中山市长江水厂V型滤池的优化控制与管理经验

中山市长江水厂为了优化V型滤池的运行,对其过滤及反冲洗过程进行了监测,通过分析滤后水和反冲洗水的浊度变化,以及滤砂变化情况等,优化了滤池运行控制参数,包括合理控制滤速、反冲洗强度及时间、调整过滤周期、更换排气阀门等,保障了滤池的稳定运行及滤后水水质,并实现了节能降耗。     

活性炭滤柱反冲洗对有机物去除效果的影响

反冲洗方式是影响活性炭滤池正常运行的关键因素。以反冲洗废水浊度、浊污比、反冲洗前后活性炭滤柱上生物量和生物活性的变化为指标,分析反冲洗后活性炭滤柱去除有机物的效果,观察4种不同的反冲洗方式对活性炭滤柱运行效果的影响。试验结果表明:在活性炭滤柱试验中,以气冲强度8 L/(s·m~2)、水冲强度11 L/(s·m~2)、膨胀度10%、历时8 min的气水混合反冲效果最好,反冲洗后活性炭滤柱对有机物的去除率增长最多。     

中山市长江水厂V型滤池优化控制与日常管理

通过相关监测及检测方法分析V型滤池过滤、反冲洗运行工况,进行相关控制及参数调整,合理控制滤速、反冲洗强度及时间,保障滤池的稳定运行及滤后水水质,实现节能降耗。     

一种整体式反滤排水体在工程中的应用

针对公路边坡挡墙及水利工程中采用的反滤与排水材料经常出现的反滤布撕裂、空洞等等问题,提出了一整套反滤土工布选用的方法,即整体式反滤排水体,对其技术特点进行了简单介绍,并指出其具有反滤排水效果好、施工简单等等优点,值得推广应用。     

地下水中生物除锰的最佳运行条件及动力学

采用生物法能够大幅度提高对地下水中Mn2+的去除效率.试验滤柱启动后,通过改变曝气强度、滤速、反冲洗强度等,总结了生物除锰的最佳运行条件;并通过分层分析滤层水质的方法研究了生物法的铁锰氧化动力学规律.     

土工织物应用于新型压密注浆土钉的试验研究

针对乳胶膜式压密注浆土钉的潜在缺陷,提出了采用土工织物替代乳胶膜改进该土钉的新思路。首先,基于自研的土工织物反滤性能测定装置,开展了一系列水泥浆液反滤试验,研究了水灰比、浆液体积和注浆压力对土工织物反滤性能的影响,得到了注浆过程中上述影响因素影响下反滤时间和水灰比的变化规律。其次,对反滤前/后的砂土进行了贯入试验,评估了由于浆液中黏性物质入渗引起的周围土体强度提高。再次,对反滤前/后的水泥试块进行了单轴压缩试验,探明了节泡（水泥试块）强度显著提高的原因是土工织物反滤过程中节泡内水灰比的降低。最后,开展了土工织物和乳胶膜式压密注浆土钉的两组对比拉拔试验,验证了土工织物改进压密注浆土钉的优越性。研究成果能为压密注浆土钉的优化和应用奠定基础。     

铁碳内电解对生物反硝化脱氮的强化效能及机理

利用小试和中试研究了铁碳内电解工艺单元对深床滤柱生物反硝化作用的强化效能,在分析其作用机理的基础上,进行了长期的现场效能验证试验。结果表明,铁碳内电解可以有效强化深床滤柱利用二沉池出水中有机物进行生物反硝化的效能;铁碳内电解对水中有机物的分子质量、亲疏水性改变作用微弱,而其对有机物分子结构中部分基团的改变可能是导致其可利用性提升的重要原因。现场长期运行结果表明,组合工艺可显著提升二沉池出水水质,处理出水水质稳定达到一级A排放标准要求。     

水库坝体土工布反滤排水体的设计与施工

结合工程实例,探讨了水库坝体加固工程中无纺土工布反滤体的设计要点及施工技术。工程实践表明,无纺土工布反滤排水体贴坡导渗具有技术可靠、施工方便、节约投资等特点,可达到工程设计要求。     

