Method for extracellular polymeric substances extraction from an aqueous stream, phosphorylated extracellular polymeric substances, and use thereof

Abstract

The present invention relates to a method for Extracellular Polymeric Substances (EPS) extraction from an aqueous stream, including phosphorylation of the EPS, phosphorylated EPS obtainable by the method according to the invention, and use of the phosphorylated EPS. The method comprises the steps of: - providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant; - heating the EPS and the phosphorus source in the alkaline reactor; - adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13; - phosphorylating the EPS with the phosphorus source; - controlling the step of phosphorylating the EPS; - solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant; - separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant; - acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4; - precipitating the phosphorylated EPS from the aqueous phase; and - separating the phosphorylated EPS from the aqueous phase.

Description

[0001] METHOD FOR EXTRACELLULAR POLYMERIC SUBSTANCES EXTRACTION FROM AN AQUEOUS STREAM, PHOSPHORYLATED EXTRACELLULAR POLYMERIC SUBSTANCES, AND USE THEREOF

[0002] The present invention relates to a method for phosphorylated Extracellular Polymeric Substances (EPS) extraction from an aqueous stream, phosphorylated EPS obtainable by the method according to the invention, and use of the phosphorylated EPS.

[0003] Phosphorus compounds are essential for the emergence of life on earth. Phosphorus is a group 15 element that has five electrons in its outer shell. By donating its electrons, phosphorus can form five covalent bonds, e.g., by combining with four oxygen atoms to form orthophosphate. Orthophosphate is chemically versatile and can form mono-, di- and tri-esters (P-O-C) with alkyl and aryl hydroxyl groups, as well as acid anhydrides (P-O-P). The ability of phosphate to form esters (nucleic acids in RNA, DNA, and phosphoproteins) and anhydrides (ATP, polyphosphate) that are stable at ambient temperatures in water made it ideal for the generation of biological molecules that predominate in living organisms. Phosphorus recovery from wastewater can take place from the liquid side streams, sludge, which have elevated phosphate concentrations.

[0004] EPS constitute an essential element within the matrix of microbial biofilms in diverse ecological contexts, particularly in wastewater treatment technologies, e.g., activated sludge systems, biofilm reactors, and granular sludge systems. EPS has potential applications across industrial sectors such as agriculture, construction, textiles, paper industry, and flame retardants production.

[0005] The waste sludge comprising EPS often also comprises significant amounts of phosphorus moieties. Said compounds are valuable and are preferably not (unnecessarily) exposed into the environment. Therefore, EPS and phosphorus moieties are removed separately from waste sludge.

[0006] Methods to incorporate phosphorus moieties by phosphorylation of polyesters or polyvinylchloride are known. Said conventional methods are not capable of removing EPS and phosphorus moieties in a single procedure. These problems prevent an efficient and effective removal of EPS and phosphorus moieties. These problems also prevent efficient and effective synthesis of the use of said compounds.

[0007] The present invention aims at obviating or at least reducing the aforementioned problems and to enable efficient and effective method for EPS extraction from an aqueous stream.

[0008] This objective is achieved with the method for Extracellular Polymeric Substances (EPS) extraction from an aqueous stream, including phosphorylation of the EPS, comprising the steps of:

[0009] - providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant; - heating the EPS and the phosphorus source in the alkaline reactor;

[0010] - adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13;

[0011] - phosphorylating the EPS with the phosphorus source;

[0012] - controlling the step of phosphorylating the EPS;

[0013] - solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant;

[0014] - separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant;

[0015] - acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4;

[0016] - precipitating the phosphorylated EPS from the aqueous phase; and

[0017] - separating the phosphorylated EPS from the aqueous phase.

[0018] EPS are a complex high-molecular-weight mixture of polymers excreted by microorganisms, produced from cell lysis and adsorbed organic matter from wastewater. They are a major component in microbial aggregates for keeping them together in a three-dimensional matrix. Phosphorus species are present in EPS in different speciation (e.g., phosphorus esters, polyphosphorus, ortho- phosphorus, etc.).

[0019] The phosphorus species, also referred to as phosphorus source, are mainly microbially produced before extraction. Expected species are organophosphorus groups in phosphorylated protein, sugars, and lipids and could also be polyphosphates, pyrophosphates, and orthophosphates.

