Surface Clogging Research Articles

Combined clogging of suspended particle and algae during the recharge with the Yellow River water in the Yufuhe River channel of North China Plain

ABSTRACT Managed aquifer recharge (MAR) is an effective measure for integrated water resources in the North China Plain (NCP). During the recharging, the combined clogging in the aquifer caused by algae and suspended solid (SS) is a problem that was easily ignored by researchers. In this research, a sand column model was designed to investigate the SS-algae combined clogging mechanism in the porous medium during the Yellow River water recharge in the Yufuhe River channel of NCP. The SS-algae combined plugging of the medium appeared earlier and the plugging degree was more serious compared with the SS-only clogging and the algae-only clogging during the infiltration. Meanwhile, the surface clogging degree of the medium is more serious, and the interior is smaller in comparison to the SS-only group and the algae-only group. The filter cake and algae mat are the signs of SS clogging and algae clogging, and the algae mat structure in the SS-algae group is more dense compared to the algae-only group. In the combined clogging experiment, the outflow concentration of SS and algae in the medium is less than the SS-only group and the algae-only group. In addition, algae and SS can limit each other's migration in the medium.

Adsorption performance of g-C3N4/graphene, and MIL-101(Fe)/graphene for the removal of pharmaceutical contaminants: a molecular dynamics simulation study

The rising presence of drug-related contaminants in water sources is a major environmental and public health concern. Several studies have addressed the hazardous influence of these pollutants on the lives of over 400 million people worldwide. In this study, we used molecular dynamics simulations to evaluate the efficacy of two promising composite materials for the removal of pharmaceutical contaminants by using the adsorption technique. Graphitic carbon nitride/graphene (g-C3N4/graphene) and metal-organic framework (MIL-101(Fe))/graphene have been simulated for the first time for the removal of three of the most common pollutants (acetaminophen (AC), caffeine (CAF), and sulfamethoxazole (SMZ)). The nanocomposite structure has been created and optimized using the geometry optimization task in the DFTB Modules in the Amsterdam Modeling Suite. We summarized the condition of the essential parameters (Temperature, pressure, and density) of the simulation box during the MD-simulation to ensure the accuracy of our MD-simulation results. The adsorption process, van der Waals interactions, and the adsorption capacity have been calculated by using the Reactive Forcefield (ReaxFF) software. We found that the combination of MIL-101(Fe)/graphene had a higher adsorption capacity for the removal of pharmaceutical contaminants than g-C3N4/graphene. At 40 Picosecond (Ps), 80 molecules of each pharmaceutical contaminants (AC, CAF and SMZ) have been adsorbed by MIL-101(Fe)/graphene with higher exothermic energy equated to (−1174, −1630, and − 2347) MJ/mol respectively. While for g-C3N4/graphene at 40 Ps, 70 molecules of each pharmaceutical contaminants have been adsorbed with exothermic energy equated to (−924, −966, and − 1268) MJ/mol respectively. Also, our results showed that the combination of g-C₃N₄/graphene and MIL-101(Fe)/graphene both have remarkable properties that make them effective at resisting surface clogging. Finally, the results showed that the adsorption kinetics followed a pseudo-first order model, while the adsorption isotherms for AC, CAF and SMZ adhered to Freundlich model.

Investigation of the effect of sediment clogging on the hydraulic conductivity of porous asphalt mixes using CFD and DEM methods

This study investigated the impact of sediment clogging on the hydraulic performance of porous asphalt (PA) pavements using a novel numerical approach combining the discrete element method (DEM) and computational fluid dynamics (CFD). In particular, image analysis techniques captured the morphology of real aggregates for the 3D appearance information. Then, the information was used to reproduce aggregates and their gradation in asphalt mixes using DEM, including sediments causing clogging of the PA. The samples in the DEM were transferred to CFD for hydraulic performance simulation. DEM samples were prepared with air voids content of 20% and 25%. Clogging particles with different sizes of 0.5 mm and 0.75 mm were used. The study found that clogging particles can move to deeper layers of the PA pavement but have a high potential to be trapped in upper layers and cause clogging issues in the top 5 mm and middle-to-bottom sections. Due to surface clogging, the air voids content for the 20% porosity PA sample was reduced by approximately 2% on average, whereas up to 7% reduction in air voids content was observed for the 25% PA sample. This led to 37.35% and 42.7% reduction in hydraulic permeability, respectively. The reduction in air voids content below 10 mm from the surface is negligible (0.3–0.7% reduction). Due to the clogging development inside the pore structure, the surface runoff on the top of the sample increases by 8.1% for the 20% air voids asphalt sample case and 37.5% for the 25% voids sample.

