BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is best understood by reference to the embodiments described in the subsequent section accompanied with the following drawings.
FIG. 1 is a schematic diagram of a cylindrical FTC for CDI treatment taken from U.S. Pat. No. 6,462,935.
FIG. 2A shows a metal sheet with thickness t and through holes of three different sizes, wherein the largest hole A is for placing the plate on one electrical rod with electrical insulation, B for electrical conduction between the plate and other electrical rod, and C for water to flow through.
FIG. 2B is a diagram of insulator in form of insertion ring IR for securing an electrode plate on one electrical rod.
FIG. 2C is a schematic diagram showing the connection of a metal sheet with two electrical rods. The metal sheet has electrical connection to one rod and electrical insulation with the other.
FIG. 2D is a schematic diagram of electrode set of ozone reactor or FTC.
FIG. 3 is a block diagram of O3/CDI hybrid water treatment system for continuous water treatments.
FIG. 4 shows the TDS (total dissolved solid) reduction curves of 10 inorganic salts by a tandem of five FTC (flow through capacitor) modules.
FIG. 5A shows the decomposition of 1% ammonia water as reflected by the increase of solution conductivity by a submerged ozone reactor.
FIG. 5B shows the reduction of the conductivity of ozone treated ammonia water by a single FTC.
DETAILED DESCRIPTION OF THE INVENTION AND BEST MODES
The preferred embodiments of each component of the O3/CDI hybrid water treatment system of the present invention are presented in the subsequent sections.
FTC (Flow Through Capacitor)
FTC is the heart of CDI where ions are removed so that the TDS of water can be reduced to the desired levels. FIG. 1 shows a prior FTC roll disclosed in U.S. Pat. No. 6,462,935, which is currently owned by the assignee of the present invention. As shown in FIG. 1, the FTC is constructed by winding two electrodes, 201 and 202 with two separators 203 concentrically around a central water inlet 102 into a cylindrical roll. Before winding, each electrode sheet is attached an electrical lead (not shown in FIG. 1) for connecting to an outside potential source. After winding, both ends of the FTC roll are sealed hermetically. Water enters the FTC roll from the holes provided on the tube 102, and exits the FTC from the sidewall of the FTC roll. The thickness of the separator 203 defines the electrode gap that greatly affects the strength of static electric field created by a potential applied across the two electrodes. The smaller the gap the stronger the field will be, and the more ions will be adsorbed and removed from water. Nevertheless, a narrow electrode gap will restrict the water flow in the FTC resulting in cross contamination to the FTC at regeneration. When the treated water contains low ionic species, for example, tap water, the cylindrical FTC as depicted in FIG. 1 can quickly remove ions and convert the hard water into soft water. Even the raw tap water can be used to rinse the electrodes at regeneration without degrading the capacity of FTC. On the other hand, when the intake is seawater, the winding and long path of the wound FTC shows the following difficulties:
- 1. Water distribution at the holes of the central water inlet is non-uniform resulting in a low efficiency of electrode utilization. In other words, not every area of the electrode surface provided has been utilized for ion adsorption leading to ion removal and TDS reduction.
- 2. At the regeneration of FTC, the desorbed ions are difficult to flush out, and some of them are trapped inside the FTC, which significantly contaminate the water quality at the next run of ion removal.
In order to solve the cross contamination and to improve the electrode utilization rate, the present invention offers an innovative design for the configuration of FTC. FIG. 2A shows the building block of the new FTC design. A metal sheet of titanium or stainless steel with thickness t is used as the substrate for coating an active material to form an ion-adsorbing electrode. The active material can be activated carbon, carbon nanotube (CNT) or fullerene (C60). Alternatively, a carbon cloth can replace both of the substrates and the active materials thereon as the ion-adsorbing electrode by itself. If activated carbon is chosen as the active material, it can be secured on the metal substrate via a binder using roller or spin coating. However, the binder has an adverse effect due to binder masking of the effective surface that activated carbon can impart to the electrodes of FTC. Often, there is as high as high as 60% of the carbon surface blocked by the binder. Such disadvantage of binder can be eliminated by a direct growth of CNT or C60 as the adsorbing material on the substrate plates. An in-house study of fabricating binder-free electrodes for the new FTC is in progress. There are three types of perforated holes in different diameters on the electrode plate as shown in FIG. 2A. Holes A and B are designed to secure the electrode plate on two electrical rods, wherein A is for creating an electrical insulation between the metal sheet and the rod, and B is for making an electrical conduction between the metal sheet and the rod. For the electrical insulation purpose, an insulator such as a non-conductive plastic insertion ring is inserted at hole A. On the other hand, hole B is made in the same dimension as the electrical rod so that the metal sheet can be inserted snuggly on the supporting rod forming a good contact and a low electrical resistance. The third type of hole, C, is in a plural number and in a diameter of 2 mm or less to allow water to flow through freely in cascade from one metal sheet to subsequent metal sheets vertically or horizontally. Other patterns of holes C on the metal sheet are feasible if water retention time and water flow rate can be optimally adjusted. If a carbon cloth is used as the electrodes of FTC, holes C may not be needed as water may trickle through the electrodes. Trickling is commonly seen in medium filters or ion-exchange beds used in water treatments. The key of treatment is dependent upon a high surface area to volume ratio.
