Microbiology, chemistry and biofilm development in a pilot drinking water distribution system with copper and plastic pipes

We studied the changes in water quality and formation of biofilms occurring in a pilot-scale water distribution system with two generally used pipe materials: copper and plastic (polyethylene, PE). The formation of biofilms with time was analysed as the number of total bacteria, heterotrophic plate counts and the concentration of ATP in biofilms. At the end of the experiment (after 308 days), microbial community structure, viable biomass and gram-negative bacterial biomass were analysed via lipid biomarkers (phospholipid fatty acids and lipopolysaccharide 3-hydroxy fatty acids), and the numbers of virus-like particles and total bacteria were enumerated by SYBR Green I staining. The formation of biofilm was slower in copper pipes than in the PE pipes, but after 200 days there was no difference in microbial numbers between the pipe materials. Copper ion led to lower microbial numbers in water during the first 200 days, but thereafter there were no differences between the two pipe materials. The number of virus-like particles was lower in biofilms and in outlet water from the copper pipes than PE pipes. Pipe material influenced also the microbial and gram-negative bacterial community structure in biofilms and water.     

The effects of changing water flow velocity on the formation of biofilms and water quality in pilot distribution system consisting of copper or polyethylene pipes

We studied the effects of flow velocity on the formation of biofilms and the concentration of bacteria in water in copper and plastic (polyethylene, PE) pipes. The formation of biofilms increased with the flow velocity of water. The increase in microbial numbers and contents of ATP was clearer in the PE pipes than in the copper pipes. This was also seen as increased consumption of microbial nutrients in the pipeline system. This indicates that the mass transfer of nutrients is in major role in the growth of biofilms. However, the increased biomass of biofilms did not affect microbial numbers in the water. Rapid changes in water flow rate resuspended biofilms and sediments which increased the concentrations of bacteria and copper in water. The disturbance caused by the changing water flow was also seen as an increase in the particle counts and water turbidity recorded with online instrumentation.     

Volatile organic compounds in natural biofilm in polyethylene pipes supplied with lake water and treated water from the distribution network

The objective of this work was investigation of volatile organic compounds (VOC) in natural biofilm inside polyethylene (HDPE) pipelines at continuously flowing water. VOC in biofilm may contribute to off-flavour episodes in drinking water. The pipelines were supplied with raw lake water and treated water from the distribution network. Biofilm was established at test sites located at two different drinking water distribution networks and their raw water sources. A whole range of volatile compounds were identified in the biofilm, including compounds frequently associated with cyanobacteria and algae, such as ectocarpene, dictyopterene A and C', geosmin, beta-ionone and 6-methyl-5-hepten-2-one. In addition, volatile amines, dimethyldisulphide and 2-nonanone, presumably originating from microorganisms growing in the biofilm, were identified. C8-compounds such as 1-octen-3-one and 3-octanone were believed to be products from microfungi in the biofilm. Degradation products from antioxidants such as Irgafos 168, Irganox 1010 and Irganox 1076 used in HDPE pipes, corresponding to 2,4-di-tert-butylphenol and 2,6-di-tert-butylbenzoquinone, were present in the biofilm.     

Effects of disinfectant and biofilm on the corrosion of cast iron pipes in a reclaimed water distribution system

The effects of disinfection and biofilm on the corrosion of cast iron pipe in a model reclaimed water distribution system were studied using annular reactors (ARs). The corrosion scales formed under different conditions were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM), while the bacterial characteristics of biofilm on the surface were determined using several molecular methods. The corrosion scales from the ARs with chlorine included predominantly α-FeOOH and Fe₂O₃, while CaPO₃(OH)·2H₂O and α-FeOOH were the predominant phases after chloramines replaced chlorine. Studies of the consumption of chlorine and iron release indicated that the formation of dense oxide layers and biofilm inhibited iron corrosion, causing stable lower chlorine decay. It was verified that iron-oxidizing bacteria (IOB) such as Sediminibacterium sp., and iron-reducing bacteria (IRB) such as Shewanella sp., synergistically interacted with the corrosion product to prevent further corrosion. For the ARs without disinfection, α-FeOOH was the predominant phase at the primary stage, while CaCO₃ and α-FeOOH were predominant with increasing time. The mixed corrosion-inducing bacteria, including the IRB Shewanella sp., the IOB Sediminibacterium sp., and the sulfur-oxidizing bacteria (SOB) Limnobacter thioxidans strain, promoted iron corrosion by synergistic interactions in the primary period, while anaerobic IRB became the predominant corrosion bacteria, preventing further corrosion via the formation of protective layers.     

