Removal of humic acid using TiO2 photocatalytic process--fractionation and molecular weight characterisation studies

The photocatalytic removal of humic acid (HA) using TiO₂ under UVA irradiation was examined by monitoring changes in the UV₂₅₄ absorbance, dissolved organic carbon (DOC) concentration, apparent molecular weight distribution, and trihalomethane formation potentials (THMFPs) over treatment time. A resin fractionation technique in which the samples were fractionated into four components: very hydrophobic acids (VHA), slightly hydrophobic acids, hydrophilic charged (CHA) and hydrophilic neutral (NEU) was also employed to elucidate the changes in the chemical nature of the HA components during treatment. The UVA/TiO₂ process was found to be effective in removing more than 80% DOC and 90% UV₂₅₄ absorbance. The THMFPs of samples were decreased to below 20 μg l⁻¹ after treatments, which demonstrate the potential to meet increasingly stringent regulatory level of trihalomethanes in water. Resin fractionation analysis showed that the VHA fraction was decreased considerably as a result of photocatalytic treatments, forming CHA intermediates which were further degraded with increased irradiation time. The NEU fraction, which comprised of non-UV-absorbing low molecular weight compounds, was found to be the most persistent component.     

Spectroscopic study of the degradation of antibiotics and the generation of representative EfOM oxidation products in ozonated wastewater

This study examined effects of ozonation on thirteen fluoroquinolone, macrolide and lincosamide antibiotics present in municipal wastewater. Transformations of effluent organic matter (EfOM) caused by ozonation were characterized using absorbance/fluorescence spectroscopy and high performance size exclusion chromatography (HPSEC). Concentrations of aldehydes and carboxylic acids generated via the oxidation of EfOM were also determined. The absorbance and fluorescence of ozonated wastewater decreased with increasing ozone dose or treatment time. HPSEC data showed that these phenomena corresponded to the oxidation of all EfOM fractions, with some preference towards the degradation of the EfOM molecules with high apparent molecular weight. The removal of antibiotics and production of aldehydes and carboxylic acids were strongly correlated with the changes in both EfOM absorbance and fluorescence. Applications of a model describing the concurrent degradation of trace level contaminants and relative changes of EfOM emission allowed achieving a good fitting between the experimental and modeled ΔC/C₀ vs. ΔA/A₀ and ΔC/C₀ vs. ΔF/F₀ data.     

混凝对二级出水中有机物分布特性的影响

以城市污水处理厂二级出水为研究对象,通过烧杯实验,确定了以三氯化铁(FeCl3)和聚合氯化铝(PAC)为混凝剂时两种混凝剂的最佳投加量,在此基础上采用XAD树脂分离技术和超滤膜法对水中溶解性有机物(DOM)进行分级表征,研究了混凝前后水中DOM的亲疏水特性、分子量分布规律以及比紫外吸收值(SUVA)和E4/E6(A465nm/A665nm)的变化.结果表明,当FeCl3和PAC投加量分别达到30 mg/L和60 mg/L时,可以使出水水质满足《城镇污水处理厂污染物排放标准》(GB18918-2002)中的一级A标准;FeCl3对含碳碳不饱和双键及芳香环的有机物的去除效果优于PAC;FeCl3对小分子有机物的去除效率更高,而PAC对分子量＞100 000的大分子有机物的去除效果优于FeC13;混凝处理对疏水性有机物的去除效果优于对亲水性有机物的去除效果,同时其对酸性物质的去除效率高于对非酸性物质的去除效率.     

