CA1116765A - Method of dewatering aqueous waste sludge - Google Patents
Method of dewatering aqueous waste sludgeInfo
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- CA1116765A CA1116765A CA000306772A CA306772A CA1116765A CA 1116765 A CA1116765 A CA 1116765A CA 000306772 A CA000306772 A CA 000306772A CA 306772 A CA306772 A CA 306772A CA 1116765 A CA1116765 A CA 1116765A
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- waste water
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Abstract
METHOD OF DEWATERING AQUEOUS, WASTE SLUDGE
Abstract of the Disclosure A method of dewatering proteinaceous aqueous waste sludge having a high fat content from food cannery waste water wherein the solids concentration of the sludge is increased from about 10% to about 40% by weight is disclosed. The method comprises adjusting the pH of the sludge to the isoelectric point of the proteinaceous material present in the sludge, adding an organic polymer and separating the solids by high gravity centrifugation so that a concentration of about 20 to about 40% by weight is obtained. The process is particularly suitable for concentrating the solids of sludge derived from fish waste water.
Abstract of the Disclosure A method of dewatering proteinaceous aqueous waste sludge having a high fat content from food cannery waste water wherein the solids concentration of the sludge is increased from about 10% to about 40% by weight is disclosed. The method comprises adjusting the pH of the sludge to the isoelectric point of the proteinaceous material present in the sludge, adding an organic polymer and separating the solids by high gravity centrifugation so that a concentration of about 20 to about 40% by weight is obtained. The process is particularly suitable for concentrating the solids of sludge derived from fish waste water.
Description
67~
METHOD OF DEWATERING AQUEOUS WASTE SLUDGE
Background of the Invention .
This invention relates generally to the treatment o~ aqueous waste sludge rom food canneries and more specifically to a novel and useful method of concentrating the solids content of sludge derived from ~ish waste water from about 10~ to about ~ 40% by wei~ht.
- Previously, liquid waste from fish processing plants have heen dischar~ed without any treatment. However, this can be harmful to the environment because the primary waste material consists o bits and pieces of whole fish which are in a partially decomposed state. Since the pieces o fish are organic in nature, they create an oxygen demand on the receivinq waters, thus depleting the amount or oxygen available to aquatic life inhabiting the receiving waters. The public concern of environmental problems relating to the quality of waste water effl~ent has caused state and federal regulatory agencies to ~ -491 7~5
METHOD OF DEWATERING AQUEOUS WASTE SLUDGE
Background of the Invention .
This invention relates generally to the treatment o~ aqueous waste sludge rom food canneries and more specifically to a novel and useful method of concentrating the solids content of sludge derived from ~ish waste water from about 10~ to about ~ 40% by wei~ht.
- Previously, liquid waste from fish processing plants have heen dischar~ed without any treatment. However, this can be harmful to the environment because the primary waste material consists o bits and pieces of whole fish which are in a partially decomposed state. Since the pieces o fish are organic in nature, they create an oxygen demand on the receivinq waters, thus depleting the amount or oxygen available to aquatic life inhabiting the receiving waters. The public concern of environmental problems relating to the quality of waste water effl~ent has caused state and federal regulatory agencies to ~ -491 7~5
- 2 -impose strict guidelines concerning the disposal of such waste material. Enforcement of these guidelines in a typical fish processing plant may require costly disposal methods. For example, it's a common practice in the fish processing industry to have waste sludge dewatered by conventional methods to a concentration of about 6 to 20~ solids and taken to a l~quid waste disposal site for disposal. This process is highly uneconomical.
Dewatering processes known in the ~rt for concentrating aqueous waste sludge from a 6 to 20~ by weight solids content may include gravity filtration, vacuum filtration, centriuga-tion, ~lota~ion, and sedimentation. In addition to these mechanical dewaterlng methods, lt has become standard practice in the art to chemlcally condltion the waste water prlor to sludge ormatlon and dewaterlng.
The waste water can b~ treated in any o~e of a variety of conventional procedures to produae the sludge material that can be treated in the process of the present invention.
In the broader aspects of the process o~ the present invention, the process may comprise waste water treatment to aid in the formation of sludge material as well as treatment of the sludge material to concentrate the solids content to a~out 40~ by weight.
With no intent to limit the invention, any means that can aid in the formation of bubbles in the waste water, whether it be compressed air, aspiratea air or electrolytically produced gas bubbles may be utili~ed. The bubbles in the waste water suspend solids as well as fats and oils and move them to the surface of tne water being treated.
