NZ539681A - Separation of fat and protein components from DAF sludge - Google Patents

Abstract

A process for treating DAF sludge to enable separation into its fat and protein component parts, said process comprising the steps: (a) adjusting the DAF sludge pH to below 4.2; (b) mixing an emulsifying agent into the sludge of step (a) at a concentration of between 0.1 and 3.0% v/v; (c) heating the mixture of step (b) to boiling point; (d) allowing the mixture of step (c) to cool and stand until the protein and fat component parts separate out; and (e) removing each separate component parts of step (d). Also disclosed is the use of the fat rich and protein rich components separated out for biodiesel, livestock food products and fertilisers.

Description

53 w/ NEW ZEALAND PATENTS ACT, 1953 No: 539681 Date: 28 April 2005 # COMPLETE SPECIFICATION DAIRY PRODUCT AND PROCESS We, FONTERRA CO-OPERATIVE GROUP LIMITED, Fonterra Centre, 9 Princes Street, Auckland, New Zealand, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) INTELLECTUAL PROPERTY OFFICE OF N1. 27 APR 2006 received DAIRY PRODUCT AND PROCESS FIELD OF THE INVENTION The present invention relates to a process for treating the waste material produced by the dairy industry and converting it into value added products such as feed supplements for livestock, fertilizer and/or biodiesel.

BACKGROUND OF THE INVENTION The waste material from the dairy industry (such as from cheese, milk and butter plants) generally comprises wastewater streams containing soluble inorganic matter (such as alkalis, acids etc), insoluble organic solids (such as milk solids, fats, oils, greases etc) and soluble organic matter (such as lactose sugars, flavourings, and dissolved proteins (e.g. whey)). Before the wastewater can be disposed of, some or all of these contaminants will require treatment.

Dissolved air flotation (DAF) systems are commonly used in wastewater processing plants in several industries including the dairy industry. The DAF system separates the insoluble solids from the liquid whereby gas bubbles, (injected into the wastewater solution) adhere to the insoluble particles and form a floating layer of sludge which is mechanically scraped off as it forms.

The DAF sludge comprises an emulsion of fat and protein in water and is produced in significant quantities by the dairy industry. Disposing of the DAF sludge is both problematic and expensive.

The common method of disposal is to bury it or to plough it into arable land. However, due to the high fat content of the sludge, this method of disposal can cause a pollution problem. Another method is to use microorganisms for anaerobic or aerobic digestion of the organic matter contained in the sludge. Both methods are expensive and can ultimately pollute water sources. lq Another option is to separate out the fat and protein components of the DAF sludge and either dispose of them separately or convert them into raw materials for use in other industries.

One such method involves heating the DAF sludge and centrifiiging it to produce fat, aqueous and solid layers. However, the separation is poor and mixing occurs between the layers.

Alternatively, the DAF sludge could be disposed of by blending it with existing products (such as fertilizer or animal feeds), however such blended products are less valuable and less desirable than unblended products and the cost of processing the DAF sludge into a blendable product (by drying, for example) is expensive as DAF sludge is generally about 80% moisture.

It would be desirable to provide a process for treating DAF sludge from dairy waste material whereby the protein and fat components of the sludge can be efficiently separated and converted into value added products thereby reducing the cost and pollution problems associated with the disposal of DAF sludge from dairy waste material.

It is an object of the present invention to go some way towards achieving this desideration and/or to provide the public with a useful choice.

SUMMARY OF THE INVENTION The present invention provides a process for treating DAF sludge to enable separation into its fat and protein component parts, said process comprising the steps: (a) adjusting the DAF sludge pH to between 2.5 and 4.5; (b) mixing an emulsifying agent into the sludge of step (a) at a concentration of between 0.1 and 3.0% v/v; (c) heating the mixture of step (b) to boiling point; (d) allowing the mixture of step (c) to cool and stand until the fat and protein component parts separate out; and (e) removing each separated component part of step (d).

The component parts of the DAF sludge are separated into 1) a liquid butterfat phase, which is present on the top of an aqueous phase; 2) an aqueous (water) phase, present beneath the butterfat phase; and 3) a protein-rich phase, which is present as a precipitate at the bottom of the aqueous phase.

