WO2002094722A1

WO2002094722A1 - Flocculant derived from a vegetable source and method for flocculation

Info

Publication number: WO2002094722A1
Application number: PCT/DK2002/000335
Authority: WO
Inventors: George Mhlanga
Original assignee: Biss-Biosystems Aps
Priority date: 2001-05-22
Filing date: 2002-05-21
Publication date: 2002-11-28
Also published as: WO2002094722B1; EP1417154A2

Abstract

The present invention concerns a flocculant derived from a vegetable source and the use of the flocculant in a method for separation of suspended particles and colloidal substances from an aqueous liquid. The method comprises treating an aqueous liquid containing aggregates of suspended solid particles or colloids, coagulant, and particulate carrier with a flocculant and then separating the resulting flocs from the aqueous liquid. In the method, environment-friendly mucilage derived from a vegetable source is applied as the flocculant, which may be easily degraded in the nature and digested by man and other organisms without any risk of health hazard.

Description

FLOCCULANT DERIVED FROM A VEGETABLE SOURCE AND METHOD FOR FLOCCULATION

Introduction

The present invention relates to flocculant derived from a vegetable source and the use of the 0 flocculant in a method for separation of suspended solid particles or colloids from an aqueous media. The method is useful for purification or clarification of a large number of aqueous media. Examples of aqueous media, which may be treated according to the 5 present invention, are wastewater from industrial plants, surface water from rivers and lakes for the production of tap water, and water discharged from traditional wastewater treatment plants. In the method, environment-friendly mucilage derived from a 0 vegetable source is applied as a flocculant, which may be easily degraded in the nature and digested by man and other organisms without any risk of health hazard.

5 Technical background

Solids dispersed in aqueous liquids will tend to precipitate when the liquid is left stagnant. However, small solid particles or colloids will, even after a prolonged period of stagnant time, still be 0 present as a dispersed phase in the liquid. These dispersed substances may be the cause of a turbid liquid and/or a high content of organic matter in the liquid. Therefore, a removal of these substances is often desirable. 5 The dispersed solid particles or colloids may be separated from the aqueous liquid in many different ways according to the prior art. A widely applied method is flocculation of the particles with a suitable flocculant and subsequently removal of the resulting floes. The flocculants used in these days are mostly of synthetic nature. Examples of synthetic flocculants are anionic and cationic polymers, such as polyacrylamid, polyacrylic acid and polymeth- acrylic acid. For many applications these synthetic flocculants may have good flocculation properties, but one main disadvantage of some of these synthetic flocculants is that they are difficult to degrade in nature and therefore may be a potential health hazard to man. Moreover, many people tend to prefer natural products to synthetic substances when possible. Therefore, there is a need for development of natural flocculants with good flocculation properties similar to the synthetic flocculants.

In the prior art several attempts have been made to provide suitable methods for purification of aqueous liquids using natural polysaccharides or derivatives thereof as flocculants. EP 471 597 Al discloses a composition suitable for flocculation. The composition comprises a mixture of a microbial polysaccharide composed of glucose and rhamnose subunits as well as a natural polysaccharide. The microbial polysaccharide is obtained from a Pseudomonas or an Alcaligene strain. The natural polysaccharide is preferable alginate. No use of a coagulant is suggested.

In JP 2000095802 the use of a polysaccharide obtained from a microbial strain is disclosed. The polysaccharide is obtained from a Gram-negative bacterium and comprises subunits of glucoronic acid, glucose, galactose and fructose. The polysaccharide may be used for precipitating dye particles in a coloured wastewater. In DE 29 15 872 a microbial polysaccharide containing the subunits galactose, glucose, mannose and glucoronic acid is described. The microbial polysaccharide might be a suitable flocculant . Polysaccharides of microbiological origin might be useful flocculants. However, it might be difficult to obtain an appropriate strain producing the polysaccharide of interest. Also a high level of know-how as well as considerable investment is required in order to produce microbiological polysaccharides. Furthermore, many people prefer products of vegetable origin to products of microbiological origin.

Vegetable polysaccharide flocculants have been suggested in FI 77682, wherein a synergistic mixture of cassia-galactomannan, agar and/or xanthan is disclosed. A coagulant is not used.

If a vegetable flocculant is applied, purification or concentration of the vegetable substances of interest in the extract may be profitable. Such a process is described in US 6,264,853, in which the treatment is based on size exclusion as the extract is subjected to ultrafiltration. In the process the small molecular weight species remain with the fil- trate, while the high molecular weight species are retained. Ultrafiltration is preferably carried out for size exclusion of 5,000 Daltons (lOkDa) or greater for example 5kDa to 500kDa. In this case all the active substances are recovered. In the script it is recommended to use a filter size starting from 30kDa to lOOkDa in order to isolate aqueous aliphatic alcoholic extracted substances from flax.