According to the present invention and in conjunction wlth conventional procedures for treating aqueous waste water, it is possible to concentrate the waste-water from a fish pro-___ _, _. _, . _ _ .. ..... .. _ . ... ..... , .. , .. . . .. . .. . .. . .. . . . , . . ... . .. .. ...
....... .. ... . . p . .
7~
cessing plant having a total solids content of about .02 to 0~5%by weight and a high fat content to a solids concentration of about 20 to 40% by weight by means of forming a sludge material and then forming a flocculent material within the sludge and agglomerating that material and separating insoluble material.
As will be described hereinafter, the concentrated sludge containing proteinaceous materials can be further subjected to a dry rendering process and produce blended meat and bone meal and blended tallow or made into fertilizer.
Alternatively, the dewatered sludge can be incinerated. Thus, by concentrating the sludge to a relatively high solids content not only are reduced disposal costs realized, but also efficient a]ternate uses of the sludge can be obtained.
Summary of the Inv~ntion Briefly, the present invention comprehends a method of dewatering aqueous waste water and sludge contalning a high fat content. The method comprises addin~ a poly~alent metal salt to the waste water to form a floc. An organic polymer is then added to agglomerate the floc to finite particles that float to the surface of the waste water. Bubbles are formed in the waste water. The particles of floc from the surface of the waste water are combined with any sediment that has formed. The pH of this waste water sludge mixture is then adjusted to within the range of 4.0 - 5.0, sufficient to reach the isoelec~ric point of the protein, causing the protein to precipitate. An organic G
~ ,,. . ~
;7~;
polymer is added to the sludge mixture to agglomerate sludge particles. The solid material is then separated from the sludge to provide a solids content of about 10 to 40 percent by weight, preferably 25 to 40~ by weight.
These and other aspects and advantages of the invention will become apparent hereinafter.
Description of the Drawings In the drawings which illustrate an embodiment of the present invent:ion, FIGURE 1 is a flow diagram illustrating the process of the present invention.
Description of the Preferred Embodiments ... .
The present invention was developed largely for treating aqueous sludge from the processing of food, particularly fish having a high fat content :Ln the range of 40 to 70% by weight. Therefore, it will be explained largely with respect to fish processing and has special application to such processing, although it can be used for other food processes in the broader aspects of the invention.
Conventional methods of treating sludge obtained from waste water commonly involve three general steps: the creation of flocculent material, agglomerating that material and separating that insoluble material from the indigenous liquid.
However, it is increasingly more difficult to apply these steps and dewater sludge containing a high fat or oil content. The specific gravity differential in the aqueous supernatant and insoluble solid material is decreased as the fat or oil content is increased in the aqueous sludge. Notwithstanding this problem, a critical feature of the present invention is the adjustment of the pH of the sludge to about the isoelectric i7~
point of the protein material present in the sludge, and optionally heating the sludge, to provide proper agglomeration of flocculent material in the sludge. Further, another critical feature of the present invention involves the separation and concentration of solid material by high gravity centrifugation to unexpectedly provide a dewatered sludge with a concentration of solid material in the range of about 20 to 40% by weight.
Accordingly, waste water which is obtained from the processing of canned food products, particularly canned fish products such as tuna is stored in collection tank 1 after passing through rotostrainers. Waste water treatment can be accomplished b~ any conventional procedure and the following procedure is meant to be illustrative and not intended to limit the invention. Prior to entering the tank, the waste water is passed through a screen having openings the size of about .010 to .030 inches to remove large bones and meat particles as well as impurities~ The waste water typl~ally comprises about 0.02 to 0.5% by weight total solids and about 0.02 to 0.06% by weight fat on a dry basis. The proteinaceous material content may vary from about 25 to about 45~ by weight. The solid material consists mainly of small particles of meat, bone and scales.
Other insoluble material includes native fish oil and soybean oil from the packing process. Soluble material in the waste water, besides water from the wash down, thawing, cooling and draining operations consists primarily of soluble protein from cooking water, blood and press water from the processing of fish -~
by-products, etc. As an optional feature, compressed air may be added to tank 1 to help prevent the proliferation of anaerobic bacteria and to insure the growth of the natural bacteria present in the waste water. The air can be supplied at a low~pressure sufficient to overcome the static pressure of the water. Preferably, about 2 to 10 psi is utilized.
.. , ;: .
, ~ :
- ~ ~491 7tG~i The waste water is then passed th.ough a line to dissolved air flotator 2. A metal salt 3 is fed into the line. Generally speaking, most suspended liquids or solids in waste water possess a negative charge and polyvalent metal salts are often added to react with the negative particles, and by coa~u~ation, to break an~ colloidal emulsion that may have formed. These metal salts, such as sodium aluminate, aluminum sulfate, alumt fe~ric sulate, ferric chloride, lime and other calcium salts, etc., ionize to their h~droxide structure and form flocculen~ particles. About 4 ppm to about 40 ppm active metal ion species are used in the practice of this invention.
