The effect of filter pore size on the evaluation of aluminum coagulants to remove fulvic acid from water

Evaluation of aluminum coagulants to remove fulvic acid from water depends on the process of separating the precipitate from the liquid phase. Membrane filters are often used for this purpose. The degree of separation was found to depend on the filter pore size. Differences in removal efficiencies of up to 80% were observed when membrane filters with pore sizes of 0.45 and 0.10 μm were used for the solid-liquid separation. Membrane filters with a pore size of 0.45 μm under certain experimental conditions demonstrated deep-filter characteristics in the sense that in the initial steps of filtration, when the filter was clean, small particles were filtered through, but as the filter pores became clogged, the efficiency of the filter improved.     

Fabrication of a multi-walled carbon nanotube-deposited glass fiber air filter for the enhancement of nano and submicron aerosol particle filtration and additional antibacterial efficacy

We grew multi-walled carbon nanotubes (MWCNTs) on a glass fiber air filter using thermal chemical vapor deposition (CVD) after the filter was catalytically activated with a spark discharge. After the CNT deposition, filtration and antibacterial tests were performed with the filters. Potassium chloride (KCl) particles (< 1 μm) were used as the test aerosol particles, and their number concentration was measured using a scanning mobility particle sizer. Antibacterial tests were performed using the colony counting method, and Escherichia coli (E. coli) was used as the test bacteria. The results showed that the CNT deposition increased the filtration efficiency of nano and submicron-sized particles, but did not increase the pressure drop across the filter. When a pristine glass fiber filter that had no CNTs was used, the particle filtration efficiencies at particle sizes under 30 nm and near 500 nm were 48.5% and 46.8%, respectively. However, the efficiencies increased to 64.3% and 60.2%, respectively, when the CNT-deposited filter was used. The reduction in the number of viable cells was determined by counting the colony forming units (CFU) of each test filter after contact with the cells. The pristine glass fiber filter was used as a control, and 83.7% of the E. coli were inactivated on the CNT-deposited filter.     

Dechlorination of trichloroethylene by Ni/Fe nanoparticles immobilized in PEG/PVDF and PEG/nylon 66 membranes

The highly reactive bimetallic Fe/Ni nanoparticles immobilized in nylon 66 and PVDF membranes were synthesized and characterized for dechlorination of trichloroethylene (TCE) under anoxic conditions. Scanning electron microscopy (SEM) images and electron probe microanalysis (EPMA) elemental maps showed that the distribution of Fe in nylon 66 membrane was uniform and the intensity of Ni layer was higher than that in PVDF membrane. The particle sizes of bimetallic Fe/Ni in PVDF and nylon 66 membranes were 81 ± 12 and 55 ± 14 nm with the Ni layers of 12 ± 3 and 15 ± 2 nm, respectively. Low agglomeration of immobilized Fe/Ni nanoparticles in nylon 66 membrane was observed, presumably attributed to the more multifunctional chelating groups in membrane. A rapid hydrodechlorination of TCE with ethane as the main end product was observed by the immobilized Fe/Ni nanoparticles. The pseudo-first-order rate constants for TCE dechlorination were 6.44 ± 0.32 and 1.66 ± 0.08 h⁻¹ for nylon 66 and PVDF membranes, respectively. In addition, the efficiency and rate of TCE dechlorination increased upon increasing the mass loading of Ni, ranging between 2.5 and 20 wt%, and then decreased when further increased the Ni loading to 25 wt%. In addition, the stability and longevity of the immobilized Fe/Ni nanoparticles was evaluated by repeatedly injecting TCE into the solutions. A rapid and complete dechlorination of TCE by trace amounts of Fe/Ni nanoparticles was observed after 16 cycles of injection within 10 days, indicating that the immobilization of Fe/Ni nanoparticles in the hydrophilic nylon 66 membrane can retain the longevity and high reactivity of nanoparticles towards TCE dechlorination.     

GB/T6165-2008计数法与国际现行标准化测试方法的实验比较

以过滤元件最易透过粒径(MPPS)效率为评价基准,进行了比较评估.介绍了参考过滤器的主要性能参数及测试过程主要参数.评估结果表明,新版国家标准中的计数法与现行美国标准接近,相比于现行的欧洲及日本标准,更接近于MPPS基准效率,可满足国际市场的要求.     

