WO2000073220A1

WO2000073220A1 - A disposal method for pig ordure

Info

Publication number: WO2000073220A1
Application number: PCT/KR2000/000537
Authority: WO
Inventors: Joo-Sik Choi; Se-Keun Kwon; Woan-Soo Kim
Original assignee: Choi Joo Sik; Kwon Se Keun; Kim Woan Soo
Priority date: 1999-05-29
Filing date: 2000-05-25
Publication date: 2000-12-07
Also published as: KR100407554B1; KR20010053264A

Abstract

Disclosed is a disposal method of pig ordure. Pig ordure is primarily separated into solid and liquid by use of an inorganic coagulant. In this solid-liquid separation, the inorganic coagulant causes oxidation of pig ordure and generates gas while coagulating solids of the pig ordure. Meanwhile, the pig ordure is aerated by stirring to cause bubbles. Along with the gas, the bubbles float the coagulated solid of the pig ordure. These solids are removed. Then, the liquid is neutralized in pH and secondarily subjected to solid-liquid separation by use of an organic polymer coagulant. Thirdly, the secondariliy treated effluent is treated through biological treatment processes. In reference to tanks, a primary treatment step of reacting pig ordure with an inorganic coagulant is conducted in a reactor. A secondary treatment step is carried out in a neutralization tank, a coagulation tank and a flotation or a sedimentation tank, in order. For a third treatment step, a biological treatment tank and a sedimention tank are used. Finally, the sludge is allowed to stand in a sludge reservoir, concentrated in a thickener and dehydrated in a dehydrator. The method greatly reduces gravimetric loads of pollutants, volume of various baths and loads of subsequent processes. Thus, the method brings about significant economic benefits in reduced facility cost and maintenance costs, as well as demonstrating a maximal efficiency of ordure treatment.

Description

A DISPOSAL METHOD FOR PIG ORDURE

TECHNICAL FIELD

The present invention relates to a disposal method for pig ordure.

PRIOR ART

From livestock farms, ordure from cattle, fowl and/or pigs are produced. Of these, cattle ordure and fowl ordure are relatively low in moisture content such that they are frequently processed into fertilizer on location and/or are used in the manufacture of organic fertilizer. However, because one average pig produces as much as several kilograms per day of ordure in a slurry state, livestock farms, which usually raise hundreds to tens of thousands of pigs, have to solve the problem of disposing of scores of tons of solid and liquid ordure excreted from such a multitude of pigs everyday. In Korea, since public treatment facilities of livestock wastewater are designed to treat only the liquid of the ordure (design standard: biological oxygen demand (BOD) 5,000 mg/1). they are not quite capable of practical treatment of the ordure which is in a state of mixed solid and liquid ordure and as high in concentration as BOD 20,000 mg/1.

Conventionally, a standard activated sludge method or its modified variations are prevalently used in livestock wastewater treatment. For example, in the case that livestock wastewater is treated by a standard activated sludge process, the wastewater is deprived of various impurities, made homogeneous in a reservoir bath and adjusted in pH as necessary. The pH-adjusted wastewater is diluted with

10-20 volumes of water and then, transferred to an aeration tank having activated aerobic bacteria in the wastewater. Next, it is moved to a sedimentation tank. The separated supernatant is sterilized before being discharged while the sediment is dehydrated to such a moisture content that it is able to be buried in landfill or burned up. Such conventional processes, however, suffer from various problems.

For instance, because a large quantity of diluting water is required, the conventional processes are difficult to conduct in a water-deficient place. In addition, the addition of a large quantity of diluting water results in an increase in the total sewage amount, requiring extremely large facilities for the aeration and the sedimentation. Also, the size of the facility is directly associated with an increase in the power cost for water pumping and aeration, the maintenance cost and the operation cost.

DISCLOSURE OF THE INVENTION

The present invention is a method for water treatment of livestock farming ordure, particularly the slurry state of pig ordure, after taking into account that conventional methods lack a proper step of primarily separating solids and liquids and are not able to treat the large quantity of pig ordure that is discharged everyday.

It is an object of the present invention to provide a disposal method of pig ordure, with which not only can economic benefits be realized, including the shortening of the treating period, the reduction of the volumetric area of the system, the simplicity of the process equipment and the curtailment of expenditure for initial facilities, but also the stability of the finally treated water quality is obtained by reduction of influent load to the next processes. Based on the present invention, the above object could be accomplished by a provision of a disposal method of pig ordure containing a high concentration of solid, comprising the steps of: generating bubbles in the pig ordure by use of an inorganic coagulant with a pH adjustment in the range of 3.5 to 6, to float the solid with bubbles, said solid being phase-separated from liquid of the pig ordure; neutralizing and coagulating the liquid by use of an organic polymeric coagulant to float the residual solid of the liquid, said residual solid being phase-separated from the liquid; biologically treating the liquid; and dehydrating the separated solid.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a flow chart of the treatment steps of pig ordure of the present invention.