Compressed air at about 40 to 75 psi is added to the waste water through restricted valve 4. The use of compressed air is not intended to be unduly limi.tative for any bubble forming substance may be utilized such as aspirated air or electrolytically produced gas. As the air pressure iel released, bubbles form which will eventually float foraign particles and suspended solids together with ~ats and oils to the surface of the water in dissolved air flotator 2. There is a bene~icial relationship between the bubblesr particles and solids which become attached thereto. The particles and solids act as nuclei for the bubbles so that the material can be floated to the surface of the water.
Preferably, about 8 to 10 ppm trivalent aluminum ions are pre-ferred.
To further aid flocculent formation, a polymer 5 may be added to the aerated w~ste water in the line going to dissolved air f~otator 2. The addition of the polymer leads to the forma-tion and agglomeration of floc to finlte particles that ~loat to the sur~ace of the water and are skimmed off by a sweep arm and 30 collected in holding tank 6. While the lnventlon is not restricted to a particular organic polymer~ ~t has been found that both ~ 7~ ~ !9 anionlc and cationic polymers such as acrylamide or other water soluble salts o~ acrylic acid can be utilized. These polymers are characterized by having an intrinsic viscosity at 30C in an aqueous bu~er at pH 7.0, as measured by a G'annon-Fenski capillary viscometer, o~ at least from about 0.17 to about 24 dec,liter per gram. These polymers are known in the art and are avallable ~rom several commercial sources. Pre~erably, Percol~
726, available ~rom Allied Collolds, Inc. Ridgewood,.New Jersey, is utilized. Generally, about .5 ppm to about 15 ppm polymer is used in the in~tant process.
Arter the waste water enters ~lotation tank 2, the top M oat sludge is removed and is added to holdlng tank 6, also sediment ~rom the flotator ls collected by a bottom sweep arm through an oriflce and optlonally adde~d to holding tank 6. The sediment con~ists Or coarse grlt material comprising bits of bones and meat and other impurlties that pass through the screen ln the line berore the collection tank 1. The partic1es are too large ~or agglomeratlon and ~lotatlon The solids content o~
the sludge in holding tank 6 1s about 5 to 10% by weight and the rat content is about 40 to 70% by weight.
The clari~led liquld ~rom ~lotator 2 is substantially ~ree Or impurities and withln regulatory guidelines so it can be pumped into a sewer wlthout creating environmental problems.
It can be wlthdraun ~rom ~lotator 2 in the middle Or the tank, equidistant from the top where the top ~loat sludge is located and the bottom~ where the sediment is collected.
The material present in holding tank 6 comprises a ~lotable scum and sedimented grit material. This putrid material, ~hlch is transported to liquld waste disposal areas in prior art processes at a great expense is conducive to rapid bacterial growth and has little commercial value as a fertilizer or feed.
~ 8 --The rollowing steps are crltical to the process of the present inventlon.
The sludge ls treated with an acld 7 to precipltate the tuna proteln by lowering the pH to an acldic value near or -at the isoelectric point o~ the protein, usually a pH of 4 - 5 wlth the addition o. any protor. donating compound, such as mlneral acids, preferably sulfuric, hydrochloric, nitric or phosphoric acids. In ract, any acid will lower the pH of the ~lxture to the preferred pH range to precipitate the protein.
Most preferably, sulfuric acid will be used to lower the pH to pre~erably 4.5.
The acid treated sludge is then passed through a line to a high graYity centrifuge 8 such as one available from thè
Sharples Company. that separates a solid phase ~rom a liquid phase in such a manner to leave a clarlfied centrate as the liquid phase that can be recycled in the proc:ess and a dewatered sludge cake as ~he solid phase. Usually, a i~orce o~ at least about 750XG is necessary ror the proper separation. The higher the gra~itational force the greater the facility for separation. Prior to this separation however, the acid treated sludge must again be treated with agglomerating polymer 5 to aid in the flnal floccua-tlon and separatlon o~ ~aterials. In thls step, the agglomerating polymer should be added until the clarity of centrate cannot be ~urther improved. Typically~ this should be in amounts ran~ing ~rom about 5 ppm to about 500 ppm and preferably about 100 to 200 ppm.
