GB2408045A

GB2408045A - A method for preparing a seaweed based soil enriching composition

Info

Publication number: GB2408045A
Application number: GB0419861A
Authority: GB
Inventors: Jeremiah John O'mahony; John Paul Mullins; Henry Joseph Lyons; William John Chambers
Original assignee: ALGATECH Ltd
Current assignee: ALGATECH Ltd
Priority date: 2003-11-12
Filing date: 2004-09-07
Publication date: 2005-05-18
Anticipated expiration: 2024-09-07
Also published as: GB2408045B; GB0419861D0

Abstract

A method for preparing a seaweed-based soil enriching composition comprises soaking fresh seaweed in a dilute phosphoric acid aqueous solution, and then subsequently rinsing the seaweed in fresh water. The phosphoric acid solution removes phytotoxic polyphenol compounds from the seaweed. Preferably the seaweed is chopped to a maximum dimension of approximately 12mm and is soaked in the dilute phosphoric acid solution for a time period of approximately 20 minutes at room temperature. The rinsed seaweed is then subject to an alkaline extraction to extract humic acids in a liquid slurry. The liquid slurry is filtered to provide a liquid plant growth promoting composition and the remaining sludge is mixed with seaweed meal to provide a soil conditioning composition.

Description

"A method for preparing a seaweed based soil enriching composition" The

present invention relates to a method for preparing a seaweed based soil enriching composition, which may be in the form of a plant growth promoting s composition and a soil conditioning composition.

Seaweed based soil enriching compositions have many desirable characteristics for use in agriculture and horticulture, and in particular, for promoting plant growth.

Seaweed itself has for many years been known to contain compounds which are particularly desirable for use as plant growth promoters. Originally seaweed was only suitable for use in coastal areas as a soil enriching composition, since transportation costs, and the possibility of the plant growth promotion properties of the seaweed deteriorating during transportation tended to render it inefficient for inland use. However, more recently advances have been made in the processing of seaweed which permits the extraction of substances which are known to have good plant growth promoting properties. This, thus, permits seaweed based soil enriching compositions to be produced in concentrated form which renders the compositions to be particularly suitable for transportation, and thus, use in inland areas away from coastal areas.

However, as well as comprising substances which have plant growth promoting properties, seaweed is also known to comprise phytotoxic compounds which inhibit plant growth. Because of this, in general, it is necessary to significantly dilute the concentration of the seaweed based soil enriching compositions, in order to minimise the plant growth inhibiting properties of the phytotoxic compounds. Dilution of up to x300 is required for some concentrated forms of seaweed soil enriching compositions. This is undesirable, since as well as diluting the effect of the phytotoxic compounds, the plant growth promoting effect of the plant growth s promoting substances are also diluted, thus significantly limiting the plant growth promoting properties of the diluted compositions.

There is therefore a need for a method for preparing a seaweed based soil enriching composition which overcomes these problems.

The present invention is directed towards providing such a method, and the invention is also directed towards providing a seaweed based soil enriching composition in which the phytotoxic compound content is minimised.

According to the invention there is provided a method for preparing a seaweed based soil enriching composition comprising the steps of soaking untreated seaweed in a dilute phosphoric acid solution for removing polyphenol compounds from the seaweed, and subsequently rinsing the seaweed with water.

In one embodiment of the invention the rinsing of the seaweed is carried out with fresh water.

In another embodiment of the invention the seaweed is chopped prior to soaking.

Preferably, the seaweed is chopped into pieces of maximum dimension not exceeding 30mm. Advantageously, the seaweed is chopped into pieces of maximum dimension in the range of 5mm to 20mm. Ideally, the seaweed is chopped into pieces of maximum dimension in the range of 10mm to 12mm.

s In one embodiment of the invention the seaweed is soaked in the dilute phosphoric acid solution for a time period in the range of 5 minutes to 60 minutes. Preferably, the seaweed is soaked in the dilute phosphoric acid solution for a time period in the range of 10 minutes to 45 minutes. Advantageously, the seaweed is soaked in the dilute phosphoric acid solution for a time period of approximately 20 minutes.