[0020] It is noted that the amount of the phosphorus source may change for each aqueous stream. Therefore, the method according to the invention may comprise the step of determining and / or monitoring and / or measuring the amount of phosphorus source in the aqueous stream.

[0021] Said step of determining and / or monitoring helps to optimize EPS extraction from the aqueous stream.

[0022] An advantage of the method according to the invention is that the EPS present in the aqueous stream is chemically induced during the extraction process. As a result, an efficient and effective phosphorylation is achieved.

[0023] It is noted that the step of heating may be performed before, during, and / or after the steps of adjusting the pH of the aqueous stream and / or the aqueous reactant and / or phosphorylating the EPS with the phosphorus source. Furthermore, in a preferred embodiment, the aqueous stream may be pre-heated to the desired temperature.

[0024] It is also noted that the step of adjusting the pH of the aqueous stream and / or the aqueous reactant may be performed before, during, and / or after the steps of providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor, heating the EPS and the phosphorus source in the alkaline reactor, and / or phosphorylating the EPS with the phosphorus source.

[0025] The method according to the invention may start with the step of providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant. Said step may be followed by the step of heating the EPS and the phosphorus source in the alkaline reactor, and the step of adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13. These steps are followed by the step of phosphorylating the EPS with the phosphorus source and the step of solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant.

[0026] An advantage of the steps of heating and adjusting the pH is that an efficient and effective phosphorylation of the EPS is achieved. In addition, the heating and alkaline pH enables that the EPS and / or phosphorylated EPS is solubilised in an aqueous phase of the aqueous reactant.

[0027] Phosphorylation is described as the transfer of a phosphate group to a molecule. In this case the phosphate group that is preferably already present in the aqueous stream is transferred to the EPS. This results in the phosphorylated EPS.

[0028] In addition, the step of solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant may be followed by the step of separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant. It is noted that the other phases may include phases such as organic phases, and / or solid phases.

[0029] An advantage of the separating step is that a clean aqueous stream is obtained without undesired organic phases and / or solids. Said cleaned aqueous stream may be used for further extraction of the phosphorylated EPS.

[0030] The method according to the invention further includes the step of acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4. It was found that also during the step of acidifying the aqueous phase phosphorylation may occur. Therefore, higher conversions of EPS to phosphorylated EPS are achieved. Furthermore, the method according to the invention may further include the step of precipitating the phosphorylated EPS from the aqueous phase.

[0031] The acidic environment enables the precipitation of the phosphorylated EPS. Therefore, the step of separating the phosphorylated EPS from the aqueous phase may be performed.

[0032] An advantage of the method according to the invention is that the EPS and phosphor source (also referred to as phosphor moieties) may be removed as a single compound. As a result, less handlings must be performed to recover the EPS and the phosphorus. In addition, the phosphorylation of the EPS increases the value of the EPS as phosphorylated EPS can be used in a wide range of applications. For example, phosphorylated EPS may be used as a coating in slow- release fertilizers, as a bio-stimulant, as a binding agent in building materials, and as flame retardant.

[0033] In a preferred embodiment according to the invention, the method according to the invention enables at least the formation of 0.01 gram organic P per gram COD in the aqueous solution, preferably 0.015, more preferably 0.02, and most preferably 0.03 gram organic P per gram COD in the liquid phase. In some of the presently preferred embodiments of the invention the method enables at least a conversion of 50% of the phosphorus content in EPS is organic phosphorus, preferably at least 75% of the phosphorus content in EPS is organic phosphorus, more preferably at least 90% of the phosphorus content in EPS is organic phosphorus, most preferably at least 95% of the phosphorus content in EPS is organic phosphorus.

[0034] The steps of phosphorylating the EPS with the phosphorus source and acidifying the aqueous phase comprising solubilised phosphorylated EPS enable the aforementioned conversion rates, resulting in the formation of 0.01 gram organic P per gram COD in the aqueous solution, for example. In some embodiments this may correspond to a conversion of at least 50% of the initial amount of EPS to phosphorylated EPS.

