纳滤膜和低压反渗透膜去除水中氟的对比研究

通过采用NF/RO膜技术去除水中氟离子的试验研究,探讨了膜回收率、操作压力、水的pH、进水含盐量以及运行时间等参数对NF/RO膜除氟效果的影响.试验中确定NF/RO膜的最佳回收率均为15%.结果表明:在相同操作条件下(0.16～0.21 MPa),RO的膜通量是NF的1/2左右,而其F-去除率比NF高2%～15%;水的pH影响NF/RO膜对氟的去除效果,pH越高,膜对氟的去除率越高;随着进水含盐量的增加,NF/RO膜对F-的去除率下降;随着运行时间的增加,RO膜等对F-的去除率基本保持不变,NF膜下降明显.建议RO膜除氟最低压力应高于0.2 MPa;膜法除氟应尽量在弱碱性环境中操作.     

Use of fouling resistant nanofiltration and reverse osmosis membranes for dyeing wastewater effluent treatment.

Dyeing wastewater was post-treated by using nanofiltration (NF) and reverse osmosis (RO) membranes. To reduce membrane fouling, poly (vinyl alcohol) (PVA) with a neutral charge was coated on NF and RO membranes. The effect of surface charge and surface roughness on membrane fouling was investigated. Dyeing wastewater was pre-treated by using coagulation, activated sludge process, and MF process to investigate the effect of the pre-treatment on the membrane fouling. It is demonstrated that the extent of fouling is significantly influenced by the surface roughness and the surface charge on the NF and RO membranes. A membrane with a smooth and neutral surface was fouled less. The pre-treatment was essential for avoiding NF and RO membranes fouling. The quality of the final permeate was acceptable for water reuse.     

Investigation of microbial communities on reverse osmosis membranes used for process water production.

In the present study, the diversity and the phylogenetic affiliation of bacteria in a biofouling layer on reverse osmosis (RO) membranes were determined. Fresh surface water was used as a feed in a membrane-based water purification process. Total DNA was extracted from attached cells from feed spacer, RO membrane and product spacer. Universal primers were used to amplify the bacterial 16S rRNA genes. The biofilm community was analysed by 16S rRNA-gene-targeted denaturing gradient gel electrophoresis (DGGE) and the phylogenetic affiliation was determined by sequence analyses of individual 16S rDNA clones. Using this approach, we found that five distinct bacterial genotypes (Sphingomonas, Beta proteobacterium, Flavobacterium, Nitrosomonas and Sphingobacterium) were dominant genera on surfaces of fouled RO membranes. Moreover, the finding that all five "key players" could be recovered from the cartridge filters of this RO system, which cartridge filters are positioned before the RO membrane, together with literature information where these bacteria are normally encountered, suggests that these microorganisms originate from the feed water rather than from the RO system itself, and represent the fresh water bacteria present in the feed water, despite the fact that the feed water passes an ultrafiltration (UF) membrane (pore size approximately 40 nm), which is able to remove microorganisms to a large extent.     

Influence of organic and colloidal fouling on the removal of sulphamethoxazole by nanofiltration membranes.

This study investigated the effects of organic and colloidal fouling on the removal of a representative micropollutant sulphamethoxazole by two commercially available NF membranes. Alginate, bovine serum albumin and colloidal silica were selected as model foulants to simulate hydrophilic and hydrophobic organic fractions, and colloidal matter that are often found in treated effluent and surface water. Membrane fouling was related to the membrane and foulant characteristics and subsequently the separation behaviour of the micropollutant sulphamethoxazole under different solution pH. On the basis of these results, it was confirmed that membrane fouling is strongly dependent on both the foulant and membrane characteristics. The complex relationship among retention mechanisms, fouling mechanisms and the effects of fouling on retention was systematically delineated. Of the three model foulants selected for this study, colloidal fouling resulted in the most significant reduction in retention of sulphamethoxazole as well as inorganic salts, while flux decline as a result of colloidal fouling was quite moderate. Reduction in retention caused by fouling was attributed to a phenomenon known as cake-enhance concentration polarisation, which was a predominant mechanism of colloidal fouling. In addition, the reported results suggested that the effect of fouling on retention is also membrane pore size dependent.     

