摘要
以国内投产最大规模的纳滤水厂为研究对象 ,针对“常规工艺+超滤+纳滤”的深度处理工艺,结合水厂运行实况、进行水质分析和工艺处理效能研究。研究表明纳滤工艺可有效去除原水中的类腐殖酸和类富里酸物质等有机物,对原水中溶解性有机碳去除率达到82%。三卤甲烷类消毒副产物(THMs-DBPs)生成势实验显示纳滤出水THMs-DBPs浓度为14.45~18.65 μg·
饮用水处理工艺始终在不断提高完善。从工艺升级看,传统的“混凝-沉淀-过滤-消毒”四步工艺逐渐走向深度处理工艺。随着工业化进程加剧,工业制造产生的有机污染物通过人类使用途径和制造过程中不可避免的泄露途径,导致自然水体和饮用水厂原水中有机污染物浓度增
饮用水深度处理工艺主要在常规工艺后增设臭氧活性生物炭工艺或者膜法处理。目前在全国范围来看,深度处理中臭氧活性生物炭工艺应用范围最广,但工艺仍存在微生物泄露和氧化过程生成中间体等挑
NF膜截留物质粒径约为1 nm,介于超滤和反渗透之
本文以国内目前最大规模的纳滤饮用水厂——张家港市第四水厂为例,综合调研水厂运行数据和日常运行维护措施,分析了水厂工艺水质监测数据、各处理单元出水中DOM去除特征和消毒副产物(DBPs)前体物变化情况等。研究表明纳滤水厂产水能够满足《生活饮用水卫生标准》(GB5749-2022)要求、提升饮用水品质。大型纳滤水厂的成功实践为NF膜在市政饮用水处理领域的应用和推广提供了技术支撑。
选取中国江苏省张家港市第四水厂。当地综合考虑经济发展及改善饮用水品质的需要,2018年率先在全国进行大型NF膜饮用水厂工程探索,并于2020年投产使用。张家港市第四水厂纳滤高品质饮用水提标扩建工程荣获“2022全球水奖年度最佳水项目”。水厂使用长江水作为原水,采用“折板混凝–水平沉淀–浸没式超滤–保安过滤器–三段式纳滤–氯消毒”的双膜法深度处理工艺,供水规模达到2×1

图1 纳滤饮用水厂工艺简图
Fig.1 The treatment process diagram of nanofiltration drinking water treatment plant (NF-DWTP)
整个水厂膜工艺共计10条平行生产线。每条生产线由“超滤池-保安过滤器-三段式纳滤”构
运行参数 | 数值 |
---|---|
最高运行压力 | 600 psi (41Bar) |
最高运行温度 | 45℃ |
最大给水浊度 | 1 NTU |
游离氯限值 | < 0.1 ppm |
连续运行pH范围 | 2~11 |
短时清洗pH范围 | 1~12 |
最大进水SDI | 5 |
按照水厂工艺沿线分布,分别在各处理单元处取得原水(RW)、平流沉淀池出水(SW)、超滤膜单元出水(UW)、保安过滤器出水(CW)、第1段纳滤出水(NW1)、第2段纳滤出水(NW2)、第3段纳滤出水(NW3)和出厂水(EW)。将取得的水样当天送回实验室4 ℃下冷藏保存,使用醋酸纤维针孔过滤器(0.45 μm)过滤备用。
使用三维荧光分光光度计(3D-EEM,F-2 700,日立,日本)分析水样DOM。仪器波长扫描速度设置为12 000 nm·mi
将50 mL待测水样加入棕色玻璃瓶,在标准条件下用过量的游离氯对样品进行氯化,通过N,N-二乙基对苯二胺比色法和便携式分光光度计(DR1 900,HACH,美国)测量残留氯浓度,残留氯浓度保持在3~5 mg·
在水厂各工艺单元运行过程中,超滤单元后设置监测点以确定预处理系统出水水质。沉淀池出水和超滤出水浊度如

图2 预处理系统产水水质
Fig.2 Water quality of the treated water from pretreatment system
DOM广泛存在于自然界水体,是碳水化合物、多糖、氨基酸蛋白质、脂质、腐殖质和人为制造的有机污染物等不同化合物的复杂混合