FIG. 2 shows an illustrated diagram of the main reaction of the present invention.

FIG. 3 shows a schematic diagram of the reactor selected in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, pig ordure is disposed of by sequentially and continuously performing the following steps:

1 ) Bubbling by use of an inorganic coagulant to separate pig ordure into solid and liquid constituents

2) Neutralization and coagulation

3) Biological treatment

4) Dehydration

In the bubbling step, an inorganic coagulant is added into pig ordure with stirring to oxidize the pollutants and to cause a decrease in pH to generate a gas.

Upon stirring, air is introduced into the pig ordure and, together with the generated gas, produces bubbles. Meanwhile, solid of the pig ordure are coagulated as a result of the action of the inorganic coagulants. The bubbles float the coagulated solid of the pig ordure to the upper part of a pig ordure slurry. Accordingly, the solids are phase- separated from the liquid of the pig ordure and thus can be primarily removed with relative ease. In addition to floated suspended solid, colloid and coagulable dissolved solids are removed in coagulation process through the bubbling.

The liquid remaining after primary solid-liquid separation is neutralized in pH, and subjected to secondary solid-liquid separation by use of an organic polymeric coagulant. In this regard, the residual solids are removed by floatation or sedimentation in the form of flocks.

In the biological treatment step, the pollutant remaining after the secondary solid-liquid separation are treated through a known biological method, along with the liquid resulting from dehydration of the solid sludge, and discharged.

Finally, in the dehydrating step, the separated solid are dehydrated for disposal.

A detailed description will be given of the present invention in conjunction with the drawings. With reference to Fig. 1, there is a process flow of the disposal of pig ordure. In order to remove solid constituents of pig ordure through primary solid- liquid separation, first, the pig ordure is reacted with inorganic coagulants in a reactor 1. Depending on their type, the inorganic coagulants are used at concentrations of 1/1-1/20 of the suspended pig ordure solid in the reactor 1 while maintaining 3.5-6 in pH. During this step, both the suspended solids (SS) and the organic materials, which affect the biological oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC) of the pig ordure, are reduced by at least about 80 %. The reactor is shown in a schematic enlarged view in Fig.3. The removal method of the solid is as follows.

Suitable for use in the present invention are inorganic coagulants that contain Fe or Al. In this regard, poly ferric sulfate (PFS), poly aluminum chloride

(PAC), ferrous sulfate (FeSO₄), ferric sulfate (Fe₂(SO₄)₃), aluminum sulfate

(Al₂(SO₄)₃), ferrous chloride (FeCl₂), and ferric chloride (FeCl₃) may be used alone or in mixed combinations thereof.

When added to alkaline pig ordure of pH 8 or higher, the inorganic coagulants cause an oxidation and a hydration as well as give rise to a decrease in pH of the ordure owing to their low pH.

Such a decrease in pH generates gases such as carbon dioxide (CO₂), methane (CH₄), hydrogen sulfide (H₂S) and ammonia (NH₃) from the pig ordure solution in the reactor, as shown in Fig. 2. Also, the pig ordure solution is stirred to facilitate the coagulation of the solid of the pig ordure. Upon the stirring, the pig ordure is aerated. Along with the generated gas, the introduced air brings about bubbles. Thus, these bubbles float the coagulated solid . Care must be taken not to decrease the pH of the solution to less than 3.5. The pH conditions of less than 3.5 do not enable any greater removal of solids, and just use up more chemicals. In addition, if excessive amounts of bubbles form and float the solid sludge to a substantial extent, it becomes difficult to separate the liquid. On the other hand, if the pH is adjusted to above 6, bubbles occur, but at such a low amount as not to allow sufficient solid-liquid separation. If the stirring is too vigorous, the solid separated by the bubbles may be again dissolve in the liquid.

If the pH is adjusted within the range of 3.5-6, the bubbles and the remaining liquid have a volumetric ratio of about 50 : 50 (following a lapse of two hours after inorganic coagulants are introduced). The liquid, which is mainly present in the lower part of the reactor 1 , is discharged to a neutralization tank 2 and then to a coagulation tank 3, thereby separating solid and liquid.

