Wastewater treatment

A method is provided for the treatment of wastewater of pH ranging from about 1.5 to 3 containing at least about 100 ppm phosphorus as phosphate ions, at least about 50 ppm fluorine as fluoride ions and ammonia in excess of about 15 ppm NH.sub.3 (N)--T, the method comprising removing the phosphate and fluoride ions from the wastewater in a two-stage precipitation step; the first stage precipitation being conducted at a pH ranging from about 3.5 to 6.5 using an alkaline material selected from the group consisting of limestone (CaCO.sub.3) and lime [CaO or Ca(OH).sub.2 ] sufficient to form a precipitate which is removed to provide a filtrate of the wastewater which is treated in a second stage precipitation at a pH of at least about 10.5 using lime as the alkaline material sufficient to form a precipitate which is removed to provide substantially a clear effluent containing ammonia. The method also includes, if necessary, treating the ammonia-containing effluent with an alkaline material selected from the group consisting of lime and caustic sufficient to raise the pH to provide a free ammonia equivalence (FAE) of at least about 12.4; the free ammonia equivalence being determined as follows: EQU FAE=pH+(.theta./15).sup.0.5, wherein pH is the pH value of the effluent and .theta. is the temperature of said effluent in degrees Fahrenheit. The effluent is then gas stripped to lower the total ammonia content thereof to a value of less than about 10 ppm NH.sub.3 (N)--T. The gas stripping is controlled to maintain the free ammonia equivalence of the effluent at a value of at least about 12.4, following which the stripped effluent is acidified to lower the un-ionized ammonia content to less than about 0.05 ppm NH.sub.3 (N).

This invention relates to a method for treating phosphate-containing 
wastewater in order to remove polluting constituents therefrom, such as 
phosphate ions, fluoride ions, and ammonia-nitrogen. 
STATE OF ART 
It is known to treat wastewater to remove phosphate ions and fluoride ions 
therefrom, and in particular, ammonia-nitrogen [NH.sub.3 (N)--T], in order 
to minimize pollution of the environment. State and federal agencies have 
steadily increased the requirements for wastewater treatment, the 
elimination of ammonia and other impurities to substantially non-toxic 
levels being an essential and important requirement before the effluent 
thereof is disposed of into the immediate environment. 
Ammonia concentrations, whether total ammonia or un-ionized ammonia, are 
expressed on the basis of the amount of nitrogen contained in the ammonia. 
In order to emphasize the use of this basis of measurement, total ammonia 
will be symbolically expressed as "NH.sub.3 (N)--T" and un-ionized ammonia 
or free ammonia as "NH.sub.3 (N)". 
A particular wastewater of concern is that derived from the manufacture of 
phosphate chemicals and/or wastewater derived from fertilizer plants. Such 
wastewaters, which are generally stored in ponds, usually contain fluoride 
ions, phosphate ions, and ammonium ions, among other impurities. Ammonia 
as un-ionized ammonia [NH.sub.3 (N)] is particularly critical, especially 
if disposed of in surface waters, such as streams, harbors, etc., 
containing fish life or other forms of aquatic life. Fish are very 
sensitive to small amounts of un-ionized ammonia, in the neighborhood of 
less than about one part per million. 
It is known to treat phosphate-containing wastewater. For example, in U.S. 
Pat. No. 4,320,012 to Palm et al, a method is disclosed for treating 
wastewater derived from phosphoric acid manufacture. In phosphate 
complexes of the type for the manufacture of phosphate chemicals or for 
the manufacture of wet process phosphoric acid, water is employed as a 
coolant for gas streams created within the complex. According to the Palm 
et al patent, the cooling water absorbs and dissolves various materials 
and is sent to a pond for cooling. Such waters have a pH in the range of 
about 1.5 to 2 and contain dissolved solids, such as fluorides and 
phosphates. 
Because limits have been set by various state and federal agencies as to 
the acceptable amounts of fluorides, phosphates, and ammonia [NH.sub.3 
(N)--T] permitted in surface waters, such impurities must be removed 
before wastewater is disposed of into the environment. 
The method proposed by Palm et al for removing phosphates and fluorides 
comprises neutralizing the wastewater in two stages. The acidic wastewater 
is first neutralized to a pH of about 3 to 4.5 to precipitate solids 
therefrom, said solids comprising calcium fluoride, calcium phosphate and 
calcium sulfate or gypsum, where sulfate ions are present. The 
neutralizing agent employed may be finely divided limestone (CaCO.sub.3) 
or lime (CaO or Ca(OH).sub.2), limestone being preferred in the first 
stage neutralization for economic reasons. 
