Removal of biodegradable dissolved organic carbon in a water treatment plant

A new scheme of treatment has been developed in the water treatment plant of Ivry-sur-Seine near Paris. This treatment consists of a pretreatment of preozonization, contact coagulation, coagulation on a filter, slow sand filtration, ozonization and GAC filtration. We have tested the efficiency of this new line of treatment for the removal of BDOC and have attempted to correlate the results with the removal of organic matter (global parameters). Results show a very good efficiency of slow sand filtration and we think that this treatment step allows production of a biologically stable water.     

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.     

A method for the measurement of biodegradable organic carbon in waters

In the last few years several methods have been proposed for determining biodegradable dissolved organic carbon (BDOC) in waters. A modification of an original method for measuring BDOC is proposed. This method is suitable for discrete samples and for measuring the biodegradability of organic compounds dissolved in water. It consists of a dynamic procedure that measures the decrease in the dissolved organic carbon (DOC) in the sample of water. The sample is recirculated through a glass column containing a biofilm attached to a novel support medium. The method has been used to study waters at different steps in a water-treatment process and to measure the biodegradability of different dissolved organic substances in water.     

Assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC):: complementary measurements

The objective of this study was to evaluate the necessity of measuring both assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) as indicators of bacterial regrowth potential. AOC and BDOC have often been measured separately as indicators of bacterial regrowth, or together as indicators of bacterial regrowth and disinfection by-product formation potential, respectively. However, this study proposes that both AOC and BDOC should be used as complementary measurements of bacterial regrowth potential. In monitoring of full-scale membrane filtration, it was determined that nanofiltration (NF) removed over 90% of the BDOC while allowing the majority of the AOC through. Heterotrophic plate counts (HPC) remained low during the entire period of monitoring due to high additions of disinfectant residual. In a two-year monitoring of a water treatment plant that switched its treatment process from chlorination to chlorination and ozonation, it was observed that the plant effluent AOC increased by 127% while BDOC increased by 49% after the introduction of ozone. Even though AOC is a fraction of BDOC, measuring only one of these parameters can potentially under- or over-estimate the bacterial regrowth potential of the water.     

Implications of organic carbon in the deterioration of water quality in reclaimed water distribution systems

Changes in water quality in reclaimed water distribution systems are a major concern especially when considering the potential for growth of pathogenic microbes. A survey of 21 wastewater process configurations confirmed the high quality effluent produced using membrane bioreactor (MBR) technology, but suggests that other technologies can be operated to produce similar quality. Data from an intensive twelve-month sampling campaign in four reclaimed water utilities revealed the important trends for various organic carbon parameters including total organic carbon (TOC), biodegradable dissolved organic carbon (BDOC), and assimilable organic carbon (AOC). Of the four utilities, two were conventional wastewater treatment with open reservoir storage and two employed MBR technology with additional treatment including UV, ozone, and/or chlorine disinfection. Very high BDOC concentrations occurred in conventional systems, accounting for up to 50% of the TOC loading into the system. BDOC concentrations in two conventional plants averaged 1.4 and 6.3 mg/L and MBR plants averaged less than 0.6 mg/L BDOC. Although AOC showed wide variations, ranging from 100 to 2000 μg/L, the AOC concentrations in the conventional plants were typically 3-10 times higher than in the MBR systems. Pipe-loop studies designed to understand the impact of disinfection on the microbiology of reclaimed water in the distribution system revealed that chlorination will increase the level of biodegradable organic matter, thereby increasing the potential for microbial growth in the pipe network. This study concludes that biodegradable organic carbon is an important factor in the microbial quality and stability of reclaimed water and could impact the public health risk of reclaimed water at the point of use.     

优化混凝控制水中可生物降解有机物

研究了优化混凝条件下对水中可生物降解有机物的去除效率，并和水厂实际运行效率进行了比较。结果表明：①最优混凝的pH＝6．5—7．0，②最优混凝剂量一般为30—40mg/L，②优化混凝明显提高了混凝工艺对有机物的去除效率，对TOC、AOC和BDOC的去除率分别比水厂实际运行效率提高了9％～21％、0～29％和7％～24％。     

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.     

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。     

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.     

Indigenous bacterial inocula for measuring the biodegradable dissolved organic carbon (BDOC) in waters

A collaborative study was carried out in order to compare the biodegradable dissolved organic carbon (BDOC) analysis using different indigenous mixed bacterial populations as inocula. The variables examined in the study were the laboratories, the water samples (raw, ozonated or finished water), the origin of the inoculum: suspended bacteria from river waters and attached bacteria onto sand taken from drinking water treatment plants. Variances associated with individual components of this study were isolated: the laboratories represented the highest source of variation (56.6–70.7%), while the inoculum origin contribution to the increase of variance is lower (12–26%). As a conclusion, indigenous mixed bacterial populations (suspended or attached bacteria) may be used reliably as standard inocula in BDOC determinations without introducing excessive variability.     

