WO2007020218A1

WO2007020218A1 - Process to remove non-biodegradable compounds from an aqueous composition and apparatus therefor

Info

Publication number: WO2007020218A1
Application number: PCT/EP2006/065192
Authority: WO
Inventors: Cornelis Gijsbertus Van Ginkel; Roy Geerts
Original assignee: Akzo Nobel N.V.
Priority date: 2005-08-12
Filing date: 2006-08-09
Publication date: 2007-02-22

Abstract

The present invention relates to a process to remove a non-biodegradable compound from an aqueous composition comprising the following steps (i) reacting insoluble Mn(III) and/or Mn(IV) compounds with one or more non-biodegradable compounds at a pH in the range of 1 to 7.5 to yield a Mn(II) compound and one or more biodegradable fragments, and (ii) oxidizing the Mn(II) compound to (a) Mn(III) and/or Mn(IV) compound(s) in the presence of microorganisms at a pH in the range of 7 to 10, wherein the microorganisms are present in the reaction mixture of step (i) and step (ii) of the process.

Description

ACR 3130 R

PROCESS TO REMOVE NON-BIODEGRADABLE COMPOUNDS FROM AN AQUEOUS COMPOSITION AND APPARATUS THEREFOR

The present invention relates to a process to remove (in)organic substances which are difficult or impossible to treat biologically in conventionally operated plants from an aqueous composition and to an apparatus therefor.

Many industrial processes produce waste water streams containing inorganic and/or organic compounds that are difficult or even impossible to remove biologically from the water and of which the discharge into the environment is undesirable. Such compounds as are difficult or impossible to remove from a water stream using conventional biological methods are hereinafter called nonbiodegradable compounds.

Examples of non-biodegradable compounds can be found among chelating agents, which are compounds used to reduce the chemical activity of metal ions which would otherwise adversely affect industrial processes. Generally, if these agents are not recycled, they remain in the water phase because they are water-soluble and, as a result, they are discharged with the waste water. Examples of such chelating agents are EDTA (ethylene diamine tetraacetic acid), PDTA (propylene diamine tetraacetic acid), and DTPA (diethylene triamine pentaacetic acid). Because of their non-biodegradability, such agents may end up in the environment in spite of biological waste water treatment, which is undesired.

Although the above-mentioned chelating agents themselves are not readily biodegradable, treatment of EDTA and PDTA in biological systems maintained under alkaline conditions is feasible (PCT/EP96/02584, "Microbiological degradation of alkylene amine acetates" (1997); CG. van Ginkel and R. Geerts, "Full-scale biological treatment of industrial effluents containing EDTA" in Biogeochemistry of Chelating Agents, ACS Symposium Series, Vol. 909 (2005), pp. 195-203). A chemical conversion of the chelating agents to more readily ACR 3130 R 2

biodegradable compounds by contacting the chelating agents with chemical oxidants is also known.

US 3,487,016 discloses the chemical oxidation of components in waste water in the presence of a manganese-containing oxide catalyst.

B. Nowack and AT. Stone, "Homogeneous and Heterogeneous Oxidation of Nitrilotrismethylenephosphonic Acid (NTMP) in the Presence of Manganese (II, III) and Molecular Oxygen", J. Phys. Chem. B, 2002, 106, pp. 6227-6233 disclose the oxidation of nitrilotrismethylenephosphonic acid by reacting this acid with Mn(III)OOH.

JP 2001 354595 discloses the decomposition of halogenated compounds in soil, sludge, lake water or river water using a manganese dioxide, which manganese dioxide may be adsorbed onto a carrier.

Said manganese (Mn) compounds are quite expensive and if they are not returned to an oxidized state, they cannot be reused. Moreover, the Mn(II) compounds cannot remain in the water stream, as they themselves constitute a pollutant.

To convert Mn(II) compounds into the desired Mn(III) and/or Mn(IV) compounds, sometimes a chemical conversion is performed which results in the use of more chemicals (e.g. hydrogen peroxide), which is also undesirable both environmentally and economically.

US 3,337,452 for example discloses the removal of impurities in waste water by oxidative decomposition with manganese dioxide at an acidic pH and effecting reoxidation with simultaneous precipitation of the manganese oxide in the alkaline range using air or oxygen as the oxidant. This in the Examples results in the manganese compound being reused a maximum of 18 times. ACR 3130 R 3

In several further documents the oxidation of Mn(II) compounds with oxygen is disclosed. This oxidation of Mn(II) at a pH of 8.4 proceeds slowly over the years in the absence of catalysts (D. Diem and W. Stumm, "Is dissolved Mn(II) being oxidized by O₂ in absence of Mn-bacteria of surface catalysts?", Geochimica et Cosmochimica Acta, 48 (1984), pp. 1571 -1573). At pH 8 and pH 9, the half-lives of Mn(II) in the presence of oxygen were established to be approximately 700 and 7 days, respectively (B. Wehrli, "Redox Reactions of Metal Ions at Mineral Surfaces" in W. Stumm, Ed., Aquatic chemical kinetics reaction rate processes in natural water, New York: Wiley (1990), pp. 311-336).