Following removal of the precipitate, the aqueous effluent remaining is 
neutralized further in a second stage at a pH of about 9 to 10 using lime 
wherein a flocculent precipitate is obtained which further reduces the 
amount of retained fluorides and phosphorus to meet the limits prescribed 
by federal and state regulatory agencies. However, when this process is 
conducted on a commercial scale, the final effluent, following the second 
neutralization, tends to have a milky appearance (i.e., still contains 
significant amounts of suspended solids) and may require additional 
dilution water of higher purity to achieve receiving water standards for 
impurity discharge. In addition, this patent does not disclose a method 
for the removal of ammonia from wastewater. 
The prior art is replete with methods for removing ammonia from wastewater. 
For example, in U.S. Pat. No. 4,045,341 a method is disclosed for treating 
wastewater containing ammonium ions, sulfate ions and organic substances. 
Calcium hydroxide or calcium oxide is added to the wastewater to lower the 
sulfate ion concentration and to liberate the ammonium ions as un-ionized 
ammonia. The ammonia is then removed by stripping with hot air. 
According to U.S. Pat. No. 4,093,544, wastewater is de-ammoniated by first 
increasing the pH of the water to over 10 following which a vacuum is 
applied to the upper surface thereof, whereby the ammonia is desorbed from 
the wastewater effluent. Temperature is important for achieving high 
conversion. Thus, at a pH of 10.5 and a temperature of 20.degree. C., 
there is a 90% conversion to free ammonia. 
U.S. Pat. No. 4,306,978 discloses a method for the lime stabilization of 
wastewater sludge. The sludge is dewatered to a solids content of about 
10% to 60% by weight. Calcium oxide is then added to provide a high pH 
(e.g., increase it to 11) and cause a rise in temperature to 95.degree. 
C.-100.degree. C. This destroys microorganisms and also produces free 
ammonia which is recovered. 
According to the state of the art discussed in the aforementioned U.S. Pat. 
No. 4,093,544, ammonia stripping of ammonia-nitrogen from wastewater has 
at least some theoretical advantages in that this system can treat 
effluent from conventional wastewater treatment equipment. Circulated air, 
as the stripping agent removes a certain portion of the ammonia as free 
ammonia, provided the pH of the wastewater is increased to concentrate the 
nitrogen in the form of ammonia gas within the wastewater compared to the 
amount of nitrogen in the form of dissolved ammonium ions. However, 
ammonia stripping does not remove all of the ammonia. 
It would be desirable to provide a method for treating wastewater derived 
during the manufacture of phosphoric acid or other phosphate chemicals 
wherein phosphate and fluoride impurities are removed and wherein a clear, 
non-milky effluent is provided. It would also be desirable to include 
within the aforementioned method an improved ammonia stripping system 
using known equipment wherein substantially high concentrations of ammonia 
of over about 15 ppm can be treated to provide removal of total ammonia 
[NH.sub.3 (N)--T] in the effluent to a level not exceeding about 10 ppm 
and by subsequent treatment decrease the level still further to an 
un-ionized ammonia content of less than about 0.05 ppm and, more 
preferably, not exceeding about 0.02 ppm. 
OBJECTS OF THE INVENTION 
It is thus an object of the invention to provide a method for removing 
impurities from wastewater and provide an effluent thereof that can be 
safely discharged into the environment after suitable pH adjustment. 
Another object is to provide an improved method for treating wastewater 
from which phosphate and fluoride ions have been previously removed, the 
total ammonia being stripped to less than 10 ppm and the un-ionized 
ammonia lowered to less than about 0.05 ppm.

SUMMARY OF THE INVENTION 
The invention is carried out using two process stages; a first process 
stage in which the phosphate and fluoride ions are removed and a second 
process stage in which the ammonia is removed. 
