SOLIDS SEPARATION TECHNOLOGY

Background of the Invention

1. Field of the Invention

The present invention relates generally to the fields of handling and treating low

solids suspensions and separating the solids from the liquids. More specifically, it

concerns chemical compositions, methods and apparatus for separating organic colloidal

suspensions into a clean water component and a high solids component, and recovering

the beneficial minerals and nutrients of the suspension by utilizing a combination of

chemical treatment and mechanical separation techniques. In other embodiments of

the invention, these compositions, methods and apparatus are used to clean industrial

effluents from impurities and toxins. More specifically yet, the present invention

concerns chemical compositions, methods and apparatus for separating a waste

manure stream from farm operations into a solids component and a water component.

2. Description of Prior Art

A. Separating solids from a liquid or solid suspension

The use of chemicals for binding colloidal fines and solids in a suspension is well

known in the art. U.S. Patent No. 3,994,806 discloses a composition comprising a 5 to

20 percent aqueous solution of a mixture of dimethyl diallyl ammonium chloride

homopolymer and polyacrylamide in a weight ratio of from 10 to 1 to 20 to 1. In the

flocculation and removal of suspended matter from water, combinations of cationic and

nonionic water-soluble polymers are found to be more effective than equivalent

concentrations of cationics alone, and significantly lower concentrations of the

combination are found to be equivalent in effect to higher concentrations of cationic

polymers alone. U.S. Patent No. 4,931,190 is directed to a method for dewatering thin

slurries of very fine clay or clay-like material to yield high solids content filter cake, for

example, 40% solids and greater, by the use of flocculating agent combinations

involving polyethylene oxide-type flocculating agents and polyacrylamide-type

flocculating agents. The method generally involves admixing the combination of

flocculating agents with the slurry, dewatering the slurry by means of a mechanical

dewatering apparatus and feeding the thickened slurry to a belt press filter. U.S. Patent

No. 5,213,693 teaches a novel composition comprising a dry blend of the two polymers

that can be formed to provide a combined solution for mixing with a suspension. The

composition is used on sewage sludge and other organic suspensions for filter press or

belt press dewatering by substantially simultaneous treatment with a cationic coagulant

polymer and a cationic flocculant polymer. In U.S. patent No. 5,846,433, a suspension

is dosed with a coagulant and then with a flocculant and is dewatered to form a

thickened sludge or cake and separated liquor, and control of the dewatering

performance is improved by adding the flocculant at a predetermined dosage,

monitoring the charge in the separated liquor (or monitoring other dewatering

parameter of the separated liquor or suspension) and adding coagulant at a dosage

selected in response to the monitored charge or other parameter value in order to

maintain the value substantially at a pre-selected optimum value. U.S. Patent No.

6,805,803 discloses a process of flocculating and dewatering an aqueous suspension of

suspended solids comprising (a) a concentrated polymer solution and, (b) a dilute

polymer solution, characterized in that the concentrated and dilute polymer solutions

are introduced into the substrate substantially simultaneously. Preferably the

concentrated and dilute polymer solutions are introduced into the suspension as an

aqueous composition comprising a dilute aqueous solution of polymer and a

concentrated solution of polymer. The process brings about improvements in filtration

and cake solids.

B. Separating solids from liquid manure

Manure is hazardous to humans, animals and the environment. Untreated

manure, typically containing animal feces and urine, is a perfect medium for the

proliferation of microbes and parasites. Manure also emanates gases produced by

decomposition such as hydrogen sulfide, methane, ammonia, and carbon dioxide.

These gases do not only produce a foul smell, but, in high enough concentrations, each

of these gases may pose a health threat to humans and livestock. Manure runoffs also

pose a contamination threat to rivers, streams and groundwater.

