Concurrent monitoring of vessels and water turbidity enhances the strength of evidence in remotely sensed dredging impact assessment

Remotely sensed assessment of dredging impacts on water turbidity is straightforward when turbidity plumes show up in clear water. However, it is more complicated in turbid waters as the spatial or temporal changes in turbidity might be of natural origin. The plausibility of attributing turbidity patterns to dredging activities would be greatly enhanced when demonstrating association between dredging infrastructure and water turbidity. This study investigated the possibility to strengthen the inference of dredging impact while simultaneously monitoring vessels and water turbidity in the northern Poyang Lake, China, where dredging was first introduced in 2001 and rapidly extended onwards. Time-series of Landsat TM and MODIS images of 2000-2005 were used to estimate the distribution and number of vessels as well as water turbidity. MODIS images revealed a significant increase in water turbidity from 2001 onwards. Landsat TM image analysis indicated a simultaneous increase in the number of vessels. Regression analysis further showed a highly significant positive relationship (R2=0.92) between water turbidity and vessel number. Visual interpretation of ship locations led to the conclusion that clear upstream waters developed turbidity plumes while passing the first cluster of vessels. We concluded that dredging caused the increase in water turbidity, and simultaneously monitoring the water turbidity and vessels enhanced the strength of evidence in remotely sensed dredging impact assessment.     

纳米SiO2的分散表征及其强化混凝低温低浊水研究

采用原子力显微镜、激光粒度仪对超声分散纳米SiO2的粒径分布、微观形状等进行了表征，并使用该纳米分散液对低温、低浊水进行了强化混凝研究。结果表明：纳米SiO2可均匀、稳定地分散在水溶液中，平均粒径为30nm，形状呈球形，在pH值为3～12时其表面带负电；将其用于强化混凝处理低温、低浊水时可以显著降低出水浊度，提高所形成矾花的密实程度，同时改善矾花的沉降性能。     

Detecting chlorophyll, Secchi disk depth and surface temperature in a sub-alpine lake using Landsat imagery

Some bio-physical parameters, such as chlorophyll a concentration, Secchi disk depth and water surface temperature were mapped in the sub-alpine Lake Iseo (Italy) using Landsat Thematic Mapper (TM) data acquired on the 7 March 1997. In order to adequately investigate the water-leaving radiance, TM data were atmospherically corrected using a partially image-based method, and the atmospheric transmittance was measured in synchrony with the satellite passage. An empirical approach of relating atmospherically corrected TM spectral reflectance values to in situ measurements, collected during the satellite data acquisition, was used. The models developed were used to map the chlorophyll concentration and Secchi disk depth throughout the lake. Both models gave high determination coefficients (R2 = 0.99 for chlorophyll and R2 = 0.85 for the Secchi disk) and the spatial distribution of chlorophyll concentration and Secchi disk depth was mapped with contour intervals of 1 mg/m3 and 1 m, respectively. A scene-independent procedure was used to derive the surface temperature of the lake from the TM data with a root mean square error of 0.3 degrees C.     

低温低浊水混凝实验研究

针对石墩子山水厂低温低浊（每年11月份至第二年4月份）的特点,对乌拉泊水库原水和乌拉泊水库原水与滤池反冲洗排水在配水井内的混合水进行混凝实验,实验表明：对于低温低浊水,PAC的最佳投加量为12mg/L,以PAM为助凝剂,除浊效果较好;PAM的投加时间对絮凝效果有较大的影响。     

Biological and chemical factors influencing shallow lake eutrophication: a long-term study

The focus of eutrophication research has tended to be upon short-term and experimental studies. However, given the range of factors that can influence eutrophication dynamics, and that these matter over a range of time scales, some discrete, some continuous, eutrophication dynamics may only be fully investigated when long-term, time-series data are available. The present study aims to evaluate the interacting effects of abiotic processes and biotic dynamics in explaining variations of phytoplankton biomass in a eutrophic shallow lake, Barton Broad (Norfolk, UK) using a long-term data set. Multivariate statistical analysis shows that the inter-relationships between phytoplankton variability, nutrient and grazing factors were highly sensitive to seasonal periodicity. In spring phytoplankton biomass was related to phosphorus, nitrogen and silicon. In summer phytoplankton biomass was associated with phosphorus, nitrogen and zooplankton. In autumn phytoplankton was related to phosphorus, nitrogen, silicon and zooplankton. In winter, no significant relationship could be established between phytoplankton and environmental variables. This paper improves our understanding of the governing role of nitrogen, phosphorus, silicon and zooplankton upon phytoplankton variability, and hence, improves management methods for eutrophic lakes.     