The solids which still remain in the liquid separated as a result of the primary solid-liquid separation, are neutralized in pH with alkaline chemicals, such as sodium hydroxide (NaOH), in the neutralization tank 2. After the solid and liquid are transferred from the neutralization tank 2 to the coagulation tank 3, organic polymeric coagulants are added at a concentration of 1/2,000-1/5,000 of the suspended solids to achieve the coagulation of the suspended solids, followed by separation of the suspended solids from the liquid in a floatation or sedimentation tank 4. Upon this secondary separation, there are removed 50 % or more of the pollutants which remain in the ordure solution which has undergone the primary solid-liquid separation. The organic polymeric coagulants useful in the invention are ionic. Cationic and anionic coagulants may be used alone or in combination. The coagulated solid pollutants from the primary and the secondary solid-liquid separation are further treated in a sludge dehydrator 9. The effluent from this dehydration, together with the effluent obtained after the secondary solid- liquid separation, are streamed into a biological treatment process 5 in which the remaining pollutants are further removed by a known biological method. The sludge produced in the biological treatment process 5 and the sludge obtained after the primary and secondary solid-liquid separation are decomposed in combination with wood materials, such as sawdust, chaff and leaf mold, to produce an organic fertilizer. The method of the present invention requires 20-25 % less added wood materials for the production of organic fertilizer than do conventional methods. Also, the decomposing and drying time can be reduced to one month or less.

A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLE

To a pig ordure slurry containing a high concentration of solids, wherein both biological oxygen demand (BOD) and suspended solids (SS) were as high as

20,000 mg/1, poly ferric sulfate (PFS), poly aluminum chloride (PAC), aluminum sulfate (Al₂(SO₄)₃), ferrous chloride (FeCl₂), ferric chloride (FeCl₃), ferrous sulfate

(FeSO₄), and ferric sulfate (Fe₂(SO₄)₃) are added at concentrations of 1/1-1/20 of the suspended solids by coagulant types. The addition of the coagulants adjusted

the pH of the slurry to 3.5-6 and caused the generation of bubbles by which the solids of the slurry were phase-separated. The results attributed to the inorganic coagulants are given in Table 1 , below.

In Table 1, the pig ordure slurry was analyzed for biological oxygen demand (BOD), chemical oxygen demand (COD), and suspended solids (SS) according to a water-pollution process testing method. Total organic carbon

(TOC) was analyzed with the aid of TOC 5000 analyzer (Shimatsu), based upon the instrumental analysis of the Standard Method. Samples, denoted by 'Sol.' in Table 1, were filtered through a GF/C filter and then through a 0.45 μm filter, and analyzed for the concentration of soluble pollutants in liquid . TABLE 1 Primary Removal of Pollutants by Inorganic Coagulants

COD _n SS TOC BOD

Cone. Removal Cone. Removal Cone. Removal Cone. Removal Samples (mg/L) Rate (%) (mg/L) Rate (%) (mg/L) Rate (%) (mg/L) Rate (%)

Pig ordure 14400 - 22500 - 11700 - 21300 -

'PFS 930 94 3900 83 870 93 2820 87

²PAC 1100 92 4300 81 1060 91 3100 85

³Fe₂(SO₄)₃ 1600 89 4600 80 1120 90 3520 84

⁴Al₂(SO₄)₃ 1900 87 5160 77 1300 89 3810 82

⁵FeCl₃ 2100 85 4900 78 1260 89 4100 81

⁶Fe₂(SO₄)₃ 10400 28 21100 6 7200 39 16200 24

⁷Sol.Pig ordure 7100 - - - 5500 - 10200 -

⁸Sol. Fe₂(SO₄)₃ 1020 86 - - 820 85 1900 81

⁹Sol. Fe,(SO₄), 2200 69 - . 1920 65 3300 68

Note:' Addition of PFS 3,000 mg/1 Pig ordure 1 L (suspended solids cone. 20,000 mg/1), pH=6

² Addition of PAC 5,000 mg/1 Pig ordure 1 L (suspended solids cone.

20,000 mg/1), pH=5.5

³ Addition of Fe₂(SO₄)₃ 5,000 mg/1 Pig ordure 1 L (suspended solids cone.

20,000 mg/1), pH=4.5 ⁴ Addition of Al₂(SO₄)₃ 17,000 mg/1 Pig ordure 1 L (suspended solids cone.

20,000 mg/1), pH=5 ⁵ Addition of FeCl₃ 20,000 mg/1 Pig ordure 1 L (suspended solids cone.

