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1.
The physicochemical processes that affect acid mine drainage (AMD) in unsaturated waste rock piles and the capabilities of small-scale laboratory experiments to predict AMD from waste rock are not well understood. An integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated. This paper describes the design, construction and instrumentation of three field-scale experimental waste rock piles (test piles), and six active zone lysimeters at the Diavik diamond mine in the Northwest Territories, Canada. The test piles are comprised of granitic and sulfide-bearing metasedimentary waste rock excavated during open pit mining operations. One test pile contains waste rock with a target S content of <0.04 wt.% S; the second test pile contains waste rock with a target S content of >0.08 wt.% S; and the third test pile contains the higher sulfide waste rock (>0.08 wt.% S) and was re-sloped and capped with a low permeability till layer and a low sulfide waste rock cover. The first two test piles are approximately 15 m high with bases of 50 m by 60 m, and the re-sloped test pile has a larger base of 80 m by 125 m. Instrumentation was selected to measure matrix flow, geochemistry of pore water and drainage, gas-phase O2 concentration, temperature evolution, microbiological populations, waste rock permeability to air, and thermal conductivity, as well as to resolve mass and flow balances. Instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time. Instruments were installed at a density such that the number of instruments that survived construction (40% to >80% by instrument type) was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles. 相似文献
2.
Bioreactor landfills are operated for rapid stabilization of waste, increased landfill gas generation for cost-effective energy
recovery, gain in landfill space, enhanced leachate treatment, and reduced post closure maintenance period. The fundamental
process of waste stabilization in bioreactor landfill is recirculation of generated leachate back into the landfills. This
creates a favorable environment for rapid microbial decomposition of the biodegradable solid waste. In order to better estimate
the generated leachate and design of leachate recirculation system, clear understanding of the permeability of the Municipal
Solid Waste (MSW) with degradation and the factors influencing the permeability is necessary. The objective of the paper is
to determine the changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition. Four small-scale
bioreactor landfills were built in laboratory and samples were prepared to represent each phase of decomposition. Then, the
changes in hydraulic properties of MSW in bioreactor landfill with time and decomposition were determined. A series of constant
head permeability tests were performed on the samples generated in laboratory scale bioreactor landfills to determine variation
of permeability of MSW with degradation. The test results indicated that the permeability of MSW in bioreactor landfills decreases
with decomposition. Based on the test results, the permeability of MSW at the first phase of degradation was estimated as
0.0088 cm/s at density 700 kg/m3. However, with degradation, permeability decreased to 0.0013 cm/s at the same density, for MSW at Phase IV. 相似文献
3.
Demolition of old buildings to create space for new development resulted in the near surface soil (topsoil) to be mixed with particles derived mostly from concrete wastes. This condition could affect the infiltration capacity and surface runoff, therefore, storm-water management of the area. This paper presents results of study on the effect of concrete waste particles on the hydraulic properties and infiltration capacity of the topsoil. Laboratory tests were performed to compare the hydraulic properties of the topsoil and the mixture of topsoil and concrete particles. Laboratory infiltration column test was performed on the mixture to evaluate its infiltration capacity. Results from the laboratory tests indicated that the presence of particles from concrete waste decreased the water-holding capacity and permeability, thereby the infiltration capacity of the ground surface. The results were supported by numerical analysis performed using the same material and boundary conditions as the column test. Parametric study was performed on both the topsoil and the mixture to extend the results of infiltration test to different materials under different ranges of rainfall intensity. The parametric study showed that the presence of concrete particles increased the run-off and the effect increased as the rainfall intensity increased. Therefore, the increase in runoff coefficient should be considered for the storm-water management when the near surface soil is mixed with concrete waste. 相似文献
4.
5.