FIG. 2B shows a preferred embodiment of a securing device for attaching an electrode plate on two electrical rods. The device is an insertion ring, IR, made of an insulating material, such as plastic including polyethylene, polypropylene, Teflon, or Bakelite. The outside diameter (OD) of the insertion ring IR is same as the diameter of hole A on the electrode plate as shown in FIG. 2A, while the inside diameter (ID) of IR is sufficient to hold a metal ring with the same diameter as the electrical rod (the metal ring is not shown in FIG. 2B for clearance). Therefore, the metal ring can fit snuggly on both of the insertion ring IR and the electrical rod. The thickness h of IR defines the electrode gap for the FTC of the present invention. Other means capable of preventing electrical short, and other ways capable of forming good electrical connection, for the electrode plates and the electrode rods can be used as well to construct the innovative FTC.
FIG. 2C shows the connection of a metal sheet with two electrical rods R1 and R2 via the insertion ring IR. As mentioned above, a metal ring at the middle of IR is not shown in FIG. 2C for clearance. Every electrode plate of FIG. 2C attached to R1 through hole B, as well as to R2 via hole A, will be sandwiched by two insertion rings IR sitting on holes A of two electrode plates hanged on the same electrical rod R1. The same configuration is applied to every metal sheet that is attached to the electrical rod R2 though hole B. The new FTC of the present invention is thereby constructed by alternating the insertion of holes A and B of the metal sheets on the electrical rods R1 and R2. In other words, every two adjacent metal sheets are disposed on the electrical rods with the hole A facing the hole B. The hole B of every metal sheet is sandwiched by two holes A of two adjacent metal sheets, and vice versa. A complete electrode set of the innovative FTC is shown in FIG. 2D. Each electrical rod of R1 and R2 holds the same number of metal sheets connected to their electrical rod in parallel, respectively. When the whole stack of electrodes of the FTC of FIG. 2D are squeezed, each metal sheet will be in close contact with the two metal rings in the two insertion rings IR sitting above and below the hole B of that sheet. Since all metal sheets have the same composition, they can serve as either positive or negative electrode. The polarity of metal sheets is determined by the charge applied to the electrical rod. Then, the rod and all of its intimately connected plates via holes B will carry the same polarity. In order to provide a good electrical contact for the metal sheets and their supporting rod, two insulating plates F1 and F2 are squeezed from both ends of the stack of metal sheets and insertion rings using the four nuts N1 to N4. As the metal sheets and the insertion rings are pressed against one another, the metal rings in the middle of insertion rings will touch the metal sheets tightly via holes B. Therefore, the metal sheets and their supporting rod are connected electrically through the metal rings. All nuts, metal rings, and electrical rods of the innovative FTC of the present invention are made of a corrosion resistant metal, such as, titanium. If copper or stainless steel is used for the foregoing components, the metal should have a good protection against corrosion. A FTC as depicted in FIG. 2D can be used to conduct CDI treatments in a closed mode or an open mode. In the closed mode, the FTC is enclosed in a housing, and water are deionized upon flowing through the charged FTC. Alternatively, the FTC of FIG. 2D can be placed in an open water body at any depth to remove ions from the water using electricity from batteries or renewable energies. No power station is needed for the open mode FTC to operate at remote areas. The in-house studies have discovered that the new FTC of FIG. 2D has a high efficiency of electrode utilization, and the FTC is virtually free of cross contamination.