JP 53013549 discloses the removal of chemical oxygen-demanding components from waste water by decomposition in the presence of a higher metal catalyst, for instance manganese, obtained by air oxidation of a lower metal compound in the alkaline state, followed by oxidizing of the COD component at a pH of between 2 and 10. The reduced (manganese) metal catalyst may be oxidized by aeration.

In US 2002/1000734 the reuse of a manganese compound through sintering is described. This sintering process is energy consuming especially because prior to sintering, the manganese(ll) compounds have to be isolated from the water stream.

J.J. Morgan, "Kinetics of reaction between O₂ and Mn(II) species in aqueous solutions" in Geochimica et Cosmochimica Acta, Vol. 69, No. 1 , pp. 35-48, 2005 discloses the oxidation of Mn(II) by bacterial oxidation under (slightly) alkaline conditions.

W. Driehaus et al, Oxidation of Arsenate(ll) with Manganese Oxides in Water Treatment", Wat. Res. Vol. 29, No. 1 , pp. 297-305, 1995 discloses that the seeding of bacteria is probably involved in the oxidation of manganese. The experiments on which these assumptions are based are performed in tap water that has a slightly alkaline pH. ACR 3130 R 4

K.H. Nealson et al. in Adv. Appl. Microbiol., Vol. 33 (1988), pp. 279-318, disclose the microbial oxidation of manganese(ll) compounds. This oxidation is explicitly mentioned to be performed under neutral conditions.

There is a need for a simple process to remove non-biodegradable compounds from an aqueous composition. Furthermore, there is a need for a process to remove non-biodegradable compounds from an aqueous composition which preferably requires a minimum amount of chemicals to be added and provides an increased recycling/reuse of the reactive compounds that are used in the removal, so that the process will be environmentally friendly and economically feasible.

Now a process to remove one or more non-biodegradable compounds from an aqueous composition is provided comprising the steps of

(i) reacting insoluble Mn(III) and/or Mn(IV) compounds with one or more non-biodegradable compounds at a pH in the range of 1 to 7.5 to yield a Mn(II) compound and one or more biodegradable fragments, and (ii) at least partially oxidizing the Mn(II) compound formed in step (i) to yield Mn(III) and/or Mn(IV) compound(s) at a pH in the range of 7 to 10 in the presence of microorganisms, wherein the microorganisms are present in the reaction mixture of step (i) and step (ii) of the process.

In a preferred embodiment the process comprises an additional step (iii) in which the biodegradable fragments obtained from oxidation of the nonbiodegradable compounds with insoluble Mn(II) and/or Mn(IV) compounds are at least partially further degraded in the presence of microorganisms.

Surprisingly, it was found that the microorganisms that enable oxidation of Mn(II) compounds to Mn(III) and/or Mn(IV) compound(s) and the ACR 3130 R 5

microorganisms that biodegrade the compounds obtained after oxidation of the non-biodegradable compounds (hereinafter denoted as biodegradable fragments) using Mn(III) and/or Mn(IV) compounds are able to withstand the extreme pH conditions of step (i) and step (ii), contrary to what documents disclosing the microbial oxidation of manganese(ll) compounds teach and/or suggest.

Accordingly, the microorganisms need not be separated from the reaction mixture but can remain in the aqueous composition during steps (i) and (ii) and optionally also during step (iii) of the process and in a preferred embodiment can be recycled to be reused.

A particular advantage of the process according to the invention is that the Mn(II) compounds also need not be separated from the aqueous composition in which they are formed after the insoluble Mn(III) and Mn(IV) compound(s) have reacted with the non-biodegradable compounds, but instead are returned to the +3 and/or +4 oxidized state in the reaction mixture. Since the Mn(III) and Mn(IV) compounds are insoluble, they can be separated from the treated aqueous composition together with the microorganisms (also denoted hereinafter as biomass) via conventional techniques employed therefor. Thus, these manganese compounds can be recycled together with the biomass to be reused. Reuse of 40 times of both the manganese compound and the microorganisms is easily achieved. In a preferred embodiment more than 50 times reuse can be achieved, even more preferably more than 60 times.

