Patent Publication Number: US-2009223900-A1

Title: Wastewater treatment apparatus and method

Description:
This application claims priority to U.S. provisional application 61/068,080, filed Mar. 4, 2008, the contents of which are hereby incorporated by reference. 
    
    
     FIELD  
     This invention relates generally to treating contaminated liquids and, more particularly, to a biologically-contaminated wastewater sterilization process and apparatus. 
     BACKGROUND  
     Industry and sanitation facilities use millions of gallons of potable water each day. In use, this water is contaminated and cannot be further used without decontaminating the water. For example, a contamination problem exists with regard to water used in paper mills. Water is used in great quantities in the manufacture and processing of paper. This processing water becomes bacteria-contaminated and must be decontaminated for reuse, usually via use of chemical treatments. 
     In general, the treatment of bacterially-contaminated water or wastewater is a problem world-wide, both as regards treating industrial and sanitation wastewater for return to the habitat and the provision of adequate quantities of drinking water for human consumption. Several methods are currently used to treat contaminated wastewater. These include distillation, chemical treatment, reverse osmosis, and ultraviolet treatment. Each of these methods has its shortcomings, such as capacity and expense. 
     There is a need for apparatus and a process for decontaminating bacterially-contaminated wastewater and for providing a process and apparatus for producing safe drinking water from bacterially-contaminated water. 
     SUMMARY  
     It is therefore an object of this invention to provide apparatus and a process for eliminating bacterial contamination of process water that eliminates the necessity for repeated treatment by chemicals. 
     It is also an object to provide a need for apparatus and a process for decontaminating bacterially-contaminated waste water and for providing a process and apparatus for producing safe drinking water from bacterially-contaminated water. 
     As used in this application, the term “contaminated wastewater” shall mean water contaminated by aerobic and anaerobic bacteria. The terms “potable water” and “safe drinking water” are used interchangeably. 
     According to a preferred embodiment of this invention, apparatus is provided for decontaminating contaminated wastewater by sterilizing it. A piping circuit interconnects a supply tank, three heat exchangers, a holding tank, and a storage tank. The circuit and storage tank are sanitized by flushing with hydrogen peroxide. One heat exchanger transfers heat from the sterilized water to the unsterilized water. A closed hot water piping circuit interconnects a hot water boiler, the holding tank and two other heat exchangers. The piping interconnecting the holding tank and two heat exchangers is an insulated manifold where contaminated wastewater is sterilized by the heat from circulating process water from the boiler via the closed hot water piping circuit. Wastewater is pumped through the piping and heated by process hot water in the holding tank to kill the bacteria in the wastewater, and is stored and may be covered by a layer of nitrogen for use immediately or eventually. The eventual use can be as processing water in a paper mill or for drinking or for return to the habitat or other uses requiring decontaminated water. 
     In one aspect, this invention features a process for sterilizing contaminated wastewater, which comprises the steps of providing a sanitized fluid handling system, pumping the contaminated wastewater through the system at a predetermined flow rate, heating the contaminated wastewater to a sterilizing temperature of about 210° F. for a predetermined time to sterilize the wastewater, cooling the sterilized wastewater to a temperature below 100° F., and transferring the sterilized wastewater to a fluid collection tank, which may be a stationary or transportable storage tank or the supply system for a further use, such as for potable or drinking water. 
     In another aspect of this invention, the process includes the optional further step of excluding oxygen from the collection tank by covering the sterilized wastewater with a blanket of nitrogen. 
     In yet another aspect, this invention features fluid handling and sterilizing apparatus for sterilizing contaminated wastewater, which includes a supply tank for holding the contaminated wastewater, and a sterilizing unit for heating the contaminated wastewater to a sterilizing temperature. A heat exchanger transfers heat from the sterilized wastewater to the contaminated wastewater, thus preheating the contaminated wastewater and cooling the sterilized wastewater. A wastewater piping circuit connects the supply tank to the heat exchanger and connects the heat exchanger to the sterilizing unit for handling the contaminated wastewater, and connects the sterilizing unit to the heat exchanger and exits the heat exchanger for handling the sterilized wastewater. A pump pumps process water through the piping circuit at a predetermined pressure in order to maintain all wastewater in a liquid state, regardless of temperature. 
     In a further aspect of this invention, the sterilizing unit includes a heating unit, a second heat exchanger for transferring heat from the heating unit to the contaminated wastewater to raise the temperature of the contaminated wastewater to a sterilizing temperature, a holding tank for maintaining the heated wastewater at the sterilizing temperature, and a third heat exchanger for transferring heat from the sterilized wastewater to the heating unit to cool the sterilized wastewater. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Further features of the inventive embodiments will become apparent to those skilled in the art to which the embodiments relate from reading the specification and claims with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic representation of the apparatus and process according to this invention; 
         FIG. 2  is a simplified version of the schematic of  FIG. 1 , depicting system temperatures measured during successful operation of a sterilizing system according to this invention; 
         FIG. 3  is a plan view of the system of  FIG. 1 , shown mounted on a semi-trailer; and 
         FIG. 4  is a side view of the system of  FIG. 1 , shown mounted on a semi-trailer. 
     
