JP7553248B2 - Treatment method for removing oil from wastewater - Google Patents

Description

The present invention relates to a flocculation treatment method that can form strong large flocs and efficiently remove oil from oil-containing wastewater. The treatment method includes the step of adding at least one polynaphthalene derivative having a specific formula and a water-soluble cationic (co)polymer.

In many industries, it is necessary to treat wastewater to remove the oil it contains (food factories, automobile factories, printing plants, oil field wastewater, etc.). In general, the wastewater produced is difficult to treat due to the large amount of oil.

Various types of treatment exist. For example, document JP2014-158993 describes the use of cationic polymer flocculants to treat oil-containing wastewater. However, cationic polymer flocculants do not produce strong flocs, making solid-liquid separation difficult.

Document JP6-296977 describes the combination of an inorganic flocculant, such as polyaluminum chloride, with an anionic polymer flocculant to treat oil-containing wastewater. However, the flocculation strength of the inorganic flocculant is weak. Even when combined with the anionic polymer flocculant, the flocculation strength is still not sufficient to efficiently remove the flocs. Furthermore, the inorganic flocculant causes many handling constraints in the treatment process.

Document JP2011-131164 describes the use of a water-soluble cationic polymer followed by the addition of a second polymeric flocculant to treat oil-containing wastewater, but this method does not produce strong large flocs. Furthermore, this method requires the addition of an acidic additive to reduce the viscosity of the wastewater and is limited with respect to the oil content of the sludge to be treated.

In view of the above, there remains a need for more effective treatment in the oil-containing wastewater treatment industry.

JP2014-158993 JP6-296977 JP2011-131164

P. J. Flory, Principles of Polymer Chemistry, Cornell University Press (1953), Chapter VII, pp. 266-315 Macromolecules, an Introduction to Polymer Science, edited by F. A. Bovey and F. H. Winslow, Academic Press (1979), pp. 296-312.

The object of the present invention is to provide a method for treating oil-containing wastewater and for removing a large portion of the oil therefrom, which is capable of forming strong large flocs.

The method of the present invention is a method for producing a compound of the general formula (I)

Formula (I)
[Wherein,
R ₁ , R ₂ , R ₃ and R ₄ are each independently selected from the group consisting of hydrogen, (C _1-8 )-alkyl, CH ₂ -OC _1-8 alkyl, -C(-O)-OC _1-4 alkyl, -C(-O)-NH-C _1-8 alkyl, C _1-8 OH (C _1-8 alkyl group having one OH group), sulfonate (SO ₃ ^- ), sulfonic acid (SO ₃ H) and halogen;
one or more of R ₁ , R ₂ , R ₃ and R ₄ are anionic groups or groups that undergo a post-hydrolysis reaction to provide an anionic group;
n is a natural number comprised between 2 and 100, preferably between 2 and 50, more preferably between 2 and 30, even more preferably between 2 and 10.
The method includes the step of adding a water-soluble polynaphthalene derivative having the formula:

Thus, the water-soluble polynaphthalene is a polymer of naphthalene, preferably of the same naphthalene monomer (same R ₁ -R ₄ substituents). However, due to optional post-hydrolysis of any of R ₁ -R ₄ , the water-soluble polynaphthalene may have monomer units with different R ₁ -R ₄ groups. In fact, the post-hydrolysis may be partial. It is called post-hydrolysis because it is carried out after the naphthalene monomer has polymerized. The post-hydrolysis reaction may be carried out before or after the addition of the water-soluble polynaphthalene derivative to the oil-containing wastewater.

Here and hereinafter, an alkyl group is a linear or branched C _x H _2x+1 group, for example CH ₂ CH ₂ CH ₃ or CH(CH ₃ ) ₂ for C ₃ -alkyl.

The above feature "one or more of R ₁ , R ₂ , R ₃ and R ₄ are anionic groups" may correspond to the case where any one or more of R ₁ through R ₄ are sulfonate or sulfonic acid groups.

It has been found that oils, being hydrophobic, interact with the naphthalene moiety of the water-soluble polynaphthalene derivatives. This interaction forms an anionic coating of the oil due to the anionic groups of the water-soluble polynaphthalene derivatives. This anionic coating of the oil allows the water-soluble cationic (co)polymer to interact with the oil more easily, resulting in the formation of strong, large flocs.