Vapor adsorption characteristics of toluene in an activated carbon adsorbent-loaded nonwoven fabric media for chemical filters applied to cleanrooms

Chemical filters are used extensively in the cleanrooms of the semiconductor factories to remove airborne molecular contamination (AMC). Adsorption by activated carbons (AC) as media within the chemical filter is one of the practical methods for removal of gaseous contamination in a cleanroom. The objective of this study is to evaluate coconut shell activated carbon adsorbent-loaded nonwoven fabric media performance by determining the breakthrough curves, the linear driving force (LDF), the intra-particle diffusion characteristics, the empty bed contact time (EBCT) and the bed depth service time (BDST), the mass-transfer zone (MTZ), and pressure drop. The testing conditions were maintained at 28 ± 1 °C, and relative humidity at 40 ± 2% with face velocities of 0.076, 0.114 and 0.152 m/s for removal efficiency and capacity determination. The challenge gas concentrations of toluene were fixed at 10, 31, 42 and 70 ppm to accelerate the breakthrough of media adsorption. The concentrations were measured by a real-time photoionization detector. Results showed that breakthrough curves correlate to the challenge vapor concentration and the face velocity. Saturated adsorption ratio was increased with raised challenge gas concentration and increased face velocity significantly.     

Comparative performance of membrane filters vs. high-surface area filtration cartridges for the determination of element concentrations in freshwater systems

Interdisciplinary studies on trace element cycles in aquatic environments may require the simultaneous use of small- and large-scale filtration devices to collect all the necessary sample aliquots for the different scientific objectives (e.g. trace element and organic carbon analysis, chronic toxicity testing, and characterization of colloidal matter). This study compares the performance of membrane filters (MF, Millipore-approx. surface area 0.002 m2) and two large-surface area filtration cartridges (Calyx, MSI and Polypro, CUNO approx. surface area 1 m2) in three freshwater systems with contrasting characteristics. Membrane filters and filtration cartridges fractionate water samples in a comparable way except for some elements (Al, Mn, Pb, and Ti) and when dealing with high-turbidity, organic-rich matrices. Estimation of the actual filters' pore size using the single particle counting technique gives cut-offs of 0.2-0.3, 0.7 and 2 microm for membrane filters, Polypro cartridge and Calyx cartridge respectively, explaining many of the differences observed between membrane and cartridge filters. Direct involvement of filter manufacturers to determine actual filter cut-offs during environmental applications would be highly beneficial to increase the comparability of the measurements of filterable element concentrations. Better harmonization of filtration procedures (filter type, actual filter cut-off, in situ vs. ex situ filtration) among laboratories in different countries is also necessary in order to improve consistency of environmental databases.     

On the use of filters for distinguishing between dissolved and particulate fractions in natural waters

The influence of filtration on the colloid content of a natural sample as a function of filter load has been studied. Two membrane filters and one glass fibre filter commonly used for the filtration of natural samples have been tested.Membrane filters are shown to be unsuitable for the separation of suspended matter unless the effects of filter load are studied. The importance of the colloidal particles passing normal filters in interpreting the transport of trace metals in the environment is stressed.     

Using phosphoric acid-impregnated activated carbon to improve the efficiency of chemical filters for the removal of airborne molecular contaminants (AMCs) in the make-up air unit (MAU) of a cleanroom

A coconut shell activated carbon precursor was modified by impregnation with phosphoric acid. The effects of the particle diameter of the impregnated activated carbons (IACs) on the thickness, pressure resistance, and face velocity of a chemical filter were investigated. Furthermore, volatile organic compounds (VOCs) adsorption experiments were carried out to determine the relationship between the removal efficiency and the chemical properties of the adsorbents. The effects of various parameters such as challenge gas concentration, saturated adsorption ratio, impregnation method and impregnant contents were investigated. The results showed that the effect of face velocity on pressure resistance is larger than that of the thickness, that 0.25 M phosphoric acid impregnation of activated carbon can raise VOC removal efficiency by 2–3% (toluene: from 95.8% to 98.1%, isopropanol: from 95.2 to 97.2%), and that the optimal impregnation time is around 1.5 h. A simple shaking impregnation method exhibited better performance than the ultrasonic method.     

