一体式PAC-UF工艺处理微污染地表水试验研究

采用粉末活性炭和超滤(PAC/UF)一体式工艺去除微污染水源水中的常规指标和嗅味物质,对比分析了投加PAC后膜污染变化情况。结果表明:与常规水处理工艺相比,一体式PAC/UF工艺大大降低了出水浊度,提高了对有机物的去除效果,能有效去除嗅味物质。该组合工艺主要依靠PAC的吸附作用去除有机物,CODMn和UV254去除率分别为33. 0%和51. 5%;在曝气条件下,对嗅味物质土溴素(GSM)、2-甲基异莰醇(2-MIB)、甲硫醚(DMS)和二甲基三硫醚(DMTS)的去除率均在95%以上。向浸没式膜池中投加PAC,过滤初期可以缓解膜污染,但过滤后期反而会加剧膜污染。     

投炭点对混凝/沉淀/膜滤去除水中有机物的影响

通过模拟试验,考察了粉末活性炭(PAC)投加点(混凝前投加、与混凝剂一起投加、沉淀后投加)对混凝/沉淀/膜滤组合工艺去除东江原水中CODMn和UV254的影响;同时采用吸附试验考察了吸附时间对PAC去除沉后水中溶解性有机物的影响。试验结果表明,在相同的PAC投加量下,在沉淀之后投加最有利于发挥PAC的吸附效能,提高组合工艺对水中有机物的去除率;同时,15 min和30 min的吸附时间对PAC去除沉后水中溶解性有机物的影响不大。由此认为,在混凝/沉淀之后采用膜滤,并将投炭点移至膜滤单元,可更加有效地发挥组合工艺各环节的优势,提高水处理效果。     

PAC/AC吸附与超滤膜组合去除二级出水中有机物

对粉末活性炭(PAC)和活性焦(AC)两种吸附材料与超滤膜组合工艺对城市污水处理厂二级出水中有机物的去除能力进行了考察,并对两种组合工艺对膜比通量的影响进行了探讨。结果表明:PAC和AC的最佳投加量均为40mg/L;PAC和AC吸附可提高超滤膜对二级出水中有机物的去除效果,PAC/AC吸附-超滤组合工艺对UV254的去除率可达67.5%⁶9.8%,对DOC的去除率可达46.5%69.8%,对DOC的去除率可达46.5%⁴7.2%;在最佳投加量条件下,AC吸附可减少膜比通量的下降,而PAC由于投加量过大,导致膜比通量下降较快。     

PAC/UF工艺处理微污染水源水的膜污染特性

为了考察粉末活性炭(PAC)和超滤(UF)的协同作用,构建了PAC/UF短流程工艺小试装置,研究了该工艺对微污染水源水中有机物的去除效果,并对膜污染特性进行了综合评价。结果表明,在保证DOC和UV_(254)去除效果的前提下,PAC的最佳投加量为50 mg/L、最佳吸附时间为2 h;在最佳投加量下,PAC吸附时间从10 min增至120 min时,UF膜的可逆污染阻力由5. 91×10~(11)m~(-1)降至5. 20×10~(11)m~(-1);在最佳吸附时间内,PAC投加量从25 mg/L增至100 mg/L时,UF膜的可逆污染阻力由5. 70×10~(11)m~(-1)降至5. 12×10~(11)m~(-1)。通过对PAC吸附前后原水的分子质量分布、亲疏水性以及三维荧光进行测定,初步揭示了PAC缓解膜污染的机理,PAC吸附主要通过去除疏水性小分子有机物和腐殖酸等大分子有机物引起的不可逆污染来缓解膜污染。     

粉末活性炭/污泥回流工艺强化膜前预处理的研究

采用粉末活性炭(PAC)吸附/混凝沉淀/浸没式超滤膜组合工艺处理苏州市某河水,考察了PAC/污泥回流工艺对膜前预处理的强化效果及对膜污染的影响,并与常规混凝沉淀、污泥回流强化混凝沉淀、PAC吸附/混凝沉淀等3种预处理工艺进行了对比。结果表明,PAC/污泥回流强化预处理工艺对浊度、DOC、UV254和THMFP的去除率分别为80.2%、47.5%、42.3%和52.3%,均比其他预处理工艺的高,对MW30 ku和MW1 ku有机物的去除效果明显。PAC/污泥回流强化预处理和超滤膜组合工艺对浊度、DOC、UV254和THMFP的去除率分别可达到99.2%、54.1%、47.2%和60.2%;经过15 d的运行,超滤膜的跨膜压差基本保持稳定,而其他预处理工艺虽能在一定程度上减轻膜污染,但无法避免不可逆膜污染的发生。     