Reducing the effects of clogging and surface wear on the radiative properties of concrete blocks produced with recycled glass by incorporating titanium dioxide nanoparticles

ABSTRACT This study aimed to demonstrate how incorporating titanium dioxide nanoparticles into concrete blocks made with recycled glass mitigates the effects of clogging and surface wear on pavement radiative properties. Using a reference concrete, four variants were formulated: with colourless, green, and amber glass, and a photocatalytic concrete with colourless glass. Three accelerated processes were applied to the concrete blocks in field: clogging, wear, and clogging on a worn surface. After each cycle of clogging and/or wear, solar reflectance and thermal emittance were measured to calculate the solar reflectance index (SRI). Surface clogging decreased the SRI for all concrete types, albeit less for photocatalytic concrete with colourless glass. SRI decreased with wear until a mean texture depth (MTD) near 0.80 mm, where a stabilisation trend was noted across all concretes. Photocatalytic concrete with colourless glass consistently showed the highest SRI values relative to the MTD. Clogging on worn surfaces indicated superior radiative properties for photocatalytic concrete with colourless glass at surface contamination degree (SCD) values less than 40%. In conclusion, conventional concretes with glass had inferior radiative properties compared to reference concrete. However, photocatalytic concrete with colourless glass showed superior radiative properties, indicating that nano-TiO2 addition reduced clogging and wear effects.

Experimental investigation of an optimized indirect free cooling system including a dry cooler equipped with evaporative cooling pads for data center

Different heat rejection systems could be used to discharge the heat of liquid cooled data center to the ambience. The dry cooler as an indirect free cooling solution is one of the most used, where outside air is applied as a cooling fluid for its finned heat exchangers (FHEXs). In ambiences where dry coolers ambient temperatures are higher than supplied FHEX’s water temperature, evaporative cooling system can be used as pre-coolers. This paper presents an experimental investigation conducted on an indirect free cooling system including a dry cooler equipped with evaporative cooling pads (IFC+EC) under 20 K data center temperature difference for high outdoor conditions, variable fan speed, reduction in cooling pad’s surface and increasing in water supply temperature. The results show that the dry cooler is successfully operated under 20 K temperature difference. Furthermore, by increasing the air speed from 2 m/s to 3 m/s, the pads’ outlet air temperature increases by 0.6 K, the relative humidity tends to decrease about 9% and its efficiency decreases from 97% to 88%. Surface clogging had no significant impacts. A slight rise of 1.24 K in air outlet temperature and a decrease of about 3.3% and 2.5% in relative humidity and cooling pad thermal efficiency respectively were detected while increasing water supply temperature from 23 °C to 44 °C. This allowed authors to propose an optimized IFC+EC system with precooling DC supply water before the dry cooler to reduce its cooling demand by at least 31%.

Simulation study on clogging of suspended particles in in-situ leaching of uranium at different concentrations and flow velocity

Clogging problem has become one of the key problems restricting the mining efficiency of in-situ leaching of uranium, and the related research on the law and mechanism of physical clogging has not been reported. In order to identify and understand the complicated law and mechanism, experimental device is established to simulate the physical clogging caused by suspended particles in the uranium process, the physical clogging law and mechanism under different concentrations and velocity of flow are studied. The experimental results show that with the concentration of suspended particles increasing from 100, 200, 300 to 400 mg/L, the permeability of porous media gradually decreases, and the clogging phenomenon becomes more and more obvious. When the size of suspended particles is small and the velocity is 15 mL/min, the porous medium will not appear clogging, while the velocity is 25mL/min, the whole porous medium will slowly appear internal deposition clogging. When the size of suspended solids is larger and the flow rate is 9, 12, 15mL/min, the higher the velocity, the faster the clogging will be, and backwash can alleviate the surface clogging but cannot change the final clogging result. According to the experiment and actual situation, the physical clogging in in-situ leaching of uranium is mainly surface clogging and filter clogging.