Although Applicant does not wish to be bound by any theory, it is envisaged that the reactions of the process according to the present invention are as follows: In step (i) the non-biodegradable compound is at least partially oxidized with Mn(III) and/or Mn(IV) compounds under appropriate pH conditions to yield fragments which are biodegradable. In step (ii) Mn(II) is oxidized in the presence of microorganisms. The microorganisms normally use oxygen from the air. A schematic representation of this process is depicted in Figure 1. ACR 3130 R 6

Step (iii), wherein the fragments obtained after oxidation of the nonbiodegradable compounds are at least partially further degraded in the presence of microorganisms, can take place before step (ii), simultaneously with step (ii), and/or after step (ii). However, preferably it takes place simultaneously with step (ii). In a particularly preferred embodiment of the present invention, after the non-biodegradable compounds have been oxidized, the obtained fragments are degraded to eventually yield H₂O, CO₂, and inorganic compounds.

Microorganisms suitable for step (ii) of the process of the present invention include bacteria, algae, and fungi. Microorganisms for step (ii) include Arthrobacter sp. as described by S. M. Bromfield and D.J. Davis in "Sorption and Oxidation of Manganous Ions and Reduction of Manganese Oxide by Cell Suspensions of a Manganese Oxidizing Bacterium", Soil Biol. Biochem. Vol. 8 (1976), pp. 37-43; manganese oxidizing bacteria as described by R. Schweisfurth in Landwirtsch. Forschung Vol. 31 (2-3) (1978), pp. 127-132; bacillus strains as described by K.H. Nealson and J. Ford in "Surface Enhancement of Bacterial Manganese Oxidation: Implications for Aquatic Environments", Geomicrobiol. J., 2 (1980), pp. 21-37, and pseudomonas and micro-algae cultures as described in A.C. Green and J. C. Madgwick in "Microbial Formation of Manganese Oxides", Appl. Environ. Microbiol. 57 (1991 ), pp. 1114-1120. These microorganisms use Mn(II) as energy source and/or serve as surface and/or enable indirect oxidation of Mn(II) by changing the environmental conditions. Preferably, microorganisms present in activated sludge or in biofilms or maintained in a reactor through filtration are used.

Though in some documents (see, e.g., S. M. Bromfield and D.J. Davis in "Sorption and Oxidation of Manganous Ions and Reduction of Manganese Oxide by Cell Suspensions of a Manganese Oxidizing Bacterium", So/7 Biol. Biochem. 8 (1976), pp. 37-43; R. Schweisfurth in Landwirtsch. Forschung 31 (2- 3) (1978), pp. 127-132; A.C. Green and J.C. Madgwick in "Microbial Formation of Manganese Oxides", Appl. Environ. Microbiol. 57 (1991 ), pp. 1114-1120), it ACR 3130 R 7

has been described that bacteria capable of oxidizing a manganese(ll) compound are also active at a pH between 5 and 7, we have found that in the process of our invention the activity of these bacteria at a pH of 5 to 7 is so low at any rate that the conversion of Mn(II) to Mn(III) and/or Mn(IV) is not detectable. Hence it is necessary for step (ii) of the process according to our invention to be conducted at a pH of 7 to 10.

Microorganisms suitable for step (ii) and optionally step (iii) of the process of the present invention include bacteria, algae, and fungi. Preferably, microorganisms present in activated sludge or in biofilms or maintained in a reactor through filtration are used. For an optimal process performance of the biological Mn(II) oxidation in step (ii) where the pH can be controlled and the amount of NH₄ ⁺ can be minimized through biological oxidation to nitrate, biomass and Mn(IV) and/or Mn(III) compounds are recycled.

In one embodiment of the process, steps (i) and (ii) are performed simultaneously at a pH in the range of between 7 and 7.5, preferably at a pH of approximately 7. Steps (i), (ii), and (iii) can be performed simultaneously at a pH in the range of between 7 and 7.5, preferably at a pH of approximately 7. It is noted that this embodiment of the present invention can be formed in any conventionally used biological treatment plant.

In a preferred embodiment of the process, steps (i), (ii), and optionally (iii) are performed continuously or the process is performed as a sequencing batch process. Especially for large volumes (being volumes of more than 100 m³/hour) a continuous process is preferred, while for smaller volumes (of less than 100 m³/hour, preferably less than 10 m³/hour) a sequencing batch process is preferred.