In another embodiment of the invention the dilute phosphoric acid solution is an aqueous solution, and contains phosphoric acid in an amount in the range of 5% volume to 12% volume of the aqueous solution. Preferably, the dilute phosphoric acid aqueous solution contains phosphoric acid in an amount in the range of 7% volume to 11% volume of the aqueous solution. Advantageously, the dilute phosphoric acid aqueous solution contains phosphoric acid in an amount of approximately 10% volume of the aqueous solution. Ideally, the dilute phosphoric acid solution is at approximately room temperature.

In another embodiment of the invention the rinsed seaweed is subjected to an alkaline extraction step for extracting humic acid substances therefrom, and a liquid slurry resulting from the alkaline extraction step which contains the humic acid substances is subjected to a separating step for separating the liquid slurry into a liquid and a sludge, the liquid containing the humic acid substances and forming the soil enriching composition as a plant growth promoting composition in liquid form.

In a further embodiment of the invention the alkaline extraction step is carried out at a temperature not less than 140 C. Preferably, the alkaline extraction step is carried out at a temperature in the range of 140 C to 160 C.

In one embodiment of the invention the alkaline extraction step is carried out at a pressure of at least 3 bar. Preferably, the alkaline extraction step is carried out at a pressure in the range of 3 bar to 6 bar. Advantageously, the alkaline extraction step lo is carried out at a pressure of approximately 4 bar.

In another embodiment of the invention the alkaline extraction step is carried out for a time period of at least 4 hours. Preferably, the alkaline extraction step is carried out for a time period in the range of 4 hours to 10 hours.

In another embodiment of the invention the sludge resulting from the alkaline extraction step is mixed with seaweed meal to form the soil enriching composition as a soil conditioning composition.

In a further embodiment of the invention the sludge is mixed with the seaweed meal in an amount 20% weight to 35% weight of the seaweed meal.

In one embodiment of the invention the seaweed meal is dried to a moisture content in the range of 7% to 11% prior to mixing with the sludge.

In another embodiment of the invention the seaweed meal was prepared from chopped seaweed.

s Preferably, the seaweed is fresh seaweed.

In one embodiment of the invention the seaweed is subjected to soaking in the dilute phosphoric acid solution within 1 hour to 48 hours of being harvested. Preferably, the seaweed is subjected to soaking in the dilute phosphoric acid solution within 2 hours to 6 hours of being harvested. Advantageously, the seaweed is subjected to soaking in the dilute phosphoric acid solution within approximately 3 hours of being harvested.

In another embodiment of the invention the seaweed is selected from any one or 1 S more of the following seaweeds: Ascophyllum nodosum, Fucus vesiculosus, Fucus serrates, Laminaria digitata, and Laminaria hyperborea.

Additionally the invention provides a seaweed based soil enriching composition prepared according to the method according to the invention.

In one embodiment of the invention the seaweed based soil enriching composition is a plant growth promoting composition in liquid form.

In another embodiment of the invention the seaweed based soil enriching composition is in liquid form.

In a further embodiment of the invention the seaweed based soil enriching composition is a soil conditioning composition.

In a still further embodiment of the invention the seaweed based soil enriching composition is in granular form.

The invention will be more clearly understood from the following description of the following non-limiting examples of preferred seaweed based soil enriching compositions prepared by methods according to the invention.

In the following examples two types of soil enriching compositions according to the invention were prepared from fresh seaweed harvested from the Atlantic shoreline along the Kerry coast. One of the soil enriching compositions was a plant growth promoting composition and was prepared in liquid form, and the other soil enriching composition was a soil conditioning composition and was prepared in granular form.

