Abstract:
A method for removing arsenic from drinking water using a flexible modular absorption system. Modules containing adsorption media may be connected through a modular header system in various configurations, for example, lead-lag or parallel. Once the adsorption media is exhausted, the adsorption media may transported to a central facility for regeneration and then returned to the customer for reuse. The customer has no on-site operation, chemicals, secondary waste or sludge to manage. Off-site regeneration can be combined with responsible metals recovery and waste residuals disposal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/673,652 filed Apr. 21, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates to a method of removing arsenic from potable water supplies using a flexible modular absorption system, and in particular to such a method which uses modular regenerable adsorption vessels which may be connected in various configurations for flexibility and expandability.  
         [0005]     2. Brief Description of the Related Art  
         [0006]     By January 2006, municipalities will face a deadline for a new more stringent standard for the removal of arsenic from drinking water. The standard will fall from 50 ppb to 10 ppb. In many areas, naturally occurring arsenic-containing waters or contaminated groundwater is present. The conventional processes for the removal of arsenic rely on chemical processes which utilize the chemical reaction of arsenic with iron compounds. The most common techniques involve precipitation followed by coagulation and filtration. However, these conventional processes are less desirable for treatment of the small quantities of water required in many applications, for example, water flows of 1000-5000 gallons per minute or less. Furthermore, the water sources for many municipalities vary considerably during the year in terms of available flows and arsenic loadings.  
         [0007]     Some new techniques for the treatment of water to remove arsenic also rely on the chemical reaction of arsenic with iron compounds, but the iron compounds, such as iron oxide or iron hydroxide, are used in the form of granules. The granules form an adsorption medium which removes the arsenic from the water. The drawback to these systems is that the granules tend to break up and produces fines which must be removed and discarded. It is suggested by recent reports that such fines may tend to leach arsenic when the fines are disposed in landfills.  
         [0008]     Attempts to solve this problem have led to the production of various media where an iron compound is incorporated into or coated onto into a substrate. Examples are U.S. Pat. Nos. 6,790,363; 6,042,731; 6,203,709; 6,599,429; 5,369,072; and 6,200,482. U.S. Pat. No. 6,521,131 assigned to SolmeteX, Inc. discloses an absorbent material for removing mercury from water which comprises a mercury-selective chelating group bound in a porous resin. SolmeteX also offers a nanoparticle based selective resin for the removal of arsenic from water. This resin, called ArsenX np  is based on hydrous iron oxide particles and provides a durable substrate for an absorption medium.  
         [0009]     Typically such arsenic adsorption media are provided in large tanks through which the water to be treated is passed. The media are placed in the tanks by sluicing the media in a quantity of water and the spent media are removed in the same fashion. The spent media is placed in smaller totes for return to a regeneration facility. Such arrangements may exacerbate the problem of fines when friable media is sluiced from one container to another. Alternatively, arsenic absorption media may be regenerated on-site but there are substantial drawbacks in that more operator attention is required, more chemical handling occurs, and there are potential environmental problems required by the disposal of wastes from the regeneration of the media.  
         [0010]     The prior art methods for removing arsenic from drinking water therefore have a number of drawbacks, especially for smaller municipalities. The prior art methods require significant amounts of operator attention, expose the municipality to environmental liability through the handling of chemicals and wastes, are relatively inflexible in responding to natural variations in water flows and arsenic loading.  
         [0011]     References mentioned in this background section are not admitted to be prior art with respect to the present invention.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     The present invention addresses these problems by providing for a method for arsenic removal from potable water supplies the employs a flexible modular adsorption system. Vessels containing adsorption media may be connected through a modular header system in various configurations, for example, lead-lag or parallel, in order to have the flexibility to address variations in loading and flow. Preferably, the medium used in the modules for arsenic removal is SolmeteX regenerable arsenic removal media.  
         [0013]     It is known to employ adsorption media to adsorb targeted ions onto regenerable selective adsorption media, including ion exchange and modified ion exchange media. When a vessel is exhausted, it can be disconnected from the system, transported with the exhausted (loaded) adsorption media to a central facility for regeneration and then returned to the customer for reuse. The media is contained in the vessel and in not sluiced out of the vessel into separate containers, thus avoiding potential damage to the media and the production of fines. The customer, for example, a municipality, thus avoids on-site operation, and the management of chemicals, secondary waste or sludge. Off-site regeneration can be combined with responsible metals recovery and waste residuals disposal to minimize environmental concerns.  