Non-biodegradable compounds are defined as compounds that do not pass the OECD 301 biodegradability test. Examples of preferred compounds which are not readily biodegradable that can be removed from aqueous compositions by ACR 3130 R 8

the process of this invention include chelating agents, such as ethylene diamine tetraacetic acid (EDTA), 1 ,3-propylene diamine tetraacetic acid (PDTA), and diethylene triamine pentaacetic acid (DTPA). Other preferred examples of substances oxidized by manganese(lll) and/or Mn(IV) compounds are phosphite, phosphonates such as nitrilotris(methylene)phosphonic acid (Nowack and Stone, "Degradation of Nitrilotris(methylenephosphonic Acid) and Related (Amino)Phosphonate Chelating Agents in the Presence of Manganese and Molecular Oxygen", Environ. ScL Technol. 34 (2000), pp. 4759-4765), arsenite (Scott and Morgan, "Reactions at Oxide Surfaces. 1. Oxidation of As(III) by Synthetic Bimessite", Environ. Sci. Technol., 29 (1995), pp.1898- 1905, and 17α-ethynylestradiol (EE2) (de Rudder et al., "Advanced water treatment with manganese oxide for the removal of 17α-ethynylestradiol (EE2)", Water Res. 38 (2004), pp. 184-192.

In another preferred embodiment the water-insoluble Mn(III) and/or Mn(IV) compounds comprise Mn(III) and/or Mn(IV) compounds that settle, Mn(III) and/or Mn(IV) compounds that attach to solid particles (carriers), or Mn(III) and/or Mn(IV) compounds that are kept in the system by membrane filtration. Suitable manganese(lll) compounds include manganite (γ-MnOOH), groutite (α- MnOOH), and feitknechtite (β-MnOOH). Suitable manganese(IV) compounds include pyrolusite (β-MnO₂) and vemadite (5-MnO₂).

In another preferred embodiment the insoluble manganese(lll) or manganese(IV) compounds comprise a sedimented Mn(III) or Mn(IV) compound, i.e. a Mn(III) or Mn(IV) compound adsorbed onto a carrier. Alternatively, the manganese compounds are kept in the system by membrane filtration. In this way the Mn(II) compounds, which in general are soluble in water, are not capable of leaving the process reactor and can be substantially retained in the process and recycled to their oxidized Mn(III) or Mn(IV) equivalent. In a preferred embodiment in step (ii) 90 wt% of the manganese(ll) compounds present are recycled to their oxidized Mn(III) or Mn(IV) state, more ACR 3130 R 9

preferably at least 95 wt%, even more preferably at least 98 wt%, most preferably at least 99 wt%.

To acquire a pH in the range of 1 to 7.5, preferably 1 to 7, in step (i) of the process, preferably a conventional acid is used. Such conventional acids are known to the person skilled in the art and include HCI, H₂SO₄, HBr, HNO₃, H2CO₃, and (concentrated) aqueous solutions thereof. Most preferably, HCI or H₂SO₄ is used. A pH of at least 3 is preferred. Most preferably, however, a pH of at least 4 is employed.

Further, it has been found that depending on the non-biodegradable compound to be removed from the aqueous composition, the optimum pH values are chosen at a different value. For example, for removing PDTA the pH preferably is about 5. For removing DTPA and EDTA the pH preferably is about 4.

To acquire a pH of 7 to 10, preferably 7 to 8.5, in step (ii) of the process, preferably conventional bases are added to the reaction mixture. Such conventional bases are known to the person skilled in the art and include hydroxide salts, such as hydroxide salts of (earth)alkali metals and precursors thereof and (concentrated) aqueous solutions thereof. Preferred bases are CaO and NaOH.

It has been found that the optimum pH of the aqueous composition is not only dependent on the properties of the non-biodegradable compound to be removed, but also on the properties of the microorganisms employed in step (ii) and, preferably, in step (iii). However, the skilled person will be able to select the optimum pH ranges using the indications given in this specification together with routine experimentation. ACR 3130 R 10

In a preferred embodiment of the process the temperature of the aqueous composition to be treated is between 4 and 37⁰C. In a more preferred embodiment, the initial temperature of the aqueous composition to be treated is maintained during the complete process according to the present invention to save heating or cooling of the waste water stream.

The aqueous composition may be any waste water stream from either a domestic or an industrial source or a mixture thereof. It is preferably a waste water stream from industry. Particularly preferred are waste streams from the pulp and paper industry, boiler cleaning and descaling processes, and the photographic industry. The aqueous composition may comprise more components besides the non-treatable compounds, such as biodegradable compounds, salts, and solids like sand, clay, and silica.