粉末活性炭吸附对超滤膜污染的影响研究

进行了粉末活性炭(PAC)吸附缓解浸没式和内压式超滤膜污染试验研究,并探讨了PAC吸附缓解膜污染的机理。浸没式超滤膜试验结果表明:PAC通过吸附溶解小分子有机物,减少了膜孔堵塞和膜孔内吸附污染,缓解了运行初期通量的快速下降;但PAC在膜表面的累积会降低浸没式超滤膜的起始通量。内压式超滤膜试验结果表明:膜前PAC吸附预处理能提高对有机物的去除效能,降低膜表面的污染负荷,从而降低TMP及其增长速度。     

粉末活性炭/超滤组合工艺运行优化研究

采用粉末活性炭(PAC)/浸没式超滤膜组合工艺处理深圳市某水库原水,考察了PAC投加量、排污周期和曝气强度对有机物的去除以及膜污染的影响,以优化工艺运行。结果表明,投加PAC强化了对有机物的去除,投量为10 mg/L时,对CODMn和UV254的去除效果最佳,去除率分别为42%和35%;膜池内活性炭随过滤的进行逐渐达到吸附饱和,对CODMn、UV254的去除率分别下降了3%和5%,24 h排污一次有助于保持组合工艺对有机物相对较高的去除效果;增加曝气强度,将气水比提高为12∶1,不仅能够强化对有机物的去除,同时还可减缓滤饼层及膜孔内污染的形成。     

BPAC对超滤膜处理微污染源水过程中膜污染的控制

采用粉末活性炭(PAC)与超滤膜(UF)相结合,经微生物富集形成生物粉末活性炭/超滤(BPAC/UF)系统,并以天津工业大学畔湖水模拟饮用水水源,考察该工艺的膜污染情况。结果表明:BPAC/UF系统可以很好地去除NH3-N,去除率达65%,对CODMn也有一定的去除效果;相对于UF系统,BPAC/UF系统可以减缓膜污染;生物活性炭对水中有机物的降解避免了有机物堵塞膜孔,减缓了不可逆污染;生物活性炭的形成使得系统中的EPS含量增加,这是造成膜表面滤饼层形成速率过快的主要原因。     

预处理对东江原水超滤过程中膜污染的控制作用

以珠江流域东江水作为原水,研究不同预处理(混凝、吸附、氧化)及其组合对水体中有机污染物的去除效果及对超滤膜污染的控制作用。试验结果表明,针对东江原水中天然有机物的去除,聚合氯化铝(PACl)、粉末活性炭(PAC)和高锰酸钾(KMnO4)的最佳投加量分别为20、30、0. 1 mg/L;三种单一预处理方法能够在一定程度上缓解膜通量衰减,而两两组合预处理则能够进一步提高膜运行通量;对于聚偏氟乙烯膜,PACl+PAC组合预处理对膜污染的控制作用最好。对于UV254和蛋白质,PACl和KMn O4对其去除效果优于PAC;对于多糖,三种预处理方法对其去除效果均不佳(<40%),其中PAC略好于PACl和KMn O4。此外,三种单一预处理方法对腐殖酸类荧光物质的去除效果高于蛋白质类荧光物质,而组合预处理能够更加显著地降低这两类荧光物质的响应强度,其中PACl+PAC组合预处理对有机物各荧光组分的去除效果最佳。通过对膜污染物成分的识别分析可知,东江原水中造成超滤膜污染的物质有腐殖酸类、多糖类和蛋白质类物质,而化学不可逆污染物主要为多糖类物质及少量的腐殖酸类物质,化学可逆污染物主要为蛋白质类物质及部分腐殖酸类物质。     

