Capacitive electrostatic process for inhibiting the formation of biofilm deposits in membrane-separation systems

Inactive Publication Date: 2005-12-01
PITTS M MICHAEL JR +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0020] Therefore, according to these and other objectives, the present invention consists of utilizing a high-voltage capacitive electrostatic device operated at more than 10,000 volts, preferably at 30,000 and higher voltages, to prevent the formation of biofilms and correspondingly improve the performance of membrane-separation processes. The device is used in connection with conventional membrane-separation processes, particularly reverse-osmosis units, wherein species of a given ionic polarity are separated from water. The device is immersed in the water flowing across the membranes and is operated continuously at very high voltages, preferably greater than 30,000 volts DC. The charge on the wetted surface of the suspended particles is altered by the ele

Problems solved by technology

Water treatment systems are-commonly subject-to-reduced efficiency and failure as a result of scaling and clogging by solid particles suspended in the aqueous medium, as well as by the formation of biofilms that adhere to exposed surfaces in the equipment.
Corrosion caused by biofilms, biosludge and scale deposits is also a source of equipment failure and maintenance challenges.
To the extent that prior-art system have been successful in facilitating the removal of suspended material, they still have not prevented the formation of mineral and organic deposits, especially biofilms, on filtration membranes and wetted surfaces of water treatment plants.
Such intimate contact is very important because any air space left between the metal and the dielectric, such as produced by blisters or bubbles in the dielectric layer, causes electrical arcing that eventually perforates the Teflon® layer, shorts the electrode to the water body, and greatly reduces the electrostatic efficiency of the device.
Moreover, a large air space would form yet another dielectric layer within the system, which is undesirable because of the very low capacitance of air which would further reduce the overall capacitance of the system.
The devices of the prior art are limited in their application by twofold problems.
Because of its well-known physical properties, PTFE material such as Teflon® is not suitable for adherence to the surface of metal conductors other than by heat-shrink processes.
Any attempt to cover an electrode with Teflon® by a process other than heat-shrinking, such as would be required for an electrode having a non-cylindrical shape, would necessarily compel the formation of seams and connections which would be very difficult to achieve and prone to breakdown during use.
In addition, due to the non-stick properties of the mater

Method used

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  • Capacitive electrostatic process for inhibiting the formation of biofilm deposits in membrane-separation systems
  • Capacitive electrostatic process for inhibiting the formation of biofilm deposits in membrane-separation systems
  • Capacitive electrostatic process for inhibiting the formation of biofilm deposits in membrane-separation systems

Examples

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Example

EXAMPLE 1

[0063] An 18-inch ceramic electrode configured according to the device 10 and a 30 kV DC power supply were installed in the pump suction of a reverse osmosis unit at a soft drink bottling plant. The object of the installation was to study the effect of the high-voltage capacitive electrostatic field created by the device 10 on RO membranes as a means for maintaining the membranes free of biological deposits. The reverse osmosis unit in the test was an Osmonics Model OSMO 43CHF-PR216KY / DLX, having a permeate rate at 25° C. of about 450 liters per minute and a concentrate rate of about 135 liters per minute, with primary and final maximum and minimum pressures of 400 psi and 250 psi, respectively. The Osmonics unit consisted of a 3-2 series array configuration (as illustrated in FIG. 9) with each vessel housing five Filmtec membranes Model Number BW30-330. Feed water was taken from city water with about 300 ppm in total dissolved solids. Pretreatment for the water involved s...

Example

EXAMPLE 2

[0067] The capacitive electrostatic device of the invention was utilized to determine whether improvements could be obtained in a system for producing high purity water in a microelectronics plant that included two independent RO units in series. The system used an initial 2-1-1 array configuration, wherein the permeate of the first unit became the feed to a second unit having a 2-1 array, both units being equipped with Hydranautics Model 8040-LHY-CPA2 membranes. Prior to use of the electrostatic device, maintenance personnel cleaned the membranes approximately every two to three weeks. The membranes were cleaned again at the time of installation of the electrostatic device. As a part of normal feed pretreatment, a chemical dispersant was being added to the feed stream of the first RO unit. This dispersant feed was reduced by 50% after the test began.

[0068] Three weeks after the test started at about 35,000 volts DC, one vessel from each unit was opened for inspection. Wh...

Example

EXAMPLE 3

[0071] This test was conducted at a grain refinery where a permeate product for process water makeup was being produced by two independent and identical reverse-osmosis systems with a 5-3-1 configuration operating in parallel. The two RO systems shared the same water source and pretreatment system. The pretreatment consisted of a peroxide / air process to oxidize high contents of hydrogen sulfide in the water, followed by a catalytic carbon bed to remove residual sulfides, and bag filters for final polishing. The first RO unit had new membranes installed prior to the test while the second RO unit continued to operate with fouled membranes.

[0072] Fouled membranes on both units had been usually replaced every three months with clean modules, and the fouled modules were being sent out to the manufacturer for cleaning. The high voltage power supply and the electrostatic capacitor of the invention were installed and placed in operation for 27 days at 30,000 volts DC. On the sixt...

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Abstract

A high-voltage capacitive electrostatic device is used to improve the performance of membrane-separation processes, particularly reverse-osmosis units, wherein species of a given ionic polarity are separated from water. The device is immersed in the water flowing across the membranes and is operated continuously at very high voltages, preferably greater than 30,000 volts DC. The charge on the wetted surface of the suspended particles is altered by the electrostatic field so generated and is found to reduce biofilm formation, thereby materially enhancing the performance of the membrane-separation system. The application of high-voltage electrostatic fields is also found to reduce corrosion of metallic surfaces in the system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation application of copending U.S. Ser. No. 10 / 047,493, filed Jan. 14, 2002, which was a CIP application of U.S. Ser. No. 09 / 416,255, filed Oct. 12, 1999, abandoned.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention generally relates to methods for the electrostatic treatment of water streams. In particular, the invention describes a method for preventing the formation of deposits, especially biofilm deposits, on conventional membrane-separation systems by the application of a capacitive electrostatic device. [0004] 2. Description of the Related Art [0005] Water treatment systems are-commonly subject-to-reduced efficiency and failure as a result of scaling and clogging by solid particles suspended in the aqueous medium, as well as by the formation of biofilms that adhere to exposed surfaces in the equipment. Corrosion caused by biofilms, biosludge and scale deposits is also a...

Claims

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Application Information

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IPC IPC(8): B01D61/02B01D61/04B01D61/14B01D61/16B01D65/08C02F1/44C02F1/48C23F15/00C25F1/00
CPCB01D61/025B01D61/04C23F15/00B01D61/145B01D61/16B01D65/08B01D2311/04B01D2321/22C02F1/441C02F1/444C02F1/48C02F2303/04C02F2303/08C02F2303/20B01D2311/2603
Inventor PITTS, M. MICHAEL JR.ROMO, RODRIGO F.V.
Owner PITTS M MICHAEL JR
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