CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national stage application of International Patent Application No. PCT/CN2016/093965, filed Aug. 8, 2016, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates a novel hand-carry gravity-driven (or mechanically-enhanced) water filter with high throughput and water disinfection capabilities. The present water filter can supply safe drinkable water by simple purification of various contaminated waters, such as river water, rain water, emergency water in disaster areas, etc.

BACKGROUND OF THE INVENTION

Timely supply of safe water at outdoor or emergency situation is critical for human health. Water filters in current use for these applications are mostly composed of membranes prepared by the phase inversion method. However, due to the low porosity and high mass transfer resistance of these membranes, the throughput of the filters is limited.

Although the existing methods are effective for water treatment, they are limited when used as portable water filtration devices. In particular, the methods of coagulation, flocculation and sedimentation for cleaning water, and chlorine, ozone or ultraviolet radiation for disinfecting water are practical and suitable for centralized water treatment facilities. However, distillation and electrodialysis processes are not suitable for portable outdoor water purification technology due to their high energy consumption. Granular media filtration and adsorption methods suffer from low efficiency, which makes it difficult to use them for outdoor water purification.

Membrane technologies have recently come into use for water purification. Reverse osmosis (RO) and nanofiltration (NF) membranes are being used for water treatment. However, high pressure is needed in these two processes, which means high energy consumption. Low external pressure is needed in ultrafiltration (UF) and microfiltration (MF) processes. However, the low rejection performances of the existing UF and MF membranes limit their uses in outdoor applications. More recently, forward osmosis processes have attracted more attention for outdoor water purification. However the draw solution used in this process limits its application.

Nanofiber-based membranes have high porosity and controllable pore size, which can significantly improve the efficiency of a water filter. However, there is little evidence of the use of nanofiber membrane-based water filters with designed structure and surface chemical properties in products or potential products that provide such gravity-driven outdoor water treatments.

SUMMARY OF THE INVENTION

The present invention relates to a water filter formed for effective removal of a wide range of contaminants (e.g., pathogens, suspended solids and heavy metals) as part of a purification process. The purification process can be carried out under the force of gravity (with an option for mechanically-enhanced filtration) without electricity.

In one exemplary embodiment of the invention, the water filter is small enough to be hand carried. Also, because of the membrane used, the filter has a high throughput and can be developed for outdoor applications. In particular, the membrane has a novel composite structure (i.e., an interwoven composite structure).

The water filter of the present invention can supply safe drinkable water by simple purification of various contaminated waters, such as river water, rain water and emergency water in a disaster area etc. Because the purification process can be carried out under the force of gravity (with an option for mechanically-enhanced filtration) without electricity, it is particularly useful for outdoor application where an energy source is not available. The invention may also find applications for wastewater treatment, wastewater reclamation, and desalination (e.g., membrane modules used in membrane bioreactors, as a pretreatment step and polishing step for reverse osmosis).

Silver nanoparticles may be loaded in-situ on the surface of the membrane to provide for water disinfection. The filter is effective for removal of a wide range of contaminants (e.g., pathogens, suspended solids and heavy metals). The water filter has excellent antifouling properties as well as the anti-microbial properties, and can be easily regenerated by water flushing or physical cleaning. Further, the membranes may be mounted in a folded configuration to increase the effective membrane surface area.

Thus, particles (e.g., suspended inorganic particles and organic particles), biological entities (e.g., pathogen and bacteria), and heavy metal ions (e.g., Pb2+, Cd2+, Ni2+and Cr6+) can be removed after purification by this water filter.

In one embodiment, the present invention relates to a composite membrane comprising polymeric nanofibers, the composite membrane having a composite structure of large diameter nanofibers and small diameter nanofibers having a number average diameter in the range of 100-1000 nm, the polymeric nanofiber membrane has a porosity in the range of 75-95% and a mean pore size in the range of 10-1000 nm.

In a further embodiment, the composite membrane has a thickness of 50-500 μm.

In still a further embodiment, the large diameter nanofibers have diameters in the range of 200-1000 nm and the small diameter nanofibers have diameters in the range of 100-500 nm.

In still a further embodiment, the polymeric nanofibers comprising different polymeric nanofibers (hydrophobic or hydrophilic).

In still a further embodiment, the polymers forming the polymeric nanofibers are selected from a group consisting of poly(acrylonitrile) (PAN), poly(vinyl alcohol) (PVA), poly(vinyl fluoride) (PVDF), chitosan, polysulfone (PSf), polyethersulfone (PES), poly(methyl methacrylate) (PMMA) and poly(vinyl butyral) (PVB).

In still a further embodiment, the composite membrane further comprising nano-beads or microspheres.