This interaction between (1) oil, (2) water-soluble polynaphthalene derivatives, and (3) water-soluble cationic (co)polymers makes it possible to treat difficult sludges with high oil content.

Another advantage of the method is that the water-soluble polynaphthalene derivatives reduce the viscosity of the sludge to be treated. In fact, wastewater from industries such as food, automotive or printing is viscous due to the large amount of oil it contains. By adding the water-soluble polynaphthalene derivatives, the viscosity is reduced and the wastewater is easier to treat and consumes less energy.

The water-soluble polynaphthalene derivatives are added at low dosages, reducing the amount of water-soluble cationic (co)polymer required to treat the sludge.

The method of the present invention also works under acidic conditions. The pH of wastewater derived from food sludge is acidic (pH less than 7) in summer due to acidic fermentation of the sludge. This type of sludge is difficult to flocculate using conventional flocculants due to the low pH. Therefore, the present invention can be carried out at any pH.

As used herein, the term "water-soluble polymer" refers to a polymer that, after being properly mixed with water, produces an aqueous solution (10 g/l at 25°C) free of insoluble particles.

As used herein, the term "A and/or B" means "A" or "B" or "A and B."

The post-hydrolysis reaction is a chemical reaction on the polymer after it has been formed by polymerization of the monomers. This step consists in reacting the hydrolyzable functional groups of the monomers, preferably non-ionic monomers, more preferably monomers containing hydrolyzable functional groups (preferably amides or esters), with a hydrolyzing agent. This hydrolyzing agent may be an enzyme, an ion exchange resin, or an alkali metal. Preferably, the hydrolyzing agent is a Brönsted base, for example NaOH or KOH. During this post-hydrolysis step of the polymer, the number of carboxylic acid functional groups (COOH) and/or carboxylate functional groups (COO ^- ) is increased. In practice, the reaction between the hydrolyzing agent (for example a Brönsted base) and the hydrolyzable functional groups present in the polymer (for example amide or ester functional groups) generates carboxylate groups. The hydrolysis may be partial or complete.

Naphthalene Derivative Polymers The water-soluble naphthalene derivative polymer may be any water-soluble naphthalene derivative polymer having at least one anionic charge. In other words, at least one of its monomer units has at least one anionic group. It can be represented by the general formula (I):

Formula (I)
[Wherein,
R ₁ , R ₂ , R ₃ and R ₄ are each independently selected from the group consisting of hydrogen, (C _1-8 )-alkyl, CH ₂ -OC _1-8 alkyl, -C(-O)-OC _1-4 alkyl, -C(-O)-NH-C _1-8 alkyl, C _1-8 OH (C _1-8 alkyl group having one OH group), sulfonate (SO ₃ ^- ), sulfonic acid (SO ₃ H) and halogen;
one or more of R ₁ , R ₂ , R ₃ or R ₄ is an anionic group or a group that undergoes a post-hydrolysis reaction to provide an anionic group;
n is a natural number comprised between 2 and 100, preferably between 2 and 50, more preferably between 2 and 30, even more preferably between 2 and 10.
Corresponds to.

Preferably, the water-soluble polynaphthalene derivative has one or more of R ₁ , R ₂ , R ₃ or R ₄ that are anionic groups prior to addition to the wastewater to be treated.

Preferably, the water-soluble polynaphthalene derivative of formula (I) has a sulfonic acid group or a sulfonate group. In other words, one or more of _R1 , _R2 , R3 or _R4 is preferably a sulfonic acid or a _sulfonate . Even more preferably, the water-soluble polynaphthalene derivative of formula (I) is 2-polynaphthalenesulfonic acid or a salt thereof.

Typically, the salts are alkali metal (Li, Na, K, ...), alkaline earth metal (Ca, Mg, ...) or ammonium salts, in particular quaternary ammonium salts. The preferred salt is Ca.

When a divalent counterion is used, the divalent counterion forms an ionic bond with the anionic charge of the water-soluble polynaphthalene derivative of formula (I). In fact, the divalent counterion is shared by two anionic groups. This results in a water-soluble polynaphthalene derivative network as the one in Figure 1 for the specific case of a polymer having a monomer unit with sulfonate _SO3 ^- group and Ca2 ⁺ counterion.