As stated hereinabove, the Palm, et al. patent discloses a method for 
treating phosphate-containing wastewater for removing impurities therefrom 
by using a double-neutralization process in which acidic wastewater of pH 
about 1.5 to 2.0 is neutralized in a first stage with finely divided 
limestone (CaCO.sub.3) to a pH of about 4 to remove such impurities as 
fluoride ions, phosphate ions, and the like, in the form of a precipitate 
which is removed to provide an effluent or raffinate which is treated in a 
second stage by further neutralization to raise the pH to about 9 to 10 to 
precipitate additional fluorides and phosphates, generally as a flocculent 
precipitate having a low settling rate. 
However, as stated earlier, the final effluent, following removal of the 
second precipitate, tends to still contain significant amounts of 
fluoride, phosphates, and suspended solids which may not comply with 
standards for receiving waters. The solids tend to deposit due to delayed 
precipitation downstream of the discharge point which can have an adverse 
affect on the subsequent treating steps. 
Thus, with the present invention, there is a substantial reduction in 
delayed precipitation downstream of discharge such that there is an 
increase in overall efficiency of the method. Scaling is minimized, 
particularly at the spray nozzles and on the bed packing material used in 
the spray towers. 
In addition, by removing the phosphate and fluoride ions, among other 
impurities first, the potential of decreasing the total ammonia NH.sub.3 
(N)--T content to below 10 ppm during gas stripping is improved. 
In addition, I have found that by carrying out the second stage 
precipitation at a higher neutralization pH of at least about 10.5, e.g., 
about 10.8 to about 12, more efficient settling characteristics are 
obtained and lower amounts of fluorides, phosphates and suspended solids 
are achieved. I have further found that less flocculating agents are 
required to collect the precipitate, thus decreasing the cost of treatment 
of the overall process. I have also found that I can produce a 
substantially clear effluent from which ammonia can be removed directly 
and readily. 
Advantageously, at least a portion of the sludge from the second stage 
settler may be recycled to the second stage precipitation to further 
improve lime utilization and the settling characteristics prior to ammonia 
removal. 
In summary the invention is directed to a method for the treatment of 
wastewater of pH ranging from about 1.5 to 3 containing at least about 100 
ppm phosphorus as phosphate ions, at least about 50 ppm fluorine as 
fluoride ions and ammonia in excess of about 15 ppm NH.sub.3 (N)--T. The 
method comprises first removing the phosphate and said fluoride ions from 
the wastewater in a two-stage precipitation step; the first stage 
precipitation being conducted at a pH ranging from about 3.5 to 6.5 using 
an alkaline material selected from the group consisting of limestone 
(CaCO.sub.3) and lime [CaO or Ca(OH).sub.2 ] sufficient to form a 
precipitate which is removed to provide an effluent of the wastewater 
which is treated in a second stage precipitation at a pH of at least about 
10.5 using lime as the alkaline material sufficient to form a precipitate 
which is removed to provide substantially clear effluent containing 
ammonia. 
The ammonia-containing effluent is then treated with an alkaline material 
selected from the group consisting of lime and caustic sufficient to raise 
the pH to provide a free ammonia equivalence (FAE) of at least about 12.4; 
the free ammonia factor being determined as follows: 
EQU FAE=pH+(.theta./15).sup.0.5 
wherein pH is the pH value of the effluent and .theta. is the temperature 
of the wastewater in degrees Fahrenheit. The effluent is then gas stripped 
to lower the total ammonia content thereof to a value of less than about 
10 ppm NH.sub.3 (N)--T, the gas stripping being controlled to maintain the 
free ammonia equivalence of the effluent of at least about 12.4. The 
stripped effluent is then acidified to lower the un-ionized ammonia 
content to less than about 0.05 ppm NH.sub.3 (N). 
DETAILS OF THE INVENTION 
In its broad aspects, the present invention, employs two processing steps 
in which solids are removed in the first process step and ammonia removed 
in the second process step. 
A typical pond water containing phosphate ions, fluoride ions and 
ammonia-nitrogen which may be treated in accordance with the invention has 
the following composition: 
TABLE 1 
______________________________________ 
Substance Range, ppm 
______________________________________ 
pH 1.5-3 
Fluoride ions (F) 
500-8000 
Phosphate ions (P) 
1000-10,000 
Total solids (TDS)* 
10,000-50,000 
Total NH.sub.3 (N)--T 
50-1,000 
______________________________________ 
*Total dissolved solids. 
