The present invention relates to a process for reducing or preventing bulking sludge and/or foaming in activated sludge plants for wastewater treatment. The invention furthermore relates to a composition and to the use of said composition in wastewater treatment.

Sewage and industrial wastewaters can be treated in activated sludge plants. The process is usually as follows. Atmospheric air or pure oxygen is bubbled through primary treated sewage or industrial wastewater combined with microorganisms to develop a biological floe (the so-called Activated Sludge) which reduces the organic carbon, nitrogen, and phosphorus content of the wastewater. The combination of raw sewage or industrial wastewater and biological mass is commonly known as Mixed Liquor Suspended Solids (MLSS). In all activated sludge plants, once the sewage or industrial wastewater has received sufficient treatment, the treated MLSS is passed into settling tanks (clarifiers) and the clarified effluent is run off and optionally undergoes further treatment. Part of the settled Suspended Solids is returned to the aeration system to re-seed the new sewage or industrial wastewater entering the tank. This fraction is called Return Activated Sludge (R.A.S.). Excess sludge which eventually accumulates beyond what is returned is called Waste Activated Sludge (W.A.S.). W.A.S. is removed from the treatment process to keep the ratio of biomass to food supplied (sewage or wastewater) or the sludge retention time in balance.

Despite decades of progress and operation, serious operating problems still occur with the activated sludge process. One major problem is the regular occurrence of excessive growth of filamentous bacteria, a phenomenon known as "filamentous bulking sludge" or simply "bulking sludge". Filamentous organisms extend from the floes into the bulk solution, resulting in poor settability of the activated sludge, which may lead to activated sludge being carried over in the effluent from the clarifier. P. Madoni et al. describes in Wat. Res. Vol. 34, No. 6 (2000), pages 1767-1772, that bacterial identification revealed that Microthrix parvicella was the most common filamentous microorganism involved in bulking.

S. Rossetti et al. summarize in FEMS Microbiology Reviews 29 (2005), pages 49-64, the microbiology and physiology of Microthrix parvicella and the methods of its growth control in activated sludge wastewater treatment plants. It describes that this filamentous bacterium is of high interest because of its worldwide involvement in severe bulking at wastewater treatment plants. It describes that addition of polyaluminium chloride is an effective method of controlling M. parvicella in wastewater treatment plants.

P. H. Nielsen et al. in Acta hydrochim. Hydrobiol. 33 (2005), 3, pages 255-261 , teaches that the filamentous bacterium Microthrix parvicella is causing problems worldwide with foaming and bulking in activated sludge wastewater treatment plants. It discloses that polyaluminium chloride (PAX-14) can control the growth of M. parvicella in activated sludge systems to a large extent.

M. parvicella, however, is not the only filamentous bacterium causing the described bulking problems. Proliferation of other filamentous bacteria also provokes bulking in activated sludge wastewater treatment plants. Recent studies have revealed that for instance the filamentous bacterium Eikelboom Type 0092 and other members of the phylum Chloroflexi have been associated with bulking incidences as well (see C. Kragelund et al. in FEMS Microbiol. Ecol. 59 (2007) pages 671 -682 and L. Speirs et al. in Appl. Environ. Microbiol. Apr. 2009, pages 2446-2452).

As already known from P. H. Nielsen et al. in Acta hydrochim. Hydrobiol. 33 (2005), 3, pages 255-261 , and S. Rossetti et al. in FEMS Microbiology Reviews 29 (2005), pages 49-64, any polyaluminium chloride added to control growth of M. parvicella leaves other filamentous bacteria more or less unaffected. As a result, in many activated sludge plants, bulking sludge is not effectively reduced or prevented by addition of polyaluminium chloride. Accordingly, it is an object of the present invention to provide an efficient method for reducing or preventing bulking sludge in activated sludge wastewater treatment plants by controlling not only the growth of M. parvicella, but the growth of other filamentous bacteria such as filamentous Chloroflexi, Nocardia spp., Type 021 N or Thiothrix spp. species as well.

