Method for processing paint sludge

A process for treating paint sludge in which previously cured paint sludge powder is used as a diluent and mixed with wet paint sludge. The paint powder/sludge mixture is agitated and heated to cure the paint sludge. Processing can occur either continuously or in batch mode, and can be accomplished using a mixer charged with heated gases, or a heated mixer.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for treating paint sludge having 
both solid and liquid components. More specifically, the present invention 
relates to a drying and curing treatment for processing waste paint sludge 
into a dried powder which is suitable for recycling or convenient 
disposal. 
For many years now environmental interests have sought to limit the type 
and quantity of industrial waste, including paint sludge. In response, 
manufacturers have developed various methods for treating paint sludge and 
creating useful byproducts from it. 
One principal and troublesome source of paint sludge is the automotive 
industry. When an automobile is painted in a paint booth, for example, the 
excess paint solids are collected, typically in a wet booth or a 
water-wash system. The effluent from such systems is a dilute mixture of 
water, paint resins, detackifying compounds and other minor constituents. 
A majority of the water from this effluent is recovered for reuse in the 
wet booth, leaving a relatively thick and viscous paint sludge. 
It will be appreciated by those skilled in the art that the waste paint 
sludge treated in accordance with the present invention is a complex 
material and is different from most other waste sludges. For example, 
paint sludge includes a variety of polymeric resins, volatile organic 
compounds ("VOC's"), such as thinners and solvents, as well as 
detackifying agents and flocculants. The resident polymeric paint resins 
are uncured and in a liquid or semi-liquid phase. These resins can "cure" 
or cross-link upon the heating and volatilization of the constituent 
liquid components. Paint sludges may also include inorganic pigments and 
heavy metals. These components are often hazardous and/or toxic. 
Disposal of paint sludge is a problem of considerable complexity. Various 
kinds of sophisticated equipment have been used to process paint sludge. 
Currently available disposal technology is based upon the principles of 
incineration, chemical and physical treatment, and solidification, as 
discussed in U.S. Pat. Nos. 4,750,274 and 4,980,030, hereby incorporated 
by reference. The equipment disclosed in these patents has met with 
considerable commercial success, although this equipment is relatively 
expensive to construct, operate and maintain. 
Prior art methods for drying paint sludge have relied upon specially 
designed drying methods. A machine known to perform adequately is the 
assignee's own DRYPURE.RTM. drier, described in U.S. Pat. No. 4,750,274, 
which uses a hollow flight screw mixer heated with hot oil. The operation 
of this equipment requires the use of a suitable scouring aggregate such 
as small stone chips or gravel. 
The DRYPURE.RTM. process has been a commercial success. However, the 
DRYPURE.RTM. machine is relatively expensive. It is also susceptible to 
the operational problem that the paint sludge can transform into an 
extremely viscous "sticky phase" that can lock up the machine. When heated 
paint sludge is in the sticky phase, it has the consistency of taffy with 
excessively high cohesive and adhesive properties, and if allowed to cool 
in this condition, the sludge will "set" into a solid mass. This 
phenomenon can also damage drier or mixer components, and once transformed 
to this sticky phase, the sludge can only be removed from the processing 
equipment in a laborious fashion. In the past it has been difficult to 
prevent sludge transformation to the sticky phase in a predictable and 
consistent manner. While use of the scouring aggregate in the DRYPURE.RTM. 
process addresses this problem, removal and disposal of the aggregate is 
difficult and increases the costs of the process. 
Known thermal techniques for processing paint sludge also require 
significant warm-up times and corresponding cool-down times, due to their 
relatively large thermal mass. For example, with the screw mixer disclosed 
in U.S. Pat. No. 4,750,274, the "thermal mass" (i.e., the mass that must 
be heated to heat the sludge) includes a good deal of equipment and system 
components unrelated to the sludge, including oil tanks, piping, jackets 
containing oil, etc. 
A further problem associated with known thermal drying techniques for 
processing paint sludge is their relatively high operational and 
maintenance costs. 
With treatment systems other than those involving paint sludge, it has also 
been known to back-mix wet or sticky materials with dry materials to 
facilitate drying. However, it is not believed that curing of the material 
to be treated has been accomplished with such systems. 
Accordingly, it is an object of the present invention to provide an 
efficient, simple and economical thermal drying device and technique for 
processing paint sludge. 
It is also an object of the invention to provide a paint sludge processing 
technique which does not require disposal or replacement of a scouring 
aggregate. 
