NL2030182B9 - Organic method for buffering coir products - Google Patents

Abstract

The present invention relates to a method for buffering a coir product, in particular coir pith and coir chips, comprising contacting the coir product for a period of time with a solution comprising a calcium compound and a weak acid. Preferably, the weak acid is a weak organic acid selected from formic acid, acetic acid, benzoic acid, oxalic acid and citric acid, and the calcium compound is selected from calcium oxide, calcium hydroxide, and calcium carbonate. The present invention further relates to a buffered coir product having an EC value of 0.2 mS/cm or less, obtainable by the method of the present invention.

Description

ORGANIC METHOD FOR BUFFERING COIR PRODUCTS

The present invention relates to a method for buffering coir products, such as coir pith and coir chips and to the products thus obtained.

Coir pith and coir chips, commonly known as coir, are obtained from the fibrous husk (exocarp) of the coconut (Cocos nucifera). Coir pith consists of short fibers and spongy pith that are the by-product in the processing of husk to coir fiber. It is found between the hard, internal shell and the outer coat of the coconut, while coir chips are made from the entire husk. It is hydrophilic and quickly absorbs water making it a beneficial product for plant growers.

Coconut trees have a naturally high tolerance for salt (sodium chloride). This in turn means that the cation exchange sites on the coir particles are naturally saturated with sodium. Coir also naturally contains large amounts of potassium. Coir has a salt content or Electrical Conductivity (EC) level of 2 to 6 mS/cm which is far too high for a growing medium and it therefore needs to be treated before use.

This treatment is called buffering. Buffering of coir comprises washing away the free monovalent sodium, potassium and chloride ions and subsequently replacing sodium and potassium bound to the cation exchange sites on the coir particles with divalent calcium and optionally magnesium and washing away the excess sodium and potassium that is released. The replacement of bound sodium and potassium ions is done with a chemical process using a solution of calcium nitrate or magnesium sulfate. Figure 1 shows a schematic representation of the buffering process.

After buffering, the coir is dried and compressed into various sizes before shipping.

The shipped compressed coir, also known as coco peat, coir fiber pith, coir dust, coir chips, husk chips or only as ‘coir’, is generally further subjected to a rehydration and enrichment step to provide a usable substrate. The compressed coir is first rehydrated and subsequently NPK (nitrogen, phosphorus and potassium) fertilizers are added to provide substrates having balanced nutritional conditions.

The disadvantage of the known buffering method is, however, that large quantities of the elements nitrogen and sulphur end up in the wastewater which is then no longer suitable for irrigation and may pollute the groundwater and even so the drinking water. Excess nitrogen may lead to a build-up that is harmful to nature by unbalancing ecosystems, damaging soil health, contributing to global warming in the form of nitrous oxide, etc.

It is therefore an object of the present invention to provide an improved process for buffering coir products that is environmentally friendly.

The present invention thus relates to a method for buffering coir products, comprising contacting the cotr product for a period of time with a solution comprising a calcium compound and a weak acid.

It was found that the combination of calcium carbonate with citric acid works particularly well for buffering the coir. The additional advantage is that these compounds are organic and not detrimental to the environment. Citric acid consists solely of the elements hydrogen, carbon, and oxygen. It does not leave behind other elements like nitrogen.

More in general, the weak acid is a weak organic acid. Other suitable acids, besides citric acid, are formic acid, acetic acid, benzoic acid, and oxalic acid.

Instead of calcium carbonate, the calcium compound can be calcium oxide or calcium hydroxide. A suitable source of the calcium compound can be chalk, lime or limestone. Lime is a calcium-containing inorganic mineral composed primarily of oxides, and hydroxide, usually calcium oxide and/ or calcium hydroxide. Limestone is a sedimentary carbonate rock that mainly comprises calcium carbonate. Limestone is a general term for rocks that contain 80% or more of calcium or magnesium carbonate. Limestone is also known as calcitic lime. Chalk is a type of limestone. The key difference between limestone and chalk is that the limestone contains the minerals calcite and aragonite whereas chalk is a form of limestone which contains only calcite.

Calcite and aragonite are different crystal forms of calcium carbonate (CaCO:). Another type of carbonate rock is dolomite, which contains a high percentage of the mineral dolomite,

CaMg(COas),. Dolomite can also be used in the invention but then the exchange is not only with calcium but also in part with magnesium. All these sources of the calcium compound are used in powder form. According to the invention the calcium compound is preferably a calcium carbonate- containing compound or composition. Particularly preferred are limestone and dolomite.

