Composite coagulants

Field of the disclosure

The present disclosure relates to a composite coagulant, a method of making the composite coagulant, and a method of treating wastewater using the composite coagulant.

Background of the disclosure

Microplastic pollution is of increasing concern. A significant source of microplastic pollution results from the washing of textiles, for example, each cycle of a washing machine can release contaminants such as micro and nanoplastic fibres into the environment.

Micro/nano-plastics have proved exceedingly challenging to remove from wastewater streams. Filtration is the major technique used to remove suspended contaminants, however filtration is expensive, as micro/nano-plastics rapidly clog filters. Furthermore, filters may not be effective for nano-plastics as they commonly have pore sizes in the tens of microns, and are not adapted to deal with additional contaminants, such as suspended oil or chemical droplets.

Centrifugation is also not well adapted for the removal of microplastics from wastewater because microplastics often have a density that is close to that of water and thus require the employment of very high levels of energy to effect removal.

Release of such wastewater to the environment contributes to micro/nano plastic pollution that permeates the global food chain.

Accordingly, there is a need for improved wastewater treatments to remove or reduce micro and nanoplastics from water prior to discharge of the water into the environment.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of the disclosure

In a first aspect of the present disclosure there is provided a composite coagulant comprising one or more particulate materials, wherein the one or more particulate materials are at least partially coated with one or more ionic polymers, and wherein the one or more particulate materials are insoluble or sparingly soluble in water.

In embodiments of the first aspect there is provided a coagulating composition comprising: a. the composite coagulant as herein disclosed; and b. a liquid wherein the weight percentage of the liquid is not more than about 99% of the total weight of the coagulating composition.

In embodiments the weight percentage of the liquid is not more than about 95wt%, or not more than about 90wt%, or not more than about 85wt%, or not more than about 80wt%, of the coagulating composition.

In embodiments the weight percentage of the composite coagulant in the coagulating composition is at least about 1wt %, or at least about 5wt%, or at least about 10wt%, or at least about 15wt%, or at least about 20wt%, or at least about 25wt%, or at least about 30wt%, of the coagulating composition.

Advantageously, the composite coagulants and coagulating compositions as described herein are able to capture suspended microplastics, preferably microfibers present in water.

In embodiments, the weight ratio of particulate material to ionic polymer is from 1:99 to 99:1. In some embodiments the weight ratio of the particulate material to ionic polymer is from about 1 : 19 to 19: 1. Alternatively, in some embodiments the weight ratio of the particulate material to ionic polymer is from about 1 :9 to 9:1.

In some embodiments the weight ratio of the particulate material to ionic polymer is from about 1 :5 to 5: 1.

In some embodiments the weight % of ionic polymer in the composite coagulant is from 1 wt.% to about 5 wt.%, or alternatively from about 20 wt.% to about 50 wt%, or alternatively from about 50 wt% to about 80 wt.%.

In some embodiments, the weight % of ionic polymer in the composite coagulant is from 1 wt.% to about 5 wt.%.

In other embodiments, the weight % of ionic polymer in the composite coagulant is from about 95 wt.% to about 99 wt.%.

In other embodiments, the weight % of ionic polymer in the composite coagulant is from about 20 wt.% to about 80 wt.%.

In some embodiments there is provided a coagulating composition as described herein, wherein the liquid does not comprise substantially any free polymer, preferably wherein the liquid does not comprise more than 5 wt.% free polymer; and wherein the wt.% of the free polymer is calculated as a percentage of the total amount of polymer in the composition.

In embodiments, the ionic polymer comprises positively charged groups, negatively charged groups, or a combination thereof.

In embodiments, the ionic polymer is a cationic polymer or an anionic polymer.

In embodiments, the ionic polymer is charged when in an aqueous solution.

In embodiments, the ionic polymer is derived from one or more of quaternary ammonium monomer, cationic amino acids, allylamine monomer, 2-(dimethyl amino)ethyl acrylate, 2-(dimethyl amino)propyl acrylate, 2-(dimethyl amino)ethyl methacrylate, 2-(dimethyl amino)propyl methacrylate, 3-(diethylamino)ethyl acrylate, 3-(diethylamino)propyl acrylate, 3-(diethylamino)ethyl methacrylate, 3-(diethylamino)propyl methacrylate, diallyldimethyl ammonium halide, triallymethyl ammonium halide, vinylalkylpyrrolidinium halide, vinylpyrrolidone, allylalkylpyrrolidionium halide and diallylpyrrolidinium halide, chitosan, and chitosan derivatives, acrylic monomer, acrylate monomer, sulfonate monomer, phosphate monomer, or anionic amino acids, methacrylic acid, acrylic acid, itaconic acid, p-styrene carboxylic acids, p-styrene sulfonic acids, vinyl sulfonic acid, vinyl phosphonic acid, ethacrylic acid, alpha-chloroacrylic acid, crotonic acid, fumaric acid, citraconic acid, mesaconic acid and maleic acid.

In embodiments, the one or more ionic polymer is a polyquaternary ammonium, a polyallylamine, a polyacrylate, a poly(acrylic acid), a poly(methacrylate), a poly(methacrylate) derivative or a polymer comprising sulfonate or phosphate groups, natural polymers containing amine groups such as chitosan and chitosan derivatives; cellulose derivatives or gums containing acid-groups, or sugar based derivatives containing acid groups, for example, alginates.

In embodiments, the one or more ionic polymer is polydiallyldimethylammonium chloride (PolyDADMAC), poly(allylamine hydrochloride), polymethacrylate, poly(styrene sulfonate), or poly(glutamate).

In embodiments neither the particulates nor the ionic polymers comprise cyclodextrin.

In embodiments, the composite coagulant comprises at least a first polymer layer adsorbed to the surface of the particulate material and at least a second polymer layer, said second polymer layer having an opposite charge to the first polymer layer adsorbed to the first polymer layer.

Advantageously by using multiple polymer layers in the composite coagulate the final charge of the composite coagulant can be the same or different to the surface charge of the particulate.

In embodiments, the particulate material has a surface charge, said surface charge being the opposite charge to the charge of the one or more ionic polymers adsorbed on the particulate material surface. In embodiments, the particulate material comprises one or more of a clay, an insoluble salt, an insoluble metal oxide, a silicate, or a carbonaceous material.

In embodiments, the particulate comprises one or more of kaolin, calcite, alumina, silica, sand, and activated charcoal.

In embodiments, the composite coagulant sediments in an aqueous liquid. In embodiments the particulate material sediments within 10 minutes, or within 5 minutes, or within 2 minutes, or within 1 minute. In alternative embodiments the particulate material comprises particles which have a density closer to that of the aqueous liquid and sedimentation occurs over 1 hour, or 2 hours, or 3 hours.

In alternative embodiments, sedimentation occurs over a long period of time in a settling tank. In embodiments sedimentation occurs in a settling tank over a period of from about 1 hour to about 1 week, for example a period of 2 hours or 1 day, or 2.5 days.

In embodiments sedimentation may be accelerated by centrifugal forces.

Advantageously the particulate component has a higher density compared to water and enables captured fibre to sink to the bottom of the tank. During the sinking the attached composite coagulant can further aggregate with more fibres and particle contaminants which improves coagulation of the contaminants and may increase microplastic removal efficiency.

