The effect of boiling water on disinfection by-product exposure

Chloraminated and chlorinated waters containing bromide were used to determine the impact of boiling on disinfection by-product (DBP) concentrations. No significant changes were detected in the concentrations of the dihalogenated haloacetic acids (DXAAs) (i.e., dichloro-, bromochloro-, dibromoacetic acid) upon boiling of chloraminated water, whereas the levels of the trihalogenated haloacetic acids (TXAAs) (i.e., trichloro- (TCAA), bromodichloro- (BDCAA), dibromochloroacetic acid (DBCAA)) decreased over time (e.g., 9-37% for TCAA). Increased DXAA concentrations (58-68%) were detected in the boiled chlorinated sample, which likely resulted from residual chlorine reacting with DXAA precursors. TCAA concentration was unchanged after boiling chlorinated water for 1 min, but a 30% reduction was observed after 5 min of boiling. BDCAA concentrations decreased 57% upon boiling for 1 min and were completely removed after 2 min of boiling, whereas DBCAA was removed after boiling chlorinated water for 1 min. Trihalomethane concentrations were reduced in both chloraminated (74-98%) and chlorinated (64-98%) water upon boiling. Boiling chloraminated water for 1 min reduced chloroform concentration by 75%. Chloroform was reduced by only 34% in chlorinated water after a 1 min boil, which indicates that simultaneous formation and volatilization of chloroform was occurring. Most of the remaining DBPs (e.g. haloketones, chloral hydrate, haloacetonitriles) were removed by at least 90% after 1 min of boiling in both samples. These data suggest that other mechanisms (e.g., hydrolysis) may have been responsible for removal of the non-volatile DBPs and further highlight the importance of examining individual species when estimating thermal effects on DBP concentrations.     

Effect of river water, sediment and time on the toxicity and bioavailability of molinate to the marine bacterium Vibrio fischeri (Microtox)

The toxicity and bioavailability of molinate to Vibrio fischeri (Microtox((R))) were determined in both laboratory and river water in the absence and presence of sediment after 0, 24, 48, 72 and 96-h exposure. The bioavailability of molinate, expressed as 5min EC50s (bioluminescence) and their fiducial limits calculated using initial measured concentrations, to V. fischeri in laboratory water in the absence and presence of sediment ranged from 1.8 (1.7-2.1) to 3.6 (3.5-3.7) mgL(-1) and 1.3 (1.2-1.4) to 4.2 (3.5-4.5) mgL(-1), respectively. The corresponding values in river water and river water plus sediment were 1.7 (1.6-1.8) to 3.8 (3.6-4.1) and 1.3 (1.3-1.4) to 4.6 (4.2-4.9) mgL(-1), respectively. River water did not significantly (P>0.05) reduce the bioavailability of molinate to V. fischeri compared to that of laboratory water. However, the presence of sediment significantly (P<0.05) reduced the bioavailability of molinate to V. fischeri in both waters. The exposure time also significantly (P<0.05) reduced the bioavailability of molinate to V. fischeri in both waters in the presence and absence of sediment. The type of water did not significantly (P>0.05) affect the loss of molinate during the 96-h exposure period. However, the presence of sediment significantly (P<0.01) increased the loss of molinate from the test solutions, probably by binding to the sediment particles. Exposure period and concentration levels significantly (P<0.05) affected the loss of the herbicides over the 96h.     

上海某地铁车站深基坑周围土体沉陷研究

根据某地铁车站基坑工程实例,利用一些半理论半经验性的公式分项估算了基坑开挖、降承压水引起坑周土体沉陷,并比较分析了土体沉陷的计算结果与现场实测值,从而提出了一些基坑开挖与降承压水引起坑周土体沉陷的结论和控制建议,以供类似工程参考。     

Cometabolism of trihalomethanes by mixed culture nitrifiers

Three mixed-culture nitrifier sources degraded low concentrations (25-450 microg/L) of four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Individual THM rate constants (k1THM) increased with increasing THM bromine-substitution with TBM>DBCM>BDCM>TCM and were comparable to previous studies with the pure culture nitrifier, Nitrosomonas europaea. A decrease in temperature resulted in a decrease in both ammonia and THM degradation rates with ammonia rates affected to a greater extent than THM degradation rates. The significant effect of temperature indicates that seasonal variations in water temperature should be a consideration for technology implementation. Product toxicity, measured by transformation capacity (T(c)), was similar to that observed with N. europaea. Because both rate constants and product toxicities increase with increasing THM bromine-substitution, a water's THM speciation is an important consideration for process implementation during drinking water treatment. Even though a given water is kinetically favored, the resulting THM product toxicity may not allow stable treatment process performance.     

