Removal of silver nanoparticles in simulated wastewater treatment processes and its impact on COD and NH(4) reduction

The increasing utilization of silver nanoparticles in industrial and consumer products has raised concern to wastewater treatment utilities due to its antimicrobial activity. In this work, the removal of citrate stabilized silver nanoparticles (Ag-NPs) during the wastewater treatment processes and its impact on treatment performance were examined. During simulated primary clarification, over 90% of the Ag-NPs remained in the wastewater, indicating that the majority of silver nanoparticles in sewage would enter the subsequent treatment units. During sequencing batch reactor processes, silver nanoparticles were effectively removed in each cycle throughout the 15-d experimental duration. Continuous input of silver nanoparticles into the wastewater did not significantly alter chemical oxygen demand (COD) removal. NH(4) removal was reduced at the beginning of the SBR experiment but quickly recovered at the later stage of the experiment. This study demonstrated that in the near future it is unlikely that citrate-stabilized Ag-NPs released into sewage will cause significant adversary effects on the COD and NH(4) removal of activated sludge processes in municipal wastewater treatment plants.     

酪氨酸氯化过程中光谱变化特征及消毒副产物的生成规律

考察酪氨酸在不同投氯量条件下氯化后的余氯,紫外吸光度值和荧光光谱,以及消毒副产物对羟基苯乙腈(4-HBC)的生成特性。结果表明,随着投氯量的增加,余氯呈现先增加再减小再增加的趋势。在投氯量为0～0.5 mmolCl2/L时,增加投氯量可提高氯化后溶液的UV254、UV274和UV280值以及4-HBC的生成量,表明低投氯量时氯化可提高溶液中不饱和键的含量;而投氯量为0.5～1 mmol Cl2/L时,增加投氯量降低UV254、UV274和UV280值以及4-HBC的生成量,表明过量的氯亦可破坏溶液中的不饱和键。荧光光谱测试实验亦发现:在投氯量为0.05 mmol Cl2/L时,酪氨酸溶液氯化后的荧光峰强度明显增加,表明氯化可生成荧光强度较高的产物。过量的氯(0.5～1 mmol Cl2/L)则可破坏溶液中的荧光结构,降低荧光峰强度直至未检出。     

纤维膜过滤特性的数值模拟

一个高性能过滤膜除了与纤维自身结构参数有关联外,过滤时的操作条件对其也有重要影响。为研究纤维膜过滤效率、过滤压降与过滤速度、孔隙率以及过滤膜厚度之间的关系,以更好地对实际过滤进行优化,本研究从纤维膜的过滤机理进行出发,采用FLUENT多孔介质离散相模型对纤维过滤器的流场进行模拟。结果表明,膜前后压降会随着过滤速度和膜厚度的增大而增大;一定范围内纤维膜孔隙率适度增加,截留率变化不大,但是膜压差会逐渐减小;同时过滤速度对颗粒截留率有影响,速度增大时,粒子轨迹发生偏移,导致过滤膜一部分过早发生堵死,而一部分作用减弱,影响了过滤效果。     

Fe_2O_3和K_2CO_3对钙基添加剂脱硫脱硝的影响

在研究焦炭燃烧过程中使用钙基添加剂固硫的基础上,探讨了Fe_2O_3或K_2CO_3对CaO脱硫脱硝的影响。实验结果表明:添加剂的种类对焦炭燃烧过程中排放的SO_2和NO的浓度及总量均有一定的影响;加入Fe_2O_3或K_2CO_3替代部分CaO后,焦炭燃烧过程中排放的SO_2和NO比单独加入CaO时均有所下降;向焦炭中分别混合3.0%(w)CaO),1.5%(w)CaO+1.5%(w)Fe_2O_3,1.5%(w)CaO+1.5%(w)K_2CO_3的添加剂时,焦炭的SO_2排放总量分别降低了69.93%,75.98%,79.98%,NO排放总量分别降低了64.38%,79.73%,84.14%;加入Fe_2O_3或K_2CO_3后,钙基添加剂的表面性质发生了变化,同时增加了反应的活性中心数,因而复合添加剂能更有效地进行脱硫脱硝。     

Dissolved black carbon in grassland streams: Is there an effect of recent fire history?