The acid treated sludge, having a solids content of about 5~ to 10% by weight and a fat content Or about 40 to 70~
by weight on a dry basis ls concentrated to a solids content Or about`20 to 40% ~y weight. A typlcal compositlon of sludge con-~entrated by the process of the present lnvention is as ~ollows:
. ~ . .
y yl TABLE I
-Percent Total Solids 38 Protein 13 Total Lipids 19 Water 62 The dewatered sludge with a solids concentration of about 2~to 40% ls formable and can be easily handled. The costs for disposing this sludge material in a landfill area are minimal compared to the higher moisture sludge rendered by conventional dewatering processes which contains more water therefore being hea~ier and more costly to dispose of.
~ A modified embodiment of the process for dewatering waste water sludge comprises heating the sludge materlal prior to lts introduction into the centri~uge. This is not intended to be limiting, for the acid precipitation at an elevated tempera ture only promotes coagulation and precipitation of the protein.
The heating must be at a temperature range surriciently hlgh and for an effective amount of time to coaF,ulate the protein material present in the sludge. ~he temperature range may preferably be rrom about 170F to 212F. I~ this procedure is ~ollowed, the pH o~ the sludge must still be ad~usted to a range of about 4 to 5 prior to entering the high speed centrlfuge.
As previously discussed, due to the relatively high concentration o~ solids in the dewatered sludge treated by the process of the instant invention it may be suitable for a number o~ uses or disposal methods.
~ he dewatered sl~ldge~ contalning about 20 to about 40%
by welght solids may be combined with meat and bone cscraps and cooked in a dry rendering kettle at about 212 to 250"F for about 120 minutes and then passed through an expeller press to form blended mea~ and bone meal and blended tallow. Further, an animal food product may be obtalned by blending the dewatered sludge concentrated in the process of the present invention with ~re3h fish scrap or meal.
.~`
,. .
Sr-491 ~6 7~ ~ -The composition o~ the sludge shown ln Table I on a dry basis has a fat content of 50% and a protein level of 33%. These levels are sufriclent for formulating an animal ~ood.
Addltionally, if the dewatered sludge is not sub~ect to ~urther processing, it may be disposed of in a solid waste landflll area at a lower cost than sludge containing larger amounts of water or lncinerated and the residual ash.may be disposed of ~n a land~ill area.
To assure that one having ordinary skill in the art understands the invention, the ~ollowing examples are set forth as illustrated embodiments of the ~nvention and are not to be taken in any manner as limitlng the scope o~ the invention which 1~ defined by the appended claims.
xample I
Waste water in the amount oi~ 200,000 gallons weighing 834 tons havlng a solids content Or 0"12% by welght, a ~at content of 0.07~ by weight and a protein content o~ 0.05% by ~eight is passed through a screen having a pore size of 0.030"
to a holding tank where it is subJected to 14 psi o~ compressed air. The waste water is then treated with 50 ppm o~ 42% by welght sodium aluminate and sub~ected to 60 psi of compressed air while in a line going to a dissolved air ~lotator. Just prior to entering the ~lotator, 4 ppm Percol~ 726 1~ added. The top M oat scum and sediment is collected ~rom the ~lotator and treated with about 1.8 liter sulfuric acid to ad~ust the pH of the material to 4.3. Then, 250 ppm PercoP 726 is added to the materlal and it is passed through a Sharples Sludgepak ~ high gravity centrifuge. The centri~uge is operated at 1300XG. The sludge collected from the centri~uge had a solids content Or 36.3%
~ -491 ~67~
by weight and wa~ disposed of in a solid waste land~ill.
Example II
The process of ~xample I was followed, but after treating the waste water material with an acid to adjust the pH to 4~5 prior to entering the high gravity centrifuge, it ; was heated to 200~F or five minutes. It was then subjected to high gravity centrifugation and resulted in a sludge having a solids content of 39.5~ by weight.
As various changes could be made in~the above methods and products without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustr~tive and not in a limiting sense.
Dewatering processes known in the ~rt for concentrating aqueous waste sludge from a 6 to 20~ by weight solids content may include gravity filtration, vacuum filtration, centriuga-tion, ~lota~ion, and sedimentation. In addition to these mechanical dewaterlng methods, lt has become standard practice in the art to chemlcally condltion the waste water prlor to sludge ormatlon and dewaterlng.
The waste water can b~ treated in any o~e of a variety of conventional procedures to produae the sludge material that can be treated in the process of the present invention.
In the broader aspects of the process o~ the present invention, the process may comprise waste water treatment to aid in the formation of sludge material as well as treatment of the sludge material to concentrate the solids content to a~out 40~ by weight.
