Ayush Agrawal
Did you know that our many day-to-day items like personal care products, textiles, kitchenware, paints and sporting goods contain nanoparticles? Did you know that nanomaterials are also extensively used in energy applications ranging from batteries and fuel cells to catalysis for improving process efficiency? The presence of engineered nanoparticles in everyday products has exponentially increased in recent years. In addition to carbonaceous nanoparticles, silver nanoparticles, and oxides of titanium, silicon, zinc, iron and aluminum are the most commonly found engineered nano-objects. At nanoscale, these engineered materials offer many unique properties that differ from bulk and dissolved counterparts. Over the last 15-20 years, production of engineered nanoparticles have increased from thousands of kilograms to thousands of tons. If something sounds too good to be true, then it probably is! The increased usage of engineered nanoparticles has led to increased amount of nanoparticles being discharged in waste streams of both industry and household. Moreover, growing usage of nanoparticles in process industry as catalysts, additives, adsorbents etc., has led to heavy discharge of nanosized mineral particles in the waste treatment sludge. Therefore, proper analytical tools and methods to understand the behavior and fate of these nanoparticles from both energy and environmental perspectives is needed.
The way things are right now, it is quite a standard procedure to analyze and characterize these engineered nanoparticles when they are in pristine and concentrated form during production. However, things get much more difficult when these are released into the environment! These nanoparticles are not only in very low concentration, but also mixed with other material. Therefore, we need to find a way to accurately measure and quantify these particles in environmental concentration, which can be as low as parts per billion. To give you an idea, it is like finding something the size of a single tennis ball on planet Earth. A detailed knowledge of all the processes involved in release, transformation and partitioning of key species into different chemical and physical forms becomes necessary for the development of after-treatment processes and control measures regarding the waste disposal. In Switzerland, in 2019, about 3.6 Millions tones were combusted in waste incinerators. Other thermal treatment facilities such as wood and sludge combustion plants are also substantial waste and pollution sources. Guidelines for the handling, treatment and disposal of waste, and for gas and particle emission can only be achieved owing the further developing of the treatment and after-treatment technologies, improving the capabilities and the lifetime of the used cleaning systems to remove the potential contaminants.
Figure 43.1 – Nanoparticles’ journey to environment from its production to usage to disposal
A success of waste management depends strongly on the characterization of problematic compounds present in waste before and after treatment. Up to now, knowledge and understanding of the behavior of metal containing nanoparticles in thermal waste treatment processes are very limited because of the lack of suitable online measurement tools. It is well known that off-line (static) analyses only provide average values for the entire sampling time, i.e. significant information on changes in critical species, is averaged out. Usually, chemical characterization and particle-size analysis are made separately on sampled residues, giving merely averaged data about the concentration and the size-distribution. Moreover, problems related to cross-contamination, material loss and physical/chemical alteration during sampling could not be excluded. Due to the lack of online analytical techniques at present, arbitrary assumptions and classifications cannot be excluded. This puts potential risks to the further technological development and improvement of waste related solutions.
Implementation of highly sensitive online methods can assist systematic development of technologies of waste treatment, and to establish particle-reduction measures, which will be necessary to further reduce emissions of fine and ultrafine particles by incineration plants. Robust online analytical techniques can locate the main sources of problematic compounds such as heavy metals and subsequently restrict their appearance in the waste stream. Regarding metal containing nano-objects there are, at present, neither standard procedures to measure their flows on-line nor models which allow to predict their fate along the chain of waste treatment processes. Therefore, detailed chemical size-resolved information will help in process development with respect to plant efficiency, legal compliance in pollution control, and the future adaptation of waste treatment regulations if needed. Furthermore, such online analytical methods are needed to learn more about the influence of process conditions and to characterize a broad and realistic spectrum of nano-objects. Once a process and the behavior of such nanoparticles are well understood there is a chance to use more simple measures to control the process with respect to their fate. Projects that aims to demonstrate the possibility to characterize and understand the behavior of the nanosubstances along the Waste-Treatment-Disposal chain by using online techniques, will have significant impact to establish appropriate analytical procedures to deal with nano-materials in waste.
Eventually, all material containing engineered nanoparticles will become waste. The growing quantity of these nanoparticles used in different technologies and fields, and their potential health and environment impact, necessitate the assessment of their life cycle and towards understanding their fate along the entire value chain of waste treatment. As Galileo once said, “Measure that which is measurable and make measurable that which is not,” it is our responsibility as scientists and engineers to make this happen!
References:
M. Hussain, Handbook of Nanomaterials for Industrial Applications, Newark, NJ, United States: Elsevier, 2018.
S. Thomas, Y. Grohens und Y. B. Pottathara, Industrial Applications of Nanomaterials, Elsevier, 2019.
H. Wigger, W. Wohlleben und B. Nowack, «Redefining environmental nanomaterial flows: consequences of the regulatory nanomaterial definition on the results of environmental exposure models, » Environmental Science Nano, Bd. 5, pp. 1372-1385, 2018.
F. Piccinno, F. Gottschalk, S. Seeger und B. Nowack, «Industrial production quantities and uses of ten engineered nanomaterials in Europe and the world, » Journal of Nanoparticle Research, Bd. 14, Nr. 1109, 2012.
R. Gupta und H. Xie, «Nanoparticles in Daily Life: Applications, Toxicity and Regulations,» Journal of Environmental Pathology, Toxicology and Oncology, Bd. 37, Nr. 3, p. 209–230, 2018.
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