Treatment of dairy wastewater by two-stage membrane operation with ultrafiltration and nanofiltration

Treatment of dairy wastewater by a two-stage membrane process with ultrafiltration (UF) and nanofiltration (NF) was investigated. The results showed that the flux of UF was higher at pH = 4.6 than that at pH = 8 because the resistance of the fouling membrane was lower at the isoelectric point of protein (pH = 4.6) in UF operation. Protein rejection exceeded 99% by UF + NF operation. Lactose rejections were 98.5 and 54% for UF + NF90 and UF + NF270 respectively. Experiments on membrane cleaning showed that the fouling layer of UF and NF was mainly protein and casein which could be removed by aqueous NaOH with pH = 10. The result of long-term experiments showed that the chemical oxygen demand (COD) of NF90 permeates was below 70 mg/L consistently and the wastewater could be concentrated to 24% by a two-stage membrane process.     

Wastewater treatment with anaerobic membrane bioreactor and reverse osmosis.

Domestic wastewater from a new city district in Stockholm has been treated by an anaerobic membrane bioreactor (AMBR) followed by reverse osmosis (RO). The main objectives were to study the gas production, the reduction of organic matter and nutrient recovery. The AMBR was operated at 22 degrees C (equal to the average temperature in the influent) and a hydraulic retention time of 0.6 d. The results show that the reduction of organic matter, nitrogen and phosphorus over the AMBR was approximately 92, 9 and 9%, respectively. A stable gas production was registered throughout the evaluation period. The overall removal efficiency, i.e. including the RO, was >99% for TOC, >91% for Kj-N and about 99% for P. Adding a reverse osmosis (RO) unit to the AMBR makes it possible to produce a concentrated, nutrient rich product well suited for agricultural use. The quality of the concentrate is, in terms of nutrient concentration and heavy metal content, similar to source separated human urine, i.e. nitrogen content about 3 g N/L and <2 mg Cd/kg P. However, addition of acid is required to prevent precipitation/fouling of the RO. The total electricity use for operation for the system, including the RO-unit, is estimated to be 3-6 kWh/m3.     

Survey on production quality of electrodialysis reversal and reverse osmosis on municipal wastewater desalination

Water shortage has become an emerging environmental issue. Reclamation of the effluent from municipal wastewater treatment plant (WWTP) is feasible for meeting the growth of water requirement from industries. In this study, the results of a pilot-plant setting in Futian wastewater treatment plant (Taichung, Taiwan) were presented. Two processes, sand filter - ultrafiltration - reverse osmosis (SF-UF-RO) and sand filter - electrodialysis reversal (SF-EDR), were operated in parallel to evaluate their stability and filtrate quality. It has been noticed that EDR could accept inflow with worse quality and thus required less pretreatment compared with RO. During the operation, EDR required more frequent chemical cleaning (every 3 weeks) than RO did (every 3 months). For the filtrate quality, the desalination efficiency of SF-EDR ranged from 75 to 80% in continuous operation mode, while the conductivity ranged from 100 to 120 μS/cm, with turbidity at 0.8 NTU and total organic carbon at 1.3 mg/L. SF-EDR was less efficient in desalinating the multivalent ions than SF-UF-RO was. However for the monovalent ions, the performances of the two processes were similar to each other. Noticeably, total trihalomethanes in SF-EDR filtrate was lower than that of SF-UF-RO, probably because the polarization effects formed on the concentrated side of the EDR membrane were not significant. At the end of this study, cost analysis was also conducted to compare the capital requirement of building a full-scale wastewater reclamation plant using the two processes. The results showed that using SF-EDR may cost less than using SF-UF-RO, if the users were to accept the filtrate quality of SF-EDR.     