Both types of FTC as depicted in FIG. 1 and FIG. 2D are operated using the same protocol. When a plural number of FTC units of FIG. 1 or FIG. 2D are employed for CDI treatment, they are charged in parallel to remove ions from water, therefore, only one voltage is required to charge every FTC unit in the pack in operation. Depending on the conductivity of water to be treated, the operational voltage can be set from 1V to 9V DC. The higher the conductivity, the lower the voltage will be. When the FTC units become saturated as indicated by the decrease of charging current, and the FTCs require regeneration. During regeneration, at least 30% of the electricity input for ion removal can be directly recovered and stored for latter use. The energy recovery is accomplished simply by connecting the saturated FTCs to a load, for example, supercapacitor. At the discharge of FTCs, the adsorbed ions will automatically leave the electrodes and become collectable for reuse or easy disposal. As FTCs are discharged, they are electrically connected in series to expedite the recovery of electricity accompanied with complete de-sorption of the adsorbed ions.
Flow Through Ozone Reactor
The present invention also applies the electrode set of stacking configuration as FIG. 2D for the construction of an innovative ozone reactor that can generate ozone directly in water. Furthermore, all components and fabricating processes for the ozone reactor are similar to those for the innovative FTC as described above. Nevertheless, there are some distinctive differences between the FTC as depicted in FIG. 2D and the new ozone reactor. The differences are summarized as follows:
- 1. Titanium metal is the substrate for the ozone reactor, whereas the FTC can use a cheaper substrate, such as, stainless steel. The environments in the ozone reactor is extremely harsh, thus, titanium is required to resist the oxidative corrosion.
- 2. Platinum, iridium oxide, or synthetic diamond film is the active material for the ozone reactor, whereas carbonaceous material serves as the ion-adsorbing medium for the FTC. Ozone is generated on the aforementioned precious material when the material is charged as anode.
- 3. The electrodes of the ozone reactor can be in the form of mesh, screen or plate, whereas the electrodes of FTC has smaller openings relatively.
- 4. The ozone reactor can remove numerous neutral contaminants resulting in the reduction of BOD and COD through complete oxidation, whereas the FTC removes ionic species resulting in the reduction of TDS via surface adsorption.
- 5. The ozone reactor can continuously remove BOD and COD without the need of regeneration, whereas the FTC requires frequent cleaning.
- 6. The ozone reactor provides a non-selective and destructive treatment, whereas the FTC offers a non-destructive treatment, and different ions may be adsorbed and released at different stages of CDI operation.
- 7. Power is consumed at the ozone reactor, whereas residual power can be directly, without energy conversion, recovered from the FTC during regeneration.
- 8. The electrode polarities of the ozone reactor are switched at a preset time interval, whereas the FTC is switched between charging (to adsorb ions) and discharging (to regenerate the electrodes) at a longer time interval.
In addition to the same configuration of electrode assembly, the ozone reactor and the FTC of the present invention also share the use of supercapacitor as a key component for power management. For saving energy, both of the ozone reactor and the FTC are operated using PWM (pulse width modulation) instead of continuous power provision. Not only the water treatments are more energy effective on using PWM, a balance state that may exist in ozone formation and ion adsorption can be disrupted via the intermittent power supply. As a result, water treatments for reducing TDS, COD and BOD of water using CDI and flow-through ozone may be facilitated by applying the PWM technique. Similar to the FTC of FIG. 2D, the ozone reactor can be operated in either closed or open mode. The constant polarity switching of the new ozone reactor is designed to provide the following benefits to the ozone treatment:
- 1) Every electrode disposed in the reactor can serve as the anode to generate ozone in water.
- 2) Since the electrodes work only “half” of the operation time as anode, their service life can be prolonged.
- 3) Fouling of electrodes is inhibited due to every electrode will become the anode thereon deposits will be destroyed by ozone.
