GB1602459A - Process for the treatment of food and fermentation effluents - Google Patents

Description

(54) PROCESS FOR THE TREATMENT OF FOOD AND FERMENTATION EFFLUENTS (71) We, THE DISTILLERS COMPANY LIMITED, a British Company, of 12 Torphichen Street, Edinburgh EH3 8YT, Scotland, 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:- This invention relates to a method of removing the suspended solids in a fermentation effluent or food effluent.

The effluent from a fermentation process, especially from a cereal fermentation process such as the effluent from a whisky distillation, is an aqueous medium containing dissolved and insoluble, generally suspended, biologically active solids so that it has a high BOD value. Depending on the origin of the effluent some of the coarser undissolved solids (supergrains) may be removed, by a simple filtration process, as a wet cake which can be used as an animal feed or can be further processed. Much of the insoluble solids cannot, however, be so removed and where discharge of the high BOD liquid is commercially unacceptable it is conventional to recover the total solids as dry powder, pellets or cake for animal feeds by evaporation. Such evaporation processes involve high energy costs.

Thus many effluents from fermentation processes may include a substantial proportion of very fine suspended solids, for example, suspended solids below 40 microns in size, typically bacterial cells, yeast cells and other debris with particle size below 20 microns. A significant proportion. or in some instances substantially all, of these fine suspended solids may be proteinaceous in nature. Their removal from the effluent is difficult to achieve by filtration but is desirable both as a way of reducing the biological oxygen demand of the effluent and as a way of producing an animal feedstuff.

It is well known that micro-organisms can be grown in a medium containing biologically active material and then harvested, thus reducing the BOD of that medium. Thus Church et al in Food Technology February 1973 page 36 describe growing fungi in corn and pea waste so as to convert dissolved and suspended organic matter into a mycelium.

Fungal growth was conducted for periods of 16 hours and more. Similarly Church et al in Developments in Industrial Microbiology volume 13 1972 page 30 describe growing fungi in pea waste for more than 18 hours to convert dissolved and suspended'matter into mycelium.

Hang et al in Applied Microbiology 1975 page 879 describes growing fungus in spent grain liquor, for example one containing 336 mg/l suspended solids, for periods in excess of 48 hours and similarly Updegraff in Developments in Industrial Microbiology volume 14 1972 page 317 describe growing fungi in spent wash from a rum distillery or in coffee waste again for prolonged periods, for example growth in coffee waste is conducted for periods of above 2 days. In all these processes it seems to have been accepted to be desirable to convert a substantial part of the suspended solids into fungal mycelium or into a soluble material and the fungal growth periods have therefore been chosen to be sufficiently long to permit this to occur. These long growth periods, which are essential for operating any of the described processes for dealing with wastes containing suspended solids, seriously reduce the viability of the process from a commercial point of view since it is essential in effluent treatment to have as rapid throughput as possible.

The invention is based on the realisation that whereas in the prior art attempts were always made to reduce the suspended solids content by biological means this is wholly unnecessary and that the suspended solids can be removed simply by mechanical means after appropriate fungal growth.

Thus a method according to the invention of reducing suspended solids in a fermentation or food effluent comprises growing a fungus in the effluent to produce a liquor containing substantially all the suspended solids and fungal mycelium and then filtering this liquor through a filter that retains substantially all the fungal mycelium and suspended solids but would not have retained substantially all the suspended solids without the fungal growth. Thus in the invention the fungal growth conditions are such that there is no significant reduction in suspended solids content as a result of the growth of fungal mycelium but the solids are then removed by simple filtration in combination with the fungal mycelium. It is easily possible so to select the fungus and conduct the growth that the fungal mycelium promotes filtration by entrapping the suspended solids and thus holding them in position as the filtrate passes through the filter element.

The invention is of particular value for reducing the content of suspended solids below 40 microns in size and generally is conducted by growing the fungus for periods of up to 12 hours as a maxiumum. The preferred period is from 3 to 8 hours.

The solids collected by the filtration consist of the fungal mycelium and the initial suspended solids, these being substantially unchanged and retaining their initial nutritional value.

Preferably the method of the invention results in more than 50% of the solids remaining unchanged in this manner, for instance more than 75% and preferably it results in at least 50% and preferably at least 75%, of the initial suspended solids being removed by the final filtration step.