The present invention also relates to an apparatus suitable for the process for removing non-biodegradable compounds from an aqueous composition according to the present invention comprising (a) a first reactor for reacting insoluble Mn(III) and/or Mn(IV) compounds with one or more non-biodegradable compounds at a pH in the range of 1 to 7.5 to yield a Mn(II) compound and one or more biodegradable fragments, the first reactor being provided with an inlet for the aqueous composition and an outlet connected to (b) a second reactor to convert the Mn(II) compound to insoluble Mn(III) and/or Mn(IV) compounds in the presence of microorganisms and the biodegradable fragments of step (a) at a pH in the range of 7 to 10, the second reactor being provided with an outlet connected to (c) a separating device that separates the treated aqueous composition and the water-insoluble Mn(III) and/or Mn(IV) compounds and microorganisms (also denoted as biomass), the separating device being provided with two outlets, a first outlet for the output stream comprising the treated aqueous composition and a second outlet connected to the first reactor for recycling a stream comprising the insoluble Mn(III) and/or Mn(IV) compounds and the biomass. ACR 3130 R 11

The apparatus according to the invention includes but is not limited to specially adapted embodiments of conventional apparatuses such as an activated sludge treatment plant, a membrane bioreactor, a sequencing batch reactor, two packed beds in series, an activated sludge treatment plant in series, or a membrane reactor in series apparatus. Schematic flow diagrams of said specially adapted apparatuses are given in Figure 2. In the activated sludge treatment based and sequencing batch reactor based apparatuses, the Mn(III) and/or Mn(IV) compounds are kept in the system by a sedimentation unit, in the membrane reactor by a membrane filtration unit, and in the packed bed reactor they are adsorbed onto a carrier.

The present invention is illustrated by the following examples:

EXAMPLES

The COD, ammonia, nitrate, and total nitrogen were determined with test kits of Hach Lange (Dusseldorf, Germany).

The NPOC content was determined using a TOC-V_CPH+TNM-I analyzer (Shimadzu Corporation, Kyoto, Japan). Prior to analysis samples were passed through a cellulose nitrate membrane filter (8 μm pore diameter) to remove the bigger particles. Prior to injection into the TOC apparatus the samples were acidified with a 2 N HCL solution and purged with oxygen for 2 minutes.

Example 1 (Bio)-chemical chelate oxidation by Mn(IV) and/or Mn(III) compound(s) in a sequencing batch reactor (SBR) (Steps (i), (H), and (Hi))

In a SBR with a working volume of 1.5 L the (bio)-chemical oxidation of DTPA with Mn(III) and Mn(IV) compounds and the retention of manganese were tested. The SBR was filled 0.25 L of activated sludge (4 g/L DW) and 0.25 L of domestic waste water spiked with Mn(II) and DTPA. The activated sludge and the domestic waste water were collected from WWTP Nieuwgraaf in Duiven, ACR 3130 R 12

The Netherlands. WWTP Nieuwgraaf is an activated sludge plant treating predominantly domestic sewage.

The DTPA and Mn(II) concentrations in the waste water were 0.5 mM and 2 mM, respectively. The SBR was run with a 24-hour cycle. The pH was maintained at acidic or neutral immediately after filling. After this 6-hour period the pH was increased and maintained under slightly alkaline conditions for 17 hours to enable oxidation of Mn(II). After the alkaline period the sludge and the Mn(IV) and Mn(III) compounds were settled and 250 ml of the supernatant were withdrawn. The supernatant was analyzed for total nitrogen, COD, NPOC, and DTPA. Prior to analysis samples were filtrated over a 0.45 μm cellulose nitrate filter. For analysis of DTPA 0.5 ml of a 5.0 mM hydroxylamine hydrochloride solution was added to 1.5 ml_ of the filtered samples. Domestic waste water spiked with DTPA and Mn(II) was added daily. The SBR reactor was run with an infinite sludge retention time (SRT). The temperature in the SBR reactor was set at 2O⁰C.

During the first 17 days a cycle of 6 hours at pH 7, 17 hours at pH 8.5, and 1 hour to settle, fill, and draw was maintained. During this period no DTPA and almost no NPOC was removed. After day 17 the pH during the 6-hour period was decreased from pH 7 to pH 6. From day 17 the DTPA removal increased and reached an average of 95% DTPA removal. This result is in line with the result found in the CAS test run at pH 6. A second SBR reactor was run with a 6-hour period at pH 4, a 17-hour period at pH 8.5, and an hour to settle, fill, and draw. From the start a high DTPA removal was achieved, while the NPOC removal increases over time and levels of approximately 80% achieved indicate that DTPA was removed completely. The increase in NPOC removal is attributed to the acclimatization of microorganisms to the oxidation products of DTPA. At the end of this experiment (days 60 to 70) less than 10% of the manganese added was detected in the effluent of the reactor, indicating an almost complete recovery of the manganese used to oxidize DTPA. Also, this example shows that the activated sludge (microorganisms) survives 70 pH variations of pH 4 to pH 8.5, as demonstrated by the increasing removal ACR 3130 R 13

(biological oxidation) of organic carbon (NPOC) in the domestic waste water, and that the manganese compound can be oxidized and reused 70 times.