The innovative ozone reactor of the present invention does not use any ion exchange membrane. Although the membrane can separate ozone from hydrogen resulting in a higher oxidant concentration, but the membrane is expensive and vulnerable to scaling and particulate fouling. If a membrane is employed in the new ozone reactor of the present invention, neither the closed mode ozonation, wherein water flows through the reactor sitting in a housing, nor the open mode ozonation, wherein the reactor is submerged in an open body of water at any depth, is allowed due to the blockage of water flow by the membrane or quick fouling of membrane, respectively. During either mode of ozonation, the ozone reactor is surrounded by contaminants, and the latter will react with ozone as soon as the micro bubbles of the oxidative gas are formed. Because of the close proximity, the reaction between contaminants ozone will be faster than that between ozone and hydrogen. In other words, there is a plentiful amount of ozone in water for the in-situ destruction of contaminants. The in-house studies have found the distinctive odor of ozone in the water stream after it passed the ozone reactor. On the other hand, the presence of hydrogen may be beneficial to the removal of any reducible pollutants in the water to be treated. Ozone can provide a complete oxidation with destructive effect equivalent to incineration, therefore, all neutral contaminants will be converted to gaseous, ionic, or a mixed products in a less toxicity than the original pollutants. Once the pollutants become ionic species, the FTC will quickly remove the ionic byproducts from water. Similar to the CDI treatments, the operational voltage of the ozone reactor depends on the conductivity of water to be treated. Generally, the voltage is less than 24V DC. If the treated water is extremely conductive, for example, seawater, it is preferred set the voltage no more than 5V DC to avoid an excess current applied to the ozone reactor. When the current density is above 1 A/cm2, the ozone forming materials, such as, platinum and iridium oxide, may peel off the titanium substrate. Ozone concentration in water is sensitive to water temperature, and low water temperature can stabilize the presence of ozone in water. Thus, water circulation due to the flow-through operation will keep the water temperature of the ozone reactor low and constant, and the water movement will promote the oxidation of pollutants as well. Under the condition of high halide ion concentrations, for example, 50 ppm or above, the flow-through ozonation of the present invention will generate hypohalite ions in addition to ozone. Nevertheless, the hypohalite ions are also potent oxidants for the removal of BOD and COD. The hypohalite ions can stay in water at a much longer time than ozone, and water containing the disinfecting anions is good for storage and transportation as a bactericide. More importantly, the hypohalite ions of the present invention are produced on-line and the residual ions after the disinfection can be removed by CDI.
Supercapacitors
As described in the foregoing sections, supercapacitor is a key component for managing the power utilization in the operations of the new FTC and the new ozone reactor of the present invention. Supercapacitor receives its name of “super” from its capability of storing hundreds to thousands times energy of the conventional capacitors. Like the latter, supercapacitor is a passive energy-storage device with fast charging and discharging rates. However, due to the large capacitances in a small volume, supercapacitors have the following unique properties as added values.
- 1. Within the rated working voltages, the capacitors can be charged with any magnitude of currents. Henceforth, the residual current of saturated FTC units, large or small electricity, can be quickly and completely transferred to supercapacitors for storage for latter use. By discharging the saturated FTC units in series, the transfer of the residual energy of FTC to supercapacitors can be expedited. Desorption of the adsorbed ions from the electrodes of FTC is promoted as well.
- 2. When the FTC units and the ozone reactors of the present invention demand large currents for operation, supercapacitors can fulfill the needs in a real-time response. This will save the cost of water treatments for a power supply with large current output, for example, 50 A or above, is very expensive. By the provision of low currents from an economical potential source, supercapacitors can deliver tens times of current for large-scale water treatments. Because the load for the potential source is low, fire hazard is thus prevented.
- 3. Supercapacitors can deliver a power at many folds of an input power without energy conversion and electrical components, such as, transformer and converter. On the other hand, supercapacitors can serve as energy buffer for storing the energy recovered from the regeneration of FTC. The energy storage of supercapacitors is conversion free as well. Energy is directly deposited and withdrawn at a very minimal loss. Using supercapacitors for the power management of water treatments, the energy consumption of the treatments will be highly cost effective.
- 4. Supercapacitors have a long lifetime without maintenance. The capacitors also have good temperature characteristics and outdoor suitability. Supercapacitors are known to assist the ignition of engines at frigid temperatures.
- 5. The working voltage of supercapacitors is low, which is consistent with the low operational voltages of the FTC and the ozone reactor of the present invention. Low operational voltage allows the water treatments to be driven by batteries, fuel cells, and renewable energies (e.g., solar cells and wind turbines). The latter potential sources are generally low in power output that can be easily compensated by the use of supercapacitors.