While the existence of black carbon as part of dissolved organic matter (DOM) has been confirmed, quantitative determinations of dissolved black carbon (DBC) in freshwater ecosystem and information on factors controlling its concentration are scarce. In this study, stream surface water samples from a series of watersheds subject to different burn frequencies in Konza Prairie (Kansas, USA) were collected in order to determine if recent fire history has a noticeable effect on DBC concentration. The DBC levels detected ranged from 0.04 to 0.11 mg L^?1, accounting for ca. 3.32 ± 0.51% of dissolved organic carbon (DOC). No correlation was found between DBC concentration and neither fire frequency nor time since last burn. We suggest that limited DBC flux is related to high burning efficiency, possibly greater export during periods of high discharge and/or the continuous export of DBC over long time scales. A linear correlation between DOC and DBC concentrations was observed, suggesting the export mechanisms determining DOC and DBC concentrations are likely coupled. The potential influence of fire history was less than the influence of other factors controlling the DOC and DBC dynamics in this ecosystem. Assuming similar conditions and processes apply in grasslands elsewhere, extrapolation to a global scale would suggest a global grasslands flux of DBC on the order of 0.14 Mt carbon year^?1.     

The role of humic acid in the toxicity of arsenite to the diatom Navicula sp.

Dissolved organic matter (DOM) affects arsenite [As(III)] toxicity by altering its sorption equilibrium at the cell wall interface. A better understanding of such mechanism is of great importance to assess As(III) ecotoxicity in aquatic systems. Batch experiments were conducted to study the effects of DOM on the regulation of As(III) sorption and toxicity in the diatom Navicula sp. The influence of humic acid (HA) on As(III) toxicity was assessed by measuring algal growth, chlorophyll a, and reactive oxygen species (ROS), whereas As(III) mobility across the cell wall was estimated by determining the concentration of intracellular, cell-wall-bound, and free As(III) ions in cell media. Results showed that the effects of HA on arsenite toxicity varied depending on various combinations of As(III)-HA concentrations. EC₅₀ had an approximate threefold increase from 8.32 (HA-free control) to 22.39 μM (at 20 mg L^?1 HA) when Navicula sp. was exposed to 1.0–100.0 μM of As(III), compared to an overall low complexation ratio of HA-As(III) in a range of 0.91–6.00 %. The cell wall-bound and intracellular arsenic content decreased by 19.8 and 20.3 %, respectively, despite the lower arsenite complexation (2.10?±?0.16 % of the total As). Meanwhile, intracellular ROS was decreased by 12.6 % in response to 10.0 μM As(III) and 10 mg L^?1 HA vs. the HA-free control. The significant contrast indicated that complexation alone could not explain the HA-induced reduction in arsenite toxicity and other factors including HA–cell surface interactions may come into play. Isotherms describing adsorption of HA to the Navicula sp. cells combined with morphological data by scanning electron microscopy revealed a protective HA floccule coating on the cell walls. Additional Fourier transform infrared spectroscopic data suggested the involvement of carboxylic groups during the adsorption of both HA and As(III) on the Navicula sp. cell surface. Collective data from this study suggest that cell wall-bound HA can moderate As(III) toxicity through the formation of a protective floccule coating occupying As(III) sorption sites and decreased effective functional groups capable of binding As(III). Our findings imply that As(III) toxicity can be alleviated due to the increased hindrance to cellular internalization of As(III) in the presence of naturally abundant DOM in water.     

基于铝盐混凝污泥的新型LCFM吸附性能评价

利用自来水厂铝盐混凝污泥为主要原料开发出一种新型轻质陶粒滤料(LCFM),评价了LCFM在静态吸附及动态过滤条件下对污染物的去除效果。结果表明,在静态吸附温度为(25.0±1.0)℃、p H=7,t_(吸附)=24 h条件下,LCFM对氨氮、总磷和有机物具有良好的吸附效果。在过滤系统中控制进水p H=7.0~8.0,过滤周期约10 h时,系统对氨氮、总磷和COD等污染物的去除效果较好,去除率分别为80%、95%和70%。比表面积分析仪分析显示,LCFM中的孔道以中微孔为主,集中分布在60.0 nm左右,比表面积为71.47 m~2/g,同时,LCFM中含有的金属离子在吸附过程中与污染物可能存在的交换反应或沉淀反应(x PO_4~(3-)+3M~(x+)=M_3(PO_4)_x)强化了LCFM对污染物的吸附效果。     