In each and every example the fresh untreated seaweed was chopped into pieces, and immediately upon being chopped, the seaweed was soaked in a bath containing a dilute phosphoric acid aqueous solution in order to remove polyphenol compounds, which are believed to be the phytotoxic substances of seaweed. The chopping was carried out in a hammer mill. On completion of the soaking, the dilute phosphoric acid solution was drained from the chopped seaweed, and stored for use with the next batch of seaweed. It has been found that at a concentration in the s range of approximately 7% to 12% volume, the dilute phosphoric acid aqueous solution is suitable for treating six batches of seaweed. After the dilute phosphoric acid aqueous solution had been drained from the seaweed, the chopped soaked seaweed was rinsed with fresh water to remove excess residues of phosphoric acid.

The rinsed seaweed was then processed as will be described in the following

0 examples.

Example 1

In this example the two seaweed based soil enriching compositions were prepared.

S The seaweed included the following types: Ascophyllum nodosum, Fucus vesiculosus, Fucus serrates, Laminaria digitata, Laminaria hyperborea.

The seaweed was chopped into pieces of maximum dimension of approximately 1 Omm to 1 2mm within approximately 3 hours of being harvested.

The dilute phosphoric acid aqueous solution in which the seaweed was soaked contained phosphoric acid in an amount of approximately 10% volume. The chopped seaweed was added to the dilute phosphoric acid aqueous solution in an amount of 150kgs of chopped seaweed to 100 litres dilute phosphoric acid aqueous solution, and was left to soak for a time period of approximately 30 minutes. After being chopped and soaked in the dilute phosphoric acid aqueous solution and then rinsed, the seaweed was subjected to an alkaline extraction step for extracting humic acid substances therefrom. The alkaline extraction step was carried out by adding s 25kgs of the seaweed and 2.25kgs of potassium carbonate (K2CO3) to 200 litres water in a pressure vessel. The contents of the pressure vessel were heated to a temperature of approximately 140 C and were maintained at the temperature of 140 C at a pressure of approximately 4 bar for a time period of approximately 4 hours in the pressure vessel.

At the end of the alkaline extraction step a liquid slurry resulted which was then filtered to provide the liquid plant growth promoting composition containing the humic acid substances. The filtration was carried out using a decanter and a clarifier. The decanted and clarified liquid plant growth promoting composition was found to IS contain 12% w/v solids, and was found to have significant plant growth promoting properties, and was suitable for spreading on land in a dilute aqueous solution whereby the plant growth promoting composition was diluted in water at a dilution of x100 to x300.

A sludge remaining after filtering of the liquid slurry was used in the preparation of the soil conditioning composition. The sludge had a moisture content of the order of 90%, and was found to contain polysaccharides, for example, alginates, oligosaccharides and monosaccharides as well as insoluble fibres, all of which have soil conditioning properties. However, the sludge was found to have a pH of the order of 10, and thus would have been unsuitable for land spreading. The soil conditioning composition was prepared by mixing the sludge with seaweed meal in the ratio one part sludge by weight to three to four parts seaweed meal by weight.

The seaweed meal was prepared from a mixture of the following types of seaweed, s namely, ascophyllum nodosum and fucus vesiculosus, and was chopped and placed in a rotary drum dryer at a temperature of approximately 300 C for a time period of the order of 30 minutes, in order to reduce the moisture content of the chopped seaweed to approximately 7% to 11% prior to being mixed with the sludge. After the sludge and the seaweed meal were mixed, the resulting composition was in granular form, with a peaVearth like consistency, and had a moisture content of the order of 20% to 30% with a pH of the order of 7.5% to 8.5%. The soil conditioning composition was thus suitable for spreading on land and mixing with soil, and was found to have significant soil conditioning properties. It was found that by spreading the soil conditioning composition on land at a rate of approximately 75gms per square metro of land, particularly good soil conditioning results were achieved.

Additionally, the soil conditioning composition may also be mixed with soil and/or sand to prepare and/or repair amenity turves.