Coupled thermo-mechanical constitutive damage model for sandstone

Underground rock dynamic disasters are becoming more severe due to the increasing depth of human operations underground. Underground temperature and pressure conditions contribute significantly to these disasters. Therefore, it is important to understand the coupled thermo-mechanical (TM) behaviour of rocks for the long-term safety and maintenance of underground tunnelling and mining. Moreover, investigation of the damage, strength and failure characteristics of rocks under triaxial stress conditions is important to avoid underground rock disasters. In this study, based on Weibull distribution and Lemaitre’s strain equivalent principle, a statistical coupled TM constitutive model for sandstone was established under high temperature and pressure conditions. The triaxial test results of sandstone under different temperature and pressure conditions were used to validate the model. The proposed model was in good agreement with the experimental results up to 600 °C. The total TM damage was decreased with increasing temperature, while it was increased with increasing confining pressure. The model’s parameters can be calculated using conventional laboratory test results.     

Method for quantitative analysis of flocculation performance

The sedimentation rate and the post-sedimentation residual turbidity of flocculated suspensions are properties central to the design and operation of unit processes following flocculation in a water treatment plant. A method for comparing flocculation performance based on these two properties is described. The flocculation residual turbidity analyzer (FReTA) records the turbidity of flocculent suspensions undergoing quiescent settling. The fixed distance across which flocs must travel to clear the measurement volume allows sedimentation velocity distributions of the flocculent suspension to be calculated from the raw turbidity data. By fitting the transformed turbidity data with a modified gamma distribution, the mean and variance of sedimentation velocity can be obtained along with the residual turbidity after a period of settling. This new analysis method can be used to quantitatively compare how differences in flocculator operating conditions affect the sedimentation velocity distribution of flocs as well as the post-sedimentation residual turbidity.     

基于三维形貌参数的偶合节理峰值抗剪强度公式

 节理表面形貌是影响节理峰值抗剪强度的重要因素,采用人工模拟材料节理分别在0.5,1.0,1.5,2.0,3.0 MPa的法向应力下进行直剪试验,研究三维形貌参数与峰值抗剪强度之间的关系。选用节理面有效三维平均倾角 、粗糙度系数 、最大可能接触面积比 作为表征节理面粗糙度的参数。直剪试验前、后采用TJXW–3D型便携式岩石表面形貌测量仪对节理表面进行形貌数据测试;根据直剪试验结果建立节理峰值剪胀角与三维形貌参数 , , 之间的关系;建议采用新的强度准则计算节理的峰值抗剪强度。新公式的计算结果与试验值具有较好的一致性,并将其与Barton公式的计算结果进行比较,可知Barton公式的计算结果低于试验实测值。     

Mapping of the water quality of Lake Erken, Sweden, from imaging spectrometry and Landsat Thematic Mapper

Hyperspectral data have been collected by the Compact Airborne Spectrographic Imager (CASI) and multispectral data by the Landsat Thematic Mapper (TM) instrument for the purpose of mapping lake water quality. Field campaigns have been performed on Lake Erken in Sweden during the summer of 1997. Water samples have been collected and analysed in laboratory. Continuously measured variables from a boat have added a spatial dimension to the ground truth dataset. The data have been used to construct algorithms, based on remotely sensed data, for the retrieval of water quality parameters. The correlation between the continuous data and the collected CASI data has been investigated. Algorithms using both the point sampling results and the continuous data have been developed. Maps based on data from each instrument, showing the distribution of chlorophyll, are presented. Problems of having few water sampling stations, and the potential of using sub-water optics models are addressed as well. Tests were performed on MERIS bands and found useful for mapping chlorophyll and turbidity, and algorithms have been suggested for future use with MERIS.     