With no intent to limit the invention, any means that can aid in the formation of bubbles in the waste water, whether it be compressed air, aspiratea air or electrolytically produced gas bubbles may be utili~ed. The bubbles in the waste water suspend solids as well as fats and oils and move them to the surface of tne water being treated.
According to the present invention and in conjunction wlth conventional procedures for treating aqueous waste water, it is possible to concentrate the waste-water from a fish pro-___ _, _. _, . _ _ .. ..... .. _ . ... ..... , .. , .. . . .. . .. . .. . .. . . . , . . ... . .. .. ...
....... .. ... . . p . .
7~
cessing plant having a total solids content of about .02 to 0~5%by weight and a high fat content to a solids concentration of about 20 to 40% by weight by means of forming a sludge material and then forming a flocculent material within the sludge and agglomerating that material and separating insoluble material.
As will be described hereinafter, the concentrated sludge containing proteinaceous materials can be further subjected to a dry rendering process and produce blended meat and bone meal and blended tallow or made into fertilizer.
Alternatively, the dewatered sludge can be incinerated. Thus, by concentrating the sludge to a relatively high solids content not only are reduced disposal costs realized, but also efficient a]ternate uses of the sludge can be obtained.
Summary of the Inv~ntion Briefly, the present invention comprehends a method of dewatering aqueous waste water and sludge contalning a high fat content. The method comprises addin~ a poly~alent metal salt to the waste water to form a floc. An organic polymer is then added to agglomerate the floc to finite particles that float to the surface of the waste water. Bubbles are formed in the waste water. The particles of floc from the surface of the waste water are combined with any sediment that has formed. The pH of this waste water sludge mixture is then adjusted to within the range of 4.0 - 5.0, sufficient to reach the isoelec~ric point of the protein, causing the protein to precipitate. An organic G
~ ,,. . ~
;7~;
polymer is added to the sludge mixture to agglomerate sludge particles. The solid material is then separated from the sludge to provide a solids content of about 10 to 40 percent by weight, preferably 25 to 40~ by weight.
These and other aspects and advantages of the invention will become apparent hereinafter.
Description of the Drawings In the drawings which illustrate an embodiment of the present invent:ion, FIGURE 1 is a flow diagram illustrating the process of the present invention.
Description of the Preferred Embodiments ... .
The present invention was developed largely for treating aqueous sludge from the processing of food, particularly fish having a high fat content :Ln the range of 40 to 70% by weight. Therefore, it will be explained largely with respect to fish processing and has special application to such processing, although it can be used for other food processes in the broader aspects of the invention.
Conventional methods of treating sludge obtained from waste water commonly involve three general steps: the creation of flocculent material, agglomerating that material and separating that insoluble material from the indigenous liquid.
However, it is increasingly more difficult to apply these steps and dewater sludge containing a high fat or oil content. The specific gravity differential in the aqueous supernatant and insoluble solid material is decreased as the fat or oil content is increased in the aqueous sludge. Notwithstanding this problem, a critical feature of the present invention is the adjustment of the pH of the sludge to about the isoelectric i7~
point of the protein material present in the sludge, and optionally heating the sludge, to provide proper agglomeration of flocculent material in the sludge. Further, another critical feature of the present invention involves the separation and concentration of solid material by high gravity centrifugation to unexpectedly provide a dewatered sludge with a concentration of solid material in the range of about 20 to 40% by weight.
Accordingly, waste water which is obtained from the processing of canned food products, particularly canned fish products such as tuna is stored in collection tank 1 after passing through rotostrainers. Waste water treatment can be accomplished b~ any conventional procedure and the following procedure is meant to be illustrative and not intended to limit the invention. Prior to entering the tank, the waste water is passed through a screen having openings the size of about .010 to .030 inches to remove large bones and meat particles as well as impurities~ The waste water typl~ally comprises about 0.02 to 0.5% by weight total solids and about 0.02 to 0.06% by weight fat on a dry basis. The proteinaceous material content may vary from about 25 to about 45~ by weight. The solid material consists mainly of small particles of meat, bone and scales.
Other insoluble material includes native fish oil and soybean oil from the packing process. Soluble material in the waste water, besides water from the wash down, thawing, cooling and draining operations consists primarily of soluble protein from cooking water, blood and press water from the processing of fish -~
by-products, etc. As an optional feature, compressed air may be added to tank 1 to help prevent the proliferation of anaerobic bacteria and to insure the growth of the natural bacteria present in the waste water. The air can be supplied at a low~pressure sufficient to overcome the static pressure of the water. Preferably, about 2 to 10 psi is utilized.
.. , ;: .