Another important object of the invention is to provide a method for 
processing paint sludge into a fully dried, frangible and cured powder, 
while minimizing sludge transformation into the sticky phase and its 
deleterious effects. 
These and other objects and advantages of the present invention will become 
apparent to those of ordinary skill in the art from a reading of the 
following description of the preferred embodiments and the appended 
claims. 
SUMMARY OF THE INVENTION 
The present invention satisfies these and other objects, while also 
preserving the advantages of known methods for processing paint sludge, 
and avoiding the disadvantages associated with such methods. 
The process of the present invention for treating paint sludge includes the 
use of a dried and cured powder derived from previously processed paint 
sludge. The cured powder is mixed with the paint sludge to be processed 
within a containment vessel to form a powder/sludge mixture. The mixture 
is heated, preferably within a substantially inert environment, at a 
temperature and for a time sufficient to cure the polymeric paint resin 
and to volatilize water and VOCs present in the sludge. The mixture is 
agitated during heating in a manner that will promote adequate mixing and 
heat transfer without substantially increasing the cohesive and adhesive 
properties of the mixture. 
In a preferred embodiment, cured powder is mixed with an incoming stream of 
paint sludge continuously, and removal of the cured powder is done 
periodically, while still maintaining a minimum powder treatment amount 
within the containment vessel. At the end of a day or shift, for example, 
no further sludge is added, and the remaining mixture within the vessel is 
heated for a sufficient time to ensure that the last portion of paint 
sludge added to the vessel has been fully cured. 
In another embodiment, cured paint powder is mixed with paint sludge to be 
treated in a mixing vessel, and the powder/sludge mixture is then 
transported (by a screw conveyor, for example) into a second containment 
vessel. This second vessel may be a drier, such as a heated mixer, or may 
instead be a fluidized bed, for example. Further agitation and continued 
heating, or combinations of these processing procedures may be 
accomplished in yet another containment vessel. 
The powder/sludge mixture preferably has a "powder/sludge ratio" which is 
at least 1 part by weight of cured powder to about 1 part by weight of 
paint sludge, or 1:1. Preferably the powder/sludge ratio is at least 3:1, 
and may be much greater, such as 10:1 or even greater, depending upon the 
throughput required, the equipment used, the type of sludge processed, and 
whether the process is performed in a continuous or batch mode. Obviously, 
when the system is operated in the continuous mode this ratio will vary 
unless a "steady state condition" is reached, which is defined here as the 
point in the process at which the rate of sludge added to the mixer is 
equal to the rate at which the sludge is curing within the mixer. If the 
process is performed in a step-by-step "batch" mode, the powder sludge 
ratio is preferably between about 2:1 and 10:1. 
To obtain a cured powder end product, the powder/sludge mixture is 
preferably heated to a temperature of at least about 400.degree. F. within 
the containment vessel, for a time period of between about 30 minutes and 
one hour, prior to removal of any of the cured powder from the containment 
vessel. 
Heating of the mixture can be accomplished through direct contact with a 
heated gas such as steam, or through indirect heating (e.g., using a 
heated mixer). An insulated paddle mixer is preferred, and provides 
sufficient agitation so that good heat exchange contact is achieved 
between the paint powder/sludge mixture and the heated gases, without 
providing excessive shearing forces which can induce transformation to the 
paste-like sticky phase with excessive cohesive and adhesive properties. 
Gases generated by heating the paint sludge may be incinerated/oxidized, 
and the hot exhaust may be recovered and provided to a heat exchanger to 
enhance efficiency. These gases may also be condensed, and the resulting 
condensate may be treated or otherwise recirculated or disposed of. 
The dried and cured end product from the process may be easily crushed or 
pulverized to obtain a desired size and consistency, and it can be used as 
landfill, as a constituent within building materials such as asphalt, or 
for other purposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiment of the present invention utilizes previously dried 
and fully cured powder that has been processed from wet paint sludge. This 
cured powder is mixed with wet paint sludge to be processed, and acts as a 
"curing facilitator" or a diluent to reliably dry and cure the paint 
sludge and transform it into a non-toxic powder. "Cured" is defined here 
as a condition in which the paint sludge has been fully dried, with 
substantially all the volatile constituents being driven off, and the 
resident paint resins cross-linked sufficiently to prevent any reversion 
to a liquid, semi-liquid or "plastic" state. 