住宅给水系统中按户计收水费技术探讨

结合住宅给水系统中按户计收水费技术，分析了旧住宅给水系统在运行中的弊端，从而提出改进管道系统设计，在一户一表、水表出户、卡式水表、远程抄表等方面提出按户计收水费的技术措施。     

典型岩石和土的Skempton系数特征

在理论分析和试验研究基础上,主要探讨了具有典型代表性的岩石和土(砂岩、粘土、重塑土)在饱和非排水状态下、在不同围压下和不同加载率下Skempton系数的变化规律以及发生这种规律的基本原因。提出了对结构性较强的孔隙介质,必须加以考虑水的压缩性的基本观点,这种研究对三峡库区岩体和土体的力学特性和坝基及堤防施工具有重要的指导意义。     

Effects of the nuisance algae, Cladophora, on Escherichia coli at recreational beaches in Wisconsin

Recreational beaches constitute a large part of the 12 billion dollar per year tourism industry in Wisconsin. Beach closures due to microbial contamination are costly in terms of lost tourism revenue and adverse publicity for an area. Escherichia coli (E. coli), is used as an indicator of microbial contamination, as high concentrations of this organism should indicate a recent fecal contamination event that may contain other, more pathogenic, bacteria. An additional problem at many beaches in the state is the nuisance algae, Cladophora. It has been hypothesized that mats of Cladophora may harbor high concentrations of E. coli. Three beaches in Door County, WI were selected for study, based on tourist activity and amounts of algae present. Concentrations of E. coli were higher within Cladophora mats than in surrounding water. Beaches displayed an E. coli concentration gradient in water extending away from the Cladophora mats, although this was not statistically significant. Likewise, the amount of Cladophora observed on a beach did not correlate with E. coli concentrations found in routine beach monitoring samples. More work is needed to determine the impact of mats of Cladophora on beach water quality, as well as likely sources of E. coli found within the mats.     

A comparative study of different control strategies for indoor air humidity

There has been a rising concern in controlling the high indoor humidity of hot and humid countries. When an air-conditioned space experiences only part of its design heat load, its humidity tends to rise as a result of the air-conditioning system trying to control the indoor temperature by reducing its cooling capacity. In this study, the part-load dehumidification performances of three temperature control strategies are compared, namely, chilled water flow control, bypass air control and the variable air volume control. Coil simulations are employed to study the part-load performance of these control strategies. The coil model has been validated with experimental data to within ±6.5%. The relative humidity of a space depends of factors such as design sensible heat factor of the space, temperature control strategy employed and load condition experienced by the space. Simulation results have indicated that chilled water control strategy results in the highest indoor humidity throughout the range of conditions studied while variable air volume system provides highly effective dehumidification performance of the cooling coil. Bypass air control appears to be a good option for adoption as it is able to provide an acceptable humidity over a wide range of load conditions without having to affect the air movement within the space.     

提升给排水科学与工程专业水力学课程教学质量的探索

水力学是土建、水利类学科专业必修课程,也是本科教育阶段给排水科学与工程的核心专业基础课。课程的教学效果对本科生后期学习涉及水力学相关知识的专业课程至关重要。文章针对提升给排水科学与工程专业水力学课程教学质量进行探索性研究。研究认为采用多元教学模式,例如自主互动、"粉笔+黑板"板书教学与视频动画等多媒体相结合的形式,是一种理想的教学模式,其将启发式和讲授式教学相融合,努力提高学生的动手实践能力,积极引导本科生自主创新。这种教学模式可以充分调动学生学习积极性,促使教学质量得到提升,最终取得良好的教学效果。     

水井抽水过程消耗的功和能

本文试图从功和能的角度分析抽水井的能量转化。抽水过程是通过抽水设备输入一定能量，克服井管内外的摩阻，把水由地下提升到地表的作功过程。抽水设备输入的有用功是决定水井出水量分配和产生能量转化，即引起水头下降的根本原因。按能量守恒定律，抽水设备输出的有用功，一部分消耗于井管内的阻力损失；另一部分传递到井底推动地下水向井汇流。