In the method of the invention, the coir product is thoroughly mixed with a solution, usually in water, that comprises the weak acid and calciam compound. The coir can be spread out on a surface and sprayed with the solution with a hose or via sprinklers. The solution must be mixed well to avoid settling of the calcium compound. Preferably, in preparing the treatment solution, the acid is dissolved in water first after which the calcium compound is added. It is preferred that the components are first mixed into water before use.

Coir from different origins can have differences in complexation and the concentrations of the weak acid and calcium compound may thus vary. A high amount of sodium and potassium in the coir requires higher concentrations of divalent ions Ca?* and Mg* to replace all monovalent cations.

The same applies to the calcium compound. The carbonate content of limestone or dolomitic lime determines the capacity of the lime to neutralize acidity. This is called the neutralizing value. Neutralizing value, also called calcium carbonate equivalent (CCE), is expressed as a percentage relative to pure calcium carbonate, which is given a value of 100%. The lower the CCE value, the more limestone is needed to neutralize the coir’s acidity. The method of the invention works well when the neutralizing value is at least 50%.

Dolomite lime also comprises magnesium carbonate.

The skilled person is capable of determining the concentration of the calcium compound and the weak acid to be used in the method of the invention based on knowledge of the neutralizing value of the calcium compound and the origin of the coir.

In one embodiment, the solution comprises 2-8 g/l, preferably 2.5-7 g/l, more preferably 3- 6 g/l, even more preferably 3.3-3.5 g/l, most preferably about 3.4 g/l citric acid.

When other acids, such as formic acid, acetic acid, benzoic acid, and oxalic acid, are used, the concentration in g/l needed can be determined by the following formula: g/l acid = (mol H*/ (number of acid groups * 100)) * molar mass of the acid

The “mol H™ should be about 50 mmol/l. The following Table 1 shows the ranges for the other acids.

Table 1

Acid Molar mass | Number of acid groups | Amount needed (g/1)

CTT ee ee ma arse

In one embodiment, the solution comprises 0.5-5 g/l, preferably 0.75-4 g/l, more preferably 1-3 g/l, even more preferably 1.5-2.5 g/l, most preferably about 2.25 g/l calcium carbonate.

The pH of the solution lies between 1.0 and 5.0, preferably between about 2.0 and 3.0.

If necessary to obtain the desired result, contacting the coir product for a period of time with a solution comprising a calcium compound and a weak acid can be repeated one or more times.

The period of time of the contact is at least 10 minutes, preferably at least 20 minutes, more preferably at least 25 minutes. However, the method can also be performed for as long as 15 hours or even days.

The method can be performed by placing the coir product on a stationary surface, such as a floor, but can also be performed by transporting the coir product on a conveyer belt and spraying the solution thereon. In this embodiment, the treatment is continuous.

The acid in the treatment solution dissolves the calcium ions in the calcium compound.

The calcium ions compete with the sodium and potassium ions in the complex to replace them. The sodium and potassium ions end up in the water.

Subsequently, the buffered coir product is rinsed to finally remove most of the sodium and potassium ions. Suitably, the rinsing comprises one or more washing steps with water with an EC value of less than 0.5 mS/cm until the EC value of the buffered coir is 0.2 mS/cm or less.

Preferably, washing is repeated until the EC of the drain water is below 0.5 mS/cm.

To determine whether the coir is sufficiently buffered, a chemical analysis can be performed in which the concentration of a number of freely available elements present in H2O or bound to the complex, determined by means of barium chloride (BaClz), is compared with the RHP regulations.

In the BaCl, method, BaCl: is added to the batch of treated material. Ba® replaces all Ca? and Mg* from the coir product. The concentrations of the free calcium and magnesium ions as well as any remaining sodium or potassium ions can be determined. In a separate batch containing only water and no barium chloride, these four ions are determined as well. Subtracting the concentration in water from the concentration in barium chloride gives the total amount of ions complexed to the coir product. According to RHP (Regeling HandelsPotgronden) requirements there must be a difference of less than | mmol of sodium and less than 2 mmol of potassium between the concentration in barium chloride (BaCly) and in water (HO). This means that the amount of sodium and potassium ions still complexed to the coir products should be less than 1 mmol and 2 mmol, respectively. RHP is a quality mark that indicates that a substrate complies with the quality requirements concerning for instance water uptake, air content, pH, EC and nutrients. It also offers more security that the substrate is pure and clean and that it can be used without risks for the culture. The RHP quality mark monitors the quality of growing media in the chain, from raw materials production until processing and delivery at the company of the user.