The particulate may be a nanoparticle, or a large particle with an elongated morphology.

In embodiments the particulate has an average size of from about 20 nm to about 50 microns.

In some embodiments the particulate has an average size of from about 20 nm to about 1000 nm.

In some embodiments the particulate has an average size of from about 1 micron to about 20 microns. In embodiments the particulate has an average size of from about 0.25 microns to 20 microns. In other embodiments the particulate has an average size of from about 1 micron to about 30 microns; even more preferably from about 10 to about 20 microns.

Advantageously composite coagulants comprising particulates with an average size or length from about 1 to about 30 microns are able to capture suspended contaminants and rapidly sediment, facilitating separation of the captured contaminants.

In embodiments the composite coagulants are provided as a dry powder. In embodiments, they are provided as a suspension or a paste comprising from about 1% to about 99% by weight of the composite coagulant as herein described and water. In some embodiments the composite coagulants are provided as a concentrated suspension.

In preferred embodiments the concentration of composite coagulant is from 10% to 80%, preferably 40% to 65%.

Advantageously, formulations of the composite coagulants as a dry powder, paste or suspension are simple to store, and transport and can be directly dosed into the wastewater system when required.

In a second aspect of the present disclosure there is provided a method of removing contaminants from water comprising:

-combining a composite coagulant and contaminated water; to form a modified composite coagulant comprising contaminants; and

-separating the modified composite coagulant comprising contaminants from the water; wherein the composite coagulant comprises one or more particulate materials which are at least partially coated with one or more ionic polymers, and wherein the one or more particulate materials are insoluble or sparingly soluble in water.

In embodiments of the second aspect the composite coagulant is pre-formed prior to being combined with the contaminated water. In some embodiments the composite coagulant is formulated as a suspension or paste. In embodiments of the second aspect of the present disclosure there is provided a method of removing contaminants from wastewater comprising:

- combining the composite coagulant as herein described and wastewater; and

- separating the coagulant comprising suspended solids.

In embodiments of the second aspect there is provided a method of removing contaminants from water comprising:

- combining a) the composite coagulant or coagulating composition as herein described or a suspension or a paste as herein described, or powder or formulation as herein described, and b) the contaminated water; to form a modified composite coagulant comprising contaminants; and

- separating the modified composite coagulant comprising contaminants from the water.

In embodiments the composite coagulant is pre-formed prior to being combined with the contaminated water.

In some embodiments the method as herein described further comprises addition of an additional coagulant to the water.

In embodiments, at least 80% of the contaminants, preferably 90% of the contaminants, are removed from the water. In preferred embodiments the contaminants are suspended solids.

In embodiments, the contaminated water is wastewater, for example laundry wastewater, industrial wastewater or blackish water, preferably laundry wastewater.

In embodiments, the contaminants comprise fibres, particles or emulsion droplets. In embodiments, the contaminants are microfibers, for example fibres released from clothing.

In embodiments, the contaminants are microplastics, for example irregular shaped plastic fragments.

In embodiments, the contaminants comprise synthetic, non-synthetic or composite (ie blends of synthetic and non-synthetic) polymers. In embodiments the contaminants comprise polyester, acrylic or polyamides.

In embodiments, the separation step comprises one or more of sedimentation, centrifugation, and high-throughput gravity separation. In embodiments, the separation step does not comprise filtration.

In alternative embodiments the composite coagulants comprise magnetic particulates and the separation step comprises use of magnetic fields to enhance separation.

By avoiding the necessity for an expensive filtration step, the use of the composite coagulants of the present disclosure provides an economic and scalable treatment protocol to separate microplastics, and in particular microfibers, from wastewater.

In some embodiments the separation step comprises filtration with a mesh to remove contaminants with a size of 100 microns or more.

In a third aspect of the present disclosure there is provided a method of making the composite coagulant as herein described, wherein the one or more particulate materials is combined with the one or more ionic polymers for sufficient time for the polymers to adsorb at the particle surface.

In embodiments, the composite coagulant is prepared as a dried powder, and dry ionic polymer and dry particulate material are combined and mixed.

In embodiments the composite coagulant is prepared as a slurry in water.

In embodiments, the percentage of solids (particulate material and ionic polymer) is from about 20 wt% to about 80 wt% of the mixture. As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Further aspects of the present disclosure and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 . Schematic of composite coagulant proposed structure according to an embodiment of the present disclosure.

Figure 2. Scanning Electron Microscopy image of dry composite coagulant particles.

Figure 3. Photograph of wastewater showing turbidity and suspended materials

Figure 4. A) Optical microscopy image of fibers and suspended solid particles in wastewater and B) optical microscopy image of decanted wastewater sample after the addition of a composite coagulant.

Figure 5. A) Scanning Electron Microscopy (SEM) image of the centrifuged solids separated from wastewater sample and B) scanning electron microscopy image of decanted wastewater sample after the addition of a composite coagulant.

Figure 6. Transmission Electron Microscopy image of the solid separated from wastewater sample by centrifugation (500 nm scale bar).

Figure 7. A: Photograph of wastewater sample after mixing with the composite coagulant; B: photograph of the wastewater sample after mixing with the composite coagulant after 2 hours showing solid settlement due to the coagulant; C: photograph of the decanted solid waste.

Figure 8. Optical Microscopy image of removed microfibers with attached composite coagulant. Figure 9. Scanning Electron Microscopy image of the removed fibers with attached composite coagulant.

Detailed description of the embodiments

It will be understood that the disclosure described and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the disclosure.

The present disclosure relates to composite coagulants which contain a particulate core and an ionic polymer coating. By design, the polymer coating helps the composite coagulant to attract and retain suspended microfibers in the water and the particulate component causes the coagulated-fibre to sink to the bottom of a vessel.

Definitions

For purposes of interpreting this specification, terms used in the singular will also include the plural and vice versa. For example, “a” means one or more unless indicated otherwise.

The use of the term “about” includes and describes the value or parameter per se. For example, “about x” includes and describes “x” perse. In some embodiments, the term “about” when used in association with a measurement, or used to modify a value, a unit, a constant, or a range of values, refers to variations of up to ±5% and/or ±10%. For example, “about 60°C” in some embodiments includes 54°C - 66°C and/or 57°C - 63°C.

Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any materials and methods similar or equivalent to those described herein can be used to practice or test the present disclosure, the preferred materials and methods are now described.

Similarly, the general chemical terms used in the formulas described herein have their usual meaning. One skilled in the art will recognise many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present disclosure. The present disclosure is in no way limited to the methods and materials described.

The term “measurement” used in the specification should be construed in its broadest sense, including quantitative and qualitative measurement. Unless otherwise stated it should be understood that measurements are conducted at ambient conditions, ie room temperature and pressure.

One skilled in the art will recognise many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present disclosure. The present disclosure is in no way limited to the methods and materials described.

The term “(s)” following a noun contemplates the singular or plural form, or both.

The term “and/or” can mean “and” or “or”.

Unless the context requires otherwise, all percentages referred to herein are percentages by weight of the composition.

Unless the context requires otherwise, all amounts referred to herein are intended to be amounts by weight.

