From water purification to gas mask filters: the wide…

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ith a total sales of 617 million euros in 2020 worldwide, the BRITA Company produces water jugs, kettles and tap attachments integrated with disposable filters. The filters, which contain activated carbon and ion-exchange resin, have the goal to remove substances that may impair taste, to reduce the carbonate hardness (limescale) as well as copper and lead [1]. This process that is performed daily on drinking water at home, is called adsorption. This phenomenon is a separation process involving the selective transfer of solutes (adsorbates) in a fluid phase to the surface of a solid (adsorbent). Through adsorption, small particles or dissolved contaminants in water can be removed. However, adsorption should not be confused with absorption, in which particles penetrate into another substance, just like a sponge that soaks in liquids. While adsorption describes the enrichment of absorbates onto the surface of an adsorbent, absorption is defined as a transfer of a substance from one bulk phase to another bulk phase [2]. The substance is enriched within the receiving phase and not only on its surface, as it can be seen in Figure 1. The dissolution of gases in liquids is a typical example of absorption.

Figure 1: Schematic representation of: (a) adsorption and (b) absorption processes.

The commonly used material for water treatment through adsorption is activated carbon. This adsorbent is a carbonized and chemically activated material through oxygen treatment, that results in millions of tiny pores between carbon atoms opening up. This highly porous material presents surface area values usually between 500–1500 m2/g and can be used in a powdered or granular form. Due to its active adsorption sites, high surface area, porous structure, surface reactivity, inertness, and thermal stability, this material is a popular choice among adsorbent materials applied industrially [3].

Besides water purification, the adsorption technique has many other applications. Some of them are included in our daily life, such as applying silica or aluminium gels in packaging to remove moisture and control humidity. Others are used industrially, such as the removal of undesirable colouring matter. Adsorbent materials can remove colours from solutions by adsorbing coloured impurities. As shown in Figure 2, Tourmaline, a naturally-occurring borosilicate mineral, was successfully used to remove red dye [4]. Other industrial applications includes the separation of noble gases, where the difference in the degree of adsorption in the adsorbent materials allows to separate a gas mixture; and chromatographic analysis based on selective adsorption to separate a mixture. For example, in column chromatography, a long and wide vertical tube is filled with a suitable adsorbent, and the solution of the mixture is poured from the top and then collected one by one from the bottom [5].

Figure 2: adsorption of diazo dye DR23 onto powdered tourmaline.
Source: https://doi.org/10.1016/j.arabjc.2016.04.010

Another popular use of the adsorption principle is for gas masks. To filter out harmful gases such as methane, chlorine and sulphur dioxide, the gas mask filters are made with adsorbent materials (usually with activated carbon) to purify the air. From the inlet of the gas mask, the air flows through a particulate filter, followed by an adsorbent filter, and then through another particulate filter, which traps charcoal dust, according to Figure 3 [6].

Figure 3: typical disposable filter cartridge for a respirator.
Source: https://science.howstuffworks.com/gas-mask2.htm

References

[1] BRITA – key facts & figures, 2022. https://www.brita.co.uk/facts-figures (accessed 13/01/2022)

[2] Worch, E. (2021). Adsorption technology in water treatment. de Gruyter.

[3] Soni, R., Bhardwaj, S., & Shukla, D. P. (2020). Various water-treatment technologies for inorganic contaminants: current status and future aspects. In Inorganic Pollutants in Water (pp. 273-295). Elsevier.

[4] Liu, N., Wang, H., Weng, C. H., & Hwang, C. C. (2018). Adsorption characteristics of Direct Red 23 azo dye onto powdered tourmaline. Arabian journal of chemistry, 11(8), 1281-1291.

[5] Application of Adsorption: Definition and Examples, 2022. https://www.embibe.com/exams/application-of-adsorption/ (accessed 13/01/2022)

[6] How Does a Gas Mask Protect Against Chemical Warfare?, 2013. https://www.nationalgeographic.com/science/article/130830-gas-masks-syria-israel-chemical-warfare (accessed 13/01/2022)

The leading-role in food production: phosphorus rocks

Source: http://www.kuglercompany.com/crop-care/fertilizer-application

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t is undeniable that phosphorus is vital for life – literally. It is an essential nutrient for all living forms since it plays an important role in DNA/RNA molecules, and is also related to cellular energy transport via ATP (i.e. the P in ATP – the molecule that carries energy around cells) [1]. Phosphorus is not found free in nature, due to its reactivity to air and many other oxygen-containing substances, but it is widely available in different minerals. Phosphorus rocks are a non-renewable resource originated from igneous rocks and marine sedimentary deposits. The widely used approach to obtain these rocks which contain a high content of phosphorus is by mining [2, 3].