In US 5,174,903 a method is disclosed, wherein an acidified wastewater is treated with lignin as a coa- gulant and a natural polymer capable of efficiently flocculating the dispersed solids. The natural polymer may be selected from e.g. alginate, xanthan gum, carrageenan, agar and dextran gum.

US 3,830,736 pertains to a clarification method, which comprises initial coagulation of organic matter in the water with a trivalent metal cation and subsequent addition of an anionic derivative of a galactomannan gum. The conventional settling techniques are not suitable for the treatment of liquids containing suspended particles or colloids. For example, while natural polysaccharides may form floes, these floes tend to form semi-stable networks, which are only settling very slowly, and in the presence of entrained air they even float on the surface of the liquid. Thus, relatively large settling ponds or tanks are required in order to hold the volume of liquid. It has been suggested to accelerate the precipitation of suspended solids and colloids in liquids from industrial processes by use of particulate solids.

WO 90/09222 discloses a process for clarifying liquids produced in the mining industry, such as liquids containing cyanide precipitates produced in the gold mining industry, liquids containing sodium oxalate produced in the Bayer process, and liquids produced in the process for the recovery of mineral sands from swamps. The process implies addition of an inert particulate carrier and a flocculant to the liquid. The liquid may be subjected to a pre- clarification step of aggregation or agglomeration of the suspended particles using a coagulant. The flocculant is a polyelectrolyte, and only a synthetic flocculant has been mentioned in the examples.

US 5,387,405 describes a process for treatment of liquids produced in the Bayer process for production of alumina from bauxite. The liquids contain finely divided red mud particles primarily made up of iron oxides or iron hydroxides. In this process the red mud particles are separated from the remaining liquid by addition of a soluble carbohydrate polymer and a particulate solid. The soluble carbohydrate polymer may be a polysaccharide polymer of biological origin selected from the group consisting of dextran, zooglan, lactan, pullalan, and mixtures thereof, dextran being preferred. Treatment of the liquid with a coagulant is not suggested. US 5,453,206 discloses a process for removing silica in dissolved or colloidal form from an aqueous liquor in order to prevent the formation of hard deposits in cooling water systems, which progressively reduces the heat transfer. The process involves initial coagulation with e.g. an aluminium salt and subsequent addition of an inert particulate carrier and a flocculant. The flocculant is any suitable cat- ionic, non-ionic or anionic polyelectrolyte, but only the synthetic cationic polyelectrolyte Zetag 92 is disclosed in the examples.

Recently a method involving addition of particulate solids to the liquor to be treated is suggested. In US 5,770,091 it is suggested that a flow of wastewater is treated by a method that includes mixing the liquor with a coagulant and subsequently injecting sand and flocculation agent. The flow is subjected to turbulence and allowed to settle. The flocculant is an organic polyelectrolyte, which is not described in details.

WO 00/27755 discloses a composition for purification treatment of wastewater. The composition comprises calcium hydroxide or bentonite in powdered form, active vegetable carbon, aluminium sulphate hydrate and homopolymers of acryl amide or copolymers of acrylamide and salified acrylic acid. This composition is added to the wastewater and the resulting dispersion is stirred. According to the disclosure two layers are formed in a few seconds : a layer of purified water, which is suitably recovered and reused, and a layer of shovelable muds.

In one aspect of the present invention the object is to obtain an effective separation of dispersed particles in an aqueous liquid using a flocculant and, if required, a coagulant and/or a particulate carrier. The flocculant is easily accessible as a product derived from a vegetable source e.g. mucilage derived from any part of a terrestrial plant . In another aspect a clarification process is provided producing water in the quality of drinking water, which may be consumed without concern as to the content of potentially health hazardous substances.

Description of the invention

The present invention concerns mucilage derived from vegetable matter by an extraction method comprising the steps of: _, (a) submersing the vegetable matter in a suitable aqueous liquid,

(b) maintaining the vegetable matter in the aqueous liquid at least for a period of time sufficient for the mucilage to emerge on the exterior of the vegetable matter,

(c) treating the vegetable matter with suitable means for liberating the mucilage from the vegetable matter,

(d) separating the mucilage from the spent vegetable matter,

(e) concentrating the mucilage in the aqueous liquid, and, optionally,

(f) drying the mucilage to form a solid powdery product . The present invention also concerns a method for separation of suspended solid particles or colloids from an aqueous liquid comprising the steps of a) providing an aqueous liquid, containing aggregates of suspended solid particles or colloids, a flocculant and optionally a coagulant and/or a particulate carrier, where the coagulant if present is added in an amount sufficient for coagulation of the solid particles or the colloids, b) reacting the mixture of step (a) for a period of time sufficient for the formation of floes, and c) separating the floes from the aqueous liquid, wherein the flocculant is a dried or concentrated mucilage derived from a vegetable source .