The effect of the fungal growth is not only to enmesh the suspended solids but also to reduce the BOD of the liquor, and thus the liquor resulting from the filtration can more readily be discharged, since it will have lower suspended solids and lower BOD or can be subjected to further treatment, for example a further fungal growth step according to the invention or evaporation or other conventional treatment.

The food or fermentation effluent treated according to the invention may be one containing residual dispersed starch other carbohydrates or readily metabolisable substrates such as glycerol or lactic acid. A typical medium would be the effluent from a food or beverage manufacturing process, preferably the effluent from a cereal fermentation. The cereal fermentation is preferably of maize or barley. Thus the effluent may be the effluent from the production of gin spirit or other spirits but the effluent from whisky distillation is particularly suitable.

The effluent from a malt whisky distillery is pot ale, while the effluent from a grain whisky distillery is spent wash. In general the effluent will contain from 0.4 to 1.5% suspended solids, usually from 0.6 to 1.3%, and will contain from 1.0 to 4.0% dissolved biologically active solids, usually from 1.5 to 3.0%. A typical pot ale contains 0.6% suspended solids and 3.0% dissolved solids, whilst a typical spent wash contains 1.3% suspended solids and 1.5% dissolved solids.

The action of the fungus is to form a network to produce readily filterable insoluble solids e.g. by agglomerating or otherwise building up the average particle size of the insoluble solids to a readily filterable level. It is therefore preferred to use a filamentous fungus that has the property of absorbing and/or enmeshing small particles.

It may be desirable with some effluents to further flocculate the solids (both the initial solids and the fungal mycelium) by the use of appropriate chemical flocculating agents that are acceptable in animal feeds. These may be added prior to or during or after the growth of the fungus.

The filtration step may be conducted using a suitable filter element. Elements which pass only particles below 40 microns may be used, but coarser mesh sizes are generally preferred, however, typically up to 500 microns or even 1 millimetre in size. A particularly suitable mesh size is 250 microns. Any suitable filter element may be used including cloth filters and wedge wire screens. Thus the sophisticated and difficult techniques such as are conventionally used to harvest microbial cells are not needed in this invention.

The solids separated by the filtration step may for example be pressed to a dry matter of up to 40% and then dried to give a product which may be used as an animal feedstuff in the same way as the residue currently obtained by evaporation of the effluent from a cereal fermentation is used. The inclusion of the fungus further enhances the nutritional value of the product per unit weight due to an increase in the relative contents of protein and fat.

In a method for treating the effluent from a ceral fermentation as described in this invention it is economically desirable to operate non-aseptically. Sterilization of the medium and prevention of recontamination is expensive and could be uneconomic in an effluent process producing animal feed. It is possible to maintain the enviroment in the fermenter under conditions of pH and temperature such that there is substantial growth of no contaminating organism. Suitable nonaseptic conditions which will control the growth of contaminating micro-organisms, include a pH of below 4 and/or a temperature above 40"C, preferably a pH of below 3.5, e.g. 3.0 to 3.5 at a temperature of for instance 25 to 30"C or a pH of 3.5 to 4.0 at a temperature of above 40"C, e.g. 45q7 C.

Under these conditions only the inoculated organisms, selected for their ability to grow rapidly in the particular effluent under the defined conditions of pH and temperature, will grow readily and normally any contaminating organism will not compete effectively.

Where it is desirable to achieve a final BOD lower than can be achieved with one fungal strain then the fermentation can be inoculated with a second organism adapted to the physical conditions of the fermenter.

For example a yeast may be used along with a fungus, both being capable of growth at a temperature of 25 to 30"C at a pH below 3.5, e.g. 3.0 to 3.5 or at a temperature above 40"C, e.g. 45 to 48"C and at a pH below 4.0, e.g. 3.5 to 4.0, these conditions being such that when the selected organisms are grown in pot ale, spent wash, other cereal fermentation effluent, or in fact any suitable aqueous culture medium, there will be substantially no growth of other micro-organisms.

Thus a preferred process according to the invention comprises filtering pot ale or spent wash to remove large particles such as supergrains, growing a filamentous fungus, alone or with a yeast, under non-aseptic conditions in the medium at a pH below 4.0 or a temperature above 40"C whereby there is no substantial growth of any other organism in the medium, and filtering the product from the medium using a 40 micron or larger, preferably a 250 micron, 500 micron or 1 millimetre aperture filter.