反硝化生物滤池深度处理酸洗废水试验研究

以酸洗废水的二级出水为研究对象,考察了反硝化生物滤池的挂膜启动速度,研究了滤池的脱氮效果及其影响因素。结果表明:采用接种挂膜法,以驯化后的反硝化污泥为种泥,反硝化生物滤池13 d后便可稳定运行,此时对NO-3-N的去除率为97.87%,且无NO-2-N的积累;稳定运行期间,当进水p H值为6.5~7.5、温度为24~28℃、C/N值为4.0、HRT为20 min时,对TN、NO-3-N的去除率分别为87.70%和97.49%,出水NO-2-N为0.56 mg/L;分析反硝化生物滤池内不同氮素形态沿程分布发现,TN、NO-3-N浓度随滤层高度的增加而降低,NO-2-N浓度则呈现先上升后下降的趋势,0~600 mm滤层对TN、NO-3-N的去除贡献率最大,分别为97.46%和96.70%,因此确定最佳滤层高度为600 mm。     

加肋土工膜表面形态与界面剪切强度相关性研究

为了研究加肋土工膜表面形态对加肋土工膜与土工布界面剪切强度的影响,基于分形几何理论,采用立方体覆盖法得到不同加肋形式土工膜的表面分维数D。在原有直剪试验结果的基础上,对不同加肋土工膜分形维数D与界面剪切强度进行分析,经研究表明加肋土工膜与土工布界面抗剪强度随着分形维数D的增加而加强,因此可以运用分形维数来评测加肋土工膜与土工布的界面剪切强度。通过添加吻合度系数JMC以及经验系数η对JRC-JCS模型进行修正,代入加肋土工膜与土工布直剪试验结果中反算得加肋土工膜表面粗糙度系数JRC与分形维数D的定量关系,在此基础上得到加肋土工膜与土工布界面抗剪强度的经验估算关系式。最后,采用加肋土工膜与土工布界面剪切强度的经验估算关系式估算界面剪切强度,并将经验公式估算值和直剪试验实测值进行对比,结果表明:计算结果和试验结果吻合良好,所推导的计算公式计算精度和可靠性能满足工程估算的要求。     

Geotextile filtration opening size under tension and confinement

Nonwoven geotextiles have been used as filters in geotechnical and geoenvironmental works for half a century. They are easy to install and can be specified to meet the requirements for proper filter performance. There are situations where a geotextile filter may be subjected to tensile loads, which may alter relevant filter properties, such as its filtration opening size. Examples of such situations are silty fence applications, geotextile separators, geotextile tubes and geotextiles under embankments on soft soils. This paper investigates the effects of tensile strains on geotextile pore dimensions. A special equipment and testing technique allowed tests to be carried out on geotextile specimens subjected to tension and confinement. The results obtained showed that the variation in filtration opening size depends on the type of strain state the geotextile is subjected, under which the geotextile pore diameter may remain rather constant or increase significantly. However, confinement reduces the geotextile filtration opening size independent on the strain mobilised. An upper bound for the filtration opening size of strained nonwoven geotextiles is introduced and was satisfactory for the geotextile products tested.     

Comparison of the behaviour of various geotextiles used in the filtration of clayey sludge: An experimental study

This paper presents the results of an experimental study of various geotextiles used to filter clayey sludge. The use of geotextiles to filter clayey sludge or suspensions of fine particles in water is more complex than that for filtering suspensions of granular soils. In practice, such applications generally use flocculants to postpone the formation of a low-permeability filter cake. The objective of the present study, which does not use flocculants, is to determine how geotextile characteristics affect the capacity of the geotextile to filter clayey sludge. Three key questions are addressed: (1) What are the main differences between vertical and horizontal filtration? (2) How do geotextile characteristics (nature, opening size, permeability, etc.) affect its capacity to filter clayey sludge (3) How do clayey sludge characteristics (i.e., grain size distribution and concentration)? and the type of flow (i.e., constant head or constant flow) affect the filtering capacity of geotextiles? To evaluate the capacity of a geotextile to filter clayey sludge, we propose three relevant criteria and analyse two filtration phases induced by different cake-formation processes (controlled by the geotextile and controlled by the filter cake). To determine the main differences between vertical and horizontal filtration, the settling of fines in the testing device and its influence on the results are analysed and discussed. This study shows that, for the various clayey sludge tested, the geotextiles (needle-punched nonwoven and thermally bonded nonwoven) with the smallest opening sizes (O₉₀?≤?60?μm) give the most promising results for filtering fines without the use of flocculants. Of these geotextiles, the thermally bonded nonwoven structure seems to offer the best filtration performance for the largest range of fines concentration in the sludge.     

