Micron-pore-sized metallic filter tube membranes for filtration of particulates and water purification

Multi-Scale Polyimide/Carbon Fibers Hybrid Filters for Hot Gas Filtration

Increasing air pollution caused mainly by exhaust emission has become a serious concern for public health. In order to efficiently control the exhaust emission from the origin, hot gas filtration is required in many industries, such as thermal power regeneration, metal refining/recycling, and biomass/coal gasification. This study aimed to develop a hybrid filter composed with ultrafine fibrous polyimide (PI) filtration layers and carbon woven fabric supporting layers for hot gas filtration. Uniform PI ultrafine fibers around 200 nm with small pores about 2.2 μm were electrospun on carbon fabrics supporting layers to serve as the filtration layer. During filtration test, NaCl aerosols (0.3 mm), which mimicked PM 2.5 particles were accumulated on the top of filtration layer and formed dust cake, but limited aerosols were observed on the carbon fabric supporting layers. It was proved that PI fiber mats played the key role in filtration. The filtration efficiency could be maintained above 95% after 9 min and reached 99.4 %. This research proved that the multi-scale polyimide/carbon fibers hybrid filters possessed the potential to serve as filtration media in bag filters for hot gas filtration.

Improved measurement for volatile particles: vapor-particle separator design and laboratory tests

Sampling and measurement of volatile particles is a challenging task. It has been hampered by lack of a reliable technique capable of accurately capturing the phase-partition process of the pollutants without generating bias and artifacts in the data. The objective of this research is to design a new vapor-particle separation technique for performing the phase separation on-line (the sampling aspect), which, simultaneously, enables characterization of the vapors and particles. The new vapor-particle separator (VPS) consists of a thin metallic microporous membrane for (1) extraction of vapor molecules that are thermally desorbed from the condensed particulate phases and (2) collection of the vapors for subsequent chemical analysis. We evaluated this new separator using synthetic particles made of nonvolatile and or semi-volatile chemicals, and reported the laboratory test results in this paper. The laboratory particle test results showed reasonably high particle transmission efficiency across all particle sizes. The thermal dynamics of nanoparticles was succinctly observed on-line. The results successfully demonstrated the ability of VPS to separate particles and vapors thus enabling a faithful observation of the thermal behavior. We believe the new technology will make a great contribution to the measurement of volatile particles.

Concentration and detection of Salmonella in mung bean sprout spent irrigation water by use of tangential flow filtration coupled with an amperometric flowthrough enzyme-linked immunosorbent assay

The development of a culture-free method for Salmonella screening of spent irrigation water derived from sprouting mung bean beds is described. The system used tangential flow filtration (TFF) to nonspecifically concentrate cells from large (2- to 10-liter) sample volumes. The retentate (100 ml) from the TFF was then flowed over an anti-Salmonella antibody-modified cellulose acetate membrane. The captured Salmonella was detected by reacting with a secondary anti-Salmonella and goat anti-rabbit biotin labeled antibody, followed by avidin-tagged glucose oxidase. The hydrogen peroxide generated from the enzymic oxidation of glucose was amperometrically detected at an underlying platinum electrode. It was found that 10 liters of Salmonella suspensions of 2 log CFU/ml could be concentrated to 4 log CFU/ml with 60% recovery regardless of the flow rate (112 to 511 ml/min) or transmembrane pressure (0 to 20 lb/in2) applied. The solids content of spent irrigation water negatively affected the filtration rate of TFE. This was most evident in spent irrigation water collected in the initial 24 h of the sprouting period, where the solids content was high (4,170 mg/liter) compared with samples collected at 96 h (560 mg/ liter). Trials were performed using mung bean beds inoculated with different Salmonella levels (1.3 to 3.3 log CFU/g). By using the optimized TFF and flowthrough immunoassay it was possible to detect Salmonella in spent irrigation water at levels of 2.43 log CFU/ml within 4 h. The integrated concentration and detection system will provide a useful tool for sprout producers to perform in-house pathogen screening of spent irrigation water.