Farms have several options for manure management: solid material handling,

slurry handling, liquid manure handling, treatment in an anaerobic lagoon, composting,

and a combination of these. One of the more common management practices is to

collect the manure in large lagoons or digesters where the manure is treated with

anaerobic bacteria that digest organic matter by liquefying it and then converting it

primarily into carbon dioxide, methane, ammonia, and hydrogen sulfide. The manure,

typically between 1% to about 5% solids, and most typically to about 2% solids, is

relatively easy to handle and can be disposed of in crop field irrigation. The manure

can also be handled by using conventional irrigation equipment and without the need to

use special pumps. Disposal through irrigation normally carries a low risk of

contaminating the ground water in situations where the soil is sufficiently thick to filter

out these contaminants before reaching the ground water. Slurry manure, i.e. manure

with a solids content of about 5% to about 7%, is more difficult to handle and requires

special pumps and irrigation equipment.

There are several disadvantages to using liquid manure in this fashion, however.

1) The valuable nutrients and minerals in the manure are not being effectively utilized,

2) It requires expensive storage and handling equipment, 3) A large quantity of water is

locked in with the manure and can not be beneficially used, 4) In northern states the

ground is frozen during the winter months and irrigation can not be used to dispose of

the liquid manure since it would cause runoffs that could contaminate rivers and

streams and 5) Ground water contamination can occur where the soil is not very

effective in filtering out the contaminants contained in the stream.

Manure is a foul smelling mixture of about 98% water and 2% solids. The solids

portion contains valuable nutrients and minerals most notably phosphates and nitrates

suspended in a colloidal state. It would be therefore desirable to recover these

components for use in fertilization and to release clean and usable water.

Attempts to separate manure solids material from liquids in the past included

mechanical means, chemical means or a combination of the two. Mechanical

separation means alone proved to have low separation efficiency as the colloidal fines

tend to stay with the liquid portion. Combinations of mechanical and chemical

separation methods have had more success but generally required slow and expensive

multiple batch floatation stages in order to achieve the required high separation

efficiencies.

U.S. Patent No. 6,749,068 describes a separation process using a sloped

screen of small openings and using air flow to enhance liquid drainage. U.S. Patent Nos

5,205,930 and 6,651,822 are directed toward a mechanical separator pressing the

solids using a screw feeder. U.S. Patent No. 5,268,100 discloses liquid slurry

introduced at a top in-feed end of the screen and moved downwardly along the in-feed

section of the screen by a paddle conveyor. Separation of solids occurs primarily along

the in-feed screen section. The slurry is then moved angularly upwardly along the

discharge section of the screen for final dewatering.

Chemical additives used to effect the agglomeration of particles onto solids

material were coagulant flocculant chemicals known in the art such as aluminum

sulfate, calcium hydroxide, calcium carbonate, calcium sulfate, anionic polymers, and

cationic polymers such as polyacrylamide. For example, U.S. Pat. No. 4,079,003

teaches the use of longitudinally spaced paddles for moving and agitating a mixture,

particularly when the minimum solids concentration is in excess of 25%, so as to

achieve an agglomeration of solids into a solid friable material, largely as a result of

large quantities of lime to generate heat and cause dehydration and solidification. U.S.

Patent No. 5,401,402 discloses a method of treating sewage sludge, in which the

sludge is mixed with an alkaline material in such a way as to provide intimate surface

contact that enables the alkaline material to permeate even small particles of the

sludge, and to deliver the resultant product in a granular form. The sludge and alkaline

material are delivered to a mixing chamber and are confronted therein with a screw

type mixer having generally helical flighting carried by a shaft, with the mixer being

rotatably driven in generally horizontal arrangement to convey the mixture toward an

outlet. U.S. Patent No. 6,824,691 discloses a process for treating liquid manure with a

tertiary or quaternary polyacrylamide in an amount of between 80 ppm and 140 ppm

and stirring for a time ranging from 5 to 15 minutes to flocculate the colloidal

suspension onto the solids. The solids are separated from the liquid by floatation. U.S.