Biofilm responses to ageing and to a high phosphate load in a bench-scale drinking water system

The effects of ageing and of phosphate load on drinking water biofilms developed on a polycarbonate substratum in the pseudo-equilibrium state have been evaluated. Phosphate was added in an amount higher than the stochiometric nutrient requirements of bacteria, at concentrations commonly applied in a drinking water distribution system for corrosion control. Multiple parameters were monitored: heterotrophic plate counts (HPCs), total direct counts (TDCs) and potential exoproteolytic activity (PEPA) in order to characterise changes in bacterial biofilms. The total carbohydrate, amino acid and phosphate contents of biofilms were analysed to characterise and monitor the biochemical composition of the biofilm.The three enumeration methods showed that a pseudo-equilibrium state was reached after 7 weeks of colonisation after which, the bacterial growth rate in the biofilm was 0.1 log per week on average. Bulk phosphate addition doubled the phosphate in the biofilm, but did not affect the other biological, physiological or chemical parameters measured.Polysaccharides increased in the biofilm with ageing and the dynamics of individual carbohydrate synthesis also varied with the age of the biofilm. Once pseudo-equilibrium, it was found that the total proteins were globally constant, whereas the spectra of some individual amino acids of the proteins had significantly changed.     

Persistence and decontamination of surrogate radioisotopes in a model drinking water distribution system

Contamination of a model drinking water system with surrogate radioisotopes was examined with respect to persistence on and decontamination of infrastructure surfaces. Cesium and cobalt chloride salts were used as surrogates for cesium-137 and cobalt-60. Studies were conducted in biofilm annular reactors containing heavily corroded iron surfaces formed under shear and constantly submerged in drinking water. Cesium was not detected on the corroded iron surface after equilibration with 10 and 100 mg L⁻¹ solutions of cesium chloride, but cobalt was detected on corroded iron coupons at both initial concentrations. The amount of adhered cobalt decreased over the next six weeks, but was still present when monitoring stopped. X-ray absorption near-edge spectroscopy (XANES) showed that adhered cobalt was in the III oxidation state. The adsorbed cobalt was strongly resistant to decontamination by various physicochemical methods. Simulated flushing, use of free chlorine and dilute ammonia were found to be ineffective whereas use of aggressive methods like 14.5 M ammonia and 0.36 M sulfuric acid removed 37 and 92% of the sorbed cobalt, respectively.     

Association and decontamination of Bacillus spores in a simulated drinking water system

The objective of this work was to elucidate the disinfectant susceptibility of Bacillus anthracis Sterne (BA) and a commercial preparation of Bacillus thuringiensis (BT) spores associated with a simulated drinking water system. Biofilms composed of indigenous water system bacteria were accumulated on copper and polyvinyl chloride (PVC) pipe material surfaces in a low-flow pipe loop and uniformly mixed tank reactor (CDC biofilm reactor). Application of a distributed shear during spore contact resulted in approximately a 1.0 and 1.6 log₁₀ increase in the number of spores associated with copper and PVC surfaces, respectively. Decontamination of spores in both free suspension and after association with biofilm-conditioned pipe materials was attempted using free chlorine and monochloramine. Associated spores required 5- to 10-fold higher disinfectant concentrations to observe the same reduction of viable spores as in suspension. High disinfectant concentrations (103 mg/L free chlorine and 49 mg/L monochloramine) yielded less than a 2-log₁₀ reduction in viable associated spores after 60 min. Spores associated with biofilms on copper surfaces consistently yielded higher Ct values than PVC.     

Effects of temperature and biodegradable organic matter on control of biofilms by free chlorine in a model drinking water distribution system

