With the increasing demands on water supplies and tighter regulations, much research is being performed water treatment processes. Subjects of study include improving processes to allow treated water to be used in secondary applications, optimizing filtration processes to remove biological contaminants and reduce membrane fouling, monitoring filter breakthrough to minimize maintenance requirements or contamination, and verifying ability to remove the increasing load of nano-particulates in the waste water stream. Due to the massive quantities processed, even small improvements in process performance and efficiency have a large impact on resulting water quality and energy consumption. Numerous technologies exist for monitoring particle size and concentration in the micron size range, but Nanoparticle Tracking Analysis (NTA) is a unique technology that provides greater insight into the sub-micron size range that is so important to many of these advanced water treatment processes.
Detecting and Counting Particles
Both Dynamic Light Scattering (DLS) and NTA measure the Brownian motion of nanoparticles whose speed of motion, or diffusion coefficient (Dt), is related to particle size through the Stokes-Einstein equation. In NTA, laser light scatters from particles in suspension and a video camera captures the images of those particles moving under Brownian motion. By tracking and quantifying the particles’ diffusion, the particle diameter can be determined through the Stokes-Einstein equation. The direct view of the sample also allows visual inspection for an additional qualitative confirmation. [1,2]Qualifying Filtration Processes
Ling et al [3] have used NTA to measure particle (50–500 nm) concentration upstream and downstream of a filter in order to determine the filtration efficiency of a model membrane filter for application in the purification and disinfection of drinking water and also the removal of nanoparticles from highly pure chemicals used in industry. NTA measurements were found to be reliable within a certain concentration limit (about 108 –1010 particles/mL) and that experimental results were comparable with previously published data obtained using an aerosolization method, thus validating the capability of the NTA technique. Microfiltration (MF) can serve as a pre-treatment for other processes like ultrafiltration, or as a post-treatment for granular media filtration. Qualifying and monitoring the performance of a filtration process is important for optimizing process conditions. One large scale application is for waste water or drinking water treatment. Subsequent stages of treatment can remove the finer sizes, such as virus and engineered nanoparticles, finally yielding only dissolved materials. Processes include microfiltration (MF), reverse osmosis (RO), and ultraviolet (UV) treatment. The following example shows the progressively lower concentrations (y axis) and generally reducing size of the peak. Microfiltration proved very effective at removing particles in the 10’s to 100’s of nanometer range. RO removed most of the remainder. After UV treatment, there were essentially no particles visible to the NTA technique. The rinse of the RO filter showed progressively higher concentrations of background material, but particles were below the NTA detection limit. Other tests showed a slight increase in total bacteria concentration across these same samples and a definite increase of total protein and carbohydrates. >> Download the full Application Note as PDFMalvern provides the materials and biophysical characterization technology and expertise that enables scientists and engineers to investigate, understand and control the properties of dispersed systems. These systems range from proteins and polymers in solution, particle and nanoparticle suspensions and emulsions, through to sprays and aerosols, industrial bulk powders and high concentration slurries. Used at all stages of research, development and manufacturing, Malvern’s instruments provide critical information that helps accelerate research and product development, enhance and maintain product quality and optimize process efficiency. Our products reflect Malvern’s drive to exploit the latest technological innovations. They are used by both industry and academia, in sectors ranging from pharmaceuticals and biopharmaceuticals to bulk chemicals, cement, plastics and polymers, energy and the environment. Malvern systems are used to measure particle size, particle shape, zeta potential, protein charge, molecular weight, mass, size and conformation, rheological properties and for chemical identification, advancing the understanding of dispersed systems across many different industries and applications. www.malvern.com Material relationships http://www.malvern.com/en/ [email protected]
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