CA1090016A - Organic waste drying process - Google Patents

Abstract

ABSTRACT

A process for drying organic,waste, such as sewage sludge, by contacting the organic waste with hot vapors wherein the dried material is extruded to form compacted granules having good flow characteristics and suitable for application by com-mercial fertilizer spreaders.

Description

~90016 SPECI,;~[,CA,TI~ON

The inventi~on xelates to the drying oE solid mater~
ial by contactin~ the solid material w;th hot vapors. The invention also relates to the drying of organic waste such as sewa~e sludge and to the production of fertilizer or soil ~uilders from organic waste. The invention more speci~ically relates to the conversion and finishing of the dried material to a more commercially acceptable and marketable form by pelletization in an extruder~
The large amounts of organic waste which are produced annually and the need to dispose of this waste have prompted attempts to develop economic organic waste disposal methods. It is known in the art to dry organic waste by contact with hot vapors. The prior art processes have features in common with the subject process. First, the vaporous effluent of the drying zone is often passed into a solids-vapor separation zone to co]~ect or remove particles of the solid product. This zone typically com-prises one or more cyclone-type separators. Second, it is known in the art to recycle a portion of the dried product and to admix this dry material with the incoming feed material to form a somewhat drier char~e material which is ~ed to the drying zone. This procedure is pri-marily intended to expedite the feeding of the organic waste into the drying zone and to lessen accumulation of the ra~ ~aste material on the walls of the drying zone.
The use of a preferred toroidal drying zone in a process for the trea-tment of organic wastes is taught in -1~9~6 Un,~te.d ~ta,te~s. Pa,tent 3 ! 80.2,089. Thi:s re~erence'shows the di~scharge of the toroidal dryer being directed into a cyclone sepaxatoX and the recycli,ng Q~ th.e,' separator off-gas to the drying zoneO The preferred toroidal dryer may be essentially the same in structure as the size reduction apparatus referred to as a fluid energy or jet mill. This apparatus is described at pages 8-43 of the 4th Edition of The Chemical Engineers' Handbook published by McGraw-Hill Book Co., 1963. The subject dryer is operated in a manner similar to many of these mills except for the use of h -.'.
heated gas streams as the high-velocity streams charged to the apparatus.
It is believed that heretofore the effluent of the drying zone has not been extruded. Instead, it has typi-' 15 - cally been compressed as in a roller compacting mill to form sheets or flakes which were then passed into a crush-ing or granulating device. The resultant granules are then screened to remove fines and oversized particles '-' which are recycled. Material produced in this manner normally has poor flow characteristics and is difficult to mix and to apply with any conventional equipment.
The invention provides an improved process for drying solid organic wastes by contact with a hot vapor. The invention also provides an improved finishing operation for use with.such.a process. The subject drying process includes the steps of collecti,ng dri.ed solid waste parti-cles from the e,ffluent of the drying zone and then passing the dried material through an extrusion zone. The process : .3-.'` .

~)9~Q16 thereby provides a more uniform product than the prior art compaction methods and also reduces the amount of product which is of an unacceptable size and which must be recycled to the compaction/breaking equipmen-t.
In one particular aspect the present invention provides a process for drying a feed stream comprising water and organic waste which comprises the steps of:
(a) passing the feed stream into a drying zone operated at drying conditions and effecting the evaporation of water contained in the feed stream and the production of a drying zone effluent stream comprising particulate organic waste and water;
(b) separating the drying zone effluent stream in a solids-vapor separating zone to produce a vapor stream comprising water vapor and a dry solids stream comprising particulate organic waste and containing less than about 15 wt. % water; and (c) extruding a first portion of the dry solids stream in an extrusion zone to form a product stream having a bulk density within the range of about 481 to 1041 kg/m3.

To insure a complete understanding of the inventive concept, a schematic illustration is presented in the Drawing. In this embodiment an organic waste stream com-prising sewage sludge from a municipal treatment center and containing about 20% by weight solids is fed into the process in line 1. This material is passed into a mixing zone 2 and commingled with a fluffy dry recycle material from line 3.
The resultant feed stream is passed into the drying zone 5 through line 4 and contacted in a toroidal dryer with a stream of hot vapors. These vapors are generated by the combustion of fuel entering the process via line 17 with air from a source not shown. Preferably, the combustion products ~ 4_ .: , .