Fungi suitable for use in the methods of the invention can be obtained by routine techniques. Suitable fungi include Aspergillus oryzae, A. fumigatus, A. niger, Trichoderma viride, Fusarium semitectum and Geotrichum candidum. A particularly useful fungus is a strain of Aspergillus fumigatus that will grow at a pH below 4.0 and at a temperature above 40 C. Aspergillus fumigatus is a commonly occurring fungus that can readily be found in a wide variety of decaying vegetable matter and isolated by inoculation and incubation at a temperature above 40"C on a medium at a pH below 4.0 and containing the appropriate effluent. Routine techniques, well known to those skilled in the art, are used to produce variants and mutants and selection techniques applied to these strains will isolate those which will perform acceptably, operating optimally at a pH below 4.0, preferably between pH 3.5 and pH 4.0 and at a temperature above 40"C, preferably between 45 and 47"C. Although it is not essential it is preferred that an asporogenous or sparsely sporing mutant is obtained.

Where lower final BOD is desirable, as outlined above, a suitable yeast to use in the method is one capable of growth above 40"C, preferably at 45 to 47"C and at a pH below 4.0, preferably at pH 3.5 to 4.0, particularly suitable is a member of the genus Candida.

Such a yeast is commonly present in spent wash contaminated by distillery plant, from where it may be isolated by routine techniques.

A strain of Aspergillus fumigatus and a thermophilic yeast of the Genus Candida that will grow rapidly under the above conditions, preferably pH 3.5 to 4.0 and a temperature of 45 to 47"C, are very useful in the invention when grown in spent wash under these conditions. Thus they grow and rapidly utilise dissolved biologically active solids while no substantial growth of any other micro-organism occurs. Pot ale may be too concentrated for optimum growth of these strains but satisfactory results can be achieved by dilution of the pot ale, for example so that its dissolved solids content is reduced from, say 3% to 1.5%. Thus the selected strains grow best in a medium containing less than 2% dissolved biologically active solids and which has a pH of 3.5 to 4.0 and a temperature of 45 to 47"C.

Another filamentous fungus that is particularly useful in this invention is a strain of Geotrichum candidum. Some pot ale and spent wash samples contain Geotrichum candidum and by selective cultivation under conditions of pH below 3.5 and a temperature of 30"C, using a medium based on spent wash or pot ale, one can obtain a strain suitable for use in the methods described. It is also possible to grow a yeast at the same conditions of pH and temperature, namely below pH 3.5 and a temperature of 30'C, and a yeast suitable for growth at these conditions is a strain of Candida utilis.

The fungus and, where appropriate, the yeast, may be grown in the invention in a fermenter, or a series of fermenters, under aerobic conditions. A suitable method of aeration is by the use of an air lift fermenter.

The growth may be batch but is preferably continuous. Particularly in some distillery effluents the growth of the fungus first utilises the lactic acid present in the medium and then the glycerol, and for these effluents it is preferable to use two fermenters in series.

It is important that the feed rate of effluent to the first stage is so rapid that the lactic acid is never completely utilised in this stage. Rapid growth of the fungus occurs in the first stage and if the lactic acid is depleted a lag occurs in the growth resulting in a wash out of the culture. The overflow from the first fermenter passes into the second fermenter and the residual lactic acid and glycerol are utilised in the second stage.

By the use of one, or with some effluents two, fermenters it is relatively easy to reduce the biological oxygen demand of the aqueous medium from an initial value of around 20,000 mg./litre to a final value of around 6,000 and by providing a further fermenter the final value can be reduced to around 2,000 mg./litre or less. If the filtrate from the final filtration has an acceptably low BOD value it may be discharged. If not it may be treated further by conventional means such as biological tower treatment or it may be subjected to evaporation to produce a solid that itself can be used as an animal feedstuff either alone or after admixture with the solid residue obtained in the filtration.

A further advantage of the invention is that the removal of the glycerol reduces the viscosity and/or stickiness of the residue and that this, along with the insoluble solids removal, allows easier evaporation to a higher dry matter and results in a syrup from the evaporation which is easier to handle and to dry.