Ultrafine particle removal by residential heating,ventilating, and air‐conditioning filters

This work uses an in situ filter test method to measure the size‐resolved removal efficiency of indoor‐generated ultrafine particles (approximately 7–100 nm) for six new commercially available filters installed in a recirculating heating, ventilating, and air‐conditioning (HVAC) system in an unoccupied test house. The fibrous HVAC filters were previously rated by the manufacturers according to ASHRAE Standard 52.2 and ranged from shallow (2.5 cm) fiberglass panel filters (MERV 4) to deep‐bed (12.7 cm) electrostatically charged synthetic media filters (MERV 16). Measured removal efficiency ranged from 0 to 10% for most ultrafine particles (UFP) sizes with the lowest rated filters (MERV 4 and 6) to 60–80% for most UFP sizes with the highest rated filter (MERV 16). The deeper bed filters generally achieved higher removal efficiencies than the panel filters, while maintaining a low pressure drop and higher airflow rate in the operating HVAC system. Assuming constant efficiency, a modeling effort using these measured values for new filters and other inputs from real buildings shows that MERV 13–16 filters could reduce the indoor proportion of outdoor UFPs (in the absence of indoor sources) by as much as a factor of 2–3 in a typical single‐family residence relative to the lowest efficiency filters, depending in part on particle size.     

Particle Ripening, Removal and Breakthrough in Drinking-Water Filtration: Implications for the Capture of Cryptosporidium and Giardia Cysts

An increasing number of reported outbreaks of Cryptosporidiosis, associated with the water supply, have led to an upsurge in interest in particle analysis in drinkingwater treatment. This paper describes recent observations of rapid-gravity filter performance using particle-size distribution analysis. Experimental rapid sand filters were constructed and operated using a suspension of PVC particles, and samples for particle analysis were collected at several depths and various times during the filter cycle. Ripening and early breakthrough of Cryptosporidium oocyst size particles were observed during the study, and 1 β particles exhibited the worst capture efficiency. Flow disturbances were found to reduce particle-capture efficiency including Cryptosporidium and Giardia cyst sizes.     

Quantitative filter forensics: Size distribution and particulate matter concentrations in residential buildings

We applied filter forensics, the analysis of dust from the heating, ventilation, and air-conditioning (HVAC) filters, to measure particle size distribution in 21 residences in Toronto, Canada over a year. Four filters with different nominal efficiencies (Minimum Efficiency Reporting Value (MERV) 8–14 from ASHRAE Standard 52.2) were deployed in each residence each for three months, while the effective filtration volumes (the product of flow rate, runtime, and in-situ filter efficiency) were characterized over each filter lifetime. Using extraction and laser diffraction, we found that approximately 90% of the volumetric distributions were >10 µm and the volume median diameter (VMD) ranged from 23.4 to 75.1 µm. Using quantitative filter forensics (QFF), total suspended particle (TSP) concentrations ranged from 2.9 to 823.7 µg/m³ (median = 89.8 µg/m³) with a moderate correlation with the content of TSP on the filters (in terms of g) and with the TSP effective filtration volume (m³) indicating the importance of both filter forensics and HVAC metadata parameters to QFF concentration estimates. There was no strong correlation between PM₁₀ or PM_2.5 concentrations and hourly airborne particle number concentrations measured by low-cost sensors suggesting an evaluation of QFF is warranted, particularly for the exploration of smaller particles.     

颗粒物尺度对滤料过滤性能的影响

介绍了不同学者对滤料过滤机理的研究结果,实验研究了颗粒物尺度对粗、中、高效滤料过滤效率和过滤阻力的影响,对合理选择空调系统过滤材料提出了建议。     

Effects of particle size on flame spread over magnesium powder layer

The spreading of a flame over a layer of magnesium powder has been examined to clarify the mechanisms of flame spread over metal powder layers and to establish effective ways to extinguish metal fires. Four grades of magnesium powder were used, with average grain diameters of 60, 170, 360 and 500 μm. The flame spread rate for larger particle sizes (D>170 μm) increased slightly with increasing particle size. However, the flame spread rate for smaller particle sizes (D<63 μm) increased sharply. The detailed surface temperature history of the magnesium powder layer was measured using infrared thermography (IR). Based on the temperature distribution in the pre-heat zone, the characteristic length l, characteristic depth δ, and characteristic time τ were calculated. The characteristic scale ratio, L/δ, for the larger particle sizes (D>170 μm) is almost unity, which suggests that the dominant heat transfer mechanism is heat conduction through the magnesium powder layer (solid phase). However, the L/δ for the smaller particle sizes (D<63 μm) is about 2.7, suggesting that the dominant heat transfer mechanism is convection. The flame spread rate over the magnesium powder layer was calculated by the de Ris model, a one-dimensional flame spread model, and a surface flash model. For larger particle sizes (D>170 μm), there is good agreement between the experimental flame spread rate and the flame spread rate estimated by the one-dimensional model. However, the flame spread rate was underestimated by the de Ris model, apparently because the de Ris model only considers heat feedback from the gas phase. For small-particle sizes (D<63 μm), there is good agreement between the experimental flame spread rate and the flame spread rate estimated by the surface flash model. This suggests that the flame spread over a small-particle layer can be described by a mechanism rather similar to that of gas phase flame propagation.     