Combination of sequencing batch reactor and vertical flow treatment wetlands: A full-scale experience for rum distillery wastewater treatment in a tropical climate

Distillery wastewater is a difficult type of wastewater to treat because of its low pH (pH = 3.3), high chloride and sulfate content, high organic matter concentrations (3.2 gTSS/L, 6.8 gBOD5/L and 14.6 gCOD/L). Moreover, the rum production is intermittent over the season (5 months per year). The acidity of this type of wastewater, combined with the relatively underbalanced nitrogen concentrations, requires the addition of specific chemicals such as soda solution and urea, when a biological treatment technology is envisioned. In this full scale experiment, located in a tropical zone (Martinique island), the objective was to demonstrate the ability of treatment chain composed of a sequencing batch reactor (SBR) followed by vertical flow treatment wetlands (VFTWs). The objective was to use VFTWs for treatment polishing as well as sludge/water separation and sludge treatment over years. The VFTWs are planted with Heliconia psittacorum and Cyperus papyrus. The monitoring occurred during three rum production seasons. The treatment chain allows an overall average removal of TSS of 92% and 96% for organic matter (COD and BOD5). The average annual load applied to the filter in operation was 32 kgTSS/m²/y, which is equivalent to 78 kgTSS/m²/y over the distillation period. The applied load was too high for the plants tested and lead to plant death and surface clogging of the filters. Nevertheless, this experiment allowed specifying the way to operate the whole treatment plant as well as acceptable daily loads that should be applied on the VFTWs. Even if the operation of the filters and the selection of plants in a tropical climate still need to be optimized, this combination of intensive and extensive processes is an effective and sustainable nature-based solution for rum distillery wastewater treatment.

Visualisation of clogging in green infrastructure growing media

ABSTRACT Growing media in green infrastructure (GI) designed for stormwater management plays a critical role in providing hydrological benefits. However, sediment deposition by urban stormwater can cause clogging and reduce the infiltration capacity. This study introduces a new approach to characterise the impact of clogging of GI that uses fluorescent tracer particles. Results are compared for two contrasting growing media: Grey to Green Substrate (G2G) and Marie Curie Substrate (MCS). Results showed that most sediment particles were retained on the surface of both growing media, and surface clogging in G2G caused a decrease in infiltration capacity. Sediment vertical movement was observed in both growing media, but particles travelled deeper in MCS. Vertical sediment movement is influenced by the growing media’s pore size distribution, and a high clogging risk is expected in growing media with a pore size distribution that is close to the particle size distribution of the incoming sediment particles.

Supporting evidences for vegetation-enhanced stormwater infiltration in bioretention systems: a comprehensive review.

Stormwater mitigation efficiency of bioretention systems relies for a large part on their capacity to infiltrate rapidly received runoff. Within this context, the primary aim of this literature review was to clarify the vegetation influences on bioretention media hydraulic conductivity, with the ultimate goal of improving guidance on plant choice for system durability. A thorough synthesis of studies dealing with the comparison of plant species, functional types, or traits on infiltration-related processes in biofilters was achieved. Overall, results converged to a positive impact of plants on water infiltration and percolation, either under greenhouse or field conditions. In most cases, vegetation selection had a determining role in maintaining initial media infiltration rates, with in terms of improvement: turfgrass < prairie grass < shrubs < trees. Wind-induced movements of rigid foliage or stems are believed to avoid complete surface clogging. Species with thick, rhizomatous or fleshy (with maximum root diameter near the centimeter range), and tap or deep root systems could be preferred to maximize infiltration rates in permeable bioretention media. In fine-textured soils, higher specific root length, root length density, or mass density could also enhance infiltration. Root mass densities (0.1-2.2kg.m3) were positively linked with infiltration rates in unlined systems while roots around 1mm diameter would favor macropore-related preferential flows and increased hydraulic conductivity. Finally, implementation of high-diversity plant communities would ensure the presence of a more functionally rich vegetation community with species possessing adequate physiological adaptations (including root system architecture) to local environmental conditions for perennial cover and proper bioretention hydrological functioning.