Dynamics of cyanobacterial bloom formation during short-term hydrodynamic fluctuation in a large shallow, eutrophic, and wind-exposed Lake Taihu, China

Short-term hydrodynamic fluctuations caused by extreme weather events are expected to increase worldwide because of global climate change, and such fluctuations can strongly influence cyanobacterial blooms. In this study, the cyanobacterial bloom disappearance and reappearance in Lake Taihu, China, in response to short-term hydrodynamic fluctuations, was investigated by field sampling, long-term ecological records, high-frequency sensors and MODIS satellite images. The horizontal drift caused by the dominant easterly wind during the phytoplankton growth season was mainly responsible for cyanobacterial biomass accumulation in the western and northern regions of the lake and subsequent bloom formation over relatively long time scales. The cyanobacterial bloom changed slowly under calm or gentle wind conditions. In contrast, the short-term bloom events within a day were mainly caused by entrainment and disentrainment of cyanobacterial colonies by wind-induced hydrodynamics. Observation of a westerly event in Lake Taihu revealed that when the 30 min mean wind speed (flow speed) exceeded the threshold value of 6 m/s (5.7 cm/s), cyanobacteria in colonies were entrained by the wind-induced hydrodynamics. Subsequently, the vertical migration of cyanobacterial colonies was controlled by hydrodynamics, resulting in thorough mixing of algal biomass throughout the water depth and the eventual disappearance of surface blooms. Moreover, the intense mixing can also increase the chance for forming larger and more cyanobacterial colonies, namely, aggregation. Subsequently, when the hydrodynamics became weak, the cyanobacterial colonies continuously float upward without effective buoyancy regulation, and cause cyanobacterial bloom explosive expansion after the westerly. Furthermore, the results of this study indicate that the strong wind happening frequently during April and October can be an important cause of the formation and expansion of cyanobacterial blooms in Lake Taihu.     

潮汐流-潜流组合人工湿地污水净化效率

构建了潮汐流-潜流组合和潜流-潮汐流组合人工湿地对污水进行处理,分别研究2种组合人工湿地对污水的净化效果。结果表明,在平均进水COD浓度为214．28mg／L、NH4＋-N浓度为10．57mg／L、PO34--P浓度为5．44mg／L、TN浓度为10．25mg／L,水力负荷为o．2m3／（m2·d）的条件下,潮汐流-潜流组合人工湿地对COD、PO34--P的去除率分别为58．28％和46．99％,与潜流-潮汐流组合人工湿地处理效果相近;对NH4＋-N、TN,潮汐流-潜流组合人工湿地的去除率分别为69．93％和71．03％,比潜流-潮汐流组合人工湿地分别高15％和33％。潮汐流-潜流人工湿地的组合,在系统内实现了硝化-反硝化的组合,强化了系统对TN的净化效果,其对TN的净化效果比-般的潜流和表面流人工湿地组合提高20％～30％。总体上,潮汐流-潜流组合人工湿地具有更好的净化效果。     

丝瓜瓤固定化脱色菌Enterobactor sp.S8 对活性黑5的脱色

利用植物载体丝瓜瓤对肠杆菌(Enterobactor sp.S8)进行固定,并对活性黑5进行脱色研究.探讨了固定化菌体的菌龄、菌量、pH、温度对染料脱色的影响.研究了该固定化菌体的重复利用和动力学实验.结果表明,最佳脱色条件为:菌龄3d、接菌量2％、温度30℃、pH 6.0.该固定化菌体对不同初始浓度活性黑5的脱色符合二级反应动力学方程.经9次重复利用后的该固定化菌体,其脱色率仍达76.8％.在优化实验条件下,根据降解3d前后的紫外-可见光谱图分析可知,活性黑5并非完全被降解为CO2和H2O,而是生成一些小分子有机中间体.