A problem with the removal of microplastics from wastewater is that due to their size and surface charge they often form stable suspensions. Coagulant agents or ionic surfactants may be added to neutralise the surface charge and destabilise the contaminants. Large sized particulates may also sediment, but are easily redispersed by liquid flow, making them difficult to separate. A complimentary flocculation agent, and/or secondary separation step is usually required to facilitate collection of the coagulated contaminants.

In contrast the composite coagulants of the present disclosure due to their composite nature are able to concurrently coagulate and sediment charged contaminants present in wastewater facilitating the removal of the contaminants from the wastewater. Composite Coagulant

As used herein the term composite coagulant refers to a coagulant comprised of at least one polymer and a water insoluble or sparingly soluble particulate material.

Coagulating composition

As used herein the term coagulating composition refers to a composition comprising a composite coagulant as described herein and a liquid, preferably an aqueous liquid, more preferably water.

In some embodiments of the present disclosure the weight percentage of the liquid is not more than about 99% of the total weight of the coagulating composition.

In other embodiments the weight percentage of the liquid (as a % of the total weight of the coagulating compositions) is not more than about 99wt%, or 98wt%, or 97wt%, or 96wt%, or 95wt%, or 94wt%, or 93wt%, or 92wt%, or 91wt%, or 90wt%, or 85wt%, or 80wt%, or 75wt%, or 70wt%, or 65wt%, or 60wt%, or 55wt%, or 50wt%, of the total weight of the coagulating composition.

In alternative embodiments the weight percentage of the liquid in the coagulating composition is from about 1wt% to about 99wt% or any other range falling within this range. For example in embodiments the weight percentage of the liquid in the coagulating composition is from about 10wt% to about 60wt%, or from about 40wt% to about 80wt%, or from about 80wt% to about 95wt%.

In embodiments the weight percentage of the composite coagulant in the coagulating composition is at least about is at least about 1wt%, or at least about 2 wt%, or at least about 3wt%, or at least about 4wt%, or at least about 5wt%, or at least about 10wt%, or at least about 15wt%, or at least about 20wt%, or at least about 25wt%, or at least about 30wt%, of the coagulating composition.

In alternative embodiments the weight percentage of the composite coagulant in the coagulating composition is from about 1wt% to about 99wt%, or any other range falling within this range. For example in embodiments the weight percentage of the liquid in the coagulating composition is from about 10wt% to about 40wt%, or from about 20wt% to about 50wt%, or from about 15wt% to about 45wt%. In some embodiments of the disclosure, the coagulating composition as herein described, the liquid does not comprise substantially any free polymer, preferably wherein the liquid does not comprise more than 5 wt.% free polymer; and wherein the wt.% of the free polymer is calculated as a percentage of the total amount of polymer in the composition.

In other embodiments the liquid does not comprise more than 5wt% free polymer, or more than 4wt% free polymer, or more than 3 wt% free polymer, or more than 2 wt% free polymer, or more than 1 wt% free polymer.

In embodiments the coagulating composition further comprises an additional coagulant, for example but not limited to, aluminium sulphate, calcium salts, barium salts, iron salts or a combination thereof.

In some embodiments, the additional coagulant is not a polymeric coagulant.

Polymer

The ionic polymer may comprise a single type of monomer (homopolymers) or may comprise more than one type of monomer (heteropolymers or copolymers). Typically, homopolymers and copolymers are named according to the functional group formed between two monomer residues in the polymer chain. For example, the monomers of a polyester are linked by ester functional groups.

In embodiments there is provided the composite coagulant as herein described, wherein the one or more ionic polymer is a polyquaternary ammonium, a polyallylamine, a polyacrylate, a poly(acrylic acid), or a polymer comprising sulfonate or phosphate groups.

In preferred embodiments the one or more ionic polymer is polydiallyldimethylammonium chloride (PolyDADMAC), poly(allylamine hydrochloride), polymethacrylate, poly(styrene sulfonate).

Alternatively the polymer may be described as derived from one or more monomers. In embodiments, there is provided the composite coagulant as herein described, wherein the ionic polymer is derived from one or more of quaternary ammonium monomer, cationic amino acids, allylamine monomer, acrylic monomer, acrylate monomer, sulfonate monomer, phosphate monomer, or anionic amino acids.

The polymer may comprise methacrylic acid, acrylic acid, itaconic acid, p- styrene carboxylic acids, p-styrene sulfonic acids, vinyl sulfonic acid, vinyl phosphonic acid, ethacrylic acid, alpha-chloroacrylic acid, crotonic acid, fumaric acid, citraconic acid, mesaconic acid and maleic acid. The polymer may comprise 2-(dimethyl amino) ethyl and propyl acrylates and methacrylates, and the corresponding 3-(diethylamino) ethyl and propyl acrylates and methacrylates, diallyldimethyl ammonium halide, triallymethyl ammonium halide, vinylalkylpyrrolidinium halide, vinylpyrrolidone, allylalkylpyrrolidionium halide and diallylpyrrolidinium halide.

The polymer may be a natural polymer comprising amine groups such as chitosan or chitosan derivatives, cellulose derivatives, or gums containing acid groups or sugar based derivatives containing acid groups such as alginates.

In alternative embodiments the polymer may be an a-chiral polymer. Additionally, or alternatively, the polymer may be a synthetic polymer.

In some embodiments the polymer does not comprise cyclodextrin. In other embodiments the polymer does not comprise chitosan.

In some embodiments the polymer is an inorganic polymer, for example but not limited to, polysilane, polysiloxanes, polysilicate, polysilazanes, polysulfide, poly(Fe ³⁺ ) and poly(AI ³⁺ ).

In embodiments the ionic polymer may be a co-polymer.

Some copolymers comprise monomers linked by different functional groups, for example, monomers linked by ester and amide functional groups. A copolymer comprising more than one type of functional linking group between its monomers may typically be named for the predominate linking group, however, the polymer may be named by reference to either functional group linker. So, for example, a copolymer comprising ester and amide bonds between monomers may be referred to as a polyester or a polyamide. Copolymers may be random copolymers, alternating copolymers, arranged in blocks (sometimes referred to as block copolymers) or grafted copolymers.

Copolymers may be synthesised from at least two monomers chosen to lend different structural and physical characteristics to the copolymer. The linkage and percentage of the two monomers can lead to copolymers with different properties, eg surface charge and/or adsorption behaviour. The structure of the copolymer may be tuned to optimise compatibility of the copolymer with the particulate.

The ionic polymers can be a homopolymer, heteropolymer, copolymer, random copolymer, alternating copolymer, blockcopolymer or a grafted copolymer.

In some embodiments, the copolymer may comprise 2, 3, 4, or more different monomers. In some embodiments, the copolymer consists of 2 monomers.

In some embodiments the molecular weight of the polymer is greater than 200 g/mol. In some embodiments the molecular weight of the polymer is from 200 g/mol to 1 million g/mol.

The ionic polymer may be a high molecular weight polymer, having a molecular weight of at least 1000 g/mol, preferably 10,000 g/mol or more. In embodiments more than one ionic polymer with different molecular weights may be used. The ionic polymers may independently have molecular weights of at least 1000 g/mol, at least 2000 g/mol, at least 3000 g/mol, at least 4000 g/mol, at least 5000 g/mol, at least 6000 g/mol, at least 7000 g/mol, at least 8000 g /mol, at least 9000 g/mol at least 10,000 g/mol, at least 15,000 g/mol at least 20,000 g/mol, at least 30,000 g/mol, at least 40,000 g/mol, at least 50,000 g/mol, at least 60,000 g/mol, at least 70,000 g/mol, at least 80,000 g/mol, at least 90,000 g/mol, at least 100,000 g/mol, or more.

