Carbon nanotube composite membranes for small ‘designer’ water treatment systems

Small water systems that serve fewer than a few thousand persons are often less safe and less sustainable than large drinking water systems due to lack of suitable technologies. This ongoing research aims to develop a novel water treatment technology for small communities. By layering structured, functional carbon nanotubes (CNT) onto low pressure membranes (LPMs), composite membranes were prepared to remove different organic and inorganic contaminants from water, including heavy metals, viruses, natural organic matter, and organic micropollutants. The removal efficiencies varied from over 99.9% (for cadmium) to above 60% (for humic substances). A low-cost CNT formed an antifouling layer that removed membrane foulants by depth filtration, thereby extending the membrane filtration cycle over five-fold. When the CNTs were layered inside hollow fiber membranes, superb backwashable properties were observed, allowing the operation of CNT-modified membranes under full-scale treatment conditions. Moreover, a systematic study of CNT rejection by LPMs found that commercially available LPMs efficiently prevented CNT breakthrough, thus ensuring nanosafety of the treated water. By varying the composition and structure of functional CNT layers, energy-efficient composite membranes may be economically produced for designer water treatment systems and applied in small communities.