[0035] In a preferred embodiment according to the invention, the phosphorus source is a polyphosphate and / or a pyrophosphate, preferably the polyphosphate and / or the pyrophosphate is one or more selected from the group of tetrasodium pyrophosphate, sodium tripolyphosphate, sodium trimetaphosphate, tetrasodium pyrophosphate anhydrous, tetrapotassium pyrophosphate, sodium hexametaphosphate.

[0036] It is noted that said phosphorus source may already be present in the aqueous stream. In addition to, or alternatively, said phosphorus source may be added to the aqueous stream such that the desired concentration of the phosphorus source is optimized. Preferably, said optimization is performed by the addition of phosphorus containing salts. As a result, the quality and properties of the end product, such as EPS, can be kept constant. It was found that the phosphorus source being a polyphosphate and / or a pyrophosphate provides efficient and effective phosphorylation of EPS.

[0037] It will be understood that the actual phosphorus concentration will be optimized based on multiple factors such as the nature of the EPS, the available phosphorylation sites, the type of P salt added etc. Experiments have shown that the aqueous stream is preferably provided with a possible range of g P : g EPS in the aqueous stream between 0.0001 : 1 and 1:1, more preferably between 0.001:1 and 0.001 and 0.1.

[0038] The step of controlling the step of phosphorylating the EPS improves the phosphorylation process by optimizing the process conditions such that the phosphate(s) present in the aqueous stream end up in the extraction / separation process. Phosphorylating the EPS is optimized, preferably by a controller that is integrated in the overall process controller, involving controlling the pH and / or temperature, and if needed from the (low) level of phosphates in the aqueous stream adding phosphorous components. The control step preferably enables control of the properties of the ‘end-product’.

[0039] In a further preferred embodiment according to the invention, the method further comprises the step of aerating the aqueous stream in a buffer tank, wherein the aqueous stream is stored in the buffer tank for a time in the range of 5 minutes to 4 hours, preferably for a time in the range of 5 minutes to 3 hours, more preferably for a time in the range of 5 minutes to 2 hour, most preferably for a time in the range of 5 minutes to 1 hour.

[0040] An advantage of aerating the aqueous stream in a buffer tank is that hydrolysis of the phosphorus source is reduced or prevented. As a result, the phosphorus source can be used in phosphorylation of the EPS in the method according to the invention. In addition, an optimal balance between the phosphorus source and the EPS is achieved.

[0041] Furthermore, it was found that the time of storing the aqueous stream is as short as possible. Shortening the residence time of the aqueous stream in the buffer tank reduces or prevents the hydrolysis of the phosphorus source. As a result, the amount of polyphosphates and pyrophosphates may be controlled.

[0042] The step of aerating is preferably performed before the step of providing an aqueous steam comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant. Performing said aerating step before the step of providing an aqueous steam comprising EPS and a phosphorus source to an alkaline reactor enables to (further) control the phosphorylation and reduce and / or prevent the addition of polyphosphate and / or pyrophosphates to the aqueous reactant. In fact, such aerating enables the formation of natural polyphosphate and / or pyrophosphates. Therefore, the extraction of EPS from an aqueous stream may be further controlled.In addition, the aerated aqueous stream is used in the step of providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant.

[0043] In a further preferred embodiment according to the invention, the method further comprises the step of controlling one or more of the steps: heating the EPS and the phosphorus source in the alkaline reactor; adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13; phosphorylating the EPS with the phosphorus source; acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4. An advantage of the step of controlling one or more of the abovementioned steps is that the phosphorylation of the EPS can be controlled such that at least 50% of the phosphorus content in EPS is organic phosphorus. In addition, the controlling step enables to adjust the conditions of the method according to the invention in response to the influx of the aqueous stream. The composition of said aqueous stream may differ due to the fluctuations in the wastewater treatment process.

[0044] In a further preferred embodiment according to the invention, the method further comprises the step of additionally adding polyphosphate and / or pyrophosphates and / or salts containing phosphorus to the alkaline reactor.

[0045] The step of additionally adding polyphosphate and / or pyrophosphates and / or salts containing phosphorus to the alkaline reactor enables to achieve a full phosphorylation of the EPS. In addition, said additional addition of polyphosphate and / or pyrophosphates and / or salts containing phosphorus enables to have a predictable phosphorylation and enables to control and tune the product (EPS) quality and properties.