A field experiment is being carried out at the Diavik diamond mine in northern Canada to investigate the influence of unsaturated flow behavior on the quality of drainage from mine waste rock piles in a region of continuous permafrost. This paper is part of a series describing processes affecting the weathering of waste rock and transport of reaction products at this site; here the focus is on unsaturated water flow and its role in mass loading. Two 15 m-high instrumented test piles have been built on 60 m by 50 m collection systems, each consisting of lysimeters and a large impermeable high-density polyethylene (HDPE) liner. Collection lysimeters are installed nearby to investigate infiltration in the upper 2 m of the waste rock. Porosity, water retention curves, and hydraulic conductivity functions are estimated from field measurements and for samples ranging in size from 200 cm3 to 16 m3. Net infiltration in 2007 is estimated to have been 37% of the rainfall for mean annual rainfall conditions. Early-season infiltration freezes and is remobilized as the waste rock thaws. Wetting fronts migrate at rates of 0.2–0.4 m d−1 in response to common rainfall events and up to 5 m d−1 in response to intense rainfall. Pore water and non-reactive solutes travel at rates of <10−2 to 3 × 10−2 m d−1 in response to common rainfall events and up to 0.7 m d−1 in response to intense rainfall. Time-varying SO4 mass loading from the base of the test piles is dictated primarily by the flow behavior, rather than by changes in solute concentrations. 相似文献
6.
An approximate analytical solution for measuring air permeability of asphalt samples partially saturated with water 总被引：1，自引：1，他引：0
In coastal areas, abnormally high pressure may be caused by the tide-induced water table variation under extensive pavements,
particularly during rainfall. To simulate the rainfall infiltration effects on the air permeability of asphalt pavements in
coastal area, column-shaped asphalt sample was fixed in the upper part of a steel cylinder with its upper surface saturated
with ponding water (depth < 5 mm) and open to the atmosphere. The cylinder’s lower part formed an air chamber. The chamber
was pressurized and then the air therein was released naturally through the sample. The pressure variation with time in the
chamber was recorded for analysis. Based on the Green–Ampt piston model for the surface water infiltration, an approximate
analytical solution was derived to describe the pressure–time relationship in the chamber. A new parameter called the escape
pressure was introduced to describe the air pressure needed for the chamber air to break through the capillary pressure induced
by the ponding water. The analytical solution gave good estimations of both the escape pressures and the harmonic averages
of the permeabilities of the wet and dry parts of 14 samples in the sense that excellent fittings were obtained between the
observed and predicted air pressures in the air chamber. The estimated escape pressure ranges from 0.0 to 1.74 kPa. The harmonic
average of the permeabilities of the wet and dry parts is 5–94% of the dry sample’s permeability. 相似文献
7.
Liu Zhang-Rong Cui Yu-Jun Ye Wei-Min Chen Bao Wang Qiong Chen Yong-Gui 《Acta Geotechnica》2020,15(10):2865-2875
Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range (>?10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (<?10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion.
相似文献8.
节理岩体几何结构非常复杂,研究其渗流特性对于指导含水岩层稳定性分析具有重要价值。应用离散裂隙网络模型DFN方法,基于VC++6.0软件平台,建立了平面渗流分析方法,分析了节理岩体不同几何分布情况下的渗透率张量特征,通过定义渗流定向性系数对岩体渗流的定向性特征进行了定量分析。结果表明：单组节理岩体渗流具有明显的各向异性特征,渗流定向性随着节理角度变化显著;节理随着节理贯通性增加,节理渗透率呈现对数增加趋势;两组节理情况下,各向异性特征随着节理组间夹角变化;两组节理岩体渗流特征研究中,正交分布下,岩体仍存在各向异性,但渗流定向性系数较低;当节理倾角服从正态分布时,随着节理倾角标准差增大,渗透率增加;两组节理夹角不同时,节理渗透主方向倾角随着夹角增大而相应增大,基本沿两组节理夹角方向的角平分线方向。 相似文献
9.
