不同给水处理工艺的饮用水生物稳定性研究

以生物可同化有机碳（AOC）作为饮用水生物稳定性的评价指标,对常规处理工艺和臭氧／生物活性炭（O3／BAC）深度处理工艺控制AOC的效果进行了研究。结果表明：两种工艺都会使出厂水的生物稳定性变差,常规处理工艺和深度处理工艺使出厂水的AOC平均浓度分别增加了26％、70％;尽管砂滤和BAC滤池去除AOC的效果良好,但O3氧化和氯胺消毒会大幅度提高AOC浓度。因此,有必要采取减少后臭氧投加量或单独采用BAC、增加生物滤池接触时间以及减少消毒剂投加量等措施来控制AOC浓度,促使出厂水水质达到生物稳定。     

臭氧一生物活性炭工艺去除饮用水中AOC的研究

AOC是衡量饮用水生物稳定性的重要指标。研究发现,不同的臭氧投加量下砂滤出水的AOC变化不显著,考虑氧化作用和消毒效果,将最佳的臭氧投量确定为1～2mg／L。生物活性炭（BAC）滤池改善了臭氧氧化后出水的生物稳定性,对TAOC的去除率稳定在28％～65％,而对AOC—P17的去除效果优于AOC—NOX的,因而表现出一定的选择性。较长的空床接触时间（EBCT）并不能保证对AOC的良好去除,但有利于TOC的去除,同时水温的降低一定程度上影响了BAC对AOC的去除效果。     

北方某城市给水管网水质生物稳定性研究

以我国东北某市市政给水管网为研究对象,采用AOC和BDOC指标共同评价了管网水的生物稳定性。研究结果表明：管网水中AOC为39—379μg/L,BDOC为0．8～2．8mg／L,属于生物略不稳定的饮用水;随着管网的延长,水中的AOC和BDOC浓度总体上处于降低趋势,余氯浓度对AOC和BDOC浓度的变化均有较大影响;冬、夏两季节,管网水中AOC占BDOC的比例分别为5．8％和6．2％。     

给水处理工艺中AOC去除效果的研究进展

可同化有机碳(AOC)作为水质生物稳定性的评价指标,被国内外研究学者广泛研究。传统的水处理工艺对AOC的去除效果有限且不稳定,饮用水深度处理工艺对AOC的影响各有不同。主要介绍了国内外在AOC去除方面的研究进展,包括常规处理工艺、吸附过滤、臭氧氧化等给水处理工艺,并总结了生物处理工艺有效提高生物稳定性的研究方向。     

生物活性炭技术的安全性评价

生物活性炭技术在很大程度上提高了饮用水的安全性：一方面它可以有效去除水中的微量有机污染物、消毒副产物及前质、臭氧化副产物等，提高了饮用水的化学安全性；另一方面能明显降低水中的AOC浓度，提高了生物稳定性，进而增加了饮用水的生物安全性。但是在生物活性炭技术应用过程中也存在着影响饮用水安全性的因素，例如出水的细菌数问题以及生成的新化学物质毒性问题。随着化学分析技术和生物检测技术的发展，更多有毒有害的化学物质和致病微生物将会被人们所发现，因此如何保障饮用水的安全性仍将是今后生物活性炭技术研究的重大课题。     

以AOC评价管网水中异养菌的生长潜力

对澳门管网水中异养菌二次生长和水质生物稳定性指标的相关关系的研究结果表明：（1）澳门管网水基本属于生物稳定的饮用水；（2）澳门管网沿途水中可同化有机碳（AOC）和可降解溶解性有机物（BDOC）的变化不明显；（3）降水量和水温对于AOC的季节变化有很大影响，而原水水质、处理工艺和水温则对BDOC的季节变化有很大影响；（4）由于管网水中AOC和异养菌计数（HPC）有明显的相关关系，而BDOC与HPC间无明显的相关关系，故建设将AOC作为评价管网水中异养菌二次生长潜力的首要指标。     