In a preferred embodiment, the water-soluble polynaphthalene derivative of formula (I) is calcium 2-polynaphthalenesulfonate. In this case, three of R1, _R2 , _R3 and _R4 are hydrogen atoms, _and one of _R1 , _R2 , _R3 and _R4 is a sulfonate group. More preferably, _R1 is _SO3 , and _R2 , _R3 and _R4 are hydrogen atoms, or _R4 is _SO3 , and _R1 , _R2 and _R3 are hydrogen atoms.

When a structured network is formed, the water-soluble polynaphthalene derivative network generally contains between 30 and 500 units of the derivative of formula (I), preferably between 20 and 100 units, more preferably between 10 and 50 units, and even more preferably between 5 and 30 units.

The water-soluble polynaphthalene derivatives of formula (I) according to the present invention preferably have a weight average molecular weight (M _w ) comprised between 400 g/mol and 30000 g/mol, more preferably comprised between 400 g/mol and 15000 g/mol, even more preferably comprised between 400 g/mol and 5000 g/mol.

Weight average molecular weights are determined using known methods such as GPC analysis using polystyrene standards. Methods for determining molecular weights of polymers are well known. Methods are described, for example, in (i) P. J. Flory, "Principles of Polymer Chemistry," Cornell University Press (1953), Chapter VII, pp. 266-315, or (ii) "Macromolecules, an Introduction to Polymer Science," F. A. Bovey and F. H. Winslow, eds., Academic Press (1979), pp. 296-312. As used herein, the weight average and number average molecular weights of the polymers of the invention are obtained by integrating the area under the peak corresponding to the polymer of the invention, which is usually the major high molecular weight peak, excluding peaks associated with diluents, impurities, unbound polymer chains, and other additives.

The water-soluble polynaphthalene derivative of formula (I) may be used in any form known to those skilled in the art, such as an aqueous solution, a powder, a water-in-oil emulsion, or a polymer dispersion in brine. Preferably, the water-soluble polynaphthalene derivative of formula (I) is used as an aqueous solution.

Water-soluble cationic (co)polymers The water-soluble cationic (co)polymers may be natural (co)polymers such as xanthan gum, guar gum or polysaccharide compounds, or synthetic or semi-synthetic (co)polymers. Preferably, the water-soluble (co)polymers are synthetic (co)polymers.

Semi-synthetic (co)polymers refer to natural (co)polymers that have undergone chemical reactions by grafting various synthetic substituents. Those skilled in the art will recognize this type of reaction as being classical chemical reactions applied to natural (co)polymers.

The water-soluble cationic (co)polymer comprises at least one water-soluble cationic monomer, which may be synthesized from a combination of one or more water-soluble cationic monomers and/or one or more water-soluble nonionic monomers and/or one or more water-soluble anionic monomers and/or one or more water-soluble zwitterionic monomers and/or one or more hydrophobic monomers. Preferably, the water-soluble cationic (co)polymer comprises at least one water-soluble cationic monomer and one water-soluble nonionic monomer.

The water-soluble cationic monomers that may be used in the present invention are preferably selected from water-soluble vinyl monomers, more specifically from acrylamide, acrylic, allyl or maleic acid types having quaternary ammonium groups. In particular, but without limitation, quaternized dimethylaminoethyl acrylate (DMAEA), quaternized dimethylaminoethyl methacrylate (DMAEMA), quaternized dimethyldiallylammonium chloride (DADMAC), acrylamidopropyltrimethylammonium chloride (APTAC), methacrylamidepropyltrimethylammonium chloride (MAPTAC) and mixtures thereof. Preferably, at least one cationic monomer is quaternized dimethylaminoethyl acrylate (DMAEA).

The water-soluble cationic (co)polymer preferably comprises up to 100 mol% water-soluble cationic monomer. The water-soluble cationic (co)polymer preferably comprises more than 30 mol%, preferably more than 50 mol%, more preferably more than 70 mol%, even more preferably more than 90 mol% water-soluble cationic monomer.