Example 2 Chemical oxidation of EDTA, PDTA, and DTPA (step (i))

The chelates ethylene diamine tetraacetic acid (EDTA), 1 ,3-propylene diamine tetraacetic acid (PDTA), and diethylene triamine pentaacetic acid (DTPA) (Dissolvine^®) were obtained from Akzo Nobel, BU Functional Chemicals, Amersfoort, The Netherlands. Mn(III) and Mn (IV) compounds were synthesized by increasing the pH of a Mn(II) solution in the absence of microorganisms. Two liters of a 20 g/L MnCb solution were stirred and aerated with pressured air during 24 hours. The pH of this solution was kept at 10 with 5 M NaOH using a Consort R301 pH controller (SaIm en Kipp BV, Breukelen, The Netherlands). After 24 hours the resulting suspension was concentrated and repeatedly washed with water using settling to remove excess salts until a stable pH was obtained. The average oxidation state of manganese was not determined. The pH was then set to 7 by adding 2N HCI. The manganese oxide concentration was determined by measuring the dry weight. The manganese oxide suspension (5 ml_) was dried for 24 h at 104⁰C and weighed.

Chemical oxidation of the above-mentioned chelates with Mn(III) and (Mn(IV) compounds was investigated in batch experiments performed in 300 ml_ Erlenmeyers. 75 ml_ of an aqueous solution containing 0.25 mM of the chelate and 2.5 mM of Mn(IV) and Mn(III) were mixed with 50 ml_ of a 0.2 M buffer. Glycine hydrochloride (pH 3), sodium acetate acetic acid (pH 4 and 5), triethanolamine hydrochloride sodium hydroxide (pH 7) buffers were used. The mixtures were shaken at 125 rpm in the dark at 25⁰C. At different time intervals samples were taken for analysis of the chelate concentration. To stop oxidation 0.5 ml_ of a 5.0 mM hydroxylamine hydrochloride (a strong reducing agent) solution was added to 1 ,5 ml_ of filtered sample (0.45 μm cellulose nitrate filter). ACR 3130 R 14

The chelates were analyzed by high performance liquid chromatography (HPLC). The HPLC system consisted of a pump (high precision model 300, Separations, Hendrik ldo Ambacht, The Netherlands) an auto-sampler (spark model basic marathon, Separations, Hendrik ldo Ambacht, The Netherlands), an lonpac AS7 column and a AG7guard-column (Dionex, Bavel, The Netherlands), and a UV/VIS detector (ABI 759A, Separations, Hendrik ldo Ambacht, The Netherlands). The concentration of the chelates was measured at a wavelength of 330 nm. The mobile phase was 50 mM nitrate in de- mineralized water containing 50 mM sodium acetate, pH = 2.7 ± 0.2. The flow rate was 0.5 mL/min. Samples were prepared by mixing 4 mL of sample with 1 mL of an iron nitrate solution (12 mM Fe(NU₃)₃ solution) containing 150 mM nitric acid). After 15 minutes of complexation the samples were filtered over a 0.45 μm filter. 50μL samples were injected into the HPLC system.

It was found that EDTA is oxidized by Mn(III) and/or Mn(IV) within a few hours at pH 3. The time required at pH 5 is a few days.

After the oxidation steps, the samples were contacted with 20 ml of activated sludge (2 to 3 g/L DW). Activated sludge was collected from the Nieuwgraaf waste water treatment plant (WWTP) in Duiven, The Netherlands. The pH was increased by the addition of NaOH and maintained at pH 9 for 48 hours to enable conversion of the formed Mn(II) into Mn(III) and Mn(IV) compounds. Analysis using Hach/Lange test kits (Hach Lange, Dusseldorf, Germany) showed that >99.9% of the formed Mn(II) had been converted into Mn(III) and Mn(IV).