As the vegetable matter, terrestrial plants are preferred, but maritime plants may also be considered. The mucilage may be derived from any part of the plant, including seeds, flowers, leaves, roots, rhizomes, and from the plant in its entirety. In one aspect of the invention the vegetable matter are seeds from a terrestrial plant .

The vegetable flocculant is derived from the seeds by extraction using a suitable aqueous liquid, which may be a mixture of water and organic solvents. The organic solvents may be any solvent miscible with water. Examples of organic solvents are ethanol, acetone, diethyl ether, pyrimidine and ethyl acetate. Generally, it is preferred to use water as the only component of the aqueous liquid for extraction.

The seeds to be extracted may be treated prior to the extraction by initial grounding to an appropriate particle size. Because of the grounding the interior of the seeds are exposed and the subsequent extraction is facilitated.

In a preferred embodiment the seeds are shelled and the flocculant is extracted only from the shells of the seeds. In this way, the extract obtained is more pure, because the somatic content of substances found in the interior of the seeds as for example proteins, amino acids, and enzymes are not extracted into the aqueous solution. Therefore only the pure active flocculant is recovered and no additional con- tamination of the aqueous liquid to be treated will take place as the unwanted somatic substances in the extract are avoided.

Certain seeds may be extracted without initial grounding because the mucilage in the interior of the seed has an ability to be transported to the exterior of the seed coating. These kind of seeds are usually preferred and the flocculant is then obtained by submersing the seeds in a suitable aqueous liquid, maintaining the seeds in the aqueous liquid for a period of time sufficient for the mucilage to emerge on the exterior of the seed shells, treating the seeds with appropriate means for liberating the mucilage from the remaining seed and recovering the mucilage .

It is believed that the aqueous liquid penetrates the seed shell and swells the mucilage found as a hard vitreous layer on the inside of the coating. Because of the swelling, the volume of the mucilage increases, resulting in migration of the swelled mucilage through small holes or cracks in the coating and emerges on the exterior thereof. Alternatively, the swelling mucilage may burst the coating. The seeds are suitably submersed and maintained in the aqueous liquid for more than 1 hour, preferably more than 8 hours. The aqueous liquid may have any temperature suitable for the extraction. Normally, extraction temperatures not above 70°C produce a good yield. The vegetable flocculant is generally mucilage, which adheres to the coating of the seed. The mucilage may be liberated from the seed coating using chemical means, such as suitable solvents or co- solvents and subsequently recovered by an appropriate method. It is, however, preferred to avoid the use of chemicals and instead liberate the mucilage from the seed coating by vigorously stirring of the aqueous liquid containing the seeds. The stirring speed should be as high as to sufficiently disrupt the adherence between the mucilage and the seed shell. As an example, a suitable stirring speed may be 200 to 300 revolutions per minutes (rpm) .

Afterwards the aqueous liquid containing the mucilage is separated from the spent seeds. The spent seeds are then subjected to a second extraction according to the method out-lined above and the two extracts are assembled. The combined aqueous extracts may be used in the separation method of the invention without further treatment. Alternatively, the combined aqueous extract may be subjected to an evaporation process in order to increase the concentration of mucilage before a drying process produces a solid powdery product. The concentrated mucilage may be obtained by arranging the extract in a mesh and allowing the aqueous liquid to drip off or it may be obtained by the use of ultrafiltration. The ultrafiltration process is preferably carried out for size exclusion of 5,000 Daltons (5kDa) or greater for example 5kDa to 500kDa. In this case all the active substances are recovered. Use of a filter at 20kDa allows some of the polymers to leach out and this is detected by adding alcohol (isopropanol) to the filtrate.

The solid powdery product may be obtained by spray drying or lyophilising the combined or the concentrated extract . In a preferred embodiment the powdery product is obtained by spray drying. Alternatively, the solid product may be obtained by precipitation using salts or solvents. The main advantage of drying the mucilage before use in the separation method is that it is much easier to handle and measure out a uniform solid product than an extract solution of low and fluctuating concentration. Furthermore, the total volume to be treated is only increased at a minimum even though the mucilage normally is dissolved or swelled in a small amount of aqueous liquid prior to use in order to obtain a fast dispersion of the flocculant in the water to be treated.

In a preferred embodiment the mucilage is obtained by extraction of the seed shells, then the extract is concentrated by the use of ultrafiltration, and a powdery product is finally produced by the use of drying such as spray drying.

The mucilage may be modified by the use of chemicals in order to obtain a flocculant usable for spe- cific flocculation of a certain kind of particle in the aqueous liquid to be treated by the method according to the present invention. But usually this chemical modification is not necessary because the native flocculation ability of the mucilage applicable to flocculate a variety of different kinds of particles .