Vibrational classification of secondary material resources. Industrial applications

The article considers various approaches aimed to increase versatility and ensure improvement of the existing vibrational classification equipment and technology in order to achieve higher capacity, equipment utilization, and process indicators. It is shown that one of the main methods to ensure higher reliability of classification equipment (such as vibrating screens) is to improve the vibration drives. This allows obtaining a higher equipment utilization factor by increasing the net operating time under process load over long operation periods from the existing value of 0.92&ndash;0.93 up to 0.97. Capacity improvements for vibrating screens used in the processing of minerals and metal powders may be ensured through the use of screening surfaces of complex shapes, including by applying both the traditional coarse-to-fine screening sequence and the reverse fineto-coarse sequence with the use of vertical or inclined sieves. A complex screening surface arrangement was successfully implemented in the design of a vibrating screening separator for the primary sorting of municipal solid waste (MSW). With equal performance in terms of initial MSW capacity and power consumption, the proposed separator weighs 4 to 7 times less, while its sorting efficiency for the target fractions is 2&ndash;2.5 times greater than that of traditional trommels. It also eliminates film material clogging of screening surfaces, which is a typical operational disadvantage of all trommel screens.This study was carried out with the financial support of the Russian&nbsp;Science Foundation (project No. 20-79-10125).

Zero additional maintenance stormwater biofilters: from laboratory testing to field implementation

Abstract Stormwater biofilters are one of the most widely used nature-based solutions for urban water management. In the last 20 years, biofilters have been extensively studied for their pollutant removal performance; however, their application in the field is limited by high maintenance requirements. In this work, we propose the concept of zero additional maintenance (ZAM) biofilters as a solution to this challenge. To understand the design and operation of ZAM biofilters, a three-stage research programme was conducted to (i) examine filter media configurations that could protect against surface clogging, (ii) test the pollutant removal performance of a variety of lawn grasses, and (iii) validate the laboratory findings through field monitoring. The results showed that a protective filter media layer delayed the onset of clogging. Five lawn grasses – Kenda Kikuyu, Empire Zoysia, Santa Ana Couch, Village Green Kikuyu and Palmetto Soft Leaf Buffalo – were found to effectively reduce nitrogen concentrations and meet other local pollution reduction requirements. Monitoring of three field-scale ZAM biofilters confirmed their high nutrient and heavy metal removal performance. Overall, the findings of these three studies confirm the potential for well-designed ZAM biofilters to achieve stormwater management requirements with no additional maintenance compared with standard street landscaping.

Comparison between sand and clay clogging mechanisms of pervious concrete pavement

Pervious concrete (PC) pavement has been widely accepted as a green infrastructure but is prone to clogging. This study comparatively investigated sand and clay clogging mechanisms of PC and vertical sediment distributions of sand-clogged and clay-clogged PCs. Clay and three sizes of sand were used to clog PC under two exposure methods (no drying and drying). X-ray computed tomography (CT) was used to scan the clogged samples before and after 30 pressure washing cycles. The clogged permeability and permeability after each washing cycle were measured. The clogging patterns of sand depend mainly on sand particle sizes relative to PC pore sizes. The applied fine sand, coarse sand, and medium sand cause easy-passing clogging, surface clogging, and full-depth clogging, respectively. After clay clogging, more than 77% of the total retained clay occurs within the vertical region 24–72 mm below the sample surface; the most clogging (the lowest-permeability layer) occurs at a depth of approximately 48 mm. The dried clay retained within the region 40–120 mm below the surface (especially within the lowest-permeability layer) is hard to wash away because the drying process increases the cohesion of internal clay particles and clay adhesion to the rough, tortuous pore wall of PC. The clogged normalized permeability of 0.154 and permeability recovery ratio of 4.91% in dried clay-clogged samples are lowest among all the samples. However, pressure washing readily washes away the retained undried clay. Accordingly, it is recommended that pressure washing is used to eliminate the clogging effect of dried clay before hot, sunny exposure conditions dry the retained clay. This study provides evidence for developing effective pavement maintenance strategies.