As a matter of fact, the FTC as depicted in FIG. 1 has the same configuration of supercapacitor. Both capacitive devices require an electrolyte to perform. The electrolyte provides ions for adsorption and desorption at charging and discharging of the capacitors, respectively. The major difference between the FTC and supercapacitor is that the electrolyte for FTC is the running water to be treated, whereas the electrolyte is sealed permanently in the housing of supercapacitor. As large electrode areas of FTC, which is attained by using plural FTC units, are required for desalting industrial wastewater, supercapacitors must be connected in series to cope with the high voltage created in the discharging of FTC units in series. Charging of serially connected supercapacitors at the regeneration of FTC may create an imbalance distribution of voltage among the capacitors. The capacitor with the highest voltage will fail first dragging the whole pack down with it. An assembly method of connecting the supercapacitor elements within a single housing can solve the problem of voltage imbalance. The foregoing in-cell series assembly provides a uniform temperature and vapor pressure environments for all supercapacitors in the housing. Therefore, the whole pack of capacitors is charged as one unit resulting in equal share of the total voltage. The automatic even distribution of voltage prevents the use of protection circuits for each supercapacitor of the serially connected pack. Like other energy-storage devices, not every bit of energy stored in supercapacitors is potent to work. During the discharge of a supercapcitor, if the voltage of supercapacitor has decayed to under the working threshold, the rest of energy in the capacitor will be ineffective. By cycling two identical groups of supercapacitor between charging and discharging, or charging and discharging swing (CD swing), only the effective energy of the supercapacitors will be utilized and replenished leading to energy conservation. In the operation of CD swing, at all times, there will be one group of supercapacitors undergoing discharge in synchronization with the other group at recharging. As the discharging group has consumed its effective energy, it will undergo recharging (to refill the used portion) and the other group (after the replenishment of energy) will immediately take the discharging position, and vice versa. Due to the continuous discharge of capacitors, the power supply using the CD swing can consistently deliver peak powers to water treatments under the PWM and other controls as proposed by the present invention. The CD swing is designed to improve the energy efficiency of the supercapacitor for power applications, which in turn will reduce the energy cost of water treatments on incorporating the capacitors in the power supply system. Incidentally, the CDI operation is also a CD swing, that is, plural FTC units are periodically and reciprocally switched between charging and discharging. While desalted water is produced at the charging of FTC units (in parallel), FTC units are regenerated in conjunction with the recovery of electricity and ions at the discharging of FTC units (in series).
O3/CDI Hybrid Water Treatment System
The flow through ozone reactor, the FTC, and DC power supplies using the supercapacitors operated via CD swing are integrated to form a preferred embodiment of compact and self-sustained water treatment system as shown in FIG. 3. As seen in the drawing, the intake water will be pumped at an inlet 1 into the O3/CDI hybrid water treatment system. After simple filtration at the filter 2, which can consist of sand, charcoal, activated carbon, or other inexpensive filtering media, the water will be treated at the flow through ozone reactor 3. All the neutral contaminants in the water will be oxidized in a circulation between reactor 3 and a storage tank 4 until all neutral pollutants are decomposed completely into gaseous and ionic products. The ozonated water is then degassed and filtered at filter 5 for further treatment by a FTC unit 6. During the ozonation, some original ion, for example, Fe2+, will be oxidized to form a fine precipitate, for example, Fe2O3. Therefore, filtering the precipitate becomes necessary before the CDI treatment. Other original non-oxidizable ions plus the ozonation ions can be removed and collected at FTC 6. The CDI treatment via FTC 6 can be operated till the desired TDS is reached, then, the treated water is discharged at an outlet 7. From inlet 1 to outlet 7, the intake water is treated continuously by on line ozonation and deionization without the addition of any chemical. As described in the section of flow-through ozone reactor, the reactor is capable of cleaning itself for continuous operation. On the contrary, the FTC unit though requires frequent regeneration and rinsing, the process is completed through discharging to the supercapacitor without using any chemical. Therefore, the O3/CDI hybrid water treatment system offers chemical free and pollution free water treatments. Moreover, there is no limitation on the concentration of neutral species, such as, ammonia, nor on the ion contents of water that can be treated by the O3/CDI hybrid water treatment system of the present invention. Without dilution, water as concentrate as seawater can be directly desalinated to potable water by the system of the present causing no damage to the ozone reactor or the FTC unit.