The liquid butterfat phase can be sold to the tallow industry or into the biodiesel industry, and the protein-rich phase into the livestock food industry or used on the land as a nitrogenous fertilizer.

The present invention is also directed to a fat rich component isolated from DAF sludge by the method of the invention and to a biodiesel fuel comprising the fat rich component of the invention.

The present invention is also directed to a protein rich component isolated from DAF sludge by the method of the invention and to a livestock food product or fertilizer comprising the protein rich component of the invention. The invention is also directed to a use of the protein rich component of the invention in the manufacture of a livestock food product or nitrogenous rich fertilizer.

The term 'comprising' as used in this specification and claims means 'consisting at least in part of, that is to say when interpreting independent claims including that term, the features prefaced by that term in each claim all need to be present but other features can also be present." The invention will now be described in more detail with specific reference to the figures of the accompanying drawings in which: Figure 1 shows a schematic plan of the process of the invention; Figure 2 shows a photograph of the three separation phases of a DAF sludge sample treated by the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the efficient and economically beneficial disposal of DAF sludge produced as a by-product of the dairy industry.

It has surprisingly been found that relatively simple treatment steps can result in excellent separation of DAF sludge into its fat and protein component parts.

The present invention is thus directed to a process for treating DAF sludge to enable separation into its fat and protein component parts, said process comprising the steps: (a) adjusting the DAF sludge pH to below 4.2; (b) mixing an emulsifying agent into the sludge of step (a) at a concentration of between 0.1 and 3.0%. v/v; (c) heating the mixture of step (b) to boiling point; (d) allowing the mixture of step (c) to cool and stand until the protein and fat component parts separate out; and (e) removing each separate component parts of step (d).

Preferably, the pH of the DAF sludge is adjusted to between pH 3.5 and 4.0 in step (a) with mineral acid, such as sulphuric acid, hydrochloric acid, or the like.

A relatively inexpensive commercial hydrophilic non-ionic emulsifier, such as Tween 20, Tween 80 or Orisurf NP9, is then mixed to the pH adjusted DAF sludge of step (a) at a concentration of between 0.5 and 2.5% v/v, preferably at a concentration of between 0.5 and 2.0% v/v, or 0.5 and 1.0% v/v and most preferably at a concentration of 1.0% v/v.

The mixture is then heated in a heating vessel to boiling point either by direct steam injection or by indirect heating. The mixture is held at boiling point for between 1 and 10 minutes, preferably between 2 and 7 minutes, or between 2 and 5 minutes, most preferably for 2 to 4 minutes.

The heating source is then removed from the mixture and the mixture is allowed to cool and stand until the protein and fat component parts separate out. Preferably the mixture is allowed to cool and stand for between 5 and 30 minutes, more preferably for between 5 and 20 minutes, and most preferably for 10 minutes.

After cooling and standing for this period of time the DAF sludge clearly separates into three phases. A fat phase, an aqueous phase and a protein phase. The fat is present in a liquid form on top of the aqueous phase and the protein is present as a preceptate in the bottom of the aqueous phase. There is no mixing of the fat and protein phase so that the present invention provides a surprisingly efficient and cost effective method of separating out the fat or protein components of DAF sludge.

The separate fat and protein components are then removed from the heating vessel.

The fat can be sold to the tallow industry or into biodiesel industries and the protein can be sold to the livestock food industry or can be disposed of onto land as a nitrogenous fertiliser. Thus, making the disposal of DAF sludge by the present method extremely cost effective.

The aqueous (water) phase contains essentially water only (95-98%) and this can be disposed of by spraying onto land/crops etc for irrigation or by pouring into the sewage system without risk of pollution. Some soluble whey protein may be present in the aqueous phase but at very low concentrations that would not require any further treatment for disposal purposes.

A schematic diagram of the process of the present invention is shown in figure 1.

The present invention is also directed to the fat and protein rich components isolated by the method of the invention described above, and to a biodiesel fuel comprising the fat rich component of the invention. The invention is further directed to a livestock food product or fertilizer comprising the protein-rich component of the present invention. This invention is also directed to a use of the protein rich component, produced by the process of the present invention in the manufacture of a livestock food product or a nitrogenous rich fertilizer.

The invention will now be illustrated by specific examples.

