Technical field of the Invention

The present invention relates to a process for the treatment of waters containing ammonia, also referred to as ammonia condensed waters, aimed to the reuse thereof.

Background

The condensed waters deriving from industrial productive processes, for example a production process of a protein hydrolysate of animal origin, are characterized by the presence of ammonia nitrogen and possibly trace sulphides.

It is therefore necessary to treat such ammonia condensed waters to recover ammonium bicarbonate, to be reused within production processes, and to obtain purified water, which may in turn be used, for example, as cooling water for cooling towers or for steam production.

According to known methods, the ammonia nitrogen can be removed from the condensed water characterized by a basic pH by acidification with sulphuric acid (H2SO4) to form ammonium sulphate (NEU^SC . The thus prepared water may be treated with a reverse osmosis plant.

Anyway, the acidification with HiSC has some drawbacks, such as: a) the retentate consists of an ammonium sulphate solution, which cannot be reused in industrial productive processes, for example for the production of a protein hydrolysate, and therefore it must necessarily be disposed; further, when sulphides are present in the condensed water, b) the formation of colloidal sulphur (S) causes the occlusion of the reverse osmosis plant membranes; and c) the sulphides discharge, such as H2S, produces a typical and unpleasant odor, perceived at very low concentration thresholds.

Therefore, there is still the need to provide a process for the treatment of waters containing ammonia aimed to the reuse thereof, allowing to overcome the above mentioned drawbacks.

Brief description of the Figures

Figure 1 and Figure 2 show the distribution of the species as a function of pH.

Summary of the Invention

The invention relates to a process for the treatment of water containing ammonia, such as ammonia condensed water, aimed to the reuse thereof, comprising the following steps: al) possible cooling of the ammonia condensed water at a basic pH at a temperature equal to or lower than 35 °C; and bl) adding carbon dioxide (CO2) as acidifying agent to the condensed water to obtain a saline solution; cl) treating the saline solution obtained directly in step bl) with a reverse osmosis plant.

Detailed description of the Invention

The industrial productive processes for the preparation of protein hydrolysates, in particular of animal origin, such as a process providing for collagen hydrolyzation, lead to the formation of an aqueous solution containing peptides and amino acids. Such solution is concentrated by water evaporation, leading to the formation of the so-called condensed water.

The condensed water to be treated according to the present invention, hereinafter referred to as ammonia condensed water, may be characterized by an ammonia nitrogen content up to 10,000 ppm, preferably the content ranges between 2,000 ppm and 10,000 ppm, more preferably ranges between 2,000 ppm and 6,000 ppm, and possibly by trace sulphides, for example in an amount ranging up to 500 ppm, preferably ranging between 50 ppm and 500 ppm, more preferably ranging between 50 ppm and 200 ppm, and/or by other pollutants such as phenols.

Object of the present invention is a process for the treatment of waters containing ammonia aimed to the reuse thereof, comprising the steps of: bl) adding carbon dioxide (CO2) as acidifying agent to the condensed water to obtain a saline solution; cl) treating the saline solution obtained directly in step bl) with a reverse osmosis plant.

According to the present invention, before step bl) the process may optionally comprise the cooling step al) of the ammonia condensed water characterized by a basic pH at a temperature equal to or lower than 35 °C.

The temperature in step al), measured at 1 atm, is equal to or lower than 35 °C, preferably is comprised between 15 and 35 °C, more preferably is comprised between 15 and 25 °C.

In step bl), carbon dioxide is added up to a pH comprised between 6.0 and 7.5, preferably between 6.5 and 7.5, more preferably up to a pH equal to 7.

Using CO2 as acidifying agent, a (concentrated) ammonium bicarbonate (NH4HCO3) saline solution at the end of step bl) and step cl) (retentate) of the process is obtained, to be reused in the production process, for example, of a protein hydrolysate.

Using CO2 as acidifying agent has the further advantage that possible calcium (Ca ²⁺ ) and magnesium (Mg ²⁺ ) residues in the condensed waters are broken down by the formation of insoluble carbonates.