Three large-scale instrumented waste rock piles were constructed at the Diavik Diamond Mine in the Northwest Territories, Canada. These experimental waste rock piles (test piles) are 15 m high and are part of an integrated field and laboratory research program to characterize and compare low-sulfide waste rock and drainage at various scales. During test pile construction, samples of the <50 mm fraction of waste rock were collected from two types of waste rock that are segregated during mining operations based on S content. The samples were analyzed for S content and particle size distribution. One test pile contained waste rock with an average of 0.035 wt.% S in the <50 mm fraction, within the operational S target of <0.04 wt.% S for the lower S waste rock type. The second test pile contained waste rock with an average of 0.053 wt.% S in the <50 mm fraction, lower than the operational S target of >0.08 wt.% S for the higher S waste rock type. The third test pile has a low permeability till layer and a low sulfide waste rock thermal layer covering a core of waste rock with average 0.082 wt.% S in the <50 mm fraction, which is within the operational S target of >0.08 wt.% S for the higher S waste rock. Particle size distributions for the lower and higher S waste rock are similar, but the higher S waste rock has a higher proportion of fine-grained particles. Sulfur determinations for discrete particle sizes of the <50 mm fraction illustrate higher S concentrations in smaller particles for both the lower S waste rock and the higher S waste rock. Similarly, S concentrations calculated for the >10 m scale, from composite blast hole cuttings, are lower than those calculated for the <50 mm scale. Acid–base accounting using standard methods and site-specific mineralogical information was used to calculate the ratio of neutralization potential to acid generating potential. A comparison of calculation approaches to pH and alkalinity data from humidity cell and test pile effluent suggest that ratios are very sensitive to the calculation method. The preferred calculation method was selected by comparing calculation results to pH and alkalinity data from humidity cell effluent collected over 95 weeks and test pile effluent collected over five field seasons. The preferred acid–base accounting values were obtained by calculating the average neutralization potential divided by the average acid potential of a sample set. This approach indicates that waste rock with >0.05 wt.% S is of uncertain acid-generating potential and effluent data indicate this waste rock generates acidic effluent; whereas lower S waste rock does not produce acidic effluent, consistent with the acid–base accounting predictions. 相似文献
10.
Modeling of damage,permeability changes and pressure responses during excavation of the TSX tunnel in granitic rock at URL,Canada 总被引：1，自引：0，他引：1
Jonny Rutqvist Lennart Börgesson Masakazu Chijimatsu Jan Hernelind Lanru Jing Akira Kobayashi Son Nguyen 《Environmental Geology》2009,57(6):1263-1274
This paper presents numerical modeling of excavation-induced damage,
permeability changes, and fluid-pressure responses during excavation of a test tunnel associated with the tunnel
sealing experiment (TSX) at the Underground Research Laboratory (URL) in Canada. Four
different numerical models were applied using a wide range of approaches to model damage
and permeability changes in the excavation disturbed zone (EDZ) around the tunnel.
Using in situ calibration of model parameters, the modeling could reproduce observed
spatial distribution of damage and permeability changes around the tunnel as a
combination of disturbance induced by stress redistribution around the tunnel
and by the drill-and-blast operation. The modeling showed that stress-induced
permeability increase above the tunnel is a result of micro and macrofracturing
under high deviatoric (shear) stress, whereas permeability increase alongside
the tunnel is a result of opening of existing microfractures under decreased mean
stress. The remaining observed fracturing and permeability changes around the periphery
of the tunnel were attributed to damage from the drill-and-blast operation. Moreover,
a reasonably good agreement was achieved between simulated and observed
excavation-induced pressure responses around the TSX tunnel for 1 year following its
excavation. The simulations showed that these pressure responses are caused by
poroelastic effects as a result of increasing or decreasing mean stress, with
corresponding contraction or expansion of the pore volume. The simulation results
for pressure evolution were consistent with previous studies, indicating that the
observed pressure responses could be captured in a Biot model using a relatively
low Biot-Willis’ coefficient, α ≈ 0.2,
a porosity of n ≈ 0.007, and a relatively
low permeability of k ≈ 2 × 10−22 m2,
which is consistent with the very tight, unfractured granite at the site. 相似文献
11.