The ionic polymer may be an oligomer or a short-medium chain polymer. As used herein, the term “oligomer” describes a short polymer chain. In some embodiments, an oligomer may be a polymer comprising up to about 300, 250, 200, 150, 125, 100, 90, 80, 70, 60, 50, 40, 30, 20 or 10 monomers. In some embodiments, the ionic polymer may comprise a number of monomers from any of these values to any other value, for example, from about 10 to about 300 monomers or from about 30 to about 100 monomers. The degree of polymerisation is the number of repeating units contained within a molecular chain. In the case of large polymers, the actual degree of polymerisation may not be known and polymers and oligomers are usually referred to by their average molecular weight.

The molecular weight of a polymer is the molar mass expressed in grams, and can be determined using size exclusion chromatography, otherwise referred to as Gel Permeation Chromatography (GPC), by measuring the retention time required for a polymer to permeate a column compared to a similar standard of known molecular weight.

Particulate

The disclosure provides a combination of a particulate and a polymer that advantageously has improved coagulant properties for the coagulation and separation of dispersed contaminants in wastewater. Many combinations of polymer and particulate may be suitable.

The polymer and particulate may be chosen such that the particulate material has a surface charge, said surface charge being the opposite charge to the charge of the one or more ionic polymers adsorbed on the particulate material surface. For example if the particulate has a negative surface charge, the ionic polymer is a cationic polymer. Alternatively, if the particulate has a positive surface charge, the ionic polymer is an anionic polymer.

Alternatively, more than one polymer may be used and deposited in layers such that the first polymer has the opposite charge to the surface charge of the particulate and the second polymer has an opposite charge to the charge of the first polymer and the same charge as the surface charge of the particulate. For example, the particulate may have a positive charge, the first polymer may be an anionic polymer and the second polymer may be a cationic polymer. Multiple polymer layers of alternating charge may be used. Without wishing to be bound by theory, it is proposed that the separability of the coagulated contaminants is enhanced due to the high density and/or size of the particulates. The particulates are chosen such that the composite coagulant sediments in an aqueous environment. In embodiments, the particulates are micro-particles.

In some embodiments, the particulates have an average size of 10 microns.

In some embodiments, the particulates have an average size of from 20 nm to 50 microns.

In embodiments the particulates have an average length of from about 20 nm to about 1000 nm.

In embodiments the particulates have an average length of from about 1 micron to about 50 microns, preferably from about 1 to about 30 microns, more preferably from about 10 to about 30 microns, even more preferably about 20 microns.

Advantageously composite coagulants comprising particulates in the size range of from about 10 to about 30 microns are able to sediment more rapidly compared to smaller particulates. However, surprisingly, composite coagulants made from larger particles are also able to capture substantially all of the suspended solid contaminants in the water being treated. In other words, the composite coagulants having particulates of this size range sediment faster compared to composite coagulants having smaller particulates without compromising the quality or amount of suspended solid capture.

In some embodiments the particulates are elongated mineral fibres with a length up to 500 microns.

In embodiments the particulate material comprises one or more of a clay, an insoluble salt, a mineral salt, a mineral powder an insoluble metal oxide, a silicate or a carbonaceous material.

In preferred embodiments the particulate comprises kaolin, calcite, alumina, silica, sand, or activated charcoal.

The terms insoluble salt and insoluble metal oxide refers to a solid having a solubility of less than 0.1 g in 100 mL of wastewater solution. Alternatively, this may be expressed as the insoluble salt or insoluble metal oxide having a solubility of less than 10 ppm in the wastewater solution. The insoluble salts and insoluble metal oxides remain substantially insoluble at the operating conditions (ie pH and temperatures) of the wastewater requiring treatment.

In embodiments the particulate material comprises a sparingly soluble salt or sparingly soluble metal oxide. As used herein the term sparingly soluble salt/oxide refers to a salt/oxide that as a solubility of from about 1 g to about 3g in 100 mL of wastewater solution. The sparingly soluble salts and sparingly soluble metal oxides remain sparingly soluble at the operating conditions (ie pH and temperatures) of the wastewater requiring treatment.

In embodiments the particulate material comprises an insoluble or sparingly soluble metal hydroxide, for example calcium hydroxide, magnesium hydroxide, iron hydroxide, copper hydroxide, nickel hydroxide or aluminium hydroxide.

The purpose of the particulate portion of the composite coagulant is to increase the density of the coagulant and to cause the coagulant comprising contaminants to sediment or be separated using density based methods, for example, centrifugation. Accordingly the size and material of the particulate are chosen such that they sediment in the water being treated.

Accordingly, in some embodiments the particulate is not a polymeric particulate. In alternative embodiments the particulate is not a porous particulate. In some embodiments the particulate does not comprise porous activated carbon. In other embodiments the particulate does not comprise cyclodextrin. In other embodiments the particulate does not comprise polymeric cyclodextrin.

In some embodiments of the disclosure the particulate is a magnetic particulate, preferably a ferromagnetic particulate, and may comprise iron oxide, or nickel oxide or cobalt oxide.

Relative amounts of particulate and polymer

In embodiments, the weight ratio of particulate material to ionic polymer is from 1 :99 to 99:1. In some embodiments the weight ratio of the particulate material to ionic polymer is from about 1 : 19 to 19: 1 . Alternatively, in some embodiments the weight of the particulate material to ionic polymer is from about 1 :9 to 9:1. In other embodiments the weight ratio of the particulate material to ionic polymer is from about 1:5 to 5:1.

In some embodiments the weight % of ionic polymer in the composite coagulant is from 1 wt.% to about 5 wt.%, or alternatively from about 20 wt.% to about 50 wt%, or alternatively from about 50 wt% to about 80 wt.%.

In some embodiments, the weight % of ionic polymer in the composite coagulant is from 1 wt.% to about 5 wt.%. In other embodiments, the weight % of ionic polymer in the composite coagulant is from about 95 wt.% to about 99 wt.%.

In other embodiments, the weight % of ionic polymer in the composite coagulant is from about 20 wt.% to about 80 wt.%.

In some embodiments the particulate is at least partially coated with the polymer to form the composite coagulant. In other embodiments the particulate is fully coated with the polymer.

The weight ratio of the polymer to the particulate may be chosen based on the size of the particulate. Particulates having a smaller size have more surface area and therefore require a higher amount of polymer to coat the particles. Conversely, the same mass of larger particulates will have a smaller surface area and require less polymer to coat the surface.

In embodiments the weight% of the polymer in the composite coagulant is relative to the particulate size such that the particulate is fully coated. For example, in embodiments where the particulates have an average size of 1 micron the weight% of the polymer is about 50wt%; in embodiments where the particulates have an average size of 10 microns the weight% of the polymer is about 4%. In embodiments where the particulates have an average size of about 20 microns, the weight% of the polymer is about 0.1%.