混凝—微滤工艺去除膜反洗水中有机物的试验研究

采用混凝-微滤工艺处理混凝-超滤中试装置的膜反洗水(MBW),将试验原水和出水经不同截留分子质量的超滤膜过滤,分析了不同分子质量区间的有机物分布.此外通过改变混凝剂(FeCl3)投量、采取投加粉末活性炭(PAC)等措施,考察了MBW中有机物的去除率与FeCl3投量、处理工艺(混凝-微滤、混凝-PAc吸附-微滤工艺)的关系.研究结果表明,MBW中DOC主要分布在分子质量>30 ku和分子质量<1 ku的区间内,THMFP、UV254主要集中在分子质量<1ku的区间内;混凝过程能有效去除分子质量>30 ku的大分子有机物,PAC能有效去除小分子有机物;随混凝剂投量的增加,对DOC、UV254、THMFP的去除率均有不同程度的提高.     

Adsorption combined with ultrafiltration to remove organic matter from seawater

Organic fouling and biofouling are the major severe types of fouling of reverse osmosis (RO) membranes in seawater (SW) desalination. Low pressure membrane filtration such as ultrafiltration (UF) has been developed as a pre-treatment before reverse osmosis. However, UF alone may not be an effective enough pre-treatment because of the existence of low-molecular weight dissolved organic matter in seawater. Therefore, the objective of the present work is to study a hybrid process, powdered activated carbon (PAC) adsorption/UF, with real seawater and to evaluate its performance in terms of organic matter removal and membrane fouling. The effect of different PAC types and concentrations is evaluated. Stream-activated wood-based PAC addition increased marine organic matter removal by up to 70% in some conditions. Moreover, coupling PAC adsorption with UF decreased UF membrane fouling and the fouling occurring during short-term UF was totally reversible. It can be concluded that the hybrid PAC adsorption/UF process performed in crossflow filtration mode is a relevant pre-treatment process before RO desalination, allowing organic matter removal of 75% and showing no flux decline for short-term experiments.     

Assessing PAC contribution to the NOM fouling control in PAC/UF systems

This paper investigates the powdered activated carbon (PAC) contribution to the fouling control by natural organic matter (NOM) in PAC/UF hybrid process, as well as the foulant behaviour of the PAC itself. Solutions of NOM surrogates (humic acids, AHA, and tannic acid, TA) and AOM/EOM (algogenic organic matter/extracellular organic matter) fractions from a Microcystis aeruginosa culture were permeated through an ultrafiltration (UF) hollow-fibre cellulose acetate membrane (100 kDa cut-off). The greatest impairment on flux and the poorest rejection were associated with polysaccharide-like EOM substances combined with mono and multivalent ions. PAC, either in the absence or in the presence of NOM, did not affect the permeate flux nor the reversible membrane fouling, regardless of the NOM characteristics (hydrophobicity and protein content) and water inorganics. However, PAC controlled the irreversible membrane fouling, minimising the chemical cleaning frequency. Furthermore, PAC enhanced AHA and TA rejections and the overall removal of AOM, although it was apparently ineffective for the highly hydrophilic EOM compounds.     

PAC/PS预处理对水中镉的去除及UF膜污染控制

采用粉末活性炭耦合过硫酸盐(PAC/PS)作为超滤的预处理工艺,考察其对原水中镉和天然有机物的去除效果,以及对超滤膜污染控制的影响。结果表明,对于镉超标6倍的原水水样,当PAC和PS投加量分别为30 mg/L和300μmol/L、接触时间为60 min时,UV₂₅₄、DOC和镉的去除率分别可达到91.7%、68.2%和92.7%,镉浓度可降至《生活饮用水卫生标准》(GB 5749—2006)规定的限值(5μg/L)以下;与直接超滤相比,设置PAC/PS预处理工艺后超滤膜比通量提升了50.5%,XDLVO预测模型中胶体污染物-超滤膜相互作用的总界面能降低了75.38%,超滤膜污染减轻。     

Performing a microfiltration integrated with photocatalysis using an Ag-TiO2/HAP/Al2O3 composite membrane for water treatment: Evaluating effectiveness for humic acid removal and anti-fouling properties