         [0014]     The modular system of the present invention allows such centralized regeneration and waste disposal techniques to be applied to arsenic removal. Modular systems provide simple, cost-effective, flexible and easily expandable solutions to the problem of arsenic removal. When the adsorption media is exhausted, palletized vessels with media may be shipped to a central facility for media regeneration, equipment inspection and maintenance. Modules can be provided in various sizes. Multiple modules can handle a wide range of flow rates from 100 GPM to &gt;1,000 GPM.  
         [0015]     The advantages of the present invention are that it is user friendly, environmentally sound, and cost effective for arsenic removal.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]      FIG. 1  is an elevation view of a palletized modular vessel comprising a vessel for containing arsenic absorption media.  
         [0017]      FIG. 2  is an elevation view of a pair of the modular vessels of  FIG. 1  showing modular inlet and outlet headers and piping for flexibly connecting the modular vessel.  
         [0018]      FIG. 3A  is a schematic diagram of the pair of modular vessels of  FIG. 2  showing valving for connecting the modular vessels in various configurations.  
         [0019]      FIG. 3B  is a table showing the operation of the valves of  FIG. 3A  to connect the modular vessels in parallel, lead-lag (serial) or stand-alone configurations.  
         [0020]      FIG. 4A  is a schematic diagram of the pair of modular vessels of  FIG. 2  showing a modular backwash header in addition to modular inlet and outlet headers and further showing valving for connecting the modular vessels in various configurations.  
         [0021]      FIG. 4B  is a table showing the operation of the valves of  FIG. 4A  to connect the modular vessels in parallel, lead-lag (serial) or stand-alone configurations and also showing the operation of the valves to backwash the vessels.  
         [0022]      FIG. 5  is a perspective view of a assemblage of several pairs of modular vessels of the present invention showing the connection of adjacent modular inlet and outlet headers. Two pairs of vessels are shown in the connected configuration and one pair of vessels is shown prior to connection.  
         [0023]      FIG. 6  is a perspective view of the assemblage of modular vessels of  FIG. 5  showing all three pairs of vessels in a connected configuration. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     With respect to  FIGS. 1-6 , the preferred embodiments of the present invention may be described. The method the present invention employs a modular system that is cost effective, simple, flexible and expandable. The system may include single or multiple modular absorption vessels. No on-site chemical usage or storage is required. Waste is not generated on-site, therefore no transportation or storage of waste is required and environmental liability is limited. The modules serve as on-site service vessels and shipping containers for off-site regeneration. Exhausted vessels are exchanged with regenerated replacements.  
         [0025]     By using modular vessels connected with a modular header system, a wide range of flow rates can be accommodated. The modular vessels can be connected in various configurations depending on the needs at a particular facility or a particular time. The modular vessels can be mounted on skids or in a trailer for short or long term service. Further, the modular vessels can be expanded in increments to meet any flow rate requirements. By using a modular system, installation of additional modular vessels is expedited.  
         [0026]     As an alternative, exhausted media can be removed from the modules and shipped to a central regeneration facility in shipping totes. Shipping totes can also be used for storage of spare media.  
         [0027]     Further, the modular system of the present invention can be used with non-regenerable media. The exhausted media can be shipped to a central facility for disposal in order to avoid on-site waste disposal problems.  
         [0028]     A single palletized modular vessel  10  is shown in  FIG. 1 . The palletized modular vessel  10  comprises a vessel  11  for containing absorption media, a pallet  12  for containing the vessel  11 , an inlet  13  and an outlet  14 . As can be seen from  FIG. 2 , the palletized modular vessels  10  can be provided in palletized pairs  20  with a modular header for each such pair  20 . Single modular vessels can also be provided with a modular header. The modular header comprises an inlet header pipe  21  and an outlet header pipe  22 . The inlet and outlet pipes  21 ,  22  can be connected to an adjacent modular header for adjacent modules, thereby allowing any number of palletized modular vessels to be interconnected. The connection between adjacent modular headers may be by any method of interconnection known to those skilled in the art.  FIG. 5  shows two pairs of interconnected modular vessels  30 ,  31  and a additional pair of modular vessels  32  before connection.  FIG. 6  shown the pair of modular vessels  32  after connection to the pre-existing configuration of modular vessels  30 ,  31 .  