氯及氯胺消毒对饮用水生物稳定性的影响研究

以可同化有机碳(AOC)和微生物再生长潜能(BRP)作为饮用水生物稳定性的评价指标,通过静态消毒试验研究了氯及氯胺的投加对饮用水生物稳定性的影响,并在此基础上提出通过投加消毒剂控制饮用水生物稳定性的合理建议。     

臭氧—生物活性炭工艺去除饮用水中AOC的研究

AOC是衡量饮用水生物稳定性的重要指标.研究发现,不同的臭氧投加量下砂滤出水的AOC变化不显著,考虑氧化作用和消毒效果,将最佳的臭氧投量确定为1～2 mg/L.生物活性炭(BAC)滤池改善了臭氧氧化后出水的生物稳定性,对TAOC的去除率稳定在28%～65%,而对AOC-P17的去除效果优于AOC-NOX的,因而表现出一定的选择性.较长的空床接触时间(EBCT)并不能保证对AOC的良好去除,但有利于TOC的去除,同时水温的降低一定程度上影响了BAC对AOC的去除效果.     

饮用水的生物稳定性研究进展

近些年的研究表明：当水厂出水中含有一定量的有机物时，细菌将附着于管网管壁生长形成生物膜，导致管网腐蚀和结垢降低管网的输水能力，继而导致二级泵站动力消耗增加，并会导致用户水质恶化，色度和浊度上升；生物膜与管网水中病源微生物会对饮用者的健康造成直接的威胁，即这类出水的生物稳定性较差。目前，国际上大都采用测定AOC（Assimilable organic carbon）即可同化有机碳来判定饮用水的生物稳定性。本文将针对近些年来针对AOC的研究成果进行论述。     

再生水深度处理工艺对AOC的去除效果

生物可同化有机碳(AOC)是有机物中最易被微生物用于合成菌体、支持异养菌生长繁殖的营养基质,是评价再生水水质生物稳定性的重要指标。对北京市3座再生水厂不同深度处理工艺出水AOC浓度变化情况进行分析,结果表明:经臭氧氧化后AOC升高了12%~233%,导致再生水水质生物稳定性降低;经微滤(MF)后出水AOC变化率为-7%~5%,对再生水水质生物稳定性影响不大;曝气生物滤池和反渗透出水AOC分别降低了18%~86%和54%~83%,可有效提高再生水水质生物稳定性。     

Investigation of assimilable organic carbon (AOC) in flemish drinking water

The aim of the study was to investigate the drinking water supplied to majority of residents of Flanders in Belgium. Over 500 water samples were collected from different locations, after particular and complete treatment procedure to evaluate the efficiency of each treatment step in production of biologically stable drinking water. In this study assimilable organic carbon (AOC) was of our interest and was assumed as a parameter responsible for water biostability. The influence of seasons and temperature changes on AOC content was also taken into account. The AOC in most of the non-chlorinated product water of the studied treatment plants could not meet the biostability criteria of 10 mug/l, resulting in the mean AOC concentration of 50 microg/l. However, majority of the examined chlorinated water samples were consistent with proposed criteria of 50--100 microg/l for systems maintaining disinfectant residual. Here, mean AOC concentration of 72 microg/l was obtained. Granular activated carbon filtration was helpful in diminishing AOC content of drinking water; however, the nutrient removal was enhanced by biological process incorporated into water treatment (biological activated carbon filtration). Disinfection by means of chlorination and ozonation increased the water AOC concentration while the ultraviolet irradiation showed no impact on the AOC content. Examination of seasonal AOC variations showed similar fluctuations in six units with the highest values in summer and lowest in winter.     