0~6 ~re used to form at least part of the hot vapors and are passed directly into the dryer~ The drying zone effluent stream carried by line 6 therefore contains -the dried solid particles contained in the sewage sludge of line 1, combustion products and the additional water vapor driven off the dried sludge.
The drying zone effluent stream is passed into a solids-vapor separation zone 7 wherein the combustion products and water vapor are concentrated into a vent gas stream removed from the process in line 8. The solid particles of dried sludge are collected as a dry solids stream transported in line 9. Preferably this separation ~ 4a-090(~
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o~ th.e ~s.olid$ a,nd ~apor~s~i;s ef"f,ected thxou~h.the. u$.e. o~
one or ~oxe`cyclone.~type separa,tors., A f;'rst port;,on of the dry solids stre.am is passed into l;ne 10 and mixed with a`recycle fines stream from line 11. This portion of the dry solids st~ream is t:hen passed through line 12 i,nto an extrusion zone 13. In this zone the dry solids are compacted and pushed through a die to produce pellets having an average bulk density which is about 2-4 times greater than that bf the.unpelleted dry solids. These 1~ pellets are removed in line 14 as a product stream. As a second finishing step the product stream is thén passed through a fines separation zone 15 wherein by air blowing -or screening any dus,t, undersized particles, and over~
sized par'ticles are removed. The fines are passed through 15 line 11 and the finished product is removed in line 16.
The drying of organic waste is normally a multistep process which may be discussed in terms of the separate operations and their interac-tion. The overall objective of the drying procedure is to dispose of the organic waste and to convert it to a useful and pre~erably market-able product. In the subject process the organic waste is dried and formed into pellets which may be sold as fertilizer or soil conditioner. The inventive concept is mainly concerned with.the step of forming the dried material into pellets, but the other steps will be described in some detail to provide a basis ~or under-standing the invention.
A,s used herein the term "organi,c waste" is i.ntended ', . ': ' 1~)9~

to re~e~ to ca~on~contaIning substances that are deriyed directly~fxom l~ing or forme~ly livIng organis~s. Speci-fic example$ ~nclude human sewa~e, fat, meat scraps, bones, hair, skin, ~eces and manure ~rom animal sources, beét pulp, fruit pumice, vegetable and fruit peels and culls, eggs, straw and animal bedding, bagasse, fermentation and distillation residues from vegetable sources, cellulose and protein production plant effluents, kelp and pharma-ceutical wastes. In the preferred embodiment the feed stream to the process comprises a sewage sludge produced in a municipal sewage treatment plant. It may be a pri-mary, secondary, or tertiary sludge, which is digested or undigested. Preferably the feea stream to the process contains about 20 wt.%"or~more solids.
- These organic wastes may be dried to form a slow release fertilizer and soil builder. In order to distrib-ute such a fertilizer in the large scale operations or modern commercial agriculture, it is necessary to utilize mechanical spreaders, for which reason the fertilizer 2Q particles should be relatively dense and approximately uni~orm in size and shape. In the prior art the dried organic waste was compressed to solid pieces which were then crushed to form particles of various sizes and shapes, This method also formed sizable amounts of dust.
~5 The product particles then had to be sized as by screen-ing wi:th the off-size material being recycled. The amount of this o~f-size material has reached over 50% of the material being compressed. It is an objective of ~`