According to a preferred aspect of the invention, carbon dioxide (CO2) is added in step bl) under pressure, at a pressure lower than or equal to 4.0 bar, preferably lower than or equal to 3.5 bar, more preferably lower than or equal to 3 bar.

Step cl) of treating the saline solution obtained directly in step bl) with a reverse osmosis plant, consists of performing one or more subsequent steps, preferably two or more, more preferably three or more, of filtration by reverse osmosis of the saline solution through the osmotic membrane to obtain “purified water” according to the invention. The permeate obtained from a first osmosis step is again passed through the osmotic membrane to separate the residual ammonia nitrogen, and so on, until obtaining a permeate, referred to as “purified water” according to the invention, whose residual ammonia nitrogen concentration is equal to or lower than 15 ppm, preferably is equal to 10, more preferably is equal to or lower than 1.5 ppm, even more preferably is equal to or lower than 1 ppm.

According to the present invention, the expression “obtained directly in step bl)” means that the saline solution obtained at the end of step bl) is subjected directly to the treatment with a reverse osmosis plant consisting of one or more subsequent steps, preferably two or more, more preferably three or more, of filtration by reverse osmosis, for example without any intermediate evaporation step.

Advantageously, according to the process of the invention, adjusting the pH between an osmosis step and the subsequent is not necessary.

The process may further comprise an optional step a2) of filtration through activated carbon and/or a subsequent micro- or nano-filtration of the optionally cooled condensed water obtained in step al).

The process may further comprise a possible step a3) before step bl) of: a3) adding hydrogen peroxide as oxidizing agent to the ammonia condensed water at a basic pH, optionally obtained at the end of step al) and/or a2).

The possible oxidative treatment with hydrogen peroxide (H2O2) of step a3) leads to the oxidation of sulphides (S ² ‘), if any, to sulphates (SC ^2- ).

In fact, step a3) allows the remotion of the sulphides (S ² ‘) present in the condensed water using hydrogen peroxide as oxidizing agent, which is easy to use, has low cost, and produces water as a by-product. At pH > 9.2 the oxidation reaction of the sulphides to sulphates is fast and characterized by yields near to 100%. Due to the basic pH in the condensed water, the complete oxidation of the sulphides to sulphates is obtained as by the reaction scheme below:

According to the present invention, the expression “a basic pH” means a pH comprised between 9.0 and 11.0, preferably between 9.5 and 10.5, more preferably pH~10 or equal to 10.

A further object of the invention is a process comprising the following steps: al) cooling the ammonia condensed water at a basic pH at a temperature equal to or lower than 35 °C; and a2) filtration through activated carbon and/or a subsequent micro- or nano-filtration of the cooled condensed water obtained in step al); and a3) adding hydrogen peroxide as oxidating agent to the condensed water obtained in step a2); and bl) adding carbon dioxide (CO2) as acidifying agent to the condensed water of step a3) to obtain a saline solution; and cl) treating the saline solution obtained in step bl) with a reverse osmosis plant.

A further object of the invention is a process comprising the following steps: al) cooling the ammonia condensed water at a basic pH at a temperature equal to or lower than 35 °C; and a3) adding hydrogen peroxide as oxidating agent to the cooled ammonia condensed water at a basic pH of step al); and bl) adding carbon dioxide (CO2) as acidifying agent to the condensed water of step a3) to obtain a saline solution; and cl) treating the saline solution obtained in step bl) with a reverse osmosis plant.

A further object of the invention is a process comprising the following steps: al) cooling the ammonia condensed water at a basic pH at a temperature equal to or lower than 35 °C; and a2) filtration through activated carbon and/or a subsequent micro- or nano-filtration of the cooled condensed water obtained in step al); and bl) adding carbon dioxide (CO2) as acidifying agent to the condensed water of step a2) to obtain a saline solution; and cl) treating the saline solution obtained in step bl) with a reverse osmosis plant.