The objective is realized with the process of the present invention wherein an aluminium salt and at least one fatty amine or fatty amine derivative are used. More particularly, the present invention relates to a process for reducing or preventing bulking sludge and/or foaming in an activated sludge plant for wastewater treatment, wherein an aluminium salt and at least one fatty amine or fatty amine derivative are used. Generally, in the process according to the present invention, a wastewater to be treated is contacted with micro-organisms. The term wastewater in this respect is meant to denote any aqueous stream that carries wastes from households, businesses, and industries and that is not suitable for reuse or is not allowed to be discharged unless treated by a wastewater facility. Air or oxygen is bubbled through so that a biological floe is formed, the activated sludge. This can be done in a tank, often denoted as aeration tank. As mentioned before, a mixture of wastewater and activated sludge is generally denoted as MLSS. Subsequently, the MLSS is passed into one or more clarifiers. Part of the settled activated sludge, i.e. the R.A.S. , is reused by contacting it with wastewater still to be treated. The aluminium salt and the at least one fatty amine or fatty amine derivative according to the invention are preferably added to the return activated sludge, to mixed liquor suspended solids in the aeration tank, to wastewater to be treated (so prior to the contacting step with microorganisms), to a settling tank or any combination thereof. For the sake of clarity, it is noted that the aluminium salt and the at least one fatty amine or amine derivative are not added to waste activated sludge (i.e. excess sludge which eventually accumulates beyond what is returned and which is removed from the treatment process to keep the ratio of biomass to food supplied (sewage or wastewater) or the sludge retention time in balance).

The fact that the process according to the present invention wherein an aluminium salt is used in combination with a fatty amine or fatty amine derivative leads to improved settability of the activated sludge, results in a few additional advantages. For example, the activated sludge plant will have an improved performance due to an increased sludge retention time. In more detail, in activated sludge plants, wastewater that has been treated in an aeration tank is separated from the suspended solids (i.e. activated sludge) by the process of gravity sedimentation in clarifiers. Activated sludge floes settle toward the bottom of the clarifier in a quiescent environment. This separation leads ideally to the formation of an effluent (wastewater having low levels of suspended solids) in the upper portion of the clarifier and a thickened sludge in the bottom portion of the clarifier. Part of the thickened sludge is returned to the aeration tank (R.A.S.). The higher the part returned to the aeration tank, the higher the so-called Sludge Retention Time (SRT) in the plant. Obviously, good settability of the activated sludge will allow operation at increased SRT. Hence, because the use of the combination of an aluminium salt and at least one fatty amine or fatty amine derivative in an activated sludge plant will have the effect of improved settability of the activated sludge, the performance of activated sludge plants can be improved. Furthermore, foaming is reduced.

One of the major drawbacks of activated sludge treatment in general is excess sludge production. It is well known that increasing the SRT or reducing the sludge loading rate will lead to a reduction of excess sludge production. This inverse relationship arises from the concept of maintenance energy, where most of the incoming energy, i.e. the reduced (in)organic compounds, is used for cell maintenance such as maintaining the internal osmotic condition, pH, mobility, etc. Increased cell lyses and cryptic growth may also contribute to low sludge yield at high SRT. By increasing the suspended solids concentration in the activated sludge treatment system it would theoretically be possible to reach a situation in which the amount of energy provided in the form of (in)organic substances equals the maintenance energy. In consequence, maintenance of high suspended solid concentrations in the bioreactor, thereby increasing the SRT, reduces the excess activated sludge production. Limitation of the increase in suspended solids concentrations in activated sludge plants primarily stems from the settability of the activated sludge. As described above, the settability of the activated sludge is improved by the addition of a combination of an aluminium salt and at least one fatty amine or fatty amine derivative, allowing maintenance of higher suspended solids concentrations in activated sludge treatment systems and thus generating less excess sludge production.

Excess sludge of biological treatment plants is usually dewatered by filtration or centrifugation to suspended solids contents in excess of fifty percent by weight. The costs of this process are also determined by the dewaterability of the sludge. The dewaterability of sludge is reduced when settling of the sludge mass becomes difficult. Poor dewaterability in centrifuges and belt presses is therefore often associated with the settability of activated sludge. Improving the settability of activated sludge through the addition of aluminium salt with fatty amine therefore also improves handling of the excess sludge (reduces the cost of dewatering sludge).

The aluminium salt to be used in the process according to the present invention is preferably selected from the group consisting of aluminium chloride, aluminium sulphate, sodium aluminate, potassium aluminate, polyaluminium chloride and mixtures thereof.

