Performance of an immobilized cell biofilter for ammonia removal from contaminated air stream

The performance of a lab scale biofilter packed with biomedia, encapsulated by sodium alginate and polyvinyl alcohol was used for treating ammonia (NH(3)) gas at different loading rates. The metabolic end products during NH(3) oxidation were NH(4)(+), NO(3)(-) and NO(2)(-). It is noteworthy to mention that the immobilized cell biofilter required no separate acclimatization period and showed high removal efficiencies during the start of continuous experiments. The removal efficiency was nearly 100% when ammonia loading was 4.5gm(-3)h(-1) and the maximum elimination capacity achieved in this study was 5.5gNH(3)m(-3)h(-1) at a loading rate of 7.5gm(-3)h(-1). Shock loading studies were carried out to ascertain the response of the immobilized cells to fluctuations in inlet concentration and flow rate. The inlet loading rates were varied between 0.05 and 6gNH(3)m(-3)h(-1) during this phase of operation. The biofilter responded effectively to these shock loading conditions and recovered rapidly within 4-8h. Pressure drop values were consistently less and insignificant. The results from this study indicated that this immobilized cell biofilter could be considered as a potential option to treat NH(3) under steady and transient state operation.     

Determination of benzene, toluene, ethylbenzene, xylenes in water at sub-ng l-1 levels by solid-phase microextraction coupled to cryo-trap gas chromatography-mass spectrometry

A trace analytical method of benzene, toluene, ethylbenzene and xylenes (BTEX) in water has been developed by using headspace solid-phase microextraction (HS-SPME) coupled to cryo-trap gas chromatography-mass spectrometry (GC-MS). The chromatographic peak shape for BTEX was improved by using cryo-trap equipment. The HS-SPME experimental procedures to extract BTEX from water were optimized with a 75 microm carboxen/polydimethylsiloxane (CAR/PDMS)-coated fiber at a sodium chloride concentration of 267 g l(-1), extraction for 15 min at 25 degrees C and desorption at 290 degrees C for 2 min. Good linearity was verified in a range of 0.0001-50 microg l(-1) for each analyte (r(2)=0.996-0.999). The limits of detection (LODs) of BTEX in water reached at sub-ng l(-1) levels. LODs of benzene, toluene, ethylbenzene, m/p-xylene and o-xylene were 0.04, 0.02, 0.05, 0.01 and 0.02 ng l(-1), respectively. The proposed analytical method was successfully used for the quantification of trace BTEX in ground water. The results indicate that HS-SPME coupled to cryo-trap GC-MS is an effective tool for analysis of BTEX in water samples at the sub-ng l(-1) level.     

Atmospheric peroxides over the North Pacific during IOC 2002 shipboard experiment

Atmospheric hydrogen peroxide and methyl hydroperoxide were determined onboard the Melville over the North Pacific from Osaka to Honolulu during May-June 2002. The concentrations of H(2)O(2) and CH(3)OOH increased from 0.64+/-0.57 ppbv and 0.27+/-0.59 ppbv in subpolar region (30-50 degrees N) to 1.96+/-0.95 ppbv and 1.56+/-1.3 ppbv in subtropical region (24-30 degrees N). The increase in concentrations towards the Equator was more pronounced for CH(3)OOH than H(2)O(2). In contrast, the levels of O(3) and CO were decreased at lower latitudes as air mass was more aged, denoted by the ratios of C(2)H(2)/CO and C(3)H(8)/C(2)H(6). CH(3)OOH concentrations showed a clear diurnal variation with a maximum around noon and minimum before sunrise. Frequently, the concentrations of peroxides remained over 1 ppbv in the dark and even gradually increased after sunset. In addition, the ratios of C(2)H(4)/C(2)H(6) and C(3)H(6)/C(3)H(8) were increased in aged subtropical air, which implies that these alkenes were emitted from the ocean surface. As a result, the reaction of these biogenic alkenes with O(3) was suggested to be a potential source for peroxides in aged marine air at lower latitudes.     

Protein tyrosine dephosphorylation during copper-induced cell death in rice roots

Early signalling events that control the process of heavy metal-induced cell death are largely unknown in plants. In mammals protein tyrosine phosphorylation plays an important role in the activation of programmed cell death. We thus examined the involvement of tyrosine phosphorylation in Cu-induced rice cell death. This investigation demonstrates that Cu induces cell death and DNA fragmentation in rice root cells. In the presence of Cu, the level of phosphotyrosine accumulation declined in the band of 45 kDa, p45. To analyze the role of tyrosine dephosphorylation for the regulation of Cu-induced cell death more precisely, we increased levels of tyrosine phosphorylation using the protein tyrosine phosphatase inhibitor, sodium orthovanadate (Na(3)VO(4)). Treatment of rice roots with Na(3)VO(4) blocked Cu-induced cell death and protein tyrosine dephosphorylation. In addition, the antioxidant GSH and the calcium chelator EGTA significantly abolished Cu-induced cell death and protein tyrosine dephosphorylation. These results provide evidence that dephosphorylation of a tyrosine-phosphorylated protein, p45, is an important step in the Cu-triggered signalling transduction pathway.     