It was furthermore found that PDTA is oxidized within 1 hour at pH 3, while at pH 4 or 5, it takes up to 6 hours. Oxidation of DTPA by Mn(III) and/or Mn(IV) takes a few days at pH 7. ACR 3130 R 15

Example 3

Chemical oxidation of different DTPA metal complexes by Mn(IV) species (Step

⁽0⁾

Batch experiments with different DTPA metal complexes were carried out to determine the effect of different counterions on the chemical oxidation of DTPA with Mn(III) and/or Mn (IV) compound(s). Materials and methods are described in Example 1. The experiments were performed at pH 5. The metal chelates were made by mixing the metal chloride salt with DTPA-H5 in a 1 :1 molar ratio. The DTPA concentrations were measured over time in the same manner as described for Example 1 and from the DTPA decrease the 50% degradation time was determined (Table I).

Table I. Stability constants and times required to achieve 50% degradation of various DTPA-metal complexes.

For all counterions fast to extremely fast oxidation of DTPA was observed.

Example 4

(Bio)-chemical chelate oxidation by Mn(IV) and/or Mn(III) compound(s) in a Contiuously-fed Activated Sludge (CAS) reactor (Steps (i), (Hi)) The (bio)-chemical removal of the chelating agents EDTA, DTPA, and PDTA using Mn(III) and/or Mn (IV) compounds was studied in glass-constructed units. A schematic representation of a CAS-reactor for laboratory scale tests is given ACR 3130 R 16

in Figure 3. The unit consists of a storage vessel (A), a dosing pump (B), an aeration section (C), a settling section (D), a collecting vessel (E), and an air supply (F). The units employed consisted of an aeration vessel (c) with a capacity of 0.40 L, from which the solution was passed continuously to a settler with a capacity of 0.37 L. The flow of the medium through the reactor was maintained by using a peristaltic pump. The treated effluent was collected in a container. Activated sludge and domestic waste water (DW) were collected from the Nieuwgraaf waste water treatment plant (WWTP) in Duiven, The Netherlands. CAS reactors were started with activated sludge (2 to 3 g/L Dry Weight). Domestic waste water spiked with one of the above-mentioned chelating agents at a concentration of 200 mg/L was used as the aqueous composition to be treated. Mn(III) and Mn (IV) compounds were added to the CAS reactor on a daily basis, resulting in a chelate : combined Mn(III) and Mn (IV) compounds molar ratio of approximately 1 : 20.

The CAS reactors were operated at a hydraulic retention time (HRT) of 48 hours and an infinite sludge retention time (SRT). The temperature in the CAS reactor was 2O⁰C. The pH was maintained with a Consort pH controller (SaIm en Kipp BV, Breukelen, The Netherlands) and with a 0.5 N H₂SO₄ solution. Aeration was achieved with an approximate air flow of 10 L/h through a capillary leading to the bottom of the aeration vessel. Sludge accumulating around the top of the aeration vessel was brushed back into the system once a day. Samples for analysis of remaining chelating agent, ammonia, nitrate, total nitrogen, chemical oxygen demand (COD), and non-purgeable organic carbon (NPOC) were taken directly from the aeration vessel. These samples were filtered over a 0.45 μm cellulose nitrate filter. For analysis of the chelating agent 0.5 ml_ of a 5.0 mM hydroxylamine hydrochloride solution was added to 1.5 ml_ of sample.

At pH 4 in the CAS reactor 92% of EDTA (200 mg/L) present in the aqueous composition was removed. The NPOC removal was 95%, demonstrating biodegradation of the EDTA oxidation products (see Table II). ACR 3130 R 17

A DTPA removal percentage of 89 was achieved in CAS reactors fed with domestic waste water spiked with 200 mg/l DTPA at pH 4 (see Table II). The high NPOC and COD removal percentages demonstrate almost complete degradation of DTPA. A removal of 82% of PDTA was achieved in a CAS reactor maintained at pH 5. At this pH, 70% NPOC was removed (see Table II).

In another CAS reactor without biomass a comparable PDTA removal was achieved. However, the NPOC removal was only 24%. No nitrate and only minor amounts of ammonia were measured in a CAS reactor operated without biomass. In contrast, nitrate was measured in CAS reactors inoculated with activated sludge. These results demonstrate that the oxidation products of PDTA are biodegraded in the CAS unit.

Table Il Removal percentages of DTPA, EDTA, PDTA organic N, NPOC, and COD in CAS units.

n.d. not determined

Example 5 Manganese retention in CAS reactor (step H)

The manganese retention by means of settling Mn(III) and Mn (IV) compounds was studied in CAS units. These CAS units were fed with domestic waste water containing 4 g/L of activated sludge (see Example 4), EDTA, and Mn(II). The pH was controlled with a Consort pH controller (SaIm en Kipp BV, Breukelen, The Netherlands) and NaOH. Other process parameters of the CAS unit were ACR 3130 R 18 identical to those of the CAS unit treating the EDTA. For analysis of the Mn(II) filtered and unfiltered samples of the effluent were used. To 1 ml_ of unfiltered sample 9 ml_ of a 5 mM hydroxylamine hydrochloride solution were added, this to convert Mn(III) and Mn (IV) compounds present in the effluent into Mn(II). The manganese removal was calculated with the Mn(II) concentrations measured in the influent and the effluent. The manganese content was determined with Hach/Lange test kits (Hach Lange, Dusseldorf, Germany).