垃圾填埋体不均匀沉降等容易引起压实黏土防渗层开裂,显著降低其防渗性能。将裂隙作为高渗透性的多孔介质材料,建立了含单一裂隙压实黏土层的饱和/非饱和渗流模型,数值研究了含裂隙黏土层中的优势渗流过程,对比分析了裂隙位置、深度、宽度和渗透系数对压实黏土层水分击穿时间和稳定渗漏量的影响。结果表明,含裂隙压实黏土层的渗流过程可分为3个阶段：初始阶段、击穿阶段和稳定阶段;底部裂隙对压实黏土层防渗性能的影响较小,而顶部裂隙和贯通裂隙的影响较大;水分击穿时间随裂隙深度增大而迅速缩短,为保证黏土层防渗性能,宜将裂隙深度控制在0.1倍土层厚度以内;水分击穿时间和稳定渗漏量随裂隙宽度、渗透系数的增大而分别缩短和增加,且当其达到一定值后逐渐趋于稳定;裂隙贯通后将显著降低压实黏土层的防渗性能,其稳定渗漏量随裂隙宽度和渗透系数的增大而呈线性增长。 相似文献
12.
Hema Siriwardane Igor Haljasmaa Robert McLendon Gino Irdi Yee Soong Grant Bromhal 《International Journal of Coal Geology》2009,77(1-2):109-118
The permeability of coal samples from Pittsburgh Seam was determined using carbon dioxide as the flowing fluid. The confining pressure was varied to cover a wide range of depths. The permeability was determined as a function of exposure time of carbon dioxide while the confining stress was kept constant. The porosities of the coal samples were found to be very low and most of the samples had porosities less than 1%. The permeability of these coal samples was very low—less than 1 μD. Since the objective of this study was to investigate the influence of CO2 exposure on coal permeability, it was necessary to increase the initial permeability of the coal samples by introducing a fracture. A longitudinal fracture was induced mechanically, and CT scans were taken to ensure that the fracture was present throughout the sample and that the sample was not damaged otherwise during the process. In this study, the permeability of coal was determined by using pressure transient methods. Two types of pressure pulses were used: A-spike and Sine-6 pressure transients. It was first established that the permeability of fractured coal samples did not change with exposure time when an inert gas (Argon) was used as the fluid medium in the experiments. However, the permeability of coal samples decreased significantly when carbon dioxide was used as the fluid medium. This reduction can be attributed to the coal swelling phenomenon. The results show that the permeability reduction in fractured coal samples can be over 90% of the original value, and the exposure time for such reductions can range from 1.5 days up to a week, typically about 2 days under laboratory conditions. The permeability decreased significantly with the increase in confining pressure. The higher confining pressure appears to close internal fractures causing a reduction in permeability. 相似文献
13.
黑方台浅层黄土渗透特性对比试验研究 总被引：1，自引：0，他引：1
位于黄土高原的甘肃黑方台由于常年的农业灌溉导致地下水位抬升诱发了大量黄土滑坡,造成很大损失,研究灌溉水在非饱和黄土中的渗透特性对该地区滑坡的防控具科学指导意义。本论文通过现场双环试验、原状样室内变水头渗透试验、重塑样室内变水头渗透试验,对黑方台黄土的渗透特性进行对比分析,最后通过高密度电法及探井测量进行对比验证。得出以下结论:（1）3类试验方案中非饱和黄土的渗透系数均随着干密度的增大呈线性减小;（2）同一条件下的黄土,双环试验所得渗透系数最大,原状样次之,重塑样最小;干密度越大,3类渗透系数差异性越小;（3）高密度电法验证与双环试验结果最接近,探井验证得出高密度电法在黄土地区的适用性。 相似文献
14.
高压实膨润土的非饱和渗透膨胀模型 总被引：1，自引：0，他引：1
高放废弃物深地质处置库中,作为缓冲/回填材料的高压实膨润土的设计功能是,遇水吸湿导致土体膨胀变形,以密封高压实膨润土块体砌置时形成的块体与块体之间和块体与围岩之间的施工缝隙以及围岩中因处置库开挖卸载引起的裂缝,形成阻障围岩中地下水渗入内库引起核素迁移,与库内高放废物的辐射扩散的人工屏障。高压实膨润土在自由膨胀条件下的膨胀应变和非饱和渗透系数由渗透试验测得;孔隙比和吸力的关系由压汞试验测得。吸力和含水率的函数关系可由土-水特征曲线测试试验得到。因此,自由膨胀条件下膨润土的非饱和渗透膨胀模型由膨胀应变、非饱和渗透系数和孔隙比与吸力的函数关系建立。结果表明：渗透系数和体积应变都随吸力减小而增加,因为吸力减小会导致孔隙比增加。这一发现有助于设计高放废物的最终处置方案。 相似文献
15.