Examples of seeds, which may be used for the production of the mucilage according to the present invention, include linseeds and seeds from the

Lameaceae-Labiatea family. Seeds from the Lameaceae-

Labiatea family are commonly referred to as chias and may be obtained from the species Hyptis suaveolens

(L) Poi t, Salvia hispanica L, Salvia tiliaefolia Vahl , Salvia seemannii Epling, S . columbariae Benth, S . carduacea Benth, and S . polystachya .

Other possible candidate seeds for suitable mucilage are seeds from Tamarind indica (Tamarind gum) , Brassica alba (white mustard) ; Lepidium sativum (cress) ; seeds from Lesquerella (Lesquerella fendleri ) ; Plantago seeds (husk, obtainable from the varieties P. arenaria, P. fastigia, P. lancelota, P. psyllium, P. ovata Forsk.), and Ocium seeds (O. canum Sims, O. basilicium Linn, O. gratissimum L . , 0. adscendens Willd . , O. sanctum, O. killimandscharicum G. , O. pilosu , and 0. rubrum) .

Presently, flax is preferred as the source for seeds from which the flocculant is derived. Seeds from flax (Linum usi tatissimum L . ) are usually called linseeds. The flax plant is adaptable for a variety of soils and climates. Thus flax may be grown locally in remote areas for the production of the flocculant for use in the method of the invention.

The linseed also contain a considerable amount of linseed oil, which may be removed from the linseeds after the extraction with the aqueous liquid by mechanical compression or by extraction with a lipo- phillic solvent. Linseed oil has several applications, including livestock feed, paint, ink, linoleum, varnish and oilcloth. The remaining spent seeds from the compression are rich in proteins, fibres, minerals and low molecular weight components. By the initial recovery of mucilage according to the invention, the protein and fibres may be easily concentrated or isolated by aqueous processes such as centrifugation, isoelectrical precipitation of proteins, and ultrafiltration for concentration of proteins, for food and non-food purposes. The spent seeds may be heated or dried and pressed into cakes for livestock. Thus, after the extraction obtaining the flocculant for use in the present invention, the re- maining part of the seeds may be treated in an environment-friendly way. Furthermore, the flocculant as well as the remaining seeds from the aqueous extraction of the linseeds may enter into the ecological system without harmful influence on said system. In another aspect of the invention the vegetable flocculant is derived from Cyampopsis tetragonoloba

(guar gum) , Ceratonia siliqua (carob gum, locust gum) , Caesalpinia spinosa (tara gum) , Abelmoschus esculentus (okra) , Triumfetta lappula L . (burweed) , Amorphophallus konjac (konjacmannan) , Anacardiaceae

(jhingan gum) and Veronia anthelmintica (butea gum) .

One preferred mucilage is konjakmannan. Konjakmannan may be derived from various parts of the plant

Amorphophallus konjak. As an example, the roots and the rhizomes may be harvested, comminuted and the mucilage extracted with an aqueous solvent . The extract may be used directly in the method of the present invention or it may be concentrated and/or dried as stated above for seed mucilage. Mucilage extracted from the vegetable matter is generally polysaccharides. Structurally they are far more complex than simple polysaccharides like starch, cellulose, glycogen etc. Mucilage is neither completely insoluble nor completely soluble in water. Generally, it gives rise to gel-like structures in aqueous systems. Mucilage and gums are closely rela- ted in a chemical and functional manner. Therefore, the term "mucilage" , as used in the present description and in the claims, also covers gums with flocculating properties.

The term "particulate carrier", as used herein, refers to a solid particle, which is not substantially attacked by the liquid and which maintain a proper chemical and physical stability. The particulate carrier usually has a density higher than the density of the liquid containing the particles and colloids to be removed. Preferably, the particulate carrier is sand. However, the particulate carrier may also be selected from alumina, magnetite, hematite, ilmenite, calcium oxide, limestones, calcium hydroxides, slaked lime, calcium carbonates, calcium alu- minate, crushed carbon, graphite, silica, calcite, and mixture thereof. The grain size of the particulate carrier is typically smaller than approximately 300 μm and larger than 75 μm. Preferably; the grain size of the particulate carrier is between 150 and 250 μm.

Sand having a grain size of 150 to 250 μm is obtainable from various sources under the generic name micro sand. Micro sand may for other applications be used as filter aid. The coagulant according to the present invention serves the purpose of neutralizing the zeta potential of the particles or colloids to be removed. The zeta potential is the electrical charge at the boundary between a particle and the suspending medium and relates to the repelling forces between particles having the same kind of charge. The zeta potential may be positive or negative depending on the nature of the particles.

If the zeta potential of the particles to be coagulated is positive, the applied coagulant must be negatively charged. Preferred negatively charged coagulants are halides like chloride, bromide and iodide. Another negatively charged coagulant, lignin, may also be used, see US 5,174,903, the content of which is incorporated herein by reference.