The water-soluble non-ionic monomers that can be used in the present invention are preferably selected from water-soluble vinyl monomers. Preferred monomers belonging to this family are, for example, acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N-methylol acrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyridine, N-vinylpyrrolidone, acryloylmorpholine (ACMO), diacetone acrylamide, and mixtures thereof. Preferably, the non-ionic monomer is acrylamide.

The water-soluble cationic (co)polymer preferably contains up to 70 mol %, preferably up to 50 mol %, more preferably up to 30 mol %, even more preferably up to 10 mol % of water-soluble non-ionic monomers.

Preferably, the water-soluble cationic (co)polymer is a copolymer of quaternized dimethylaminoethyl acrylate (DMAEA) and acrylamide.

The water-soluble anionic monomers that may be used in the present invention are preferably selected from water-soluble vinyl monomers, more specifically acrylic acid, methacrylic acid, itaconic acid, maleic acid, sulfonated derivatives of (meth)acrylic acid, such as 2-acrylamido-2-methylpropanesulfonic acid (ATBS), vinylsulfonic acid, vinylphosphonic acid, and mixtures thereof, said anionic monomers being unchlorinated, partially chlorinated or fully chlorinated, and salts of 3-sulfopropyl methacrylate.

The salified forms advantageously correspond to alkali metal (Li, Na, K, ...), alkaline earth metal (Ca, Mg, ...) or ammonium salts, in particular quaternary ammonium. Preferred salts are the sodium salts. The non-salified forms correspond to the acid forms of the anionic monomers, for example _CH2 =CH-C(=O)OH in the case of acrylic acid.

The anionic portion of the water-soluble cationic (co)polymer can be obtained by post-hydrolysis.

The water-soluble cationic (co)polymer preferably contains up to 70 mol %, preferably up to 50 mol %, more preferably up to 30 mol %, even more preferably up to 10 mol % of water-soluble anionic monomers.

Water-soluble zwitterionic monomers that may be used in the present invention may be derivatives of acrylamide, acrylic, vinyl, allyl or maleic units (which monomers have amine or quaternary ammonium groups), and carboxylic acids (or carboxylates), sulfonic acids (or sulfonates) or phosphoric acids (or phosphates or phosphonates). In particular, and in a non-limiting manner, dimethylaminoethyl acrylate derivatives, such as 2-((2-(acryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, 3-((2-(acryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate, 4-((2-(acryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(acryloyloxy)ethyl](dimethylammonio) ) acetate, methacrylate derivatives of dimethylaminoethyl, such as 2-((2-(methacryloyloxy)ethyl)dimethylammonio)ethane-1-sulfonate, 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate, 4-((2-(methacryloyloxy)ethyl)dimethylammonio)butane-1-sulfonate, [2-(methacryloyloxy)ethyl](dimethylammonio) acetate, dimethylaminopropyl acrylamide derivatives such as 2-((3-acrylamidopropyl)dimethylammonio)ethane-1-sulfonate, 3-((3-acrylamidopropyl)dimethylammonio)propane-1-sulfonate, 4-((3-acrylamidopropyl)dimethylammonio)butane-1-sulfonate, [3-(acryloyl)oxy)propyl](dimethylammonio)acetate, dimethylaminopropyl methyl acrylamide derivatives such as 2-((3-methacrylamidopropyl)dimethylammonio)ethane-1-sulfonate, 3-((3-methacrylamidopropyl)dimethylammonio)propane-1-sulfonate, 4-((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate and [3-(methacryloyloxy)propyl](dimethylammonio)acetate.

The water-soluble cationic (co)polymer preferably contains up to 70 mol %, preferably up to 50 mol %, more preferably up to 30 mol %, even more preferably up to 10 mol % of water-soluble zwitterionic monomers.

