(4dd) Energy-Efficient Functionalized Filters with Easily Accessible Materials for Nanoparticle Removal from Water

Nanoparticles (NPs) have always been present in the environment, but recently a growing concern about excess NP contamination and related risks to the environment and human health has come to the fore. This issue is mainly driven by rapid developments in the field of nanotechnology enabling us to modify and design novel NPs, referred to as engineered nanoparticles (ENPs), with tailored properties for a variety of applications [1]. The small size of ENPs that confers valuable properties of interest to NPs is also responsible for the potential hazards associated with them. In addition to ENPs, incidental nanoparticles (INPs), such as nano-plastics, released into atmosphere due to human activities are of growing concern [2]. Although this interest in nano particle contaminant health risk in the context of ENPs is new, NPs have been affecting human health from the earliest of times. For example, viruses are important natural nanoparticles (NNPs) that have caused a massive burden on human health. The recent COVID-19 pandemic is a striking example of how virus contamination and transmission can have devastating impacts [3]. In essence, there is an emerging need for control of nano-contaminants, including but not limited to, viruses, nano-plastics, and colloidal metals produced perpetually by natural and anthropogenic activity.

Drinking water treatment plants are critical reservoirs for the accumulation and release of NP contamination and exposure because they exist at the interface of nature and human habitats. Consequently, controlling NP contamination, especially viruses, using water treatment techniques has been a fundamental engineering problem. Filtration is the basal unit operation used in water purification universally irrespective of socio-economic status, resource availability, and scale of operation. But conventional filtration techniques only offer partial NP removal at best, necessitating the use of more energy-intensive and expensive modes of filtration based on nano-porous membranes. Due to the low efficiency of conventional filtration, currently disinfection techniques are used in conjunction with filtration to achieve the regulated drinking water treatment standards for viruses. For instance, the US Environmental Protection Agency (EPA) mandates 4log₁₀ (99.99%) of virus removal from drinking water and the World Health Organization (WHO) also suggests a treatment target of 4log₁₀ for moderately contaminated source water. Although, virus removal and inactivation has been studied extensively in the context of water treatment there are currently no mandates on the removal of ENPs. There is a lack of focus on developing novel techniques for ENP removal because: i) low concentrations of ENPs exist in water sources compared to NNPs, re-shifting the focus onto NNP removal, ii) the expected financial burden to replace legacy equipment is high, and iii) the multi-barrier approach commonly used in water treatment apportions the removal of NPs to either coagulation and sedimentation or disinfection technologies based on biological contaminants [4]. Despite ongoing efforts, understanding of biological accumulation and impact of ENPs is still at a primitive stage while analysis of virus concentration and transport is years ahead due to the availability of robust surrogates and quanatification methods . Therefore, we used viruses as surrogate particles to devise novel strategies for capture and extend these techniques to the removal of ENPs and INPs.

Ongoing research efforts pertaining to the development of effective virus removal technologies for water treatment is a striking example of the trade-off between clean water production and associated energy consumption, and thus relevant to the energy-water nexus [5]. It also provides a potential roadmap for novel ENP and INP removal techniques and their targets. Firstly, reliance on size-exclusion based membranes to replace ineffective conventional filtration gives rise to a trade-off between the productivity and the level of removal efficiency achieved (Fig. 1a). Secondly, chlorination widely used as an alternative or in conjuction with conventional filtration to meet currrent requiremnts leads to the formation of disinfection byproducts (DBPs) that have been linked to cancer and other health effects [6]. Existing disinfection technologies considered as alternatives for chlorination such as ozone and UV are again expensive and energy-intensive [7]. When the embedded energy for the processing of materials and chemicals is compared among available techniques, total energy of most disinfection technologies is on par with high energy filtration technologies (Fig. 1b), while low energy chlorination represents health risks from DBPs. Also, there is no conclusive proof that disinfection can remove ENPs from water, underlining the importance of overcoming the productivity performance trade-off imposed by filtration techniques to achieve NP contaminant control. Recent studies propose chemical functionalization of low-pressure membranes or specialized membrane fabrication techniques such as electrospinning and use of nanofibrous materials to overcome this limitation [8, 9]. However, due to the use of advanced fabrication and modification strategies the widespread use of these solutions would be limited and energy intensive. Overall, it is imperative to develop novel, energy-efficient, cost efficient, and broadly applicable treatment technologies for removal of both NNPs and ENPs.

To overcome the above stated challenges with achieving energy-efficient nanoparticle filtration we designed a sustainable filter fabricated from easily-accessible materials that can be deployed with minimal cost in multiple scenarios (Fig. 1c). We showed the capability of the proposed filters to achieve highly efficient removal of NNPs, INPs and ENPs from water. We designed our filters by leveraging the water clarification capability of Moringa oleifera (MO) seeds. The MO tree is prevalent throughout tropic and sub-tropic regions, and its seeds have historically been used as a natural coagulant [10]. The seeds of this tree contain cationic proteins MO coagulant protein (MO2.1) and MO chitin binding protein (MoCBP) with established antifungal and coagulant activities [11]. Our main hypothesis is that a simple water extract from MO seeds can be used to successfully functionalize accessible substrates with cationic proteins. The functionalized substrate can then be used as an affinity based filter for removal of contaminants from water. In our previous work, we have shown that model sand particles can be functionalized by this proposed process to achieve high pathogen removal. However, challenges related to the effect of flow rate (filter loading rate) and functional sand grain size restict the applicability of the functionalized sand filters under practical conditions [12, 13]. To improve up on the sand filters, we worked with the philosohpy of frugal science to ensure the energy-efficiency and accessbilty of the proposed filter. We developed and tested the capability of MO protein functionalized natural fiber filters to remove an array of NPs from water under practically relevant conditions to build a novel platform tecnhology that can be applied at community or point-of-use scales for NP removal in a wide range of public health scenarios.

Teaching interests: During the course of my acdemic education, I got the previlage to work as teaching assistant to a range of both classroom and lab courses. Working with students during these classes and getting postitve feedback was the most gratifying part of my PhD research for me. I would like to continue to teach and my research efforts towards application of my expertise to environmental realted research. I would like to branch out into studying viral surrogates for understanding the trasnport harmful pathogens in both water and aerosol systems to placate the impacts of disease spread.

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