[0046] It is noted that said additional addition of polyphosphate and / or pyrophosphates and / or salts containing phosphorus may already be (partly) added to the aqueous stream which is provided to the alkaline reactor.

[0047] In addition, said additional polyphosphate and / or pyrophosphates and / or salts containing phosphorus may be present in the step of aerating the aqueous stream.

[0048] In a further preferred embodiment according to the invention, the method further comprises the step of providing a condensing agent to the aqueous phase comprising solubilised phosphorylated EPS. Preferably, the step of providing a condensing agent to the aqueous phase comprising solubilised phosphorylated EPS is performed after the step of separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant. In some of the presently preferred embodiments the condensing agent is added to the reactor with acidic conditions, preferably with the addition of phosphoric acid (H3PO4) as an acid and phosphorus source for phosphorylation.

[0049] It is noted that in this application a condensing agent refers to a substance added to a (chemical) reaction, for example a condensation reaction, to enable the formation of a larger molecule from smaller ones.

[0050] An advantage of providing a condensing agent to the aqueous phase comprising solubilised phosphorylated EPS is that phosphorylation under acidic conditions is promoted. For example, phosphorylation is promoted when phosphoric acid is present and the reaction is performed at elevated temperatures such as at least 80 °C. As a result, a higher conversion of EPS to phosphorylated EPS is achieved. Furthermore, the condensing agents may react with water to form new compounds, achieving low water activity as water is not a rare leaving group in the aqueous phase. Therefore, phosphorylation using H3PO4 can be promoted in wet conditions.

[0051] In a further preferred embodiment according to the invention, the condensing agent is one or more selected from the group of urea, cyanate, cyanamide, carbonyl sulphide.

[0052] It was found that the condensing agent being one or more selected from the group of urea, cyanate, cyanamide, carbonyl sulphide, provides an efficient and effective phosphorylation of the EPS under acidic conditions.

[0053] In a further preferred embodiment according to the invention, the aqueous stream originates from a wastewater treatment plant.

[0054] An aqueous stream originating from a wastewater treatment plant comprises EPS as well as phosphorus moieties. Therefore, a wastewater stream originating from a wastewater treatment plant can efficiently and effectively be processed by the method according to the invention.

[0055] Furthermore, the aqueous stream originating from a wastewater treatment plant may be referred to a sludge stream and / or aqueous / semi solid stream.

[0056] In a further preferred embodiment according to the invention, the aqueous stream further comprises solid organic matter and solid inorganic matter in the range of 5 g L1to 100 g L1, preferably in the range of 10 g L1to 90 g L1, more preferably in the range of 10 g L1to 80 g L1.

[0057] In a further preferred embodiment according to the invention, the method further comprises the step of adding a catalyst to the aqueous stream and / or the aqueous reactant and / or the aqueous phase. Preferably, the catalyst is a metal catalyst, more preferably a two valent metal catalyst.

[0058] It is noted that a metal catalyst includes catalysts comprising a metal atom.

[0059] The addition of a catalyst enables to catalyse the phosphorylation reaction under alkaline and acidic conditions as the electrophilicity of the phosphorus atoms is increased.

[0060] In a further preferred embodiment according to the invention, the catalyst comprises one or more metals from the group of Mg2+, Ca2+, Mn2+, Co2+, Ni2+.

[0061] It was found that a catalyst comprising any one of the two valent metals according to the aforementioned group provides an efficient and effective catalysis of the phosphorylation.

[0062] In a further preferred embodiment according to the invention, the step of adjusting the pH of the aqueous stream and / or aqueous reactant in the alkaline reactor to a pH in the range of 8 to 13 comprises adjusting to a pH in the range of 9 to 12, preferably to a pH in the range of 9 to 11.

[0063] In a further preferred embodiment according to the invention, the step of acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4 comprises acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1.5 to 3.5, preferably to a pH in the range of 2 to 3. In a further preferred embodiment according to the invention, wherein the step of heating the EPS and the phosphorus source in the alkaline reactor is performed at a temperature in the range of 70 °C to 100 °C, preferably a temperature in the range of 70 °C to 90 °C, more preferably a temperature in the range of 75 °C to 80 °C.

