An overview of analytical methodologies for the determination of antibiotics in environmental waters

The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes.     

基于SMP破坏准则的饱和砂土弹塑性本构模型

利用土体的塑性流动理论，提出了用于描述饱和砂土在单调荷载作用下的应力一应变反应性质的弹塑性本构模型。土体总的变形由三部分组成：即弹性应变、与体积屈服机制相关的塑性应变和与剪切屈服机制相关的塑性应变，其中与剪切屈服机制相关的塑性应变的得出是基于SMP破坏准则。通过将模型预测的结果与试验结果进行对比，表明该模型能够较为准确地描述饱和砂土在单调加载条件下的反应性质。     

Effects of several different flux enhancing chemicals on filterability and fouling reduction of membrane bioreactor (MBR) mixed liquors

The main objective of this work was to determine the effectiveness of various chemicals on filterability and fouling reduction in MBR mixed liquors. Different lab-scale experiments were conducted with a total of 7 different additives (3 cationic polymers (MPL30, MPE50, KD452), a biopolymer (Chit), a starch (Sta), and 2 metal salts (FeCl₃, PACl)). Initially, batch shaker tests were performed for each additive to determine the optimum dosages in terms of soluble microbial products (SMP) removal. Then, short-term filtration trials and critical flux tests were performed. All tested additives were able to remove SMP, but at different extent; 33, 45, 51, 36, 38, 54, and 56% for MPL30, MPE50, KD452, FeCl₃, PACl, Chit, and Sta, respectively. The cationic polymer KD452 exhibited the best performance in terms of the extent of SMP removal and the required dosage. All tested cationic polymers, starch and chitosan significantly reduced fouling rates and increased permeability values. At their optimum dosages, the cationic polymers MPE50, MPL30 and KD452 provided 96, 80 and 74% reductions in fouling rates, respectively. The enhancements in critical flux achieved by MPL30, MPE50, KD452, FeCl₃, PACl, Chit, and Sta were 38, 46, 38, 14, 14, 0, and 22% in comparison with raw mixed liquor. Cationic polymers increased critical flux values to levels above 50 L m⁻² h⁻¹. SMP removal from MBR mixed liquors and further improvement in filtration performance and fouling control did not always correlate. Overall, based on the lab-scale tests conducted, cationic polymeric additives were found to be favorable over the other additives due to their steady and successful performance in fouling control. The performance of cationic polymers was independent of small variations in dosing, while for other additives over- or under-dosing showed detrimental effects on filterability.     

Impact of cation concentrations on fouling in membrane bioreactors

In this study, the interaction of calcium, magnesium, and sodium as well as impact of monovalent to divalent (M/D) cation ratio and magnesium to calcium (Mg/Ca) ratio in the feed wastewater on membrane fouling in submerged membrane bioreactor (MBR) was investigated. The protein and carbohydrate content of soluble microbial products (SMP) and extracellular polymeric substances (EPS) as well as their relative hydrophobicities was examined. The mixed liquor and its components (soluble and suspended solids) were analyzed for their filtration resistance, as reflected by the modified fouling index (MFI). Based on the findings of this study, the optimum conditions with respect to fouling rate were calcium and sodium concentrations of 36 and 140 mg/L, respectively, M/D of 1:1 and Mg/Ca of 5:1, with all parameters on an equivalent basis. High sodium concentration at high M/D ratio was found to decrease the floc size and increase the fouling rate. At the low M/D ratio of 1:1, introduction of magnesium was beneficial in reducing the fouling rate by increasing the EPS concentration and floc size and decreasing the SMP concentration and relative hydrophobicity in the supernatant. The fouling rate was found to be statistically correlated with the concentrations of Ca, Mg, and Na, with both Ca and Na adversely impacting fouling and Mg alleviating fouling propensity.     

基于显式有限元方法的两相介质弹塑性动力反应计算分析

针对增量形式的流体饱和两相多孔介质弹塑性波动方程组,运用基于显式逐步积分格式的时域显式有限元方法对该波动方程组进行求解,并应用基于SMP破坏准则的弹塑性动力本构模型描述两相介质的动力反应性质,对两相介质在输入地震波作用下的弹塑性动力反应进行计算和分析,将计算结果与相应的弹性动力反应的计算结果进行对比;对本文应用的弹塑性...     

Shape memory epoxies based on networks with chemical and physical crosslinks

Epoxies are an important family of shape memory polymers (SMP) due to their excellent stability and thermo-mechanical endurance and the high values of shape fixity and shape recovery. Actuators based on these materials can be designed for large tensile elongations (e.g., 75% or higher) or large recovered stresses (e.g., 3 MPa or higher). However, meeting these requirements simultaneously is a difficult task because changes in the crosslink density affect both variables in opposite ways. We show that an SMP based on an epoxy network with both chemical and physical crosslinks could be strained up to 75% in four repeated shape memory cycles with tensile stresses close to 3 MPa. Shape fixity and shape recovery values were close to 98% and 96%, respectively, for everyone of the cycles, without any significant change between the first and subsequent cycles.     

岩土材料塑性应变增量方向的确定

通过与金属材料的类比,分析了岩土材料的特征面(SMP面)的特性,提出了SMP面上的应力 决定岩土材料塑性应变增量流动方向的观点,并由此推导出计算公式. 通过增加一个材料参 数,还可以考虑存在黏聚力时的情况. 由该公式计算的塑性应变增量方向得到了 试验结果的验证. 该公式也在用变换应力修正的剑桥模型中得到应用,模型预测结果能够合理反映试验数据.     

进水盐度对膜生物反应器运行效能的影响研究

进水盐度对膜生物反应器(MBR)的运行效能影响显著,尤其是进水含盐量为5 g/L时,明显恶化了污泥可滤性,膜污染速率加快;MBR混合液中溶解性微生物产物(SMP)和胞外聚合物(EPS)含量随钠离子浓度变化而变化,其中SMP中蛋白质含量与钠离子浓度密切相关;与紧密结合态EPS(TB)相比,钠离子含量对松散结合态EPS(LB)浓度的影响更大;不同盐度对COD及NH4+-N影响不明显,系统对COD及NH4+-N的去除效果稳定,分别保持在92%及94%以上,高盐度对MBR总磷去除率降低明显。     

超顺磁纳米颗粒弛豫时间传感技术在生化分析中的研究进展

该文介绍了基于超顺磁纳米颗粒的弛豫时间(T2)传感技术及其在生化分析应用中的研究进展.在均匀磁场中,超顺磁纳米颗粒状态的变化(分散或聚集)会改变磁场的均匀度进而引起周围水分子质子弛豫时间的改变,即磁弛豫时间传感效应.磁颗粒经表面修饰后与给体/受体偶联形成磁传感探针,当与待测物发生特异性反应后,引起介质磁颗粒聚集状态改变...     

Recent advances in sample preparation techniques and methods of sulfonamides detection – A review

Sulfonamides (SAs) have been the most widely used antimicrobial drugs for more than 70 years, and their residues in foodstuffs and environmental samples pose serious health hazards. For this reason, sensitive and specific methods for the quantification of these compounds in numerous matrices have been developed. This review intends to provide an updated overview of the recent trends over the past five years in sample preparation techniques and methods for detecting SAs. Examples of the sample preparation techniques, including liquid–liquid and solid-phase extraction, dispersive liquid–liquid microextraction and QuEChERS, are given. Different methods of detecting the SAs present in food and feed and in environmental, pharmaceutical and biological samples are discussed.