    
    
     DETAILED DESCRIPTION  
       FIGS. 1 and 2  of the drawings schematically depict the major components of a system  10  for continuously sterilizing contaminated wastewater according to a preferred embodiment of this invention. These comprise a supply tank  12 , a storage tank  14 , serially arranged heat exchangers  16 ,  18  and  20 , a hot water boiler  22  for heating process water, and a holding tank  24 , which may be insulated. 
     A pump  25  at supply tank  12  pumps wastewater through a piping system, which includes a supply pipe  26  from pump  25  to heat exchanger  16 , a connecting pipe  28  that connects heat exchangers  16  and  18 , wastewater manifold piping  30 ,  31  that connects heat exchangers  18  and  20  via holding tank  24 , a connecting pipe  32  that connects heat exchangers  20  and  16 , and an outlet pipe  34  that exits heat exchanger  16  and enters storage tank  14 . The direction of wastewater flow is indicated by arrows in  FIGS. 1 and 2 . Pipe  34  may alternatively connect directly into the intake of a system for further use, such as a water supply system (not shown) rather than connecting to storage tank  14 . Tanks  12  and  14  may be stationary, or mobile, such as mounted on a rail car, semi-trailer, or ship. Indeed, the wastewater sterilizing system  10  itself may be stationary or may be mounted on a similar mobile platform for transportation to a variety of locations for on-site processing and use. 
     With continued reference to  FIGS. 1 and 22 , at the initiation of the process of this invention supply tank  12  may be filled with bacterially-contaminated wastewater  40 , while storage tank  14  will normally be empty. This process is a continuous process, so that eventually tank  14  will fill with sterilized wastewater  42 . Prior to initiation of this process, at least tank  14 , and pipes  34 ,  32 ,  31  and  30 , and preferably pipes  28  and  26  may be sanitized by backflushing with a sanitizing agent, such as hydrogen peroxide, supplied from a supply  44  via a delivery nozzle  46 . Oxygen is purged from the system  10  by the simultaneous introduction of nitrogen from a supply  50  via a nozzle  52 . 
     The heating unit for the sterilizing apparatus  10  includes hot process water boiler  22 , and a second or hot process water piping system, that includes an outlet pipe  60  from boiler  22  to heat exchanger  18 , a connecting pipe  62  connecting heat exchangers  18  and  20 , and an inlet pipe  64  connecting heat exchanger  20  to boiler  22 . A pump  66  pumps water through the closed hot process water system at a predetermined pressure in the direction indicated by arrows in the drawings. The pressure of the hot process water system should be sufficient to preclude formation of steam. The heating unit, holding tank  24  and heat exchangers  18  and  20  comprise the sterilizing unit. 
     A sterilization system, illustrated in  FIGS. 3 and 4 , is mounted on a semi-trailer  70 . This system utilizes a manifold comprising about 60 feet of 4-inch stainless steel wastewater pipe and an array of 2-inch stainless steel hot water pipe—all enclosed in a stainless steel box containing 3-inch rock wool insulation. The heating system utilizes a 300,000 British Thermal Unit per hour (“BTU/hr”) propane-fired boiler and a pumping system that pumps hot process water at about 30 gallons per minute (“gpm”). A wastewater pump pumps wastewater through the system at about 17 gpm. Three substantially identical plate heat exchangers  16 ,  18 ,  20  supplied by, for example, Aluminum Plant &amp; Vessel Company Ltd. (APV”), are interconnected by insulated piping runs of about 10 feet. A generator set (not shown) may be used to provide electrical power for system  10 . 
     In an example process, a target sterilizing temperature is set at about 210° F. and a holding time of up to about 2 minutes in the sterilizing holding tank  24 . Treatment time is dependent on the volume of the piping used and treatment temperature. A preferred temperature range is about 200° F.-210° F. The temperature of the cooled sterilized wastewater is about 90° F. at pipe  34 , and a temperature below about 100° F. is preferred to facilitate handling. 