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th.;~s I~nvention t~ prov.lide a p~ocess for dryin~ or~anic waste wherei~n t~,e product has. a relatively uniform. size and shape. rt is another objective o~ th.e invention to provi,de a process for drying organic waste wherein the.
'product is relat~vely dense, Another objective is to provide a granular material with good flow characteristics.
It is yet another objective of the invention to provide an improved process for the drying of organic waste which produces a particulate product ~ithout extensive crushing of the dried organic waste.
Basic to the subject process is the use of a drying zone. This may be any mechanical contrivance in which the organic waste is dried. The dryer may be either a direct r or indirect dryer and may operate in a batch or continuous modq. The drying may therefore be effected by contacting the organic waste with a hot surface with intermittent or continuous agitation, but it is preferably accomplished by contacting the organic waste with a hot, relatively dry vapor. There are several ways in which this preferred drying may be performed. For instance, the organic waste may be passed into the raised end of a rotating cylindri-cal kiln while hot dry vapors are passed into the lower end. Other drylng system~s such as a flash-cage dryer may be used~ , In the preferred e~bodiment, the dxying zone com prises a to~.oidal dryer~ As used herein the term ~Itorol-dal dryer~' is intended to refer to a dryer in which the material to be dried is passed into an enclosed circular i .
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housing wherein the wet material is caused to circulate by hot vapors which are charged to the dr~er. It is there-fore intended to refer to a dryer similar to that described in United States Patents 3,802,089; 3,329,418;
3,403,451; 3~667,131 and 3,856,215. The material to be dried is normally passed into a lower point in a vertical-ly oriented dryer housing and caused to move horizontally by the hot vapors. The wet material is then circulated around the vertically aligned circular loop of the dryer, with dry material being selectively removed with effluent vapors. The drying conditions used in the drying zone include a pressure which may range from subatmospheric to about 7 atmospheres gauge. Preferably, the drying zone is operated at a slight positive pressure with a toroidal dryer. This pressure may be in the range of from about 0.1 to 0.6 atmospheres gauge. This pressure is required for transportation of the solids.
The drying zone may be supplied the heat required to effect the drying from any suitable source. It may there-fore be supplied by electricity or by a nuclear power plant. The preferred heating method is the combustion of a relatively sulfur-free carbonaceous fluid such as a desulfurized fuel oil or natural gas. Preferably, the combustion is completed prior to the contact of the resultant hot vapors with the organic waste. The temper-ature of the hot vapors fed to the dryer may vary from about 260 to 732C. A preferred range for this temper-ature is 399 to 677C.
It has been found by experience that a feed stream ` 1~9~

be~n~ fed to, a, to,~Q~i~d,a,l d~lyex should contain at le~st about 50 wt,% sol'i~d,s~,, Preferably, i~t conta,i,ns about 55 to 70 ~t~,% s,olids~., T~,s~ de~ree'of dryness i,s desirable to pre-vent port-~,ons of the feed stream from depositing on the internal surfaces of the dryer. That is, a soupy feed stream has a tendency to plaster ayainst the walls of the dryer with at least a portion remaining there as an undesired coating. The normal method of increasing the solids content of wastes such as municipal sludge is to recycle a portion of the dryer effluent. A representative r:ec~cle ratio is the addition of 7 lbs. of dried solids collected from the dryer effluent to S lbs. of sludge containing about 20 wt.% solids. This recycle rate wiill', of course, be adjusted for o~her solids contents in the organic waste stream fed to the process.
An alternative to the recycling of dried solids in the dewatering of the organic waste stream fea to the process. This can be done in several ways. For instance, United States Patent 3,984,329 (Cl. 210-396) presents a conveyor-type sludge filtering device. Other types of presses and filters including those utilizing a vacuum or centrifugal force to promote drainage may be used.
The effluent stream.of the dryer will contain the dried organic wastes. This material preferably has a water content of about 5~12 wt.~, but higher water con- '~
tents up to about 15 wt.% may be tolerable. ~hen the ', drying is achieved through the use of hot vapors, these vapors will also exit the drying zone and will normally .