水化深度处理渗滤液尾水中的有机物

利用水泥的水化过程易受有机物影响的特点,采用硅酸盐水泥深度处理了垃圾渗滤液膜生物反应器(MBR)工艺出水,考察了不同因素,如投加量、初始pH、反应时间及振荡速率等对于渗滤液尾水中有机物的去除效果以及最佳工艺条件,并分析了渗滤液尾水中有机物的去除机理。结果表明,水化过程对渗滤液尾水中的有机物去除性能良好,且对不同有机物具有一定的选择性,尤其对具有近紫外区(200～400 nm)吸收峰特征的有机物去除效果更佳,同时发现,当投加量为50 g/L、pH=8.3(原渗滤液pH)、反应时间为24 h和振荡速度为200 r/min时,去除效果最佳,其COD、TOC和UV254的平均去除率分别达到55.6%、62.1%和68.8%。     

Magnetic ion exchange treatment of stabilized landfill leachate

Stabilized landfill leachate is characterized by a high concentration of non-biodegradable organic matter, which is similar in chemistry to dissolved organic matter (DOM) in the natural aquatic environment. Magnetic ion exchange (MIEX) resin treatment is well-studied in drinking water for removal of DOM from natural waters. There are fewer studies evaluating MIEX treatment of waste waters, and there is no previous work evaluating MIEX treatment of landfill leachate. This work systematically evaluated MIEX treatment of stabilized landfill leachate and evaluated the results in the context of previous studies of MIEX treatment of natural and waste waters. Five leachates from four landfills were evaluated as a function of MIEX resin dose, mixing time, and regeneration efficiency. MIEX resin removed DOM from landfill leachate, even in the presence of a reported high background concentration of inorganic ions. MIEX resin that was exhausted with leachate DOM was effectively regenerated with a concentrated NaCl solution, and regenerated MIEX resin performed similarly to virgin resin. For a majority of the leachates, the removal trend for MIEX resin was color > UV-absorbing substances > dissolved organic carbon ≈ COD > total nitrogen. Finally, MIEX resin removed a wider range of DOM from leachate than coagulation. The most important contribution of this work is that MIEX treatment of leachate followed very similar trends as MIEX treatment of natural waters, which will allow previous MIEX data to be used to estimate the treatment efficiency of other waste waters.     

Molecular characterisation of the dissolved organic matter of wastewater effluents by MSSV pyrolysis GC-MS and search for source markers

Microscale sealed vessel pyrolysis (MSSVpy) was used to characterise the hydrophobic (HPO) and colloid (COL) fractions of dissolved organic matter (DOM) from the effluents (EFFs) of two waste water treatment plants (WWTPs) and several primary source waters (SWs). The EFFs showed a large range of anthropogenically sourced organics - including the metabolites of industrial chemicals (e.g., dioxanes, n- and sec-alkyl substituted benzenes and long chain alkyl phenols), pharmaceuticals (e.g., N- and S-heterocycles) and human waste (e.g., S- and N-organics, steranes/sterenes) - as well as high concentrations of alkyl aromatic and N-organic products (e.g., alkyl indoles, carbazoles and β-carbolines) attributed to the treatment biota. Some anthropogenic chemicals are potentially toxic at even trace levels, whilst the N-organics may be precursors for toxic N-disinfection by-products. Much lower concentrations of just a few of the anthropogenic and N-organic products were detected by more traditional flash pyrolysis (Flash-py) of the EFF samples, reflecting the higher sensitivity of MSSVpy to many chemical functionalities. Few of these products were detected in the corresponding MSSVpy analysis of the SWs, but these samples did show relatively high abundances of lignin (e.g., alkylphenols) and carbohydrate (e.g., furans) derived products. Their lower EFF abundances are consistent with efficient removal by the water treatment procedures applied. Conversely, the detection of the anthropogenics in the treated EFFs reflects their general resistance to treatment. Their occurrence in the HPO fractions isolated by XAD resin separation suggests a potential relationship with the structurally stable macromolecular fraction of the DOM.     