However, in most cases the zeta potential of the particles is negative, and then a cation is preferred notably a polyvalent cation as the coagulant. Preferably, the coagulant is a trivalent cation such as Al³⁺ or Fe³⁺. The trivalent cation may be added to the liquid as a suitable dissolved salt, such as an aqueous solution of aluminium sulphate, aluminium chloride, ferric chloride or the like.

Once the zeta potential has been neutralised, the coagulated particles or colloids tend to aggregate. If a particulate carrier is added to the aqueous li- quid at this point in the process, it is believed that the presence of the particulate carrier in the aqueous environment results in an attachment of the coagulated particles and colloids thereto, thus increasing the weight of the aggregates. At the subse- quent addition of flocculant the aggregated matter is gathered in floes. Therefore, if a particulate carrier is present, the rate of sedimentation is increased due to the increased weight of the floes.

Whereas the individual components in the aqueous liquid of step (a) may be added in any order, the best result is generally obtained by mixing the aqueous liquid comprising suspended solid particles or colloids to be removed with a coagulant, allowing said mixture to react for a period of time sufficient for obtaining a coagulation of the suspended solid particles or colloids and then adding the particulate carrier to the mixture.

Some aggregated matter will respond to cationic flocculants, while others will respond to anionic or non-ionic flocculants. Unmodified mucilage is generally anionic or non-ionic and is the preferable choice of mucilage for use in the method according to the invention. However, for some special applications it may be necessary or desirable to subject mucilage obtained from the vegetable matter to a chemical modification. Cationic mucilage generally contains alkaline groups like amino, amino alkyl ether, 0- or N-alkyl groups.

In a preferred embodiment of the invention an anionic flocculant is used for flocculation. The anionic flocculant contains monosaccharides having negatively charged groups. The negatively charged groups may be carboxylic, sulphate or phosphate groups. Usually, the negatively charged monosaccharides are glucuronic acid or galacturonic acid, but other kinds of negatively charged monosaccharides may occur. It is within the scope of the protection con- ferred by the present patent that the flocculant, the coagulant and/or the particular carrier may be added to the aqueous liquid in any order. Especially, the flocculant may be added to the aqueous liquid prior to, simultaneous with or subsequent to the addition of the coagulant and/or the particulate carrier.

In some cases the mucilage may be applied directly without the use of a coagulant for example in the removal of positive charged particles like heavy metals and other metals. The mucilage may be applied direct- ly in order to remove phosphor and products alike.

The time required for performing the individual steps of the method according to the invention varies widely. The coagulation usually occurs relatively fast after the addition of the coagulant, i.e. within minutes. Whether and to what extent the coagulation has occurred may be visually inspected as the liquid becomes turbid. If a particulate carrier form part of the water treatment method, it is usually added sub- sequent to and after sufficient time of coagulation. The aggregation of the coagulated particles and colloids around the particulate carrier occurs usually fast, i.e. within minutes. However, the coagulation and aggregation process may be prolonged if the aqueous liquid is not sufficiently stirred. Subsequent to satisfactory aggregation the mucilage may be added. The time required for formation of floes and the size of the floes depends on the stirring rate: the more turbulent the stirring, the faster the flocculation. However, if the stirring is very fast the floes formed tend to become small because of disruption by the turbulent flow. Furthermore, the floes formed should contain as little liquid as possible (especially in the middle) in order to facilitate an effective de-watering.

Surprisingly, the following experiments included in the description, notably Example 2, show that the efficiency of the method is somewhat sensitive to the stirring rate. It appears that the turbidity is decreased significantly when the stirring speed is increased from 30 rpm to 90 rpm. This fact suggests that the best result using the present method is obtained at a moderate to high stirring speed. The amount of flocculant and optionally particulate carrier and coagulant required for purification of the liquid to be treated may be determined by the skilled person by simple trial and error experimentation. The amount of coagulant should not be added in excess in order to keep the concentration of the coagulant at a minimum in the purified aqueous liquid. However, the zeta potential of the suspended particles has to be sufficiently neutralized. Usually the coagulant is added to the aqueous liquid in an amount corresponding to a concentration in the liquid of 1 to 50 mg/1, preferably 2 to 20 mg/1. The amount of coagulant may be larger or smaller than the above ranges depending on the amount of suspended particles in the liquid, the nature and source of the suspended particles, the components in the aqueous liquid etc.

The amount of flocculants added to the coagulated aqueous liquid has to be as large as to sufficiently flocculate all aggregated matter. However, addition of flocculants in excess will result in an increased chemical oxygen demand of the treated aqueous liquid.