Reducing the concentration of assimilable organic carbon (AOC) in treated drinking water

This study focuses on reducing the concentration of assimilable organic carbon (AOC) in treated drinking water. Experiments were conducted to evaluate the efficiency of AOC removal by biological activated carbon filters (BACF) in a pilot-scale system. The measured values of AOC in treated drinking water were approximately 59.0 ± 8.6 μg acetate-C/L. The results show that BACFs reduce the total concentration of AOC. The concentration of AOC primarily indicates microbial growth in a water supply network, and the amount of AOC in the water is significantly reduced after BACF treatment. After BACF treatment, the removal of AOC was approximately 58% after 40 min of empty-bed contact time. An AOC empirical equation was established by determining the relationship between water quality parameters, such as total organic carbon, dissolved organic carbon, UV₂₅₄, ammonia nitrogen, and total phosphorous.     

南水北调东线供水有机物含量对出厂水水质的影响

针对南水北调东线水引入胶东供水后水源水中有机碳的变化进行了分析,发现2016年以来水源水中有机碳含量显著升高,平均值在5 mg/L以上,有机碳含量的升高造成水中存在异嗅味、消毒副产物浓度升高、水质生物稳定性变差等问题。为了解目前水厂工艺对生物可同化有机碳(AOC)的去除作用和管网水质的生物稳定性状况,以某水厂为研究对象,分析了2019年2月水厂处理工艺各单元出水中TOC含量、有机碳的分子质量分布和AOC含量。结果表明,水厂处理工艺对TOC的去除率为23. 9%,出厂水中TOC含量较高。水厂原水主要以分子质量<0. 5 ku和3～5 ku的有机碳为主,各工艺段出水中不同分子质量有机碳对总溶解性有机碳的相对贡献变化不大。水厂原水AOC含量为322. 36μg/L,AOC-P17占总AOC的66. 1%,水处理工艺对AOC的总去除率为46. 1%,AOC-P17的去除率高于AOC-NOX的去除率。     

Biostability analysis for drinking water distribution systems

The ability to limit regrowth in drinking water is referred to as biological stability and depends on the concentration of disinfectant residual and on the concentration of substrate required for the growth of microorganisms. The biostability curve, based on this fundamental concept of biological stability, is a graphical approach to study the two competing effects that determine bacterial regrowth in a distribution system: inactivation due to the presence of a disinfectant, and growth due to the presence of a substrate. Biostability curves are a practical, system specific approach for addressing the problem of bacterial regrowth in distribution systems. This paper presents a standardized algorithm for generating biostability curves and this will enable water utilities to incorporate this approach for their site-specific needs. Using data from pilot scale studies, it was found that this algorithm was applicable to control regrowth of HPC in chlorinated systems where AOC is the growth limiting substrate, and growth of AOB in chloraminated systems, where ammonia is the growth limiting substrate.     

Impact of UV/H(2)O(2) advanced oxidation treatment on molecular weight distribution of NOM and biostability of water

The presence of natural organic matter (NOM) poses several challenges to the commercial practice of UV/H₂O₂ process for micropollutant removal. During the commercial application of UV/H₂O₂ advanced oxidation treatment, NOM is broken down into smaller species potentially affecting biostability by increasing Assimilable Organic Carbon (AOC) and Biodegradable Organic Carbon (BDOC) of water. This work investigated the potential impact of UV/H₂O₂ treatment on the molecular weight distribution of NOM and biostability of different water sources. A recently developed flow cytometric method for enumeration of bacteria was utilized to assess biological stability of the treated water at various stages through measurement of AOC. BDOC was also assessed for comparison and to better study the biostability of water. Both AOC and BDOC increased by about 3-4 times over the course of treatment, indicating the reduction of biological stability. Initial TOC and the source of NOM were found to be influencing the biostability profile of the treated water. Using high performance size exclusion chromatography, a wide range of organic molecule weights were found responsible for AOC increase; however, low molecular weight organics seemed to contribute more. Positive and meaningful correlations were observed between BDOC and AOC of different waters that underwent different treatments.     