Patent Nos. 5,785,730 and 5,776,350 disclose a method for separating raw

agricultural waste into a liquid portion and a nutrient enriched solids portion by adding

an effective amount of a quatemized amino methylated polyacrylamide polymer, mixing

the polymer with the raw agricultural waste, subjecting the mixture to at least one

mechanical separation means, and separately collecting the liquid and the solids

portions. Pre-grant publication No. 20050000906 discloses a method of treating

animal manure using a biological passive flotation step in a flotation unit having a

hydraulic residency time (HRT) of about 4 to about 24 hours with a polymer followed by

a skimming means for removing floating solids from at least a portion of the surface of

the manure. This is followed by a secondary floatation and skimming step having a

residence time of 0.5 - 4 hours. The claims of the publication are directed to the use of

a polymer with the preferred embodiment of a polyacrylamide. Pre-grant publication

No. 20060108291 teaches a method of treating manure comprising: a) mixing a

quantity of manure with lime such that said mixture has a basic pH; b) adding a first

coagulating polymer to said mixture, thereby promoting floe formation within said

mixture; c) separating the floe from the mixture, thereby forming solids and a liquid

portion; d) adding a second coagulating polymer and/or a struvite-promoting compound

to said liquid portion, thereby forming solids and clear liquid; and e) separating the

clear liquid from the solids."

Terminology

The invention disclosed in this application involves the removal of water from

suspensions containing colloidal fine particles that results in a high solids portion and

water that contains a very small amount of these particles. In the art and in the

specification for this application, the source suspension may be referred to as: low

solids suspension, colloidal suspension, liquid suspension, solids suspension, particles

suspension, low biosolids suspension, or dilute suspension. In the case of manure, the

source suspension may be referred to as manure, liquid manure, low solids manure,

manure slurry, or simply "manure". The solids resulting from the separation may be

referred to as biosolids, solids component, solids, manure solids, or low moisture solids

as the case may be. Agglomeration is an action by which small colloidal particles

coalesce into larger size particles. Agglomeration relates to particle size enlargement,

particle joining or particle binding. An effective mechanism to achieve this is by the

addition of a coagulant and a flocculant to a particles suspension. Coagulation is the

process by which the electrical repulsion between individual particles is reduced,

inverted, or neutralized. Flocculation is used to describe the action of polymeric

materials which form bridges between individual particles. Bridging occurs when

segments of a polymer chain adsorb on different particles and help the particles

agglomerate into larger particles. Flocculants have charged groups with a charge that

counterbalances the charge of the particles. Flocculants adsorb on the particles and

cause destabilization by bridging and/or charge neutralization. The joining and

enlargement of these particles continues for as long as the flocculant is present and the

system charge favors bridging.

Summary of the Invention

The present invention relates to a chemical composition for the agglomeration of

colloidal suspension particles into solids. This composition is a combination of a

coagulant and a flocculant that is effective for liquids that comprise organic colloidal

solids in the range of about 0.5% to about 30%. When applied in proper dosages,

water that is substantially free of these particles is released, and solids, that contain all

the beneficial elements of the suspension such as nutrients and minerals, can be easily

and speedily separated from the water by mechanical means. The separation provides

solids that can be used to take advantage of these beneficial elements, and water that

is substantially free of these elements that can be used for industrial purposes or, with

additional treatment, can be made potable. The chemical composition is effective in a

variety of applications such as cellulose, ethanol bi-products, manure, sugar cane, grain

distilled ethanol, and switch grass.

It is an object of the present invention for the coagulant and flocculant to work

on contact to separate the solids from the liquids.

It is an object of the present invention for the system and process to work on

the separation of solids and liquids in municipal sewage sludge.

The present invention also relates to a method for separating a solids

suspension, and more specifically an organic colloidal suspension, comprised of the

steps of 1) applying a chemical composition to treat the colloidal suspension particles to

agglomerate them into a solids component and to release water from the suspension,

2) separating continually the water from the solids, and 3) moving continually the water

and solids apart from each other.

The steps for continually separating water from the biosolids and moving the

water apart from the solids can be accomplished by a variety of mechanical separation

devices. These include conveyor paddles, flighted conveyors, stationary sloping screen,

a cyclone separator, gravity based separators, piston separators, vibrating screens, belt

press, roller press, shaftless spiral conveyors, or rotating screens. The preferred

embodiment for a mechanical separation device is a rotating screen combined with a

flighted screw ribbon arrangement that allows progressive thickening of the solids

suspension through the length of the screw housing while the water drains through the

screens and moves the thickened solids towards the exit.