Strength enhancement of geotextile-reinforced carbonate sand

The mechanical behavior of carbonate sand reinforced with horizontal layers of geotextile is invetigated using a series of drained compression triaxial tests on unreinforced and reinforced samples. The main factors affecting the mechanical behavior such as the number of geotextile layers, their arrangement in specimens, confining pressure, particle size distribution, geotextile type and relative density of samples were examined and discussed in this research. To make a precise comparison between the behavior of reinforced siliceous and carbonate sand, triaxial tests were performed on both types of sands. Results indicate that geotextile inclusion increases the peak strength and strain at failure, and significantly reduces the post-peak strength loss of carbonate specimens. The amount of strength enhancement rises as the number of geotextile layers increases while two other parameters including confining pressure and particle size affect adversely. The strength enhancement of reinforced carbonate sand is greater than the corresponding siliceous sample at high axial strains. Reinforced and unreinforced carbonate specimens exhibit more contractive behavior than their corresponding siliceous samples and tend to dilate at higher axial strains. By increasing the relative density of the samples, the peak strength of reinforced specimens rises due to enhanced interlocking between geotextile layers and sand particles. This process continues as long as the geotextile is not ruptured. The utilization of geotextiles with high mass per unit areas was found to be uneconomical due to slight differences between the strength augmentation of geotextiles with high and low mass per unit areas. It should be noted that geotextile layers limit the lateral expansion of specimens which leads to changing the failure pattern from a shear plane to bulging between the adjacent layers of geotextile.     

Design of non-woven geotextiles for coal refuse filtration

This paper presents research findings on grain size distribution changes of coal refuse affecting the design of non-woven geotextiles used as filters in rock drains at coal waste impoundments. The research involved performing hydraulic conductivity tests on refuse - geotextile filters followed by grain size distribution tests. Data was evaluated for geotextile filter retention, permittivity, and clogging potential requirements as published by the U.S. Mine Safety and Health Administration’s Second Edition, “Engineering and Design Manual Coal Refuse Disposal Facilities”.Key findings indicate that refuse particles undergo slaking and aggregation which change the initial grain size distribution. Grading envelopes were developed and indicate that particle size zones influence the geotextile design parameters for retention, filtration, and clogging. The clogging criteria do not appear to be easily satisfied by the typical ranges of coarse coal refuse, at pre- and post-compaction grain size, for compatibility with non-woven geotextiles having an AOS = 0.212 mm.Conclusions impacting the specification and field installation of geotextiles include: i) post grain size distribution tests are suggested to be performed on specimens and at all compaction levels to observe changes in key indices of D₈₅ and D₁₅ for meeting retention and clogging criteria requirements; ii) the evaluation of the initial refuse stability indicate that at the low compaction energy conditions, which have mobile fines and high Cu values, are initially unstable with regards to their internal soil gradation; and iii) construction of geotextile wrapped drains is preferred to be made in pre-compacted refuse lifts. This condition is beneficial because the filter becomes more stable for retention and permeability; however clogging is still a concern.     

A study on biological clogging of nonwoven geotextiles under leachate flow

This paper presents results of long-term permittivity tests using leachate to evaluate biological clogging of nonwoven geotextiles. Three types of geotextiles with varying masses per unit area were used in the tests. The identification and quantification of microorganisms in the geotextile were carried out as well as microscopic investigations. The accuracies of semi-empirical models to evaluate the kinetics of bacteria growth and to correlate hydraulic properties and microbiological parameters were examined. Permittivity tests under increasing water heads were also performed on the geotextile samples already subjected to long-term leachate flow in order to evaluate the values of water heads required to wash the biofilms out of the geotextile pores. The results of the tests showed the marked reduction of geotextile permeability due to biological clogging and that the results of the predictions by semi-empirical methods were consistent with the biological mechanisms observed.     