According to a further aspect of the invention, the process relates to the treatment of not cooled, or partially cooled, ammonia condensed water at a temperature comprised between 35 °C and 70 °C, preferably comprised between 35 °C and 65 °C, more preferably equal to 60 °C, comprising the steps of: a2) possible filtration through activated carbon and/or possible subsequent micro- or nano-filtration of the condensed water; and a3) possible adding of hydrogen peroxide as oxidating agent to the ammonia condensed water at a basic pH; and bl) adding carbon dioxide (CO2) as acidifying agent to the condensed water to obtain a saline solution; cl) treating the saline solution obtained in step bl) with a reverse osmosis plant.

The following Examples further illustrate the invention.

EXAMPLES

EXAMPLE 1 - Treatment of ammonia condensed water

The ammonia condensed water (H2O ^c )is cooled at room temperature. Once cooled, it is treated with H2O2 in stoichiometric amount, oxidizing the sulphides (S ² ‘) to sulphates (SO ₄ ² ’), and subsequently acidified with carbon dioxide (CO2) up to a pH of about 7, salifying the present ammonia thus forming ammonium bicarbonate (NH4HCO3).

Figure 1 and Figure 2 indicate the species distribution as a function of pH.

The thus prepared solution is therefore treated with a reverse osmosis plant. Subsequent steps through the osmotic membrane are performed. The permeate, obtained by a first osmosis step, is again passed through the osmotic membrane. The permeate, obtained by a second osmosis step, is again passed through the osmotic membrane to obtain purified water according to the invention. The SO ₄ ² ' ion remains as it is at pH 7.0, therefore it too will be withheld by the osmotic membrane and present in the retentate.

The result of the performed tests show how the concentration of ammonia nitrogen present in solution in the initial condensed water reduces from 1,958 ppm to 1 ppm.

The retentate, /.< ., a concentrated NH ₄ HCO3 saline solution, may be stored to be used in processes as NH ₄ HCO3 source.

EXAMPLE 2 - Comparison analysis

In Table 1 the results of the analyses performed on the initial ammonia condensed water (H2O ^C ) and on the purified water (permeate) are set.

Materials and Methods

Ammonium ions

The determination of the ammonium cations was performed by the method recommended by the EPA (United States Environmental Protection Agency) (Method n. 300.0), ISO (International Organization for Standardization), and ASTM (APAT/IRSA- CNR Analytic methods for waters 29/2003 Method n. 3030) for the cation determination in drinking and waste waters by ion chromatography. A DIONEX ICS-5000 chromatograph was used. The water soluble sample was weighted with the precision of 1/10000 g and diluted in a volumetric flask in analytical grade water. The samples were filtered on membranes of at least 0.2 pm, for complex arrays a pre-treatment on Cl 8 cartridges is performed to remove hydrophobic organic substances.

- Total nitrogen

For the determination of the total nitrogen the Kjeldahl method was used, consisting of the determination of the total nitrogen meant as addition of ammonia nitrogen and protein organic nitrogen. By this method, the nitrogen contributes due to inorganic components (nitrates, nitrites) and the organic nitrogen contributes of heterocyclic compounds, compounds containing N-N or N-0 bonds, and hydrazine, and hydroxylamine are not determined. The method consists of a first digestion of the sample with sulphuric or phosphosulphuric acid, usually at a temperature of 420 °C. In this way, all the organic material becomes carbon dioxide and evaporating water, and all the protein nitrogen (- NH2) becomes ammonium sulphate ((NEU^SCU). To speed up and make the digestion quantitative, allowing the acid to reach 420 °C, a salt mixture (in the form of tablets) is used consisting of an adjuvant (such as K2SO4, raising the acid boiling temperature) and a catalyst (such as TiCE or Q1SO4). At the end of the digestion, the ammonia is steam distilled prior alkalinization with 32% sodium hydroxide and collected in a boric acid and indicator solution buffered at pH 4.65. The ammonia concentration is therefore determined by titration with 0.1N sulphuric acid by colorimetric or potentiometric detection. EQUIPMENT:

Digestion unit BUCHI KJELDIGESTER K-446

Fume abatement unit BUCHI SCRUBBER K-415

Distillation unit BUCHI KJELMASTER K-375

Autosampler unit BUCHI KJELSAMPLER K-376

300 mL Distillation tubes in pyrex glass

Pyrex glass caps for the rack positions without sample

REACTANTS:

Digestion reactant: Phosphosulphuric acid RS for Kjeldahl method or 96% concentrated sulphuric acid

Catalyst: TiCE based catalyst (BUCHI 11057980 Kjeldahl Tablets Titanium) or CuSO4 based catalyst (BUCHI 11057982 Kjeldahl Tablets Missouri).

Scrubber Solution: 3L of 10% sodium hydroxide, with half spatula of bromothymol blue indicator.

Alkalinization agent: 32% Sodium hydroxide.

Adsorbent solution: 4% Boric acid solution (40 g/L) (or 2% - 40 g/L) with the addition of 2.5mL/L SHER indicator (BUCHI 003512) and buffered at pH 4.65 with 0.1N NaOH.

Tritant: 0.1N sulphuric acid.

Colorimetric probe storage solution: 5% aqueous solution EXTRAN MA 02 (Merck 1075532500).

Potentiometric electrode storage solution: 3M KC1 aqueous solution (22.4g/100mL), to be refreshed at each use.

The calculation of the final result is automatically performed by the titrating system. Anyway, the used formula is the following:

(Vsample-Vblank)x N 100

N tot % = - x 14 x -

1 -000 Ws

Vsample = 0. IN sulphuric acid mLs used in the sample titration Vblank = 0. IN sulphuric acid mLs used in the blank titration

N = sulphuric acid normality

Ws = sample weight.

- Sulphides

For the sulphides determination the cuvette test LCK 653 - HACH was used wherein dimethyl-p-phenylenediamine forms with hydrogen sulphides an intermediate component changing in “leuco” blue. This is then oxidized with ferric(III) ions to methylene blue. The coloration is read photometrically.

- Sulphates and chlorides

The anion determination was performed by a separation method, by ionic chromatography, on an anion exchange column. The method is recommended by EP A (Method n. 300.0), ISO and ASTM, for the anion determination in drinking and waste waters by ion chromatography. A DIONEX ICS-5000 chromatograph was used. The water soluble sample was weighted with the precision of 1/10000 g and diluted in a volumetric flask in analytical grade water. The samples were filtered on membranes of at least 0.2 pm, for complex arrays a pre-treatment on C18 cartridges is performed to remove hydrophobic organic substances.

- Total sulphur

The determination was performed following the EP A Method n. 3052 - Microwave assisted acid digestion of siliceous and organically based matrices - December 1996.

Chemical Oxygen Demand - COD

For the determination, the test LCK 514 - HACH was used which involves the reaction with a sulphuric acid and potassium dichromate solution plus silver sulphate as catalyst. Chlorides are masked with mercury sulphate. The Cr ³⁺ green coloration is read photometrically.

- Conductivity

The determination was performed following the method “Water quality - Determination of electrical conductivity,” International Standard - ISO 7888, first edition, 1985-05-15.

Table 1

.. Permeate

Parameter H2O .. „ _ „„

H2O2 & O2 pH 10.21 6.50

N (NH3) |ppm] 1,958.04 1.15

H ₂ O ^C - waters containing ammonia, or ammonia condensed waters

The process of the invention allows to obtain a purified water (permeate) wherein the amount of sulphides ions (S ² ‘) reduces from 94.4 ppm to < 0.1 ppm and the amount of ammonia nitrogen [N (NHa)] lowers from 1,958 ppm to 1.15 ppm. Further, the purified water of the invention is characterized by a conductivity (y) equal to 7.7 uS/cm.

Due to the process of the invention, reduction values of ammonia nitrogen higher than 99% are reached, as emerges clearly considering the initial ammonia nitrogen values in the waters containing ammonia, or ammonia condensed waters, of 1,958.04 ppm, and the permeate final values, of 1.15 (99.9% reduction).