         [0029]     In addition to connection to the modular headers, the modular vessels may be interconnected among themselves by other piping so as to provide flow configurations as appropriate for a particular installation. As shown in  FIG. 3A , the modular vessels A, B in a pair of modular vessels may be connected by first piping  40  from the outlet  42  of vessel B to the inlet  43  of vessel A. Second piping  41  connects the outlet  44  of vessel A to the inlet  45  of vessel B. A valve  3  is placed in piping  40  intermediate between the inlet  43  of vessel A and the outlet  42  of vessel B. Similarly, a valve  4  is placed intermediate between the inlet  45  of vessel B and the outlet  44  of vessel A. First inlet header piping  50  is operatively connected between inlet header  51  and a point between inlet  43  of vessel A and valve  3 . Second inlet header piping  52  is operatively connected between inlet header  51  and a point between inlet  45  of vessel B and valve  4 . Likewise for outlet header  53 , first outlet header piping  54  is operatively connected between outlet header  53  and a point between outlet  42  of vessel B and valve  3 . Second outlet header piping  55  is operatively connected between outlet header  53  and a point between outlet  44  of vessel A and valve  4 .  
         [0030]     To complete the valving arrangement, a valve  1  is placed in first inlet header piping  50 , a valve  2  is placed in second inlet header piping  52 , a valve  5  is placed in first outlet header piping  54  and a valve  6  is placed in second outlet header piping  55 .  
         [0031]     As shown in  FIG. 3B , various flow configurations between vessel A and vessel B are possible by opening or closing various combinations of valves  1 ,  2 ,  3 ,  4 ,  5 ,  6 . For example, lead-lag or serial configurations, where the outlet from one vessel is connected to the inlet of the other vessel, is possible with either vessel A or vessel B in the lead position. Such a configuration may be employed to improve treatment efficiency but reduced flow capacity. Alternatively, vessels A, B may be connected in parallel where respective inlets and outlets are connected to respective inlet and outlet header pipes for maximum capacity at the expense of reduced treatment efficiency. Various combinations of these two basic configurations can be used as appropriate for a particular installation or a particular situation. For example, greater flows may be required in certain time of the year and in that case a parallel configuration may be used. When arsenic levels are higher and greater treatment efficiency is necessary, the modules can be easily reconnected to provided a configuration with lead-lag flow paths.  
         [0032]     In applications where only one vessel is required, a two-vessel lead-lag configuration may be suitable to eliminate the risk of leakage after exhaustion of the primary vessel and to provide spare absorption media on-site. When the lead vessel is exhausted, it is taken out of service to be regenerated and a freshly regenerated vessel becomes the new lag unit or polisher. The lead vessel may be intentionally overrun after initial breakthrough to achieve enhanced media loading.  
         [0033]     The present invention has the advantage of flexibility. It is not uncommon for a municipality, water district, or the like with multiple wells to vary the flows per well due to changing arsenic levels, groundwater availability, or for other reasons. The modular vessels and header sections of the present invention can easily be moved from one well site to another.  
         [0034]     An alternative embodiment of the present invention incorporating backwash capability is described with reference to  FIGS. 4A  and B. As shown in  FIG. 4A , a valving arrangement as described above with reference to  FIG. 3A  is enhanced by the addition of a modular backwash header  60 . First backwash header piping  61  is operatively connected between backwash header  60  and a point between inlet  43  of vessel A and valve  3 . Second backwash header piping  62  is operatively connected between backwash header  60  and a point between inlet  45  of vessel B and valve  4 . As shown in  FIG. 4B , the addition of the backwash valving arrangement allows the vessels to be connected in lead-lag or parallel configuration as heretofore described and also to be connected to backwash either vessel A or vessel B. As would be known to those skilled in the art, automatic valves can be employed for automatic backwashing. Backwash capability is particularly important to certain types of media, including without limitation, BIRM, activated carbon, filtration media, and granular ferric media.  
         [0035]     In the case of regenerable media, the present invention allows a simple implementation of upflow regeneration, which has the benefits of high quality effluent in service and a highly concentrated regenerant, because the media remains in place in the vessel rather than being mixed while being pumped to and from shipping containers.  
         [0036]     Although the present invention has been described with particular reference to arsenic removal, the present invention is not so limited and may be employed with various other types of water treatment media, for example without limitation, activated carbon, and iron and manganese removal media.