Use of biodegradable dissolved organic carbon (BDOC) to assess the potential for transformation of wastewater-derived contaminants in surface waters

Wastewater-derived contaminants (WWDCs), such as steroid hormones, pharmaceuticals and personal care products, have been detected in surface waters at concentrations that pose potential risks to aquatic ecosystems. To assess the factors controlling biotransformation of these compounds in effluent-dominated surface waters (i.e., surface waters containing a high proportion of wastewater effluent), microcosm experiments were conducted with 10 pharmaceuticals and five steroids typically detected in wastewater effluent. Some of the compounds underwent rapid biotransformation under all conditions (estrone, 17beta-estradiol, progesterone, testosterone and triclosan), while carbamazepine was always resistant to biotransformation. For the remaining compounds, the rate of biotransformation was related to the amount and type of biodegradable dissolved organic carbon (BDOC). The rates of biotransformation of these WWDCs increased as the initial concentration of wastewater BDOC increased, indicating a relationship between microbial activity and biotransformation rate. Furthermore, BDOC derived from aquatic plants resulted in a better ability to remove certain recalcitrant compounds (gemfibrozil and sulfamethoxazole) as compared to that derived from wastewater effluent. These observations indicate that for each source of BDOC, it may be possible to use BDOC for predicting the rate of biotransformation of WWDCs in surface waters.     

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.     

Formation of assimilable organic carbon during oxidation of natural waters with ozone, chlorine dioxide, chlorine, permanganate, and ferrate

Five oxidants, ozone, chlorine dioxide, chlorine, permanganate, and ferrate were studied with regard to the formation of assimilable organic carbon (AOC) and oxalate in absence and presence of cyanobacteria in lake water matrices. Ozone and ferrate formed significant amounts of AOC, i.e. more than 100 μg/L AOC were formed with 4.6 mg/L ozone and ferrate in water with 3.8 mg/L dissolved organic carbon. In the same water samples chlorine dioxide, chlorine, and permanganate produced no or only limited AOC. When cyanobacterial cells (Aphanizomenon gracile) were added to the water, an AOC increase was detected with ozone, permanganate, and ferrate, probably due to cell lysis. This was confirmed by the increase of extracellular geosmin, a substance found in the selected cyanobacterial cells. AOC formation by chlorine and chlorine dioxide was not affected by the presence of the cells. The formation of oxalate upon oxidation was found to be a linear function of the oxidant consumption for all five oxidants. The following molar yields were measured in three different water matrices based on oxidant consumed: 2.4-4.4% for ozone, 1.0-2.8% for chlorine dioxide and chlorine, 1.1-1.2% for ferrate, and 11-16% for permanganate. Furthermore, oxalate was formed in similar concentrations as trihalomethanes during chlorination (yield ∼ 1% based on chlorine consumed). Oxalate formation kinetics and stoichiometry did not correspond to the AOC formation. Therefore, oxalate cannot be used as a surrogate for AOC formation during oxidative water treatment.     

Investigation of assimilable organic carbon (AOC) and bacterial regrowth in drinking water distribution system

This paper investigated the variation of assimilable organic carbon (AOC) concentrations in water from several typical water treatment plants and distribution systems in a northern city of China. It is concluded from this study that: (1) The AOC in most of the product water of the studied water treatment plants and the water from the associated distribution systems could not meet the biostability criteria of 50-100 microg/L. (2) Only 4% of the measured AOC concentrations were less than 100 microg/L. However, about half of the measured AOC values were less than 200 microg/L. (3) Better source water quality resulted in lower AOC concentrations. (4) The variation of AOC concentrations in distribution systems was affected by chlorine oxidation and bacterial activity: the former resulted in an increase of AOC value while the latter led to a reduction in AOC. (5) The variation of AOC concentration followed different patterns in different distribution systems or different seasons due to their respective operational characteristics. (6) Less than 30% of AOC could be removed by a conventional treatment process, whereas 30-60% with a maximum of 50-60% could be removed by granular activated carbon (GAC). (7) The observation via scanning electron microscope (SEM) on distribution pipe tubercle samples demonstrated that the pipe inner wall was not smooth and bacteria multiplied in the crevice as well as in the interior wall of distribution pipes.     