Influence of groundwater composition on subsurface iron and arsenic removal

Subsurface arsenic and iron removal (SAR/SIR) is a novel technology to remove arsenic, iron and other groundwater components by using the subsoil. This research project investigated the influence of the groundwater composition on subsurface treatment. In anoxic sand column experiments, with synthetic groundwater and virgin sand, it was found that several dissolved substances in groundwater compete for adsorption sites with arsenic and iron. The presence of 0.01 mmol L(-1) phosphate, 0.2 mmol L(-1) silicate, and 1 mmol L(-1) nitrate greatly reduced the efficiency of SAR, illustrating the vulnerability of this technology in diverse geochemical settings. SIR was not as sensitive to other inorganic groundwater compounds, though iron retardation was limited by 1.2 mmol L(-1) calcium and 0.06 mmol L(-1) manganese.     

反渗透处理高含盐废水的实验研究与膜污染分析

试验以经过混凝-超滤预处理后的高含盐废水为研究对象,考察了一级两段反渗透处理工艺对CODcr、TDS等的去除效果以及操作压力、温度、pH等因素对反渗透去除效果的影响。研究表明:在最佳工艺条件下,CODcr的去除率大于90%,TDS的去除率大于99%。反渗透处理后出水达到工业循环冷却水水质要求(GB50330-2002)。膜受污染后采用化学清洗和水力清洗相结合的方法可使膜的透水量恢复97.53%。     

How does the adsorption of microcystins and anatoxin-a on nanofiltration membranes depend on their co-existence and on the water background matrix

This work intends to study the adsorption of the cyanotoxins microcystin-LR (MC-LR) and anatoxin-a (ATX-a) on a nanofiltration membrane (150 Da molar mass cut-off and an isoelectric point of 5-6 in the presence of calcium ions), in particular, to understand the toxins' adsorption behaviour with the solution chemistry, namely with the background natural organic matter (NOM), the water pH and the co-existence of MC-LR and ATX-a. The results demonstrate that MC-LR adsorption increases with the water recovery due to MC-LR feed concentration increase. MC-LR adsorption is governed by hydrophobic interactions established between the membrane and the negatively charged MC-LR molecules, and between the MC-LR molecules. The increase of hydrophilic, positively charged low molar mass NOM and of hydrophobic, negatively charged high molar mass NOM does not impact MC-LR adsorption at pH 8. ATX-a adsorption onto the membrane is governed by electrostatic attractions with the membrane and NOM molecules. Background NOM minimises the ATX-a adsorption at pH 7 and enhances it at pH 4, i.e. NOM seems to act as a carrier for ATX-a adsorption onto the membrane. When ATX-a and MC-LR co-exist, adsorption is higher for ATX-a than for MC-LR at pH 4 and 7, and is higher at pH 4 for both cyanotoxins, consistent with the NOM interference.     

锰砂/石英砂滤池与纳滤膜组合工艺去除水中砷的研究

采用锰砂/石英砂滤池与纳滤膜组合工艺处理含砷水,考察锰砂/石英砂、纳滤膜(NF90、HL)、锰砂/石英砂滤池与纳滤膜组合工艺对水中砷的去除效果.结果表明,三价砷(As(Ⅲ))和五价砷(As(Ⅴ))经锰砂/石英砂过滤后能得到很好的去除,原水砷浓度250 μg/L,出水砷浓度小于50μg/L;纳滤膜对五价砷(As(Ⅴ))的去除能力很高,能达到90%以上,但是对三价砷(As(Ⅲ))的去除率不理想,为40%～60%;锰砂/石英砂复合滤池与纳滤膜组合工艺对水中砷有很好的去除效果,出水砷浓度均小于10μg/L,是理想的饮用水除砷方法.