Final Report: Characterisation of Ionised and Zero-Valent Metals as Disinfectants for Microbiologically Contaminated Water in Resource-Poor SettingsEPA Grant Number: SU836019
Title: Characterisation of Ionised and Zero-Valent Metals as Disinfectants for Microbiologically Contaminated Water in Resource-Poor Settings
Investigators: Sobsey, Mark D. , Singer, Philip C. , Mehendale, A. M. , Bharambhe, M. S. , Komandur, Abhinav , Malone, Alyson , Armstrong, Andrew , Garg, B.S. , Bailey, Emily , Leker, Hannah , Motte, Hunter , Bartram, Jamie , Radhakrishnan, Jani , Richardson, Jess , Rothwell, Kathleen , Cooper, Mary , Islam, Mehrin , Clear, Michael , Jathan, Nikita , Deshmukh, P. , Reddi, Prianca , Cory, Rose , Witsil, Tucker
Institution: University of North Carolina at Chapel Hill , Mahatma Gandhi Institute of Medical Sciences , Virginia Commonwealth University
EPA Project Officer: Hahn, Intaek
Project Period: August 15, 2011 through August 14, 2012
Project Amount: $14,883
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2011) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Chemical Safety , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Our project aimed to lay the foundation for the creation of a revolutionary disinfectant; one that is effective, accessible, cheap, robust, consumable, and non-toxic. This disinfectant would place immense power in the hands of those who need it most by enabling them to treat their water at point-of-use in their households and communities, thereby increasing household/community access to safe water and achieving sustainability. The objective of our research was to test the ability of various forms and doses of copper and zinc to disinfect natural water systems, arrive at an optimised means of designing a delivery system for the ideal combination we found, and subject the ideal combination to a final evaluation in which ease of use is qualitatively measured. We compared copper and zinc chloride salts to copper and zinc oxide nanoparticles, the use of the metals in waters with and without naturally-found dissolved solids, the use of the metals against Bacillus cereus spores, Escherichia coli vegetative cells, and MS-2 bacteriophage, and two different doses of the metals (a “high” dose being the maximum allowable concentration in drinking water as defined by the W.H.O./U.S. E.P.A. and a “low” dose being a tenfold reduction thereof).
- Preliminary experimentation conducted yielded excellent (> 99.9%) inactivation of test microorganisms using ionic forms of the metals in laboratory-defined water systems. These conditions were considered the “ideal” throughout our research.
- All experimental combinations were less efficacious than the preliminary experiments’ use of the ionic metals in synthetic water. This conformed to expectations that preliminary conditions were the ideal. Disinfection rates varied from 75% to 95% of original culturable organisms.
- Nanoparticles, in the form that they were used in these experiments, were (roughly speaking) less effective than the ionic metals. With one important caveat—that the form of nanoparticle used here may not have been the ideal form—this may imply that the “active form” of the metals is the ionic form.
- Dose, broadly speaking, made no difference, with the notable exception of disinfection of MS-2 and B. cereus spores in organic water. Even in those cases, results were still unexceptional, with the “high” dose yielding more disinfection than the “low” dose.
- For the use of copper nanoparticles: the presence of natural lake water in the sample matrix made no difference with regards to kinetics or final efficacy of disinfection against all organisms.
- For the use of copper and zinc oxide nanoparticles as well as zinc oxide nanoparticles alone: the presence of natural lake water in the sample matrix blunted disinfection efficacy of B. cereus spores, though it made no difference regarding disinfection kinetics across the board, nor in disinfection efficacy of E. coli cells or MS-2 virions.
- Considering only E. coli cells: nanoparticle copper and zinc in combination were more effective than nanoparticle copper alone in both waters, but similar in efficacy to nanoparticle zinc alone. This contrasts with preliminary findings using the ionic salts in synthetic water. In organic water, all ionic metal combinations behaved essentially identically.
- Considering only B. cereus spores: nanoparticle copper and zinc in combination behaved essentially identically to nanoparticle zinc alone in synthetic water and both were more effective than nanoparticle copper alone in synthetic water. In organic water, all three behaved essentially identically. In organic water, ionic copper and zinc and ionic zinc alone behaved essentially identically and both were more effective than ionic copper alone.
- Considering only MS-2 bacteriophage: all nanoparticle forms of the metal as well as ionic zinc alone in organic water were essentially ineffective as disinfectants. Ionic copper and ionic copper and zinc behaved essentially identically, and were effective in organic water, though not as effective as preliminary experimentation in synthetic water indicated they might be.
- In conditions deviating from the ideal, our results suggest that these metals, in the form tested here, cannot be the sole means of reaching E.P.A./W.H.O. standards of 99.9% reduction.
- The project overall was successful; the knowledge gained by this research will enable a highly efficacious and robust disinfectant/water treatment method based on consumable, non-toxic doses of these metals to be designed.
- Alternative nanoparticle forms of copper and zinc would likely yield different results, due to differential chemical reactivity. It is well worth investigating alternative means of engineering deliverable copper and zinc as nanoparticles.
- Our research, once finalised, has the potential to impact industries and sectors far beyond point-of-use household (POUH) water treatment. Industrial, municipal, agricultural, and wastewater treatment may all potentially benefit, as would other applications that require biocidal activity in an aqueous system.