20,000 mg/1), pH=5.5

⁶ Inhibiting bubbles by ³+antifoaming agent

⁷ Pig ordure GF/C, 0.45 μm filter filtrate ⁸³GF/C, 0.45 μm filter filtrate

⁹⁶GF/C, 0.45 μm filter filtrate

From these results, it is apparent that polymeric inorganic coagulants such as poly ferric sulfate (PFS) and poly aluminum chloride (PAC), and trivalent cation-dissociable coagulants such as ferric sulfate (Fe₂(SO₄)₃), aluminum sulfate

(Al₂(SO₄)₃) and ferric chloride (FeCl₃) can remove 80 % or more of the pollutants.

The higher removal rates of the polymeric inorganic coagulants, poly ferric sulfate (PFS) and poly aluminum chloride (PAC), compared to the other inorganic coagulants, are attributed to the fact that the polymeric inorganic coagulants can associate with greater quantities of the solid .

In this experiment, the removal results were compared when bubbles were generated and when no bubbles were generated. For this, an antifoaming agent as a bubbling inhibitor, was added at the beginning to the pig ordure to inhibit the inorganic coagulants from bubbling the pig ordure. In this case, removal rates of the solid were less than 40 %. Therefore, it can be seen that the removal rate of the pollutants is greatly decreased without bubbling.

As described above, simply coagulation of the pig ordure slurry without bubbling results in poor removal rates. The reason is that, because pig ordure usually has a moisture content of about 95 %, which is similar to that of thickened sludge (95-98 %) and lower than that of general sludge (98-99 %), only the coagulating action of the coagulants alone does not elicit an efficient solid-liquid separation effect.

In the case of an unfiltered pig ordure slurry, the removal rate of samples was found to be 89 % in COD_Mn, 90 % in TOC, and 84 % in BOD when they were treated with ferric sulfate (Fe₂(SO₄)₃). On the other hand, when the pig ordure was treated with ferric sulfate (Fe₂(SO₄)₃) in combination with an antifoaming agent which inhibited the production of bubbles, the removal rate was reduced to 28 % in COD_Mn, 39 % in TOC, and 24 % in BOD.

In the case of a filtered pig ordure slurry, the removal rate of samples was found to be 86 % in COD_Mn, 85 % in TOC, and 81 % in BOD when they were treated with ferric sulfate (Fe₂(SO₄)₃). On the other hand, when the pig ordure was treated with ferric sulfate (Fe₂(SO₄)₃) in combination with an antifoaming agent which inhibited the production of bubbles, the removal rate was reduced to 69 % in COD_Mn, 65 % in TOC, and 68 % in BOD. As recognized, the removal rate was smaller when using the filtered samples than when using the unfiltered samples.

The lower removal rate for the filtered samples, even when the antifoaming agent was added to inhibit the production of bubbles, is believed to be attributed to the fact that dissolved pollutants in pig ordure were removed by the oxidation action of the added ferric sulfate (Fe₂(SO₄)₃). The moisture content of the solid sludge resulting from the solid-liquid separation was found to be as low as about 90 %, demonstrating that the present invention taking advantage of a bubbling process is efficient for disposal of pig ordure. The removal effects through simple sedimentation, as in conventional methods, are far inferior to those achieved through the floating process which takes advantage of the pH decrease and the aeration as in the present invention.

Secondary solid-liquid separation results are given in Table 2, below. For the secondary solid-liquid separation, the supernatant from the primary solid-liquid separation using the bubbles caused by inorganic coagulants, was neutralized in pH and subjected to coagulation to form flocks which were then floated or sedimented for removal.

TABLE 2 Secondary Removal of Pollutants by Neutralization and Coagulation

COD_Mn SS TOC BOD

Samples Cone. Removal Cone. Removal Cone. Removal Cone. Removal (mg/L) Rate(%) (mg/L) Rate(%) (mg/L) Rate(%) (mg/L) Rate(%)

PFS+'polymer 490 47 410 90 440 49 1090 61

PAC+'polymer 510 54 420 91 490 54 1200 61

Fe₂(SO₄)₃ 'polymer 800 50 560 88 620 45 1410 60

Al₂(SO₄)₃+'polymer 1100 42 680 87 800 39 1680 56

FeCl₃+'polymer 1200 43 400 92 910 28 1700 59

¹ secondarily treated effluent after neutralization and coagulation of the primarily treated effluent polymer 3 mg per liter of primarily treated effluent

The results of Table 2 were obtained after the polymer, serving as an organic coagulant, was mixed with the effluent which had undergone the primary solid-liquid separation with the inorganic coagulants and the neutralization with sodium hydroxide (NaOH).