The amount of particulate carrier should generally be sufficient for allowing a major amount of coagulated particles and colloids to be attached thereto. However, care should be taken because addition of particular carrier in excess results in the presence of free particulate carrier, which is not attached to coagulated particles or colloids, and therefore tend to maintain in the liquid and possesses low sedimentation rates. Thus, excess particulate carrier affects the quality of the treated water in a negative way, especially the turbidity. Usually, the amount of particulate carrier added to the aqueous liquid is in the range of 2 g/1 to 50 g/1, preferably 5 g/1 to 20 g/1. The amount may be larger or smaller than the values indicated depending on the amount and type of particles and colloids to be removed from the aqueous liquid. The aqueous liquid to be treated according to the present invention may derive from a variety of sources, for example wastewater, sewage, effluents from industrial plants, and water from rivers, streams, lakes, ponds, reservoirs, wells and the like. The aqueous liquid, after treatment according to the present invention, may be used as tap water, recycling aqueous liquid for industrial plants, effluents for natural recipients and the like.

The suspended particles in the aqueous liquid treated according to the present invention may be colloidal or solid. Colloidal particles are typically organic materials, such as proteins, polysaccharides, and oil, but can be inorganic matter like colloidal silica or synthetic like synthetic polymers. Solid particles are typically mineral substances and precipitated salts.

The present method may be used for the production of tap or drinking water, water usable for making cement or concrete, cooling water and for removal of certain substances or impurities. Furthermore, the present method may be of interest for treatment of various wastewaters, such as effluents from the phar- maceutical industry, biotechnology industry, production of beer, purification of enzymes, and food industry.

In a preferred aspect of the invention the method is used for production of drinking water. Because the flocculant used in the present invention is derived from a vegetable source, e.g. seeds of a terrestrial edible plant, and the consumer of the drinking water is not exposed to any health hazard if a part of the mucilage added during the process remains in the water. Thus, the consumer may feel safe even when the method of the invention is not working optimally. This is in contrast to the synthetic flocculants, which is normally used.

The use of a terrestrial plant as the source for the mucilage provides for the use of the present method in remote areas of the world because the flocculant may be produced locally from crops grown on a nearby field. Moreover the method may easily be adaptable to less industrially developed areas of the world, whereby such areas will be capable to produce purified drinking water using flocculants obtained from locally grown crops. A major problem in less industrially developed areas of the world is diseases caused by impure and contaminated drinking water. The present method may be a solution to this problem.

Surprisingly, mucilage derived from a vegetable source used for flocculation in the method according to the present invention affects the coagulated aqueous liquid in a substantially similar way as the prior art synthetic flocculants. Thus, the values of the indicators applied in the following examples, that are turbidity, chemical oxygen demand, remaining coagulant and suspended solids in the aqueous liquid treated according to the present invention do not significantly differ among the synthetic and the natural flocculant .

Examples

1. Production of an aqueous extract of linseed (NF1)

100 g linseed was placed in a beaker provided with stirring. 750 ml of water at a temperature of 45°C was added to the linseeds and stirring was initiated at a rate of 200-300 revolutions per minute. The stirring was continued for 90 minutes maintaining a temperature of about 45°C. During stirring the water phase visually became opaque due to the extraction of the mucilage from the linseeds. After the extraction, the suspension was sieved separating the mucilage and the linseed. 500 ml of opaque liquid was recovered.

The remaining linseeds were subjected to a second extraction using the same directions as indicated above, with the exception that the linseed was submersed in 300 ml instead of 750 ml of water. 198 ml of opaque liquid was recovered from this second extraction. The extracts from the first and second extraction was combined and used in the subsequent experiments. The dry weight harvest in the combined extract was about 10 g per litre (1.0% ( /w) ) . This solution is referred to in the following as NF1.

2. Konj akmannan .

Konjakmannan was obtained as a spray dried product of an aqueous extract of the root of Amorphophallus konjak. Prior to the experiments a 0.3% (w/w) solution was prepared. This solution is referred to as NF3.

3. Prior art flocculant.

For comparison, a conventional flocculation agent, the polyacrylamide Floerger, AN934 PWG (obtained from Bo Jensen Vandbehandling, Denmark) was used in the experiments. The prior art flocculant was purchased as a solid. Prior to the experiments a 0.05% (w/w) solution was prepared. This solution is referred to as SYF.

4. Equipment . Cubic containers of acrylic glass (Plexiglass^®) having an internal dimension of 15 x 15 x 15 cm were used for the experiments. A volume of 2 1 water was used. A mixer provided with an adjustable speed and a paddle having a dimension of 6 x 6 cm was used for stirring.

5. Water for the experiments.

75 1 of surface water and 5 1 of bottom sediments obtained from the Norwegian river Glomma was collee- ted and used for the production of the water samples contaminated with solid and colloidal material. The experiments were conducted on samples prepared by mixing surface water contaminated with sediments to a turbidity of around 200 NTU. The contaminated water for preparation of the samples was produced by shaking the container with the sediments, allowing the suspension to precipitate in 30 minutes and finally decanting the aqueous layer.

The spiked water was obtained by mixing an appropriate amount of the contaminated water with the surface water. To attain 1 1 of sample water with a turbidity of 200 NTU around 40 ml contaminated water was mixed with 960 ml surface water.