[0064] Performing the step of heating the EPS and the phosphorus source in the alkaline reactor to a temperature in the range of 70 °C to 100 °C, preferably a temperature in the range of 70 °C to 90 °C, more preferably a temperature in the range of 75 °C to 80 °C enables an efficient and effective phosphorylation of the EPS and an increases the solubility of the phosphorylated EPS in the aqueous phase.

[0065] In a further preferred embodiment according to the invention, wherein the pH of the aqueous stream and / or the aqueous reactant is adjusted using one or more base selected from the group of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium oxide, potassium oxide, calcium oxide.

[0066] In a further preferred embodiment according to the invention, the step of acidifying the aqueous phase comprising solubilised phosphorylated EPS is performed using one or more acid selected from the group of hydrogen chloride, phosphoric acid, sulphuric acid, acetic acid, citric acid, oxalate acid.

[0067] In a further preferred embodiment according to the invention, the step of phosphorylating the EPS with the phosphorus source is performed for 30 minutes to 5 hours, preferably for 1 hour to 4 hours, more preferably for 1.5 hours to 3 hours.

[0068] In a further preferred embodiment according to the invention, the step of separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant and / or the step of separating the phosphorylated EPS from the aqueous phase comprises one or more of centrifuging, filtering, decanting.

[0069] In a further preferred embodiment according to the invention, the method further comprises the step of transferring the aqueous phase comprising solubilised phosphorylated EPS to an acid reactor.

[0070] The invention also relates to a method for manufacturing of a flame retardant, comprising phosphorylated EPS obtainable by the method according to any one of the preceding clauses.

[0071] The method for manufacturing of a flame retardant according to the invention provides the same or similar effects and advantages as those described for the method for EPS extraction from an aqueous stream, including phosphorylation of the EPS according to the invention.

[0072] The invention also relates to phosphorylated EPS obtainable by the method according to the invention. The phosphorylated EPS obtainable by the method according to the invention provides the same or similar effects and advantages as those described for the method for EPS extraction from an aqueous stream, including phosphorylation of the EPS according to the invention, and the method for manufacturing of a flame retardant according to the invention.

[0073] The invention also relates to use of the phosphorylated EPS according to the invention in flame retardants.

[0074] The use of the phosphorylated EPS according to the invention provides the same or similar effects and advantages as those described for the method for EPS extraction from an aqueous stream, including phosphorylation of the EPS according to the invention, the method for manufacturing of a flame retardant according to the invention, and the phosphorylated EPS obtainable by the method according to the invention.

[0075] An advantage of the flame retardant according to the invention is that the phosphorylated EPS is a circular product. As a result, the environmental impact of the flame retardant including the phosphorylated EPS is reduced.

[0076] Furthermore, the organic phosphorus, such as phosphoric esters and phosphoric amidates in EPS could contribute significantly to its flame retardancy by forming phosphoric acid upon heating and its role as a catalyser for the dehydration reactions forming the char layer. Orthophosphate minerals, if initially present in EPS or formed during burning, could also contribute to flame retardancy by forming a thermal stable layer e.g., hydroxyapatite. If all these phosphorus species were present in EPS, a synergic phosphorus and multivalent cation flame retardant could be anticipated. The presence of glycoproteins and amino acids in EPS could also contribute to flame retardancy along phosphorus species creating a synergic phosphorus - nitrogen based flame retardant.

[0077] The phosphorylated EPS can asl be used to improve viscoelastic properties, water-holding capacity, and emulsifying properties. For example, the phosphorus in phosphorylated EPS could contribute significantly to these properties, as it changes the surface chemistry by increasing its electronegativity and influencing the intermolecular forces. Polyphosphates and / or pyrophosphate (salts) could influence the pH or the ionic strength of the polymer would also influence the intermolecular forces and consequently the polymer properties.

[0078] Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

[0079] Figure 1 shows a schematic overview of a method according to the invention; Figure 2 shows a photo of EPS and phosphorylated EPS; and

[0080] Figure 3 shows an embodiment of a system for performing the method of figure 1. Method 10 (Figure 1) for EPS extraction from an aqueous stream, including phosphorylation of the EPS, follows a sequence of different steps.

