Increasing Loading Rate Research Articles

Progressive Damage Process and Failure Characteristics of Coal under Uniaxial Compression with Different Loading Rates

To study the effect of loading rate on the progressive damage and failure characteristics of coal, an ultrasonic detector and a camera were used to measure the P-wave velocity and record the failure process of cuboid coal samples in uniaxial compression tests with five loading rates. The mechanical properties, damage process, and failure characteristics of the samples were analysed, and the mechanism of the advancing velocity of the working face in coal failure was discussed. The results show that, as the loading rate increases, the peak strength of the sample generally shows an increasing trend, but the elastic modulus changes irregularly. The sample is more prone to local failure before the peak strength. An increase in the loading rate rapidly promotes damage in the sample and accelerates the transition from internal damage to macroscopic failure, with no obvious effect on the ratio of damage threshold to corresponding peak strength. At low loading rates, the samples mainly experienced static failure; the failure form was spalling, and the failure range was wide. At high loading rates, the samples were prone to dynamic failure in the local area, manifested as the ejection of slabs and debris. A greater loading rate produced smaller and thinner slabs and a greater ejection velocity. Properly increasing the advancing velocity of the working face is conducive to reducing spalling to prevent large-area roof fall, but it may increase the possibility of coal burst in local areas. The results of this study provide a reference for roof control and coal burst disaster prevention on the working face in deep coal mining.

The impact of a seasonal change in loading rate on the nitrous oxide emissions at the WWTP of a tourist region

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) whose production and emission must be minimised from wastewater treatment plants (WWTPs) to avoid undesirable impacts to climate change and the ozone layer. WWTPs operated in tourist regions undergo large seasonal changes to the influent loading rates of organic matter, nitrogen and phosphorus, which operators must respond to by changing their operational conditions. This study examines the impact of a change in low to high season on the N2O emissions of an activated sludge WWTP in a well-known tourist region in the Algarve, Portugal. While literature studies have suggested that increases in the nitrogen and organic loading rates can promote increased N2O emissions, we have found higher N2O emissions in the low season (7.4% kgN2O-N·kgNH4-N−1), where these loading rates were lower. It was found that the impact of accompanying operational changes to the WWTP outweighed any change caused by the increased loading rate, where the aeration rate showed a significant correlation with N2O emission dynamics. The location of the N2O fluxes observed as well as the dissolved vs gaseous N2O levels suggested that the hydroxylamine oxidation pathway was likely to be of higher relevance towards N2O production as compared to nitrifier denitrification. This study contributes towards the understanding of operational factors impacting N2O emissions at full-scale WWTPs and potential mitigation strategies.

Zeolite addition to improve biohydrogen production from dark fermentation of C5/C6-sugars and Sargassum sp. biomass

Thermophilic biohydrogen production by dark fermentation from a mixture (1:1) of C5 (arabinose) and C6 (glucose) sugars, present in lignocellulosic hydrolysates, and from Sargassum sp. biomass, is studied in this work in batch assays and also in a continuous reactor experiment. Pursuing the interest of studying interactions between inorganic materials (adsorbents, conductive and others) and anaerobic bacteria, the biological processes were amended with variable amounts of a zeolite type-13X in the range of zeolite/inoculum (in VS) ratios (Z/I) of 0.065–0.26 g g−1. In the batch assays, the presence of the zeolite was beneficial to increase the hydrogen titer by 15–21% with C5 and C6-sugars as compared to the control, and an increase of 27% was observed in the batch fermentation of Sargassum sp. Hydrogen yields also increased by 10–26% with sugars in the presence of the zeolite. The rate of hydrogen production increased linearly with the Z/I ratios in the experiments with C5 and C6-sugars. In the batch assay with Sargassum sp., there was an optimum value of Z/I of 0.13 g g−1 where the H2 production rate observed was the highest, although all values were in a narrow range between 3.21 and 4.19 mmol L−1 day−1. The positive effect of the zeolite was also observed in a continuous high-rate reactor fed with C5 and C6-sugars. The increase of the organic loading rate (OLR) from 8.8 to 17.6 kg m−3 day−1 of COD led to lower hydrogen production rates but, upon zeolite addition (0.26 g g−1 VS inoculum), the hydrogen production increased significantly from 143 to 413 mL L−1 day−1. Interestingly, the presence of zeolite in the continuous operation had a remarkable impact in the microbial community and in the profile of fermentation products. The effect of zeolite could be related to several properties, including the porous structure and the associated surface area available for bacterial adhesion, potential release of trace elements, ion-exchanger capacity or ability to adsorb different compounds (i.e. protons). The observations opens novel perspectives and will stimulate further research not only in biohydrogen production, but broadly in the field of interactions between bacteria and inorganic materials.