FIG. 3 is used to elucidate the O3/CDI hybrid water treatment system rather than restricting the scope of application of the present invention. For treating industrial wastewater of 10,000 m3 or more per day, both ozone reactor and FTC unit can be scaled up by increasing the dimensions of both types of electrodes, the number of metal sheet pairs as depicted in FIG. 2D, as well as by using plural ozone reactors and FTC units. Since the ozone throughput and ion adsorption rate are proportional to the total available electrode areas, the scale up of the O3/CDI hybrid water treatment system is straightforward for any scale of water treatments. A microprocessor controller, not shown in FIG. 3, is used for controlling the ozonation, deionization, interface between the two treatments, and power management. With the use of controller, a turn-key system of O3/CDI hybrid water treatment techniques is erected and the system can be operated automatically with very minimal human attention. Due to the chemical free operation, as well as the concise sizes of ozone reactor and FTC unit, the O3/CDI hybrid water treatment system will occupy a much smaller space area than the current water treatment techniques on the market, for example, ozonation by corona discharge, desalting by RO or ion exchange. Small space area means low cost for the water treatments. Also, the O3/CDI hybrid water treatment system can be easily retrofitted with an existing water treatment system. Using the system of the present invention as a non-chemical pretreatment for an existing water treatment facility, the expenditure for the expensive RO membranes and ion exchange resins will be greatly reduced. Supercapacitors are not shown in FIG. 3, but they are included in the DC power supplies of the drawing. According to individual power management, specific switching power supply (SPS) for any scale of water treatments can be built using the supercapacitor as the power electronics. After the power need for a water treatment is determined, the capacity of power provision of supercapacitors and the potential source to charge the capacitors can be design accordingly. The foregoing custom made SPS can offer the power needs for water treatments with the highest energy efficiency and the lowest cost.
The ozone reactor and FTC of the present invention utilize the same configuration of electrode stack as shown in FIG. 2D, which allows water treatments to be conducted in a closed mode or an open mode. FIG. 3 represents a closed mode operation wherein both ozone reactor and FTC electrodes are enclosed in a housing. Water flow though the closed system to receive ozonation and deionization in sequence without exposing to air. Such closed system can be set at a designated station, or it can be installed on a truck, pick-up or trailer to become a mobile system for driving to wherever a treatment is demanded, for example, business promotion or emergency rescue. The potential source for operating the ozonation and deionization may come from batteries, renewable energies or generators. As the rinsing water for regenerating the FTC units, it can come from a small portion of the purified effluent of the O3/CDI hybrid water treatment system. The rinsing water may be used repeatedly until it causes significant cross contamination. Even at the end of service, the rinsing water may join other wastewater for purification by the O3/CDI hybrid water treatment system. Henceforth, the water treatment system of the present invention has a water recover rate higher than 90%. When both ozone reactor and FTC unit use the configuration of FIG. 2D without housings, they will become an open mode ozonation and deionization. The open ozone reactor and FTC unit can be submerged in water at any depth to purify water surrounding the hybrid water treatment system, or water flowing through the hybrid system. Although water may not be treated in the sequence of deionization after ozonation, the pollutants in water will be oxidized or adsorbed. The open mode water treatment requires no pump, conduits and storage tanks. By installing the open ozone reactors and FTC units at the bow and stem, as well as by the starboard and port of a boat, a mobile water-treatment system on watercraft is formed. To prevent solids entrapped between electrodes, a mesh screen is provided for each ozone reactor and FTC unit. Since only low levels of ozone, for example, 10 ppb to 10 ppm, are required for the destruction of neutral pollutants and algal species in the water body of a river, and the ozone level can be controlled by the power supplied to the reactors, release of excess ozone into the atmosphere is minimal. Thus, adverse effects of ozone on human, marine life and the environments are greatly reduced. Similar situation is applied to the FTC unit of the present invention for a low power, for example, 3V×2 A or 6 W, is needed to remove ionic contaminants that are diluted by the river water. The low power application significantly reduces the hazard of electrical shock to human and marine life. When the FTC units become saturated, the saturated units can be pulled to the deck for regeneration, at the same time, regenerated units can be submerged into water for ion adsorption.
The practice of the present invention can be better understood by reference to the following examples, which are provided to illustrate the performance of ozone reactor and FTC unit individually and collectively.