It has been known that at temperatures of less than 300.degree. F., and 
sometimes as low as 212.degree. F., paint sludge will convert into an 
apparently cured state. However, it has not previously been understood or 
appreciated how the presence of spray booth chemicals within paint sludge, 
such as detackifiers or flocculants, as well as paint sludge agitation, 
impact paint sludge curing. Detackifying agents, for example, encapsulate 
the paint droplets in a film, lowering the adhesive properties of the 
paint. It has now been found that these factors can significantly effect 
curing, so that higher temperatures and longer heating dwell times are 
required than was previously thought necessary to induce cross-linking and 
curing of the paint resin. In fact, the inventors have discovered that 
temperatures of at least about 400.degree. F. are preferred to adequately 
cure paint sludge in a reasonable time. 
Thus, in accordance with the present invention, the raw paint sludge is 
mixed with cured powder and thereafter heated, preferably to at least 
about 400.degree. F., and agitated for a sufficient time to convert the 
sludge to a fully dried and cured particulate. By mixing the cured powder 
in the appropriate amounts and by utilizing the appropriate processing 
conditions, the sludge/powder mixture can be maintained in a generally 
free-flowing phase that does not agglomerate. In this state, the mixture 
has relatively low adhesive and cohesive properties and can be readily 
dried and cured without the problems attendant with sludges in the 
"sticky" phase. 
Referring to FIG. 1, a continuous paint sludge treatment process is shown, 
and forms a preferred embodiment of the present invention. A predetermined 
amount of the dried and cured powder is initially supplied to mixer 20 by 
any expedient means. Wet paint sludge is continuously transported from 
sludge hopper 26 by sludge pump 28 to mixer 20. The powder/sludge blend 
within mixer 20 is preferably maintained at a minimum temperature of at 
least 400.degree. F. While volumes and rates will vary, in a particularly 
preferred embodiment, mixer 20 may, for example, initially contain 5 cubic 
yards of dried paint powder as the wet sludge is pumped into the mixer at 
at rate of 5 gallons/minute, resulting in a total of 7 cubic yards of 
dried and cured paint powder contained within the mixer at the end of the 
process following an 8-hour shift. The amount of dried powder contained 
within the mixer at any point in time is referred to here as the "residual 
paint powder". 
At the end of a day or shift, a predetermined portion of the cured powder 
is transported from the mixer, via line 29, by pneumatic transportation 
which allows the powder to cool, and into powder bag station 22. While 
cured powder can be periodically removed during a shift, for example, a 
delay of at least one-half hour is required to cure the sludge last added 
to the mixer; therefore, it has been found advantageous to wait to remove 
a predetermined portion of the cured powder until the end of a day or 
shift. 
A steam environment is maintained within mixer 20. Lines 38 and 39 provide 
water spray and fire suppression chemicals, respectively, as needed, using 
controls 38A, 39A. The steam is continuously recirculated through mixer 
20, and is preferably directed into the mixer while the mixer paddles 
agitate the sludge to provide good heat exchange. Steam is charged into 
the mixer via line 32, which leads from heat exchanger 30, while steam 
exhausts from the mixer via line 34, and is recirculated to heat exchanger 
30 by fan 35. Burner 46 adds heat to the air, which is directed via line 
40 into the heat exchanger; excess air from the heat exchanger is released 
to the atmosphere via line 42. Heater recirculation fan 43 and combustion 
blower 45 are employed to convey the hot air within this portion of the 
system, as shown. The other effluent stream from mixer 20 includes gases 
and dust, and passes via line 51 into cyclone 50. Cyclone 50 separates the 
dust from the gas exhaust, and the dust is conveyed through line 52 back 
into powder bag station 22, which holds powder from the mixer. The 
remaining exhaust containing VOCs is conveyed by exhaust blower 58 through 
line 56 and into thermal oxidizer 60 (maintained at temperatures of 
between 1400.degree.-1600.degree. F.), which has associated with it burner 
61 and air combustion blower 62. 
In FIG. 1, T1-T6 indicate the presence of thermocouples for temperature 
measurement; A1 indicates the presence of a current sensing device; P1-P7 
indicate the presence of pressure sensing devices; L1 indicates the 
presence of a load sensing device (associated with load cell 24); and THTL 
indicates the presence of a high temperature thermal couple which 
functions to shut down burner 61 if incinerator 60 reaches a maximum 
temperature. 