Impact of UV disinfection on microbially available phosphorus,organic carbon,and microbial growth in drinking water

UV irradiation at a wavelength of 253.7 nm (UV(254)) is commonly used for drinking water disinfection. UV radiation is known to convert organically combined phosphorus to orthophosphate and to degrade natural organic matter. We studied if UV disinfection increases the amount of microbially available forms of organic carbon and phosphorus in drinking waters with different characteristics, and if these changes in water chemical quality could enhance the microbial growth in drinking water. The UV(254) dose (15-50 mWs/cm(2)) used in waterworks reduced the concentration of assimilable organic carbon and the sum of the molecular size fractions. The release of microbially available phosphorus needed higher doses (204 mWs/cm(2)) of UV(254) radiation. Of bacteria in drinking water, 90% were inactivated with UV(254)-irradiation doses below 50 mWs/cm(2). A high dose (501 mWs/cm(2)) of UV(254) radiation inhibited the microbial growth in water.     

Determination of biodegradable dissolved organic carbon in waters: comparison of batch methods

An effect of different types of bacterial inocula upon the final biodegradable dissolved organic carbon (BDOC) result was investigated in samples of both low and high BDOC concentrations. Stream water and leaf leachate samples were incubated either with free, suspended bacteria or with bacteria attached to the stream sediment particles or attached to artificial substrata. The time course of dissolved organic carbon (DOC) decomposition was observed using absorbance analysis of DOC. BDOC determination by means of commonly used suspended bacteria as the inoculum made for an underestimation of BDOC between 5% and 25%, compared with attached bacterial community (biofilm). The reason for these findings could be the higher microbial diversity, higher metabolic activity of attached bacteria and abiotic adsorption of organic molecules to inorganic support and biofilm matrix surfaces. Adsorbed DOC is easily hydrolyzed and utilized by biofilm bacteria.     

Membrane bioreactor process for removing biodegradable organic matter from water

This research investigated a membrane bioreactor (MBR) process for removing biodegradable organic matter (BOM) and trihalomethane (THM) precursors from pre-ozonated water. Bench-scale and mini-pilot-scale MBR experiments were conducted using powdered activated carbon (PAC) and acclimated biomass. Dissolved organic carbon (DOC) was removed through a combination of adsorption and biodegradation mechanisms, and the initial DOC removals depended on carbon dose, while steady-state removals were in the 20-60 percent range under various operating conditions. Both assimilable organic carbon (AOC) and total aldehydes were mostly removed to near detection limits and were not affected by PAC dosage. The AOC(NOX) removals were significantly higher than AOC(P17) or total AOC removals probably because the MBR microbial consortium was closer in characteristics to Aquaspirillum NOX than to Pseudomonas fluorescens (P17). The DOC was used instead of biodegradable organic carbon (BDOC) as a parameter for evaluating disinfection byproduct formation and bacterial regrowth potentials because BDOC assays did not yield consistent and conclusive results due to analytical difficulties. The removals of THM precursors were high when PAC was added; however, steady-state removals were a function of operating conditions and PAC dosage. Addition of PAC enhanced DOC removals and membrane permeate fluxes. Furthermore, pre-ozonation reduced membrane fouling and enhanced membrane permeate flux.     

Changes in content of microbially available phosphorus,assimilable organic carbon and microbial growth potential during drinking water treatment processes

There are regions where microbial growth in drinking water is limited by phosphorus instead of organic carbon. In phosphorus limited waters small changes in phosphorus concentration significantly affect microbial growth. We studied how water treatment processes in waterworks affect the availability of microbial nutrients and microbial growth potential in drinking water. The nutrients studied were assimilable organic carbon (AOCpotential) and microbially available phosphorus (MAP) which both were quantified by bioassays. Chemical coagulation, commonly used in surfacewater works, effectively removed AOCpotential and MAP. In contrast to activated carbon filtration, ozonation increased the concentrations of AOCpotential and MAP, and also microbial growth potential. In most of the drinking waters, microbial growth was limited by phosphorus, and microbial growth potential correlated with the MAP concentration. Microbial growth potential was lowest in drinking waters produced from surface waters with efficient treatment technique and highest in less treated ground waters.     

可生物降解有机物在水厂净水工艺中的变化

以上海市两座不同水源的典型水厂为研究对象,分析了可生物降解有机物(BOM)和总有机物(以DOC表征)在水厂常规净水工艺中的变化规律.结果表明,水厂常规工艺对AOC、BDOC与DOC的去除能力均不高,且受水温影响明显,两水厂出水均为生物不稳定性饮用水;DOC主要在沉淀单元被去除,BDOC在沉淀、砂滤单元都有去除,AOC则主要在砂滤单元被去除;加氯可造成DOC(或BDOC)向AOC的转化,使出厂水AOC浓度增加,要确保出厂水的生物稳定性,必须同步削减水中BOM与总有机物的浓度.