Characterisation of dissolved organic matter in stormwater using high-performance size exclusion chromatography

Understanding the complexity of dissolved organic matter(DOM)in stormwater has drawn a lot of interest,since DOM from stormwater causes not only environmental impacts,but also worsens downstream aquatic quality associated with water supply and treatability.This study introduced and employed high-performance size exclusion chromatography(HPSEC)coupled with an ultraviolet–visible(UV–vis)diode array detector to assess changes in stormwater-associated DOM characteristics.Stormwater DOM was also analysed in relation to storm event characteristics,water quality and spectroscopic analysis.Statistical tools were used to determine the correlations within DOM and water quality measurements.Results showed that dissolved organic carbon(DOC)and UV absorbance at 254 nm(UV_(254))as conventional DOM parameters were found to be correlated well to the changes in stormwater quality during each of the three storm events studied.Both detector wavelengths(210and 254 nm)and their ratio(A_(210)/A_(254))were found to provide additional information on the physiochemical properties of stormwater-associated DOM.This study indicated that A_(210)/A_(254) is an important parameter which could be used to estimate the DOM proportions of functional groups and conjugated carbon species.This study provided also an understanding of stormwater quality constituents through assessing variability and sensitivity for various parameters,and the additional information of rainfall characteristics on runoff quality data for a better understanding of parameter correlations and influences.     

Selective elimination of chromophoric and fluorescent dissolved organic matter in a full-scale municipal wastewater treatment plant

Effluent organic matter (EfOM) from municipal wastewater treatment plants potentially has a detrimental effect on both aquatic organisms and humans. This study evaluated the removal and transformation of chromophoric dissolved organic matter (CDOM) and fluorescent dissolved organic matter (FDOM) in a full-scale wastewater treatment plant under different seasons. The results showed that bio-treatment was found to be more efficient in removing bulk DOM (in terms of dissolved organic carbon, DOC) than CDOM and FDOM, which was contrary to the disinfection process. CDOM and FDOM were selectively removed at various stages during the treatment. Typically, the low molecular weight (MW) fractions of CDOM and protein-like FDOM were more efficiently removed during bio-treatment process, whereas the humic-like FDOM exhibited comparable decreases in both bio-treatment and disinfection processes. Overall, the performance of the WWTP was weak in terms of CDOM and FDOM removal, resulting in enrichment of CDOM and FDOM in effluent. Moreover, the total removal of the bulk DOM (P < 0.05) and the protein-like FDOM (P < 0.05) displayed a significant seasonal variation, with higher removal efficiencies in summer, whereas removal of CDOM and the humic-like FDOM showed little differences between summer and winter. In all, the results provide useful information for understanding the fate and transformation of DOM, illustrating that sub-fractions of DOM could be selectively removed depending on treatment processes and seasonality.     

Prediction of DOM removal of low specific UV absorbance surface waters using HPSEC combined with peak fitting

High performance size exclusion chromatography (HPSEC) is used in water quality research primarily to determine the molecular weight distribution of the dissolved organic matter (DOM), but by applying peak fitting to the chromatogram, this technique can also be used as a tool to model and predict DOM removal. Six low specific UV absorbance (SUVA) source waters were treated using coagulation with alum and both the source and treated water samples were analysed using HPSEC. By comparing the molecular weight profiles of the source and treated waters, it was established that several DOM components were not effectively removed by alum coagulation even after high dosage alum treatment. A peak-fitting technique was applied based on the concept of linking the character (molecular weight profile) of the recalcitrant organics in the treated water with those of the source water. This was then applied to predict DOM treatability by determining the areas of the peaks which were assigned to removable organics from the source water molecular weight profile after peak fitting, and this technique quantified the removable and non-removable organics. The prediction was compared with the actual dissolved organic carbon (DOC) removal determined from jar testing and showed good agreement, with variance between 2% and 10%. This confirmed that this prediction approach, which was originally developed for high SUVA waters, can also be applied successfully to predict DOC removal in low SUVA waters.     