Example 2

In this example, the liquid plant growth promoting composition and the soil conditioning composition in granular form were prepared using seaweed and seaweed meal similar to that described in Example 1. The seaweed was initially chopped and treated with a dilute phosphoric aqueous solution similar to the chopping and treating of the seaweed in Example 1. However, in this example the dilute phosphoric acid solution contained phosphoric acid at a concentration of approximately 7% volume, and the chopped seaweed was left to soak in the dilute phosphoric acid aqueous solution for approximately 45 minutes. The chopped seaweed having been treated with the dilute phosphoric acid solution and rinsed was then subjected to an alkaline extraction step for extracting humic acid substances therefrom. In this example the alkaline extraction step was carried out by adding 25kgs of the seaweed and 2.25kgs of K2CO3 to 200 litres water in the pressure vessel. The temperature of the contents of the pressure vessel were raised to a temperature of approximately 140 C and were maintained at that temperature at a pressure of approximately 3 bar for approximately 10 hours. The resulting liquid slurry was then filtered to provide the liquid plant growth promoting composition, and the soil conditioning composition was prepared from the sludge remaining after filtration of the liquid slurry as already described in Example 1. The liquid plant growth promoting composition was found to have significant plant growth promoting IS properties, and was suitable for spreading on land in a dilute aqueous solution whereby the liquid plant growth promoting composition was diluted x100 to x400 in water. The soil conditioning composition was found to be suitable for spreading on land for soil conditioning at a rate of approximately 75gms per square metro of land.

Example 3

In this example, the liquid plant growth promoting composition and the soil conditioning composition in granular form were prepared using seaweed and seaweed meal similar to that described in Example 1. The seaweed was initially chopped and treated with a dilute phosphoric acid aqueous solution similar to the chopping and treating of the seaweed in Example 1. However, in this example the dilute phosphoric acid aqueous solution was diluted at a concentration of 12% volume, and the chopped seaweed was left to soak in the dilute phosphoric acid aqueous solution for approximately 20 minutes. The rinsed treated seaweed was s then subjected to an alkaline extraction step for extracting humic acid substances therefrom. In this example the alkaline extraction step was carried out by adding 25kgs of the treated rinsed seaweed and 2.25kgs K2CO3 to 200 litres water in the pressure vessel. The temperature of the contents of the pressure vessel were raised to a temperature of approximately 1 60 C and were maintained at that temperature at a pressure of approximately 6 bar for approximately 4 hours. The resulting liquid sludge was then filtered to provide the liquid plant growth promoting composition, and the soil conditioning composition was prepared from the sludge remaining after filtration of the liquid slurry as already described in Example 1. The liquid plant growth promoting composition was found to have significant plant growth promoting properties, and was suitable for spreading on land in a dilute aqueous solution whereby the liquid plant growth promoting composition was diluted x100 to x300 in water. The soil conditioning composition was found to be suitable for spreading on land for soil conditioning at a rate of approximately 75gms per square metro of land.

The advantages of the method according to the invention are many. It has been found that by subjecting the fresh untreated seaweed to a soak in a dilute phosphoric acid aqueous solution, polyphenol compounds, which are believed to be the substances in seaweed which have the greatest phytotoxicity to plants are removed. While it is preferable to chop the seaweed prior to soaking for enhancing the action of the dilute phosphoric acid aqueous solution on the seaweed, this is not essential, however, it has been found that by chopping the seaweed the action of the dilute phosphoric acid tends to be increased. s

It is desirable that the dilute phosphoric acid aqueous solution should be of relatively low concentration, and preferably, should be of a concentration not exceeding 12% volume of the aqueous solution, since concentrations greater than 12% volume may cause undesirable side reactions. It will of course be appreciated that the time lo period of the soak in the dilute phosphoric acid solution can be reduced by increasing the concentration of phosphoric acid in the aqueous solution up to 12%.

Typically, it has been found that soaking for a time period of approximately 20 minutes with a dilute phosphoric acid aqueous solution of approximately 10% by volume concentration is sufficient, while reducing the concentration of phosphoric acid in the aqueous solution to 6% increases the time period to approximately 1 hour required in order to achieve sufficient removal of the polyphenol compounds.