Bacterial treatment effectiveness of point-of-use ceramic water filters

Laboratory experiments were conducted on six point-of-use (POU) ceramic water filters that were manufactured in Nicaragua; two filters were used by families for ca. 4 years and the other filters had limited prior use in our lab. Water spiked with ca. 10⁶ CFU/mL of Escherichia coli was dosed to the filters. Initial disinfection efficiencies ranged from 3 - 4.5 log, but the treatment efficiency decreased with subsequent batches of spiked water. Silver concentrations in the effluent water ranged from 0.04 - 1.75 ppb. Subsequent experiments that utilized feed water without a bacterial spike yielded 10³-10⁵ CFU/mL bacteria in the effluent. Immediately after recoating four of the filters with a colloidal silver solution, the effluent silver concentrations increased to 36 - 45 ppb and bacterial disinfection efficiencies were 3.8-4.5 log. The treatment effectiveness decreased to 0.2 - 2.5 log after loading multiple batches of highly contaminated water. In subsequent loading of clean water, the effluent water contained <20-41 CFU/mL in two of the filters. This indicates that the silver had some benefit to reducing bacterial contamination by the filter. In general these POU filters were found to be effective, but showed loss of effectiveness with time and indicated a release of microbes into subsequent volumes of water passed through the system.     

Effect of temperature on carbon nanoparticle collection efficiency using photoelectric ESP

The electrostatic precipitator (ESP) technique is a promising method for enhancing the particulate matter (PM) emission reduction efficiency of diesel engines, and is much better than the diesel particulate filter (DPF) technique. However, the ESP's low efficiency in collecting PM with diameters less than several tens of nanometers remains a problem because the particle charging efficiency decreases as the size of the nanoparticles decreases. To improve the collection efficiency of nanosized PM, we used a photoelectric charger to increase the charging efficiency of nanoparticles ahead of the ESP system. Carbon nanoparticles produced using a spark discharge generator were used to evaluate the collection efficiency of the combined photoelectric charger and ESP system. The particle sizes were measured using a scanning mobility particle sizer system at various experimental temperatures similar to the temperature of DPF systems commonly used in diesel engines. We succeeded in obtaining improved collection efficiencies at increased inner temperatures of the photoelectric charging chamber. As the temperature increased from 694 °C to 839 °C at the inlet of the photoelectric chamber, the efficiency of PM collection improved significantly to 28.5% for a particle diameter of 18.4 nm.     

Pilot-scale investigation on the removal of organic foulants in secondary effluent by slow sand filtration prior to ultrafiltration

Natural biofiltration processes have been verified as effective pre-treatment choice improving the performance of low-pressure membranes (MF/UF) in wastewater reclamation. In the present work, pilot-scale slow sand filtration (SSF) was used to simulate bank filtration at high filtration rates (from 0.25 m/h to 0.5 m/h) to filter secondary effluent prior to UF. The results showed that SSF improved the performance of UF to a large extent. Related to previous work biopolymers are considered as major dissolved organic foulants in treated wastewater. The removal of these organic foulants in slow sand filters and factors affecting the performance of SSF were investigated. It was observed that the removal of biopolymers took place mainly at the upper sand layer and was related to biological degradation. Tests on the degradability of biopolymers verified that they are biodegradable. Sixteen months monitoring of biopolymer concentration in the secondary effluent indicated that it varied seasonally. In winter season the concentration was much higher than during the summer months. Higher temperature and lower biopolymer concentration led to more effective foulants removal and more sustainable operation of SSF. During the whole experimental period, the performance of SSF was always better at filtration rate of 0.25 m/h than at 0.5 m/h. Under the present experimental conditions, SSF exhibited stable and effective biopolymer removal at temperatures higher than 15 °C, at biopolymer concentrations lower than 0.5 mg C/L and with sufficient oxygen available.     

