nanotechnology for beyond earth water treatment

ICES-2020-40

Nanotechnology for Beyond Earth Water Treatment Tanya K. Rogers1

Rice University, Houston, TX 77005

Pratiksha D. Dongare3, Alessandro Alabastri2 and Naomi J. Halas4 Rice University, Houston, TX 77005

Jordin Metz5, Jacques Mathieu6 and Pedro Alvarez7


Layne Carter8 NASA Marshall Spaceflight Center, Huntsville, AL 35182

Michael S. Wong9 and Rafael Verduzco10


NASA has embarked on a journey to enable human exploration on the Moon by 2024 and Mars by 2030. These long duration missions beyond low earth orbit (LEO) will require advanced water treatment and reuse technologies for life support systems to support crew and system needs. Resupply to deep space destinations is not desirable and sustained human presence in a lunar environment increases the necessity for robust and reliable systems. To reduce propulsion costs and transit space allocations, mass, power, and volume must be minimized for all systems. Additionally, a beyond LEO water treatment system process must be able to tolerate both operational and dormant periods. Herein, we present nanotechnologies developed by the Nanotechnology-Enabled Water Treatment (NEWT) center as advanced solutions to meet the aforementioned requirements. This survey of fit-for-purpose modular technologies includes room temperature nanocatalysis, nanophotonics, nano-selective scalant control, quorum sensing, and nano-bacteriophages for biofilm mitigation and mono-and multivalent ion control.

Ca2+ = Calcium CB = Carbon Black CSN = Calcium Selective Nanocomposite HX = Heat Exchanger In-Pd/C = Indium on Palladium ISS = International Space Station LED = Light Emitting Diode LEO = Low Earth Orbit Na+ = Sodium NASA = National Aeronautics and Space Administration

NESMD = Nanophotonics Solar Membrane Distillation NEWT = Nanotechnology Enabled Water Treatment NH4+ = Ammonium NO3- = Nitrate NP = Nanoparticle PNC = Phage-nanocomposite-conjugate PVDF = polyvinylidene difluoride UV-C = Ultraviolet-C WRS = Water Recovery System

1 PhD Candidate, Chemical and Biomolecular Engineering, [email protected] 2 Research Assistant Professor, Electrical Engineering, 6100 S. Main St, Houston, TX 3 Postdoctoral Research Associate, Electrical and Computer Engineering, 6100 S. Main St, Houston, TX 4 Professor, Electrical and Computer Engineering, 6100 S. Main St, Houston, TX 5 PhD Candidate, Chemistry Department, 6100 S. Main St, Houston, TX 6 Research Scientist, Civil and Environmental Engineering, 6100 S. Main St, Houston, TX 7 Professor and NEWT director, Civil and Environmental Engineering, Houston, TX 8 Space Station Water System Lead, NASA MSFC ES62 9 Department Chair and Professor, Chemical and Biomolecular Engineering, Houston, TX 10 Professor and Project Lead, Chemical and Biomolecular Engineering, Houston, TX

2 International Conference on Environmental Systems

I. Nanotechnology for Water Management The Nanotechnology-Enabled Water Treatment (NEWT) center is an interdisciplinary, multi-institution

nanosystems-engineering research center and the first national center to develop next-generation mobile, modular, high-performance water treatment systems enabled by nanotechnology. NEWT’s goal is to facilitate access to clean water by developing efficient water treatment systems that can tap unconventional sources to provide humanitarian water or emergency response. NEWT develops systems to treat and reuse challenging wastewaters in remote locations, focusing on sustainable and energy-efficient outcomes in regard to its water footprint. Three research thrusts, each representing a key component of the core systems, plus cross-cutting sustainability and safety theme guide fundamental research and development of novel water treatment processes and advanced materials (Figure 1). Owing to the unique physiochemical and surface properties of materials at the nanoscopic level, nanotechnology-based approaches offer new solutions to terrestrial and beyond earth water treatment.

Figure 1. Core focus groups for NEWT research and technology advancement

II. Biofilm Mitigation The International Space Station (ISS) is a hermetically closed environment inhabited by microorganisms.