The hydrophobic monomers that can be used in the present invention are preferably selected from vinyl monomers of the acrylamide, acrylic, allyl or maleic acid type, more particularly having pendant hydrophobic groups. These hydrophobic monomers are preferentially selected from acrylamide derivatives, such as N-alkylacrylamides, such as diacetoneacrylamide, N-tert-butylacrylamide, octylacrylamide; N,N-dialkylacrylamides, such as N,N-dihexylacrylamide; and acrylic acid derivatives, such as alkyl acrylates and methacrylates, and mixtures thereof. Preferably, they are selected from esters of (meth)acrylic acid having alkyl, aryl alkyl, propoxylated, ethoxylated, or ethoxylated and propoxylated chains; (meth)acrylamide derivatives having alkyl, aryl alkyl, propoxylated, ethoxylated, ethoxylated and propoxylated, or dialkyl chains; alkylaryl sulfonates; cationic allyl derivatives; anionic or cationic hydrophobic (meth)acryloyl derivatives; and anionic or cationic monomeric derivatives of (meth)acrylamide having hydrophobic chains.

The water-soluble cationic (co)polymer preferably contains less than 5 mol % of hydrophobic monomers. When hydrophobic monomers are used, they are used in an amount such that the (co)polymer remains water-soluble.

When preparing a water-soluble (co)polymer according to the present invention, the skilled artisan will know that the polymer composition cannot have more than 100% by weight of monomers, and will adjust the amount of monomers so that it does not exceed 100%.

The water-soluble cationic (co)polymers according to the present invention preferably have a weight average molecular weight between 3,000,000 g/mol and 20,000,000 g/mol, more preferably greater than 10,000,000 g/mol, more preferably greater than 12,000,000 g/mol, even more preferably greater than 15,000,000 g/mol.

According to the invention, the water-soluble cationic (co)polymers may have a linear structure, branched, star-shaped, comb-shaped, block, microblock structure, or a controlled polydispersity of molecular weight. These properties can be obtained by the choice of initiator, transfer agent, polymerization technique, such as template polymerization, controlled radical polymerization known as RAFT (reversible chain transfer by addition-fragmentation), NMP (nitroxide mediated polymerization) or ATRP (atom transfer radical polymerization), incorporation of structural monomers, concentration options. The general knowledge of the skilled person allows the skilled person to prepare water-soluble (co)polymers having one of these structural types. The water-soluble cationic (co)polymers of the invention remain water-soluble when they have a specific morphology.

The water-soluble cationic (co)polymer may be crosslinked. The crosslinking agent may be selected from the group comprising polyethylenically unsaturated monomers (having at least two unsaturated functional groups, e.g., vinyl, allyl, acrylic and epoxy functional groups). Preferred crosslinking agents are selected from methylenebisacrylamide (MBA), ethylene glycol diacrylate, tetraallyl ammonium chloride, polyethylene glycol dimethacrylate, diacrylamide, cyanomethyl acrylate, vinyloxyethyl acrylate, vinyloxymethacrylate, triallylamine, formaldehyde, glyoxal, glycidyl ethers, e.g., ethylene glycol diglycidyl ether, and epoxy, triallylamine, tetraallyl ammonium chloride (TAAC), and mixtures thereof.

When such crosslinkers are used, the amount used is such that the water-soluble cationic (co)polymer is still water-soluble.

In general, the formation of water-soluble cationic (co)polymers does not require any particular polymerization process. It can be obtained by all polymerization techniques known to those skilled in the art that advantageously result in a (co)polymer in powder form, for example gel polymerization followed by a drying and grinding step; precipitation polymerization; solution polymerization followed by a spray drying step; inverse suspension polymerization, advantageously to obtain microbeads; micellar polymerization with or without a precipitation step; post-hydrolysis or cohydrolysis polymerization; so-called "template" polymerization, radical or controlled radical, more particularly of the RAFT type (reversible addition-fragmentation chain transfer).

The polymerization of water-soluble cationic monomers is generally a free radical polymerization. According to the present invention, free radical polymerization means free radical polymerization using at least one UV, azo, redox or thermal initiator, or controlled radical polymerization technique (CRP), or matrix polymerization technique.

The water-soluble cationic (co)polymer may be used in any form known to those skilled in the art, such as an aqueous solution, a powder, a water-in-oil emulsion, or a dispersion of the (co)polymer in brine. Preferably, the water-soluble cationic (co)polymer is an aqueous solution.

Treatment Method The water-soluble polynaphthalene derivative and the water-soluble cationic (co)polymer may be added simultaneously, either as a blend or separately, or they may be added sequentially or with a period between the two additions. Preferably, there is a period between the two additions.

