Nitritation performance and biofilm development of co- and counter-diffusion biofilm reactors: Modeling and experimental comparison

A comparative study was conducted on the start-up performance and biofilm development in two different biofilm reactors with aim of obtaining partial nitritation. The reactors were both operated under oxygen limited conditions, but differed in geometry. While substrates (O₂, NH₃) co-diffused in one geometry, they counter-diffused in the other. Mathematical simulations of these two geometries were implemented in two 1-D multispecies biofilm models using the AQUASIM software. Sensitivity analysis results showed that the oxygen mass transfer coefficient (K_i) and maximum specific growth rate of ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) were the determinant parameters in nitrogen conversion simulations. The modeling simulations demonstrated that K_i had stronger effects on nitrogen conversion at lower (0-10 m d⁻¹) than at the higher values (>10 m d⁻¹). The experimental results showed that the counter-diffusion biofilms developed faster and attained a larger maximum biofilm thickness than the co-diffusion biofilms. Under oxygen limited condition (DO < 0.1 mg L⁻¹) and high pH (8.0-8.3), nitrite accumulation was triggered more significantly in co-diffusion than counter-diffusion biofilms by increasing the applied ammonia loading from 0.21 to 0.78 g NH₄⁺-N L⁻¹ d⁻¹. The co- and counter-diffusion biofilms displayed very different spatial structures and population distributions after 120 days of operation. AOB were dominant throughout the biofilm depth in co-diffusion biofilms, while the counter-diffusion biofilms presented a stratified structure with an abundance of AOB and NOB at the base and putative heterotrophs at the surface of the biofilm, respectively.     

An assessment of estrogenic organic contaminants in Canadian wastewaters

A suite of 30 primarily estrogenic organic wastewater contaminants was measured in several influent/effluent wastewater samples from four municipal wastewater treatment plants and effluents from one bleached kraft pulp mill (BKME) using an ultra-trace analytical method based on gas chromatography-high resolution mass spectroscopy (GC-HRMS). In vitro recombinant yeast assay detection of the estrogenic equivalent (EEq) on whole and solid phase extracted (SPE) and fractionated wastewater was also performed. 19-norethindrone was the most frequently detected and abundant (26-224 ng/L) of all the synthetic estrogens/progesterones in the influent samples. 17alpha-ethinylestradiol was the more frequently detected synthetic estrogen/progesterone in the effluents occurring at or below 5 ng/L with some sporadic occurrences of up to 178 ng/L. The greatest levels of steroidal estrogens in municipal effluents were E1>E2>E3 which were all <20 ng/L. Nonylphenol and di(2-ethylhexyl) phthalate were found to be the highest non-steroidal synthetic compounds surveyed in both municipal influent and effluent samples, both occurring at 6-7 microg/L in municipal effluents. BKME contained relatively large amounts of the plant sterol stigmasterol (4 microg/L) but low amounts of fecal sterols, and steroidal estrogens (E2 only at 6 ng/L) when compared to the municipal effluents. In vitro EEq in the wastewater surveyed ranged from 9-106 ng E2/L and ranked from municipal influent>municipal effluent approximately BKME, with most of the estrogenicity fractionating in the 100% methanol SPE fraction followed by a secondary amount in the diethyl ether (for municipal) or methyl-tert butyl ether (for BKME) SPE fractions. Most correlations between chemical and in vitro estrogenic equivalency were weak (p>0.05 in most cases). Unexpected inverse correlations between in vitro estrogenic activity and concentrations of the estrogenic contaminant bisphenol A were found which likely contributed to the weakness of these correlations. A modified toxicity identification and evaluation procedure was continued with the SPE extracts from the more potent 100% methanol SPE fractions of municipal effluent. High performance liquid chromatography band elution retention times, based on in vitro estrogen detection, indicated that steroidal estrogens such as E2 were responsible for most of the estrogenicity of the samples. Subsequent collection and GC-MS analysis of active bands did not confirm the presence of steroidal estrogens, but expanded the possibility of phthalate esters (i.e. dibutyl phthalate) and natural sterols (i.e. beta-sitosterol) contributing to the overall estrogenic load.     