Advantageously, coagulating compositions in which all the polymer is attached to the particulates, may be able to capture suspended contaminants in contaminated water and sediment faster compared to coagulating compositions comprising substantial amounts of free polymer.

Formulations

In embodiments there is provided a formulation comprising the composite coagulant or coagulant composition and an additional coagulant.

The additional coagulant may be a salt, for example but not limited to calcium salt, aluminium salt, barium salt or an iron salt.

In embodiments the additional coagulant is not a polymeric coagulant.

The formulations may additionally comprise other additives useful in the treatment of contaminated water. In some embodiments the formulation may comprise bleach, peroxides, chloramine, or a salts, for example sodium chloride, a fluoride salt, a calcium salt, or a magnesium salt.

Method of using

In an aspect of the disclosure there is provided a method of removing contaminants from wastewater comprising:

- combining the composite coagulant as herein described and wastewater; and

- separating the coagulant comprising suspended solids.

In an embodiments there is provided a method of removing contaminants from water comprising:

-combining a composite coagulant and contaminated water; to form a modified composite coagulant comprising contaminants; and

-separating the modified composite coagulant comprising contaminants from the water; wherein the composite coagulant comprises one or more particulate materials which are at least partially coated with one or more ionic polymers, and wherein the one or more particulate materials are insoluble or sparingly soluble in water. In embodiments the composite coagulant is provided as a pre-formed composite coagulant which is contacted with the contaminated water.

In embodiments the composite coagulant is formed by contacting the particulate with the polymer in water, and the composite coagulant suspension is then combined with the contaminated water. In preferred embodiments the composite coagulant is provided in the form of a concentrated suspension. In embodiments the composite coagulant is provided in the form of a paste.

In embodiments there is provided a method of removing contaminants from water comprising:

- combining a) the composite coagulant or composition as described herein, or the suspension or paste as described herein, or powder as described herein, or formulation as described herein, and b) the contaminated water; to form a modified composite coagulant comprising contaminants; and

- separating the modified composite coagulant comprising contaminants from the water.

In embodiments, the composite coagulant is combined with the contaminated water by adding a prescribed dosage of composite coagulant to the water. In embodiments the composite coagulant is added in the form of a paste. In embodiments the composite coagulant is added in the form of a dry powder. In embodiments the composite is added in the form of a suspension concentrate

In embodiments, the prescribed dosage of the composite coagulant added to the wastewater is from about 0.1 g/L to 10 g/L. In embodiments the prescribed dosage is from about 1 g/L to about 5 g/L.

In embodiments waste water is continuously pumped through an agitated mixing tank containing the composite coagulants and the treated water is run through a separation device, for example a hydrocyclone, to remove the fibres and surplus coagulant.

Separation Step

In embodiments, the separation step comprises one or more of sedimentation, centrifugation, and high-throughput gravity separation.

In embodiments, the separation step comprises sedimentation. In embodiments, the composite coagulant comprising contaminants sediment within 1 minute. In embodiments, the composite coagulant comprising contaminants sediment within from about 1 minute to about 1 hour, preferably within about 30 minutes, or about 20 minutes, or about 10 minutes, or about 5 minutes.

In alternative embodiments, the composite coagulant comprising contaminants sediment within from about 1 hour to about 1 day, preferably within about 3 hours, or within about 2 hours.

Preferably, sedimentation occurs without an additional flocculent.

In embodiments, the separation step comprises centrifugation.

In embodiments, the separation step comprises high-throughput gravity separations, for example using a hydrocyclone.

In embodiments the composite coagulants comprise magnetic particulates and the separate step comprises magnetic means, for example use of magnetic fields to enhance separation.

In embodiments, the separation step may additionally comprise a filtration step. Alternatively, in embodiments the separation step does not comprise a filtration step.

In embodiments, the separation step comprises filtration with a mesh to removal contaminants with a size of 100 microns or more.

The removed microplastics may be converted into useful materials for the building and construction and transport industries. Alternatively the removed microplastics can be safely disposed of in land fill or incinerated. Settling rates

As used herein, the terms settling rate, or sedimentation rate, refers to the rate at which the composite coagulants settle and is measured as the change in height in cm in a body of water over time.

Advantageously composite coagulants comprising suspended contaminants as described herein have a faster settling rate compared to the settling rate of the suspended contaminants alone. This can be understood as the particulate portion of the composite coagulant increases the density of the coagulated contaminants enhancing sedimentation.

Surprisingly, the increase in settling rate of suspended solids when composite coagulations are used to treat contaminated water is more than the increase in settling rate when only particulates are used or when particulates and polymers are sequentially added to the contaminated water.

In embodiments of the present disclosure the settling rate of the composite coagulants comprising contaminants is about 2 times as fast, or about 3 times as fast, or about 4 times as fast, or about 5 times as fast, compared to the settling rate of the suspended solid contaminants without treatment.

Without wishing to be bound by theory it is proposed that the optimum settling rate occurs when the particulates of the composite coagulant are fully coated with polymer, and there is no free polymer in the coagulating composition. The presence of excess polymer may help stabilise the suspended solids, particularly the smallest suspended solids, in solution. In some cases, this may either decrease the settling rate, or lead to a lower percentage of removal of suspended solids or both. Excess polymer coagulant is able to coagulate suspended contaminants, such as microplastics, however, in the absence of the high-density particulate component of the coagulant polymer coagulant does not increase the sedimentation of coagulated contaminants. Accordingly, compositions comprising large amounts of excess polymer are less advantageous compared to compositions comprising small amounts, or preferably no excess polymer. Contaminated water or Wastewater

Advantageously the composite coagulants as herein described may be suitable to treat different types of contaminated water, for example wastewater with different types of contaminants as the general principle of action is the same, (ie destabilise the suspension with the polymer and sediment the contaminants with the particles). As such, it can be understood that the composite coagulants may be used to treat laundry wastewater, industrial wastewater, brackish water or blackish water.

The contaminated water or wastewater may contain difficult to remove contaminants such as suspended fibres, particles or emulsion droplets. Emulsified droplets may be oils or chemicals.

In preferred embodiments the wastewater is laundry wastewater.

Typically laundry wastewater comprises detergents, microplastics and microfibers.

Typically industrial wastewater comprises oils and chemicals and micro and nanoplastics.

Typically, blackish water comprises contaminants from domestic sewage including micro and nanoplastics.

Contaminants

As used herein the term contaminants refers to pollutant species requiring removal from water, for example species requiring removal from wastewater prior to discharge into the environment. The nature of the contaminant will depend on the type of contaminated water, however typically all contaminated waters comprise particulates, surfactants, and polymeric materials.

In some embodiments the contaminants are solid contaminants.

In an embodiment of the disclosure at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, of the solid contaminants are removed. A particular challenge with the removal of fine contaminants in water is that they may form stable suspension in the water. In particular microplastics may have a density similar to water, making separation via sedimentation, or centrifugation impractical or expensive.

In embodiments of the present disclosure, the composite coagulants are adapted to remove fibres, particles, emulsion droplets and combinations thereof from contaminated water, particularly waste-water. In preferred embodiments the contaminants are microplastics, preferably microfibers.

When textiles are washed microfibers are released from the textile into the water. Textiles made from synthetic fibres or synthetic-blends shed plastic fibres that do not break down and persist in the environment. Fibres of particular concern are polyester, acrylic and polyamide fibres.