, ~ :
- ~ ~491 7tG~i The waste water is then passed th.ough a line to dissolved air flotator 2. A metal salt 3 is fed into the line. Generally speaking, most suspended liquids or solids in waste water possess a negative charge and polyvalent metal salts are often added to react with the negative particles, and by coa~u~ation, to break an~ colloidal emulsion that may have formed. These metal salts, such as sodium aluminate, aluminum sulfate, alumt fe~ric sulate, ferric chloride, lime and other calcium salts, etc., ionize to their h~droxide structure and form flocculen~ particles. About 4 ppm to about 40 ppm active metal ion species are used in the practice of this invention.
Compressed air at about 40 to 75 psi is added to the waste water through restricted valve 4. The use of compressed air is not intended to be unduly limi.tative for any bubble forming substance may be utilized such as aspirated air or electrolytically produced gas. As the air pressure iel released, bubbles form which will eventually float foraign particles and suspended solids together with ~ats and oils to the surface of the water in dissolved air flotator 2. There is a bene~icial relationship between the bubblesr particles and solids which become attached thereto. The particles and solids act as nuclei for the bubbles so that the material can be floated to the surface of the water.
Preferably, about 8 to 10 ppm trivalent aluminum ions are pre-ferred.
To further aid flocculent formation, a polymer 5 may be added to the aerated w~ste water in the line going to dissolved air f~otator 2. The addition of the polymer leads to the forma-tion and agglomeration of floc to finlte particles that ~loat to the sur~ace of the water and are skimmed off by a sweep arm and 30 collected in holding tank 6. While the lnventlon is not restricted to a particular organic polymer~ ~t has been found that both ~ 7~ ~ !9 anionlc and cationic polymers such as acrylamide or other water soluble salts o~ acrylic acid can be utilized. These polymers are characterized by having an intrinsic viscosity at 30C in an aqueous bu~er at pH 7.0, as measured by a G'annon-Fenski capillary viscometer, o~ at least from about 0.17 to about 24 dec,liter per gram. These polymers are known in the art and are avallable ~rom several commercial sources. Pre~erably, Percol~
726, available ~rom Allied Collolds, Inc. Ridgewood,.New Jersey, is utilized. Generally, about .5 ppm to about 15 ppm polymer is used in the in~tant process.
Arter the waste water enters ~lotation tank 2, the top M oat sludge is removed and is added to holdlng tank 6, also sediment ~rom the flotator ls collected by a bottom sweep arm through an oriflce and optlonally adde~d to holding tank 6. The sediment con~ists Or coarse grlt material comprising bits of bones and meat and other impurlties that pass through the screen ln the line berore the collection tank 1. The partic1es are too large ~or agglomeratlon and ~lotatlon The solids content o~
the sludge in holding tank 6 1s about 5 to 10% by weight and the rat content is about 40 to 70% by weight.
The clari~led liquld ~rom ~lotator 2 is substantially ~ree Or impurities and withln regulatory guidelines so it can be pumped into a sewer wlthout creating environmental problems.
It can be wlthdraun ~rom ~lotator 2 in the middle Or the tank, equidistant from the top where the top ~loat sludge is located and the bottom~ where the sediment is collected.
The material present in holding tank 6 comprises a ~lotable scum and sedimented grit material. This putrid material, ~hlch is transported to liquld waste disposal areas in prior art processes at a great expense is conducive to rapid bacterial growth and has little commercial value as a fertilizer or feed.
~ 8 --The rollowing steps are crltical to the process of the present inventlon.
The sludge ls treated with an acld 7 to precipltate the tuna proteln by lowering the pH to an acldic value near or -at the isoelectric point o~ the protein, usually a pH of 4 - 5 wlth the addition o. any protor. donating compound, such as mlneral acids, preferably sulfuric, hydrochloric, nitric or phosphoric acids. In ract, any acid will lower the pH of the ~lxture to the preferred pH range to precipitate the protein.
Most preferably, sulfuric acid will be used to lower the pH to pre~erably 4.5.
The acid treated sludge is then passed through a line to a high graYity centrifuge 8 such as one available from thè
Sharples Company. that separates a solid phase ~rom a liquid phase in such a manner to leave a clarlfied centrate as the liquid phase that can be recycled in the proc:ess and a dewatered sludge cake as ~he solid phase. Usually, a i~orce o~ at least about 750XG is necessary ror the proper separation. The higher the gra~itational force the greater the facility for separation. Prior to this separation however, the acid treated sludge must again be treated with agglomerating polymer 5 to aid in the flnal floccua-tlon and separatlon o~ ~aterials. In thls step, the agglomerating polymer should be added until the clarity of centrate cannot be ~urther improved. Typically~ this should be in amounts ran~ing ~rom about 5 ppm to about 500 ppm and preferably about 100 to 200 ppm.
