排队接水的争论

秋天是个干旱的季节．学校组织五·一班的全体同学给学校南面的一些大树浇水。班长刘谦同学与劳动委员张旭同学提前进行了实地考察．发现离浇树地点最近的一个水源是学校南门内的唯一的一个水龙头．

Removal of Orthophosphate from Aqueous Solution Using Natural Zeolite

This study was focused on orthophosphate adsorption on natural zeolite which was obtained from South of Thailand and has been carried out by Vanadomolybdophosphoric Acid （VMPA） and using spectrophotometry technique. The phosphate solution were prepared artificially by adding certain quantities of KH2PO4 in water at the initial orthophosphate concentration of 5, 10 and 20 mg/L. While the adsorbent quantity was 1g of natural zeolite per 50 mL, aqueous solution NaOH IN and HCI IN solutions were used as pH regulators. The effect of equilibrium pH, adsorbent mass and contact time was studied. The results showed that natural zeolite adsorption efficiency was 99.18%, 99.33% and 99.02% （5, 10 and 20 mg/L）, respectively, at pH of 12 and a contact time of 30 minutes at 298 K. Moreover, the isotherm can be used to evaluate the capacity and nature of the interaction between a sorbent and a sorbate. This work considers the Langmuir and Freundlich isotherm. Based on the R2 of adsorption isotherm studies, the adsorption data for phosphate fitted well the Freundlich isotherm for natural zeolite （R^2=0.99）, with multi-layer adsorption. The results are in good agreement with recent experimentl data.

Orthogonal Experiments for Controlling the Formation of DBPs During Preozonation of Bromide-Containing Raw Water

Orthogonal method was adopted to optimize the preozonation process and to minimize the bromate formation. Factors such as contact time, pH and ammonia concentration were investigated by orthogonal experiments to understand the interaction of various operation conditions on the formation of bromate and other disinfection byproducts(DBPs). Results showed that pH had the most significant influence on the minimization of bromate formation. The factors influencing the formation of bromate were in order of pH > contact time > ammonia concentration. For the formation of trihalomethanes(THMs) and haloacetic acids(HAAs), however, contact time significantly influenced their formation potential. In the practical preozonation process of waterworks, it is appropriate to set preozonation contact time to be 20 min. In order to minimize the formation of bromate, pH value of the raw water should be adjusted to 6. 0, and a certain concentration of ammonia could be added into the water to strengthen the minimization effect when the concentration of bromide in the raw water is higher than that in the experimental water.

Relative Effectiveness of Ultraviolet Light Irradiation and Chlorination against Indigenous Bacteriophage and Bacteria in Primary Treated Wastewater

The effectiveness of chlorine and ultraviolet light at inactivating indigenous microbes in primary treated wastewater was examined in this study. The inactivation rates for somatic colipahge and F-specific bacteriophage were less than 2.5 log and 1 log, respectively, at either free chlorine doses of 6, 15 mg/L and 30 mg/L after 30 minutes contact time. However, E. coli and total coliforms were susceptible to chlorination and inactivated more than 4 log within first 15 minutes of contact time at any chlorine dosage tested. In contrast, the inactivation of bacteriophage was increased when increasing UV fluence. At the same disinfection effectiveness against E. coli, UV disinfection was more effective than chlorination against F-specific bacteriophages.

Removal of Cadmium from Aqueous Solutions by Adsorption onto Activated Carbon Prepared from Date Stems

Activated carbon was prepared from date stems by one step H3PO4 activation and used as adsorbent for the removal of cadmium ions Cd2＋. This agricultural by-product is available in large amount in Algeria. Batch adsorption experiments were performed as a function of contact time, pH, adsorbent dose and initial cadmium concentration. It was found that the equilibrium was achieved less than 60 rain of contact time. The effect of pH on adsorption equilibrium was studied at values ranging from 1 to 6, demonstrating the importance of this parameter for an accurate evaluation of the adsorption process. Maximum adsorption was found for pH values ranging from 5 to 6.5. The models of adsorption isotherms, such as Langmuir, Freundlich and Dubinin-Radushkevich, were tested for the quantitative description of the cadmium uptake. The results obtained revealed that the cadmium was considerably adsorbed on activated carbon prepared from date stems and it could be an economical method for the removal of cadmium from aqueous solutions.

Thermodynamic analysis of liquid bridge for fixed volume in atomic force microscope

In ambient condition,capillary forces are the major contributors to the adhesive forces between the tip of an atomic force microscope(AFM) and the sample.In general,capillary forces are thought to be related to water film thickness,contact time and relative humidity and so on.In this paper,an original analysis regarding the liquid bridge,based on the surface and interface thermodynamic theory,is proposed.The cases covered in the study include the capillary forces and temperature of liquid bridge for quickly drawn liquid bridge,and for nonvolatile liquid bridge.The study results show that variation in temperature may occur in the liquid bridge when it is stretched.