Membrane filtration has been increasingly used for water treatment and wastewater reclamation in recent years. To further improve the effectiveness of membrane process and reduce membrane fouling, a highly reactive photocatalytic membrane, Ag-TiO₂/hydroxiapiate (HAP, Ca₁₀(PO₄)₆(OH)₂)/Al₂O₃, was employed to realize microfiltration (MF) coupling photocatalysis for surface water treatment. The effectiveness on the potential of membrane was investigated by removing humic acid (HA) test under different feed total organic carbon (TOC), light intensity and transmembrane pressure (TMP). The HA removal and anti-fouling property of as-prepared membrane was improved under UV irradiation, likely due to photocatalytic degradation of foulants along with filtration simultaneously. Under given feed water composition, increasing the light intensity resulted in increased removal of HA from aqueous solution. However, a limiting TMP seems to exist beyond which the increased HA removal cannot be sustained. Fouling behavior analysis indicated that the transition in fouling mode from initial pore blocking to cake filtration occurred much slower as UV irradiated. Furthermore, a superior efficiency on removal of trace organic contaminants, as well as milder flux reduction, was presented from surface water treatment, which demonstrated that the integrated system with enhanced performance is foreseen as an emerging technique for water treatment.     

Studies on the effect of humic acids and phenol on adsorption-ultrafiltration process performance

Application of pressure-driven membrane processes, such as ultrafiltration (UF) and microfiltration (MF) for surface water treatment have become very popular during last decades. Membrane fouling by humic substances (HS) is one of the major limiting factors in these processes. In order to alleviate the unfavorable effects of the presence of HS in the feed on the process performance UF and MF are often combined with adsorption on powdered activated carbon (PAC). The main goal of the present study was to evaluate the effect of humic acid (HA) on membrane fouling during UF. Moreover, the effect of PAC addition to the feed on UF process, especially on flux decline was determined. The applicability of the adsorption-ultrafiltration (PAC/UF) system to purification of water containing low (phenol) and high molecular (HA) was also investigated. Three different polymer UF membranes, prepared from polysulfone (PSF), cellulose acetate (CA) or polyacrylonitrile (PAN) were applied. It was found that the membranes prepared from PSF and CA are very susceptible to fouling caused by HA. The permeate flux decreased for ca. 50% during UF of HA solution through the PSF membrane and for ca. 45%-through the CA membrane. In the case of the PAN membrane, a negligible effect of HA on the flux was observed. On the basis of the FTIR spectra it was found that the drop in the permeate flux through these membranes may result from interactions between the negatively charged functional groups present on the membrane surface, such as carboxyl groups (CA) and sulfone groups (PSF) with HA, which results in coating of the membrane surface with HA. When PAC was added to the feed containing HA, the permeate flux through the CA and PAN membranes was maintained on a practically unchanged level. However, in case of the PSF membrane, a 50% drop in the permeate flux in comparison with the flux value, when process was conducted without PAC addition was observed. That was supposed to be due to attractive forces among hydrophobic PAC particles, HA molecules and PSF membrane surface. The performed studies showed that the application of PAC/UF system was very effective in the removal of organic substances having both, low and high molecular weights. The role of PAC suspended in a feed in the PAC/UF system is the adsorption of low molecular organic compounds, which cannot be removed by UF alone.     

Identification of effluent organic matter fractions responsible for low-pressure membrane fouling

Anion exchange resin (AER), powder activated carbon (PAC) adsorption and ozonation treatments were applied on biologically treated wastewater effluent with the objective to modify the effluent organic matter (EfOM) matrix. Both AER and PAC led to significant total organic carbon (TOC) removal, while the TOC remained nearly constant after ozonation. Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis showed that the AER treatment preferentially removed high and intermediate molecular weight (MW) humic-like structures while PAC removed low MW compounds. Only a small reduction of the high MW colloids (i.e. biopolymers) was observed for AER and PAC treatments. Ozonation induced a large reduction of the biopolymers and an important increase of the low MW humic substances (i.e. building blocks).Single-cycle microfiltration (MF) and ultrafiltration (UF) tests were conducted using commercially available hollow fibres at a constant flux. After reconcentration to their original organic carbon content, the EfOM matrix modified by AER and PAC treatments exhibited higher UF membrane fouling compared to untreated effluent; result that correlated with the higher concentration of biopolymers. On the contrary, ozonation which induced a significant degradation of the biopolymers led to a minor flux reduction for both UF and MF filtration tests. Based on a single filtration, results indicate that biopolymers play a major role in low pressure membrane fouling and that intermediate and low MW compounds have minor impact. Thus, this approach has shown to be a valid methodology to identify the foulant fractions of EfOM.     