6. Coagulant

Aluminium sulphate was used as the coagulant. A stock solution having a concentration of 700 mg alu- minium per litre was prepared and 15 ml thereof was added to each 2 1 sample to obtain a final aluminium concentration of 5.25 mg/1.

7. Particulate carrier Sand with a size between 150 and 250 μm was used as the particulate carrier. Sand of this size may be obtained from various sources and is purchased as micro sand usable as filter aid.

Example 1

Flocculation at low turbulence.

2 1 of spiked water with a turbidity of 200 NTU was loaded into a cubic container. The stirring equipment was turned on and adjusted to a speed of 200 rpm. Subsequently, 15 ml of coagulant stock solution was added and pH was adjusted to a value of 5 - 5.5. The stirring was continued at 200 rpm in 1 min and then decreased to a rate of 150 rpm. The amount and type of flocculant as indicated in Table 1 below was then added and pH was adjusted to a value of 6 - 6.5. Then the stirring rate was decreased to 25 - 35 rpm and maintained at this rate for 10 minutes. Then, the stirring was stopped and the suspension was settling for 20 minutes. The liquid above the settled matter was evaluated visually and a sample was with- drawn from the centre of the liquid phase for analysis. The particulars of the experiments and the results thereof are indicated in Table 1 below:

Table 1.

COD: Chemical Oxygen Demand

SS : Suspended solid having a size of 0.45 μm or larger

SYF: Synthetic flocculant

NF1 : Natural flocculant derived from linseeds

Example 2

Flocculation at higher turbulence

The experiment indicated in Example 1 was repeated with the only exception that the speed of the stirring was varied. Experiments were conducted at 30, 60, and 90 rpm. The results are shown in Table 2 below:

Table 2.

The results indicate that the water quality is improved by increasing the stirring speed. Especially the turbidity values are significantly reduced. The sensibility of the method for measuring COD is not as good as to reveal any decrease in this value. The values for the suspended solids are maintained at a satisfactory low level. The visual inspection of the produced floes shows that the size thereof is de- creased when the stirring speed is increased. Example 3

Flocculation in the presence of micro sand

2 1 of spiked water with a turbidity of 200 NTU was loaded into a cubic container. The stirring equipment was started and adjusted to a speed of 300 rpm. Subsequently, 15 ml of the coagulant stock solution was added and pH was adjusted to a value of 5 - 5.5. An amount of 20 g micro sand was added and stirring continued for 1 minute. The stirring was decreased to 200 rpm. The amount and type of flocculant as indicated in Table 3 below was then added and pH was adjusted to a value of 6 - 6.5. The stirring rate was continued for 1 minute. Then, the stirring was stopped and the suspension was settling for 20 minutes. The liquid above the settled matter was evaluated visually and a sample was withdrawn from the centre of the liquid phase for analysis. The particulars of the experiments and the results thereof are indicated in Table 3 below.

The results indicate that the lowest turbidity and concentration of suspended solids are obtained in batch No. 1, 5, and 9 for the flocculants SYF, NF3 , and NF1, respectively. Surprisingly, the natural flocculants have the ability to produce a water quality, which is almost similar to the quality performed by the synthetic flocculant. In fact, the lowest turbidity is obtained by use of the flocculant, NF1, derived from linseeds in batch No. 9.

COD : Chemical Oxygen Demand

SS : Suspended solid having a size of 0.45 μm or larger SYF: Synthetic flocculant NFl: Natural flocculant derived from linseeds

NF3 : Natural flocculant derived from Amorphophallus konj ak

Claims

P A T E N T C L A I M S 1. A flocculant comprising mucilage derived from vegetable matter by the use of an extraction method comprising the steps of: (a) submersing the vegetable matter in a suitable aqueous liquid,

(d) separating the mucilage from the spent vegetable matter,

(e) concentrating the mucilage in the aqueous liquid, and, optionally,

(f) drying the mucilage to form a solid powdery product .

2. A flocculant according to claim 1, wherein the mucilage is derived from any part of a terrestrial plant.

3. A flocculant according to claim 1, wherein the mucilage is derived from any part of a terre- strial plant selected from Cera tonia siliqua (carob gum, locust gum) , Caesalpinia spinosa (tara gum) ,

Abelmoschus esculentus (okra) , Triumfetta lappula L.

(burweed) , Anacardiaceae (jhingan gum) , Veronia anthelmintica (butea gum) , Hyptis suaveolens (L) Poit, Tamarind indica (Tamarind gum) , Brassica alba

(white mustard) ; Lepidiu sativum (cress) ; Plantago

(P. arenaria, P. fastigia, P. lancelota, P. psyllium,

P. ovata Forsk.), and Ocium (O. canum Sims, O. basilicium Linn, O. gratissimum L . , O. adscendens Willd. , 0. sanctum, 0. killimandscharicum G. , O. pilosum, 0. rubrum) .