Characteristics of molecular weight distribution of dissolved organic matter in bromide-containing water and disinfection by-product formation properties during treatment processes

The characteristics of dissolved organic matter (DOM) and bromide ion concentration have a significant influence on the formation of disinfection by-products (DBPs). In order to identify the main DBP precursors, DOM was divided into five fractions based on molecular weight (MW), trihalomethane formation potential and haloacetic acid formation potential were determined for fractions, and the change in contents of different fractions and total DBPs during treatment processes (pre-chlorination, coagulation, sand filtration, disinfection) were studied. Moreover, the relationship between bromide concentration and DBP generation characteristics in processes was also analyzed. The results showed that the main DBP precursors were the fraction with MW < 1 kDa and fraction with MW 3−10 kDa, and the DBP''s generation ability of lower molecular weight DOM (< 10 kDa) was higher than that of higher molecular weight DOM. During different processes, pre-chlorination and disinfection had limited effect on removing organics but could alter the MW distribution, and coagulation and filtration could effectively remove organics with higher MW. For DBPs, trihalomethanes (THMs) were mainly generated in pre-chlorination and disinfection, while haloacetic acids (HAAs) were mostly generated during pre-chlorination; coagulation and sand filtration had little effect on THMs but resulted in a slight removal of HAAs. In addition, the results of ANOVA tests suggested that molecular sizes and treatment processes have significant influence on DBP formation. With increasing bromide concentration, the brominated DBPs significantly increased, but the bromine incorporation factor in the processes was basically consistent at each concentration.     

Transport and humification of dissolved organic matter within a semi-arid floodplain

In order to understand the transport and humification processes of dissolved organic matter(DOM) within sediments of a semi-arid floodplain at Rifle,Colorado,fluorescence excitation–emission matrix(EEM) spectroscopy,humification index(HIX) and specific UV absorbance(SUVA) at 254 nm were applied for characterizing depth and seasonal variations of DOM composition.Results revealed that late spring snowmelt leached relatively fresh DOM from plant residue and soil organic matter down into the deeper vadose zone(VZ).More humified DOM is preferentially adsorbed by upper VZ sediments,while non-or lesshumified DOM was transported into the deeper VZ.Interestingly,DOM at all depths undergoes rapid biological humification process evidenced by the products of microbial by-product-like(i.e.,tyrosine-like and tryptophan-like) matter in late spring and early summer,particularly in the deeper VZ,resulting in more humified DOM(e.g.,fulvic-acid-like and humic-acid-like substances) at the end of year.This indicates that DOM transport is dominated by spring snowmelt,and DOM humification is controlled by microbial degradation,with seasonal variations.It is expected that these relatively simple spectroscopic measurements(e.g.,EEM spectroscopy,HIX and SUVA) applied to depth-and temporally-distributed pore-water samples can provide useful insights into transport and humification of DOM in other subsurface environments as well.     

贵阳南明河水中溶解有机质分子量的初步研究

采用高效液相色谱系统对南明河中的有机物含量及分子量的分布特征进行了研究。南明河有机物的分子量呈多峰状态分布,分子量分布从大于3500 Da到小于1000 Da的有机物都存在。分子量在1000 Da～3500 Da之间的有机物含量占比71％～88％,分子量小于1000 Da和大于3500 Da的有机物含量很小。从整个南明河来看,上游和下游的有机物的分子量相对比较大,而中游的分子量相对比较小。     

贵州百花湖水中溶解有机质的分子量分布随深度的变化规律

利用高效体积排阻色谱法测量了百花湖水中溶解有机质的分子量及其分布。结果表明百花湖水中溶解有机质（DOM）主要以分子量小于3500道尔顿（Da）的组分为主,其中重均（Mw）和数均（Mn）分子量分别界于2300～2500 Da和1900～2150 Da之间,说明其主要来源于降水对土壤有机物的淋滤和径流作用。根据色谱分析的结果,可以把溶解有机质的分子量分布分为四个组分：大分子量组分（MW〉3500 Da）;中等偏大分子量组分（3500～2000 Da）;中等分子量组分（2000～1000 Da）和小分子量组分（MW〈1000 Da）。由于生物活动和光降解作用以及有机物的分解作用,导致各分子量组分随深度的变化规律不同,其中分子量在3500～2000 Da之间的有机物的含量随深度的增大而增大,其余组分的含量随深度的增大而减少。计算所得的溶解有机质的Mw和Mn在表层较小,在中部随深度基本保持不变,到底部又变大。这种变化趋势与分子量组分的变化结果一致。     