Density Effect of Eisenia sp. Epigeic Earthworms on the Hydraulic Conductivity of Sand Filters for Wastewater Treatment

Inside sand filters, as inside other microporous substrates, several invertebrates create temporary burrows that impact on water movement through the filter. Lumbricids Eisenia fetida and Eisenia andrei live under a wide range of environmental conditions and have a high reproduction rate so they are good candidates for ecological engineering tests. We assessed the impact of these species at different densities (0, 100, 500, 1000 g m−2) on the hydraulic conductivity of small-sized experimental filters made of columns filled with filter sand classically used for sanitation mixed with 5% organic matter. The hydraulic conductivity was recorded every 7 days over 37 days in non-saturated conditions. On day 23, 40 g of peat bedding was added at the column surfaces to simulate a surface clogging organic matter pulse input. Columns with an earthworm density equal or superior to 500 g m−2 revealed the highest hydraulic conductivities during the first 21 days. At these densities, the hydraulic conductivity was also restored in less than 7 days after the addition of the surface organic matter, showing the influence of the earthworm species on the resilience capacity of the hydraulic conductivity. It was also highlighted that the hydraulic flow was dependent on the lumbricid densities with an optimal density/effect around 500 g m−2 in this specific substrate composition. This study showed that the feeding habits and burrowing activity of both Eisenia species significantly enhanced the hydraulic flow in a sandy substrate, providing a sustainable solution to limit the clogging of the substrate similar to the one used in filters to treat wastewater.

Experimental study of the effect of nanoscale zero-valent iron injected on the permeability of saturated porous media

Abstract In a comparison of modified nanoscale zero-valent iron (NZVI), bare NZVI used to remediate deep contaminated groundwater source areas has more advantages. However, the influence of injected bare NZVI deposition on the permeability of aquifer remains unclear, together with which are still the key factors of engineering cost and contamination removal. Hence, this study sought to assess a method of measuring hydraulic conductivity with a constant head device and to examine the permeability loss mechanism of NZVI injected into different saturated porous media, using column tests. The results showed that it was feasible to determine hydraulic conductivity by the constant head device. The permeability loss caused by NZVI injection increased with a decrease in the grain size of the porous media, and was determined by the amount and distribution of NZVI deposition. The NZVI distribution area had a good linear correlation with dispersivity of the porous media. Additionally, although surface clogging occurred in all porous media, the amount of NZVI deposition at the injection point was largest in fine sand, so that its permeability loss was the most; this was more likely to cause hydraulic fracturing and expand the area of the contaminant source zone. These results have implications for NZVI field injection for successful groundwater remediation.

Enhanced sewer self-purification with porous media: Performance evaluation with various organic loading rates and flow intermittency

Enhanced sewer self-purification is an emerging technology which supports wastewater management. To support this, we studied the removal performance of channels for enhanced sewer self-purification. Effects of organic loading rate and flow intermittency on the aerobic removal performance of biomass grown on porous sponge media were investigated. Biomass was developed until media surface clogging occurred inside two airtight channels named channel A and B, respectively. Headspace-gas oxygen consumption rates were considered as the aerobic removal performance. During surface clogging, oxygen consumption rates ranged between 12.0–16.3 gO2 m−2 d-1 for channel A fed with peptone and oleic acid and 33.2–52.4 gO2 m−2 d-1 for channel B fed with oleic acid only. The effect of flow intermittency was investigated after biomass detachment. The rates for each channel after biomass detachment were 26.6–39.7 gO2 m−2 d-1 for channel A and 78.8–88.3 gO2 m−2 d-1 for channel B. Findings highlight that even with a fully clogged surface, aerobic removal is still 63–73 % of the highest recorded rates after biomass detachment. Further, rates increased with increased organic loading rates, remained stable even with very low organic loading rate, was influenced by the type of organic substrate used, and did not significantly change with intermittent flow.