4. A flocculant according to claim 2, wherein the mucilage is derived from seeds of a terrestrial plant .

5. A flocculant according to claim 4, wherein the mucilage is derived from seed shells of a terrestrial plant.

6. A flocculant according to claim 4-5, wherein the mucilage is derived from seeds of flax (Linum usi tatissimum L . ) .

7. A flocculant according to claim 1, wherein the mucilage is guar gum derived from Cyampopsis tetragonoloba .

8. A flocculant according to claim 1, wherein the mucilage is konjakmannan derived from any part of the plant Amorphophallus konjak.

9 . A flocculant according to claim 1, wherein the mucilage is derived from chia (obtainable from Salvia hispanica L. , S. tiliaefolia Vahl , S. seemannii Epling, S. columbariae Benth, S. carduacea Benth, S. polys tachya) .

10. A flocculant according to claim 1, wherein the mucilage is derived from Lesquerela (Lesquerela fendleri) .

11. A flocculant according to any of the claims 4-6, wherein the mucilage is liberated from the seed shells by vigorously stirring the aqueous liquid containing the seeds.

12. A flocculant according to any of the claims 1-11, wherein the mucilage is recovered as an aqueous extract.

13. A flocculant according to any of the claims 1-11, wherein the mucilage is concentrated by the use of ultrafiltration.

14. A flocculant according to claim 13, obtain- able by the use of a filter size of 5kDa to 500kDa.

15. A flocculant according to claim 14, wherein the complex mucilage with a molecular weight greater than 5,000 Dalton is obtained.

16. A flocculant according to claim 13, wherein the ultrafiltration is carried out for size exclusion of about 5kDa.

17. A flocculant according to claim 16, wherein the substantially pure complex is derived from flax- seed shells and other terrestrial plants containing mucilage in their seed shells having a molecular weight of at least 5,000 Dalton.

18. A flocculant according to claim 16, wherein the fraction from the size exclusion ultrafiltration comprising the substantially pure complex is dried to form a powder.

19. A flocculant according to claim 16, wherein the retentate from ultrafiltration comprising the pure complex is concentrated to form a liquid concentrate .

20. A flocculant according to claim 5, wherein a dry mucilage is obtained by the combination of extracting only from seed shells, concentrating by the use of ultrafiltration, and drying by the use of spray drying.

21. A use of the aqueous liquid obtained according to claim 1, wherein proteins and fibres are concentrated or isolated by processes such as centrifugation, isoelectrical precipitation and ultrafil- tration of proteins for food and non-food purposes.

22. A method for separation of suspended solid particles or colloids from an aqueous liquid, com- prising the steps of

(a) providing an aqueous liquid containing aggregates of suspended solid particles or colloids, a flocculant prepared according to any of the claims 1-20, (b) reacting the mixture of step (a) for a period of time sufficient for forming floes, and

(c) separating the floes from the aqueous liquid.

23. A method according to claim 22, wherein a coagulant is added to the aqueous liquid in an amount sufficient for coagulation of the solid particles or the colloids prior to, simultaneous with or subse- quent to the addition of the flocculant.

24. A method according to claim 22-23, wherein a particulate carrier is added to the aqueous liquid prior to, simultaneous with or subsequent to the addition of the flocculant and/or the coagulant .

25. A method according to claim 24, wherein the particulate carrier is selected from alumina, magnetite, hematite ilmenite, calcite, and sand.

26. A method according to any of the claims 24-

25, wherein the size of the particulate carrier is between 45 and 300 μm.

27. A method according to any of the claims 23-

26, wherein the coagulant, if present, is a cation.

28. A method according to any of the claims 27, wherein the coagulant is Al³⁺ or Fe³⁺.

29. A method according to claim 24, wherein the aqueous liquid containing aggregates of step (a) is prepared by mixing an aqueous liquid comprising suspended solid particles or colloids with a coagulant, allowing said mixture to react for a period of time sufficient for obtaining a coagulation of the suspended solid particles or colloids prior to addition of the particulate carrier to the mixture.

30. A method according to any of the claims 22- 29, wherein the aqueous liquid is surface water from a lake or a river.

31. A method according to any of the claims 22- 29, wherein the aqueous liquid containing solid particles or colloids is wastewater from an industrial plant or municipal sewage.

32. A use of the method according to any of the claims 22-31 for the production of drinking water.

33. A use of the method according to any of the claims 22-31 for purification of enzymes.

34. A use of the method according to any of the claims 22-31 for clarification of water to be used in cement concrete manufacture .

35. A use of the method according to any of the claims 22-31 for the treatment of effluents from the production of beer.

36. A use of the method according to any of the claims 22-31 for the treatment of effluents from the pharmaceutical industry, textile industry paper manufacturing industry, paper re-cycling industry, or food industry.