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~I`V9~ 6 conta,i~n ~so,m,e'en,t~,a,~i~ned ,f,i~ne wa~te particles. The ef,f,luent q,f, the d~ n~ zone l'~s thereFor,e passed into a solids-vapor $epaxat~on zone~' Th~s zone preferably contains one or more cyclone'separators~ Most of the dried waste will be collected b~ these cyclones. The off-gas of the cyclones may be directed into a wet scrubber such as a turbulent ' contact absorber or bag-type ~ilte~. The filtered off-gas i,s then passed through an odor scrubber in which contact with deodorizing chemicals including hypochlorites, perox-ides, or permanganate can be effected if necessary. Anincineration-type odor scrubber may also be used. When the preferred toroidal dryer is used, the dried solids will be removed from the dryer suspended in the warm effluent vapors and passed to the separation zone. These effluent vapors will also comprise the evaporated water and combustion products. They may range in temperature from about 88 to 204C. and are preferably in the range of 93 to 149C. This separatory zone may be of customary design, and those skilled in the art are capable of ~ ', effecting its design and operation.
The dried organic waste is normally a fluEfy material having a bulk density of about 192 to 256 kg/m3. The dried material produced from sewage sludge also tends to adhere to itself a,nd does not readily flow or spread. It is therefore difficult to transport or to spread as fertilizer, For these reasons it has been compacted to for~ a parti,culate product having an average bulk density of about 481 to 1041 kg/m3. Preferably, the density of ~.~9~01~i the.p~oduct ~s, a,bout 481 to 801 k.g/m3. The $.e~uential compact,i~on and c~us:hi~ng operati.ons of the prior art did accom,plis~ th.e ne.ces:sary compac-tion. However~ the required machines were'relati,vely expensive, troublesome, and often 5. unreli,able. Fuxther, the product frequently still has poor flow characteristics. The prior art method also produces a large amount of off-size material as described above. It has now been found that these disadvantages of the prior art can be largely eliminated by extruding the dry material formed in the drying zone.
The invention may therefore be characterized as a pxocess for drying a feed stream comprising water and organic waste which comprises the steps of: (a) passing the feed stream into a drying zone operated at drying condi.tions and effecting the evaporation of water con-tained in the feed stream and the production of a drying zone effluent stream comprising particulate organic waste and water; (b) separating the drying zone effluent stream in a solids-vapor separating zone to produce a vapor stream comprising water vapor and dry solids stream com- ~.
prising particulate organic waste and containing less than about 15 wtr% water; and, (c) extruding a first portion of the dry solids stream in an extrusion zone to form a product stream having a bulk density within the range of about 481 to 1041 kg/m3.
The extrusion of the dry fluf~ may be performed in a customar~ manner using several types of extruders including press~type extruders or the roller and die-type 0()~6 o,f,ten u~s,ed ~n pellet~n~ operations. The preferred type of extrusi,on apparatus uses a screw~or au~er to force the dried organic waste'through a face plate having perfora-tions in the ranye of .16 to .64 cm. diameter~ The action Qf the screw within the barrel of the extruder results in the sheartng and kneading of the dried waste, and the waste thereEore may be fluxed to a plasticized material within the barrel, with the plasticized material solidi-fying upon discharge from the extr)uder. I'his plasticizing is believed to be at least in part responsible for the ,i,mproved performance of the subject process. The dried waste may be fed to the extruder at elevated temperatures up to about 93C. to promote fluxing. The temperature and pressure within the extrusion zone should be suffi-cient to effect the plasticization of the dried solids, . .
A pressure of 7.8 atmospheres or more at about 93C. or higher has been found suitable. Uniform pellet formation may be aided by the use of a rotating finger plate.
The extrudate is then passed into a particle classi-fication or fines separation zone. The zone may comprise any apparatus which will remove dust, fine particles, and oversized particles ~rom the extrudate. One such apparat-us comprises a screening~mechanism haviny two vibratiny screens to sort out those particles which will not pass through a 6 mesh screen and also those that pass through a 2Q mesh screen. The remaining product lS referred to as "minus 6 plus 20" and is typical of the size range preferred in fertilizer produc~ion. The oversize may be :

~1900~6 c.~us,~e.~ n.a,n.y~s.u~taib.le ~anneX ,a,n~ xe:turned to th.e s~creen$,.
T~Q f~nes are'xecxcled to t~e.':Ee.ed D~ the extruder, A
second type of apparatus ~h.i:ch.may be.used is one which utili,zes fluidi,zation of the fine particles in air as a '~
means of particle classification. The apparatus ~resented in United States Patent 3,825,116 performs fine particle ~separations i,n t~is manner. Cyclone separators may also be used to separate the fine particles.
In a.particularly preferred embodiment of the'inven-tion the extrusion step may be benefited through theadmixture of an extrusion aid or a plasticizer or both into the dried solids material prior to its extrusion.
These findings are based upon a series of tests wherein . ... .
dried organic waste produced from sewage sludge was --- extruded in a small bench unit having a 7.0 cm. throat, .:3 cm,, die holes, and a 3/4 H.P. motor.

Test 1 was a control test in which the dry solids were extruded without any additives. Test 6 was a repeat of this test to verify the results. The extruslon was successful but difficult. It produced suitable pellets, but considerable dust also resulted.

Test 2 was designed t~ examine the use of starch as an extrusion aid. Fl,fty ~rams of dry starch were admixed wi,th.l~0~ gram,s of th.e dried solids and extruded. The result was essentially the same as the control Tests 1 I

~L~900~ !

and 6:~

~TEST'3 , Te$t 3 was, des~gned to determi,ne whether formaldehyde would act as a plasticizer during the extrusion. As ,for,maldehyde is ~aseous at standard conditions it was used in the form of 30 wt.% aqueous solution. This solution contained a small amount of alcohol as is normally uti' li~zed to stabllize the solution. One hundred grams of the ~Soluti,on were admixed with l000 grams of dried solids and extruded. The extrusion was still difficult, but a 1 ,, ,~ hi~,ghl~ plasticized virtually dust-free extrudate was produced.

