Abstract:
The invention provides apparatus and methods for completely automated cleaning of reverse osmosis systems. This includes cleaning initiation, selection of cleaning agent, complete cleaning and rinsing, and cleaning evaluation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority under 35 U.S.C. § 119(e) from U.S. Provisional Application Ser. No. 60/948,293, filed Jul. 6, 2007, the contents of which are incorporated herein, in their entirety, by this reference. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention resides in the field of fluid purification and specifically in a fully automated membrane cleaning system and methods of using the same. More specifically, embodiments of the present invention are directed to a fully automatic system that is capable of initiating cleaning of at least one membrane based on a set of programmable parameters, wherein, based on the parameters chosen, the automated system selects a cleaning chemical, initiates cleaning, and, once cleaning is complete, evaluates the system performance to determine if additional cleaning is warranted. 
       BACKGROUND OF INVENTION 
       [0003]    The production of safe drinking water from contaminated source water has been practiced for many years. Traditionally, surface water is contaminated with particulate matter from contact with the earth and microorganisms from contact with wildlife. The salinity of water is highly variable from fresh water in streams to salt water in oceans. Common sources of water contamination include agricultural, industrial, and conflict activity. 
         [0004]    Most communities have stationary water treatment facilities designed to produce safe drinking water from the source water to the community. Natural or man-made disasters can compromise the functionality of existing water treatment facilities requiring mobile water purification equipment be deployed for disaster relief by organizations such as the Red Cross. There are also many areas that are under developed and have no water treatment infrastructure. People living and working in these areas require a mobile water purification system to treat the available water source. The military is also a large user of mobile water purification systems. 
         [0005]    Many systems have been developed to address the need for mobile water purification systems for use on source water of unknown and variable quality. However, the success of these systems has been limited. The first mobile systems developed simply filtered and chlorinated water. These systems were ineffective for treatment of salt water or chemically contaminated water. The next generation of mobile water purification systems utilized reverse osmosis (RO) to remove dissolved salts in sea water and provide some protection against chemical contamination. But, these systems fouled very quickly when they encountered turbid water. The most advanced systems currently available continue to have fouling problems, have limited ability to remove nuclear, biological, and chemical agents, and require highly trained operational personnel. 
         [0006]    There has been fairly extensive evaluation of the performance of the Army&#39;s “ROWPU” (reverse osmosis water purification unit). There have also been several iterations of this device with different flow rates. Despite several design changes, the “ROWPU” units remain plagued by fouling problems. Additionally, it has been recognized that for several contaminants of concern, reverse osmosis alone is not adequate to provide sufficient removal. Therefore, add on filter cartridges have been employed to increase contaminant removal capability. U.S. Army document TB MED 77 provides documentation of how to operate its “ROWPU” units for maximum effectiveness. This involves an extensive chain of command with approval of the water source to be treated following analysis of the source water, evaluation of any threat of warfare agents, and operation of the units by highly trained personnel. 
         [0007]    All the prior art mobile water purification systems have some deficiency. Deficiencies exist in resistance to fouling, contaminant removal capability, and operator intervention requirements. Unknown source water has a high potential to foul water purification equipment as it is likely that highly turbid water will be encountered. Many systems have inadequate particulate removal capability. For example, the use of a 5 micron cartridge filter prior to reverse osmosis. The reverse osmosis membrane has a very fine pore size of less than 0.005 microns. An abundance of particulate matter resides in the range of size difference between 5 and 0.005 microns including most microorganisms, fine sand or silt, and colloidal matter. Thus, the reverse osmosis membrane is easily fouled and difficult to remove. Biofouling is particularly difficult to remove from membranes and is well documented as a common fouling problem in membrane systems. There is also potential for oil to be present in the water source, which will readily foul membrane surfaces. Furthermore, all of the prior art systems rely on operator intervention to clean the fouled systems. 
         [0008]    The U.S. Army has also evaluated the ability of reverse osmosis to remove a number of contaminants in its Water Quality Information Paper No. IP-31-014. Some contaminants are not removed well by reverse osmosis. It is also noted that reverse osmosis membranes may become compromised. A study was presented at the American Water Works Membrane Technology Conference in 2003 that evaluated the ability of reverse osmosis membranes to remove viruses under a number of conditions including the presence of a pinhole and torn O-ring seals. Compromising of the membrane or O-ring significantly lowers the rejection ability of the reverse osmosis element. 
         [0009]    Reverse osmosis membrane systems are utilized to remove a variety of contaminants from water. These contaminants may adhere to the membrane surface or be trapped in the feedspacer of the membrane. Most membranes require cleaning on a periodic basis due to accumulation of contaminants within the membranes. Certain types of contaminants are removed by different types of cleaning agents. There are three main types of cleaning agents: high pH cleaning agents, low pH cleaning agents, and biocides. There are many varieties of these basic types of cleaning agents. For example, there are a number of different high pH cleaners that contain a variety of surfactants. When membrane systems become highly fouled they often require more rigorous cleaning, and sometimes highly specialized cleaning solutions are required. However, most membrane applications will effectively respond to the 3 major types of cleaning agents. Low pH cleaners are basically for scale removal. High pH cleaners are for organics and colloids. Biocides kill organisms. Most membrane systems have a separate cleaning skid that can be connected by hoses to the membrane banks. Cleaning chemicals are added to a tank on the cleaning skid. All valving and pump speed control is manual. 