THE FIRST PROCESS STEP 
In carrying the invention into practice, the first process step includes a 
first stage precipitation which is accomplished using lime [CaO, 
Ca(OH).sub.2 ] or limestone (CaCO.sub.3), the choice depending upon 
economic considerations. The amount added is sufficient to raise and 
maintain the pH to about 3.5 to 6.5. Referring to FIG. 1 of the drawings, 
lime or limestone 11 is added to acidic pond water or wastewater 10 fed to 
first stage precipitation 12 to raise and maintain the pH to about 3.5 to 
6.5. The lime or limestone may be added as a slurry or as a solid. The 
wastewater with the liming reagent therein is uniformly mixed at said pH 
of about 3.5 to 6.5. 
Following mixing, during which solids precipitate from solution, the 
wastewater is passed on to first stage settler 13 where the precipitate is 
collected as a slurry and solid/liquid separation effected at 14, with the 
solids removed as sludge for disposal at 15. The aqueous effluent 
remaining is passed to second stage precipitation 16 to which lime 17 [CaO 
and/or Ca(OH).sub.2 ] is added preferably as a slurry, sufficient to raise 
and maintain the pH to at least about 10.5, and preferably at about 10.8 
to about 12. 
It is important to maintain the pH at such high levels as the precipitate 
that forms settles more efficiently and clarifies more easily. In 
addition, less flocculant 19 is required to collect the precipitate, for 
example, less than 25% of what is normally used for the purpose. Any 
flocculant well known in the art can be used. Following settling at 18 
(second stage settler), a substantially clear non-milky aqueous effluent 
20 is obtained after removal of sludge 21 by solid/liquid separation, a 
portion of the sludge 21B (about 30% to 90% by volume) being preferably 
recycled to second precipitation stage 16 to improve lime utilization and 
settling characteristics. The remaining sludge 21 being discharged (21A) 
and/or recycled as 21C to first stage precipitation 12. 
The sludge 21 removed from the second precipitation stage is comprised of 
fluorides and phosphates and unreacted lime. The aqueous effluent 20 after 
pH adjustment meets the standards of the federal and state regulatory 
agencies for fluorides, phosphates and total solids, but does not meet the 
standards for the ammonia content. 
Second stage precipitation to pH values in excess of about 10.5 
significantly lowers the final concentration of phosphate and fluoride 
ions in the effluent. Two stage liming is currently conducted to provide a 
final pH value of approximately 9.5 so that the effluent can be discharged 
without further treatment. It appears that the solubility of calcium 
fluoride passes through a minimum at a pH value of about 5.5, after which 
point the solubility increases to a second maximum. I have found that by 
using the pH value of about 10.5 during the second stage neutralization, 
the fluoride ion concentration can be lowered to less than about 10 ppm 
(F), and advantageously to less than about 5 ppm (F), as compared to 
present commercial practice values of up to about 20 ppm (F) or more. At 
final pH values in excess of about 10.5 the phosphate ion concentration is 
lowered to less than about 5 ppm (P), e.g., less than about 2 ppm (P), as 
compared to present commercial practice of between about 15 to 25 ppm (P). 
Phosphates concentrations are expressed as phosphorus contained in the 
phosphates. In order to emphasize the use of this basis of measurement, 
phosphorus will be symbolically expressed as (P). 
Under current practice, at a pH level of about 9.5, the effluent 20 upon 
discharge contains an excess of about 20 ppm phosphate (P) which continues 
to precipitate with time. This results in an increase in suspended solids 
content, which suspended solids may deposit downstream of said discharge. 
The elevated level of phosphate occurring after discharge is 
disadvantageous because it increases the nutrient loading of the receiving 
waters. The method in accordance with the present invention avoids these 
problems by lowering the phosphate ion content upon discharge at 22 to 
such low levels that delayed precipitation is minimized or eliminated. 
SECOND PROCESS STEP 
Following production of the clear effluent at 22 of the flow sheet, the 
effluent is then treated for ammonia removal, the amount of ammonia in the 
effluent being in excess of about 15 ppm NH.sub.3 (N)--T. 