Additionally, the soaking of the chopped fresh untreated seaweed in the dilute phosphoric acid aqueous solution, as well as reducing the polyphenol compounds also reduces the sodium chloride content of the seaweed, which is desirable, since sodium chloride induces saline conditions in plants, which lead to osmotic pressure problems within the plants, subsequently leading to mortality. However, it has been found that the seaweed after soaking in the dilute phosphoric acid aqueous solution retains desirable trace elements, such as calcium, iron and the like, whose phosphates are insoluble. Additionally, some of the phosphate of the dilute phosphoric acid solution is absorbed and retained in the seaweed after rinsing. This phosphate also has desirable plant growth promotion properties.

s It has been found that by significantly increasing the temperature and pressure at which the alkaline extraction step is carried out, and also increasing the time period over which the alkaline extraction step is carried out significantly increases the soluble humic acid content of the plant growth promoting liquid when separated from the sludge. The humic acid substances of the plant growth promoting composition are known to be plant stimulants, and thus, carrying out the alkaline extraction process at significantly higher temperatures and pressures and for longer time periods than recommended heretofore provides a plant growth promoting composition which is high in humic acid content.

In known alkaline extraction steps, it is recommended that when carrying out the alkaline extraction step the temperature should not exceed 120 C, the pressure should not exceed 3 bar, and the time period should not exceed 4 hours. Otherwise, it was believed up to this that the resulting slurry would be too viscous and difficult to filter, thus leading to relatively low yields. However, it has been discovered that by carrying out the alkaline extraction step at the higher temperatures, pressures and for the longer time periods in the method according to the invention, the viscosity of the resulting slurry is actually reduced, thus facilitating filtering of the slurry for separating the slurry into the plant growth promoting composition, and the sludge which is subsequently mixed with the seaweed meal to form the soil conditioning composition. It has also been found that carrying out the alkaline extraction process at the higher temperatures, pressures and for the longer time periods also leads to an increase in the oligosaccharide content resulting from the hydrolysis of the alginate cellulose and lignin in the seaweed. The oligosaccharides act as "elicitors" which promote plant growth.

It is envisaged that the soil conditioning composition in granular form may be dried to a moisture content of approximately 10%, and then milled to form a powder, which could likewise be spread on land, and/or mixed with soil, sand and/or other suitable lo constituents.

Claims

Claims 1. A method for preparing a seaweed based soil enriching

composition comprising the steps of soaking untreated seaweed in a dilute phosphoric acid solution for removing polyphenol compounds from the seaweed, and subsequently rinsing the seaweed with water.
2. A method as claimed in Claim 1 in which the rinsing of the seaweed is carried out with fresh water.

lo
3. A method as claimed in Claim 1 or 2 in which the seaweed is chopped prior to soaking.
4. A method as claimed in Claim 3 in which the seaweed is chopped into pieces of maximum dimension not exceeding 30mm.
5. A method as claimed in Claim 3 or 4 in which the seaweed is chopped into pieces of maximum dimension in the range of 5mm to 20mm.
6. A method as claimed in Claim 5 in which the seaweed is chopped into pieces of maximum dimension in the range of 10mm to 12mm.
7. A method as claimed in any preceding claim in which the seaweed is soaked in the dilute phosphoric acid solution for a time period in the range of 5 minutes to 60 minutes.
8. A method as claimed in Claim 7 in which the seaweed is soaked in the dilute phosphoric acid solution for a time period in the range of 10 minutes to 45 minutes.
9. A method as claimed in Claim 8 in which the seaweed is soaked in the dilute phosphoric acid solution for a time period of approximately 20 minutes.
10. A method as claimed in any preceding claim in which the dilute phosphoric acid solution is an aqueous solution, and contains phosphoric acid in an amount in the range of 5% volume to 12% volume of the aqueous solution.
11. A method as claimed in Claim 10 in which the dilute phosphoric acid aqueous solution contains phosphoric acid in an amount in the range of 7% volume to 11% volume of the aqueous solution.
12. A method as claimed in any preceding claim in which the dilute phosphoric acid aqueous solution contains phosphoric acid in an amount of approximately 10% volume of the aqueous solution.
13. A method as claimed in any preceding claim in which the dilute phosphoric acid solution is at approximately room temperature.
14. A method as claimed in any preceding claim in which the rinsed seaweed is subjected to an alkaline extraction step for extracting humic acid substances therefrom, and a liquid slurry resulting from the alkaline extraction step which contains the humic acid substances is subjected to a separating step for separating the liquid slurry into a liquid and a sludge, the liquid containing the humic acid substances and forming the soil enriching composition as a plant growth promoting composition in liquid form.
15. A method as claimed in Claim 14 in which the alkaline extraction step is carried out at a temperature not less than 140 C.