This study used annular reactors (AR) to investigate, under controlled laboratory conditions, the effects of temperature and biodegradable organic matter (BOM) on the free chlorine residual needed to control biofilm accumulation, as measured by heterotrophic plate count (HPC) bacteria. Biofilm was grown on PVC coupons, initially in the absence of chlorine, at 6, 12, and 18 degrees C, in the presence and absence of a BOM supplement (250 microg C/L) added as acetate. During the early stages of chlorine addition, when no measurable free chlorine residual was present, a reduction in biofilm HPC numbers was observed. Subsequently, once sufficient chlorine was added to establish a residual, the biofilm HPC numbers expressed as log CFU/cm2 fell exponentially with the increase in free chlorine residual. Temperature appeared to have an important effect on both the chlorine demand of the system and the free chlorine residual required to control the biofilm HPC numbers to the detection limit (3.2 Log CFU/cm2). For the water supplemented with BOM, a strong linear correlation was found between the temperature and the free chlorine residual required to control the biofilm. At 6 degrees C, the presence of a BOM supplement appeared to substantially increase the level of free chlorine residual required to control the biofilm. The results of these laboratory experiments provide qualitative indications of effects that could be expected in full-scale systems, rather than to make quantitative predictions.     

人工挖孔桩与钢管桩在流砂地层中的结合应用

结合工程概况及其地层概况，提出了采用人工挖孔桩与钢管桩相结合的施工方案，并对其基础设计、桩基检测结果、施工顺序及技术要点进行了阐述，实践证明，该施工方案既缩短了工期，又降低了造价成本，并使整个工程的降差得到了较好的控制，效果良好，值得推广。     

长距离高扬程多起伏输水系统水锤防护措施探讨

由于地形地质条件限制,长距离高扬程多起伏输水管道易发生水锤事故,水锤防护较难.针对上述问题,本文介绍了长距离高扬程多起伏输水系统的水锤防护措施及箱式双向调压塔的工作原理,并结合具体工程案例,通过计算机软件分析了有压管道在非正常关闭时的水锤压力波动,比较了多种设备组合使用的水锤防护效果.实践证明,运用箱式双向调压塔对保护输水管道有着重要作用.     

冷轧钢厂冷水系统设矿施工及运行管理

本文简要介绍某轧钢厂工艺用冷水、空调用冷水系统的设计。在理论分析及常规调试的基础上,结合现场实际情况对冷水系统进行全面分析。针对施工及运行管理中发现的问题,寻求解决措施。     

独立别墅热水供暖系统动态模型、控制策略及能耗分析

建立了独立别墅供暖系统的非线性动态模型并分析了其动态特性,介绍了模型降阶方法及PI控制器参数的设计和整定。针对可能的供暖系统控制策略进行了动态仿真和能耗分析。仿真结果表明,单纯采用室外气候补偿控制模式并不能获得理想的控制效果;采用分室控制模式能满足室内舒适性要求并有一定的节能效果,节能率约为25%。     

Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10-30, 3-10, 1-3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.     

Model experiments with CaO,MgO and calcinated dolomite for fluoride removal in a wet scrubbing system with sea water in recirculation

Fluoride removal was studied from saline waters using CaO, MgO and calcined natural dolomite (all fired at 1273 K), as an alternative for lime slurry neutralization process. Fluoride in the form of HF was added to sea water, saline groundwater or distilled water from 50 to 158 mg dm^?3. The amount of added CaO, MgO and CaO·MgO varied from 80 to 560 mg dm^?3. Concentrations of soluble fluoride, calcium, magnesium and pH were determined in supernatant. X-ray diffraction was used to identify the precipitated solids. All three processes show very good removal of fluoride from saline water, within 90 min designed for technological process (soluble fluoride varied from 5 to 25 mg dm^?3). It can be assumed that fluoride is either present in the form of an amorphous salt or is incorporated into the crystal lattice of one of the identified solids (CaCO₃, CaCO₃·H₂O, Mg(OH)₂, Mg₂SiO₄).     

空调大温差研究（5）：空调冷水大温差系统设计方法

就冷水机组、空调机组、水泵等的选择,介绍了空调冷水大温差系统的设计方法,指出空调冷水大温差系统与常规温差的空调系统有本质区别,应选用大温差专用空调机组,采用定露点设计法,水力计算宜采用优化设计,以使冷水大温差系统获得更佳的经济性。     

空调大温差研究（4）：空调冷水大温差系统经济分析

对空调冷水大温差系统的经济性进行了分析。结果表明：当冷水机组冷水初温等于或大于7℃时,10℃温差与5℃温差时冷水机组的能耗基本相同,而发器压降明显减小;冷水系统采用10℃温差较℃温差冷水量减少一半,水泵能减少,水系统一次投资减少;即使空调机组一次投资略有增加,空调水系统的一次投资可减少5％左右。空调水系统运行 费用减少30％左右。建议在应用空调大温差技术的同时使用大温差专用空调机组。