现浇板裂缝原因分析及防治对策

对抗震区住宅采用泵送混凝土全现浇结构的常见裂缝类型进行总结,分别从设计、施工、温度影响、使用商品混凝土等方面分析其产生原因,并制定相应对策.     

从上海世博看城市建设的创新及其相关启示

本文综合介绍了上海世博会在规划设计理念上、建筑创作理念上和运营管理方式上的创新等方面的相关情况及对我国城市建设的相关启示,为读者提供可借鉴的资料,以期促进祖国现代化的进程。     

颗粒强化钛基复合材料的氧化特性

研究了以ＴｉＣ颗粒增强的钛基复合材料的氧化特性。指出ＴｉＣ增强的钛基复合材料在６５０℃以上高温有着其它耐热钛合金不可比拟的高温抗氧化性能；ＴｉＣ／Ｔｉ的反应界面层有利于氧原子的扩散，使复合材料在６５０℃以下的氧化初期氧化速度较快；但在６５０℃以下经长时间保温，其氧化特性和其它耐热钛合金相似。     

IN SITU GRADIENT DOUBLE-LAYER COMPOSITES OF Al-Fe ALLOY BY CENTRIFUGAL CASTING

ＩＮＳＩＴＵＧＲＡＤＩＥＮＴＤＯＵＢＬＥＬＡＹＥＲＣＯＭＰＯＳＩＴＥＳＯＦＡｌＦｅＡＬＬＯＹＢＹＣＥＮＴＲＩＦＵＧＡＬＣＡＳＴＩＮＧ①ＷａｎｇＱｕｄｏｎｇ，ＪｉｎＪｕｎｚｅＲｅｓｅａｒｃｈＣｅｎｔｅｒｏｆＦｏｕｎｄｒｙＥｎｇｉｎｅｒｉｎｇ，Ｄａｌ...     

IN-SITU OBSER VATION OF SINGLE-POINT WEAR OF PM Al-Ti ALLOY

ＩＮＳＩＴＵＯＢＳＥＲＶＡＴＩＯＮＯＦＳＩＮＧＬＥ－ＰＯＩＮＴＷＥＡＲＯＦＰＭＡｌＴｉＡＬＬＯＹ①ＷｕＪｉｎｍｉｎｇ，ＷｕＮｉａｎｑｉａｎｇ，ＷａｎｇＧｕａｎｇｘｉｎ，ＬｉＺｈｉｚｈａｎｇＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａ...     

利用高架桥梁支架基础作地面道路路面的分析

随着我国建筑业和桥梁工程建设的不断发展,高架桥桥梁支架技术也成为被广泛关注的对象。其广泛应用在满足了高架桥粱施工的同时,又节省了地面道路的工程量,减少了外运渣土土方的运输。本文简要分析了高架桥粱支架基础作地面道路路面的工程控制。     

A case study in evaluating the status of consolidation of a soft soil deposit by incomplete piezocone dissipation tests using laboratory and field data

By using the piezocone penetration test (PCPT or CPTu), one can develop not only a better understanding of the soil stratification, but also an understanding of soil behavior parameters related to soil compressibility, as well as soil strength. This paper describes a case study that utilizes incomplete piezocone dissipation test to estimate status of consolidation of a soil deposit. Incomplete pore pressure dissipation record of PCPT is extrapolated on an inverse time scale (1/t method) to estimate the “in situ” pore pressure and “residual excess” pore pressure. No case study has been reported in open literature where this methodology has been utilized to estimate the status of consolidation of the soil deposit. In this paper, the 1/t method was verified using dissipation data from rigorous calibration chamber tests and field test data.     

Plastic coupled instabilities of I-shaped steel beams

The paper presents the case of plastic instability of I-shaped beams where the rotation capacity is a very important characteristic in order to assure the required ductility in plastic or seismic design. The failure of such beams can be due to the local plastic plate buckling of compression flange and local plate buckling of the web in flexural compression, produced in-plane or out-of-plane. In the same time the failure can occurs by coupling of these two local buckling modes. In order to study the plastic buckling of beams and to determine the available rotation capacity which is required by the plastic or seismic design, the collapse plastic mechanism theory was developed and a specialized computer program DUCTROT-M was elaborated. The parametrical analysis reveals the paramount importance of the web to thickness ratio and furthermore the sensitivity in out-of-plane buckling of the European hot-rolled sections.