In the secondarily treated effluent, which were obtained through the floating or sedimenting after the neutralization and the coagulatation, pollutants were measured to have been removed by 40-90 %.

After the pollutants were removed in the secondary treatment step, the treated effluent were streamed into a general biological treatment process in which a tertiary treatment step is conducted. In this tertiary treatment step, the solid remaining in the effluent even after the secondary treatment step were reduced by about 80 %~90 % by biological decomposition. The results of the biological treatment are shown in the following Table 3.

TABLE 3 Removal of Pollutants by Biological Treatment

COD Mn SS TOC BOD Cone. Removal Cone. Removal Cone. Removal Cone. Removal (mg/L) Rate(%) (mg/L) Rate(%) (mg/L) Rate(%) (mg/L) Rate(%)

' sol' n+ bio. treat. 69 86 51 88 54 88 132 88 ' sol' n+ bio. treat. 77 85 49 88 58 88 133 89 ' sol' n+ bio.treat. 77 90 53 91 60 90 137 90 ' sol' n+ bio .treat. 108 90 60 91 89 89 161 90

' sol' n+ bio.treat. 117 90 48 88 87 90 223 87

¹ secondary treated effluent which were neutralized and coagulated after the primary treatment

Meeting, in quality, with the requirement standards in the areas directed by legislation, the liquids which were biologically treated could be discharged into streams without being additionally treated.

TABLE 4

Quality Standards of Discharged Water from Public Treatment Facilities and Private Treatment Facilities (2000. 1. 1 - )

Private Treatment facilities

Public Permission Declaration

Items Treatmen Specific Ordinar Specific Ordinar t Areas y Areas y Facilities Areas Areas

BOD(mg/L) <30 < 50 < 150 < 150 < 350

COD(mg/L) <50

SS(mg/L) <30 < 50 < 150 < 150 < 350 Colon bacteria (cells/mL) < 3,000 - T-N(mg/L) < 60 < 260 T-P(mgtT-) < 8 < 50

The sludge obtained in the preceding treatment steps can be disposed according to conventional disposal methods for solid of livestock ordure. The sludge was coagulated with polymeric coagulants and concentrated in the thickener, followed by dehydrating the thickened sludge in a dehydrator to give a cake and a supernatant. The dehydrated cake was made into a completely decomposed fertilizer for agricultural use with the aid of composting equipment while the supernatant was cycled through the preceding treatment steps.

For illustration, the above treatment steps were conducted in a batch type process, in which the liquid discharged after the primary solid-liquid separation were secondarily treated. A continuous type process, in which both solid and liquid are secondarily neutralized and coagulated after the primary treatment, was also highly efficient in the removal rate.

As described above, the present invention provides an improved treatment of pig ordure containing pollutants in high concentrations. Over conventional methods, the present invention has many advantages as follows. First, the solids in pig ordure are reduced by at least 80% through the primary solid-liquid separation, which reduces the load that the subsequent processes are to treat. The total volume of sewage is increased with the use of diluting water in standard activated sludge methods or their variations, which are general disposal methods of pig ordure. In contrast, the present invention treats only pig ordure without diluting water, so that there can be brought about a great reduction in the sizes of various reactors and thus in facility and maintenance expense. Also, such a reduction in the treatment load enables the subsequent steps to better the quality of the treated water, and so is more environmentally favorable. Further, in the preparation of organic fertilizers from the removed solid, wood materials are used at an amount 20-25% less than that required in conventional methods. Additionally, the putrefying and drying time can be reduced to one month or less. Moreover, the present invention can be performed by using conventional equipment and thus, is more economically favorable.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims

1. A disposal method of pig ordure containing a high concentration of solid , comprising the successive or continuous steps of: bubbling the pig ordure by use of an inorganic coagulant with a pH adjustment in the range of 3.5 to 6, to float the solids with bubbles, said the solids being phase-separated from liquid of the pig ordure; neutralizing the liquid in pH and bubbling the liquid by use of an organic polymeric coagulant to float the residual solids of the liquid with bubbles, said residual solids being phase-separated from the liquid; biologically treating the liquid; and dehydrating the separated solid .

2. The method as defined in claim 1, wherein the inorganic coagulant contains Fe or Al.

3. The method as defined in claim 1, wherein the inorganic coagulant is selected from the group consisting of poly ferric sulfate, poly aluminum chloride, ferric sulfate, aluminum sulfate, ferric chloride, and mixtures thereof.