The acid treated sludge, having a solids content of about 5~ to 10% by weight and a fat content Or about 40 to 70~
by weight on a dry basis ls concentrated to a solids content Or about`20 to 40% ~y weight. A typlcal compositlon of sludge con-~entrated by the process of the present lnvention is as ~ollows:
. ~ . .
y yl TABLE I
-Percent Total Solids 38 Protein 13 Total Lipids 19 Water 62 The dewatered sludge with a solids concentration of about 2~to 40% ls formable and can be easily handled. The costs for disposing this sludge material in a landfill area are minimal compared to the higher moisture sludge rendered by conventional dewatering processes which contains more water therefore being hea~ier and more costly to dispose of.
~ A modified embodiment of the process for dewatering waste water sludge comprises heating the sludge materlal prior to lts introduction into the centri~uge. This is not intended to be limiting, for the acid precipitation at an elevated tempera ture only promotes coagulation and precipitation of the protein.
The heating must be at a temperature range surriciently hlgh and for an effective amount of time to coaF,ulate the protein material present in the sludge. ~he temperature range may preferably be rrom about 170F to 212F. I~ this procedure is ~ollowed, the pH o~ the sludge must still be ad~usted to a range of about 4 to 5 prior to entering the high speed centrlfuge.
As previously discussed, due to the relatively high concentration o~ solids in the dewatered sludge treated by the process of the instant invention it may be suitable for a number o~ uses or disposal methods.
~ he dewatered sl~ldge~ contalning about 20 to about 40%
by welght solids may be combined with meat and bone cscraps and cooked in a dry rendering kettle at about 212 to 250"F for about 120 minutes and then passed through an expeller press to form blended mea~ and bone meal and blended tallow. Further, an animal food product may be obtalned by blending the dewatered sludge concentrated in the process of the present invention with ~re3h fish scrap or meal.
.~`
,. .
Sr-491 ~6 7~ ~ -The composition o~ the sludge shown ln Table I on a dry basis has a fat content of 50% and a protein level of 33%. These levels are sufriclent for formulating an animal ~ood.
Addltionally, if the dewatered sludge is not sub~ect to ~urther processing, it may be disposed of in a solid waste landflll area at a lower cost than sludge containing larger amounts of water or lncinerated and the residual ash.may be disposed of ~n a land~ill area.
To assure that one having ordinary skill in the art understands the invention, the ~ollowing examples are set forth as illustrated embodiments of the ~nvention and are not to be taken in any manner as limitlng the scope o~ the invention which 1~ defined by the appended claims.
xample I
Waste water in the amount oi~ 200,000 gallons weighing 834 tons havlng a solids content Or 0"12% by welght, a ~at content of 0.07~ by weight and a protein content o~ 0.05% by ~eight is passed through a screen having a pore size of 0.030"
to a holding tank where it is subJected to 14 psi o~ compressed air. The waste water is then treated with 50 ppm o~ 42% by welght sodium aluminate and sub~ected to 60 psi of compressed air while in a line going to a dissolved air ~lotator. Just prior to entering the ~lotator, 4 ppm Percol~ 726 1~ added. The top M oat scum and sediment is collected ~rom the ~lotator and treated with about 1.8 liter sulfuric acid to ad~ust the pH of the material to 4.3. Then, 250 ppm PercoP 726 is added to the materlal and it is passed through a Sharples Sludgepak ~ high gravity centrifuge. The centri~uge is operated at 1300XG. The sludge collected from the centri~uge had a solids content Or 36.3%
~ -491 ~67~
by weight and wa~ disposed of in a solid waste land~ill.
Example II
The process of ~xample I was followed, but after treating the waste water material with an acid to adjust the pH to 4~5 prior to entering the high gravity centrifuge, it ; was heated to 200~F or five minutes. It was then subjected to high gravity centrifugation and resulted in a sludge having a solids content of 39.5~ by weight.
As various changes could be made in~the above methods and products without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustr~tive and not in a limiting sense.
