Background of the Invention

This invention relates to a process for treating waste material and more particularly to a process for treating waste material such as commercial, industrial, agricultural, household and restaurant waste for the recovery of useful organic and inorganic matter contained therein.

In one particularly important aspect, the invention relates to the treatment of municipal solid waste and to the processing of swill and household garbage and sewage. The term "swill" is used throughout this specification to refer to all putrescible organic municipal and agricultural waste. Such waste includes waste food discarded by households and, particularly, hotels, restaurants and other commercial catering establishments including hospitals, and. thus can be of a high nutritional value.

Heretofore-, various methods have been devised for the treatment and disposal of waste material including landfill, ocean dumping, composting, heat treatment and incineration. With the tremendous increase in volume of waste produced, such methods have become environmentally unsafe, inefficient and very expensive. Also, swill from hotels, restaurants and other commercial catering establishments has in the past been fed to animals as a method of disposal, but in recent years this has been discouraged due to the fear of introducing diseaseto such animals.

Furthermore, conventional recycling processes used in cooperation with such disposal methods only separate out the solids from the remainder of the waste and reduce the size thereof for the recovery of ferrous metals and other useful solids such as glass and the like contained therein. This may be accomplished by subjecting the solids to magnets for the recovery of ferrous metals or by subjecting them to crushers and hammer mills for size reduction. Also, the solids may be passed through fluids moving at various speeds whereby they are separated and classified according to density and aerodynamic qualities. Such conventional recovery processes have only achieved limited success due to the fact that they recover only limited amounts of reusable material with waste material still remaining for disposal.

In addition, a result of the bans and other measures taken to discourage the feeding of swill to animals has been that the use of commercial and domestic garbage grinders for the disposal of food

wastes has increased. Thus, garbage grinders are now in use in many household kitchen sinks and, with the advent of commercial garbage grinders in hospitals, hotels, supermarkets, and so on, the food scraps from such commercial institutions which were previously collected and fed to animals as swill are now diverted into the sewage system. This diversion of the swill into the sewage system, whilst avoiding problems which would arise if it was fed to animals, gives rise to problems in itself as it causes a further load on which is often an already over-loaded sewage system.

Summary of the Invention In accordance with the present invention, there is provided a process for treating waste material for the recovery of organic and inorganic matter which is safer and more reliable than the methods mentioned above. The improved process is simple and economical of operation and recovers more useful material than the prior conventional methods. The process will therefore significantly reduce the overload of waste material going to landfills and sewage plants by recovering not only solid inorganic matter but organic matter as well.

It is an object of the invention to provide an efficient waste recovery process that is adapted to treat various type_s of waste material including materials such as paper, plastic, metal, glass, waste food, wood chips and the like for the recovery of useful organic and inorganic matter, including animal foodstuffs and fuel materials.

According to the present invention there is provided a process for treating a waste material feed¬ stock for the separation and recovery of organic and inorganic matter contained therein, which comprises the steps of:-

(i) subjecting said feedstock to conditions of heat and/or pressure to sterilize the feedstock and soften solid organic matter therein;

(ii) separating solid inorganic matter from said sterilized feedstock; and

(iii) subjecting the resulting essentially organic component of said sterilized feedstock to fermentation to form a fermentationmash.

In carrying out the present invention, separation of the solid inorganic materials from the feedstock and subjecting the organic component of the feedstock to heat and/or pressure is conveniently carried out in a single step. This may-, for example, be carried out by feeding the waste material feedstock into a container having perforations therein and mounted within a closed chamber in spaced relation to the inner surface of said closed chamber. On a small scale, this may be carried out in an autoclave, however, large scale equipment designed on similar principles can also be used. After introduction of the feedstock, it is agitated while in the container and subjected to heat and/or pressure; for example by introduction of steam to the closed chamber at a pressure from approximately

20 p.s.i. up to approximately 100 p.s.i., preferably around 60 p.s.i., for a period of, from approximately 20 minutes to approximately 2 hours, preferably about 1 hour. The conditions of heat and pressure which are thus created within the closed chamber ensure that the feedstock is rendered biologically sterile, and furthermore solid organic matter within the feedstock, particularly bones, becomes soft and pliable under these conditions. When the pressure is 0 released from the chamber, the essentially organic component of the feedstock including bones which have become soft and pliable are forced outwardly through the perforations of the container leaving solid inorganic matter such as bottles, cans and the like behind. The organic matter is thus separated from the inorganic matter. If desired, the solid inorganic matter may be further processed for recovery and recycling of any ferrous and non-ferrous metal or plastics or glass therein.