EXAMPLE 1 200ml of DAF sludge produced from dairy waste treatment was placed in a heating vessel and acidified using sulphuric acid to reduce the pH to 3.5. Emulsifier (Tween 20) was then added to give a concentration of 1% v/v, and the sludge mixture agitated before heating to boiling point by direct steam injection. The mixture was allowed to boil for 3-5 minutes. Steam injection was then discontinued and the sludge mixture allowed to cool and stand for 10 minutes. After standing for 10 minutes, the sludge had separated into three clear layers. A top layer, or fat-rich layer, containing butterfat and other fats, a middle aqueous layer that was 95-98% water, and a protein-rich layer that had precipitated at the bottom of the aqueous layer. The fat-rich and protein-rich layer were easily separated without contamination of each layer.

Additional examples carried out showed that the DAF sludge did not separate out fully when the pH was below 2.8 or above 5.0 (results not shown). In addition, the DAF sludge did not separate out fully at an emulsifier concentration of below 0.2% v/v or above 3.0% (results not shown).

EXAMPLE 2 200ml of DAF Sludge from cream plant effluent was acidified to pH 3.5, 4.0 or 4.2 using sulphuric acid. The acidified samples were heated using direct or indirect methods as described below. Some samples were tested with and some without a non-ionic detergent (Tween 20) as set out in Table 1 below: Table 1 pH Heating Method Non-Ionic detergent (Tween 20) (1% v/v) Split rating Direct Steam Injection Indirect Microwave 3.5 y - 0.3 3.5 y - 0.4 3.5 y - 0.1 3.5 y y 1.0 4.0 y y 1.0 4.2 y - 0.2 4.2 y - 0.4 4.2 y - 0.1 4.2 y y 1.0 Indirect heating was achieved by heating a beaker containing the DAF Sludge on a hot plate to boiling point. The samples were then allowed to boil for 4 minutes. For direct steam injection, steam was introduced via a 6mm glass tube immersed below the surface of the liquid to boiling, and allowed to boil for 4 minutes. For microwave heating, the sludge was placed in a microwave on high for 5 minutes.

The split rating, ie the degree of separation of the fat, protein and water layers, is based on a ranking system by observations, judging the extent to which fat rises to the surface of the sludge after the particular treatment process. A score of 1.0 represents an excellent split with a large fat layer forming on the top. A score of 0 indicates no separations occurred. An example of a split having a score of 1.0 is pictured in figure 2 which clearly shows the three distinct layers, fat at the top, protein at the bottom and an aqueous layer in the middle.

Results Whilst all of the conditions tested above gave some separation of the three phases of DAF sludge, the addition of 1% v/v non-ionic detergent, in this case Tween 20, resulted in excellent separation at pH 3.5, 4.0 and 4.2. Of the samples that did not include non-ionic detergent, indirect heating gave the best separation, followed by direct steam injection and microwave heating.

EXAMPLE 3 200ml of DAF sludge from cream plant effluent was acidified to pH 3.5 mixed with varying levels of non-ionic detergent (Tween 20) and heated by direct steam injection and boiled for 4 minutes. The samples were then left to cool and separate for 10 minutes. The split scores were then measured, as set out in Table 2, below: Table 2 Non-Ionic Detergent 0.07 0.2 0.37 0.56 0.74 (% v/v) Split Rating 0 0.2 0.1 1.0 1.0 Results In this experiment, a non-ionic detergent level of at least 0.5 was required to give an excellent separation of the fat and protein components of the DAF sludge waste. Whilst there was some separation observed with concentrations of Tween 20 at 0.2% v/v, the level of separation improved with increasing amounts of non-ionic detergent, up to 0.74%.