Claims (20)
1. An improved method of dewatering aqueous waste water and sludge containing a high fat content comprising:
a. adding a polyvalent metal salt to the waste water to form a floc, b. adding an organic polymer to agglomerate the floc to finite particles that float to the surface of the waste water, c. forming bubbles in the waste water d. combining the particles of floc from the surface of the waste water with any sediment that has formed, e. adjusting the pH of this waste water sludge mixture to within the range of 4.0 - 5.0 sufficient to reach the isoelectric point of the protein, causing the protein to precipate, f. adding an organic polymer to said sludge mixture to agglomerate sludge particles, and g. separating the solid material from the sludge to provide a solids content of about 20 to 40 percent by weight.
a. adding a polyvalent metal salt to the waste water to form a floc, b. adding an organic polymer to agglomerate the floc to finite particles that float to the surface of the waste water, c. forming bubbles in the waste water d. combining the particles of floc from the surface of the waste water with any sediment that has formed, e. adjusting the pH of this waste water sludge mixture to within the range of 4.0 - 5.0 sufficient to reach the isoelectric point of the protein, causing the protein to precipate, f. adding an organic polymer to said sludge mixture to agglomerate sludge particles, and g. separating the solid material from the sludge to provide a solids content of about 20 to 40 percent by weight.
2. The method of Claim 1 wherein the metal salt is selected from the group consisting of sodium aluminate, aluminum sulfate, alum, ferric sulfate, ferric chloride and lime.
3. The method of Claim 2 wherein the amount of the metal salt is about 4 ppm to about 40 ppm.
4. The method of Claim 1 wherein the organic polymer has an intrinsic viscosity of about 0.17 to about 24 deciliter per gram.
5. The method of Claim 3 wherein the amount of organic polymer is about .5 ppm to about 15 ppm.
6. The method of Claim 1 wherein the pH is adjusted to about 4 to 5.
7. The method of Claim 6 wherein a mineral acid is utilized to adjust the pH.
8. The method of Claim 1 wherein compressed air is applied at about 40 to about 75 psi to aid in the formation of bubbles in the sludge.
9. The method of Claim 1 wherein the sludge has a fat content of about 40 to 70% by weight.
10. The method of Claim 1 wherein the separation procedure involves centrifugation at a gravitational force of at least about 750 XG.
11. The method of Claim 1 wherein the sludge, after the addition of the organic polymer, but before the separation of solid material is treated at a sufficient temperature and for an effective amount of time to coagulate the material present in the sludge.
12. The method of Claim 11 wherein the organic polymer has an intrinsic viscosity of about 0.17 to about 24 deciliter per gram.
13. The method of Claim 11 wherein the amount of organic polymer is about 5 ppm to about 500 ppm.
14. The method of Claim 11 wherein a mineral acid is utilized to adjust the pH.
15. The method of Claim 11 wherein the sludge has a high fat content of about 40 to 70% by weight.
16. The method of Claim 11 wherein the separation procedure involves centrifugation at a gravitational force of at least about 750 XG.
17. The method of Claim 11 wherein the sludge is heated at a temperature ranging from about 170°F to 212°F.
18. The method of Claim 1 wherein the solid material is separated from the sludge to provide a solids content of about 25 to 40 percent by weight.
19. The method of Claim 11 wherein the solid material is separated from the sludge to provide a solids content of about 25 to 40 percent by weight.
20. The method of Claim 11 wherein the solid material is separated from the sludge to provide a solids content of about 25 to 40 percent by weight.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US81436077A | 1977-07-11 | 1977-07-11 | |
| US814,360 | 1977-07-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1116765A true CA1116765A (en) | 1982-01-19 |
Family
ID=25214832
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000306772A Expired CA1116765A (en) | 1977-07-11 | 1978-07-04 | Method of dewatering aqueous waste sludge |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1116765A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4988442A (en) * | 1988-11-07 | 1991-01-29 | Polypure, Inc. | Process for dewatering of biological sludge |
| US6589429B2 (en) | 2000-11-16 | 2003-07-08 | Sustainable Forest Management Network | Method of treating industrial wastewater |
| EP1972199A1 (en) | 2007-03-10 | 2008-09-24 | Messer Italia S.p.A. | Method and device for removing water from tannery waste |
| US10377652B1 (en) * | 2014-12-05 | 2019-08-13 | Fremont Industries, Inc. | Process for enhanced fractionation of recovered waste streams |
-
1978
- 1978-07-04 CA CA000306772A patent/CA1116765A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4988442A (en) * | 1988-11-07 | 1991-01-29 | Polypure, Inc. | Process for dewatering of biological sludge |
| US6589429B2 (en) | 2000-11-16 | 2003-07-08 | Sustainable Forest Management Network | Method of treating industrial wastewater |
| EP1972199A1 (en) | 2007-03-10 | 2008-09-24 | Messer Italia S.p.A. | Method and device for removing water from tannery waste |
| US10377652B1 (en) * | 2014-12-05 | 2019-08-13 | Fremont Industries, Inc. | Process for enhanced fractionation of recovered waste streams |
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