Effect of organic loading rate on the biological performance of the thermophilic anaerobic membrane bioreactor treating pulp and paper primary sludge

Waste-to-energy or value-added products have been increasingly considered in many pulp and paper mills (PPMs) worldwide. However, developing appropriate conversion technologies are a major challenge in transforming PPMs wastes into biofuels or value-added biomaterials. In the present study, a long term (320 d) anaerobic digestion of primary sludge of a thermomechanical pulp mill (TMP) was carried out for the first time in a thermophilic anaerobic membrane bioreactor (ThAnMBR). Effect of organic loading rate (OLR) in the range of 2.5–6.8 kg COD/m3 d and hydraulic retention times (HRT) of 3–8 d on the process performance was investigated. Under various OLRs, stable biogas productions were obtained, and the best results were achieved with lower OLR (2.5 kg COD/m3 d) and higher HRT (8 d), at biogas yields of 189 L biogas/kg MLSS fed. However, it was found that the biogas production and sludge biomass degradation decrease when the organic loading rate increases. The proportion of sludge reduction ranged from 28.9 to 46.7% depending on the applied OLRs. Despite varying OLRs, stable membrane performance was obtained, where the required membrane flux was easily maintained during the reactor operation. In this study, also the properties of digestate and membrane permeates were studied under different operating conditions, and they fluctuated to some extent with OLR. ThAnMBR is a promising new technology for pulp and paper mill primary sludge treatment.Graphic abstract

Treatment of Hospital wastewater with submerged aerobic fixed film reactor coupled with tube-settler

In this study, Hospital wastewater was treated using a submerged aerobic fixed film (SAFF) reactor coupled with tubesettler in series. SAFF consisted of a column with an up-flow biofilter. The biological oxygen demand (BOD)5, chemical oxygen demand (COD), nitrate and phosphate were the chosen pollutants for evaluation. The pollutants removal efficiency was determined at varying organic loading rates and hydraulic retention time. The organic loading rate was varied between 0.25 and 1.25 kg COD m−3 d−1. The removal efficiency of SAFF and tubesettler combined was 75 % COD, 67 % BOD and 67 % phosphate, respectively. However, nitrate saw an increase in concentration by 25 %. SAFF contribution in the removal of COD, BOD5 and Phosphate was 48 %, 46 % and 29 %, respectively. While for accumulation of nitrate, it was responsible for 56%, respectively. Tubesettler performed better than SAFF with 52 %, 54 % and 69 % reduction of COD, BOD5 and phosphate, respectively. But in terms of nitrate, tubesettler was responsible for 44 % accumulation. The nutrient reduction decreased with an increase in the organic loading rate. Nitrification was observed in the SAFF and tubesettler, which indicated a well-aerated system. An anaerobic unit is required for completing the denitrification process and removing nitrogen from the effluent. The better performance of tubesettler over SAFF calls for necessitates extended retention time over design criteria. Further studies are beneficial to investigate the impact of pharmaceutical compounds on the efficiency of SAFF.

The rate effect on fracture mechanics of dam concrete based on DIC and AE techniques

In order to study the effect of loading rate on fracture behavior of dam concrete, wedge splitting tests of various loading rates (0.1, 0.01, and 0.001 mm/s) are carried out on two kinds of full-graded dam concrete notched cubes with side lengths of 300 and 450 mm, respectively. Digital image correlation and acoustic emission technique are used to measure the deformation and acoustic emission parameters of the dam concrete. Test results show that: the peak load and fracture energy of dam concrete specimens increases with the increase of loading rate. And the higher the loading rate is, the fracture of concrete shows more obvious brittleness. Influenced by the boundary effect, the CTOD increases with the increasing of loading rate, however, the length of crack decreases as loading rate increases. With the loading rate increases, the energy mutation area is more obvious, while the accumulated acoustic emission energy is affected by both the loading rate and the maximum aggregate size. The number of acoustic emission three-dimensional locating points and the shear signal decrease with the increase of loading rate, which is attributed to that the faster the loading rate is, the less sufficient the development of micro cracks in concrete is. The test results can supply experimental data to the fracture mechanics of dam concrete.