Case study: a 3D resistivity and induced polarization imaging from downstream a waste disposal site in Brazil 总被引：2，自引：2，他引：0
Andréa Teixeira Ustra Vagner Roberto Elis Giulliana Mondelli Lázaro Valentin Zuquette Heraldo Luiz Giacheti 《Environmental Earth Sciences》2012,66(3):763-772
A contaminated site from a downstream municipal solid waste disposal site in Brazil was investigated by using a 3D resistivity and induced polarization (IP) imaging technique. This investigation purpose was to detect and delineate contamination plume produced by wastes. The area was selected based on previous geophysical investigations, and chemical analyses carried out in the site, indicating the presence of a contamination plume in the area. Resistivity model has successfully imaged waste presence (ρ < 20 Ωm), water table depth, and groundwater flow direction. A conductive anomaly (ρ < 20 Ωm) outside wastes placement was interpreted as a contamination plume. Chargeability model was also able to imaging waste presence (m > 31 mV/V), water table depth, and groundwater flow direction. A higher chargeability zone (m > 31 mV/V) outside wastes placement and following conductive anomaly was interpreted as a contamination plume. Normalized chargeability (MN = m/ρ) confirmed polarizable zone, which could be an effect of a salinity increase (contamination plume), and the clay presence in the environment. 相似文献
16.
P-T-X-controlled element transport through granulite-facies ternary feldspar from Lofoten,Norway 总被引：1，自引：1，他引：0
Katharina Hartmann Richard Wirth Gregor Markl 《Contributions to Mineralogy and Petrology》2008,156(3):359-375
Fluid transport on the grain-scale controls many rock properties and governs chemical exchange. Charnockites from Lofoten
indicate fluid penetration into ternary alkali feldspars controlled by their microtextures. In a process of fluid infiltration
at granulite-facies conditions (∼600°C and 8–11 kbar), tiny pyroxenes enclosed in alkali feldspar reacted to amphiboles, which
are always spatially connected to perthitic albite. Investigation of these microtextures by TEM imaging of Focused Ion Beam
(FIB) prepared foils revealed that pyroxenes in contact with albite lamellae show dissolution features. An amorphous Fe- and
Cl-bearing material interpreted to be a residuum of the percolating fluid was found within albite lamellae. Textures and mineral
compositions indicate that a Cl-rich aqueous fluid attacked the lamellae, which then provided pathways for further fluid flow.
A correspondence was found between feldspar compositions, their microtexture and their degree of alteration as a result of
their permeability for fluids at specific temperatures. Hence, in addition to pressure and temperature, small variations of
feldspar composition can strongly influence the fluid permeability of feldspathic rocks under lower crustal conditions. 相似文献
17.
The effect of the variation of river water levels on the estimation of groundwater recharge in the Hsinhuwei River,Taiwan 总被引：1，自引：1，他引：0
Jung-Wei Chen Hsun-Huang Hsieh Hsin-Fu Yeh Cheng-Haw Lee 《Environmental Earth Sciences》2010,59(6):1297-1307
Land subsidence is a serious problem in Taiwan’s Yunlin area due to groundwater overpumping. There are safety risks in the
high-speed railway structures in the areas of Siluo, Huwei, Tuku, and Yuanchang towns that run from north to south in the
Yunlin area. Therefore, it is important to increase the groundwater recharge and to remedy the land subsidence in this area.
The purpose of this study is to use the stream-flow estimation model (SF) and the groundwater flow numerical software MODFLOW
(MF) to estimate the stream infiltration with consideration to the variation of the river water level in the Hsinhuwei River.
The Ferris analytical model (FA) and MF are used to estimate the increased stream infiltration after the water level of the
river rises. The hydraulic parameters required for each model are obtained from field observations and laboratory experiments.