图3 纳滤水厂各处理单元出水三维荧光图谱
Fig.3 3D EEM spectra of each treatment unit of NF-DWTP

图4 各处理单元出水中DOM去除情况
Fig.4 The DOM removal of the treated water from each treatment unit
下面将结合区域荧光积分进一步说明。由
溶解性有机物的研究结果表明NF膜能很好去除水中有机物。为了保证后续供水水质,消毒仍然是确保饮用水生物安全的主要工艺。DBPs是消毒剂与水中有机物反应的生成物,大量研究表明饮用水中DBPs前体有机物浓度过高,消毒后大量生成的DBPs作为“三致”物质会增加饮用水潜在健康风

图5 各处理单元出水THMs-DBPs生成潜能
Fig.5 The formation potential of THMs-DBPs of the treated water from each treatment unit
预处理出水水质是否符合NF膜进水要求,对后续三段式纳滤工艺的稳定运行至关重要。研究选取了2022年3―8月的保安过滤器出水、即NF膜单元进水的SDI值和余氯值如

图6 2022年3月~8月NF单元进水SDI值和余氯值监测
Fig.6 The value of SDI and residual chlorine of the NF influent water from May to August 2022.
对于NF膜单元,除了定期进行水质检测外,整个系统运行的主要监测参数包括水压、水量和温度。研究在一年内对纳滤一段每月进水压力均值(P)、一段TMP、进水温度均值、产水率等参数进行统计。如