TEST_4 In Test 4, 300 grams of the formaldehyde solution were admixed with lO00 grams of the dried solids. The result was a soft extrudate and detectably less difficult extrusion, presumably the result of the higher water con-tent in the feed mixture.

I,n Test 5, 300 grams of water and 50 grams of starch were admixed with l000 grams of the dried solids and extruded. The result was similar to that o Test 4, again indicating that the result was attributable to the high water content.

TEST'7 In Test 7, l000 grams of dried solids were admixed , .

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w,~ith,5Q gx,a,~s o,f, ~entoni~te'(:~hich had prev,iously been a,dm,ixed w~ith 5a grams of water) and then extruded. The xesultant extrudate was sim~lar to the controls with considerable dust being produced. ~owever, the extrusion operat;on was very much easier.

I,n Test 8~ the same materials as Test 7 (1000 grams dried solids and 100 grams of a 50% wa~er-bentonite admix- ` `'`
ture) were mixed with 50 grams of the formaldehyde solu-tion and ex~uded. The results were very easy extrusion and a plasticized and dustless extrudate.

In Test 9l 50 grams of bentonite were mixed in-to 50 'grams of the formaldehyde solution, and this admixture was added to 1000 grams of dried solids and extruded. The results were similiar to Test 8 with very easy extrusion and a plasticized, dustless extrudate.

These tests indicate that the addition of formalde-hyde and bentonite aided the extrusion process in differ-ent ways. The bentonite acted as an extrusion aid whichallowed the dried solids to be more readily extruded.
The benefits of this improvement include less energy consumption, less strain on the parts o~ the extruder, and a higher capacity fo~ any gi~en extruder. The tests also indicate that the fo~maldehyde solut~on acted as a - plasticizer. ~ts addition decreased the amount of dust and produced a high quality extrudate.
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1~J9~)01~

Oth.ex ~la~stici~zex~S~ ~h,i~ch m,ax~b~ th.ought ~f o~
re~erred to as~cross~-linki.ng ~ents! ,m,a~ also be used in th.e. subject proces's. The use of t~e:se m~terials is still a comb~nation o~ art and science. It ~s, therefore, not ~os.sible to accuratel~ predict their ef~ectiveness unless the performance of closely related materials has been studied. Many materials which act as plasticizers are ~' '' described in standard references and they may be easily ' evaluated by per~orming the relatively simple tests described above.
The plasticizer may be either an organic or an i~norganic compound. A partial list of known organic cross~.linking agents which are contemplated for use as plasticizers contains various aldehydes and ketones and includes acetaldehyde, propionaldehyde, butyraldehyde, glycol aldehyae, aldol, glyceric aldehyde, glyoxal, p-glyoxal, meso xydialdehyde, acrolein, crotonaldehyde, dibroacl-olein, mucochloric acid, o-salicylaldehyde, resorcyclic aldehyde, diacetyl, acetonyl acetone, h,ydro-20. quinone, camphor, dibutyl phthalate, butyl benzylphthalate, dimethyl phthalate, diethyl phthalate, aromatic phosphates and sulfonamides, bis (2-ethylhexyl) adipate, dibutyl sebacate, raw castor oil, mineral oil, tricresyl phosphate, alkyd resins, hydrogenated terphenyls, diphenyl phthalate, polyalkylene glycol, butox-yethyl sterate and poly-~eth~lstyrene. Some of the known inorganic cross-linkin~ agents contemplated for use as a plasticizer are A1203, Cr203, Fe203, 2' 2 2 ,.

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1.~1900~L6 A12C~0413,,, Fe(NH4) ( $~ 1 2 ! Ti,(N03),4, a,nd K2A12(,SO4~.24~O.
S:ome mate~,a,ls apparently do not produce an~ visually obsexvable benefi,t during the extrusion of the dry solids waste~ For instance the starch of Test 2, a lignosulfonate '' and uXea have been found not to function as extrusion aids or plasticizers by themseIves. In contrast, bentoni~e functioned~as an extrusion aid but not as a plas-ticizer.
It is contemplated to use gypsum and clay-type materials other than bentonite as,extrusion aids. These clay-type materials may be characterized as colloidal or near colloidal mineral mixtures which are rich in hydrated silicates of aluminum, iron or magnesium, hydrated alumina or iron oxide. Examples of these materials are other mpntmorillonite minerals, fullers earth, kaolin minerals, serpentine minerals, boehmite, gibbsite and bauxitic clays. It is also contemplated that the previously listed cross-linking agents could be used to fuifill the functions of both an extrusion aid and a plasticizer.
Bentonite is, however, the preferred extrusion aid.