The results indicate that the assessment of the stream infiltration obtained through the SF and MF models are 264.2 × 104 and 170.9 × 104 m3/year, respectively. When the river water level increases by about 2.5 m, the annual stream infiltration obtained through
the FA and MF models significantly increases by 31.6 × 104 and 26.4 × 104 m3/year, respectively. Taken together, the stream storages estimated using these two models indicate that an increasing efficiency
of groundwater recharge is within the range of 10.0–18.5%. 相似文献
18.
Treatment of a potential soil capping for open-cut mines (Part 1): Influence of prior management on responses to a phyto-organic amendment 总被引：1，自引：1，他引：0
Extraction of mineral ores, and some projects in engineering geology commonly entail removal of large tracts of valuable topsoil called overburden. A potential mine overburden capping material from an Alfisol with different management histories was treated to assess its physical responses to phyto-organic amendments during storage. Although there were small inceases in hydraulic conductivity, phyto-organic amendments did not greatly improve the physical properties of the Alfisol which had previously been cultivated for several years, as changes in stability and water retention were generally not statistically significant. However, very substantial increases of stability (about 25%) and water retention about 40%) occurred in the same soil which had previously been under a long-term permanent pasture regime. As topsoils can quickly deteriorate when removed and stored, prior soil management should be taken into account where topsoil is to be removed and replaced as a capping after operations such as ore extraction. 相似文献
19.
This second paper reports the results of plant growth, plant mortality, plant leaf tissue metal and salt concentrations and
leachate quality monitoring from lysimeters in four large field trial treatments established on sulfidic waste rock/soil that
was used for haul road construction at a closed gold mine in Australia. The TerraB™, lime and clay treatments allowed good
tree growth of four Eucalypt species, compared to the control. There was no statistical difference in tree growth between
the TerraB™, lime or clay treatments over the 2 years of monitoring in this paper. However, the growth of one tree species
was poor in the TerraB™ treatment. Leaf tissue metal and major ion data are also presented. Leachate pH in the control became
increasingly acidic (pH 4.57–3.95). The addition of Ca(OH)2 and biosolids led to an initial increase in leachate pH, compared to the control; however, this has decreased over the duration
of the study (pH 5.37–4.89) and may affect the sustainable growth of plants in the future. In the TerraB™ and biosolids treatment
leachate pH increased to 6.92 after the first rainfall event and continued to increase over the duration of the study to pH
7.4 after 24 months. After 24 months average heavy metal leachate concentrations (mg/L) in the lysimeters for Al, Cd, Cu,
Mn and Zn were, control: 32.55, 5.67, 12.71, 39.29, 121.80, TerraB™: 0.07, 0.02, 0.07, 0.57, 0.23, and lime: 2.19, 1.19, 2.33,
3.6, 28.4. No leachate was available for collection from the clay treatment indicating that this technique was functioning
in terms of minimizing the infiltration of water into the mine soil. 相似文献
20.
Sulfate-reducing passive bioreactors have proved to be an effective technology for the treatment of acid mine drainage (AMD) contaminated waters over relatively short periods of time (1–5 a). However, long-term efficiency can be limited by several factors including problems related to the hydraulic properties of the reactive mixture. In this study, the effect of two hydraulic retention times (HRTs) of 7.3 d and 10 d on the performance of passive bioreactors was evaluated over an 11-month period for the treatment of a highly contaminated AMD. Evolution of the porosity and hydraulic conductivity of the reactive mixture was also evaluated during the 15-month operation of two bioreactors. Results indicated that bioreactors were effective at both HRTs for increasing the pH and alkalinity of contaminated water and for SO4 and metal removal (60–82% for Fe and up to 99.9% for Cd, Ni and Zn). Although the quality of treated effluent was significantly improved with the 10 d HRT compared to the 7.3 d HRT, results showed that the higher HRT reduced the porosity and the permeability of the reactive mixture which might lead to hydraulic related problems and, eventually, to limited efficiency in long-term operation compared to a shorter HRT. The choice of HRT for a passive bioreactor must therefore consider both the desired quality of treated effluent and the potential for deterioration of hydraulic properties in the reactive mixture. 相似文献