Inevitably, microbes accumulate in the onboard Water Recovery System (WRS), resulting in biofouling from bacteria growth/regrowth that obstructs flow paths, reduces overall system performance, limits functionality, and reduces system life and reliability. For the past decade, biofilm growth in WRS system components has been an ongoing issue. Heterotrophic biomass is consistently detected in the stationary bowl of the distillation assembly, system plumbing, and inlet valves. Biofouling at gas/liquid interfaces in the waste hygiene unit and rotary water separator has restricted flow. The accumulated release of biofilm from the water processor waste tank has clogged downstream solenoid valves, resulting in the costly replacement of the mostly liquid separator (MLS) and process pump. Define on first use(NASA) has implemented multiple methods to address these issues, including tank recycling, micron filters, reduced organic content, and regular flushes with iodinated water, but has declared biofouling as an ongoing critical challenge that needs a more effective solution, especially for long-duration planetary missions with anticipated dormant periods and limited resupply flight windows1.

A multi-pronged treatment approach that prevents biofilm formation without impacting system operation, destroys existing films, and kills suspended cells while preventing regrowth is an ideal solution. The principal determinants of bacterial rich environments are temperature and humidity, presence of disinfectants, and organic and inorganic constituents. Strategies to effectively control biological environments should target these factors and


nanotechnology-based approaches offer opportunities to enhance conventional technologies. Surface coatings and interruptions in quorum sensing can limit biofilm attachment. Nanoparticles of a variety of materials, from chitosan to silica, can kill existing microbes. Bacteriophages can selectively destroy bacteria, and coupled with nanoparticles, can penetrate a biofilm for bottom-up eradication in a way that traditional chemical disinfectants often cannot. Researchers at NEWT have developed many of these technologies and have the experience and expertise to conduct further testing in an applied system for space applications.

A. Nano-silica for Side Emitting UV-C Disinfection Ultraviolet-C (UV-C) light emitting diodes (LEDs) are a disinfection tool that uses short-wavelength UV-C

to kill or inactive microorganisms. A major technology barrier of LED disinfection is the amount of irradiation emitted, limited by LED surface area. As a result, reactors require a disproportionate amount of LED arrays for effective disinfection and produce high amounts (>85% of LED energy output) of undesired heat. To overcome the surface area barrier, NEWT researchers developed a nanotechnology-based solution to achieve side-emission of UV-C in optical fibers, increasing the irradiation area of LEDs by >100x (Figure 2). This is achieved by coating an optical fiber with modified silica nanoparticles (NP) that create light-scattering centers on the surface of the fiber. The coated fiber is overlaid with transparent polymer and prevents nanoparticle release into water and allows germicidal light to permeate. A proof-of-concept investigation demonstrated 2.9 log inactivation of Escherichia coli at a delivery dose of 15 mJ/cm2 using the silica-NP enhanced side-emitting fiber2.

Figure 2. Schematic diagram of side-emitting optical fibers enhanced with scattering centers enabled by silica nanoparticles

B. 200nm Bacteriophage as a Dormant Biocide Bacteriophages (phages) are the most abundant biological entities in the biosphere and exclusively prey on

bacteria. Average phage diameters range between 24 - 200 nm, though some filamentous phages can exceed 800 nm in length. Phages autonomously absorb to receptors on the cell surfaces of susceptible bacteria and infect the host cells by injecting their genomes through the cell membrane. While most characterized phages are considered species or strain-specific, recent efforts have demonstrated the widespread existence of broad host-range (polyvalent) phages that can infect multiple bacterial species. NEWT has developed broad-spectrum polyvalent phage-nanocomposite-conjugates (PNCs) to target multiple bacterial species in biofilms using bottom-up eradication3. For this method, magnetic iron oxide nanoparticles were coated with chitosan and treated to bind phages to the nanoparticle surface. A weak magnetic field was applied to the PNCs, which facilitated biofilm penetration and subsequent phage proliferation and propagation within the biofilm. The biofilm removal efficiency was 98.3 ± 1.4% for dual species biofilm (i.e., Escherichia coli and Pseudomonas aeruginosa) and 92.2 ± 3.1% for multi-species biofilm (i.e., E. coli, P. aeruginosa, and non-hosts Bacillus subtilis and Shewanella oneidensi) (Figure 3).