In embodiments of the present disclosure, the contaminants collected from the wastewater are polyester, acrylic and polyamide fibres

Microplastics

Typically industrial treatment of wastewater is able to remove microplastics having a larger diameter, ie diameter, the removal of microplastics is more challenging. As used herein the term microplastic refers to plastic pieces having a length less than 5 mm. As used herein the term nanoplastic refers to plastic pieces have a length less than 1000 nm.

Removal of fibres

In embodiments, at least 70% of the microfibers are removed from the wastewater using the method as described herein. In preferred embodiments, at least 80% of the microfibers are removed. In more preferred embodiments, at least 90% of the microfibers are removed.

In an embodiment of the disclosure at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% of the microfibers are removed. Method of making

In an aspect there is provided a method of making the composite coagulant as herein described comprising:

- stirring the one or more particulates in a solution with the one or more ionic polymers in solution.

In embodiments the method of making the composite coagulant further comprises partially removing the liquid of the solution to produce a concentrated suspension of composite coagulant, or fully removing the liquid of the solution to produce a dry powder of composite coagulant.

In embodiments the solution is an aqueous solution, preferably water.

The ratio of the particulate and polymer combined to make the composite coagulant depends on the size of the particulate and molecular weight of the polymer.

In embodiments, the composite coagulant comprises from about 5 to about 50% polymer. In embodiments, the composite coagulant comprises from about 50% to about 95% particulate.

In embodiments the particulate is first combined with a first polymer and stirred in a solution, and then combined with a second polymer.

Examples

Example 1 - Formation of composite coagulants

Composite coagulants were formed with a variety of polymer and particle combinations. A schematic showing a variant of the composite coagulant is shown in Figure 1 , having a mineral particle core and attached positively charged polymers. Various types of composite coagulants were made as detailed in the following examples 1A to 1J.

1A Calcite/clay/polymer high density coagulant

Calcite (50 g, 10 micron averaged particle size, Omyacarb 10, Omya) was thoroughly mixed with sodium polyacrylate (1 g, Sigma Aldrich). To this mixture, 30 g water was added and stirred for 1 minute at 1000 rpm using a mechanical stirrer to produce a white dispersion. To this dispersion, 0.5 g CaCl2 dry salt (Sigma Aldrich) was added while stirring at the same rate for another 1 minute. While under mixing (1000 rpm), 10 g solution of poly(diallyldimethylammonium chloride) (poly(DADMAC), 25 weight %, Sigma Aldrich) and then 10 g Kaolin clay was subsequently added to produce a white high density coagulant paste.

A SEM image of the dried composite coagulant comprising calcite/clay mineral with polyacrylate/polyDADMAC polymer is shown in Figure 2. This composite coagulant has a particle core with an average diameter of 10 microns. Figure 2 shows the dry particle structure of the mineral core. The attached polymer arms are not observable by electron microscopy because they are too small.

1B Clay/polymer high density coagulant

Kaolin clay (50 g, Sigma Aldrich) was thoroughly mixed with poly(DADMAC) solution (50 g, 20 weight %, Sigma Aldrich) for 5 minutes at 1000 rpm using a mechanical stirrer to produce a white high density coagulant paste.

1C Alumina/polymer high density coagulant

As in Example B but with acidic alumina (Sigma Aldrich) in place of kaolin clay.

1D Sand/fused silica/polymer high density coagulant

2 g of poly(allylamine hydrochloride) (PAH, Sigma Aldrich) was dissolved in water. To this solution, sand (10g), fumed silica (2 g) (Aerosil 50, Evonik) and 0.5g sodium bicarbonate were added and mixed for 5 minutes at 1000 rpm to produce a high-density coagulant.

1E Calcite/Polymer high density coagulant

Calcite (50 g, 10 micron averaged particle size, Omyacarb 10, Omya) was thoroughly mixed with sodium polyacrylate (1 g, Sigma Aldrich). To this mixture, 55 g water was added and stirred for 1 minute at 1000 rpm using a mechanical stirrer to produce a white dispersion. While under mixing (1000 rpm), 10 g solution of poly(diallyldimethylammonium chloride) (PDADMAC), 20 weight %, Sigma Aldrich) was subsequently added to produce a white high density coagulant paste. 1 g of this HD coagulant contains 0.43 g calcite and 0.09 g PDADMAC 20% solution. The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 4 wt%

1F Calcite/Polymer high density coagulant

Calcite (50 g, 20-micron averaged particle size, Omyacarb 20, Omya) was thoroughly mixed with sodium polyacrylate (0.01 g, Sigma Aldrich) solution in 50 g water and was stirred for 1 minute at 1000 rpm using a mechanical stirrer to produce a white dispersion. While under mixing (1000 rpm), 0.25 g solution of poly(diallyldimethylammonium chloride) (PDADMAC), 20 weight %, Sigma Aldrich) was subsequently added to produce a white high density coagulant paste. The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 0.1 wt%

1G Calcite/Polymer high density coagulant

Calcite (10 g, 1-micron averaged particle size, Omyacarb 1 , Omya) was thoroughly mixed with sodium polyacrylate (0.1 g, Sigma Aldrich) solution in 25 g water and was stirred for 1 minute at 1000 rpm using a mechanical stirrer to produce a white dispersion. While under mixing (1000 rpm), 50 g solution of PDADMAC (20 weight %, Sigma Aldrich) was subsequently added to produce a white high density coagulant paste. The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 50 wt%

1H Calcite/Polymer high density coagulant

High density coagulant paste was prepared in the same manner as in example 1F but with Omyacarb 10 (10 micron average particle size calcite particles). The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 0.1 wt%

11 Calcite/Polymer high density coagulant

High density coagulant paste was prepared in the same manner as in example 1G but with 25 g Omyacarb 10 (10 micron average size particulates) and 1 g sodium polyacrylate. The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 29wt%

1 J Calcite/Polymer high density coagulant

Calcite (20 g, 10-micron averaged particle size, Omyacarb 10, Omya) was thoroughly mixed with sodium polyacrylate (1 g, Sigma Aldrich) solution in 50 g water and was stirred for 1 minute at 1000 rpm using a mechanical stirrer to produce a white dispersion. While under mixing (1000 rpm), 50 g solution of P(AAM-co-DADMAC) (10 weight %, Sigma Aldrich) was subseguently added to produce a white high density coagulant paste. The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 20wt%

1K Calcite/Polymer high density coagulant

PSt (0.5 g, Sigma) was mixed with water (6.5 g) to produce a viscous clear solution. Calcite (1.5 g) (average particle length of 10 microns) was added to the solution and was thoroughly mixed using a vortex mixer to produce a white dispersion. To the dispersion, 1.5 g water and 0.5 g hydrated aluminium sulphate salt was added and thoroughly mixed. The weight percentage of PSt to particulate, based on the total weight of the composite coagulant is calculated to be 25wt%.