         [0010]    In 1995, Heiss designed an automatic cleaning system that had automated valves and a speed controlled pump to perform the entire cleaning and rinsing procedure. An operator was still required to add the appropriate cleaning agent, initiate the cleaning, and return the system to service when the cleaning was complete. This was a vast improvement from manual cleaning systems and allowed more consistent results. However, the issue of when to clean and what to use for a cleaning agent was not addressed by this system. 
         [0011]    U.S. Pat. No. 6,074,551 (Jun. 13, 2000) to Jones et al. describes an automated system for the sanitization of membranes by moving some valves. But, this system lacks a means of auto initiation. 
         [0012]    U.S. Pat. No. 5,494,573 (Feb. 27, 1996) to Schoenmeyr et al. describes a monitor for RO systems that displays conditions such as clogged prefilter and failed membrane. There is no action initiated or associated with the monitoring, and membrane performance monitoring is limited. 
         [0013]    U.S. Pat. No. 4,361,485 (Nov. 30, 1982) to Boonstra describes methods of cleaning RO membranes in series by recirculation of a washing liquid. 
         [0014]    Therefore, a need still exists for a membrane cleaning system that is more fully automated, thereby providing a means for fluid purification that is robust and capable of prolonged use without the supervision of highly trained personnel, while simultaneously maintaining and monitoring a high quality of fluid purification. 
       SUMMARY OF INVENTION 
       [0015]    The current invention provides automated membrane cleaning methods and devices for initiating, determining cleaning agent(s), evaluating cleaning efficacy, and evaluating the need for further actions such as additional cleaning or returning system to service. The older system requires an operator to initiate the cleaning and add appropriate chemical to the cleaning tank. The new system is fully automatic and smart. It initiates cleaning based on a set of programmable parameters including pressure, flow and analytical values at various points in the system. Based on these parameters it chooses a chemical to clean with, automatically adds that chemical to the solution tank, and initiates a cleaning. At the end of the cleaning it re-evaluates system performance and may clean with an additional chemical if performance warrants. 
         [0016]    In a preferred embodiment, all the set up parameters are adjustable. Preferably, a programmable logic controller (PLC) operates the sequence and receives input from a human machine interface into which operating parameters are entered. 
         [0017]    The major advantages to this new design are that it allows unattended system operation and provides immediate response to fouling. This fits particularly well with an interstage fluid purification system because it allows the solubilities to be pushed to the limit before the interstage treatment while the cleaning system assures a rapid response to fouling if operating conditions or variables change, and solubilites are exceeded. 
     
    
     DETAILED DESCRIPTION OF INVENTION 
       [0018]    The invention provides apparatus and methods for completely automated cleaning of reverse osmosis systems. At it&#39;s most basic, the invention includes a fluid purification system including a reverse osmosis (RO) purification unit configured to include a fully automated cleaning system. The RO unit may include one or many individual RO modules and these one or many RO units may compose the entire fluid purifying system or merely a single purification unit within a larger and diverse fluid purification system. 
         [0019]    The RO system is fitted with automated valves and at least one speed controlled pump. There is an automated cleaning inlet and cleaning outlet valve for each stage of membranes and each membrane stage is cleaned independently. Furthermore the outlet flow from each membrane stage has automated valving to allow fluid return to a cleaning tank or routing to disposal. The inlet to each stage has automated valving for input from a cleaning tank or rinse water source. The system is under the control of a PLC, which receives input from monitors of the parameters of the fluid and the membrane stages and provides control over fluids moving through the membrane stages such that cleaning cycle proceeds automatically upon detection of input parameter values, allowing for displacement of fluid in the membranes with cleaning solution, recirculation of cleaning solution at varied velocity, and displacement of cleaning solution with rinse water. 
         [0020]    The initiation of the cleaning is determined by evaluation of a number of variables in the RO system. The RO system is controlled by a logic processing device, such as a PLC or computer and has a human machine interface (HMI) having a display of variables and a means of variable and/or command entry. There are several parameters of operation that are monitored by the PLC, including permeate flow, concentrate flow, feed to concentrate differential pressure for each stage, feed conductivity, permeate conductivity, and cleaning solution pH. Additional parameters that may be monitored include concentrate conductivity and concentrate hardness. 
         [0021]    Preferably, there is a screen on the HMI that lists types of cleaning that may be performed, which may include any or all of the following: high pH, low pH, biocide or a combination of these cleaning types. For each type of cleaning, the parameters listed above may be selected to indicate whether the parameter is monitored for automatic initiation of that type of cleaning. There is also a value entry allowing input of the value or values that cause cleaning initiation. If a parameter is selected for a particular cleaning type and the initiation value is detected, the cleaning will be initiated. 
         [0022]    For acid and caustic type cleanings, the particular cleaning chemical is injected into the cleaning tank, while the solution is recirculating in the tank and the pH is monitored. When the chosen pH is attained, the cleaning will proceed. 
         [0023]    In the event of biocide cleaning, the chemical pump will operate for a preset time to provide a certain amount of biocide in the cleaning tank. 
         [0024]    When a cleaning has completed, the PLC will restart the purification system. 
         [0025]    A preferred embodiment of the invention contains an additional HMI screen where the above parameters may be selected and values may be entered for post-cleaning monitoring. These post-cleaning monitoring values may cause initiation of an additional cleaning or allow the system to continue normal operation. 
         [0026]    The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiment described hereinabove is further intended to explain the best mode known for practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.