This method constitutes a significant improvement in separation speed relative to

the prior art while utilizing relatively low cost equipment and chemicals, and achieving

high separation efficiency. Processing speeds in excess of 400 gal/min, and separation

efficiency of over 98% can be achieved. This means that over 98% of the beneficial

nutrients can be recovered in the biosolids and over 98% of the solids can be removed

from the water effluent.

The present invention relates to a method for separating liquid manure into a

solids component and water.

It is an object of this invention to provide compositions, methods and apparatus

suitable for cleaning industrial effluents and bodies of water from impurities and toxins.

Examples of uses for this technology are: cleaning river water from sediments, cleanup

of PCBs from rivers, cleanup of water from domestic uses such as pools, hot tubs and

fish tanks, and cleaning rivers and ground water of fertilizer residue.

It is an object of the present invention to provide manure biosolids suitable for

land application for use as a fertilizer with or without the use of Water Soluble

Polyacrylamides to stabilize the soil and its nutrients against erosion, crusting and to

minimize water runoff. The biosolids must be chemically stable during the separation

process and in handling, but able to break down and release the minerals and nutrients

to the soil after the application.

It is an object of the present invention to provide a separation system of manure

solids from water that is continuous and able to proceed at a rapid rate. It is further

the object of the present invention to provide a water of potable quality as the product

of the separation from manure. It is further the object of the present invention to

provide the water effluent product of this separation that is substantially devoid of

harmful bacteria to humans, livestock or the environment. It is further the object of

this invention to provide biosolids that are devoid of any unpleasant smells.

It is an object of the present invention to provide a secondary water treatment

method that allows further water clarification.

It is an object of the present invention to be able to correct the pH of the system

by adding additives, for instance, calcium which would raise the pH.

It is an object of the present invention to provide the system to treat a

polluted or dirty water system. An example of such a system is a pond which has too

much sediment floating in it, or too much fertilizer free floating in the water. The

system and process of the present invention can be used like a filter system, the dirty

water, or water with contaminants in it is pumped from the body of water to the system

of the present invention, wherein clean water is returned to the body of water. This

same system can be used to assist in treating PCBs in a body of water.

In a preferred embodiment of this invention, two chemical mechanisms are

combined to agglomerate the colloidal suspension particles together and to release

water that is relatively free of solids: coagulation and flocculation. Coagulation is the

destabilization of colloids by neutralizing the forces that keep them apart. Cationic

coagulants provide positive electric charges to reduce the negative charge, or zeta

potential, of the colloids. As a result, the particles collide to form larger particles

referred to as floes. Flocculation is the action of polymers to form bridges between the

floes and bind the particles into large agglomerates or clumps. Bridging occurs when

segments of the polymer chain adsorb on different particles and help particles

aggregate. An anionic flocculant will react against a positively charged suspension,

adsorbing on the particles and causing destabilization either by bridging or charge

neutralization. In order to effectively flocculate a colloidal suspension, a very high

molecular weight polymer, typically greater than 1 million is required. Inter-particle

bridging can occur with nonionic, cationic or anionic polymers. Both coagulation and

flocculation reactions take place as soon as the chemicals make contact with the

suspended particles and are virtually instantaneous. It is to be understood that

effective coagulants or flocculants could perform well in and of themselves, however,

when combined there is an enhanced synergistic effect.

Many factors determine the effectiveness of coagulation and flocculation. Among

these are the nature and charge of the colloidal particles, the length, charge and shape

of the polymer chain, and the ionic character of the solution.

The combination of flocculants and coagulants added to a solids suspension

accomplishes three functions: 1) the agglomeration of colloidal particles into solids, 2)

the release of the water from the suspension and 3) retention of the ionic components

such as phosphates, nitrates, sulfates, potassium ions, and sodium ions. To a great

extent flocculants alone can accomplish the separation of solids and water function

fairly effectively. The addition of coagulants, however, makes the separation of the

ionic particles and their retention onto the solids more effective.

Bivalent cationic oxides and salts are known inorganic coagulants. Examples are

calcium chloride, calcium nitrate, calcium sulfate, magnesium chloride, magnesium

nitrate, magnesium sulfate, calcium oxide and magnesium oxide. Trivalent cationic

oxides and salts perform more effectively than bivalent oxides and salts. Among these

are aluminum oxide, aluminum sulfate, aluminum chlorohydrate, aluminum perchloride

and ferric chloride. Among the known organic coagulants are quaternary polyamines

and PoIyDADMAC.