Figure 3. Simulation and experimental results of biofilm removal following treatment by free phages and different sized PNCs. The dual species biofilm before treatment (A) and after treatments with (B) free phages, (C) large PNCs, (D) medium PNCs, and (E) small PNCs for 6 hours. The left panels are simulated cross-section of dual species biofilm of E. coli (red cell) and P. aeruginosa (green cell). The blue cells represent phage-infected bacteria that have not lysed yet. Each grid represents 0.5 × 0.5 μm. The right panels are microscopic images of the surface of residual biofilms stained with SYTO 9.

The use of bacteriophages over common chemical disinfectants and biocides offers several advantages. While chemicals cannot easily penetrate and eradicate biofilms, some phages possess depolymerases which enhance biofilm penetration and degradation. Phage populations can also evolve to circumvent the development of resistance within bacterial populations. Furthermore, phages are innocuous to human health and do not require downstream removal unlike traditional chemical disinfectants. Additionally, unlike antibiotics or biocides, whose concentration decreases with time after repeated dosage, phages may continue to self-replicate and infect the target bacteria, eventually disappearing with their hosts in a typical predator−prey relationship. Moreover, a diverse library of phages can be maintained with minimal weight and space requirements. These factors, and bacteriophages ability to be stored in ambient conditions for extended periods of time, make phages an ideal technology for on-line and dormant water systems during long-duration missions.

C. Porous Nanocarriers to disrupt quorum sensing Quorum sensing is a cell-to-cell communication mechanism that functions through chemical signaling and

regulates gene expression in response to bacterial population densities. It plays a major role in biofilm formation, influencing each step in the process from establishment to maturity. Disruption of bacterial quorum sensing has shown promise for controlling biofilms. If cell-to-cell signaling can be interfered with, biofilm formation may be delayed, or the biofilm may not be as robust and therefore more susceptible to removal by various treatments. We have identified divalent metal quorum sensing inhibitors (nickel and cadmium) and demonstrated cell signaling disruption through a porous nanocarriers delivery method4 (Figure 4).


Figure 4. biofilm attachment (B) of Burkholderia multivorans 17616 in the presence of nickel, measured by absorbance at 24 h. Each bar represents the average of five experiments with a minimum of four replicates per experiment

III. Mono-and Multivalent Ion and Nutrient Control

D. Capacitive Deionization for Selective Removal of Scalant Ions NEWT has developed a chemical-free, membrane-free, and regenerable technology to remove inorganic

constituents prone to cause scaling from wastewater streams. This technology, known as capacitive deionization, is electrically driven by a low energy applied voltage. An electric potential (~1.0 V) is supplied to an anode and cathode resulting in charged species adsorbing onto the electrode surfaces. Once the electrodes reach saturation, a reverse potential or zero charge state is applied and the ions desorb resulting in a regenerated surface. Selective removal of targeted ions can be achieved by altering the electrode surfaces with unique nanomaterials (Figure 5). In order to achieve calcium selective removal, we developed a calcium-selective nanocomposite coating (CSN) of nano-sized calcium chelating resins with aminophosphonic groups in a sulfonated polyvinyl alcohol hydrogel matrix, which accomplished a Ca2+-over-Na+ selectivity of 3.5–5.4 at Na+:Ca2+ equivalent concentration ratio from 10:1 to 1:1, 94 – 184% greater than the uncoated electrode. The CSN coated electrode exhibited complete reversibility in repeated operation5.

Figure 5. Schematic Diagram of Capacitive Deionization continuous-flow reactor with calcium-selective nanocomposite electrode

E. Ambient Temperature Nanocatalysis for Selective Conversion of Nitrogen Containing Species to Desired products

Urine waste streams are rich with nitrogen containing species such as urea (13,400 mg/L) and ammonium nitrate (756 mg/L), contributing to pH shifts resulting in divalent ion precipitation and hydrolysis to toxic NH4+/NH3. NEWT has developed a method to selectively transform N-species to innocuous dinitrogen using novel “designer”


bimetallic nanocatalysts (5-7 nm). Tunable atomic configuration, metal-on-metal loading, and metal nanoparticle size are customized to influence the catalytic performance and reaction pathway. We have demonstrated that surface-tuned deposited Pd nanoparticles with indium deposits (“In-on-Pd NPs”) shows room-temperature nitrate catalytic reduction towards dinitrogen gas. Mechanistically, In-on-Pd bimetallic catalysts first oxidizes indium(spell out) in order to reduce NO3− to NO2−. Next, a series of surface reactions occur with hydrogen adatoms to further reduce the nitrite that has surface diffused to neighboring Pd sites. Selectivity in excess of 95% to nontoxic N2 was observed6 (Figure 6).