The invention further relates to the buffered coir having an EC value of 0.2 mS/cm or less, which coir is obtainable by the method as claimed.

The invention will now be illustrated in the example that follows. This example is only one way of carrying out the invention. The skilled person is capable of varying the process parameters within the boundaries that are described in this application. The analyses were carried out under

NEN-EN 13037 (sample preparation for chemical and physical tests), 13038 (EC), 13040 (pH).

In this application reference is made to the following figures that are not intended to limit the invention in any way:

Fig. 1 shows a schematic representation of the buffering process of the invention.

Fig. 2A shows the results of the growth trial with Chinese cabbage. A1 shows a group of pots with Chinese cabbage plants on the reference substrate 25 days after sowing. A2 is an individual pot with Chinese cabbage on reference substrate. A3 shows a group of pots with 5 Chinese cabbage plants on the substrate of the invention 25 days after sowing. A4 is an individual pot with Chinese cabbage on substrate of the invention.

Fig. 2B shows the results of the growth trial with lettuce. B1 shows a group of pots with lettuce plants on the reference substrate 25 days after sowing. B2 is an individual pot with lettuce on reference substrate. B3 shows a group of pots with lettuce plants on the substrate of the invention 25 days after sowing. B4 is an individual pot with lettuce on substrate of the invention.

EXAMPLES

EXAMPLE 1

Comparison between traditional treatment and treatment of the invention

In order to demonstrate that the treatment of the invention leads to a similar or even better product, a sample of 10 m* coir pith was taken directly from the installation and subjected to the traditional buffering method with calcium nitrate and the method of the invention with citric acid and limestone.

For the latter, a treatment solution was prepared by dissolving 34 kg citric acid in 2500 1 water. After the citric acid is dissolved, 22.5 kg of limestone (calcium carbonate source) is added to the solution and mixed well to avoid precipitation of the limestone.

The coir pith was placed on a clean surface and wetted with half of the above solution in such a way that the treatment solution is distributed evenly over the coir pith. The treated material was left to stand for about 30 minutes after which the remainder of the treatment solution was evenly distributed over the coir pith. The material was then left to stand for 12 hours.

Next, the material was washed with water having an EC level of less than 0.5 mS/cm until the treated material has an EC value of less than 0.2 mS/cm. The material was then dried until a moisture content of less than 50%.

The material prepared according to the traditional method with calcium nitrate (reference) and the material subjected to the above-described treatment (invention) were both analysed for the amount of sodium, potassium, calcium and magnesium ions in the surrounding water, after treatment with BaCl; and bound in the complex (amount after treatment with BaCl: minus the amount in water). For this, the well-known barium chloride method is used to release all ions from the complex. Before analysis all samples in all tests are diluted 1: 1.5. The results of the present analysis in mmol/l are shown in Table 2.

Table 2 in water in BaCl; complex sample | treatment pH* | EC* | K | Na Mg IK {Na | Ca | Mg | K | Na | Ca | Mg reference | weated with | 7.0 | 0.5 02 163 1153/70 [08 21/0602 167107 calcium nitrate, washed and dried invention | treated with | 7.3 0.1 03 05/04 <0. 10.7 1190/71 | 18 04/05 170117 citric acid and limestone, washed and dried

Tt follows from the above table that the removal of the potassium and sodium ions by the treatment of the invention is more complete than with the traditional calcium nitrate method.

EXAMPLE 2

Stability of the complex

It is important that fertilizers that are added to the coir pith substrate are not bound to the complex, but that the complex remains stable. In order to test the stability, calcium nitrate is added to the treated coir pith in various amounts and the amount of the sodium, potassium, calcium and magnesium ions bound to the complex is determined. The results are shown in Table 3.

Table 3 in water | in BaCl: complex treatment pH [EC |K [Na [Ca Mg IK | Na Mg IK | Na | Ca | Mg 2gcalciom 55 | 05 [04 07 [12104 [06 09 56 [10 [O1 01 45 06

C | 3g calcium 54 [os [04]07 [17104 [0510855 09 [oi [or 43 [04

TE TTT

= TTT ITE

From the grey columns it follows that the amount of calcium ions in the water present in the sample and obtained after the barium chloride treatment (ions in water and bound to the complex) increases upon the addition of increasing amounts of calcium nitrate but that the amount bound to the complex (amount in BaCl> minus amount in water) remains stable. This means that additives that are used in the cultivation of plants that are added to the substrate are not bound to the substrate but remain available for the plant.