Experimental Investigation of the Dynamic Tensile Properties of Naturally Saturated Rocks Using the Coupled Static–Dynamic Flattened Brazilian Disc Method

In a naturally saturated state, rocks are likely to be in a stress field simultaneously containing static and dynamic loads. Since rocks are more vulnerable to tensile loads, it is significant to characterize the tensile properties of naturally saturated rocks under coupled static–dynamic loads. In this study, dynamic flattened Brazilian disc (FBD) tensile tests were conducted on naturally saturated sandstone under static pre-tension using a modified split-Hopkinson pressure bar (SHPB) device. Combining high-speed photographs with digital image correlation (DIC) technology, we can observe the variation of strain applied to specimens’ surfaces, including the central crack initiation. The experimental results indicate that the dynamic tensile strength of naturally saturated specimens increases with an increase in loading rate, but with the pre-tension increases, the dynamic strength at a certain loading rate decreases accordingly. Moreover, the dynamic strength of naturally saturated sandstone is found to be lower than that of natural sandstone. The fracture behavior of naturally saturated and natural specimens is similar, and both exhibit obvious tensile cracks. The comprehensive micromechanism of water effects concerning the dynamic tensile behavior of rocks with static preload can be explained by the weakening effects of water on mechanical properties, the water wedging effect, and the Stefan effect.

Effect of loading rate on the mode II dynamic fracture characteristics of 40Cr steel

40Cr high strength steel is often used in aerospace and national defense fields due to its excellent mechanical properties. Therefore, the research on the mode Ⅱ dynamic fracture characteristics and failure mechanism of 40Cr high strength steel under high-speed impact has important scientific significance and engineering value. Experiments and numerical simulations were carried out to study the mode Ⅱ dynamic fracture properties of 40Cr material under high loading rates. Based on the newly designed specimen and the novel test technique for mode Ⅱ dynamic fracture, the experimental-numerical method was used to determine the dynamic stress intensity factor curve of the crack tip during the loading process. The crack initiation time of the specimen was obtained by the strain gauge pasted on the specimen, and the mode Ⅱ dynamic fracture toughness of 40Cr was finally determined. The effect of loading rate and the failure mechanism of the material were also studied. The results show that within the present loading rate range of this work (1.08−5.53 TPa·m1/2/s), the mode Ⅱ dynamic fracture toughness of 40Cr presents a positive correlation with the loading rate. Through the analysis of the fracture morphology of the recovered specimen, it is found that there exists a transition from tensile failure mode to adiabatic shear failure mode with the increase of loading rate, and the critical loading rate is about 2.92 TPa·m1/2/s. When KⅡd≤1.70 TPa·m1/2/s, the 40Cr steel mainly exhibits brittle fracture; when KⅡd is in the range of 2.12−2.92 TPa·m1/2/s, the fracture mainly presents the morphological characteristics of ductile fracture; when KⅡd ≥ 3.19 TPa·m1/2/s, the material failure is mainly caused by adiabatic shear bands. Brittle fracture is dominated by strain rate hardening mechanism, ductile fracture is dominated by strain/strain rate hardening and thermal softening mechanisms, and adiabatic shear fracture is dominated by thermal softening mechanism.