It is not necessary to utilize both a`plasticizer and an extrusion aid, and the subject drying and finish ing process may be performed using only one of them.
However, it is preferred that both of them are used. It is also preferred that a small amount of water be con-tained in eithex of the additives or in both o-f them, but that the amount of water added to the dry solids not be excessiye. It is therefore preferred that the total a,mount of water added to the dried solids to be extruded ~17~
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1~90016 is about 1.0-25.0% of the dried solids. More preferably, the total amount of water in the added plasticizer and extrusion aid is from 3-12% of the dried solids.
Basically for xeasons of economy, it is preferred that neither the extrusion aid nor the plasticizer equal more than 30 wt.% (including water) of the dried solids.
The total amount of the two additives on a water-free basis should be less than 15 wt.% and is preferably less than about 10 wt.~ of the dry solids to which it is added.
The two additives may be premixed and then combined with the dried solids or each may be individually admixed with the dried solids stream. The order of admixture is not believed to be significant. Customary mixing systems known to those skilled in the art may be utilized to per-form this admixture and also to effect the mixture of any recycled dried solids with the organic waste feed stream.
Other additives known in the art, including those added to increase the nutrient value of the product, may also be blended into the dry solids prior to extrusion.
Use of the subject method has resulted in the total amount of off-size material which must be recycled being below 25%. This-reduction is significant compared to the prior art, and allows~the process to operate at higher throughput than can be achieved with conventional compaction equipment. It also decreases the required size and utility consumption of the off-size particle recycle system. Thèse advantages are in addition to the lower cost and increased reliability of the extruder~
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There is also some indicakion that extrusion results in a product which may be stabilized at a higher water content.
Normally, the dried sludge starts to ferment or-"germi-nate'l if stored at water contents above 10-12%. If a higher wa-ter content can be tolerated in the product, the required amount of drying is reduced, fuel is conserved r and the process is more economical. The total new process therefore appears synergistic. The invention therefore achieves its objectives of providing an improved process for the drying and finishing of organic wastes.

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for drying a feed stream comprising water and organic waste which comprises the steps of:
(a) passing the feed stream into a drying zone operated at drying conditions and effecting the evaporation of water contained in the feed stream and the production of a drying zone effluent stream comprising particulate organic waste and water;
(b) separating the drying zone effluent stream in a solids-vapor separating zone to produce a vapor stream comprising water vapor and a dry solids stream comprising particulate organic waste and containing less than about 15 wt. % water; and (c) extruding a first portion of the dry solids stream in an extrusion zone to form a product stream having a bulk density within the range of about 481 to 1041 kg/m3.

2. The process of Claim 1 wherein the first portion of the dry solids stream is plasticized within the extrusion zone.

3. The process of Claim 1 wherein the feed stream is formed by admixing a second portion of the dry solids stream with an organic waste stream comprising organic waste and water.

4. The process of Claim 1 wherein the organic waste contained in the dry solids stream has a bulk density of less than about 256 kg/m3.

5. The process of Claim 1 wherein the drying zone comprises a torodial dryer.

6. The process of Claim 1 wherein the product stream is passed into a fines separation zone wherein particles of less than 20 mesh size are separated into a recycle stream, and the recycle stream is admixed with the first portion of the dry solids stream.

7. The process of Claim 1 wherein the organic waste comprises sewage sludge.

8. The process of Claim 1 wherein a plasticizer is admixed with the first portion of the dry solids stream in an amount being less than 5 wt. % of the first portion of the dry solids stream.

9. The process of Claim 1 wherein an extrusion aid is admixed with the first portion of the dry solids stream at a rate of less than 10 wt. % of the first portion of the dry solids stream.

10. The process of Claims 2 or 8 wherein the plasticizer comprises a formaldehyde solution.

11. The process of Claim 9 wherein the extrusion aid comprises bentonite.

12. The process of Claims 2, 8 or 9 wherein the total amount of water in the plasticizer and in the extrusion aid is from 1-25 wt. % of the first portion of the dry solids stream.

13. The process of Claims 1, 8 or 9 wherein the dry solids are at a temperature above 93°C during the extrusion.