As a non-limiting example, a particularly preferred embodiment of the 
present invention may be practiced using the following parameters: at line 
40 (T=1000.degree. F.); at line 41 (T=750.degree. F., 26,320 SCFM); at 
line 32 (T=800.degree. F., 527.75 lb/min, 26,915.25 SCFM); at line 34 
(T=600.degree. F., 527.75 lb/min, 22,169 SCFM; and at line 54 
(T=600.degree. F. steam, 2200 lb/min, 1572 SCFM. Burners 46, 61 may be 5 
mm BTU/hr and 3.5 mm BTU/hr, respectively. Oxidizer 60 may maintain a 
temperature of 1600.degree. F. at a 1 second dwell, and combustion blower 
62 may provide 3000 SCFM. 
In the continuous paint sludge treatment process depicted in FIG. 1, the 
weight ratio of dried and cured powder to wet paint sludge within mixer 20 
may vary substantially. At the beginning of the treatment, the ratio of 
cured powder to sludge will be very large. As the treatment progresses, 
the ratio of cured powder to sludge will optimally reach a steady state 
condition. At this steady state condition the amount of uncured sludge in 
the mixer depends on the rate at which sludge is added and the rate at 
which the sludge is curing. This latter condition is, in turn, dependent 
upon the powder bed temperature (since a higher temperature results in 
faster curing). As one example, if at the start of the treatment there is 
5 cubic yards of dry cured powder in the mixer (or about 8,000 pounds), 
and assuming the sludge requires one-half hour to dry and cure, and sludge 
is pumped into the mixer at a rate of 5 gpm,, this will result in 1,250 
pounds of sludge, or a powder/sludge ratio of 6.4:1. Thus, the 
time/temperature relationship for drying and curing sludge will vary 
significantly based upon the type of sludge, the throughput required, 
etc., and this will have a significant effect on the powder/sludge ratio, 
which must be at least 1:1, but may be 3:1 or even 10:1 or significantly 
greater. 
These temperatures, gas flow rates, sludge pump rate and holding capacities 
are typical parameters for the preferred embodiment but, obviously, may be 
varied for different systems depending on the required throughput and type 
of sludge being processed. 
In another embodiment, a step-by-step "batch" mode, the entire wet paint 
sludge load to be processed is charged to mixer 20 in a single step, and 
the sludge can be heated and processed in a manner similar to that 
described above. In the "batch" mode, the powder/sludge ratios may be 
between 2:1 and 10:1 or greater. 
It will be appreciated that the cured paint powder and paint sludge can be 
mixed in a containment vessel, and then transported by a screw conveyor or 
other means to a drier for further processing. In either the heated mixer 
or this latter "premix" embodiment, the mixer can be of various types. As 
a non-limiting example, a Pugmill mixer having a single shaft with 
multiple paddles fixed on the shaft can be used, and is available from 
McCarter Corporation of Norristown, Pa. Preferably, the drier is an 
insulated, multi-paddle mixer designed to minimize mechanical working of 
the sludge. During agitation, a blower charges superheated steam into the 
powder in the same direction as the paddle(s) are directing the powder. 
While it will be understood that many different types of equipment and 
heating alternatives and combinations can be employed using the present 
invention, mixers which exert lower shear forces on the detackified paint 
sludge particles, to minimize the exposure of raw paint particles, are 
preferred. While most commercially available mixers can be used with the 
present invention, routine testing is first required to ensure that the 
mixer is operated in a manner and at speeds that do not involve excessive 
shearing and exposure of the paint sludge resins. Mixer operators must 
strike a balance between the desire to optimize heat transfer and obtain a 
homogenous mixture, necessary for proper drying and curing, without 
causing excessive shearing. As an example, the operator can monitor the 
consistency of the sludge and the appropriate mixing speed by monitoring 
the amperage of the mixer motor; the amperage will be proportional to the 
torque of the paddle(s), which is proportional to the sludge consistency 
or "stickiness". 
With any treatment system for paint sludge there is some minimum baseline 
amount of cured paint powder or "heel," defined here as the "minimum 
powder treatment amount," necessary to ensure that the paint sludge being 
processed will dry and cure correctly. It has been empirically determined 
that, as a general rule, this minimum powder treatment amount is 
preferably at least 3 parts of cured powder to 1 part, by weight, of wet 
paint sludge. Depending on the type of sludge to be treated and the 
equipment used, however, this ratio may be as low as 1:1, and can 
certainly be greater than 3:1, as discussed above, within the size 
constraints of the mixer. 
