Removal of Bacteria and Viruses from Waters Using Layered Double Hydroxide Nanocomposites

Song Jin
Western Research Institute, Laramie, Wyoming 82072, USA

Paul Fallgren
Western Research Institute

Jeffrey Morris
Western Research Institute

Qi Chen
Shanghai Lanchin Environmental Ltd., Co.

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     Last modified: April 21, 2006

Abstract
Pathogenic bio-agents, such as bacteria and viruses, exist ubiquitously in water systems. Numerous species of bio-agents are entering drinking water sources via different pathways. The use of untreated or inadequately treated water attributes to serious water borne diseases. Layered Double Hydroxides (LDHs) are materials with unique layered structures that include expandable interlamellar spacing, anionic exchange capacities, and large surface areas. In this study, the use of LDHs and their derivatives (e.g.; organo-LDHs, calcinated LDHs) in removing bio-agents (viruses, bacteria, and other hazardous biological agents) from waters were conducted; and the methods of optimizing LDH synthesis to achieve maximum sorption capability were attempted. The objective of this work was to use LDH as a filtration material to remove bacteria, viruses and other potentially hazardous bioagents from waters. The unique feature of positive charges on the surface of LDHs makes them ideal sorbents in removing bio-agents, which are usually negatively charged. Although some bacteria and viruses may express some positive surface charges at specific pH values, the LDHs derivatives, organo-LDHs (surfactant modified LDHs), are still capable of removing them effectively.

Studies were performed in systems where LDH materials were used to remove MS2 (an indicator virus) and Escherichia coli (an indicator bacterium) from deionized tap water, and “artificial groundwater”. Our results indicate that LDHs materials have a viral adsorption efficiency of 100% and 99.9% at viral concentrations of 2 x 106 plaque forming unit (PFU)/L and 2 x 108 PFU/L, respectively. The loading ratio in MS2 adsorption is approximately 1.5 x 1011 to 8.0 x 1012 PFU /kg of LDHs. The bacterial study demonstrated adsorption efficiency of 99.9% at an E. coli concentration of 3.7 x 108 colony forming unit (CFU)/L. The loading ratio in E.Coli adsorption is approximately 2.2 x 1011 CFU/kg of LDHs.

Since the studies were performed under standard laboratory conditions, the real world performance may not be extrapolated. To address this issue, a faucet attachment device containing LDH as the filtering material was fabricated and tested its capability of removing bacteria from flowing water with minimal retention time. Efficiency of removing total bacteria from the raw water was in the range of 65%-95%.

In summary, LDH has a sandwich-like structure that consists of layers with nano-sized gap and pores, thanks to the unique arrangement of cations and hydroxides in LDH. The uniformed structure has pores < 10 nm, which excludes most bioagents from entering the pores or traps extremely small particles in the intralayers. More importantly, the configurations of LDH establish and maintain an intensive distribution of positive charges on the material surface, making it highly efficient in adsorbing negatively charged agents, including bacteria and viruses, from water systems. Currently two US patents are pending for LDH structure modification and applications.