Fouling characteristics of NF and RO operated for removal of dissolved matter from groundwater

A pilot study had been performed for about 6 months in order to investigate the removal efficiency of dissolved matter and its fouling potential during nanofiltration (NF) and reverse osmosis (RO) of local groundwater that was pretreated with an ultrafiltration (UF) membrane system. After pilot plant operation, autopsy tests were performed to identify the characteristics of foulants that were attached to the membrane surface. In the autopsy tests, the flux recovery for each specific cleaning scheme (hydraulic washing, acid cleaning, and alkaline cleaning) was also measured using a dead-end filtration cell unit. The washing solution used in each chemical cleaning was analyzed to identify major components of the foulants, and the membrane surface was observed using the scanning electron microscopy (SEM).Among three kinds of membranes tested, one NF and two RO membranes, the NF and RO1 membranes showed a rapid flux decline after 100 days of operation. Especially, the RO1 membrane showed the more serious flux decline than the NF membrane. The RO2 membrane, with the lowest recovery rate, demonstrated a gradual flux decline. The removal efficiency of dissolved inorganic matter (as conductivity) for each NF, RO1 and RO2 membrane was 76.3%, 88.2% and 95.3%, respectively. The removal of dissolved organic matter (as total organic carbon) was found to be about 80% for both NF and RO membranes used in this study. During the membrane autopsy tests, five sections of the fouled membrane were cut along each NF and RO membrane module from the feed inlet side to the concentrate outlet side, the specific flux for each membrane section was measured before and after each cleaning step. As expected, the degree of fouling was intensified along the membrane surface as the feed flow approached the outlet. Based on the analysis results of wash water used in each cleaning step, the major foulants attached to the membrane surface appeared to be Ca bound with inorganic matter and Si bound with organic matter. Fe seemed to be a great contributor to irreversible fouling. The SEM analysis indicated that the organic matter was forming the first fouling layer close to the membrane and that the inorganic matter was layered top of the organic fouling layer in a tetragonal shape. Any evidence of biofouling was not observed in this study because most of microorganisms had been already removed by the UF pretreatment.     

Identification and understanding of fouling in low-pressure membrane (MF/UF) filtration by natural organic matter (NOM)

An understanding of natural organic matter (NOM) as a membrane foulant and the behavior of NOM components in low-pressure membrane fouling are needed to provide a basis for appropriate selection and operation of membrane technology for drinking water treatment. Fouling by NOM was investigated by employing several innovative chemical and morphological analyses.

Source (feed) waters with a high hydrophilic (HPI) fraction content of NOM resulted in significant flux decline. Macromolecules of a relatively hydrophilic character (e.g. polysaccharides) were effectively rejected by low-pressure membranes, suggesting that macromolecular compounds and/or colloidal organic matter in the hydrophilic NOM fraction may be a problematic foulant of low-pressure membranes. Moreover, the significant organic fouling that is contributed by polysaccharides and/or proteins in macromolecular and/or colloidal forms depends on molecular shape (structure) as well as size (i.e. molecular weight). More significant flux decline was observed in microfiltration (MF) compared to ultrafiltration (UF) membrane filtration. MF membrane fouling may be caused by pore blockage associated with large (macromolecular) hydrophilic molecules and/or organic colloids. In the case of UF membranes, the flux decline may be caused by sequential or simultaneous processes of surface (gel layer) coverage during filtration. Morphological analyses support the notion that membrane roughness may be considered as a more important factor in membrane fouling by controlling interaction between molecules and the membrane surface, compared to the hydrophobic/hydrophilic character of membranes. Membrane fouling mechanisms are not only a function of membrane type (MF versus UF) but also depend on source (feed) water characteristics.