Continuous anaerobic digestion of zucchini stem after pretreatment

Anaerobic digestion (AD) is a widely used technology for converting organic wastes into biomethane with the advantages of clean energy production and few environmental impacts. Zucchini stem (ZS), the main waste produced from zucchini cultivation, is a potential feedstock for AD due to its high moisture and organic contents. This study investigated the methane production performance and system stability of ZS in continuous AD mode with the increase of organic loading rate (OLR). Moreover, to improve the methane production efficiency, KOH, NaOH, and alkaline hydrogen peroxide (AHP) pretreatments were also performed. The results showed that raw ZS gave a daily methane yield (DMY) of 182.1 mL g VS − 1 d −1 and volumetric methane yield (VMY) of 0.546 L L −1 d −1 at an OLR of 3.0 g VS L −1 d −1 . At the same OLR, 2% KOH-pretreated ZS significantly enhanced the DMY to 236.0 mL g VS − 1 d −1 and the VMY to 0.708 L L −1 d −1 , with a biodegradability (B d ) of 56.3%, which was 29.7% higher than that of raw ZS. However, NaOH- and AHP-pretreated ZS could not achieve stable methane generation at an OLR of 2.0 g VS L −1 d −1 . This study forms a foundation for future industrial applications of ZS; the investigated approach not only utilizes this waste efficiently and reduces its environmental pollution but also produces renewable biomethane energy and may improve the energy structure in rural areas. • Continuous anaerobic digestion (AD) of pretreated zucchini stem (ZS) was explored. • 2% KOH pretreated ZS performed stably and efficiently continuous AD system. • The highest volumetric methane yield was 0.708 L L -1 d -1 after 2% KOH pretreatment.

Increased Upper Arm Length and Loading Rate Identified as Potential Risk Factors for Injury in Youth Baseball Pitchers

Background: In the throwing elbow, increased elbow torque has been correlated with increased injury risk. Additional insight into the relationships between anthropometric factors and elbow joint loading is warranted. Purpose: To investigate the relationship among physical limb length characteristics, elbow kinetics, and elbow kinematics in youth baseball pitchers and to examine the relationship between elbow varus loading rate and elbow kinetics. Design: Descriptive laboratory study. Methods: A total of 27 male youth baseball pitchers participated (mean ± SD: age, 15.8 ± 2.7 years; height, 176.3 ± 13.0 cm; weight, 71.7 ± 16.4 kg). Upper arm (UA) and forearm (FA) lengths were measured using a moveable sensor to digitize bony landmarks. Kinematic data were collected at 240 Hz using an electromagnetic tracking system. Participants threw 3 fastballs to a catcher at a regulation distance (60 ft 6 in), and the fastest velocity trial was used for analysis. Linear regression was used to determine the relationship among limb length characteristics, elbow kinetics, and elbow kinematics after accounting for the effects of body weight and height. Results: Pitchers with longer UA length experienced increased maximum elbow varus torque (P = .005) and maximum net elbow force (P = .001). Pitchers with an increased forearm to UA ratio had decreased elbow compression force (P < .001) and exhibited a more flexed elbow at foot contact (P = .001). Pitchers with greater maximum loading rates experienced greater elbow varus torque (P = .002). Conclusion: In youth baseball pitchers, longer UA length and greater loading rate increase varus torque about the elbow during a fastball pitch. Clinical Relevance: Longer UA length and greater loading rate may place pitchers at risk of injury because of their relationship with kinetic values.

Increased Loading Rates During Gait Correlate With Morphology of Unaffected Hip in Juveniles With Treated Developmental Hip Dysplasia.

Long-term follow-up studies on children with surgically treated developmental dysplasia of the hip (DDH) have shown that not only the affected side progresses to premature osteoarthritis, but the unaffected side may also suffer from insidious hip dysplasia or osteonecrosis. The current gait analysis study identified the loading and unloading rates of the ground reaction forces (GRF) and lower limb joint axial forces during gait, and their correlations with the hip morphology in twenty juvenile patients with surgically treated unilateral DDH during toddlerhood. In a gait laboratory, each subject walked at preferred speed on a 10-m walkway while the kinematics and the GRF were measured. Loading and unloading rates of the vertical GRF and the joint axial forces were obtained as the maximum instantaneous slope of these force curves. Radiographic measurements of the hips were taken, and the correlations between the morphological parameters and the loading and unloading rates were obtained. The patients showed greater-than-normal peak loading rates of the joint axial forces, and the loading rates on both the affected and unaffected sides were strongly correlated to the acetabular index on the unaffected side, which was also significantly correlated with the peak unloading rates on the affected side. These results suggest that apart from regular follow-up of the affected hip, routine assessment of the morphological changes and/or increased loading rates on the unaffected hip is also important for early identification of any signs of insidious hip dysplasia and risk of premature degeneration of the cartilage.