Trace metal concentration in Great Tit (Parus major) and Greenfinch (Carduelis sinica) at the Western Mountains of Beijing, China

We examined the concentrations of 11 trace metals in tissues from 10 body parts of Great Tits and Greenfinches collected at Badachu Park in the Western Mountains of Beijing, China to assess the metal accumulation level, distribution among body parts, and species and gender related variations. The highest concentrations of Hg, Ni, Zn, and Mn were found in the feather; Pb and Co in the bone; Cd, Cr, and Se in the kidney, and Cu in the liver and heart. Metal concentrations had substantial interspecific variation with Great Tits showing higher levels of Hg, Cr, Ni, and Mn than Greenfinches in tissues of most body parts. Gender related variations were body part and species specific. Meta-analyses using data from this study and other studies suggested that metal concentrations of Great Tits at our study site were relatively low and below the toxic levels.     

Assessment of the relative toxicity of Cu2+ by measuring structural changes of supercoiled DNA

A method for the measurement of the relative toxicity of Cu2+ in aquatic environments is proposed. It is based on the quantitative measurement on the shape change of the supercoiled DNA after it is contacted with different levels of Cu2+ for various time intervals. In the absence of any redox reagents, all supercoiled DNA degraded into other forms of DNA after 24h incubation in the presence of 5.13 x 10(-3), 5.08 x 10(-4) and 5.35 x 10(-5)mol/L Cu2+. At a lower Cu2+ concentration (10(-6)mol/L), 44% of supercoiled DNA retained its original supercoiled form after 24 h, and 29% after 48 h. The concentration of RC50, i.e. concentration of pollutants at which 50% of the supercoiled DNA was relaxed compared to control samples, can be obtained from the does-response curves at different exposure time, which may provide a rapid and convenient approach to assess the relative toxicity of environmental pollutants.     

Relationship between carbon dioxide/methane emissions and the water quality/sediment characteristics of Taiwan's main rivers

River and sediment have unique carbon dynamics and are important sources of the dominant greenhouse gases (GHG), carbon dioxide (CO2) and methane (CH4). To understand the relationship between CO2/CH4 emissions and water quality/sediment characteristics, we have investigated critical parameters in the river water. Eight parameters of water quality (dissolved oxygen, oxidation-reduction potential [ORP], chemical oxygen demand, biochemical oxygen demand [BOD5], suspended solid, nitrate [NO3-], NH4+, and bacteria) and four sediment characteristics (total organic carbon [TOC], total nitrogen [T-N], NO3-, and ammonium [NH4+]) were measured in two of the larger rivers in Taiwan, and relevant environmental conditions were recorded. The experimental results indicated that CO2 emissions from the river were mainly affected by BOD5 concentrations and the levels of bacteria. CH4 emissions, on the other hand, were greatly affected by the ORP in the river. The correlation between CO2 emissions and sediment characteristics was insignificant (R2 < 0.3). However, TOC and T-N in the sediment may lead to increases in CH4 emissions into the atmosphere. A deeper analysis of the relationship between the different parameters and GHG emissions by ANOVA and the multiple regression method revealed that CO2 emission (y) was significantly related to bacteria number (x1) and BOD concentration (X2). The regression equation takes the form y = 0.00032x1 + 3.18089x2 + 25.37304. Also, the regression relationship between CH4 emission (y) and ORP (x) in the river can be described as y = -0.825216x + 169.02257. The relationship between CH4 emission and sediment characteristics may be described as y = 5.073962x1(TOC) + 2.871245x2(T-N) - 12.3262. Extra sampling data were collected to examine the feasibility of the developed multiple regression equations. The experimental results suggest that the emissions of such GHGs as CO2 and CH4 from rivers can be predicted using the regression equations developed here. Moreover, the emissions may be reduced by manipulating the proper factors.     

中蒙边境典型草原可燃物热解动力学研究

以中蒙边境(包括东乌旗、 二连浩特市、 新巴尔虎右旗)的草原可燃物为研究对象,利用STA 6000热重分析仪,采用热重分析法以5 ml/min,10 ml/min,20 ml/min,30 ml/min的氧气为载气,在空气气氛下,升温速率分别为40℃/min,60℃/min,80℃/min时对三个地区草原可燃物的热失重...     

科技英语文摘的文体与表达

科技论文的文摘是关系到论文能否被录用、发表及检索的重要因素。文章从文体的角度论述科技文摘的写作与翻译方法及注意问题,指出科技论文摘要应与国际惯例接轨,注意文体的严谨、准确、明了和科学性等问题;并为科技论文文摘撰写提供了重要依据。     

真空紫外光降解五氯酚钠以及过硫酸盐对反应的促进作用

研究了真空紫外光(VUV,185 am)对于水溶液中五氯酚钠的降解,反应2 h后,初始浓度为10 mg/L的五氯酚钠的去除率达到99%以上,有机氯的脱除率达到70%以上,有效地实现了五氯酚钠的脱毒.溶液初始pH值对五氯酚钠的真空紫外光解有很大影响,pH=10.9时的降解速率常数是pH=3.1时的3倍.表观一级反应速率常数随初始浓度的增加而线性下降.在反应溶液中加入过硫酸盐,可有效提高五氯酚钠的真空紫外光降解速率和矿化速率,过硫酸盐和五氯酚钠摩尔比为24时,降解速率提高3倍,反应4 h后TOC去除率达到95%.