The manganese retention in a CAS by means of settling Mn(III) and Mn (IV) compounds, was studied at a pH of 9. Mn(II) is oxidized at this pH to Mn(IV) and Mn(III) compounds. The Mn(III) and Mn(IV) compounds were then retained in the settling part of the CAS. By settling of Mn(IV) and Mn(III) compounds a 99% retention of the manganese present in the reactor was achieved (Table III).

Table III Manganese retention in a CAS reactor fed with domestic waste water spiked with Mn(II) and run at different pH values with a HRT of 48 hours.

These manganese retention values demonstrate that more than 40 times reuse of the manganese compound is indeed achievable

Claims

ACR 3130 R 19CLAIMS

1. A process to remove a non-biodegradable compound from an aqueous composition comprising the following steps (i) reacting insoluble Mn(III) and/or Mn(IV) compounds with one or more non-biodegradable compounds at a pH in the range of 1 to 7.5 to yield a Mn(II) compound and one or more biodegradable fragments, and

(ii) oxidizing the Mn(II) compound to (a) Mn(III) and/or Mn(IV) compound(s) in the presence of microorganisms at a pH in the range of 7 to 10, wherein the microorganisms are present in the reaction mixture of step (i) and step (ii) of the process.

2. A process according to claim 1 wherein steps (i) and (ii) are performed continuously or as a sequencing batch process.

3. A process according to claim 1 and 2 further comprising a step (iii) wherein the biodegradable fragments obtained after oxidation of the non- biodegradable compounds with insoluble Mn(III) and/or Mn(IV) compounds are at least partially further degraded in the presence of microorganisms, step (iii) taking place before step (ii), simultaneously with step (ii), and/or after step (ii).

4. A process according to any one of the preceding claims wherein the aqueous composition is waste water, preferably from an industrial process.

5. A process according to any one of the preceding claims wherein the Mn(III) and/or Mn(IV) compounds are selected from the group consisting of manganite (γ-MnOOH), groutite (α-MnOOH), feitknechtite (β-MnOOH), pyrolusite (β-Mnθ2), and vemadite (δ-Mnθ2). ACR 3130 R 20

6. A process according to any one of the preceding claims wherein the insoluble Mn(III) or Mn(IV) compound comprises a sedimented Mn(III) or (Mn(IV) compound, a Mn(III) or Mn(IV) compound adsorbed onto a carrier, or a Mn(III) or Mn(IV) compound kept in the system by membrane filtration.

7. A process according to any one of the preceding claims wherein the nonbiodegradable compound is selected from the group consisting of EDTA (ethylene diamine tetraacetic acid), PDTA (propylene diamine tetraacetic acid), DTPA (diethylene triamino-pentacetic acid), phosphite, phosphonates such as nitrilotris(methylene)phosphonic acid and related (amino)- phosphonate chelating agents, arsenite, 17α-ethynylestradiol (EE2), and a mixture thereof.

8. A process according to any one of the preceding claims wherein step (i) is performed at a pH in the range of between 3 and 7, step (ii) is performed at a pH in the range of between 7 and 8.5.

9. An apparatus suitable for performing the process according to any one of the preceding claims, comprising (a) a first reactor for reacting insoluble

Mn(III) and/or Mn(IV) compound(s) with one or more non-biodegradable compounds to a Mn(II) compound and one or more biodegradable fragments, at a pH in the range of 1 to 7.5, preferably 3 to 7, the first reactor being provided with an inlet for the aqueous composition and an outlet connected to (b) a second reactor for (bio)chemically oxidizing the Mn(II) compound to insoluble Mn(III) and/or Mn(IV) compound(s) and optionally degrading the remainder(s) of the biodegradable fragment(s), at a pH in the range of 7 to 10, preferably 7 to 8.5, the second reactor being provided with an outlet connected to (c) a separating device that separates the insoluble Mn(III) or Mn(IV) and biomass from the aqueous composition, the separating device being provided with two outlets, a first outlet for the output stream comprising the treated aqueous composition and a second outlet connected ACR 3130 R 21 to the first reactor for recycling a stream comprising the insoluble Mn(III) and/or Mn(IV) compounds and biomass.