The process is best conducted continuously and since the supply of the aqueous medium that is to be treated may be discontinuous it may be desirable to provide a suitable system of storage tanks prior to the fermentation stage. A suitable flow sheet is shown in the accompanying drawing. In this the aqueous medium to be treated is introduced by pipe 20 into a storage tank 1 and from there it is pumped to a fermenter 4A, optionally via the cooler 3A or the heater 3B.

The feed may come direct into the fermenter, optionally through the heater or the cooler, by-passing the tanks 1 and 2. There may be two fermenters 4A and 4B in series. The or each fermenter is an air-lift fermenter and air is blow into the bottom and exits through an air-treatment device 5 to remove any fungal spores possibly present in the effluent gases.

It may be desirable to add an anti-foam agent, such as a silicone, into the fermenter to reduce foaming, although spent wash does not usually require this as oil inherent in it reduces foaming. Dosing systems 7, 8 and 9 may be coupled with the fermenters and with the feed of aqueous medium or with the feed of water for dosing into the fermenter acid, alkali or nutrient. The nutrients that have to be added will depend on the nature of the initial aqueous medium. Nitrogen-providing nutrient is generally needed but phosphate is unnecessary with effluent from cereal fermentations.

When two stages are being used the overflow from the first fermenter 4A passes into a second fermenter 4B. Normally the liquid would have an average residence time of 3 hours in each fermentation vessel, but this would vary depending upon the effluent being treated.

The liquor resulting from the fermentation stages passes to a settling tank 10 from which the clear supernatant liquid may pass through pipe 21 to a drain whilst the remainder is pumped to a filtration system 12, often via a storage tank 11. The filtration system may be a simple drainage filter or a wedge-wire screen. For example it can merely comprise a cloth, drum or cloth band filter having a filter pore size of 40 microns or larger. Preferably it will be a filter or screen having an aperture size of 250 microns, 500 microns or 1 millimetre. The insoluble solids may then pass to a further filtration stage, 13, for example a filter press or vacuum filter.

Pressed supergrains or other solids that may have been removed from the effluent before it was fed via pipe 20 into the apparatus may be introduced before or after this stage by duct 25. The liquor separated at this stage may be recycled to the process via pipe 22 or may be taken off through pipe 23 to an evaporation stage or to a drain.

The solids from 12 and/or 13 are passed to a drier 14 which may result in the dry matter content being raised from, say, 40% to 90%.

The drier may be heated by steam through line 24. Air emerging from the drier may be treated at 15 to filter out any spores which could possibly be present. The dried solids may then be stored at 16 prior to being prepared for use as an animal feedstuff, for example by pelleting or bagging into sacks and further stored at 19 whilst air from the preparation stage is treated at 18 to remove any dust.

Six examples are given of the use of this method for the treatment of grain distillery spent wash.

Example 1 Spent wash having a BOD of 20,000 mg./litre was subjected to a process using apparatus broadly as described above, with a single fermentation stage. It was first screened to remove the supergrains, this representing about half the undissolved sol ids present, but no other pretreatment was applied to it. It was then passed into the fermenter which was maintained at a tem perature of 44 to47"C and at a pH 3.5 to 4.0, the latter being maintained by adjusting the supply of acid through 7. The nitrogenous nutrient added was ammonium sulphate at a rate of 0.7 g./litre and a trace element solution was added to give final concentra tions of MgSO4 2.0 mg./l.; FeSO4 0.22 mg./l.; ZnSO4 0.23 mg./l.; CaCl2 0.4 mg./l.; MnSO4 16.2 mg./l. and K2SO4 20 mg./l. Aspergillus fumigatus was grown in the fermenter and after a residence time of 6 hours the liquid was subjected to filtration through a 250 micron filter cloth and then pressed to produce a cake containing at least 30% dry matter. This cake contained about 70% of the original dry matter content of the liquid fed to the fermenter. The filtrate was a relatively clear liquid having a BOD of 6,000 mg./litre, and contained 0.1% suspended solids, a 94% reduction from the level of suspended solids in the starting material. The filter cake could be further dried and then pelletted ready for use as an animal feed. The product contained 47% crude protein, and was successfully fed to poultry as 10% of their diet.