Flocculants are hydrophilic polymers having a molecular weight varying from 1 to

30 million and a degree of polymerization of between 14,000 and 420,000 monomer

units. Flocculants are typically acrylamide based. They may be homopolymers and

have a nonionic nature or they may be copolymers and have a cationic or anionic

nature with a degree of ionization varying between 0 and 100%.

Anionic flocculants are obtained either by hydrolysis of the amide groups on a

polyacrylamide chain or by copolymerization of the polyacrylamide with a carboxylic or

sulfonic acid salt. The most common type of flocculant made by copolymerization is

one between an acrylamide and acrylic acid.

CH ₂

Acrylamide Acrylic acid Na-Acrylate Acrylamide copolymer

CH ₂ =CN + CH ₂ =CH ₊ NaOH=> — (CH ₂ =CN) ₁ * [CH ₂ =CH] _n

C=O S=O C=O S=O

NH ₂ OH NH ₂ Q- Na ⁺

Aery I 'amide Sulfonic Na-sulfonate_A cry/amide Copolymer acid

The anionicity of these copolymers can vary between 0% and 100% depending

on the ratio of the monomers involved.

The main characteristics of the copolymers are:

- Molecular weight: 3 to 30 million

- Viscosity at 5g/l: between 200 and 2800 cps.

Cationic flocculants are mainly derived from the copolymerization of acrylamide

with dimethylaminoethyl acrylate (DMAEA) in quaternized form.

A first reaction of DMAEA with methyl chloride allows it to be converted into a

quaternary ammonium salt in the form of chloromethylated DMEA (DMAEA-MeCI):

DMEA Methylchloride ADCl

The copolymerization of DMAEA-MeCI with acrylamide produces the cationic

polymer

The cationic charge of the copolymer is determined by the ratio of each

monomer and may vary between O and 100%.

The ester group of the copolymer is very sensitive to a pH of above 6.0:

PoI-COOH ₂ CH ₂ N ⁺ Me ₃ + OH ⁺ =I> Pol-COO ^" + HOCH ₂ N ⁺ Me ₃

Hydrolysis of the polymer reduces its efficiency by creating amphoteric polymers

and then anionic polymers. It is therefore essential to prepare these polymers at a pH

of about 5.5, even though the flocculation is carried out at a higher pH. However,

during flocculation, the floe may be converted by chemical modification of the polymer

when the contact times are long, for example during settling.

The main characteristics of the products obtained are: molecular weights ranging

from 3 to 10 million, and the viscosity at 5 g/l ranges from 100 to 1700 cps.

Processing manure in the present invention involves pumping the liquid manure

from a lagoon or an anaerobic digester, mixing the liquid manure in line with an

effective amount of a coagulant and/or an effective amount of a flocculant and then

introducing the liquid manure into a mechanical separation device. A number of

designs could be used. These include conveyor paddles, flighted conveyors, stationary

sloping screen, a cyclone separator, gravity based separators, piston separators,

vibrating screens, belt press, roller press, shaftless spiral conveyors, or rotating screens.

The preferred separation device embodiment for the purpose of this invention is

a rotating screen combined with a flighted screw ribbon arrangement that allows

progressive thickening of the manure through the length of the screw housing while the

water drains through the screens and moves the thickened manure towards the exit.

At the exit, the manure must be thick enough, i.e., at least 25% solids, so that it can be

dewatered further by a compressing device such as a press roll, or a belt press. The

rotation of the screen provides for the continuous exposure of new screen slots that

increases water removal rates and reduces the likelihood of plugging. In the preferred

embodiment, the water is drained through slotted screens located at the bottom of the

flighting screw housing. The size of the screens can range from about 250 microns to

about 4mm, with the preferred range being about 500 microns to about lmm. It is

important that the screens be flat and not made of wire for water drainage to be

effective. The screen housing is tilted about 5 degrees to about 20 degrees upward to

the direction of flow depending on the consistency of the incoming manure. The tilt

allows balancing the flow of the solids and the removal of the water through the

screens. The manure entering the separation device can be processed in a range from

about 0.5 - 30% solids, however the more typical range is from about 1 - 5% solids.