lo
16. A method as claimed in Claim 14 or 15 in which the alkaline extraction step is carried out at a temperature in the range of 140 C to 160 C.
17. A method as claimed in any of Claims 14 to 16 in which the alkaline extraction step is carried out at a pressure of at least 3 bar.
18. A method as claimed in any of Claims 14 to 17 in which the alkaline extraction step is carried out at a pressure in the range of 3 bar to 6 bar.
19. A method as claimed in Claim 18 in which the alkaline extraction step is carried out at a pressure of approximately 4 bar.
20. A method as claimed in any of Claims 14 to 19 in which the alkaline extraction step is carried out for a time period of at least 4 hours.
21. A method as claimed in any of Claims 14 to 20 in which the alkaline extraction step is carried out for a time period in the range of 4 hours to 10 hours.
22. A method as claimed in any of Claims 14 to 21 in which the sludge resulting s from the alkaline extraction step is mixed with seaweed meal to form the soil enriching composition as a soil conditioning composition.
23. A method as claimed in Claim 22 in which the sludge is mixed with the seaweed meal in an amount 20% weight to 35% weight of the seaweed meal.
24. A method as claimed in Claim 22 or 23 in which the seaweed meal is dried to a moisture content in the range of 7% to 11 % prior to mixing with the sludge.
25. A method as claimed in any of Claims 22 to 24 in which the seaweed meal Is was prepared from chopped seaweed.
26. A method as claimed in any preceding claim in which the seaweed is fresh seaweed.
27. A method as claimed in any preceding claim in which the seaweed is subjected to soaking in the dilute phosphoric acid solution within 1 hour to 48 hours of being harvested.
28. A method as claimed in Claim 27 in which the seaweed is subjected to soaking in the dilute phosphoric acid solution within 2 hours to 6 hours of being harvested.
29. A method as claimed in Claim 28 in which the seaweed is subjected to s soaking in the dilute phosphoric acid solution within approximately 3 hours of being harvested.
30. A method as claimed in any preceding claim in which the seaweed is selected from any one or more of the following seaweeds: Ascophyllum nodosum, Fucus vesiculosus, Fucus serrates, Laminaria digitata, and Laminaria hyperborea.
31. A method for preparing a seaweed based soil enriching composition, the method being substantially as described herein with reference to the accompanying

examples.
32. A seaweed based soil enriching composition prepared according to the method as claimed in any preceding claim.
33. A seaweed based soil enriching composition as claimed in Claim 32 in which the seaweed based soil enriching composition is a plant growth promoting composition in liquid form.
34. A seaweed based soil enriching composition as claimed in Claim 32 or 33 in which the seaweed based soil enriching composition is in liquid form.
35. A seaweed based soil enriching composition as claimed in Claim 32 in which the seaweed based soil enriching composition is a soil conditioning composition.
36. A seaweed based soil enriching composition as claimed in Claim 32 or 35 in lo which the seaweed based soil enriching composition is in granular form.
37. A seaweed based soil enriching composition as claimed in any of Claims 32 to 36 in which the seaweed from which the soil enriching composition is prepared is selected from any one or more of the following seaweeds: Ascophyllum nodosum, Fucus vesiculosus, Fucus serratus, Laminaria digitata, and Laminaria hyperborea.
38. A seaweed based soil enriching composition substantially as described herein with reference to the accompanying examples.
39. A seaweed based plant growth promoting composition substantially as described herein with reference to and as illustrated in the accompanying examples.
40. A seaweed based soil conditioning composition substantially as described herein with reference to the accompanying examples. s )