硅藻土强化混凝去除微污染原水中的有机物

研究了联用硅藻土与聚合氯化铝（PAC）强化混凝对有机微污染原水中不同性质溶解性有机物的去除效果。采用超滤膜和XAD系列树脂对微污染原水中溶解性有机物进行分级表征,物理分级表明分子量〈4 kD的溶解性有机物占50%以上,化学分级表明原水中以憎水酸（HoA）和亲水物质（HiM）为主。硅藻土助凝去除溶解性有机物,实验结果表明,当PAC投加量30 mg/L,硅藻土投加量0.5 g/L时,溶解性有机碳去除率由22.5%提高到26.3%。     

The impact of seasonal variations in DOC arising from a moorland peat catchment on coagulation with iron and aluminium salts

Natural organic matter (NOM) is one of the main sources of environmental pollution to drinking water supplies in much of the UK and the US. Whilst traditional treatment with trivalent coagulants has proven a successful strategy in the past, operational problems are now being reported during periods of elevated organic levels in the water. Characterisation of the pollutants in terms of polarity, molecular weight and charge, provides a method to understand the impact of the observed temporal and spatial variations in terms of a mechanistic parameter relevant to the treatment processes. Results from this study demonstrate that it is not simply the increased organic concentration, but also the change in NOM composition and character, which influences the impact on the treatment processes. Consequently, monitoring of these parameters provides an insight into how to manage the impact caused by environmental changes to the catchments.     

改性TiO_2/浮石光催化去除二级出水中有机物

为了实现城市污水厂二级出水的回用,将La3＋、Fe3＋共掺杂TiO2/浮石光催化用于二级出水中有机物的去除。在优化工艺条件下,该方法对TOC的去除率为49.0%,对UV254的去除率为76.5%;出水BDOC/DOC值大幅度提高,由最初的0.21提高到0.56,增加了出水的可生化性;二级出水中存在着影响光催化去除有机物的因素,其中阴离子对有机物的去除有一定的抑制作用;光催化反应在通过O3强化后对有机物的去除率得到提高,TOC的去除率达到75.0%,光催化和O3氧化对有机物的去除具有协同效应;随着光催化反应次数的增加,催化剂活性有下降趋势,使用10次后TOC去除率下降到第一次使用时的16.7%,再生能够使催化活性恢复到使用前的95%,催化剂在使用15次以内稳定性较好。     

Removal of dissolved organic matter in municipal effluent with ozonation, slow sand filtration and nanofiltration as high quality pre-treatment option for artificial groundwater recharge

In the paper the combination process of ozonation, slow sand filtration (SSF) and nanofiltration (NF) was investigated with respect to dissolved organic matter (DOM) removal as high quality pre-treatment option for artificial groundwater recharge. With the help of ozonation leading to breakdown of the large organic molecules, SSF preferentially removes soluble microbial by-product-like substances and DOM with molecular weight (MW) less than 1.0 kDa. NF, however, removes aromatic, humic acid-like and fulvic acid-like substances efficiently and specially removes DOM with MW above 1.0 kDa. The residual DOM of the membrane permeate is dominated by small organics with MW 500 Da, which can be further reduced by the aquifer treatment, despite of the very low concentration. Consequently, the O₃/SSF/NF system offers a complementary process in DOM removal. Dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP) can be reduced from 6.5 ± 1.1 to 0.7 ± 0.3 mg L⁻¹ and from 267 ± 24 to 52 ± 6 μg L⁻¹, respectively. The very low DOC concentration of 0.6 ± 0.2 mg L⁻¹ and THMFP of 44 ± 4 μg L⁻¹ can be reached after the aquifer treatment.     

制浆造纸废水生化出水的混凝处理研究

研究了硫酸铝和三氯化铁对制浆造纸废水生化出水的处理效果.研究发现,不调节原水pH值,硫酸铝投加量为600 mg/L或三氯化铁投加量为300mg/L时,混凝后废水的COD＜150 mg/L,色度＜50倍,出水均符合现阶段排放标准.混凝剂比较发现,在最佳反应条件下,2种混凝剂的处理效果相当,但硫酸铝混凝的成本低于三氯化铁....     