[0081] In an illustrated embodiment method 10 may start with step 12 of providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant. Alternatively, method 10 may start with step 11 of aerating the aqueous stream in a buffer tank. Step 11 or 12 may be followed by step 14 of heating the EPS and the phosphorus source in the alkaline reactor, and step 16 of adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13. Steps 14 and 16 are followed by step 18 of phosphorylating the EPS with the phosphorus source and step 20 of solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant. Preferably, method 10 comprises step 17 of providing a condensing agent to the aqueous phase comprising solubilised phosphorylated EPS and / or step 21 of lowering the temperature of the aqueous reactant after the step of solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant.

[0082] The aqueous phase may be separated in step 22 of separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant. Preferably, after step 22, step 23 of transferring the aqueous phase comprising solubilised phosphorylated EPS to an acid reactor is performed.

[0083] After step 22, method 10 may continue with step 24 of acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4, and step 26 of precipitating the phosphorylated EPS from the aqueous phase. The precipitate may be obtained by step 28 of separating the phosphorylated EPS from the aqueous phase.

[0084] In a preferred embodiment, method 10 comprises step 13 of controlling step 14 of heating the EPS and the phosphorus source in the alkaline reactor, step 16 of adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13, step of phosphorylating the EPS with the phosphorus source, and / or step 24 of acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4.

[0085] Furthermore, method 10 may comprise the step 15 of additionally adding polyphosphate and / or pyrophosphates to the alkaline reactor and / or step 19 of adding a catalyst to the aqueous stream and / or the aqueous reactant and / or the aqueous phase.

[0086] Figure 2 shows a photo of EPS before treated with the method according to the invention (left) and phosphorylated EPS obtained with the method according to the invention (right). It becomes clear that the substance becomes more compact. The phosphorylated EPS was obtained from a aerobic granular sludge having 120 g of wet aerobic granular sludge, 8.04 g of dry solids, Total P is 0.02 gP / g TS with about 25% of total P in sludge is polyphosphate (0.005 g PolyP / g TS sludge). Phosphate salt was added in the alkaline step with an equivalent to 0.49 g P, thereby increasing polyphosphate content to 0.06 g P / g TS sludge. In the process KOH was used to adjust the pH to 10, temperature was increased to 80 °C, and incubation time was about 2 hours. Phosphorus content was increased with 100% in phosphorylated EPS compared to original EPS after precipitation. The phosphorylated EPS obtained with the method according to the invention (right) becomes more compact compared to crude EPS. Furthermore, phosphorylated EPS showed better thermal stability achieving 35% higher ash content than crude EPS._The decomposition rate of the polymer decreased by 22% in the first decomposition step and 10% in the second step. The activation energy was also calculated using Kissinger model and it was shown that it increased from 86 kJ / mol to 360 kJ / mol in the first decomposition step and increased from 95 kJ / mol to 940 kJ / mol, indicating higher flame retardancy for the phosphorylated EPS.

[0087] System 102 (Figure 3) comprises wastewater treatment plant 104 having input stream 106. Excess sludge 108 is provided from plant 104 to buffer tank 110 to enable aeration. Flow 112 is subjected to EPS extraction process 114 involving alkaline solubilization in reactor 116 and then acidic precipitation in reactor 118 of flow 117 of alkaline centrate resulting from the alkaline solubilization 116. In the alkaline solubilization conditions typically involve a high pH, high temperature and an incubation time. This may involve addition of external polyphosphate or pyrophosphate salts, if needed, as additional phosphorylating agent(s) via input 120 and / or addition of metal catalysts via input 122 and / or addition of base, such as Potassium hydroxide (KOH), Sodium hydroxide (NaOH), for example, via input 124. Optionally, in the acidic precipitation reactor 118 acid can be added, such as hydrogen chloride (HC1) and / or phosphoric acid (H3PO4), for example, via input 126. In addition, or alternatively, condensing agents can be added via input 128. From system 102, phosphorylated EPS 130 can be provided. It will be understood that different embodiments of system 102 in accordance with the present invention can be envisaged.