EXAMPLE 1
10 different reagent grade salts: CuSO4, FeSO4, Ca(NO3)2. Fe(NO3)2, Al(NO3)3, NaNO3, Zn(NO3)2, K3PO4, Na3PO4 and NaCl, are individually dissolved in 1 liter deionized water to form 10 pure solutions with TDS ranging from 700 to 1000 ppm. Each solution is deionized on 5 serially connected units of cylindrical FTC, as shown in FIG. 1, individually sealed in a plastic housing with a capacity of 600 ml. During test, each solution flows through the FTC pack continuously at 1 l/min. Each FTC has a geometric area of 1400 cm2 for each electrode to form the FTC roll, and 3V DC is applied across the two electrodes of FTC for ion removal. Since the 5 units of FTC are charged in parallel, every FTC will receive 3V of charging voltage. The total charging current is about 6A. FIG. 4 shows the reduction of TDS for each salt after 3 cycles wherein every cycle contains 3 minutes of charging for deionization and 2 minutes of discharging and rinsing for regeneration. Except the salts containing SO42−, the TDS of other solutions is reduced to below 200 ppm showing that many cations and anions are easily removed by CDI. The removal of SO42− and the overall desalting rate of the solutions may be improved by using a higher voltage for deionization.
EXAMPLE 2
1.5 liters of 1% ammonia (NH3) water is prepared for ozonation using an ozone reactor as revealed in U.S. Pat. No. 6,984,295, which is currently owned by the assignee of the present invention. A pair of platinum coated titanium meshes, each is 10 cm wide by 10 cm long with opening of 3.5 mm×6.5 mm, is used to form the ozone reactor. The ozone reactor is placed in the container of 1.5 liters ammonia water under the application of 8.5V average voltage and 1.75 A average current and PWM control. Only the TDS of the ammonia water during ozonation is measured, and the hourly variation of TDS is shown in FIG. 5A. About 6 hours since the ozonation is began, the TDS of solution levels off indicating that the decomposition of ammonia by ozone has been completed. Most ammonia may be decomposed by ozone according to the following equation:
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Next, the ozonated water is deionized using a single FTC unit as example 1, as well as 3V DC for deionization. TDS of the water is reduced smoothly from 600 to 150 ppm as shown in FIG. 5B. Since TDS of the solution is reduced steadily indicating that no free ammonia molecule is available, otherwise, ammonia will be electrolyzed resulting in the increase of TDS. There are four segments of TDS reduction in FIG. 5B. At segments A and C, FTC was rinsed with tap water, but at segment B, FTC was rinsed with deionized water. About 500 ml of tap water or deionized water was used for rinsing. At segment D, a new FTC was used and it was rinsed with tap water afterwards. When a new FTC is employed, a sudden drop of TDS is observed. Thus, cross contamination is a nuisance to the deionization capability of FTC made by winding as FIG. 1. Using a clean water, such as, deionized water, for rinsing the FTC will minimize the cross contamination. This is reflected by a faster reduction of TDS at segment B. Other means including more clean water for rinsing, or plural FTC units for treatment, can also ease the contamination. Nevertheless, EXAMPLE 2 demonstrates that the O3/CDI hybrid technique can quickly treat high ammonia concentration water to potable level at low energy consumption and without the use of any chemical or any bacteria. During treatment, the neutral ammonia molecules should be oxidized before being deionized, so that the molecules would not be electrolyzed at CDI operation to impair the current efficiency.