Effects of sulfate-reducing bacteria on methylmercury at the sediment–water interface

Sediment cores(containing sediment and overlying water) from Baihua Reservoir(SW China)were cultured under different redox conditions with different microbial activities, to understand the effects of sulfate-reducing bacteria(SRB) on mercury(Hg) methylation at sediment–water interfaces. Concentrations of dissolved methyl mercury(DMe Hg) in the overlying water of the control cores with bioactivity maintained(BAC) and cores with only sulfate-reducing bacteria inhibited(SRBI) and bacteria fully inhibited(BACI) were measured at the anaerobic stage followed by the aerobic stage. For the BAC and SRBI cores, DMe Hg concentrations in waters were much higher at the anaerobic stage than those at the aerobic stage, and they were negatively correlated to the dissolved oxygen concentrations(r =- 0.5311 and r =- 0.4977 for BAC and SRBI, respectively). The water DMe Hg concentrations of the SRBI cores were 50% lower than those of the BAC cores, indicating that the SRB is of great importance in Hg methylation in sediment–water systems, but there should be other microbes such as iron-reducing bacteria and those containing specific gene cluster(hgc AB), besides SRB,causing Hg methylation in the sediment–water system.     

水环境中天然溶解有机质分子量的研究现状及意义

溶解有机质存在于所有的水环境中,它是组成不均匀、结构复杂和分子量分布很宽的有机化合物混合体。本文综述了测量溶解有机质分子量的主要方法,各种方法的原理和优缺点,其中详细介绍了高效体积排阻色谱法的原理,平均分子量和分散系数的计算,以及分子量的校正;同时介绍了可能影响分子量分布的主要地球化学因素,以及天然水中溶解有机质的分子量分布的特征。     

Comparison of two methods for detection of fecal indicator bacteria used in water quality monitoring of the Three Gorges Reservoir

Scientifically sound methods to rapidly measure fecal indicator bacteria are important to ensure safe water for drinking and recreational purposes.A total of 200 water samples obtained from the Three Gorges Reservoir during three successive one-year study periods(October 2009 to September 2012) were analyzed using multiple-tube fermentation(MTF)and most probable numbers combined with polymerase chain reaction(MPN–PCR).The MPN–PCR method was found to be significantly more sensitive than the MTF method for detecting Escherichia coli and Enterococcus spp.,and of equal sensitivity for detecting total coliforms when all surface water samples were grouped together.The two analytical methods had a strong,significant relationship,but MPN–PCR took only 12–18 hr,compared with the 3–8 days needed using the MTF method.Bacterial concentrations varied per sampling site but were significantly lower in the mainstream of the Yangtze River than those in the backwater areas of tributaries.The water quality of 85.8% of water samples from the mainstream was suitable for use as a centralized potable water source,while the water quality of 52.5% of water samples from the backwater areas was unsuitable for recreational activities.Relationships between fecal indicator bacteria showed significant correlation(r = 0.636–0.909,p 0.01,n = 200),while a weak but significant correlation was found between fecal indicators and water turbidity,water temperature,daily inflow,and total dissolved solids(r = 0.237–0.532,p 0.05,n = 200).The study indicated that MPN–PCR is a rapid and easily performed deoxyribonucleic acid(DNA)-based method for quantitative detection of viable total coliforms,E.coli,and Enterococcus spp.in surface water.     