Figure 6. Concentration−time curves of NO3−, NO 2 −, NH 4+, and N2. Reaction conditions: 40 sc% In-on-Pd NPs with 0.553 mg/L In in reactor, 600 rpm stirring rate, 1 atm pressure, ambient temperature

F. Nanophotonics for Distillation Driven by Localized Heating Nanophotonics regards the interaction of light with nanostructures. The use of nanophotonics for solar energy

driven vapor generation was initially demonstrated by Neumann et.al.7 at Rice University and has since been implemented by various research groups around the world. Researchers have demonstrated the use of different nanoparticles, such as carbon-based materials, metallic nanoparticles, semiconductor nanoparticles to achieve broadband maximum light absorption from incident sunlight by tuning their material and shape8-22. Hogan et.al.18 demonstrated that depending on nanoparticle scattering and absorption cross sections, incident light interacts differently with the nanoparticle solution and as the nanoparticle concentration increases, light gets absorbed and scattered closer to the illumination surface as shown in Figure 7a. As a result, for an optimal concentration, nanoparticle temperature increase can efficiently convert water to vapor at the liquid/air interface without increasing the bulk water temperature. Based on this light absorption localization phenomenon, NEWT researchers developed a nanophotonics-enabled solar membrane distillation (NESMD) system19, employing light absorbing carbon black (CB) nanoparticles coupled with a relatively thin ~100 microns polyvinylidene difluoride (PVDF) hydrophobic membrane. In NESMD, saline and purified water at ambient temperature flow on opposite sides of this photothermal membrane (Figure 7b.). The incident sunlight is absorbed on the nanoparticle-coated surface, generating a temperature and vapor pressure gradient across the membrane. The vapor pressure difference results in water vapor flowing from the feed side through the membrane to the distillate side, where it condenses (Figure 7c.). Salts and other pollutants are left behind at the input side of the membrane. This is a highly efficient process because only the few-microns-thick volume of water at the photothermal membrane surface is heated by the sun, leading to an effective layer-by-layer vaporization process. The solar-driven localized heating in NESMD maintains a positive temperature difference across the membrane even for larger modules and makes it a highly scalable process


Figure 7. Light localization in nanoparticles enables surface heat generation. (a) Modifying light absorbing nanoparticle concentration allows heat localization at liquid/air interface. (b) Schematic of nanophotonics-enabled solar membrane distillation (NESMD), where saline feed and purified distillate flow on two sides of a nanoparticles coated hydrophobic membrane. (c) Incident sunlight gets absorbed in few microns thick nanoparticle layer on top of the membrane and the resultant heat creates a temperature gradient across the membrane. This temperature difference creates a vapor pressure gradient, pushing water vapor from feed to distillate through the membrane, leaving salts behind and thus purifying water.

After a successful proof-of-concept NESMD demonstration with a lab scale system operating at ~20% efficiency19 and > 99% salt rejection, NEWT research efforts have been directed towards scaling up the system and increasing its performance. To facilitate NESMD scale-up, we have developed a spray-based method which can coat membranes of any size. One way to increase the efficiency of a solar driven distillation process is to use solar concentrators to illuminate the device with higher solar power. However, solar concentrators are bulky, costly and need extensive tracking infrastructure, limiting the system design flexibility and applicability. The water evaporation efficiency increases with solar power because the water vapor pressure is an exponential function of temperature and the temperature is a nearly linear function of the incident solar intensity. With this understanding, we modified the illuminated surface of the light absorbing membrane with lens arrays to create high intensity hot-spots (Figure 8a,b)20. While the input solar power in the system is unchanged, its spatial distribution is now related to the lenses focusing properties. Due to the exponential dependence of flux on intensity, the increase in flux at the high intensity focal spots exceeds the reduction in flux in the rest of the device, resulting in a higher average flux. Purified water flux from a 4 inch × 8 inch module with 1 inch and 2 inch diameter lens arrays resulted in enhancements of ~38% and ~58% respectively. The corresponding water flux enhancements for a 4 inch × 16 inch module were ~22% and ~30% respectively. Over a period of 9 hours, adding 2 inch diameter lens array to a 4 inch × 16 inch module casting 5 mm focusing spots resulted in 27% water production increase from the same solar power input, without using any bulky light concentrators (Figure 8c). This performance improvement was comparable to enhancements in other solar driven distillation systems obtained with solar concentration. This strategy can be applied to increase performance of other photothermal processes with supralinear light dependence like phase separations16 and chemical reactions.