1L Calcium Hydroxide/Polymer high density coagulant

.Calcium hydroxide (1 g, Sigma) was thoroughly mixed with sodium polyacrylate (0.1 g, Sigma Aldrich) solution in 9 g water and was thoroughly mixed using a vortex mixer to produce a white dispersion. To this dispersion, 0.2 g solution of PDADMAC (20 weight %, Sigma Aldrich) was subseguently added to produce a white high density coagulant mixture. The weight percentage of PDADMAC to particulate, based on the total weight of the composite coagulant is calculated to be 4wt%.

Example 2 - Treating laundry wastewater with a composite coagulant

2A Separation by decantation

1g composite coagulant from example 1A was added to 1L laundry wastewater in a bottle. After shaking for 30 seconds, the bottle was left un-disturbed on the bench. The composite coagulant was observed to settle to the bottom of the bottle. After 2 hours, the settled solids were carefully removed from the water by decantation. Examination by optical and electron microscopy found the decanted solids contain both micro and nanofibers as well as solid particles.

2B Separation by centrifugation

0.1g of the composite coagulant from example 1A was added to 50g of laundry wastewater in a centrifuge tube. After shaking for 30 seconds, the tube was left undisturbed on the bench. The composite coagulant was observed to settle to the bottom of the bottle (but at a very slow rate). After 2 hours, the tube was centrifuged for 1 minute at 4000 rpm to produce a visually clear supernatant and a white solid. Optical microscopy found the solid contain micro fibres and clay particles.

The experiment was repeated with the composite coagulant from example 1 B and similar results were observed.

2D Separation by sedimentation

1g composite coagulant from example A was added to 200g of laundry wastewater in a container. After shaking for 30 seconds, the container was left undisturbed on the bench. The sand was observed to settle quickly to the bottom of the bottle while the fused silica was slow to settle. Optical microscopy examination found the presence of microfibers attached to sand particles.

2E Comparison of separation of fibres with different formulations of composite coagulants from example 1

General procedure

0.2 g fibers (collected from a clothes drier) were dispersed in 400 g water using a mechanical stirrer at 2000 rpm for 5 minutes. 0.2 g of the composite coagulant was added to the dispersion and thoroughly mixed at 1000 rpm for 1 minute. The dispersion was transferred to a 500 mL measuring cylinder and left to settle. It was observed that either the fibers sunk to the bottom or floated to the air/water interface. The settling rate or sedimentation rate is estimated as the ratio between the water body height and the time it took for the water to be clear of fibers. The floating/suspended fibers were carefully collected, dried in the oven at 100°C overnight. After weighing, the % of suspended fibres was calculated.

The results of the sedimentation test comparing the performance of different composition coagulants from example 1 are shown below in table 1. Table 1. Sedimentation rates and % of suspended fibres following treatment of artificial laundry waste-water with the composite coagulants of example 1 .

As can be seen from the results in table 1 composite coagulants according to the present disclosure were able to capture substantially all of the fibres from the artificial laundry waste water. In comparison, the comparative examples which treated the artificial laundry waste water with either only a particulate, or only an ionic polymer, did not capture all of the suspended fibres. In addition, it was observed that composite coagulants with a larger particle size had faster sedimentation rates but were still able to capture substantially all of the suspended fibres.

Composite coagulants of example 11 include large amounts of Polyacrylic acid which may enhance PDADMAC attachment to the particulates. The increased anchoring of the PDADMAC on the particulate may in turn lead to improved coagulation efficiency.

Example 3 - Physical characterisation of wastewater sample before and after treatment

Samples of laundry wastewater were obtained from HealthShare (Paramatta, NSW, Australia), and are referred to hereafter as HSWW (HealthShare wastewater).

The samples were taken from a storage tank where treated wastewater is stored prior to discharge to the environment. The samples were pre-treated by a Blue Ocean filtration unit (Wientjens) using 115-micron filter. A photograph of the pre-treated HSWW is shown in Figure 3. As can be seen the water is turbid and contains suspended materials.

Table 2 shows the HSWW samples have a pH range between 7-8 and a solid content of 0.06 weight % (by gravimetry). The sample is a laundry wastewater, so it is likely that the 0.06% solid content comprises fibers, soluble salts, surfactants, suspended solid particles as well as other non-volatile organic and inorganic compounds (from human excretions and washed textiles)

Table 2. Physical properties of wastewater samples.

The solid content was characterized using optical microscopy (OM), Scanning electron Microscopy (SEM) and Transmission Electron Microscopy (TEM).

For microscopy characterization, HSWW sample was centrifuged in a 50 oil- vial at 4000 rpm for 30 minutes to separate the microfibers and other solid particles from the water. The solid was collected from the vial bottom and examined under the OM, TEM and SEM.

The OM image in Figure 4A clearly shows the presence of fibers and solid particles in the sample. Fiber sizes were found to vary from tens to hundreds of microns which was unexpected since the wastewater was filtered by the 115-micron filter of the Blue Ocean unit. Solid particle sizes were observed to be up to 25 microns.

By SEM in Figure 5A, the solid spun out from the HSWW is a mix of fibers with micron and sub-micron diameters as well as solid particles of different sizes. TEM in Figure 6 also confirms the presence of very long fibers with diameters as small as 20 nm

3A Gravimetric analysis of fiber content in wastewater

The separated solids from the wastewater sample were dried in the oven at 100°C to remove the water. Thermogravimetric analysis (TGA) was then performed on the dry sample to a temperature of 700°C in an air flow to completely remove the organic contents. An approximately 50% weight loss was recorded, indicating the centrifuged solids consisted of approximately equal amounts of inorganic and organic materials including fibers.

To further approximate microfibers weight percentage in the suspended solids, the wastewater sample was filtered using a 0.45-micron filter so all the fibers and particles with sizes greater than 450 nm were separated from the wastewater. The water solid contents before and after filtration were determined by the gravimetric method and the results are shown in Table 2.

As shown in Table 3, there was a decrease of 0.019% in the water solid content after the filtration. This was due to the removal of fibers and suspended particles with sizes larger than 450 nm. Therefore, the maximum possible content of microfibers in the HSWW was also 0.019%. However, if the filtered solids also have the same equal organic/inorganic components as in the case of centrifugation then the most likely microfiber content should be around 0.01%. Table 3. HSWW solid contents before and after filtration with a 0.45-micron filter.

3B Removal of fibres from HSWW using composite coagulants and characterisation of treated wastewater

For the current study, the coagulant prepared according to example 1A was prepared as a ready to use paste with pH 7 and approximately 60 weight % solids.

For lab scale testing, the removal of microfibers was carried out by adding 1 g of the paste mixture of the composite coagulant of example 1 A to a plastic bottle containing 1 L HSWW sample. After approximately 30 seconds of shaking, the bottle was left standing undisturbed for 2 hours to produce a much clearer water and a solid settlement at the bottom as shown in Figure 7. The solid was carefully separated by decanting the upper liquid portion, and then decanting the solid containing fraction into a smaller vial for further characterization by OM (Figure 8) and SEM (Figure 9). During the coagulant addition, the pH of the water solution was found to be unchanged at pH 7.

By OM (Figure 8), the mineral particles were found to randomly attach to microfibers along with other solid particles. The captured microfibers varied in lengths and diameters. They also seemed to entangle with each other possibly due to the interactions with the coagulant in the above-described mode. SEM image in Figure 9 confirms the removal of not only microfibers but also nanofibers by the HD coagulant. In some cases, multiple fibers were observed to interact with one coagulating particle, suggesting high removal efficiency. The SEM reconfirms the fiber entanglements, possibly happened during settling process. Fibers with nanometer sized diameters were also found to effectively be removed.