Photodegradation of methylmercury in Jialing River of Chongqing,China

Photodegradation (PD) of methylmercury (MMHg) is a key process of mercury (Hg) cycling in water systems, maintaining MMHg at a low level in water systems. However, we possess little knowledge of this important process in the Jialing River of Chongqing, China. In situ incubation experiments were thus performed to measure temporal patterns and influencing factors of MMHg PD in this river. The results showed that MMHg underwent a net demethylation process under solar radiation in the water column, which predominantly occurred in surface waters. For surface water, the highest PD rate constants were observed in spring (12 × 10^− 3 ± 1.5 × 10^− 3 m²/E), followed by summer (9.0 × 10^− 3 ± 1.2 × 10^− 3 m²/E), autumn (1.4 × 10^− 3 ± 0.12 × 10^− 3 m²/E), and winter (0.78 × 10^− 3 ± 0.11 × 10^− 3 m²/E). UV-A radiation (320–400 nm), UV-B radiation (280–320 nm), and photosynthetically active radiation (PAR, 400–700 nm) accounted for 43%–64%, 14%–31%, and 16%–45% of MMHg PD, respectively. PD rate constants varied substantially with the treatments that filtered the river water and amended it with chemicals (i.e., Cl⁻, NO₃⁻, dissolved organic matter (DOM), Fe(III)), which reveals that suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelength range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%–46%, 6.2%–12%, and 42%–65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/(m²·year) in the study site. Our results are very important to understand the cycling characteristics of MMHg in the Jialing River of Chongqing, China.     

Improving biodegradation potential of domestic wastewater by manipulating the size distribution of organic matter

Carbon source is a critical constraint on nutrient removal in domestic wastewater treatment. However, the functions of particulate organic matter (POM) and some organics with high molecular weight (HMW) are overlooked in the conventional process, as they cannot be directly assimilated into cells during microbial metabolism. This further aggravates the problem of carbon source shortage and thus affects the effluent quality. Therefore, to better characterize organic matter (OM) based MW distribution, microfiltration/ultrafiltration/nanofiltration (MF/UF/NF) membranes were used in parallel to fractionate OM, which obtained seven fractions. Hydrolysis acidification (HA) was adopted to manipulate the MW distribution of dissolved organic matter (DOM) and further explore the correlation between molecular size and biodegradability. Results showed that HA pretreatment of wastewater not only promoted transformation from POM to DOM, but also boosted biodegradability. After 8 hr of HA, the concentration of dissolved organic carbon (DOC) increased by 65%, from the initial value of 20.25 to 33.48 mg/L, and the biodegradability index (BOD5 (biochemical oxygen demand)/SCOD (soluble chemical oxygen demand)) increased from 0.52 to 0.74. Using MW distribution analysis and composition optimization, a new understanding on the characteristics of organics in wastewater was obtained, which is of importance to solving low C/N wastewater treatment in engineering practice.     

Achieving partial nitrification by inhibiting the activity of Nitrospira-like bacteria under high-DO conditions in an intermittent aeration reactor

It is generally accepted that a low dissolved oxygen(DO) concentration is more beneficial for achieving partial nitrification than high-DO. In this study, partial nitrification was not established under low-DO conditions in an intermittent aeration reactor for treating domestic wastewater. During the operational period of low-DO conditions(DO: 0.3 ±0.14 mg/L), stable complete nitrification was observed. The abundance of Nitrospira-like bacteria, which were the major nitrite-oxidizing bacteria, increased from 1.03 × 10~6to2.64 × 10~6cells/m L. At the end of the low-DO period, the batch tests showed that high-DO concentration(1.5, 2.0 mg/L) could inhibit nitrite oxidation, and enhance ammonia oxidation. After switching to the high-DO period(1.8 ± 0.32 mg/L), partial nitrification was gradually achieved. Nitrospira decreased from 2.64 × 10~6 to 8.85 × 10~5cells/m L. It was found that suddenly switching to a high-DO condition could inhibit the activity and abundance of Nitrospira-like bacteria, resulting in partial nitrification.     