The process comprises treating the wastewater with an alkaline material 
selected from the group consisting of lime and caustic sufficient to 
provide a free ammonia equivalence (FAE) therein of at least about 12.4, 
said free ammonia equivalence being determined as follows: 
EQU FAE=pH+(.theta./15).sup.0.5 
wherein pH is the pH value of the treated wastewater and .theta. is the 
temperature of the wastewater in degrees Fahrenheit. Following the 
alkaline treatment, the process further comprises gas stripping the 
treated wastewater to remove ammonia therefrom, the stripping operation 
being controlled to maintain the free ammonia equivalence of the phase 
being stripped at said value of at least about 12.4 to lower the ammonia 
content of the treated wastewater to a value of about less than 10 ppm 
NH.sub.3 (N)--T and acidifying the wastewater depleted in ammonia to lower 
the un-ionized ammonia content to less than about 0.05 ppm NH.sub.3 (N). 
Referring to FIG. 1, ammonia-containing wastewater 23 containing in excess 
of 15 ppm NH.sub.3 (N)--T is fed to reactor 24 to which an alkaline 
reagent selected for the group consisting of lime or caustic is added to 
provide an exit effluent having a free ammonia equivalence of at least 
about 12.4, advantageously above about 12.5. The free ammonia equivalence 
being determined as follows: 
FAE=pH+(.theta./15).sup.0.5 
wherein pH is the pH value of the treated wastewater and .theta. is the 
temperature of the wastewater in degrees Fahrenheit. The free ammonia 
equivalence enables the operator to adjust the pH value of the wastewater 
exiting reactor 24, for example, to at least about 10.5. However it may be 
lower or higher, e.g., about 10.5 to about 12, taking into account the 
conditions that will be encountered during the gas stripping operation. If 
wastewater 23 has a free ammonia equivalence of at least about 12.4 as a 
result of the first process step, wastewater 23 can be sent directly to 
gas stripping at 25 as shown by dotted line 23A. 
The effluent from reactor 24 is subjected to gas stripping at 25 to a total 
ammonia content of less than about 10 ppm. Gas stripping can be 
accomplished in spray towers, spray ponds, or by spraying gases through 
the treated effluent. Spray towers or spray ponds provide greater 
liquid-gas contact and are therefore, significantly more efficient in 
stripping ammonia from the wastewater. Air sparging provides less 
efficient liquid-gas contact and promotes carbon dioxide absorption, 
thereby necessitating the use of greater amounts of lime or caustic and 
handling equipment. The stripping gas can be air, excess process steam, or 
the products of combustion of a fuel. 
Regardless of the type of gas stripping employed, it is important that the 
free ammonia equivalence in the phase being stripped be maintained at a 
value at least about 12.4. Thus, when sparging a body of wastewater, the 
temperature and pH of the body of wastewater must be controlled to have a 
free ammonia equivalence of at least about 12.4. Gas stripping techniques 
that employ spraying should be controlled such that the suspended droplets 
from the spraying operation have a free ammonia equivalence of at least 
about 12.4. Gas stripping by spraying can, depending upon meteorological 
conditions, cool the gaseous phase to such an extent that the free ammonia 
equivalence can drop significantly below 12.4. For example, conditions of 
low humidity, low temperatures, high winds, or combinations thereof can 
lower the temperature of the droplets in the gaseous stage by as much as 
10.degree.-15.degree. F. or more. In order to counteract such cooling, it 
is advisable to add sufficient amounts of alkaline reagent to overcome any 
significant drop in temperature of the suspended droplets. 
Heated stripping gases can be employed to provide numerous beneficial 
effects or to minimize the impact of uncontrollable external factors. 
Thus, heated stripping gases can be employed when the ambient temperature 
or the temperature of the wastewater falls below 15.degree. C. Heated 
stripping gases can also be employed to increase the rate of stripping, 
which may be necessary due to the unusual weather conditions or due to 
space limitations that restrict the number of ponds that can be 
established. Heated stripping gases can also be used to insure more 
complete removal of un-ionized ammonia. In addition to lowering the 
temperature of the phase being stripped, gas stripping may also lower the 
pH value of the phase being stripped if the stripping gas contains acid 
forming constituents such as carbon dioxide, sulfur dioxides, or nitrous 
oxides. Precautions must be taken to maintain the free ammonia equivalence 
of the phase being stripped to at least about 12.4; thus additional 
amounts of lime or caustic can be added during stripping or, most 
conveniently, the initial additions of caustic or lime are sufficient 
great to offset the adverse effects of acid-forming constituents in the 
stripping gas. 