图7 一年内NF膜系统第一段产水管线的水压、TMP、水温和产水率变化
Fig.7 The pressure, TMP, water temperature and water production rate of feed water from the first stage of NF membrane system water yield lines within a year.
消耗项 | 消耗量 | |
---|---|---|
电力消耗/(kW·h) |
≈245/1 | |
阻垢剂(聚合有机小分子磷)/kg |
≈2.40/1 | |
还原剂(亚硫酸氢钠)/kg |
≈0.21/1 | |
单个膜段清洗 药品消耗量 | 氢氧化钠(30%)/kg | 30 |
乙二胺四乙酸二钠/kg | 200 | |
十二烷基苯磺酸钠/kg | 1.0 | |
盐酸(30%)/kg | 60 |
在纳滤饮用水厂内部,整个处理工艺由预处理系统和NF膜处理系统组成运行。预处理系统的主要功能是:直接去除悬浮颗粒;促进胶体颗粒和溶解有机物的脱稳和凝聚;防止纳滤单元进水携带颗粒物;在NF膜可承受的酸碱度范围内调节进水 pH 值以提高混凝性能;投加还原剂去除水中残留活性氯;抑制膜上微生物生长并减缓膜结垢和微生物污
对于NF膜处理单元,膜滤过程导致膜面逐渐累积和滋生各种物质、逐渐降低膜滤效率,因此NF膜处理系统污染控制是极其重要的。根据水体存在的污染物来源,膜表面污染物可以分为输入性污染物和内生性污染
膜表面水垢沉积是纳滤和反渗透等膜处理装置面对的重要问题。进水中的溶解性盐在膜面浓缩,当进料液中的盐溶液浓度超过其溶解度极限,会在膜面发生沉积结垢。通过实时投加阻垢剂是膜处理过程中减缓膜垢形成的主要控制工艺,该水厂采用聚合小分子有机磷阻垢剂减缓膜结垢进程。另一方面,进水中不可避免的携带微生物,逐渐在膜表面形成独特的“膜上膜”微生物污
NF膜元件的清洗工作分为纳滤物理清洗和化学清洗。物理清洗为常规性清洗,每隔12―24h采用NF产水作为清洗进水进行正向冲洗。根据水厂运行经验,NF物理清洗初期清洗策略参照反渗透膜清洗的设计思路进行,清洗时虽采用NF产水进行正向冲洗,但未调节清洗膜段的产水阀门,在实际中发现清洗效果不好。不调整NF产水侧流量,清洗水仍然按照该管段的设计回收率进行浓产水分离,冲洗强度和频率不能有效满足NF膜,不能有效冲洗出污染物,引起化学清洗频率加快。经过调整工艺,冲洗时关闭或者调小被冲洗段NF产水阀门、减少过膜产水分流,使70%~80%的冲洗水量在浓水侧水平流动冲洗,保证有效冲洗水流量大于正常运行时浓水侧流量,然后结合反向冲洗。现阶段冲洗效果良好,化学清洗启动正常。化学清洗采用先碱洗再酸洗、先清洗污染严重段再污染较轻段的分区清洗原则,按照“膜元件内部注满清洗液—高流量循环清洗—清洗液浸泡—中和清洗液并排空—清水冲洗膜元件”的清洗步骤进行。
张家港第四水厂NF膜组合工艺是国内首次大规模以微污染地表水为原水的饮用水深度处理工程。研究表明所使用的超滤膜结合NF膜工艺能够很好地处理微污染水源。纳滤膜能够明显去除原水中类腐殖酸、类富里酸物质以及其他溶解性有机物。各单元产水的消毒副产物生成潜能实验表明,NF膜能够有效减少DBPs前体物含量,降低后续消毒副产物的风险。水厂成功解决了多项NF膜运行维护的技术问题,诸如微生物污染、水温水质变化下的稳定运行、NF膜的长期维护清洗等,有效保障了NF膜系统稳定运行,成功探索出一条高品质饮用水可行技术路径。NF膜应用还面临膜系统进水污染潜力的精细监控、纳滤段的浓水处理、后续城市供水管网的对应提升等问题,需要在实践中不断摸索解决。
作者贡献声明
贺鑫:方案设计,调研取样,实验测试,论文写作;
王少华:协助调研,论文修改;
施立宪:协助调研,论文修改;
徐斌:论文指导;
王同春:协助调研;
唐玉霖:方案设计,论文指导修改。
参考文献
YANG Yun, ZHANG Xiangru, JIANG Jingyi, et al. Which micropollutants in water environments deserve more attention globally? [J]. Environmental Science & Technology, 2022, 56(1): 13. [百度学术]
上海市水务局. 上海市供水规划 (2017—2035)[S].上海;上海市水务局,2018. [百度学术]
Shanghai Municipal Water Affairs Authority. Shanghai water supply planning (2017-2035)[S].Shanghai:Shanghai Municipal Water Affairs Authority,2018. [百度学术]
LIM S, SHI J M L, VON GUNTEN U, et al. Ozonation of organic compounds in water and wastewater: a critical review [J]. Water Research, 2022, 213: 118053. [百度学术]
KOROTTA-GAMAGE S M, SATHASIVAN A. A review: potential and challenges of biologically activated carbon to remove natural organic matter in drinking water purification process [J]. Chemosphere, 2017, 167: 120. [百度学术]
SRIVASTAVA A, AGHILESH K, NAIR A, et al. Response surface methodology and artificial neural network modelling for the performance evaluation of pilot-scale hybrid nanofiltration (NF) & reverse osmosis (RO) membrane system for the treatment of brackish ground water [J]. Journal of Environmental Management, 2021, 278: 111497. [百度学术]
MOHAMMAD A W, TEOW Y H, ANG W L, et al. Nanofiltration membranes review: recent advances and future prospects [J]. Desalination, 2015, 356: 226. [百度学术]
OATLEY D L, LLENAS L, PÉREZ R , et al. Review of the dielectric properties of nanofiltration membranes and verification of the single oriented layer approximation [J]. Advances in Colloid and Interface Science, 2012, 173: 1. [百度学术]
HILAL N, AL ZOUBI H, DARWISH N A, et al. A comprehensive review of nanofiltration membranes: Treatment, pretreatment, modelling, and atomic force microscopy [J]. Desalination, 2004, 170(3): 281. [百度学术]
NTHUNYA L N, BOPAPE M F, MAHLANGU O T, et al. Fouling, performance and cost analysis of membrane-based water desalination technologies: a critical review [J]. Journal of Environmental Management, 2022, 301: 113922. [百度学术]
AHMAD N N R, ANG W L , LEO C P, et al. Current advances in membrane technologies for saline wastewater treatment: a comprehensive review [J]. Desalination, 2021, 517: 115170. [百度学术]
WANG Shichong, LI Lei, YU Shuili, et al. A review of advances in EDCs and PhACs removal by nanofiltration: Mechanisms, impact factors and the influence of organic matter [J]. Chemical Engineering Journal, 2021, 406: 126722. [百度学术]