Removal of diatrizoate with catalytically active membranes incorporating microbially produced palladium nanoparticles

There is an increasing concern about the fate of iodinated contrast media (ICM) in the environment. Limited removal efficiencies of currently applied techniques such as advanced oxidation processes require more performant strategies. The aim of this study was to establish an innovative degradation process for diatrizoate, a highly recalcitrant ICM, by using biogenic Pd nanoparticles as free suspension or immobilized in polyvinylidene fluoride (PVDF) and polysulfone (PSf) membranes. As measured by HPLC-UV, the removal of 20 mg L⁻¹ diatrizoate by a 10 mg L⁻¹ Pd suspension was completed after 4 h at a pH of 10. LC-MS analysis provided evidence for the sequential hydrodeiodination of diatrizoate. Pd did not lose its activity after incorporation in the PVDF and PSf matrix and the highest activity (k_cat = 30.0 ± 0.4 h⁻¹ L g⁻¹ Pd) was obtained with a casting solution of 10% PSf and 500 mg L⁻¹ Pd. Subsequently, water containing 20 mg L⁻¹ diatrizoate was treated in a membrane contactor, in which the water was supplied at one side of the membrane while hydrogen was provided at the other side. In a fed batch configuration, a removal efficiency of 77% after a time period of 48 h was obtained. This work showed that membrane contactors with encapsulated biogenic nanoparticles can be instrumental for treatment of water contaminated with diatrizoate.     

Chitosan and metal salt coagulant impacts on Cryptosporidium and microsphere removal by filtration

Maintenance of appropriate chemical pretreatment is a critical component of ensuring proper filtration performance. Pilot-scale in-line filtration studies were performed to investigate the relative impacts of chitosan, alum, and FeCl₃ coagulation on the removal of Cryptosporidium parvum oocysts and oocyst-sized polystyrene microspheres by granular media filtration. Similar removals of oocysts and microspheres were achieved when optimal coagulant doses were utilized. Sub-optimal alum and FeCl₃ coagulation resulted in a deterioration filter effluent turbidity (0.2-0.3 NTU) and total particle counts (30-100 total particles ≥2 μm/mL) that were accompanied by reduced (by ∼2-3-log) median oocyst and microsphere removals by filtration. At all doses investigated, chitosan coagulation resulted in excellent turbidity and particle reductions by filtration. Nonetheless, chitosan coagulation at doses of 0.1, 0.5, and 1.0 mg/L did not result in appreciable improvements in C. parvum oocyst removal relative to complete coagulation failure (median oocyst removals were <∼1-log). As well, oocyst-sized polystyrene microspheres appear to be reasonable indicators of C. parvum oocyst removal by in-line filtration preceded by alum and FeCl₃ coagulation, but not chitosan coagulation.     

聚四氟乙烯覆膜滤料的发展及应用特点

本文主要介绍了聚四氟乙烯覆膜滤料的发展过程,分析了聚四氟乙烯覆膜滤料表面过滤的除尘机理。通过与传统滤料相比,说明了覆膜滤料的优越性,并指出覆膜滤料具有除尘效率高、排放浓度低、运行阻力小、过滤速度高、使用寿命长和运行费用省等特点。最后介绍了覆膜滤料在水泥工业中的应用。     

Novel membrane bioreactor (MBR) coupled with a nonwoven fabric filter for household wastewater treatment

Conventional and modified membrane bioreactors (MBRs) are increasingly used in small-scale wastewater treatment. However, their widespread applications are hindered by their relatively high cost and operational complexity. In this study, we investigate a new concept of wastewater treatment using a nonwoven fabric filter bag (NFFB) as the membrane bioreactor. Activated sludge is charged in the nonwoven fabric filter bag and membrane filtration via the fabric is achieved under gravity flow without a suction pump. This study found that the biofilm layer formed inside the NFFB achieved 10 mg/L of suspended solids in the permeate within 20 min of initial operation. The dynamic biofilter layer showed good filterability and the specific membrane resistance consisted of 0.3-1.9 × 10¹² m/kg. Due to the low F/M ratio (0.04-0.10 kg BOD₅/m³/d) and the resultant low sludge yield, the reactor was operated without forming excess sludge. Although the reactor provided aerobic conditions, denitrification occurred in the biofilm layer to recover the alkalinity, thereby eliminating the need to supplement the alkalinity. This study indicates that the NFFB system provides a high potential of effective wastewater treatment with simple operation at reduced cost, and hence offer an attractive solution for widespread use in rural and sparsely populated areas.