As the organic matter of the feedstock is forced through the perforations as. described above, the material is shredded and broken up. if desired, one or more . enzymes, acids or alkalis may be added to the feedstock to assist in hydrolysis of cellulose and other components thereof prior to the alcohol production step. The feedstock is then fermented for example by means of yeasts or bacteria in the known manner to form an ethanol-containing ^* fermentation mash, and carbon dioxide produced during the fermentation may, if ^* desired, be recovered and stored for later use as required. After fermentation, ^' the fermentation mash may be separated, preferably by passage to a

OMPI

centrifuge where the solid fraction is separated from the liquid fraction thereof. The solid fraction retains high nutritional value and is preferably recovered for use as an animal foodstuff- Ethanol may be recovered from the liquid fraction by known means, preferably by distillation, and the balance of the liquid fraction then passed for further processing.

If desired, after recovery of the ethanol, the balance of the liquid fraction may be passed to a centrifuge for recovery of fats prior to. he product being passed to an anaerobic digester. In this digester, "bio-gas" is produced in the known manner and subsequently separated into methane and carbon dioxide.

If desired, the effluent from the anaerobic digester may be further processed for removal of the- remaining nutrients therein as described in more detail below.

It will be appreciated from the foregoing description that an important aspect of the present invention resides in the fermentation of the organic matter of the feedstock, for example for the production of ethanol. This production- of ethanol may be enhanced by hydrolysis of polysaccharide materials prior to fermentation and, as described above, this may be achieved by addition of an enzyme or an acid such as hydrochloric acid to the feedstock prior to fermentation. Such acids may be subsequently neutralized with basic materials such as lime to form

salts which are of benefit, for example in animal feedstuffs.

In another aspect of the present invention, there is provided apparatus for treatment of a waste material feedstock for the- separation and recovery of organic and inorganic matter therein, said apparatus comprising:-

(i) means for subjecting said feedstock to conditions of heat and/or pressure to sterilize the feedstock and soften solid organic matter therein;

(ii) means for separating solid inorganic matter from said sterilized feedstock; and

(iii) fermentation means wherein the resulting essentially organic component of said sterilized feedstock can be fermented to produce a fermentation mash.

Where an ethanol-containing fermentation mash is produced the apparatus may further comprise:- (iv) means to separate the fermentation mash into a solid fraction and a liquid fraction;

(v) distillation means for recovering ethanol from said liquid fraction; and," if desired, (vi) anaerobic digester means wherein the balance of said liquid fraction can be _digested for the recovery of methane.

Description of the Drawing Apparatus embodying features of the present invention and which may be employed to carry out a preferred embodiment of the improved process of this invention is shown schematically in Figure 1 of the accompanying drawing.

Detailed Description of Drawing . Referring now to the drawing for a better understanding of the present invention, there is shown waste material, such as industrial, commercial, agricultural or household garbage being fed into a perforated drum or container 10 having closed ends 11 and perforations 12 at the sides thereof. In actual practice, it has been found that a container 10 cylindrical in shape and having 3/4 inch perforations at its sides is satisfactory. The container 10 is shown as being mounted for rotation about its longitudinal axis 13 inwardly of a closed chamber 14 and in spaced relation to the inner surface 16 thereof as shown. In an alternative construction, however, the container 10 may be of inverted conical shape and mounted for rotation about its vertical axis.