Phosphorus rocks are used worldwide for many industrial applications such as detergents, food and drinks, metallurgy. However, the most important use of phosphorus rocks is for the production of phosphate fertilizers [4]. Agriculture is by large the main user of phosphorus globally, accounting for between 80-90% of the total world demand [5]. Phosphorus is one of the three macro-nutrients needed by plants to develop and grow. Together with nitrogen (N) and potassium (K) nutrients, phosphate (P) plays a leading-role in NPK fertilizers which are essential for optimal growth of crops [6]. Unfortunately, a shortfall of phosphorus in soils will result in a reduction of crop yield and can affect food production worldwide.

Phosphorus rocks reserves are being mined at growing rates due to increasing demand. According to the United Nations Food and Agriculture Organisation (FAO), the world demand for fertilisers was estimated to increase around 3 million tonnes every year [7]. The potential threat of phosphorus global limitation has been discussed since the quality of the existing rocks is declining, making the extraction more expensive. Indeed, in 2014, the European Commission declared phosphorus rock as one of the 20 critical resources from the European Union [8]. Estimation of the remaining time phosphate reserves will last are variable and contested, ranging between 100 to 600 years at current production rates [9]. Some researchers have applied Hubbert’s concept of “peak oil” to phosphorus rock mining and named as “peak phosphorus” [10, 11]. Peak phosphorus refers to the moment when production of phosphorus from mining reaches a maximum (its peak); followed by the decrease in quality of the remaining reserves, making it harder to access. Then, mining and processing will be more expensive, which will result in the supply decline and rapidly increase of the prices [5]. Additionally, phosphorus rocks reserves come from a limited number of countries, with large parts of the world, including Europe, being almost totally dependent on imports. As shown in Figure 1, Morocco holds the vast majority of global supplies of this resource, approximately 73%. China is currently in second place with only 4% [10]. This is geopolitically sensitive as Morocco currently occupies Western Sahara and controls its phosphate rock reserves, which could present significant food security risks.

Figure 1: Estimated global phosphorus reserve distribution (USGS, 2017).
Source: https://hess.copernicus.org/articles/22/5781/2018/#&gid=1&pid=1

In order to ensure phosphorus remains available for food production to future generations, the development of novel phosphorus recovery and reutilization initiatives through more sustainable wastewater systems is needed. In particular, human waste from households contributes largely to the amount of nutrients found in waste streams. Approximately, ~50% of the phosphate mass load in municipal wastewater treatment plants comes from human urine. Therefore, urine could play the new leading-role in food production worldwide and help current global demand for phosphorus. Thus, a new perspective that re-evaluates human urine as a reusable and eco-friendly resource should be established. Phosphorus recovery from human urine represents a new promising avenue, since the recaptured phosphorus from waste streams can be utilized for fertilizer production. Additionally, the development of new wastewater systems can offer a sustainable form of sanitation for 2.5 billion people in developing countries that still have no access to proper sanitation [12]. From the extraction and reuse of phosphate from wastewaters, it promotes a circular and sustainable closed-loop of nutrients. And, at the same time, it could increase phosphate availability for fertilizer production worldwide.

References

[1] Oelkers, E. H., & Valsami-Jones, E. (2008). Phosphate mineral reactivity and global sustainability. Elements, 4(2), 83-87. 79.

[2] Hosni, K., & Srasra, E. (2010). Evaluation of phosphate removal from water by calcined-LDH synthesized from the dolomite. Colloid Journal, 72(3), 423–431. 80.

[3] Phosphate rock, 2021. https://mineralseducationcoalition.org/minerals-database/phosphate-rock/ (accessed 30/06/21).

[4] Cordell, D., Drangert, J. O., & White, S. (2009). The story of phosphorus: Global food security and food for thought. Global Environmental Change, 19(2), 292–305.

[5] Tirado, R., & Allsopp, M. (2012). Phosphorus in agriculture: problems and solutions. Greenpeace Research Laboratories Technical Report (Review), 2.

[6] NPK: What is it and why is it so important?, 2021.  https://www.agrocares.com/2020/11/02/npk-what-is-it-and-why-is-it-so-important/ (accessed 30/06/21).

[7] FAO, 2017. World Fertilizer Trends and Outlook to 2020. Food and Agriculture Organization of the United Nations (FAO), p. 66. http://www.fao.org/3/a-i6895e.pdf (accessed 30/06/21)

[8] European Commission (2014). Press Release: 20 Critical Raw Materials – Major Challenge for EU Industry. http://europa.eu/rapid/press-release_IP-14-599_en.htm (accessed 30/06/21)

[9] Van Kauwenbergh, S. J (2010). World Phosphate Rock Reserves and Resources. Technical Bulletin IFDC-T-75.