Hydrologic impacts of retrofitted low impact development in a commercial parking lot

This paired watershed study investigated the hydrologic impacts of low impact development (LID) stormwater control measures (SCMs) receiving runoff from a highly impervious, highly connected commercial parking area located in Reynoldsburg, Ohio, USA. The site was retrofitted with a bioretention cell and permeable pavement, treating 0.60 ha and 0.42 ha of the parking lot, respectively, following a 12-month monitoring period of the existing parking lot hydrology (i.e., calibration period). Monitoring continued for an additional 20 months after construction (i.e., treatment period). The bioretention cell significantly reduced runoff depths and peak flow rates from the catchment, reducing mean values by 83% and 86%, respectively. Subsurface infrastructure (i.e., a gravel trench enclosing an adjacent sewer pipe and a nearby curb drain) was suspected to provide preferential pathways which resulted in substantial exfiltration from the cell despite poorly infiltrating underlying soils. Conversely, no significant differences in catchment hydrology were observed following the installation of the permeable pavement. The median surface infiltration rate decreased by 96% during the study, indicating that surface clogging occurred in the upper layers of the permeable pavement. Clogging was attributed to concentrated sediment loading delivered from the impervious catchment, along with lack of routine maintenance and snow plowing activities. It was concluded the loading ratio (27.6:1) of the permeable pavement was much too high, and this level of run-on should be avoided in future retrofits. Despite this, the combined effects of the bioretention cell and the permeable pavement led to significant runoff mitigation from the parking lot, reducing both runoff depths (47%) and peak flow rates (56%). Results were similar to previous studies of LID implemented in commercial catchments with lower levels of directly connected impervious cover than those herein. This study demonstrates the effectiveness of SCMs in highly impervious, highly connected catchments and their ability to mitigate runoff in commercial settings when properly sized and maintained.

Promoting Lithium Electrodeposition Towards the Bottom of 3-D Copper Meshes in Lithium-Based Batteries

Lithium (Li) has been considered as the promising negative electrode in rechargeable batteries, owing to the negative redox potential (-3.04 V vs. SHE), low density (0.534 g/cm3), and high theoretical specific capacity (3,860 mAh/g). However, the non-uniform stripping/plating process of the metallic Li is still challenging.[1] As one of the solutions, three-dimensional (3-D) metallic scaffolds were introduced to the negative electrode. The uniform electric field applied in the porous scaffolds could suppress the dendritic growth of the Li during the plating process. In addition, a decrease in the effective current density prolonged Sand’s time.[2] However, such a Li deposition mainly proceeded on the top surface and led to rapid surface clogging due to the strong surface electric field. In this presentation, we show the preferred Li deposition inside the 3-D copper (Cu) scaffold using gold nanoparticles (Au NPs). The lower Li nucleation energy barrier on the Au surface than that on the typical Cu current collector was investigated intensively.[3] However, the role of Au for spatially promoting Li deposition was not studied in depth. We added the Au NPs with an average particle size of ~7.5 nm to the bottom of 3-D Cu. The Au NPs with a total ~28 nmol reduced the charge-transfer resistance, which suggested the fast Li nucleation on the Au. In addition, we coated aluminum oxide (Al2O3) layer with ~ 26 nm of thickness on the top surface of 3-D Cu scaffold through the atomic layer deposition (ALD) process. This insulating layer further suppressed the Li deposition on the surface. As a result, apparent Li deposition towards the bottom of 3-D Cu was clearly demonstrated. During Li plating/stripping cycles, the surface clogging of the 3-D Cu/Au by an accumulation of solid electrolyte interphase (SEI) was also dramatically alleviated even in the absence of Al2O3 layer. It demonstrated the continuous Li deposition towards the bottom of the 3-D Cu/Au scaffold. Besides, symmetric 3-D Cu/Au cells exhibited over 95 % of Coulombic efficiency (CE) for ~120 cycles. The full cells comprised of the 3-D Cu/Au and LiFePO4 (LFP) electrodes delivered stable 300 cycles with a capacity of ~140 mAh/g at 1 C-rate. I will discuss the detailed role of the Au NPs and the Al2O3 layer, and comparative cell performances in the presentation.

