含氯消毒剂对原水管道中贝类的杀灭效果

原水管道中大量生长的贝类会导致管道的输送能力下降,死亡的贝壳堵塞管道和水处理构筑物,可能对水厂生产造成严重影响。文章探讨了以水处理中常用的消毒剂氯和次氯酸钠作为杀贝剂的可行性。结果表明,两种药剂都对淡水壳菜有较好的杀灭效果,在0．6～10mg／L的有效氯投加浓度下,全部杀灭壳菜的时间在14～4天之间。采用CT值法确定合理的投加剂量在2mg/L左右。     

基于OSPF协议的GracefuI Restart技术的研究与实现

随着网络规模的不断扩大,网络速度的快速提升,网络与通信的新技术不断融入,用户越来越需要更丰富、更方便、更及时的网络应用和服务,互联网的这些特征导致新一代互联网概念的产生。为了提高网络可用性,IETF提出了对路由协议的扩展来减少由于路由协议失效造成的业务损失。在网络边缘路由器和其邻居路由器都支持OSPF平稳重启情况下,即使控制平面失效,数据平面也能够继续处理和转发报文。由于减少了路由抖动,平稳重启能够增加网络稳定性并减少控制平面资源的消耗。从而不单单增强了单台路由器的可用性,更提高了整个网络的可用性。     

Environmental experts in the pharmaceutical industry — production

The processes employed in the Industry cover a wide range and bring problems of effluent disposal and deposit of solid wastes, and of emissions to the air of smoke, dust, smell and noise. It is necessary to relate legislation to required standards and to process operations and to prepare forward plans on the basis of present environmental trends. This involves the cooperation of a number of departments covering different disciplines. The actual control of environmental hazards must occur in the operating stages of manufacture and is therefore a line responsibility. The type of person suitable for the role of Environment Adviser as a staff function is discussed.     

Comparative toxicity of single and combined mixtures of selected pollutants among larval stages of the native freshwater mussels (Unio elongatulus) and the invasive zebra mussel (Dreissena polymorpha)

This study evaluated the impact of biocides (tributyltin, chlorthalonil and Irgarol 1051) and of pollutants (copper, inorganic and methyl mercury and 4-nonylphenol) occurring in Ebro River (NE Spain) on early developmental stages of native Spanish freshwater and invasive zebra mussels. Toxicity tests were conducted with embryos and glochidia of zebra mussel (Dreissena polymorpha) and the naiad species Unio elongatulus, respectively. Toxicity was quantified in terms of median effective concentration (EC50) impairing embryogenesis and glochidia viability in single and combined mixture exposures. Irgarol 1051 was not toxic at concentrations below 40 × 10³ nM. Zebra mussel embryos were on average 50 fold more sensitive to the studied pollutants than glochidia. Tributyltin was the most toxic compound with EC50s for zebra mussel embryos and glochidia, respectively, of 1.24 and 47.93 nM, followed by chlorothalonil (3.65, 176.58 nM), methyl mercury (7.06, 156.4 nM), inorganic mercury (3.64, 518.28 nM), copper (19.73, 1358.55 nM) and 4-nonylphenol (33.99, 1221.48 nM). Combined toxicity of Ebro River pollutants (copper, inorganic and methyl mercury and 4-nonylphenol) was greater than additive in zebra mussel embryos and additive in glochidia. These results indicated that contaminant levels that affect zebra mussel embryos are not toxic to early life stages of the naiad mussel species U. elongatulus.     

Sensitivity to aerial exposure: potential of system-wide drawdowns to manage zebra mussels in the Mississippi River

We report the results of five experiments performed during periods of lowered river water level in Pool 26 of the Mississippi River. Four experiments compared survivorship of zebra mussels (Dreissena polymorpha) and unionid mussels (Unionidae). Under mild spring conditions (March), survivorship of zebra mussels was similar to that of unionid mussels, but during summer (July) survivorship of zebra mussels was lower than that of unionid mussels. Survivorship of zebra mussels was greatest when attached to native unionids, compared with detached zebra mussels and zebra mussels attached rocks. A fifth experiment compared survivorship of 10 species of unionid mussels after 24 hours of aerial exposure. In general, survivorship of thick-shelled species, such as Amblema plicata, was greater than survivorship of thin-shelled species, such as Potamilus ohiensis. The experiments conducted suggest that drawdowns during warm summer conditions could have a profound, negative influence on zebra mussel demography and distribution. In contrast, unionid mussel survival was unaffected by aerial exposure of up to 24 hours during a midsummer drawdown. © 1997 John Wiley & Sons, Ltd.