The effluent from gas-stripping operation 25 containing less than about 10 
ppm NH.sub.3 (N)--T is sent to acid treatment stage 27, where sufficient 
mineral acid (26) or acid-forming constituent, e.g., sulfuric or 
hydrochloric acid is added to lower the un-ionized ammonia content to less 
than about 0.05 ppm NH.sub.3 (N). The pH may generally range from about 6 
to 8. 
A brief discussion of the processes that may be employed for removing 
ammonia is given as follows: 
Air Stripping (Towers) 
Air stripping is dependent upon pH and temperature. Ammonia stripping 
requires raising the pH to a value of at least about 10.5 and, preferably, 
in the range of about 10.8-11.5, with lime or caustic. 
As stated above ammonia stripping consists of increasing the pH of the 
wastewater to provide a free ammonia equivalence of at least about 12.4 
(FIG. 2) before passing the treated wastewater to the stripping tower. The 
formation and reformation of droplets (the phase being stripped) in the 
stripping tower provide increased air-water contact and droplet agitation 
with the passage of large quantities of air through the tower. As long as 
the free ammonia equivalence of the droplets is maintained at a value of 
at least about 12.4, the total ammonia content is readily lowered to less 
than about 10 ppm NH.sub.3 (N)--T. The stripping is preferably carried out 
in two or more stages. 
As stated hereinbefore, the rate of ammonia gas transfer from liquid to air 
is influenced by pH, temperature, relative ammonia concentrations, and 
agitation of the air-water interface. Countercurrent towers, where air 
enters the bottom and exhausts from the top while water flows down through 
the tower packing, are generally more efficient than cross-flow units. 
Pond Stripping 
Pond stripping is similar to stripping in towers. The pH is adjusted to 
provide a free ammonia equivalence of at least about 12.4 to convert the 
ammonium ion to free ammonia. Un-ionized ammonia is then stripped by 
spraying pond water into the air to give the necessary gas/liquid 
transfer. Temperature is important in achieving the desired efficiency. 
For example, under cooler ambient conditions, the efficiency is expected 
to be lower. This can be compensated for by using more ponds in series, 
using greater air circulation, heating water or by employing heated 
spraying gases. As in tower stripping, the stripping is preferably carried 
out in two or more stages. 
Advantages for pond stripping over tower stripping are low capital cost and 
simplicity of construction and operation. This method provides very 
acceptable results and is not as cost intensive as other processes. The 
use of ponds in series (i.e., more than two stages) is illustrated in FIG. 
3, the ponds being indicated by numerals 30, 31, 32 and 33. Wastewater 34 
at a pH value sufficiently high to provide a free ammonia equivalence of 
at least about 12.4, e.g., in excess of about 12.5, is delivered to pond 
30 by pump 30A, the wastewater being sprayed into the pond to effect 
removal of un-ionized ammonia. The water from pond 30 is removed by pump 
31A and sprayed into pond 31 to remove additional ammonia, and so on, to 
the last pond 33 where sufficient total ammonia [NH.sub.3 (N)--T] is 
removed from the effluent to a level not exceeding about 10 ppm. 
In spraying wastewater from pond to pond, the conditions of spraying are 
controlled such that the droplets falling in the succeeding pond have a 
free ammonia equivalence of at least about 12.4. 
FINAL pH ADJUSTMENT 
The de-ammoniated water, whether from pond stripping or tower stripping, is 
then sent to acid treatment to lower the un-ionized ammonia to less than 
about 0.05 ppm [NH.sub.3 (N)], and more preferably, not exceeding about 
0.02 ppm [NH.sub.3 (N)]. The pH may generally range from about 6 to 8. 
In lowering the un-ionized ammonia to less than about 0.05 ppm, the amount 
of mineral acid or acid-forming constituent added should be sufficient to 
provide a pH value such that the free ammonia equivalence does not exceed 
a value determined as follows: 
EQU FAE=10.2-log.sub.10 ppm NH.sub.3 (N)--T 
In achieving an un-ionized ammonia content not exceeding about 0.02 ppm, 
the amount of acid added should be sufficient to provide a free ammonia 
equivalence that does not exceed a value determined as follows: 
EQU FAE=9.8-log.sub.10 ppm NH.sub.3 (N)--T 
Although the present invention has been described in conjunction with 
preferred embodiments, it is to be understood that modifications and 
variations may be resorted to without departing from the spirit and scope 
of the invention as those skilled in the art will readily understand. Such 
modifications and variations are considered to be within the purview and 
scope of the invention and the appended claims.