DOM纳滤膜污染及对膜截留卡马西平性能的影响

研究了天然原水中溶解性有机物(DOM)对HL和ESNA1-K两种纳滤膜造成的膜污染及其对膜截留卡马西平(CBZ)性能的影响.结果表明,DOM的存在造成了严重的膜污染和通量衰减.膜污染对CBZ截留率的影响与膜本身的特性和污染物特性有关,DOM通过在膜表面形成污染滤饼层和进入膜孔内部造成的膜孔堵塞,影响弱疏水性的CBZ从水中的分离,青草沙水库原水中的DOM引起的膜污染提高了两种纳滤膜对CBZ的截留效果,而太湖DOM造成的膜污染会降低CBZ的截留效果.研究还发现,中等相对分子质量(1 500~10 000)有机物会紧密地黏附在膜表面形成滤饼层,从而改变膜表面的疏水性能,小分子主要通过进入膜孔导致膜孔径堵塞.滤饼层的疏水性和浓差极化作用以及膜孔径的堵塞造成膜通量衰减并影响CBZ去除率.应用XDLVO理论对DOM造成的膜污染的分析结果表明,太湖DOM的疏水性明显强于青草沙DOM,其分子间的聚合自由能更负,与膜的黏附自由能更负,因而造成的膜污染和通量衰减更严重.     

Water chemistry controlled aggregation and photo-transformation of silver nanoparticles in environmental waters

The inevitable release of engineered silver nanoparticles (AgNPs) into aquatic environments has drawn great concerns about its environmental toxicity and safety. Although aggregation and transformation play crucial roles in the transport and toxicity of AgNPs, how the water chemistry of environmental waters influences the aggregation and transformation of engineered AgNPs is still not well understood. In this study, the aggregation of polyvinylpyrrolidone (PVP) coated AgNPs was investigated in eight typical environmental water samples (with different ionic strengths, hardness, and dissolved organic matter (DOM) concentrations) by using UV–visible spectroscopy and dynamic light scattering. Raman spectroscopy was applied to probe the interaction of DOM with the surface of AgNPs. Further, the photo-transformation and morphology changes of AgNPs in environmental waters were studied by UV–visible spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The results suggested that both electrolytes (especially Ca^2 + and Mg^2 +) and DOM in the surface waters are key parameters for AgNP aggregation, and sunlight could accelerate the morphology change, aggregation, and further sedimentation of AgNPs. This water chemistry controlled aggregation and photo-transformation should have significant environmental impacts on the transport and toxicity of AgNPs in the aquatic environments.     

滇池沉积物不同分子量溶解性有机质分布及其与Cu和Pb的相互作用

采用平衡渗析法、离子计和光谱分析等技术研究了滇池表层沉积物中DOM(溶解性有机质)的分子量分布特征及不同分子量的DOM对Cu和Pb的结合能力. 结果表明,草海和外海沉积物中DOM的分子量组成有显著差异. 草海沉积物中DOM主要以分子量为3.5~5.0ku的组分为主;外海沉积物中DOM以分子量为0.5~2.0ku的组分为主. 滇池各级分子量DOM的腐殖化程度(以A3/A4计,A3、A4分别为DOM在300、400nm处的紫外吸光度)在1.57~6.00之间,而且DOM腐殖化程度和芳香性随着分子量的增加而增大. 离子计分析和三维荧光光谱特征表明,Cu趋向于和分子量为2.0~3.5ku的DOM结合,而Pb趋向于和分子量≤0.5ku的DOM结合. 用结合容量和分配系数(K_d)表征Cu、Pb与DOM在两相中的结合能力,分子量为2.0~3.5ku的DOM中的w(Cu)最大,草海和外海分别为717.65和340.27mg/g;分子量≤0.5ku的DOM中的w(Pb)最大,草海和外海分别为2988.84和5073.45mg/g.      

Removal of fluorescence and ultraviolet absorbance of dissolved organic matter in reclaimed water by solar light

Storing reclaimed water in lakes is a widely used method of accommodating changes in the consumption of reclaimed water during wastewater reclamation and reuse. Solar light serves as an important function in degrading pollutants during storage, and its effect on dissolved organic matter(DOM) was investigated in this study. Solar light significantly decreased the UV_(254) absorbance and fluorescence(FLU) intensity of reclaimed water.However, its effect on the dissolved organic carbon(DOC) value of reclaimed water was very limited. The decrease in the UV_(254) absorbance intensity and FLU excitation–emission matrix regional integration volume(FLU volume) of reclaimed water during solar light irradiation was fit with pseudo-first order reaction kinetics. The decrease of UV_(254) absorbance was much slower than that of the FLU volume. Ultraviolet light in solar light had a key role in decreasing the UV_(254) absorbance and FLU intensity during solar light irradiation. The light fluence-based removal kinetic constants of the UV_(254) and FLU intensity were independent of light intensity. The peaks of the UV_(254) absorbance and FLU intensity with an apparent molecular weight(AMW) of 100 Da to 2000 Da decreased after solar irradiation, whereas the DOC value of the major peaks did not significantly change.     