After the waste material is fed into the container 10, it is agitated by rotation of the container and subjected to heat and pressure by suitable means, such as by introducing steam into the closed chamber 14 for a period ranging from approximately twenty minutes to two hours to bring the pressure therein up to a pressure ranging from approximately 20 p.s.i. to 100 p.s.i. The waste material is thus biologically sterilized and the

organic matter, such as vegetable matter, bones, meat scraps, paper and the like, are softened and partially hydrolized. In actual practice, it has hnnsn found that when the steam is introduced into the chamber 14 at a pressure of approximately 60 p.s.i. for approximately one hour, the process operates satisfactorily in every respect with household garbage and sewage and food scraps from restaurants. During the steam injection period, the container 10 is agitated, such as by rotating it about its longitudinal axis 13 within the chamber 14 by a conventional drive unit, not shown.

After the waste material is sterilized and the organic matter softened, the pressure within the chamber 14 is released suddenly whereby the organic matter is separated from the inorganic matter such as bottles, cans, ceramics and the like. This is accomplished due to the sudden depressurization within .• the chamber 14 which causes the softened organic matter to be forced out of the container 10 through the perforations 12 with only solid inorganic matter being left therein.

The solid inorganic matter is removed from the container 10 by suitable means for further processing and separation into useful glass, ferrous and non- ferrous materials. This may be accomplished by passing the solids over a magnet 17 to remove the ferrous metals and then introducing the remainder thereof to a conventional crusher 18 where the glass is shattered and recovered from non-ferrous metals for reuse in a manner well understood i the art.

The softened organic matter is shredded and broken up as it is forced through the perforations 12 and is then transferred to a conventional storage container 19 where suitable additives to hydrolyse the organic matter, such as acids, alkali or enzymes, may be added. The shredded and treated organic matter is transferred from the storage container 19 to a fermentation chamber 21 where it is fermented with yeast or bacteria in a conventional manner to form an ethanol-containing mash.

The mash is separated into liquid and solid portions by passing it through a conventional centrifuge 22. This solid portion contains high nutritional value and is preferably recovered for use as an animal feed supplement. This may be accomplished by feeding in a wet state to form a wet feed or by drying the solid portion in a conventional manner to a moisture ^' content not greater than approximately 13% by weight. After drying, the solid portion is passed through a conventional milling apparatus such as a hammer mill where it is pulverized into a meal or granular type substance with high protein content.

The separated liquid portion of the mash is passed to a distillation column 23 for the recovery of ethanol, with the residue therefrom being transferred to a second centrifuge 24 for the recovery of fats and animal feed before passing the solubles into an anaerobic digester 26. To aid in.the production of ethanol, acid, such as hydrochloric acid, alkali or enzymes, such as celluloses may be added to the organic matter prior-to.fermentation. This will enhance the

hydrolysis of the polysaccharide materials contained therein. In the anaerobic digester 26, a "bio-gas" is produced and separated into carbon dioxide and methane in a conventional scrubber, not shown. In view of the fact that recovering methane, carbon dioxide and ethanol from the processes mentioned above is well known in the art, no further description is deemed necessary.

The effluent from the anaerobic digester 26 may be transferred to an algae pond 27 where algae is grown from the remaining nutrients through photosynthesis, The algae may be harvested and used as an animal feedstuff or contents of the algae pond 27 may be passed into a fish pond 28 where a portion of the algae is used primarily as a food for fish with the remainder of the pond contents being used as food for water plants. The plants may be harvested and again, either used as an animal feedstuff or returned to the anaerobic digester 26, while at the same time the water is being cleaned and recycled for use in steam production.

From the foregoing, the operation of the preferred embodiment of the improved process for treating waste material for the recovery, of useful organic and inorganic matter will be readily understood.

As an illustration of the effectiveness of the process of this invention, it is noted that in a pilot plant operation, amounts of more than 50 gallons °f anhydrous ethanol have been recovered per ton (dry weight basis) of municipal waste.

OMPI

It will thus be seen that this invention provides an improved process for treating waste material which is simple and very economical to carry out. Also this improved process permits waste material to be diverted from landfills and ^' overloaded sewage systems and converted into useful and valuable fuels and supplements for animal feed.

While the present invention has beczn shown in detail in only one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.