Mechanical behavior of coal under different mining rates: A case study from laboratory experiments to field testing

During deep mining, the excavation disturbance stress path is the domination factor for the stability of the surrounding rock mass as well as the ground pressure. One of the important parameters of the stress path is the loading or unloading rate of the disturbed rock or coal, which depended on the mining rate. To achieve a well understanding of the mining rate and its effect on the coal behavior, a preliminary case investigation of the mechanical properties of the coal at the various mining rates in both the laboratory scale and field scale was performed. Based on the uniaxial compression test and the digital image correlation (DIC) method, the mechanical behavior of the coal samples, such as the evolution of the strength, surface deformation, crack propagation, and elastic strain energy of the coal under the various loading rates were analyzed. A threshold range of the loading rate has been observed. The uniaxial compressive strength (UCS) and releasable elastic strain energy (Ue) increase with increasing loading rate when the loading rate is below the threshold. Otherwise, the UCS and Ue may decrease with the loading rate. Under the low loading rate (≤0.05 mm/min), the tensile deformation of the original defects could result in crack coalescence, whereas failure of the coal matrix is the key contributor to the crack coalescence under the high loading rate (greater than0.05 mm/min). Afterwards, with the consideration of the bearing capacity (UCS) and energy release of the mining-disturbed coal mass (Ue), a power exponential relationship between the mining rate (MR) in the field and the critical loading rate (vc) in the laboratory was proposed. The application potential of the formulas was then validated against the field monitored data. Finally, based on the critical loading rate, the released strain energy, and the monitored pressure on the roof supports, a reasonable mining rate MR for the Ji15-31030 working face was determined to be approximately 3 m/d.

The force loading rate drives cell mechanosensing through both reinforcement and cytoskeletal softening

Cell response to force regulates essential processes in health and disease. However, the fundamental mechanical variables that cells sense and respond to remain unclear. Here we show that the rate of force application (loading rate) drives mechanosensing, as predicted by a molecular clutch model. By applying dynamic force regimes to cells through substrate stretching, optical tweezers, and atomic force microscopy, we find that increasing loading rates trigger talin-dependent mechanosensing, leading to adhesion growth and reinforcement, and YAP nuclear localization. However, above a given threshold the actin cytoskeleton softens, decreasing loading rates and preventing reinforcement. By stretching rat lungs in vivo, we show that a similar phenomenon may occur. Our results show that cell sensing of external forces and of passive mechanical parameters (like tissue stiffness) can be understood through the same mechanisms, driven by the properties under force of the mechanosensing molecules involved.

Effects of a temporary increase in OLR and a simultaneous decrease in HRT on dry anaerobic digestion of OFMSW

ABSTRACT The effects of the temporary increase of organic loading rate (OLR) combined with the simultaneous decrease of hydraulic retention time (HRT) on the stability of a pilot scale dry anaerobic digester were investigated. The separately collected organic fraction of municipal solid waste in mesophilic conditions (T = 40°C) was treated. The objective of this study was to verify whether it is possible to feed the digester for short periods, about three consecutive weeks, with higher OLRs and lower HRTs than those considered optimal without generating process failure or long-term instability. Starting from stable operation at a daily OLR of 10.0 kg of total volatile solids (TVS) for digester volume and an HRT of 23 d, the reactor was fed with an OLR of 10.8, 11.7 and 12.5 kg TVS m−3 d−1 corresponding to an HRT of 21, 19 and 18 d, respectively. It was observed that after using an OLR of 10.8 and 11.7 kg TVS m−3 d−1 for 3 weeks with satisfying results, it was possible to restore stable operating conditions at an OLR of 10.0 kg TVS m−3 d−1 in a short time. Otherwise, after using an OLR of 12.5 kg TVS m−3 d−1 the anaerobic digestion was deeply unbalanced and quickly failed. In this latter case, however, it was possible to fully recover and restore the stable conditions of the process within two months.