Study on the effects of organic matter characteristics on the residual aluminum and flocs in coagulation processes

Characteristics of organic matter may affect the residual aluminum after the coagulation process. This study reported the results of a survey for one drinking water treatment plant and measured the concentration of residual aluminum species with different molecular weights. Survey results indicated that humic acid or organic matter whose molecular weight was smaller than 1500 Da had significant effects on residual aluminum. All the treatment processes were ineffective in removing dissolved organic matter whose molecular weight was smaller than 1500 Da. These results also indicated that the addition of sand or polyacrylamide in the coagulation process could greatly decrease the concentration of humic acid, and the concentration of residual aluminum also decreased. These results revealed that for all water samples after filtration, the majority of total residual aluminum existed in the form of total dissolved aluminum, accounting for 70%–90%. The concentration of residual aluminum produced in bovine serum albumin solutions indicated that when the DOC was larger than 4.0 mg/L, there were still significant differences when the solution pH value varied from 4.0 to 9.0.     

Optimization of the T3-induced Xenopus metamorphosis assay for detecting thyroid hormone signaling disruption of chemicals

T3-induced Xenopus metamorphosis is an ideal model for detecting thyroid hormone(TH)signaling disruption of chemicals. To optimize the T3-induced Xenopus assay and improve its sensitivity and reproducibility, we intend to develop quantitatively morphological endpoints and choose appropriate concentrations and exposure durations for T3 induction.Xenopus laevis at stage 52 were exposed to series of concentrations of T3(0.31–2.5 nmol/L)for 6 days. By comparing morphological changes induced by T3, we propose head area,mouth width, unilateral brain width/brain length, and hindlimb length/snout-vent length as quantitative parameters for characterizing T3-induced morphological changes, with body weight as a parameter for indicating integrated changes. By analyzing time-response curves, we found that following 4-day exposure, T3-induced grossly morphological changes displayed linear concentration–response curves, with moderate morphological changes resulting from 1.25 nmol/L T3 exposure. When using grossly morphological endpoints to detect TH signaling disruption, we propose 4 days as exposure duration of T3, with concentrations close to 1.25 nmol/L as induction concentrations. However, it is appropriate to examine morphological and molecular changes of the intestine on day 2 due to their early response to T3. The quantitative endpoints and T3 induction concentrations and durations we determined would improve the sensitivity and the reproducibility of the T3-induced Xenopus metamorphosis assay.     

天津市典型排污河水体中溶解性有机质的荧光分布特征分析

利用三维荧光光谱研究了天津市两条典型排污河(大沽排污河和北塘排污河)沿河水体中溶解性有机质(DOM)的荧光分布特征,并通过对荧光参数——紫外区类富里酸峰中心位置的荧光强度与可见区类富里酸峰中心位置的荧光强度比值(r(A,C))和激发光波长370nm时荧光发射光谱强度在450nm与500nm处的比值(f450/500)的分析,探讨了水体中DOM的来源.结果表明,大沽排污河除中游个别位置外,其它位置水体均能检出紫外区类富里酸、类蛋白、可见光区类腐殖质、紫外区类腐殖质,总体上呈中游少、上下游多的特点;而北塘排污河水体中DOM的荧光峰从上游到下游呈增多趋势,但检出数量比较少.两条排污河水体中DOM均以紫外区类腐殖质最强.两条排污河水体中DOM的荧光强度与其水质参数之间存在显著相关性,而大沽排污河的相关系数更大.结合荧光参数r(A,C)和f450/500的分析和现场对入河排污口的调研,发现两条排污河的溶解性有机质来源均以入河排污口排污汇入(陆源)为主,另外还有少量沉积物有机质释放(微生物作用).