[0088] In presently preferred embodiments steps of method 2 can be performed in system 102, wherein wastewater treatment plant 104 optimizes the activity of Polyphosphate- Accumulating Organisms (PAOs) to enhance polyphosphate accumulation, such that the polyphosphate content in output 108 is increased, which enhances phosphorylation. Buffer tank 110 is preferably designed to maintain a constant flow of surplus sludge to extraction process 114. If needed, a gravity thickener is used in and / or after buffer tank 110 in system 102. Buffer tank 110 in system 102 is aerated and preferably has a short Sludge Retention Time (SRT) to prevent polyphosphate hydrolysis during storage. In the illustrated embodiment of system 102 heat is introduced into the sludge destined for alkaline reactor 116 using steam injections or heat exchangers 132, for example. In the illustrated embodiment, sludge 112 is continuously mixed and heated until it reaches 80-90°C in reactor 116. Optionally, Potassium hydroxide (KOH) is added to achieve a pre-set pH of 9-11. In this embodiment, the reactor contents are then mixed for 30 minutes to 5 hours. The ratio of weight (gram) P (phosphorus) to weight (gram) EPS in the aqueous stream should preferably be maintained between 0.0001:1 and 1:1. If necessary, external polyphosphates or pyrophosphates salts, as well as multivalent ions like Mg2+, can be added to catalyze the reaction, via inputs 120, 122, 124. In the illustrated embodiment of system 102, flow / sludge 117 is pumped to decanter centrifuge 138 where the alkaline sludge pellet is separated from the alkaline centrate, which contains solubilized EPS. Preferably, flow / sludge 117 is cooled to 15-30°C using cooler 136. In some of the experiments, the COD of EPS in the alkaline solubilized EPS stream 117 was about 112000 mg / L. Optionally, in reactor 118 hydrochloric acid (HC1) is added to adjust the pH to 2-3. Alternatively, stream temperature at output 120 is maintained at 80°C or higher, while in reactor 118, optionally, Phosphoric acid (H3PO4) is added via input 126 to adjust the pH to 2-3, preferably along with condensing agents like urea via input 128. Acidified alkaline centrate as an output of reactor 118 is optionally pumped into disc centrifuge 134, or other suitable separating means, where the precipitated phosphorylated EPS is separated and provided as product 130.

[0089] Experiments with system 102 have indicated that at least the formation of 0.01 gram organic P per gram COD in the aqueous solution, preferably at least 0.015 gram, more preferably at least 0.02 gram, and most preferably at least 0.03 gram organic P per gram COD in the liquid phase is possible. Optionally, extracted phosphorylated EPS 130 is stored in Intermediate Bulk Containers (IBCs) and is ready for pickup for further processing and application as a flame retardant, coating, emulsifying agent or bio-stimulant.

[0090] The present invention is by no means limited to the above described preferred embodiments and / or experiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.

Claims

CLAIMS1. Method for Extracellular Polymeric Substances (EPS) extraction from an aqueous stream, including phosphorylation of the EPS, comprising the steps of: providing an aqueous stream comprising EPS and a phosphorus source to an alkaline reactor forming an aqueous reactant; heating the EPS and the phosphorus source in the alkaline reactor; adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13; phosphorylating the EPS with the phosphorus source; controlling the step of phosphorylating the EPS; solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant; separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant; acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4; precipitating the phosphorylated EPS from the aqueous phase; and separating the phosphorylated EPS from the aqueous phase.

2. Method according to claim 1, wherein the phosphorus source is a polyphosphate and / or a pyrophosphate, preferably the polyphosphate and / or the pyrophosphate is one or more selected from the group of tetrasodium pyrophosphate, sodium tripolyphosphate, sodium trimetaphosphate, tetrasodium pyrophosphate anhydrous, tetrapotassium pyrophosphate, sodium hexametaphosphate.

3. Method according to any one of the preceding claims, further comprising the step of aerating the aqueous stream in a buffer tank, wherein the aqueous stream is stored in the buffer tank for a time in the range of 5 minutes to 4 hours, preferably for a time in the range of 5 minutes to 3 hours, more preferably for a time in the range of 5 minutes to 2 hour, most preferably for a time in the range of 5 minutes to 1 hour.

4. Method according to any one of the preceding claims, further comprising the step of controlling one or more of the steps: heating the EPS and the phosphorus source in the alkaline reactor;adjusting the pH of the aqueous stream and / or the aqueous reactant to a pH in the range of 8 to 13; phosphorylating the EPS with the phosphorus source; acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4.