Example 2 Spent wash having a BOD of 20,000 mg./litre was treated as described in Example 1 excepting that the residence time in the fermenter was 3.5 hours and the overflow from this fermenter passed into a second fermenter. No further salts addition was made to the second fermenter, although acid addition was necessary to maintain the pH at pH 3.5 to 4.0. The residence time in the second fermenter was also 3.5 hours. The overflow from this second fermenter was filtered as described in the first example. The BOD of the filtrate was 5800 mg./litre. As in the first example the filter cake could be further dried and was then suitable for use as an animal feed.

Example 3 Spent wash having a BOD of 20,000 mg/litre was treated as described in example one excepting that the fermenter was inoculated with both aspergillusfumigatus and the thermophilic yeast. Salts addition and conditions of temperature and pH were as in example one. The residence time in the fermenter was 3.9 hours and the overflow was filtered as described in example one. The BOD of the filtrate was 6500 mg./litre. As in the first example the filter cake could be further dried and was then suitable for use as an animal feed.

Example 4 Spent wash having a BOD of 20,000 mg/litre was treated as described in example two excepting that the fermenters were inoculated with Aspergillus fumigatus and the thermophilic yeast. Salts additions and conditions of temperature and pH were as in example one. The residence time in the first fermenter was 3.1 hours and the overflow passed into a second fermenter with a residence time also of 3.1 hours. No further salts addition was made to the second fermenter although acid addition was necessary to maintain the pH at 3.5 to 4.0. The overflow from the second fermenter was filtered as described in example one and the BOD of the filtrate was 4,800 mg/litre. As in the first example the filter cake could be further dried and was suitable for use as an animal feed.

Example 5 Spent wash having a BOD of 20,000 mg./litre was treated in a single air lift fermenter as described in the invention. The pH was maintained between pH 3.0 and 3.5 and the temperature at 30"C. The fermenter was inoculated with Geotrichum candidum.

The nitrogeneous nutrient added was Ammonium sulphate at a rate of 1.0 g./litre and a trace element solution as in example 1.

After a residence time of 5 hours the overflow was passed over -a 250 micron screen to separate the insoluble solids. The solid was pressed to 30% dry matter and the filtrate was evaporated to a thick liquid of 52% dry matter. These could both be further dried for use as an animal feed.

Example 6 Spent wash having a BOD of 14,000 mg./litre was treated as described in example 5 excepting that the fermenter was inoculated with a mixture of Geotrichum candidum and Candida utilis. Salts additions were as in example 5 and the residence time was 5 hours. The overflow was filtered through a 250 micron filter cloth and then pressed to produce a cake of at least 30% dry matter.

The filtrate was a relatively clear liquid having a BOD of 5200 mg./litre. The filter cake could be further dried for use as an animal feed.

WHAT WE CLAIM IS: 1. A method of reducing suspended solids in a food or fermentation effluent comprising growing a fungus in the effluent to produce a liquor containing substantially all the suspended solids together with fungal mycelium and filtering the liquor through a filter that retains substantially all the fungal mycelium and suspended solids but would not have retained substantially all the suspended solids without the fungal mycelium.

2. A method of reducing the content of suspended solids below 40 microns in size of a food or fermentation effluent comprising growing of fungus in the effluent for up to 12 hours to produce a liquor containing substantially all the said suspended solids together with fungal mycelium, and filtering the liquor through a filter greater than 40 microns in size and thereby removing substantially all the suspended solids and mycelium.

3. A method according to claim 1 or claim 2 in which the fungus is grown under non aseptic conditions at a pH below 4 and/or a temperature above 40or.

4. A method according to any preceding claim in which the fungus is grown under conditions such that a filamentary mycelium is formed.

5. A method according to any preceding claim in which the content of suspended solids in the effluent at the start of the fungal growth is at least 0.6%.