The manure typically exits the rotating screen housing at about 25 - 30% solids. It can

be further dewatered to around 40 - 60% solids by pressing with a roller or by other

compressing devices.

In the typical separation process, the coagulant and flocculant are each dissolved

in a water makeup tank each at a concentration of about lg/Kg of water, or about

0.1%, and pumped into the manure separation device. They can be mixed in and

pumped from either separate tanks or mixed together and pumped from the same

makeup tank. The coagulant should be dissolved in a slightly acidic environment in a

pH range of about 6 - 6.5 preferably using a weak organic acid such as citric acid, and

the flocculant dissolved at an ionic strength of 25%. Where a pH adjustment to >7.0 is

required for the flocculant, Calcium Oxide can be used.

A multitude of embodiments are disclosed comprising a coagulant and flocculant

combination for manure treatment selected from the following list of coagulants and

flocculants. It is to be understood that this list is not exhaustive and other coagulants

and flocculants may be used in the context of the present invention.

Inorganic coagulants

Aluminum Chlorohydrate (AI ₃ CHOH ₅ CIOH),

Aluminum sulfate,

Aluminum Perchloride

Aluminum Chloride

Aluminum Nitrate

Ferric Chloride

Calcium oxide

Magnesium oxide

Aluminum oxide

Ferric oxide

Calcium chloride

Calcium nitrate

Calcium sulfate

Magnesium chloride

Magnesium nitrate

Magnesium sulfate

Organic coagulants

Polyamines

PoIyDADMAC

Cationic flocculants

Acrylamide/acryloylethyltrimethylammoniumchloride, or AM/AETAC by short notation,

Acrylamide/acrylamidopropyltrimethylammonium chloride or AM/APTAC, and

3-chloro-2-hydroxypropyltrimethylammonium chloride modified starch

Anionic flocculants

Acryiamide/sodium acrylate at pH >7

The sodium salt of Acrγlamide^-acrylamidomethylpropanesulfonic acid in the pH range

of about 2 - 12.

The application levels of the coagulant can range from about 1 - 100 mg/liter of

liquid manure, with a preferred range of about 5 - 50 mg/liter of liquid manure. The

application level for the flocculant can range from about 5 - 75 mg/liter of liquid

manure with the preferred range of about 20 - 50 mg/liter of liquid manure.

Solids separation performance is also enhanced by the addition of fiber to the

liquid manure. This fiber provides additional surface area for colloidal particles

flocculation. Preferred fibers are straw, bedding, and recycled manure solids and the

addition level should range from about 0.5% - 5% of liquid manure weight.

Performance is likewise enhanced by recycling about 0.5% - 5% of the biosolids into

the solids separation device.

The water removed from the process typically has less than about 1% solids and

with substantially reduced microbe levels compared to the liquid manure. The

unpleasant odor of the original manure is also virtually completely neutralized by the

chemical treatment. This water, while not potable, is suitable for most agricultural and

industrial uses such as irrigation and manufacturing of chemicals. The water can be

made potable, however, by further treatment with flocculants in a clarifier.

Brief Description of the Drawings

Fig 1 shows a sketch of the process components for separating liquid manure.

Detailed description of the Drawings

Fig 1 is a schematic showing the components and the flow of the process. The

colloidal suspension feed (5), which may be liquid manure or other such suspensions as

described in this application, is pumped into the separation device (1) and is blended

with the chemical feed (12). The chemicals are made up in a tank (3) using a mixer

(4), and conveyed into the separation device by pump (11). The separation device (1)

is a rotating drum having an angle of elevation (10) of about 5 - 20 degrees relative to

horizontal. The bottom of the drum has screen portions through which the water drains

(8) into collection tank (9), and a flighting ribbon (2) used for moving the progressively

thickened solids to the exit of the separation device (1). The solids exiting the

separation device (1) drop onto a hopper (6) from which they are fed under a roll press

(7) that further removes water from the solids.