Removal of perfluorooctanoate from surface water by polyaluminium chloride coagulation

Perfluorooctanoate (PFOA) has been detected in surface water all over the world, and little is known of its removal by coagulation in water treatment plants. In this study, polyaluminium chloride (PACl) was used to remove PFOA from surface water, and the effects of coagulant dose, solution pH, temperature, and initial turbidity on the removal of both PFOA and suspended solids (SS) from water were investigated. Since the SS had high sorption affinity for PFOA, most PFOA was adsorbed on the particles and removed via the SS removal in the coagulation process. PFOA concentrations in aqueous phase decreased with increasing initial turbidity and PACl dose, while they increased with increasing solution pH and temperature. Other perfluorinated compounds (PFCs) with different C-F chain lengths and functional groups were also compared with PFOA. It was proved that hydrophobic interaction played an important role in the adsorption of PFOA on the SS. The addition of powdered activated carbon (PAC) before the coagulation process significantly enhanced the removal efficiency of PFOA in water, and the residual PFOA concentrations in water were less than 1 μg/L after the addition of 1-16 mg/L PAC and subsequent coagulation when the initial PFOA concentrations were in the range of 0.5-3 mg/L.     

输配水系统中颗粒物与浊度演变特征研究

通过将颗粒物计数方法应用于城市输配水系统,研究分析了输配水系统中颗粒物数量与浊度的相关性以及其沿线变化规律.结果表明,随着水流方向,颗粒物数量有上升趋势;管网末梢颗粒物数量和浊度偏高;颗粒粒径越小,其含量越多;在一定范围内颗粒物数量和浊度有一定相关性;对颗粒物的研究比浊度更加准确和直观.此外,从颗粒物角度对水质进行特征分析,不仅为水质评价提供更多信息,还为颗粒物计数法的应用提供基础数据.     

基于Barton剪胀模型的粗糙节理渗流分析

 为研究粗糙节理在剪切过程中的渗流规律,首先,采用Barton剪胀模型分析节理在剪切过程中的剪胀效应,计算节理在不同剪切位移下的剪胀位移,采用Brown-Scholz(B-S)理论模型分析法向应力作用下的节理闭合变形;通过初始隙宽、法向闭合变形和剪胀位移建立剪切过程中的节理隙宽与法向应力和剪切位移之间的关系,在此基础上得到剪切过程中的节理渗流计算公式;然后,在对节理试件进行渗流试验的基础上,分别采用基于Barton剪胀模型的节理渗流计算公式和Barton经验公式计算通过节理试件的理论渗流流量,并将预测结果与实测值进行比较,比较结果表明,基于Barton剪胀模型的节理渗流计算公式的预测结果与实测值较为一致,而Barton经验公式预测值与实测值偏差较大,从而验证了该公式在计算节理剪切过程中的渗流情况的正确性。     

Enhanced electrocoagulation–electroflotation for turbidity removal by Opuntia ficus indica cladode mucilage

The optimisation of the electrocoagulation‐electroflotation (EC‐EF) process assisted by the mucilage of the Opuntia ficus indica (OFI), on the turbidity removal was performed through the response surface methodology (RSM). For a solution of 300 mg/L of silica gel, high turbidity removal (93.14% ± 1.31) was obtained under the optimal conditions of 2.5 mg/L, 21.2 V, 9.65 and 2.61 mS/cm for the mucilage concentration, voltage, pH and conductivity, respectively, this experimental value was close to the predicted value of 92.96% ± 0.3. OFI mucilage increases turbidity removal efficiency and reduces specific energy consumption at a fixed current density. The turbidity removal of the EC‐EF process was improved by 30.94% compared with the conventional EC–EF (EC–EF without OFI mucilage) which shows 62.02% ± 1.45 of turbidity removal.     

