Explosion regions and limiting oxygen concentrations of methyl propionate,methyl acetate,dimethyl carbonate with air and inert gas mixtures

New data about explosion regions with special focus on limiting oxygen concentrations for methyl propionate, methyl acetate, dimethyl carbonate with air in the presence of nitrogen, helium and carbon dioxide were determined at ambient initial pressure and 423 K. The measurements were executed according to EN 1839 method T. The changes of the explosion regions with temperature and type of inert gas were also modeled mathematically using an extended calculated adiabatic flame temperature profile (CAFTP) method. The shift of the explosion region boundaries with temperature when switching from nitrogen to carbon dioxide were reproduced well. For a switch to helium a good agreement could be reached only if the very high thermal conductivity of helium had been considered properly by using the Lewis number. This requires the knowledge of the respective Lennard-Jones parameters. The LOC of helium-containing mixtures can, however, be calculated with acceptable accuracy even if the Lennard-Jones parameters of the flammable substance are not known exactly by using reasonable estimations.     

Experimental study of nitrite accumulation in predenitrification biological nitrogen removal process

The effect of dissolved oxygen (DO) concentration on nitrite accumulation was investigated in a pilot-scale pre-denitrification process at room temperature for 100 days. In the first 10 days, due to the instability of the system, the DO concentration fluctuated between 1.0 and 2.0 mg/L. In the next 14 days, the DO concentration was kept at 0.5 mg/L and nitrite accumulation occurred, with the average nitrite accumulation rate at 91%. From the 25th day, the DO concentration was increased to 2.0 mg/L to destroy the nitrite accumulation, but nitrite accumulation rate was still as high as 90%. From the 38th day the nitrite accumulation rate decreased to 15%–30% linearly. From the 50th day, DO concentration was decreased to 0.5 mg/L to resume nitrite accumulation. Until the 83rd day the nitrite accumulation rate began to increase to 80%. Dissolved oxygen was the main cause of nitrite accumulation, taking into account other factors such as pH, free ammonia concentration, temperature, and sludge retention time. Because of the different affinity for oxygen between nitrite oxidizing bacteria and ammonia oxidizing bacteria when DO concentration was kept at 0.5 mg/L, nitrite accumulation occurred. __________ Translated from Environmental Science, 2006, 27(12): 2472–2476 [译自: 环境科学]     

丁草胺对镉胁迫条件下水稻生长、镉积累及活性氧代谢的影响

以2个水稻品种(秀水110和秀水11)为材料,通过水培试验和土培试验研究了除草剂丁草胺对Cd2 胁迫条件下水稻植株生长、Cd2 积累和活性氧代谢的影响.研究结果表明.水培条件下,丁草胺浓度的增加显著地加剧了Cd2 胁迫条件下水稻生长抑制程度,进一步导致叶绿素含量显著下降,促进了2个品种水稻植株对Cd2 的吸收,引起水稻叶片的O-2产生速率、H202和MDA含量增加.且显著改变了SOD、CAT和G-POD活性;同条件下丁草胺浓度的增加使水稻叶片SOD/O-2、SOD/G-POD、SOD/CAT、CAT/H2O2和G-POD/H2O2的比值均发生了偏离;推测丁草胺加剧了水稻Cd2 胁迫时植株活性氧代谢不平衡过程.土培条件下,丁草胺对水稻糙米中Cd2 积累量也具有显著促进作用.     

满江红花青素在镉胁迫下的抗氧化作用

为了研究镉胁迫诱导满江红体内花青素合成的生理功能,采用镉诱导和体外实验的方法评价了满江红体内花青素的抗氧化作用.测试指标包括还原力、清除超氧阴离子(O-2)、过氧化氢(H2O2)、羟自由基(·OH)的能力.结果表明,花青素的还原力和对氧自由基的清除作用随花青素提取物浓度的增加而增加.因此,镉胁迫下合成的花青素是一种清除活性氧自由基的良好抗氧化剂.镉胁迫对满江红活性氧代谢影响的试验结果表明,在0.5mg·L-1Cd胁迫下,满江红体内O-2和H2O2大量积累,造成活性氧胁迫,说明花青素只能在一定程度上保护满江红免受过氧化伤害.本实验初步证实,花青素含量的增加是满江红抗性机理之一,可缓解镉的毒害.     