Effect of nanohydroxyapatite on surface mineralization in acid-etched dentinal tubules and adsorption of lead ions

To study the effect of nanohydroxyapatite (nHA) for promoting surface mineralization of demineralized dentin discs and adsorption of lead ions in simulated sewage water. Sixty dentin disks were prepared from freshly extracted teeth with intact crown (including 30 premolars and 30 molars) and treated with 10% citric acid for 2 min to simulate dentinal tubules with dentin hypersensitivity. The etched dentin discs were brushed with distilled water, 0.2 g HA or 0.2 g nHA for 2 min twice a day for 7 consecutive days, after which scanning electron microscopy (SEM) was performed and calcium and phosphorus contents in the dentin discs were detected using EDS. Lead ion adsorption capacities of HA and nHA were tested by mixing 1 mL serial concentrations of HA and nHA suspensions with 50 mL lead ion solutions (1.0 mg/L). After 24 h, the residual lead ion concentration in the supernatant was measured using ICP to calculate lead ion adsorption rate and adsorption capacity of the materials. SEM showed a smooth surface and empty dentin tubules in the acid- etched dentin dics. The dentin dics treated with HA were covered with masses of particles that loosely attached to the surface, and the diameter of the dentin tubules was reduced. In nHA group, the dentin discs showed a fine and homogeneous surface clogging with a tight attachment, and the dentin tubule diameter was obviously reduced. Daily brushing with HA and nHA, especially the latter, significantly increased calcium and phosphorus contents on the surface of the dentin dics (P < 0.000). In lead ion adsorption experiment, the lead ion adsorption rate of HA decreased as its concentration increased with the highest adsorption rate of 83.01%; the adsorption rate of nHA increased with its concentration until the adsorption equilibrium was reached, and its highest adsorption rate was 98.79%. A good liner relationship was found between the adsorption ability and concentration of HA. Compared with HA, nHA has a better capacity for surface mineralization of acid-etched dentin discs and also a better ability of lead ion adsorption.

Investigation of Pellet Properties Produced from a Mix of Straw and Paper Sludge

Global energy consumption is increasing every year, and, despite their many negative impacts, fossil fuels are a major source of energy, but their reserves are gradually depleting. One of the promising but underutilized resources is plant biomass (phytomass). The main problem of plant biomass combustion is the low melting temperature of ash, but there are also problems with corrosion of heat exchangers and clogging of heat-exchanging surfaces. This work is concerned with the production of straw pellets in order to increase the melting temperature of ash by adding an additive. The paper sludge contains substances that can increase the melting point of ash and was therefore added to the pellet samples. This additive was mixed with straw in ratios from 90:10, 80:20 and 70:30 (straw/paper sludge). The use of paper sludge showed positive effects on increasing the melting temperature of the ash samples. The deformation temperature of the ash has already risen from 1020 to 1260 °C after the addition of 10% sludge, which is comparable to wood pellets.

Hybrid Effect Study of Pad-Conditioning/Slurry-Supply by High-Pressure-Micro-Jet (HPMJ) Method during CMP Process

Surface clogging of polishing pad is inevitable during CMP (Chemical Mechanical Polishing) process of semiconductor wafers. In this paper, a novel slurry-feeding system utilizing HPMJ (High Pressure Micro Jet) apparatus was presented as in situ conditioning for CMP process. Clogging of pad surface can be greatly removed; the surface damage of polishing pad can also be extremely reduced by this new method. The experimental results exhibited that the material remove rate (MRR) of HPMJ method was almost constant value 100 μm h−1. However, the MRR value of conventional slurry-dripping method was about 50 μm h−1. On the other hand, surface roughness Ra changed both in hybrid HPMJ method and conventional slurry-dripping method after long-time continuous CMP process, the average Ra of hybrid HPMJ method was about 30% smaller than that of conventional slurry-dripping method, indicating that better surface quality could be obtained by HPMJ method polishing. It was demonstrated that HPMJ method showed higher MRR and lower surface roughness Ra for polishing process. HPMJ hybrid system mentioned in this study can also be applied to the polishing process of hard-to-process wide bandgap semiconductor substrate materials, such as SiC or GaN.