Evaporation based thermal distillation processes like NESMD are essential to treat high-salinity water, but the extraction and collection of vapor occurs through an energy intensive phase change process and has intrinsically low thermodynamic efficiency20. Thus, recovering the heat utilized for vaporization represents an obvious path towards highly efficient thermal desalination systems. To achieve that, we combined NESMD system with a heat exchanger (HX) system to effectively recover vaporization energy from the condensed vapor to preheat the feed before entering the NESMD system (Figure 8. c,d)21. After rigorous experiments and theoretical calculations, we found that a NESMD+HX coupled system can act as a thermal oscillator, where evaporation-condensation and recovered latent heat can be maximized by dynamically matching feed and distillate flow rates. Additionally, it was found that, through real time modification of matched flow rates (i.e. dynamic flow control, DFC), the production rate could be furtherly optimized depending on light intensity, system size and losses. Through flow rates optimization, the thermal energy in the system is recirculated multiple times, oscillating between NESMD and HX regions. Following these thermal recovery strategies, we obtained a thermal efficiency of ~150% with a fresh water flux of ~1.1 L/(m2.h) under 0.475 Suns utilizing LED light sources. We numerically predicted water production of 20.5 L/m2 for an optimized system operating under varying ambient solar illumination during a typical sunny day in Alamogordo, NM. These advancements point towards nanophotonics-enabled desalination as a promising technology for space applications. In fact, NESMD is driven by vapor pressure gradients as opposed to gravity driven convective flow based conventional distillation processes, making it a potential solution for water treatment in space missions.


Figure 8. Schematics and mechanism of NESMD with multilens array and NESMD with heat exchanger. (a) Saline feed and purified water flow on top and bottom respectively of a carbon black coated PVDF membrane in countercurrent flow. The carbon black nanoparticles absorb incident solar radiation and lead to heat localization on top of the membrane. The heated feed evaporates on top of the membrane and condenses on the bottom in the purified water leaving salts and pollutants behind. Modification of the top surface of NESMD with multilens array leads to focusing incident sunlight in smaller regions with higher feed temperature rise (b) which lead to higher water vapor flux in smaller regions and overall improved performance. (c) Calculated flux production from 4 in. × 16 in. NESMD with 2-in.-diameter lens array with 5-mm focal spots (orange area) and bare NESMD (dark-gray area) under varying solar intensity (dashed blue line) for more than 9 h. (d) Heat exchanger (HX) coupled to NESMD allows to transfer heat from the exiting purified water to the incoming saline feed. (e) As the water vapor condenses in the purified input distillate it transfers its energy of condensation in the distillate making the distillate output warmer than input. This heat can be transferred to the input saline feed before entering NESMD with an HX with metallic layer (Copper or Aluminum) in between the top and bottom water stream. (f) Comparison of flux production from NESMD with 10 HX layers during a 9 hour day with (orange) and without (grey) dynamic flow control (right axis). Solar intensity variation in blue (right axis).

IV. Conclusions This survey paper highlighted nanotechnologies for water treatment applications in beyond earth systems.

We have described groundbreaking research efforts that enable high-surface area UV-C disinfection, dormant treatment of bacterium using autonomous nanophages, bottom-up eradication of biofilms and cell-to-cell signaling disruption through porous nanocarrier delivered quorum sensing inhibitors, selective removal of calcium scalant using nanocomposite layered capacitive deionization, room temperature nanocatalysis of nitrogen containing species to innocuous products, and nanophotonics for distillation driven by localized heating. Future work will further evaluate implementation considerations for beyond earth water systems.


Acknowledgements The authors of this work wish to acknowledgment the many professors and graduate students that have

contributed to this overall effort. This work was partially funded by the National Science Foundation (EEC-1449500) Nanosystems Engineering Research Center on Nanotechnology-Enabled Water Treatment.

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