Effects of COD/N ratio and DO concentration on simultaneous nitrification and denitrification in an airlift internal circulation membrane bioreactor

The effects of chemical oxygen demand and nitrogen(COD/N)ratio and dissolved oxygen concentration(DO)on simultaneous nitrification and denitrification(SND)were investigated using an airlift internal circulation membrane bioreactor(AIC-MBR)with synthetic wastewater.The results showed that the COD efficiencies were consistently greater than 90% regardless of changes in the COD/N ratio.At the COD/N ratio of 4.77 and 10.04,the system nitrogen removal efficiency became higher than 70%.However,the nitrogen rem...     

水体溶解有机质富集分离方法的研究进展

溶解有机质,作为全球碳循环的主要组成部分,在水生生态系统的各种物理、化学和生物过程中扮演着非常重要的角色。富集分离溶解有机质是研究其化学特征和环境地球行为的必要前提。在总结XAD树脂分离技术在溶解有机质富集分离的基础上,本文对其它三种常用的分离方法—二乙氨基乙基纤维素(DEAE)吸附分离法、超滤(UF)分离法以及反渗透(RO)分离法进行了综述。介绍了各分离方法的分离原理、分离流程、存在的优缺点及应用范围。最后对超滤或反渗透与XAD树脂相结合的联用技术在溶解有机质环境地球化学研究中的应用前景进行了展望。     

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。     

Molecular toxicity and defense mechanisms induced by silver nanoparticles in Drosophila melanogaster

The widely use of silver nanoparticles (AgNPs) as antimicrobial agents gives rise to potential environmental risks. AgNPs exposure have been reported to cause toxicity in animals. Nevertheless, the known mechanisms of AgNPs toxicity are still limited. In this study, we systematically investigated the toxicity of AgNPs exposure using Drosophila melanogaster. We show here that AgNPs significantly decreased Drosophila fecundity, the third-instar larvae weight and rates of pupation and eclosion in a dose-dependent manner. AgNPs reduced fat body cell viability in MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays. AgNPs caused DNA damage in hemocytes and S2 cells. Interestingly, the mRNA levels of the entire metallothionein gene family were increased under AgNPs exposure as determined by RNA-seq analysis and validated by qRT-PCR, indicating that Drosophila responded to the metal toxicity of AgNPs by producing metallothioneins for detoxification. These findings provide a better understanding of the mechanisms of AgNPs toxicity and may provide clues to effect on other organisms, including humans.     

Fe-N co-doped coral-like hollow carbon shell toward boosting peroxymonosulfate activation for efficient degradation of tetracycline: Singlet oxygen-dominated non-radical pathway

Fe-N co-doped coral-like hollow carbon shell (Fe-N-CS) was synthesized via a simply impregnation-pyrolysis method. The Fe-N-CS showed an excellent ability for activating peroxymonosulfate (PMS), which could degrade about 93.74% tetracycline (20 mg/L) in 12 min. The Fe-N-CS/PMS system exhibited a good anti-interference capacity of various pH, inorganic anions, HA and different water qualities. More importantly, the Fe nanoparticles were anchored uniformly in the carbon layer, effectively limiting the metal leaching. The quenching tests and electron spin resonance (ESR) manifested that non-radical singlet oxygen (¹O₂) was the main reactive oxygen species (ROS) for TC degradation. The mechanism study showed that Fe nanoparticles, defect and graphite N played a key role in activating PMS to produce ROS. Moreover, three probable degradation pathways were proposed by using LC-MS measurements. Generally, this work had a new insight for the synthesis of heterogeneous Fe-N-C catalysts in the advanced oxidation process based on PMS.     

Effects of wastewater discharge on formation of Fe plaque on root surface and radial oxygen loss of mangrove roots

Effects of wastewater discharge on radial oxygen loss (ROL), formation of iron (Fe) plaque on root surface, and their correlations in Bruguiera gymnorrhiza (L.) Poir and Excoecaria agallocha L. were investigated. ROL along a lateral root increased more rapidly in control than that in strong wastewater (with pollutant concentrations ten times of that in municipal sewage, 10NW) treatment, but less Fe plaque was formed in control for both plants. For B. gymnorrhiza receiving 10NW, Fe plaque formation was more at basal and mature zones than at root tip, while opposite trend was shown in E. agallocha. At day 0, the correlation between ROL and Fe plaque was insignificant, but negative and positive correlations were found in 10NW and control, respectively, at day 105, suggesting that more ROL was induced leading to more Fe plaque. However, excess Fe plaque also served as a ‘barrier’ to prevent excessive ROL in 10NW plants.