     The system  10  is fogged with a mist composed of a mixture of nitrogen and hydrogen peroxide emitted from tanks  44 ,  50  through a dual nozzle to sanitize the system. After the system is activated and brought to temperature, wastewater is pumped through the sanitized system. Temperatures in all segments of the system are monitored, as is water flow. Example temperatures are depicted in  FIG. 2 . Samples are taken of sterilized wastewater to confirm that sterilization is complete. The present invention makes it possible to sterilize contaminated wastewater without using bactericides or other chemicals. 
     This process is quite economical, as the heating unit recovers about 98% of the boiler  22  heat. Thus, only about 2% boiler makeup is necessary. This economy results from the use of heat exchangers to transfer heat. As  FIG. 2  shows, the incoming about 80° F. contaminated wastewater (at pipe  26 ) is pre-heated to about 140° F. in heat exchanger  16  by about 150° F. sterilized wastewater (pipe  32 ), the wastewater cooling to an exit temperature of about 90° F. at pipe  34 . The pre-heated contaminated wastewater is elevated to a sterilizing temperature in heat exchanger  18  by about 245° F. hot process water from boiler  22  (via pipe  60 ) to a temperature of about 210° F., as measured in pipe  30  and in holding tank  24 , which receives the wastewater from heat exchanger  18 . Hot process water exits heat exchanger  18  at about 175° F. via a pipe  61  and is coupled to an input of heat exchanger  20 . Sterilized wastewater, which exits holding tank  24  via pipe  31  at about 210° F., reheats the hot process water from heat exchanger  18  to about 200° F. in heat exchanger  20 , the sterilized wastewater exiting heat exchanger  20  via pipe  32  at about 150° F. Thus, boiler  22  is supplied with about 200° F. intake process water, which it needs to elevate in temperature only about 45° F. 
     With continued reference to  FIG. 2 , in operation bacterial contamination is removed from wastewater by a sterilizing process and apparatus  10 . A wastewater piping circuit  26 ,  28 ,  30 ,  31 ,  32 ,  34  interconnects a supply tank  12 , three serial heat exchangers  16 ,  18 ,  20 , and a storage tank  14 . The circuit and storage tank are sanitized by flushing with a mist of hydrogen peroxide  44  and nitrogen  50 . One heat exchanger  16  transfers heat from the sterilized wastewater to the unsterilized wastewater. A closed hot process water piping circuit  60 ,  62 ,  64  interconnects a hot process water boiler  22  and the other two heat exchangers  18 ,  20 . The wastewater is sterilized in an insulated holding tank  24  interconnecting the other two heat exchangers  18 ,  20 . Wastewater is pumped through the piping and heated by hot process water in the manifold to kill the bacteria, and is covered by a layer of nitrogen  54  in the storage tank  14 . 
     Preferably, a mist or fog of nitrogen and hydrogen peroxide is used to sanitize the system  10 . Sanitizing chemicals other than hydrogen peroxide may also be used to kill any bacteria in the system. As wastewater from supply  40  transits wastewater piping  26 ,  28 ,  30 ,  31 ,  32  and  34  into storage tank  14 , this fog is forced into storage tank  14 , where the condensed hydrogen peroxide will be drained and the nitrogen will blanket wastewater  42  to exclude contact with oxygen. 
     The nitrogen blanket may be maintained during any subsequent shipping of tank  14  to a distant terminus by truck, rail or ship. Depending on the degree of sterilization maintained (a function of time and equipment), the transported wastewater may again undergo the same sterilization process by another or similar installation of sterilizing equipment  10 . 
     While only a preferred embodiment has been illustrated and described, obvious modifications are contemplated within the scope of this invention, as defined by the appended claims. For example, other types of heating systems could be used to sterilize the wastewater, although systems using a liquid are preferred because of their efficiency. As another example, solar heating panels may be used in place of boiler  22  or in combination therewith, within the scope of the invention.