Enhanced creep resistance of Ti30Al25Zr25Nb20 high-entropy alloy at room temperature

Several previous studies have shown that the dissolution of Al in a solid solution single phase BCC is high unfavorable in TiZrNb system. In this work, a novel Ti30Al25Zr25Nb20 high-entropy alloy (HEA) with a single body-centered cubic (bcc) structure was developed. The Young's modulus and nano-hardness of this HEA measured by continuous stiffness measurement (CSM) technique were 158.2 ± 5.2 GPa and 8.9 ± 0.2 GPa, respectively. The creep behaviors of this HEA at a constant temperature of 20 °C under different loading rates and peak loads were studied by nano-indentation technique. The result indicated that with the increase of loading rates and peak loads, the creep displacement increased, but the creep strain rate sensitive index first decreased and then increased, and the physical mechanisms are interrupted by introducing dislocation activation volume. The reason might attribute to the hysteresis diffusion effect. Compared with other metallic structural materials, Ti30Al25Zr25Nb20 HEA possesses a relatively high dislocation activation volume and low creep strain rate sensitive index value, indicating a significantly high creep resistance.

A Study on Rupture Resistance of Groundnut (cv. SAMNUT 22) Kernel

This study was done to assess the influence of compression loading rate and kernel size on the rupture resistance of groundnut (cv. SAMNUT 22) kernel. These groundnut kernel mechanical parameters (rupture force, deformation at rupture, rupture power, firmness and toughness) were evaluated under three loading rates (15 mm min-1, 20 mm min-1 and 25 mm min-1), and three size categories (small, medium and large). The groundnut kernels were harvested at peak maturity stage, and tested in accordance to ASTM International standards. Results obtained from the tests showed that the rupture resistance of SAMNUT 22 kernel was highly dependent on its size and the loading rate. Generally, as the loading rate increases, the mechanical parameters values declined significantly (p ≤ 0.05). Rupture force, deformation at rupture point, rupture power and the firmness increased as the kernel size increases; but in contrast, the kernel toughness decreases as its size increased. An average force of 57.96 N ruptured the large kernel, while a lower force of 27.35 N ruptured the small kernel. Moreover, the large kernel recorded the highest firmness (59.03 N mm-1), when compared to the medium (51.69 N mm-1) and small (44.98 N mm-1) size kernel. In terms of rupture power, the small kernel power ranged from 0.1002 W (15 mm min-1) to 0.084 W (25 mm min-1); medium size kernel ranged from 0.115 W (15 mm min-1) to 0.074 W (25 mm min- 1); while the large size kernel ranged from 0.135 W (15 mm min-1) to 0.104 W (25 mm min-1). These results portrayed importance of sorting of the groundnut kernels before processing unit operation, as it will help to conserve power and energy during the processing operation.

A rate-dependent phase-field framework for the dynamic failure of quasi-brittle materials

In recent years, phase-field theory has become an efficient approach for predicting damage and fracture of engineering materials. However, the rate-dependence of quasi-brittle materials is not considered in most exiting models. To address this issue, we develop a new phase-field damage model for the dynamic failure of quasi-brittle solids based on the microforce balance law, within which a linear viscoelastic constitutive relation in effective stress space and a hyperbolic phase-field evolution equation are incorporated. Then several representative numerical examples are presented to demonstrate the ability of the proposed model in characterizing the dynamic failure process of quasi-brittle solids. Good agreements are achieved between numerical predictions and theoretical and experimental results. In particular, the increase of tensile strength and the transition of failure modes of concrete-like materials with the increase of loading rates can be well reproduced.

Dynamic flexural failure of rocks under hydrostatic pressure: Laboratory test and theoretical modeling