5. Method according to any one of the preceding claims, further comprising the step of additionally adding polyphosphate and / or pyrophosphates and / or salts containing phosphorus to the alkaline reactor.

6. Method according to any one of the preceding claims, further comprising the step of providing a condensing agent to the aqueous phase comprising solubilised phosphorylated EPS.

7. Method according to the foregoing claim, wherein the condensing agent is one or more selected from the group of urea, cyanate, cyanamide, carbonyl sulphide.

8. Method according to any one of the preceding claims, wherein the aqueous stream originates from a wastewater treatment plant.

9. Method according to any one of the preceding claims, wherein the aqueous stream further comprises solid organic matter and solid inorganic matter in the range of 5 g L1to 100 g L ', preferably in the range of 10 g L1to 90 g L1, more preferably in the range of 10 g L1to 80 g L1.

10. Method according to any one of the preceding claims, further comprising the step of adding a catalyst to the aqueous stream and / or the aqueous reactant and / or the aqueous phase.

11. Method according to the foregoing claim, wherein the catalyst is a metal catalyst, preferably a two valent metal catalyst.

12. Method according to claim 10 or 11, wherein the catalyst comprises one or more metals from the group of Mg2+, Ca2+, Mn2+, Co2+, Ni2+.

13. Method according to any one of the preceding claims, wherein the step of adjusting the pH of the aqueous stream and / or aqueous reactant in the alkaline reactor to a pH in the range of8 to 13 comprises adjusting to a pH in the range of 9 to 12, preferably to a pH in the range of 9 to11.

14. Method according to any one of the preceding claims, wherein the step of acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1 to 4 comprises acidifying the aqueous phase comprising solubilised phosphorylated EPS to a pH in the range of 1.5 to 3.5, preferably to a pH in the range of 2 to 3.

15. Method according to any one of the preceding claims, wherein the step of heating the EPS and the phosphorus source in the alkaline reactor is performed at a temperature in the range of 70 °C to 100 °C, preferably a temperature in the range of 70 °C to 90 °C, more preferably a temperature in the range of 75 °C to 80 °C.

16. Method according to any one of the preceding claims, wherein the pH of the aqueous stream and / or the aqueous reactant is adjusted using one or more base selected from the group of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium oxide, potassium oxide, calcium oxide.

17. Method according to any one of the preceding claims, wherein the step of acidifying the aqueous phase comprising solubilised phosphorylated EPS is performed using one or more acid selected from the group of hydrogen chloride, phosphoric acid, sulphuric acid, acetic acid, citric acid, oxalate acid.

18. Method according to any one of the preceding claims, further comprising the step of lowering the temperature of the aqueous reactant after the step of solubilising the phosphorylated EPS in an aqueous phase of the aqueous reactant.

19. Method according to the foregoing claim, wherein the temperature of the aqueous phase is lowered to a temperature in the range of 10 °C to 40 °C, preferably to a temperature in the range of 15 °C to 35 °C, more preferably to a temperature in the range of 15 °C to 30 °C.

20. Method according to any one of the preceding claims, wherein the step of phosphorylating the EPS with the phosphorus source is performed for 30 minutes to 5 hours, preferably for 1 hour to 4 hours, more preferably for 1.5 hours to 3 hours.

21. Method according to any one of the preceding claims, wherein the step of separating the aqueous phase comprising solubilised phosphorylated EPS from other phases present in the aqueous reactant and / or the step of separating the phosphorylated EPS from the aqueous phase comprises one or more of centrifuging, filtering, decanting.

22. Method according to any one of the preceding claims, further comprising the step of transferring the aqueous phase comprising solubilised phosphorylated EPS to an acid reactor.

23. Method for manufacturing of a flame retardant, comprising phosphorylated EPS obtainable by the method according to any one of the preceding clauses.

24. Phosphorylated EPS obtainable by the method according to any one of the claims 1 to 23.

25. Use of the phosphorylated EPS according to claim 24 in flame retardants.

26. Flame retardant comprising a phosphorylated EPS.

27. System for performing the method according to any one of the claims 1 to 23.

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