EXAMPLE 3

Cultivation trial

In order to test whether the coir product is suitable as a substrate in plant cultivation, a growth trial was performed with a traditional coir product as a reference material and a coir product treated according to the invention.

The reference material (referred to as REF) and a sample of organic coir pith treated as described in Example 1 (referred to herein as GRI-KET) are fertilized with KCM Multi Mix 11+25+9+7MgO+TE and calcium nitrate to an EC of about 0.8-0.9 mS/cm and a pH about 6.0.

The reference mixture and the samples were used for a growth trial with Chinese cabbage and lettuce.

For each object, 4 pots are filled with coir product of sample REF or GRI-KET. 20 Seeds were sown in each pot and kept in a greenhouse at a target temperature of 20/18°C (day/night).

Dutch tap water suitable for human consumption was used for watering the plants.

Seven days after sowing, the number of germinated seeds was counted. Determination of the growth took place 25 days after sowing by determining the fresh and dry weight of the plants.

The results are shown in Table 4.

Table 4 germination percentage (%) REF 100 inhibition of germination (Ge) 10 Joo fresh weight after 25 days (mg/plant) 894 ww dry weight after 25 days (mg/plant) REF en |e [os

The inhibition of germination should be lower than 10% to be acceptable, which is the case for the seeds germinated on the substrate treated according to the invention. For growth, the maximum inhibition that still falls within the bandwidth is 20%. Both crops show a growth inhibition lower than 20%. It follows that the method of the invention is suitable for preparing a coir product that can replace the traditionally treated coir products in cultivation.

At the end of the test, at day 25, pictures of the various objects were made (Figure 2A for

Chinese cabbage and Figure 2B for lettuce). This shows that the plants grown in the substrate according to the invention are similar to the plants grown in the traditional substrate buffered with

IO calcium nitrate.

Claims (18)

CONCLUSIONS CLAIMS 1. Method for buffering a coconut fiber product, in particular coconut marrow and coconut chips, comprising contacting the coconut fiber product for a period of time with a solution comprising a calcium compound and a weak acid. A method according to claim 1, wherein the weak acid is a weak organic acid selected from formic acid, acetic acid, benzoic acid, oxalic acid and citric acid. The method of claim 2, wherein the weak acid is citric acid. The method of claim 3, wherein the citric acid is citric acid monohydrate (COH8O7.H:O). A method according to any one of claims 1 to 4, wherein the calcium compound is selected from calcium oxide, calcium hydroxide and calcium carbonate, The method of claim 5, wherein the calcium compound is calcium carbonate. A method according to claim 6, wherein the calcium carbonate is used in the method in the form of a calcium carbonate-containing composition, in particular limestone, dolomite lime and/or chalk. A method according to any one of claims 1 to 7, wherein the neutralizing value of the calcium-containing composition is 50% or higher. A method according to any one of claims 1-8, wherein the solution contains 2-8 g/l, preferably 2.5-7 g/l, more preferably 3-6 g/l, even more preferably 3.3-3.5 g/l, most preferably about 3.4 g/l citric acid. A method according to any one of claims 1 to 8, wherein the solution comprises one or more of formic acid, acetic acid, benzoic acid, oxalic acid in an amount determined by the following formula: g/l acid = (mol H* / (number of acid groups * 100)) * molar mass of the acid where the “mol H*” is about 50 mmol/l. A method according to any one of claims 1-10, wherein the solution contains 0.5-5 kg/l, preferably 0.75-4 kg/l, more preferably 1-3 kg/l, even more preferably 1, 5-2.5 kg/l, most preferably about 2.25 kg/l of calcium carbonate. A method according to any one of claims 1-11, wherein the time period of the contact is at least 10 minutes, preferably at least 20 minutes, more preferably at least 30 minutes and preferably less than 15 hours. A method according to any one of claims 1-12, wherein the electrical conductivity EC of the solution is between 0.5 and 2.0 mS/cm, preferably between about 1.0 and 1.5 mS/cm. A method according to any one of claims 1-13, wherein the pH of the solution is between 1.0 and 5.0, preferably between about 2.0 and 3.0. The method of any of claims 1-14, further comprising the step of rinsing the treated coco fiber. The method of claim 15, wherein the rinsing comprises one or more washing steps with water having an EC value of less than 0.5 mS/cm, until the EC value of the treated coconut fiber is 0.2 mS/cm or less . A buffered coconut fiber product with an EC value of 0.2 mS/cm or less obtainable by the method according to any one of claims 1-16. A buffered coconut fiber product according to claim 17, having a pH between 5.0 and 7.0, preferably between 5.5 and 6.5, more preferably about 5.0.