[10] Cordell, D., & White, S. (2013). Sustainable phosphorus measures: strategies and technologies for achieving phosphorus security. Agronomy, 3(1), 86-116.

[11] Ashley, K., Cordell, D., & Mavinic, D. (2011). A brief history of phosphorus: from the philosopher’s stone to nutrient recovery and reuse. Chemosphere, 84(6), 737-746.

[12] Rollinson, A. N., Jones, J., Dupont, V., & Twigg, M. V. (2011). Urea as a hydrogen carrier: A perspective on its potential for safe, sustainable and long-term energy supply. Energy and Environmental Science, 4(4), 1216–1224.

From coffee to tea drinking: my PhD journey from…

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t the beginning of 2019, I was close to obtain my Master’s Degree in Brazil in Chemical Engineering, so naturally I started to think about what I wanted to do next career wise. In fact, conducting research day to day was something that was very exciting for me: I used to spend my entire days at the lab doing experiments and the time just flew by, it just felt right. Also, having the autonomy to develop my own research interests was something that kept me motivated while I was developing my Master’s studies. By that moment, I knew I wanted to keep working as a researcher, and pursuing a PhD position felt like the right direction.

To give some context on why I decided to change coffee beans for tea bags, I should mention that I had studied previously in Scotland for 1 year during university, as I was awarded an international exchange scholarship. I had an amazing experience at the University of Strathclyde (I do not miss the windy weather though!), in which I felt I grew as much personally as I did professionally. This background gave me the confidence to start searching for PhD positions abroad. It did feel a bit overwhelming going after a PhD in Europe, as it would be 3 years living almost 10.000 Km away from home, but I was not ready to give it up without even trying. Regarding my research interests, I have always been interested in processes and development of materials that could minimize environmental hazards to increase sustainability, so when I came across the early-stage researcher position in the REWATERGY Marie Curie European Industrial Doctorate, I knew it was the perfect match: the project focused on the enhancement of  energy and nutrient recovery from wastewater streams inspired by the circular economy concept. Besides, the PhD position was at the prestigious University of Cambridge, with an additional inter-sectoral experience at Delft IMP, a Company located in the Netherlands. Needless to say that it felt like the perfect opportunity to gain experience in both academia and private R&D sectors.

Luckily, all the recruitment was being done online, so I could participate smoothly, as at the moment I had just got recruited for an Engineer position at a Brazilian company. I applied for the PhD position and a while later I got an email saying that my CV matched the position, and I got invited to do a round of interviews in order to be evaluated. The first one was with the entire consortium, there were around 15 people in the Skype call. I remember I was a little bit tense, since it is always a bit nerve wrecking trying to show your personality in a different language than your mother tongue, but I had confidence in myself and it went really well. They mainly asked questions about my background, and I was happy to be able to come across as my true self. After that, I was soon invited to do a second interview with  my future two advisors, Laura and David. The final interview lasted approximately 1 hour and it was focused on science related questions. This last interview was very formal and serious, and it was very hard for me to read the room. I knew I had prepared myself and that I was on my top game, but I could not anticipate the outcome, and I must admit it was a bit nerve wrecking. A few days later I received an e-mail where I was offered the PhD position, and I’ve never felt so happy! Coming from a small city in Brazil and heading to a PhD abroad always felt more like a dream than a reality.

After that, I started with all the bureaucratic formalities that involves moving to a different country. My visa processing was quite long and took more time than expected, but even so, Laura, as my academic advisor, was very understanding and helpful. I was able to delay the start of my PhD contract until I got everything in place. Arriving at Cambridge mid-October, was a big life change to be honest. I left Brazil in the spring, with lovely sunny and warm days, suddenly to arrive in the English fall with temperatures around 10 °C! I know that for most people living in Europe it is not even that cold, but I was freezing from day one. Later, I got to finally meet Laura in person and I have to say that I am very happy to have a woman as one of my advisors. In Brazil, having women in leadership positions is still scarce (especially in science), so it is definitely a motivation and an inspiration to have Laura’s guidance and mentorship along my career path. 

Now, fast forward to the end of 2020, I am happily surprised on how much my life has changed so far. Of course, the COVID-19 pandemic has disrupted everybody’s life in so many different ways, but still I believe I have grown so much during this period. I have been through my 3-month evaluation and 1st year viva, in which I was successfully approved in both of them. Additionally, I have been privileged to work at an international and collaborative environment with a powerful and stimulating female guidance. I even had the courage to cycle during the fall and winter seasons: I still freeze, but at least now I can cope! Most importantly, I feel that I have matured scientifically, and that becoming an independent researcher is indeed my cup of tea.

Sunset in Cambridge, Uk.
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