Aniline and 2,4,6-trinitrotoluene associate preferentially to low molecular weight fractions of dissolved soil organic matter

Aniline and 2,4,6-trinitrotoluene (TNT) were equilibrated with particulate (POM) and dissolved organic matter (DOM) from an organic soil at different compositions of adsorbed major cations (Na, Al) and pH (aniline: 3.7–5.1, TNT: 4.8–5.0). After separation of POM, concentrations of ¹⁴C-labelled aniline and TNT* (including TNT degradation products) were determined in DOM size fractions using size-exclusion chromatography (SEC) and UV-detection. Concentrations in the <3.5 kDa size fraction were 2.8–6.0 and 8.5–9.5 times higher for aniline and TNT*, respectively, as compared to the >40 kDa fraction. Thus, both aniline and TNT* were preferentially associated to the smallest DOM size fraction. The significant binding to DOM (similar extent as to POM) and the fact that the <3.5 kDa DOM fraction was less susceptible to flocculation by major metals suggests that the mobility of aniline and TNT is highly affected by the solubility of soil organic matter.     

改性TiO2/浮石光催化去除二级出水中有机物

为了实现城市污水厂二级出水的回用,将La3+、Fe3+共掺杂TiO2/浮石光催化用于二级出水中有机物的去除。在优化工艺条件下,该方法对TOC的去除率为49.0%,对UV254的去除率为76.5%;出水BDOC/DOC值大幅度提高,由最初的0.21提高到0.56,增加了出水的可生化性;二级出水中存在着影响光催化去除有机物的因素,其中阴离子对有机物的去除有一定的抑制作用;光催化反应在通过O3强化后对有机物的去除率得到提高,TOC的去除率达到75.0%,光催化和O3氧化对有机物的去除具有协同效应;随着光催化反应次数的增加,催化剂活性有下降趋势,使用10次后TOC去除率下降到第一次使用时的16.7%,再生能够使催化活性恢复到使用前的95%,催化剂在使用15次以内稳定性较好。     

Different stabilities of multiwalled carbon nanotubes in fresh surface water samples

The stability of multiwalled carbon nanotubes (MWNTs) in particulate aggregates and surfactant-facilitated suspensions after being mixed into eight types of fresh surface water samples was investigated. MWNTs in particulate aggregates could not be stabilized in any of the water samples except for the one having relatively high content of dissolved organic matter with the aid of sonication. Sodium dodecyl benzenesulfonate (SDBS), polyethylene glycol octylphenyl ether (TX100) and cetyltrimethyl ammonium bromide (CTAB) were used to prepare MWNT suspensions. SDBS- and TX100-stabilized MWNTs could partly remain suspending after being mixed into the water samples, whereas CTAB-stabilized MWNTs readily sedimentated due to the surface charge neutralization by the surface water contained negatively-charged anions and colloids. This is a first systematic study examining the stability of carbon nanotubes in natural surface waters, the results from which will be useful for understanding the transport, fate and ecological effect of carbon nanotubes in the aqueous environment.     

钙离子对混凝去除水体中铜绿微囊藻的影响

以铜绿微囊藻为对象,研究了钙离子对聚合氯化铝（polyaluminumchloride,PAC）混凝沉淀藻细胞的影响及其可能的机理。结果表明,添加钙离子对PAC混凝去除模拟水样藻细胞和浊度均具有促进作用。在PAC摩尔浓度较低时（0.02 mmol·L-1）,最高可将除藻率和除浊率分别提高66.4%和76.8%。三维荧光及总溶解性有机碳（total dissolved organic carbon,TDOC）分析表明钙离子对去除水中溶解性胞外有机物（dissolved extracellular organic matter,dEOM）没有显著作用。利用Zeta电位和絮体形态对其影响混凝除藻效果的可能机理进行探究,发现钙离子能通过压缩双电层和吸附电中和提高藻细胞表面的Zeta电位,从而促进胶体脱稳凝聚。推测钙离子通过与铜绿微囊藻表面的黏附型胞外有机物（bound extracellular organic matter,bEOM）发生阳离子架桥作用促进藻细胞脱稳混凝沉淀。钙离子能够促进铜绿微囊藻脱稳,但是絮体粒径、强度、恢复能力的主要影响因素还是PAC摩尔浓度。     

Characterization of dissolved organic matter in the rhizosphere of hyperaccumulator Sedum alfredii and its effect on the mobility of zinc