The water-soluble polynaphthalene derivative and the water-soluble cationic (co)polymer may be added to the sludge to be treated in any order. The water-soluble polynaphthalene derivative may be added first, followed by the water-soluble cationic (co)polymer, but it is also possible to add the water-soluble cationic (co)polymer before the water-soluble polynaphthalene derivative. Preferably, the water-soluble cationic (co)polymer is added first.

The amount of water-soluble polynaphthalene derivative to be added to the sludge to be treated depends on many parameters (sludge composition, pH...). Preferably, in the method according to the invention, the water-soluble polynaphthalene derivative is added in a mass range of 10 to 10,000 ppm based on the amount of oil-containing wastewater to be treated. The skilled person will know by routine experimentation the amount of water-soluble polynaphthalene derivative required.

The amount of water-soluble cationic (co)polymer added to the sludge to be treated depends on many parameters (sludge composition, pH...). Preferably, in the method according to the invention, the water-soluble cationic (co)polymer is added in a mass range of 10 to 10,000 ppm based on the amount of oil-containing wastewater to be treated. The skilled person will know by routine experimentation the amount of water-soluble cationic (co)polymer required.

The mass ratio between the water-soluble polynaphthalene derivative and the water-soluble cationic (co)polymer is preferably comprised between 0.5 and 5, preferably between 1 and 2.

The treatment can be used for any wastewater, in particular, but not limited to, wastewater originating from food factories, automobile factories, printing factories, dry cleaning factories, oil field wastewater, and any industry where oil-containing wastewater needs to be treated. Preferably, the method of the present invention is particularly efficient for wastewater originating from food factories and industries where the oil content is high, up to 10% by volume. If the oil content in the wastewater is more than 10%, it is easily removed by oil/water separators or centrifuge devices. The wastewater to be treated is preferably originating from a food factory.

In a particular embodiment of the present invention, the method comprises the steps of:

Formula (I)
[Wherein,
R ₁ , R ₂ , R ₃ and R ₄ are each independently selected from the group consisting of hydrogen, (C _1-8 )-alkyl, CH ₂ -OC _1-8 alkyl, -C(-O)-OC _1-4 alkyl, -C(-O)-NH-C _1-8 alkyl, C _1-8 OH (C _1-8 alkyl group having one OH group), sulfonate (SO ₃ ^- ), sulfonic acid (SO ₃ H) and halogen;
one or more of R ₁ , R ₂ , R ₃ or R ₄ is an anionic group or a group that undergoes a post-hydrolysis reaction to provide an anionic group;
n is a natural number comprised between 2 and 100, preferably between 2 and 50, more preferably between 2 and 30, even more preferably between 2 and 10.
and a water-soluble cationic (co)polymer are added to the oil-containing wastewater to be treated.

In a particular embodiment of the invention, the method comprises the step of adding 2-polynaphthalenesulfonic acid or a salt thereof and a water-soluble cationic copolymer of quaternized dimethylaminoethyl acrylate (DMAEA) and acrylamide.

The present invention will be further described with reference to the following examples. The following examples are merely illustrative of the present invention and are not intended to be limiting. All percentages are by weight (w%) unless otherwise specified.

FIG. 1 shows a structured network of the calcium salt of 2-polynaphthalenesulfonate. FIG. 1 shows the flocculation of sludge using only water-soluble cationic polymer under pH control. FIG. 1 illustrates the flocculation of sludge using the method according to the invention under pH control. FIG. 4 shows the pH values of FIGS. 2 and 3.

Abbreviations used:
AM: acrylamide;
DMAEA: quaternized dimethylaminoethyl acrylate;
DMAEMA: Quaternized dimethylaminoethyl methacrylate;
AA: acrylic acid;
PNS: Polynaphthalene sulfonate

1. Conventional Sludge Various polymers commonly used in oily wastewater treatment were tested and compared with the treatment according to the present invention.

The characteristics of the sludge are detailed in Table 1.

The polymers tested are listed in Table 2.

Test procedure:
In the jar tester, 250 mL of sludge is collected. The polymer to be tested is added in the same amount and the sample is stirred at 250 rpm for 1 minute.