EXAMPLE 4 200ml of DAF sludge from cream plant effluent or from milk plant effluent (see Table 3, below for properties of each sample) was acidified to pH 3.5 or 3.9 with sulphuric acid and 1% or 2% Tween 20 or 1% Tween 80 non-ionic detergent added. The samples were then heated with direct steam injection (DSI) or by direct heating and boiled for 4 minutes. On cooling the separation of the fat and protein components was measured by split rating as set out in Tables 4 and 5 below: 8 Table 3 Properties of DAF Sludge samples Sample Total Solids (% m/m) Initial pH Fat % (m/m) Protein % (m/m) Cream plant effluent 14.1 4.7 8.9 3.2 Milk plant effluent 18.1 4.0 11.4 4.2 Table 4 Separation trials with cream plant effluent sludge samples pH Detergent Heating Method Split Rating 3.5 Tween 20 1% DSI4 min 1.0 3.9 Tween 20 1% DSI4 min 1.0 3.5 Tween 20 2% DSI 4 min 0.7 3.9 Tween 20 2% DSI 4 min 0.6 3.5 Tween 80 1% DSI 4 min 0.7 3.9 Tween 80 1% DSI 4 min 0.6 3.5 Tween 20 1% Indirect 4 min 1.0 3.9 Tween 20 1% Indirect 4 min 0.8 Table 5 Separation trials with milk plant effluent sludge samples pH Detergent Heating Method Split Rating 3.5 Tween 20 1% DSI 4 min 0.9 3.9 Tween 20 1% DSI 4 min 0.8 3.5 Tween 20 2% DSI 4 min 0.9 3.9 Tween 20 2% DSI 4 min 0.7 3.5 Tween 80 1% DSI 4 min 0 3.9 Tween 80 1% DSI 4 min 0 3.5 Tween 20 1% Indirect 4 min 0.8 3.9 Tween 20 1% Indirect 4 min 0.8 Results The results show that the process of the present invention is successful in separating DAF sludge from more than one source. Both the DAF sludge from cream plant effluent and from milk plant effluent were able to be satisfactorily separated under similar conditions. When Tween 20 was used as the non-ionic detergent at 1% v/v, using DSI or indirect heating at pH 3.5 or 3.9, excellent separation was observed. Tween 20 at 2% v/v gave better separation of both types of effluent at pH 3.5 and Tween 80 only gave satisfactory results for the cream plant effluent. Tween 80 was not able to cause separation of the DAF sludge from the particular milk plant effluent tested.

EXAMPLE 5 100ml of DAF sludge from milk plant effluent and from cheese plant effluent were acidified to pH 3.1,3.5 or 3.9 with sulphuric acid, heated with 1% v/v Tween 20 or 1% v/v Orisurf NP9 using direct steam injection and boiled for 4 minutes. On cooling all samples separated to acceptable standards (ie split rating 0.8-1.0). The fat content of the separated fat layer and percentage fat yield were measured and compared to the fat content of the original sludge samples as set out in Tables 6-8, below: Table 6 Properties of the sludge samples Sample Total solids Initial pH Fat (%m/m) Protein (%m/m) Milk plant effluent 8.2 3.6 4.8 2.7 Cheese plant effluent 16.2 6.2 7.4 3.3 Table 7 Separated fat data Average fat (g) ± SD Sample pH 3.10 pH 3.50 pH 3.9 Milk plant effluent (Tween 20) 4.24 ± 0.4 4.22 ± 0.21 1.31 ±0.91 Cheese plant effluent (Tween 20) 2.86 ±0.86 3.11 ±0.45 3.71 ±1.47 Milk plant effluent (Orisurf NP9) 2.22 ± 0.74 2.87 ± 0.27 2.63 ± 0.84 n = 6 Table 8 Percentage yield of separated fat Average yield % ± SD Sample pH 3.10 pH 3.5 pH 3.9 Milk plant effluent (Tween 20) 73.18± 11.12 66.57 ± 17.55 Cheese plant effluent (Tween 20) .54 ± 16.41 32.26 ± 26.55 .96 ± 11.84 Milk plant effluent (Orisurf NP9) 48.69 ±8.15 56.67 ±5.30 59.05 ± 13.08 11 = 6 Results The best separation was achieved using milk plant effluent and Tween 20 at a pH of 3.10 where an average fat yield of 73% was achieved. Tween 20 was more effective at separating fat than Orisurf NP9 and the milk plant effluent separated better than the cheese plant effluent. These results confirm that the process of the present invention gives a good separation and recovery of fat from waste dairy effluents. 11 Conclusions The results of the aforementioned examples provide evidence of the effectiveness of the present invention in separating the protein and fat components of waste dairy effluents. The separated fat and protein components can easily be recovered for use in other industries such as biodiesel (for fat) and livestock feeds (for proteins) etc. The results of fat yield in particular suggest that this process could be scaled up to an industrial scale for the cost effective recovery of fat from dairy waste effluents.