Numerical parametric investigation of infiltration in one-dimensional sand–geotextile columns

Geotextiles are routinely used in separation and filtration applications. Design of these systems is currently based on saturated properties of the geotextiles and the surrounding soils. However, in the field, soil and geotextile can be in an unsaturated state for much of their design life during which they are essentially hydraulically non-conductive. Periodic wetting and drying cycles can result in rapid and large changes in hydraulic performance of soil–geotextile systems. The writers have reported the results from physical water infiltration tests on sand columns with and without a geotextile inclusion. The geotextile inclusions were installed in new and modified states to simulate the influence of clogging due to fines and to broaden the range of hydraulic properties of the geotextiles in the physical tests. This paper reports the results of numerical simulations that were undertaken to reproduce the physical tests and strategies adopted to adjust soil and geotextile properties from independent laboratory tests to improve the agreement between numerical and physical test results. For example the paper shows that the hydraulic conductivity function of the geotextile must be reduced by up to two orders of magnitude to give acceptable agreement. The lower hydraulic conductivity is believed to be due to soil intrusion that is not captured in conventional laboratory permeability tests. The calibrated numerical model is used to investigate the influence of geotextile and soil hydraulic conductivity and thickness as well as height of ponded water at the surface on wetting front advance below the geotextile and potential ponding of water above the geotextile due to a capillary break mechanism. A simple analytical model is also developed that predicts the maximum ponding height of water above the geotextile based on two-layer saturated media and 1-D steady state flow assumptions. The analytical model is used to generate a design chart to select geotextiles to minimize potential ponding of water above the geotextile. Ponding can lead to lateral flow of water along the geotextile in reinforced wall, slope, embankment and road base applications.     

Changes in filtration opening size of woven geotextiles subjected to tensile loads

A modified hydrodynamic sieving technique in which the geotextile is subjected to a tensile load is described. This load may be either uni-axial or bi-axial. To date tests have been conducted on two different woven slit-film polypropylene geotextiles and the results illustrate a marked change in the filtration opening size of the geotextiles as the tensile load is increased. The opening size of the thicker geotextile decreased with increasing biaxial load, whereas the opposite occurred for the thinner of the two geotextiles. The geotextiles were loaded up to only about 10% of their minimum ultimate tensile strength and the filtration opening size changed by up to 28%. It is suggested that this effect cannot be ignored in applications where there are in-plane tensile stresses.     

单向拉伸对土工织物反滤性能影响的试验研究

为研究单向拉伸对土工织物反滤性能的影响，选取两种条膜机织有纺织物和两种短纤针刺无纺织物，将不同拉应变下的织物与非连续级配土组成反滤系统，利用梯度比渗透仪测试系统反滤参数随拉应变的变化。根据反滤设计的透水、保土和防淤堵3个准则，分析拉应变对透水率、漏土量、梯度比等各参数的影响。试验结果表明：随着拉应变增加，有纺织物透水及防淤堵性能增强，保土性能减弱；无纺织物则相反，透水及防淤堵性能减弱，保土性能增强；同种土工织物厚度越大，拉应变对其反滤性能影响越大。     

Analysis of geotextile filter behaviour after 21 years in Valcros dam

In 1970, nonwoven geotextiles were used for the first time in an earth dam. The geotextile acted as a filter for the toe drain and on the upstream slope below the rip-rap. In 1992, samples were taken from both locations and performance tests were conducted in the laboratory. This paper presents the main results of the hydraulic behaviour of the geotextile filter in association with the soil of the dam. Also microscopic analyses are presented and, as the filter is considered to be performing well, selected filter criteria are checked.     

Interface shear strength between geosynthetic clay liner and covering soil on the embankment of an irrigation pond and stability evaluation of its widened sections

Geosynthetic clay liners (GCLs) are typically used for widening sections of an embankment. They are also used as low permeability liners to minimize water leakage from reservoirs such as irrigation ponds. However, few investigations have been carried out on the specific properties of GCLs, such as granulated bentonite sandwiched between geotextiles, their internal shear strength, and the shear strength at the interface between a GCL and an embankment body. In this study, a series of direct box shear tests were performed to determine the shear strength properties of bentonite and compacted soils as well as at the interface between a GCL and bentonite or compacted soil. In addition, a series of field-loading tests were conducted to investigate the failure behaviour of an embankment body containing a GCL when changes in the water content of the bentonite of the GCL in a real embankment occur. Furthermore, the stability of widened embankment bodies that incorporated GCLs were evaluated. The main conclusions of this study are as follows: (1) The shear strength of the interface between the covering soil and geotextiles varied according to the soil type, geotextile type, and the submergence period, (2) the maximum safety factor was observed at the interface between decomposed granite soil and the geotextiles, while the minimum safety factor was observed at the interface between the bentonite and the geotextiles, and (3) the influence of GCLs on the instability of a widened embankment was extremely small.