The treated wastewater after decantation was examined by OM and SEM. By OM, there was no apparent presence of microfibers as shown in Figure 4B. However, there were suspended particles, potentially due to the surplus composite coagulant.

The SEM of the treated wastewater in Figure 5B shows only the presence of solid particles. No fibers of any kinds were observed which indicates their total removal by the composite coagulant.

3C Qualitative assessment of HSWW before and after treatment by dynamic light scattering (PLS)

DLS is a laser based light scattering technique which provides average particle sizes and particle size distributions (PDI). The results of the DLS analysis of the HSWW samples before and after treatment with the composite coagulant shown in Table 4. Z averages are averaged particle sizes for the whole sample. However, a sample can contain multiple size distributions such as Peaks 1, 2, 3 depending on how many suspended solid materials are in the water phase. Particle size distributions (PDI) provide an indication of how broad the size distributions are. Untreated HSWW (S1) had the highest PDI of 0.6 and Peak 3 size at 5457 nm indicating many suspended materials (including microfibers) with different sizes in the sample. After addition of the composite coagulant (S2), the PDI significantly reduced to 0.4 due to suspended fibers/particles removal. Peak 3 size of 5184 nm was still present due to the surplus composite coagulant. However, for S3 sample, all micron sized particles were removed with additional centrifugation.

Table 4. Sizes and size distributions of suspended fibers and particles in wastewater sample before and after the addition of the composite coagulant (of example 1 A)

3D Quantitative assessment of solid content of HSWW before and after treatment with a composite coagulant. The amount solid content of HSWW samples before and after composite coagulant addition are listed in in Table 5. As shown, the solid content of HSWW after HD coagulant addition was measured to be 0.035% by gravimetry (Solid 2). Therefore, the reduced solid (RS) content of 0.027% is calculated by subtracting the HSWW before HD coagulant addition (Solid 1) and Solid 2. The decrease in solid content was attributed to the removal of aggregated fibers and solid particles. This reduction was even more than the one (0.019%, Table 2) due to 0.45-micron filtration. The result supports the qualitative assessments indicating an almost total removal of fibers. The use of HD coagulant was probably more efficient than 0.45-micron filtration because more solid contaminants were removed in the process. Table 5. Change of solid contents after the addition of HD coagulant.

The effect of composite coagulant amounts on the wastewater solid contents is presented in Table 6. As shown, the larger amount of the coagulant used the larger decrease in wastewater solid contents after removal of solid settlements from the bottle. 0.5 g HD coagulant per 1 kg HSWW sample seemed to be the minimum amount which contributed to a significant decrease of the wastewater content.

The results of example 3 show that addition of the composite coagulants of the present disclosure was very efficient in removing microfibers from a sample of wastewater from NSW, Australia health hospital laundry service, with an efficiency up to close to 100%. Comparative Example A - Treating laundry wastewater with particulates only

1g of Omyacarb 10 and 0.1 g of uncoated Kaolin was added to 1 L laundry wastewater in a bottle. After shaking for 30 seconds, the bottle was left un-disturbed on the bench. The particulates were observed to settle to the bottom of the bottle. After 2 hours, the settled solids were carefully removed from the water by decantation. Examination by optical and electron microscopy found the decanted solids and water supernatant to contain both micro and nanofibers as well as solid particles.

Comparative Example A2- Treating laundry wastewater with particulates only

0.2 g of cloth fibres (collected from a clothes drier) were dispersed according to the general procedure of example 2E. A calcite paste was prepared by mixing 0.086 g Omyacarb 10 with 1 g water. This calcite paste was added to the fibre dispersion and thoroughly mixed at 1 K rpm for 1 minute. Settling test was repeated as in the previous example and was found to be 1.4 cm/min. 38% fibres stayed floating at the air/water interface.

Comparative Example B- Treating laundry wastewater with polymer only

0.1g of poly(DADMAC) was added to 1L laundry wastewater in a bottle. After shaking for 30 seconds, the bottle was left un-disturbed on the bench. . Large aggregates were observed to settle to bottom of the bottle. After 2 hours, the settled solids were carefully removed from the water by decantation. Examination by optical and electron microscopy found the decanted solids and water supernatant to contain both micro and nanofibers as well as solid particles.

Comparative Example B2- Treating laundry wastewater with polymer only

0.2 g of cloth fibres (collected from a clothes drier) were dispersed according to the general procedure of example 2E.. A PDADMAC was prepared by mixing 0.02 g PDADMAC 20% coagulant solution (Sigma) with 1 g water. This solution was added to the fibre dispersion and thoroughly mixed at 1 K rpm for 1 minute. Settling test was repeated as in the previous example and was found to be 1.6 cm/min. 50% fibres stayed suspended in the water body.

Comparative Example C- Treating laundry wastewater with seguential additions of (i) particulate and then (ii) polymer

0.2 g of cloth fibres (collected from a clothes drier) were dispersed according to the general procedure of example 2E. A calcite paste was prepared by mixing 0.086 g Omyacarb 10 (10 microns average particle size) with 1 g water. This calcite paste was added to the fibre dispersion and thoroughly mixed at 1 K rpm for 1 minute. A PDADMAC was prepared by mixing 0.02 g PDADMAC 20% coagulant solution (Sigma) with 1 g water. This solution was added to the fibre dispersion and thoroughly mixed at 1K rpm for 1 minute. Settling test was repeated as in the previous example and was found to be 1.8 cm/min. 31% fibres stayed floating at the air/water interface.

Comparative Example D- Treating laundry wastewater with sequential additions of (i) polymer and then (ii) particulate.

0.2 g of cloth fibres (collected from a clothes drier) were dispersed according to the general procedure of example 2E. A PDADMAC was prepared by mixing 0.02 g PDADMAC 20% coagulant solution (Sigma) with 1 g water. This solution was added to the fibre dispersion and thoroughly mixed at 1 K rpm for 1 minute. A calcite paste was prepared by mixing 0.086 g Omyacarb 10 (10 microns average particle size) with 1 g water. This calcite paste was added to the fibre dispersion and thoroughly mixed at 1 K rpm for 1 minute. Settling test was repeated as in the previous example and was found to be 1.5 cm/min. 17% fibres stayed floating at the air/water interface.

Example 4 iron-oxide -chitosan coagulant

Citric acid (1 g, Sigma) was mixed with water (50 g) to produce a viscous clear solution. Iron oxide pigment (10 g, Bayer) (average particle length 0.8 pm; particle length range 0.2 to 1 pm) was added to the solution and was thoroughly mixed using a mechanical mixer to produce a red dispersion. To the dispersion, 2.5 g chitosan (shrimp shells, Sigma) was slowly added under stirring. This was followed up by 1 g of 16% HCI to produce a red and viscous pigment dispersion.

0.2 g of cloth fibres (collected from a clothes drier) was dispersed according to the general procedure of example 2E. 0.2 g HD coagulant from the above was diluted with 1 g water and was added to the dispersion and thoroughly mixed at 1K rpm for 1 minute. 100% fibres were collected by placing a magnet on the side of the glass container.