Permeability of low molecular weight organics through nanofiltration membranes

The removal of natural organic matter (NOM) using nanofiltration (NF) is increasingly becoming an option for drinking water treatment. Low molecular weight (LMW) organic compounds are nevertheless only partially retained by such membranes. Bacterial regrowth and biofilm formation in the drinking water distribution system is favoured by the presence of such compounds, which in this context are considered as the assimilable organic carbon (AOC). In this study, the question of whether NF produces microbiologically stable water was addressed. Two NF membranes (cut-off of about 300 Da) were tested with different natural and synthetic water samples in a cross-flow filtration unit. NOM was characterised by liquid chromatography with organic carbon detection (LC-OCD) using a size-exclusion column in addition to specific organic acid measurements, while AOC was measured in a batch growth bioassay.Similarly to high molecular weight organic compounds like polysaccharides or humic substances that have a permeability lower than 1%, charged LMW organic compounds were efficiently retained by the NF membranes tested and showed a permeability lower than 3%. However, LMW neutrals and hydrophobic organic compounds permeate to a higher extent through the membranes and have a permeability of up to 6% and 12%, respectively. Furthermore, AOC was poorly retained by NF and the apparent AOC concentration measured in the permeated water was above the proposed limit for microbiologically stable water. This indicates that the drinking water produced by NF might be biologically unstable in the distribution system. Nevertheless, in comparison with the raw water, NF significantly reduced the AOC concentration.     

Mechanistic and kinetic evaluation of organic disinfection by-product and assimilable organic carbon (AOC) formation during the ozonation of drinking water

Ozonation of drinking water results in the formation of low molecular weight (LMW) organic by-products. These compounds are easily utilisable by microorganisms and can result in biological instability of the water. In this study, we have combined a novel bioassay for assessment of assimilable organic carbon (AOC) with the detection of selected organic acids, aldehydes and ketones to study organic by-product formation during ozonation. We have investigated the kinetic evolution of LMW compounds as a function of ozone exposure. A substantial fraction of the organic compounds formed immediately upon exposure to ozone and organic acids comprised 60-80% of the newly formed AOC. Based on experiments performed with and without hydroxyl radical scavengers, we concluded that direct ozone reactions were mainly responsible for the formation of small organic compounds. It was also demonstrated that the laboratory-scale experiments are adequate models to describe the formation of LMW organic compounds during ozonation in full-scale treatment of surface water. Thus, the kinetic and mechanistic information gained during the laboratory-scale experiments can be utilised for upscaling to full-scale water treatment plants.     

Comparison of methods for the measurement of biodegradable organic carbon and assimilable organic carbon in water

In the last few years different methods for determining assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) in drinking water have been proposed. However, there is no agreement on the most suitable methods for the assessment of treatment processes. A comparison of six methods, one for AOC(P17) determination and five for BDOC determination, using water samples taken at different steps in a water-treatment process in Sant Joan Despí (Barcelona, Spain) is reported. Results show that the biodegradable matter values given by AOC measurements are substantially lower than those obtained using BDOC methods. The various BDOC methods do not differ significantly in their results.     

Formation of assimilable organic carbon (AOC) and specific natural organic matter (NOM) fractions during ozonation of phytoplankton

Ozonation of natural surface water increases the concentration of oxygen-containing low molecular weight compounds. Many of these compounds support microbiological growth and as such are termed assimilable organic carbon (AOC). Phytoplankton can contribute substantially to the organic carbon load when surface water is used as source for drinking water treatment. We have investigated dissolved organic carbon (DOC) formation from the ozonation of a pure culture of Scenedesmus vacuolatus under defined laboratory conditions, using a combination of DOC fractionation, analysis of selected organic acids, aldehydes and ketones, and an AOC bioassay. Ozonation of algae caused a substantial increase in the concentration of DOC and AOC, notably nearly instantaneously upon exposure to ozone. As a result of ozone exposure the algal cells shrunk, without disintegrating entirely, suggesting that DOC from the cell cytoplasm leaked through compromised cell membranes. We have further illustrated that the specific composition of newly formed AOC (as concentration of organic acids, aldehydes and ketones) in ozonated lake water differed in the presence and absence of additional algal biomass. It is therefore conceivable that strategies for the removal of phytoplankton before pre-ozonation should be considered during the design of drinking water treatment installations, particularly when surface water is used.