EXAMPLE 3
6 g of ammonia is dissolved in 2 liters tap water, which is mixed with 1 liter of filtered seawater (TDS=35,000 ppm). The salted ammonia water as prepared is first oxidized using an ozone reactor with electrode configuration of FIG. 2D concealed in a plastic housing as EXAMPLE 1. Iridium oxide (IrO2) is used as the ozone-forming material coated on titanium mesh, which has an opening of 1.5 mm×3.0 mm. A total of 32 pieces IrO2/Ti disk electrodes of 5.3 cm diameter are disposed in the housing. The power for ozonation is set at 12V×10 A with the electrode polarities switched once every minute. The ammonia brine is circulated between the ozone reactor and a reservoir Table 1 lists the hourly variation of TDS, pH, voltage and current of ozonation
TABLE 1
|
|
Ozonation of ammonia brine using an iridium oxide ozone reactor
|
Time (hr)
TDS (ppm)
pH
Voltage (V)
Current (A)
|
|
0
11,030
10.4
3.8
10
|
1
12,300
9.90
3.9
10
|
2
12,300
9.70
3.9
10
|
3
12,300
9.20
3.9
10
|
4
12,500
7.90
4.0
10
|
5
12,400
8.17
4.0
10
|
6
12,400
8.18
4.0
10
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If 2 liters tap water is mixed with 1 liter seawater, the mixture has alkalinity of pH 7.6. As soon as ammonia is added to the foregoing mixture, pH of the mixture jumps to 10.4. With the progress of ozonation, pH of the ammonia brine is decreasing. Thus, a complete oxidation of ammonia should be reached between the 3rd and 4th hour ozonation according to Table 1. If the weight ratio between ammonia and ozone is 1:1, the ozone reactor of the present reactor should generate more than 1.5 g of ozone per hour. A neutral pH levels, all neutral ammonia molecules in water will turn ammonium (NH4+). The pH of water should be at least 10.5 for ammonia to be stripped as vapor. The applied current for ozonation is fixed at 10 A, whereas the operational voltage is automatically determined by the conductivity of water. Due to constant circulation, the water temperature varies between 23° C. and 25° C., which is very close to the ambient temperature. After ozonation, the oxidized water is subjected to deionization using stack configuration as FIG. 2D for the FTC as well. The foregoing FTC contains 80 pieces of titanium disk plates (0.5 mm thickness and 5.3 cm diameter with a pattern of perforated holes as depicted in FIG. 2A) coated with activated carbon as the ion-adsorbing material. The disk electrodes are divided in two groups, and each group is electrically connected to an electrical post. A potential of 3V DC is applied across the two posts for desalting the oxidized water of Table 1. In 30 cycles of CDI operation, TDS of the water is reduced from 12,400 to 400 ppm. Treatment of 3 liter wastewater containing 2000 ppm ammonia and at least 10,000 ppm salt, which is beyond the capability of the biological method and RO without chemicals, is successfully accomplished in a no pollution fashion by the O3/CDI hybrid technique of the present invention.
EXAMPLE 4
20 liters of wastewater of a steel plant is treated to reduce its COD from 314 ppm to below 100 ppm. The water was first oxidized then desalted on a O3/CDI hybrid unit as shown in FIG. 3. Table 2 shows the results at each stage of treatment:
TABLE 2
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Reduction of the COD of a wastewater, original
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COD = 314 ppm, by O3/CDI
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Total Electrode
Power
Treatment
COD
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Treatments
Area (cm2)
(V × A)
Time
(ppm)
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Ozonation
100
5 × 20
1 hour circulation
235
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CDI
30,000
6.5 × 14
One pass
90
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Table 2 indicates that the total electrode area for the ozone reactors is much smaller than that for CDI, and it is reflected by the degree of COD reduction. Since the water contains NH3, which is oxidized to NO2− or NO3− during ozonation, CDI will have a faster removal rate for the ions than the oxidation of ions by O3. The flow of water was 1.5 l/min for both treatments, and it took about 13 minutes for the treated water to pass through the FTC modules. Had the water allowed to pass the FTC units one more time, the COD would be reduced further. No chemical or bacteria is used, therefore, the treatments by O3/CD are clean, economical and fast.
Conclusion
From the above examples and other in-house tests, the present invention clearly provides a solution of chemical free, low energy consumption and low space area for various water treatments. Removal of TDS, COD and BOD can be completed in one line or in open water body. Expansion of the O3/CDI hybrid system for any scale of water treatment is straightforward and easy. Both of the ozone reactor and FTC unit are modular, they can be added with the increasing amount of water for treatment. All materials used for constructing the ozone reactor and FTC unit are environmental friendly, and the metal components are recyclable. Electricity is used to generate ozone, as well as to control the adsorption and desorption of ionic contaminants in a clean, fast and high efficiency state. Supercapacitor is used in the custom design of the power needs of the O3/CDI hybrid water treatment system leading to energy conservation and high dependability. As no chemical or bacteria is used, ions remain in the original states and become recyclable at the FTC unit of CDI treatment. Even the common salt of seawater is a precious resource to human life and animal life, as well as to many industrial productions. The application of the O3/CDI hybrid system of the present invention is almost endless. Most importantly, the system offers a natural and economical solution for water treatments.
Patent Application
20070272550