6. A method according to any preceding claim in which the fermentation effluent is pot ale or spent wash.

7. A method according to claim 6 in which the fungus is grown in pot ale or spent wash from which supergrains have been removed by filtration.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. 47% crude protein, and was successfully fed to poultry as 10% of their diet. Example 2 Spent wash having a BOD of 20,000 mg./litre was treated as described in Example 1 excepting that the residence time in the fermenter was 3.5 hours and the overflow from this fermenter passed into a second fermenter. No further salts addition was made to the second fermenter, although acid addition was necessary to maintain the pH at pH 3.5 to 4.0. The residence time in the second fermenter was also 3.5 hours. The overflow from this second fermenter was filtered as described in the first example. The BOD of the filtrate was 5800 mg./litre. As in the first example the filter cake could be further dried and was then suitable for use as an animal feed. Example 3 Spent wash having a BOD of 20,000 mg/litre was treated as described in example one excepting that the fermenter was inoculated with both aspergillusfumigatus and the thermophilic yeast. Salts addition and conditions of temperature and pH were as in example one. The residence time in the fermenter was 3.9 hours and the overflow was filtered as described in example one. The BOD of the filtrate was 6500 mg./litre. As in the first example the filter cake could be further dried and was then suitable for use as an animal feed. Example 4 Spent wash having a BOD of 20,000 mg/litre was treated as described in example two excepting that the fermenters were inoculated with Aspergillus fumigatus and the thermophilic yeast. Salts additions and conditions of temperature and pH were as in example one. The residence time in the first fermenter was 3.1 hours and the overflow passed into a second fermenter with a residence time also of 3.1 hours. No further salts addition was made to the second fermenter although acid addition was necessary to maintain the pH at 3.5 to 4.0. The overflow from the second fermenter was filtered as described in example one and the BOD of the filtrate was 4,800 mg/litre. As in the first example the filter cake could be further dried and was suitable for use as an animal feed. Example 5 Spent wash having a BOD of 20,000 mg./litre was treated in a single air lift fermenter as described in the invention. The pH was maintained between pH 3.0 and 3.5 and the temperature at 30"C. The fermenter was inoculated with Geotrichum candidum. The nitrogeneous nutrient added was Ammonium sulphate at a rate of 1.0 g./litre and a trace element solution as in example 1. After a residence time of 5 hours the overflow was passed over -a 250 micron screen to separate the insoluble solids. The solid was pressed to 30% dry matter and the filtrate was evaporated to a thick liquid of 52% dry matter. These could both be further dried for use as an animal feed. Example 6 Spent wash having a BOD of 14,000 mg./litre was treated as described in example 5 excepting that the fermenter was inoculated with a mixture of Geotrichum candidum and Candida utilis. Salts additions were as in example 5 and the residence time was 5 hours. The overflow was filtered through a 250 micron filter cloth and then pressed to produce a cake of at least 30% dry matter. The filtrate was a relatively clear liquid having a BOD of 5200 mg./litre. The filter cake could be further dried for use as an animal feed. WHAT WE CLAIM IS:

1. A method of reducing suspended solids in a food or fermentation effluent comprising growing a fungus in the effluent to produce a liquor containing substantially all the suspended solids together with fungal mycelium and filtering the liquor through a filter that retains substantially all the fungal mycelium and suspended solids but would not have retained substantially all the suspended solids without the fungal mycelium.

2. A method of reducing the content of suspended solids below 40 microns in size of a food or fermentation effluent comprising growing of fungus in the effluent for up to 12 hours to produce a liquor containing substantially all the said suspended solids together with fungal mycelium, and filtering the liquor through a filter greater than 40 microns in size and thereby removing substantially all the suspended solids and mycelium.

3. A method according to claim 1 or claim 2 in which the fungus is grown under non aseptic conditions at a pH below 4 and/or a temperature above 40or.

4. A method according to any preceding claim in which the fungus is grown under conditions such that a filamentary mycelium is formed.

5. A method according to any preceding claim in which the content of suspended solids in the effluent at the start of the fungal growth is at least 0.6%.

6. A method according to any preceding claim in which the fermentation effluent is pot ale or spent wash.

7. A method according to claim 6 in which the fungus is grown in pot ale or spent wash from which supergrains have been removed by filtration.

8. A method according to any preceding

claim in which the mycelium and suspended solids are removed by filtration through a filter of 250 microns or more.

9. A method according to any preceding claim in which the fungal growth is conducted for from 3 to 8 hours.

10. A method according to claim 1 or claim 2 in which the effluent is a fermentation effluent containing suspended yeast particles.

11. A method according to claim 1 substantially as herein described with reference to any of the examples.

12. An animal feedstuff comprising the filter residue obtained in a method according to any preceding claim.