大,比通量衰减越快,且分子量较小的有机物通量衰减程度大于分子量较大有机物;在分子量分布相同区间内,亲水性有机物的比通量衰减较慢,说明相同分子量时,膜对亲水性物质的截留率较低,而疏水性物质是引起膜通量衰减的主要原因.     

Membrane flux dynamics in the submerged ultrafiltration hybrid treatment process during particle and natural organic matter removal

Exponential relationship was developed to quantify the normalized membrane flux dynamics during the filtration period and fitted the results well.     

Effect of coagulation pretreatment on the fouling of ultrafiltration membrane

The purpose of this study is to understand the effect and mechanism of preventing membrane fouling, by coagulation pretreatment, in terms of fractional component and molecular weight of natural organic matter （NOM）. A relatively higher molecular weight （MW） of hydrophobic compounds was responsible for a rapid decline in the ultrafiltration flux. Coagulation could effectively remove the hydrophobic organics, resulting in the increase of flux. It was found that a lower MW of neutral hydrophilic compounds, which could remove inadequately by coagulation, was responsible for the slow declining flux. The fluxes in the filtration of coagulated water and supernatant water were compared and the results showed that a lower MW of neutral hydrophilic compounds remained in the supernatant water after coagulation could be rejected by a membrane, resulting in fouling. It was also found that the coagulated flocs could absorb neutral hydrophilic compounds effectively. Therefore, with the coagulated flocs formed on the membrane surface, the flux decline could be improved.     

Fouling of nanofiltration membrane by e uent organic matter: Characterization using di erent organic fractions in wastewater

The UF membrane with molecular weight cuto (MWCO) ranging from 2 to 100 kDa and XAD-8 resin were employed to identify the characteristic of molecular weight (MW) distribution of wastewater e uent organic matter (EfOM) in terms of TOC and UV254, as well as the amounts of the hydrophilic/hydrophobic organic fractions in di erent MW ranges. Then, the nanofiltration (NF) membrane fouling experiments were carried out using the above fractionated water to investigate the e ect of MW distribution and hydrophilic/hydrophobic characteristics of EfOM on the membrane flux decline using the fractionated water samples. The experimental results have shown that 45.61% of the total organics belongs to the low MW one, among which the percentage of the hydrophilic organics with low MW (less than 2 kDa) was up to 28.07%, while that of the hydrophobic organics was 17.54%. In particular, the hydrophilic fraction was found to be the most abundant fraction in the e uents. MW distribution has a significant e ect on the membrane fouling. When the MWwas less than 30 kDa, the lower the MW, the larger was the specific flux decline, while in the case of MW higher than 30 kDa, the higher the MW, the larger was the specific flux decline, and the decline degree of low MW organics was larger than the high MW one. With the same MW distribution range, specific flux decline of the hydrophilic organic was considerably slower than that of the hydrophobic organic, which indicated that the hydrophobic organic fractions dominantly contribute to the flux decline.     

Fouling of nanofiltration membrane by effluent organic matter： Characterization using different organic fractions in wastewater

The UF membrane with molecular weight cutoff (MWCO) ranging from 2 kDa to 100 kDa and XAD-8 resin were employed to identify the characteristic of molecular weight (MW) distribution of wastewater effluent organic matter (EfOM) in terms of TOC and UV254, as well as the amounts of the hydrophilic/hydrophobic organic fractions in different MW ranges. Then, the nanofiltration (NF) membrane fouling experiments were carried out using the above fractionated water to investigate the effect of MW distribution and hydrophilic/hydrophobic characteristics of EfOM on the membrane flux decline using the fractionated water samples above. The experimental results have shown that 45.61% of the total organics belongs to the low MW one, among which the percentage of the hydrophilic organics with low MW (less than 2 kDa) was up to 28.07%, while that of the hydrophobic organics was 17.54%. In particular, the hydrophilic fraction was found to be the most abundant fraction in the effluents. MW distribution has a significant effect on the membrane fouling. When the MW was less than 30 kDa, the lower the MW, the larger was the specific flux decline, while in the case of MW higher than 30 kDa, the higher the MW, the larger was the specific flux decline, and the decline degree of low MW organics was larger than the high MW one. With the same MW distribution range, specific flux decline of the hydrophilic organic was considerably slower than that of the hydrophobic organic, which indicated that the hydrophobic organic fractions dominantly contribute to the flux decline.     

Drinking water production by ultrafiltration of Songhuajiang River with PAC adsorption

In recent years, membrane ultrafiltration （UF） of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To evaluate the performance of ultrafiltration membranes for treatment of surface water in North China, a 48-m^2 low pressure hollow fiber membrane ultrafiltration pilot plant was constructed. Ultrafiltration was operated in cross-flow and with powdered activated carbon （PAC） adsorption. Turbidity was almost completely removed to less than 0.2 NTU （below Chinese standard 1 NTU）. It was found that PAC addition enhanced organic matter removal. The combined process of PAC/UF allowed to 41% removal of CODMn, 46% removal of DOC and 57% decrease in UV254 absorbance. The elimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PAC concentration was below 30 mg/L, backwashing could recovery the membrane flux with backwash interval/backwashing duration of 1/30.     

Drinking water production by uitrafiltration of Songhuajiang River with PAC adsorption

In recent years, membrane ultrafiltration (UF) of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To evaluate the performance of ultrafiltration membranes for treatment of surface water in North China, a 48-m2 low pressure hollow fiber membrane ultrafiltration pilot plant was constructed. Ultrafiltration was operated in cross-flow and with powdered activated carbon (PAC) adsorption. Turbidity was almost completely removed to less than 0.2 NTU (below Chinese standard 1 NTU). It was found that PAC addition enhanced organic matter removal. The combined process of PAC/UF allowed to 41% removal of CODMn 46% removal of DOC and 57% decrease in UV254 absorbance. The elimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PAC concentration was below 30 mg/L, backwashing could recovery the membrane flux with backwash interval/backwashing duration of 1/30.     

超滤及其组合工艺对污水的深度处理试验

超滤及其组合工艺 ,混凝 UF和粉末活性炭 (PAC) UF对污水深度处理的试验结果表明 ,超滤对水中浊度几乎可以完全去除 ,对细菌和大肠杆菌的去除效率大于 99% ,对水中有机物、氨氮、总铁和总锰也均有一定的去除。超滤前加混凝预处理或粉末活性炭吸附后 ,提高了水中有机物的去除率 ,同时减轻了膜污染 ,提高了膜通量和产水量。此外 ,三种工艺在等量冲洗用水的条件下 ,适当缩短过滤周期 ,增加反冲洗频率均提高了单位能耗产水量。