Dynamic flexural failure of rocks is commonly encountered near deep underground openings due to the bending load derived from earthquakes or production blasts in rock engineering. Meanwhile, deep underground rock is also generally subjected to static hydrostatic pressure. Thus, it is desirable to investigate dynamic flexural failure characteristics and mechanisms of rocks under static hydrostatic pressure. In this study, the dynamic flexural tensile strengths of Laurentian granite (LG) under five hydrostatic pressures (i.e., 0 MPa, 5 MPa, 10 MPa, 15 MPa and 20 MPa) were measured by using a triaxial split Hopkinson pressure bar (SHPB) system in combination with the semi-circular bend (SCB) method. The experimental results indicate that dynamic flexural tensile strength under a certain hydrostatic pressure rises with the loading rate, and dynamic flexural tensile strength at a certain loading rate increases with the hydrostatic pressure due to the closure of microcracks in rocks. In addition, an empirical formula is proposed to successfully predict both the rate dependence and the hydrostatic pressure effect on the dynamic flexural tensile strength. Moreover, the parameter in terms of the hydrostatic pressure is first introduced in the two-parameter tensile strength model, which is improved in this study to quantitatively rationalize the discrepancy between the dynamic intrinsic tensile strength and the dynamic flexural tensile strength for rocks under hydrostatic pressures, and to further establish the relationship between the hydrostatic pressure and the characteristic material length δ for rocks. Meanwhile, the characteristic material length is optimized by the particle swarm optimization method and the value of δ decreases with the hydrostatic pressure due to the closure of microcracks and pores. Besides, an equation is established to describe the relation between the hydrostatic pressure and the characteristic material length. In addition, the morphology of the main fracture in the tested SCB specimens is digitized and the fractal dimension is applied to quantitively describe the fracture surfaces roughness. There is no clear trend to indicate the influence of hydrostatic pressure on the surface roughness, whereas there is generally a decrease of fractal dimension with increasing loading rate for LG under each hydrostatic pressure.

Anaerobic mono-digestion of sugarcane trash and bagasse with and without pretreatment

The effect of organic loading on process performance and methane yields during anaerobic mono-digestion of sugarcane trash (ST) and sugarcane bagasse (SB) with and without dilute sulphuric acid impregnated steam explosion was investigated. At first, biochemical methane potential (BMP) of ST and SB was performed at 37 °C in batch assays with an inoculum to substrate (ISR) ratio of 2 on VS basis. Methane yields of 161.8 ± 4 and 187.9 ± 2.4 N mL g−1 VSadded were obtained for ST and SB, respectively. These yields were 55.6 and 53.8 % of the theoretical methane potentials for ST and SB respectively. Later, semi-continuous reactor experiments were conducted using four stainless steel reactors with working volume of 10 L and hydraulic retention time (HRT) of 35 d at 37 °C. Reactors were fed with untreated ST, untreated SB, steam exploded trash (TT) and steam exploded bagasse (TB). In all four reactors, methane production increased with increase in organic loading rate (OLR) from 1.5 to 2.5 gVS L-1 d-1. However, higher methane yields were noticed in TT (226 ± 37 NmL g-1VSfed) and TB (236 ± 22 NmL g-1VSfed) than for ST (121 ± 24 mL g-1VSfed) and SB (148 ± 25 mL g-1VSfed). Increase in OLR from 2.5 to 3.5 gVS L-1d-1 resulted in decreased methane yields and pseudo state stable conditions. Thus, steam explosion with dilute H2SO4 catalyst can improve the methane yields of both ST and SB.

A Fixed Bed Pervious Concrete Anaerobic Bioreactor for Biological Sulphate Remediation of Acid Mine Drainage Using Simple Organic Matter

The development of low-operational-cost and low-operational-complexity active sulphate (SO4) reducing bioremediation for Acid Mine Drainage (AMD) is an ongoing pursuit towards sustainable mining. This study introduces a fixed bed pervious concrete anaerobic bioreactor as a second stage AMD remediation process. The study investigated the pH self-regulation capabilities, SO4 remediation capabilities and the rate limiting parameters of the bioreactor using glucose as an organic matter source. The AMD was pre-treated using a permeable reactive barrier. A 21-day trial comprised of an increase in the SO4 loading rate while reducing the organic loading rate was undertaken to identify performance limiting conditions. A daily average SO4 concentration reduction rate of 55.2% was achieved over the initial 13 days of the experiments. The study found that a COD to SO4 ratio and VFA to alkalinity ratio below 5:1 and 0.5:1 respectively were performance limiting. The bioreactor was capable of self-regulating pH within the neutral range of 6.5 and 7.5. The study findings indicate that the bioreactor design can reduce operational costs and operational complexity of active AMD bioremediation.