Pot experiments were performed to investigate the characteristics of dissolved organic matter (DOM) in the rhizosphere soil of hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of Sedum alfredii and its effects on the mobility of zinc (Zn). DOM was fractionated using XAD resins into six fractions. The acid fraction was the predominant component of DOM in the rhizosphere of S. alfredii, with hydrophilic acid (HiA), hydrophilic base (HiB), and hydrophilic neutral (HiN) in HE-DOM being 1.6, 1.9, and 1.2 times higher respectively, as compared to NHE-DOM. ATR-FTIR results showed that DOM in the rhizosphere of S. alfredii consisted of a mixture of hydroxylated and carboxylic acids, and HE-DOM exhibited more CO, OH, CC and CO functional groups than NHE-DOM. Resin equilibration experiment results indicated that DOM from the rhizosphere of both ecotypes of S. alfredii had the ability to form complexes with Zn, whereas the degree of complexation was significantly higher for HE-DOM (60%) than NHE-DOM (42%). The addition of HE-DOM significantly (P < 0.05) increased the solubility of four Zn minerals while NHE-DOM was not as effective at the same concentration. It was concluded that DOM derived from the rhizosphere of hyperaccumulating ecotype of S. alfredii could significantly increase Zn mobility through the formation of soluble DOM-metal complexes, this might be one of the important mechanism by which S. alfredii is involved in activating metal in rhizosphere.     

Nonlinear binding of phenanthrene to the extracted fulvic acid fraction in soil in comparison with other organic matter fractions and to the whole soil sample

Fractions of soil organic matter in a natural soil were extracted and sorption (or binding) characteristics of phenanthrene on each fraction and to the whole sample were investigated. The organic carbon normalized single point sorption (or binding) coefficient followed lipid > humin (HM) > humic acid (HA) > fulvic acid (FA) > whole soil sample, while the nonlinear exponent exhibited lipid > FA > HA > whole soil sample > HM. FA showed nonlinear binding of phenanthrene as it often does with other fractions. HM and HA contributed the majority of organic carbon in the soil. The calculated sorption coefficients of the whole soil were about two times greater than the measured values at different equilibrium phenanthrene concentrations. As for phenanthrene, the sorption capacity and nonlinearity of the physically mixed HA-HM mixtures were stronger as compared to the chemically reconstituted HA-HM composite. This was attributed to (besides the conditioning effect of the organic solvents) interactions between HA and HM and acid-base additions during fractionation.     

Hydrogeological and biogeochemical constrains of arsenic mobilization in shallow aquifers from the Hetao basin, Inner Mongolia

Little is known about the importance of drainage/irrigation channels and biogeochemical processes in arsenic distribution of shallow groundwaters from the Hetao basin. This investigation shows that although As concentrations are primarily dependent on reducing conditions, evaporation increases As concentration in the centre of palaeo-lake sedimentation. Near drainage channels, groundwater As concentrations are the lowest in suboxic-weakly reducing conditions. Results demonstrate that both drainage and irrigation channels produce oxygen-rich water that recharges shallow groundwaters and therefore immobilize As. Groundwater As concentration increases with a progressive decrease in redox potential along the flow path in an alluvial fan. A negative correlation between SO₄²⁻ concentrations and δ³⁴S values indicates that bacterial reduction of SO₄²⁻ occurs in reducing aquifers. Due to high concentrations of Fe (>0.5 mg L⁻¹), reductive dissolution of Fe oxides is believed to cause As release from aquifer sediments. Target aquifers for safe drinking water resources are available in alluvial fans and near irrigation channels.     

利用强化混凝去除水源水中天然有机物的研究进展

总结了近年来利用强化混凝去除水源水中天然有机物的研究,重点讨论了其作用机理和主要影响因素.水源水中天然有机物的含量和成分会因水源地和时间的不同而存在差异,对水源水中天然有机物的了解是保证强化混凝效果的基本前提.不同混凝条件下,强化混凝的主导作用机理不同.铁盐混凝剂、较低pH值、较高混凝剂投量和阳离子有利于提高强化混凝的效果.