Occurrence of nitrifying bacteria and nitrification in Finnish drinking water distribution systems

Microbiological nitrification process may lead to chemical, microbiological and technical problems in drinking water distribution systems. Nitrification activity is regulated by several physical, and chemical, and operational factors. However, the factors affecting nitrification in the distribution systems in boreal region, having its specific environmental characteristics, are poorly known. We studied the occurrence and activity of nitrifying bacteria in 15 drinking water networks distributing water with very different origin and treatment practices. The waters included chloraminated surface water, chlorinated surface water, and non-disinfected groundwater. The networks were located in eight towns in different parts of Finland. Our results showed that nitrifying bacteria are common in boreal drinking water distribution systems despite their low temperature. Surprisingly high numbers and activities of nitrifiers were detected in pipeline sediment samples. The numbers of ammonia-oxidizing bacteria and their oxidation potentials were highest in chloraminated drinking water delivering networks, whereas the nitrite-oxidizing bacteria were present in the greatest numbers in those networks that used non-disinfected groundwater. The occurrence of nitrifying bacteria in drinking water samples correlated positively with the numbers of heterotrophic bacteria and turbidity, and negatively with the content of total chlorine. Although nitrifying bacteria grew well in drinking water distribution systems, the problems with nitrite accumulation are rare in Finland.     

呼延水厂低温低浊水的絮凝试验研究

针对太原市呼延水厂出水浊度不达标的问题进行了絮凝试验研究.结果表明:该厂原水属低温低浊水,有机胶体较多,絮凝效果差,其根本原因是絮凝剂投量不足.进一步的试验表明:以聚合氯化铝(PAC)为絮凝剂、以活化硅酸为助凝剂,除浊效果较好;活化硅酸的投加时间对絮凝效果有较大的影响,以快速混合用时1min、聚合氯化铝投量为15 mg/L、延迟30 s后投加0.5～1mg/L的活化硅酸(以SiO2,计)为最佳运行条件;滤池反冲洗排水回流至配水井有利于低温低浊水的处理,并可节省絮凝剂或助凝剂的投量.     

浮沉池工艺在给水处理中的应用研究

介绍了浮沉池工艺的产生、适应的原水条件,以及影响浮沉池工艺运行的因素。浮沉池工艺适应于低温低浊水和高藻水的处理,并能很好地应对突发的高浊度。水温、浊度、混凝条件、溶气系统、水力负荷、斜管（板）装置、排渣排泥系统都会影响浮沉池的运行。     

低温低浊水处理工艺研究

针对低温低浊水质难于处理的原因进行分析,对国内外常用低温低浊水处理技术如生物法、微絮凝过滤、气浮、强化混凝等工艺进行简要分析、评价,并提出强化混凝处理低温低浊水的优势,指出该处理工艺具有良好的应用前景。     

高放废物处置库花岗岩热–力耦合模拟研究

 根据典型高放废物处置库概念模型,应用FLAC3D有限差分程序模拟计算了数百年内热–力耦合(TM)条件下高放废物地质处置库围岩的温度场、应力场和变形场的变化特征,初步得到在一定废物罐热源强度及衰变函数条件下花岗岩体的热力学特征及处置巷道工程设计的合理间距。模拟结果表明：在－500 m水平建造处置库,按设定的释热强度,处置坑合理间距为8～12 m,废物罐表面温度为130 ℃,处置坑中线岩体最高温度为40 ℃,并保持数百年左右。     

聚合氯化铝铁对低温低浊海水混凝效果的影响

采用聚合氯化铝铁(PAFC)对低温低浊海水进行混凝烧杯试验。结果表明,在海水水温低于10℃、浊度低于50 NTU时,PAFC的最佳投药量为15 mg/L,此条件下浊度、CODMn及UV254的去除率分别达到91.57%,54.47%和32.56%。通过试验比较了PAFC和聚合氯化铝(PAC)对低温低浊海水的混凝效果,得出PAFC的混凝效果优于PAC。     

The impact of rainstorm events on coagulation and clarifier performance in potable water treatment

This paper examines turbidity removal at a water treatment works in England that receives raw water which is difficult to treat during certain rainstorm events. Rainstorm events lead to elevated levels of turbidity and organic matter found in river waters. A robustness index based on settled turbidity was used to identify periods and events that adversely affected the treatment process. This coupled with raw water sampling data indicated that a change in nature and an increase in natural organic matter (NOM) concentrations occurred following rainstorm events. Experimental work investigated the effect of temperature and NOM on the coagulation process and the results show how increasing levels of NOM significantly impaired the coagulation of particulate material, leading to an increase in settled turbidity.