In still a further embodiment, the nano-beads or microspheres have an average diameter of 20-2000 nm.

In still a further embodiment, the composite membrane further comprising a surface coating of polydopamine compounds.

In still a further embodiment, the composite membrane further comprising in-situ surface loaded silver nanoparticles.

In still a further embodiment, the in-situ surface loaded silver nanoparticles are reduced by the pre-coated polydopamine layer.

In still a further embodiment, the in-situ surface loaded silver nanoparticles have a loading amount of 0 wt. %-5.0 wt. %.

In still a further embodiment, the in-situ surface loaded silver nanoparticles have an average diameter of 0-100 nm.

In one embodiment, the present invention relates to a gravity-driven nano-fibrous membrane filter comprising: a support structure forming an open top volume; and a composite membrane according to the preceding embodiments on at least a bottom of the support structure, said composite membrane having a folded configuration, said filter accepting feed water at the open top and allowing cleaned water to exit below the membrane at the bottom.

In a further embodiment, the filter further comprising a mechanically assisted vacuum system for drawing feed water entered at the top of the filter through the membrane.

In still a further embodiment, the mechanically assisted vacuum system comprises a piston located below the filter and a handle connected to the piston that allows the piston to be pulled down creating a vacuum on the opposite side of the membrane from the feed water.

In still a further embodiment, silver is loaded onto the composite membrane to provide water purification.

In one embodiment, the present invention relates to a process for fabricating a nanofibrous membrane comprising the steps of: preparing a solution by mixing and annealing in a sealed container a polymer mixture consisting of a certain amount of polymer and additives in an organic solvent at 50˜90° C. until homogenous, cooling the polymer mixture to room temperature; applying voltage in the range of 10-30 kV (preferably 15-25 kV) to the solution at room temperature as it is ejected in a stream from a syringe toward a rotating metal drum; feeding the solution from the syringe at the rate 0.5-2.0 mL/h (preferably 1.0-1.5 mL/h); and collecting the stream as nanofibers on the rotating metal drum at a distance of 5.0-20.0 cm (preferably 10-15 cm) from the exit of the syringe.

In one embodiment, the present invention relates to a non-solvent induced phase separation (NIPS) process for fabricating a nanofibrous membrane comprising the steps of: preparing a solution by mixing and annealing in a sealed container a polymer mixture consisting of a certain amount of polymer and additives in an organic solvent at 50˜90° C. until homogenous, cooling the polymer mixture to room temperature; casting with a thickness the solution at room temperature onto a clean and smooth glass plate; quickly and smoothly immersing the glass plate into a coagulation water bath; and after the substrate is formed by phase inversion, removing the excess solvent and additives by soaking in DI water.

In one embodiment, the present invention relates to a process for fabricating a composite membrane nanofiber structure, comprising the steps of: preparing a compound by mixing and annealing in a sealed container a polymer mixture consisting of a certain amount of polymer and additives in an organic solvent at 50˜90° C. until homogenous, cooling the polymer mixture to room temperature; fabricating a membrane substrate from the room temperature polymer mixture; and subjecting the membrane substrate to interfacial polymerization by bringing it into contact with a polyamine aqueous solution for 1-1200 seconds (preferably 30-600 s), removing the excess polymer solution from the surface of the substrate, immediately bringing the substrate into a TMC n-hexane solution for 1-600 s (preferably 10-300 s), and after the desired active layers have been formed, rinsing the membrane thoroughly with hexane and storing it in DI water at 15-25° C. (preferably 20° C.) before characterization.

In a further embodiment, the step of bringing the membrane substrate into contact with the polyamine aqueous solution is performed by pouring it into the polyamine aqueous solution.

In still a further embodiment, the step of bringing the substrate into the TMC n-hexane solution is performed by pouring it into the TMC n-hexane solution.

In still a further embodiment, the process further including a step of loading silver nanoparticles in-situ on the surface of the membrane to provide for water disinfection.

In still a further embodiment, the step of silver loading the membrane comprises the steps of coating DOPA or L-DOPA on the surface of the membranes by simple immersion in a Tris buffer solution; and immersing the membranes into a silver nitrate aqueous solution.

In still a further embodiment, the step of coating the membranes is carried out with a 0.5-5.0 g/L solution bath of DOPA or L-DOPA for 0.5 hours to 24 hours with a pH of 7.0 to 9.0 for the Tris buffer solution.

In still a further embodiment, the step of immersing the membranes in the silver nitrate aqueous solution is carried out with a 0.5-10.0 g/L (preferably 1.0-5.0 g/L) silver nitrate aqueous solution for 0.5 hours to 10 hours.