HE Xin, TANG Yulin, WU Haowei, et al. Fouling investigation of cartridge filter (CF) used as “firewall” in a nanofiltration drinking water plant [J]. Environmental Research, 2022, 212: 113289. [百度学术]
FARHAT N M,CHRISTODOULOU C, PLACOTAS P, et al. Cartridge filter selection and replacement: optimization of produced water quantity, quality, and cost [J]. Desalination, 2020, 473: 114172. [百度学术]
王少华,施卫娟,贺鑫,等.纳滤深度处理在饮用水厂的应用与实践[J].给水排水, 2021, 47(10):13. [百度学术]
WANG S H, SHI W J, HE X, et al. Application and practice of nanofiltration advanced treatment in water treatment plant [J]. Water & Wastewater Engineering, 2021, 47(10):13. [百度学术]
EPA. Method 551.1. determination of chlorination disinfection byproducts, chlorinated solvents, and halogenated pesticides/herbicides in drinking water by liquid-liquid extraction and gas chromatography with electron-capture detection;revision 1.0[S]. Cincinnati: EPA, 1995. [百度学术]
BERG S M, WHITING Q T, HERRLI J A, et al. The role of dissolved organic matter composition in determining photochemical reactivity at the molecular level [J]. Environmental Science & Technology, 2019, 53(20): 11725. [百度学术]
SHI W, ZHUANG W E, HUR J, et al. Monitoring dissolved organic matter in wastewater and drinking water treatments using spectroscopic analysis and ultra-high resolution mass spectrometry [J]. Water Research, 2021, 188: 116406. [百度学术]
FANG Chao, YANG Xu, DING Shunke, et al. Characterization of dissolved organic matter and its derived disinfection byproduct formation along the yangtze river [J]. Environmental Science & Technology, 2021, 55(18): 12326. [百度学术]
RICHARDSON S D, PLEWA M J, WAGNER E D, et al. Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research [J]. Mutation Research/Reviews in Mutation Research, 2007, 636(1): 178. [百度学术]
EPA. Stage 2 disinfectants and disinfection byproducts rule: national primary and secondary drinking water regulations: final rule. federal register 71[S]. Cincinnati: EPA,2006. [百度学术]
国家市场监督管理总局,国家标准化管理委员会. 生活饮用水水质标准: GB5749-2022[S]. 北京:中国标准出版社,2022. [百度学术]
The State Administration for Market Regulation,National Standardization Administration Commission. Drinking water quality standards: GB5749-2022 [S] Beijing: China Standards Publishing House, 2022. [百度学术]
JEONG S, VOLLPRECHT R, CHO K, et al. Advanced organic and biological analysis of dual media filtration used as a pretreatment in a full-scale seawater desalination plant [J]. Desalination, 2016, 385: 83. [百度学术]
FEO-GARCíA J, RUIZ-GARCÍA A, RUIZ-SAAVEDRA E, et al. Cost assessment in SWRO desalination plants with a production of 600
RACHMAN R M, GHAFFOUR N, WALI F, et al. Assessment of silt density index (SDI) as fouling propensity parameter in reverse osmosis (RO) desalination systems [J]. Desalination and Water Treatment, 2013, 51(4/6): 1091. [百度学术]
KIM Y M, KIM S J, KIM Y S, et al. Overview of systems engineering approaches for a large-scale seawater desalination plant with a reverse osmosis network [J]. Desalination, 2009, 238(1/3): 312. [百度学术]
CHELLAM S, SARI M A. Aluminum electrocoagulation as pretreatment during microfiltration of surface water containing NOM: a review of fouling, NOM, DBP, and virus control [J]. Journal of Hazard Mater, 2016, 304: 490. [百度学术]
YU Haikuan, CHANG Haiqing, LI Xing, et al. Long-term fouling evolution of polyvinyl chloride ultrafiltration membranes in a hybrid short-length sedimentation/ ultrafiltration process for drinking water production [J]. Journal of Membrane Science, 2021, 630: 119320. [百度学术]
SUTZKOVER-GUTMAN I, HASSON D. Feed water pretreatment for desalination plants [J]. Desalination, 2010, 264(3): 289. [百度学术]
DE VRIES H J, STAMS A J M, PLUGGE C M. Biodiversity and ecology of microorganisms in high pressure membrane filtration systems [J]. Water Research, 2020, 172: 115511. [百度学术]