It will be appreciated by a skilled worker that the composition and properties of dairy plant effluents, and the resulting DAF sludge will vary from plant to plant and from day to day in any one plant. The optimum pH and emulsifier concentration for each waste stream will thus have to be tested prior to large scale separation using the process of the present invention.

It is not the intention to limit the scope of the invention to the abovementioned examples only. As would be appreciated by a skilled person in the art, many variations are possible without departing from the scope of the invention as recited in the appended claims.

INDUSTRIAL APPLICATION The present invention provides a process for treating DAF sludge, a waste by-product of the dairy industry which is difficult and expensive to dispose of, into value added products. Specifically the valuable components of the DAF sludge, such as protein and fat, can be efficiently and cost-effectively separated and recovered. The fat can be used in the tallow and/or biodiesel industries and the protein can be used in the livestock feed and/or fertiliser industries. 12

Claims (28)

WHAT WE CLAIM IS:

1. A process for treating DAF sludge to enable separation into its fat and protein component parts, said process comprising the steps: (a) adjusting the DAF sludge pH to below 4.2; (b) mixing an emulsifying agent into the sludge of step (a) at a concentration of between 0.1 and 3.0%. v/v; (c) heating the mixture of step (b) to boiling point; (d) allowing the mixture of step (c) to cool and stand until the protein and fat component parts separate out; and (e) removing each separate component parts of step (d).

2. A process as claimed in claim 1, wherein the pH of the DAF sludge is adjusted in step (a) to between pH 3.5 and 4.0.

3. A process as claimed in claim 1 or 2, wherein the pH of the DAF sludge is adjusted in step (a) with a mineral acid.

4. A process as claimed in claim 3, wherein the mineral acid is selected from sulphuric acid or hydrochloric acid.

5. A process as claimed in claim 1, wherein the emulsifying agent is a hydrophilic non-ionic emulsifier.

6. A process as claimed in claim 5, wherein the emulsifying agent is Tween 20.

7. A process as claimed in claim 1, wherein the emulsifying agent is mixed in step (b) at a concentration of between 0.5 and 2.5% v/v.

8. A process as claimed in claim 7, wherein the emulsifying agent is present at a concentration of between 0.5 and 2.0% v/v.

9. A process as claimed in claim 8, wherein the emulsifying agent is present at a concentration of 1.0% v/v. 13

10. A process as claimed in claim 1, wherein the mixture is heated at step (c) by direct steam injection or by indirect heating.

11. A process as claimed in claim 1, wherein the mixture is held at boiling point for between 1 and 10 minutes.

12. A process as claimed in claim 11, wherein the mixture is held at boiling point for between 2 and 7 minutes.

13. A process as claimed in claim 12, wherein the mixture is held at boiling point for 3 to 5 minutes.

14. A process as claimed in claim 1, wherein the mixture of step (d) is allowed to cool and stand for between 5 and 30 minutes.

15. A process as claimed in claim 14, wherein the mixture is allowed to cool and stand for between 5 and 20 minutes.

16. A process as claimed in claim 15, wherein the mixture is allowed to cool and stand for 10 minutes.

17. A fat rich component isolated by the method of any one of claims 1-16.

18. A protein rich component isolated by the method of any one of claims 1-16.

19. A biodiesel fuel comprising the fat rich component of claim 17.

20. A livestock food product or fertilizer comprising the protein-rich component of claim 18.

21. A use of the protein rich component of claim 18 in the manufacture of a livestock food product or a nitrogenous rich fertilizer. 14

22. A use of the fat rich component of claim 17 in the manufacture of a biodiesel fuel.

23. A process as claimed in claim 1 substantially as herein described or exemplified and with or without reference to the accompanying drawings.

24. A fat rich component as claimed in claim 17 substantially as herein described with reference to any example thereof.

25. A protein rich component as claimed in claim 18 substantially as herein described with reference to any example thereof.

26. A biodiesel fuel as claimed in claim 19 substantially as herein described with reference to any example thereof.

27. A livestock food product as claimed in claim 20 substantially as herein described with reference to any example thereof.

28. A use as claimed in claim 21 or 22 substantially as herein described with reference to any example thereof. INTELLECTUAL PROPERTY OFFICE OF N.Z. 16 JUL 2007 r e ceived 15