The powder/sludge mixture in the mixer is continuously heated at a 
temperature of at least 400.degree. F., for at least about 30 minutes, 
(and with some sludges for up to one hour), to ensure that the paint 
sludge is cured. These conditions are, of course, also sufficient to drive 
off all the water and liquid solvents present in the paint sludge. It has 
been found that curing can occur at temperatures of 375.degree. F., and 
possibly as low as 350.degree. F. with certain paint sludges. However, the 
minimum preferable treatment temperature is at least about 400.degree. F. 
to accommodate a broad range of paint sludges. 
Mechanical working of the paint sludge in the powder/sludge mixture must be 
controlled in accordance with the practice of the present invention so 
that a minimum number of paint droplets in the powder/sludge mixture are 
sheared or smeared to expose raw paint. This, in turn, will prevent the 
paint sludge from transforming into the sticky phase. It is, therefore, 
important that the agitation of the powder/sludge mixture be limited so 
that the cohesive and adhesive properties of the mixture do not 
appreciably increase during heating and drying. Through this careful 
handling, and by controlling the temperatures and dwell times as indicated 
here, the paint resins within each discrete paint droplet in the mixture 
will cross-link and cure, with each droplet forming a hard particle of 
plastic that will not revert to a liquid or semi-liquid phase. 
The "seed batch" of dried and cured powder, necessary for use of the 
present invention, can be obtained in a number of ways. For example, the 
process disclosed in U.S. Pat. No. 4,750,274 can be used to treat paint 
sludge. Alternatively, paint sludge can be treated with chemicals, such as 
surfactants, or chemically dried with calcium oxide. Alternatively, a 
suitable particulate such as sand could be used. 
To provide a working example of the treatment process of the present 
invention in the "batch" mode, 500 pounds of cured powder is added to 200 
pounds of paint sludge consisting of 80% water, by weight. After the first 
treatment there will be 540 pounds of powder in the batch. Load cell(s) 24 
is positioned beneath the mixer to continuously monitor the weight of the 
powder/sludge mixer. After the second treatment, again adding 200 pounds 
of the sludge, there will be 580 pounds of cured powder in the batch. 
Assuming the maximum powder treatment amount is 1200 pounds of powder, 
when this maximum amount has been reached, only then must a portion of the 
dried and cured powder be removed from the batch. 
In another example according to the present invention carried out in the 
"batch" mode, four cubic yards of cured paint powder and one cubic yard of 
wet paint sludge were mixed and heated, dried and cured as described 
above. It was found that since the volume of the wet paint sludge will 
typically be reduced by a factor of five, on completion of the drying 
cycle 4 and 1/5 cubic yards of cured paint powder was present in the 
dryer. 1/5 cubic yard of cured paint powder was then removed from the 
dryer, a new charge of wet paint sludge was added to the dryer, and the 
process was repeated. The inventor has successfully treated paint sludge 
according to the present invention using a multi-paddle mixer, and has 
found, as discussed above, that a preferred heating method is to directly 
heat the sludge using hot gases charged to the mixer. This improves heat 
transfer efficiency and overcomes the surface area heating limitation of a 
heated jacket mixer, discussed immediately below. In a preferred heating 
method, some of the vapors from the mixer are superheated, using a heat 
exchanger, and then returned to the mixer. 
The present invention is more economical than known sludge treatment 
systems employing a heated jacket. With the heated jacket mixer, the 
sludge tends to stick to the walls of the mixer, forming an insulating 
blanket which interferes with effective heating of the powder. Also, with 
such prior art systems, to increase the drying power by a factor of two, 
the machine size needs to be doubled, since the surface area varies 
linearly with the size of machine. However, with the present invention, 
the drying power increases with the cubic root of the linear dimension of 
the mixer. For example, the prior art system disclosed in U.S. Pat. No. 
4,750,274, treating the same four cubic feet of paint sludge volume, will 
need to be sized to accommodate a sludge cube with more than six times the 
surface area. Since the ratio between volume and surface area continues to 
increase with the linear sludge dimension, this difference only becomes 
more dramatic as the size of the system increases. Thus, it can be seen 
that the present invention provides a great advantage in space savings and 
overall efficiency compared to known prior art sludge heating systems. 
While it will be understood that various heating and processing methods can 
be used, it is currently believed that a continuous treatment process 
employing direct heating using an inert or oxygen-free gas is superior to 
other known methods for practicing the present invention. 