Floc size was determined visually.

After a second shear step at 250 rpm for 30 seconds, the flocculation strength was determined by the change in floc size.

After flocculation, filter the sludge through a sieve with a pore size of 250 microns. Determine the volume of the filtrate by measuring its mass.

The results are shown in Table 3.

These examples show that the addition of water-soluble polynaphthalene sulfonates improves floc formation; their size and strength are increased compared to conventional flocculant polymers. This makes wastewater treatment easier and more convenient, as the flocs are more easily removed.

2 Oily acidic sludge:
Another advantage of the method according to the invention is that it works on acidic sludge.

Sludges with different pH are tested with water-soluble cationic polymers and compared with the method according to the invention. The diameter of the flocs is measured and given in mm (for example, D1 means 1 mm diameter, D5 means 5 mm diameter).

The results are shown in Table 4.

Water-soluble cationic polymers alone are unable to dewater the sludge, even at pH 10, due to small and weak flocs.

By combining a water-soluble cationic polymer with a water-soluble polynaphthalene sulfonate, it can be seen that significant floc formation begins at pH 5.

3 Performance Comparison To clearly demonstrate the improvement of the method of the invention, two samples of oil-containing wastewater are compared: a first treatment (A) consists in adding a water-soluble cationic polymer (250 ppm) and a second treatment (B), corresponding to the invention, consists in adding a water-soluble polynaphthalenesulfonic acid (150 ppm) followed by a water-soluble cationic polymer (150 ppm).

The addition of water-soluble polynaphthalene sulfonate removes almost twice as much oil as the amount removed by adding only the water-soluble cationic polymer (this corresponds to a 200% increase in the amount of oil removed). With respect to the initial oil content, the total oil removed from the oil-containing wastewater increases by 41%.

Claims (8)

A method for treating oil-containing wastewater, comprising:
Formula (I)
[Wherein,
R ₁ , R ₂ , R ₃ and R ₄ are each independently selected from the group consisting of hydrogen, -(C _1-8 )-alkyl, -CH ₂ -OC _1-8 alkyl, -C(-O)-OC _1-4 alkyl, -C(-O)-NH-C _1-8 alkyl, -C _1-8 OH, sulfonate SO ₃ ^- , sulfonic acid SO ₃ H, and halogen;
one or more of R ₁ , R ₂ , R ₃ and R ₄ are anionic groups or groups that undergo a post-hydrolysis reaction to provide an anionic group;
n is a natural number between 2 and 100.
and a water-soluble cationic (co)polymer ,
The water-soluble polynaphthalene derivative of formula (I) is an alkaline earth metal salt of 2-polynaphthalenesulfonic acid . 2. The method of claim 1, wherein the water soluble cationic (co)polymer comprises at least one cationic monomer selected from quaternized dimethylaminoethyl acrylate (DMAEA), quaternized dimethylaminoethyl methacrylate (DMAEMA), quaternized dimethyldiallyl ammonium chloride (DADMAC), acrylamidopropyl trimethyl ammonium chloride (APTAC), methacrylamidopropyl trimethyl ammonium chloride (MAPTAC), and mixtures thereof . 3. The method of claim 1 or 2 , wherein the water-soluble cationic (co)polymer consists of quaternized dimethylaminoethyl acrylate (DMAEA) and acrylamide. 4. The method according to claim 1 , wherein the water-soluble polynaphthalene derivative has a weight average molecular weight comprised between 400 g/mol and 30000 g/mol. 5. The method according to any one of claims 1 to 4 , wherein the amount of water-soluble polynaphthalene derivative is comprised between 10 ppm and 10,000 ppm based on the weight of the oil-containing wastewater to be treated. 6. The method according to claim 1 , wherein the weight ratio between the water-soluble polynaphthalene derivative and the water-soluble cationic (co)polymer is comprised between 0.5 and 5. 7. The method according to any one of claims 1 to 6 , wherein a water-soluble cationic (co)polymer is added to the oil-containing wastewater to be treated before the water-soluble polynaphthalene derivative. 8. The method according to any one of claims 1 to 7 , wherein the oil-containing wastewater originates from a food factory.