In another preferred embodiment, remaining vapors not used for mixing can 
be collected and condensed into a liquid using appropriate ductwork to 
direct these vapors to a condenser. This minimizes or eliminates the need 
for costly air pollution control equipment. The resulting condensate can 
then be sent to a waste water treatment system. 
It will be understood that the cured paint powder can be dried to any 
desired extent. This may depend on the post-treatment steps or on ultimate 
use (e.g., recycling sludge back into system, use as landfill, 
incineration, etc.) to be made of the sludge, since control over material 
dryness can enhance (for example) sludge recyclability. 
Using the present invention, a variety of different paint sludges have been 
successfully transformed into a dried, frangible and cured powder. It is a 
robust and reliable technique which is easy to operate and relatively 
safe. Also, the need for a costly hot oil system with a heated jacket 
mixer is eliminated, because heating can be accomplished using a gas-fired 
heat exchanger. Better heat transfer and lower thermal mass also results 
in faster and more efficient heating and cool-down of the system. As an 
example, the drier of the present invention requires about 30-45 minutes 
to heat to an appropriate operating temperature, while the heated jacket 
system described in U.S. Pat. No. 4,750,274 requires several hours of 
heating start-up time, to treat the same amount of sludge. Further, the 
method of the present invention is more compact and requires less floor 
space than current systems. It is also estimated that the capital costs 
for building a comparable machine of the present invention are 
substantially less, and possibly one-half or less, than the capital costs 
of the machine described in the '274 patent. 
The basic treatment steps of the present invention, when used in the 
"batch" mode, are illustrated in block diagram form in FIG. 2. First, 
cured paint powder 120 is blended with wet paint sludge from hopper 26 
(conveyed by pump 28) within batch drier/mixer 20. Gas emissions from the 
mixer can be filtered (step 125) and condensed (step 130). The resulting 
condensate may be conveyed via condensate drain 140 for disposal in a 
waste treatment plant or sewer 145; remaining effluent may be conveyed by 
blower 150 into superheater 160. The superheated gas can be recirculated 
into mixer 20. Alternatively, it may be preferred to incinerate gas 
emissions from the mixer, rather than condensing them, for economical 
reasons. Following drying at the end of a day, a shift, or other 
appropriate time interval, a portion of the cured paint powder can be 
removed from the dryer and conveyed to a hopper (not shown). This 
processed powder can be used as a fuel, as landfill, or for other 
purposes. 
It will be appreciated that the choice of using the "batch" or "continuous" 
processing mode will depend upon the required throughput of sludge to be 
processed, the particular equipment chosen, the type of sludge and the use 
to be made of the sludge. 
Referring now to FIG. 3, a preferred embodiment of the apparatus of the 
present invention is shown. On the primary side of heat exchanger 45, hot 
air circulates from heat exchanger 45, through the ductwork 57, through 
fan 62, and into burner 78, as indicated by the arrows. Burner 78 includes 
inner and outer tubes 78A and 78B, respectively, with inner tube 78A being 
perforated. Hot air passes between tubes 78A and 78B and is directed back 
to heat exchanger 45, as also indicated by the arrows. 
Still referring to FIG. 3, on the secondary side of heat exchanger 45, 
superheated steam passes through ductwork 58 and into mixer 10, as 
indicated by the arrow. Filters 20 are positioned above mixer 10, and 
accept superheated steam from mixer 10. The steam then passes from filters 
20, through blower 50 and ductwork 55, and back into heat exchanger 45. 
It will be appreciated that the resulting effluents from the process can be 
used in a variety of ways. Condensate produced from the mixing process can 
be recycled back to the booth water within the paint spray booth. Cured 
paint powder from the drier can also be sent to a crusher, where the 
solids can be pulverized by any means well known in the art. The dried and 
cured solids can then be conveyed to, for example, a landfill. 
Alternatively, the cured powder can be used as an ingredient for asphalt, 
concrete, mastics, sealants and similar materials. The resulting powder 
from the sludge processed according to the present invention may also find 
advantageous use as a fuel, due to its BTU value. 
The foregoing description of the preferred embodiments of the present 
invention has been presented for purposes of illustration and description. 
The described embodiments are not intended to be exhaustive or to limit 
the invention to the precise form disclosed. Obviously many modifications 
and variations are possible in light of the above teachings. The 
embodiments which were described were chosen in order to best explain the 
principles of the invention and its practical applications. It is 
therefore intended that the scope of the invention, as defined by the 
following claims, be interpreted to include all equivalent treatment 
systems falling within the spirit of the present invention.