The term fatty amine as used throughout the description is meant to denote a primary amine, a secondary amine, or a tertiary amine with at least one fatty alkyl chain, with a fatty alkyl chain being a saturated or unsaturated carbon chain containing 8 to 24 carbon atoms, preferably containing 10 to 22 carbon atoms, and most preferably containing 12 to 20 carbon atoms. The fatty amine may comprise more than one amine moiety. Other substituents attached to the amine nitrogen can for example be an alkyl group such as methyl or ethyl. In case the substituents attached to the amine nitrogen comprising at least one fatty alkyl chain as defined above are hydrogen and/or alkyl groups, the compound is a fatty amine according to the present invention. It is also possible that other substituents than an alkyl group are attached to the amine group nitrogen (in addition to at least one fatty alkyl chain as defined above). In that case, the compound is denoted throughout the description as a fatty amine derivative. Said other substituent is selected from the group consisting of substituents comprising an aromatic group, such as a benzyl group; hydroxylated alkyl groups, such as a hydroxyethyl group; polyoxyethylene groups; aminoalkyl groups; and carboxylated alkyl groups such as a carboxymethyl group. A salt of a fatty amine is also denoted throughout the description as a fatty amine derivative. It is noted that neither the term fatty amine nor the term fatty amine derivative includes a quaternary ammonium compound (also generally known as quats, i.e. positively charged polyatomic ions of the structure NR ₄ ⁺ , R being e.g. an alkyl group or an aryl group).

Preferred is the use of a fatty amine or a fatty amine derivative comprising one or more aminoalkyl groups. Suitable fatty amines and fatty amine derivatives comprising one or more aminoalkyl groups that can be used in the process according to the present invention are (fatty alkyl)monoamines according to the formula R1 NH ₂ , wherein R1 is an aliphatic group having 8-24, preferably 10-22 carbon atoms; (fatty alkyl) diamines according to the formula R2NHCH ₂ CH ₂ CH ₂ NH ₂ , wherein R2 is an aliphatic group having 8-24, preferably 10-22 carbon atoms; and linear (fatty alkyl)triamines according to the formula R3NHCH ₂ CH ₂ CH ₂ NHCH ₂ CH ₂ CH ₂ NH ₂ , wherein R3 is an aliphatic group having 6-24, preferably 8-22 carbon atoms.

Suitable fatty amines are primary, secondary or tertiary fatty amines such as n- decyl amine, n-dodecyl amine, (coco alkyl)amine, n-tetradecyl amine, n- hexadecyl amine, n-octadecyl amine, oleyl amine, (tallow alkyl)amine, (rapeseed alkyl)amine, (soya alkyl)amine, erucyl amine, (coco alkyl)amine, N-(n-decyl)-trimethylene diamine, N-(n-dodecyl)-trimethylene diamine, N-(coco alkyl)-trimethylene diamine, N-(oleyl alkyl)-trimethylene diamine, N-(rapeseed alkyl)-trimethylene diamine, N-(soya alkyl)-trimethylene diamine, N-(tallow alkyl)-trimethylene diamine, N-erucyl trimethylene diamine, N-(n-decyl)-N ^' -(3- aminopropyl)-1 ,3-propane diamine, N-(n-dodecyl)-N ^' -(3-aminopropyl)-1 ,3- propane diamine, oleyl-1 ,3-diaminopropane, N-(coco alkyl)-N ^' -(3-aminopropyl)- 1 ,3-propane diamine, N-(rapeseed alkyl)-N ^' -(3-aminopropyl)-1 ,3-propane diamine, N-(soya alkyl)-N ^' -(3-aminopropyl)-1 ,3-propane diamine, N-oleyl-N ^' -(3- aminopropyl)-1 ,3-propane diamine, N-(tallow alkyl)-N ^' -(3-aminopropyl)-1 ,3- propane diamine, N-erucyl-N ^' -(3-aminopropyl)-1 ,3-propane diamine, N-(3- aminopropyl)-N ^' -[3-(9-decylamino)propyl]-1 ,3-propane diamine, N-(3-amino- propyl)-N ^' -[3-(9-dodecylamino)propyl]-1 ,3-propane diamine, N-(3-aminopropyl)- N ^' -[3-(9-(coco alkyl)amino)propyl]-1 ,3-propane diamine, N-(3-aminopropyl)-N ^' - [3-(9-(rapeseed alkyl)amino)propyl]-1 ,3-propane diamine, N-(3-aminopropyl)-N ^' - [3-(9-(soya alkyl)amino)propyl]-1 ,3-propane diamine, N-(3-aminopropyl)-N ^' -[3- (9-octadecenylamino)propyl]-1 ,3-propane diamine, N-(3-aminopropyl)-N ^' -[3-(9- (tallow alkyl)amino)propyl]-1 ,3-propane diamine, and N-(3-aminopropyl)-N ^' -[3- (9-erucylamino)propyl]-1 ,3-propane diamine.

Secondary dialkyl amines such as di-n-decylamine and bis(n-decyl)amine can also be used. An example of a secondary methylalkylamine is (coco alkyl)methylamine.

An example of a tertiary trialkylamine is tri(coco alkyl)amine. An example of a tertiary dialkylmethylamine is di(coco alkyl)methylamine. An example of a tertiary alkyldimethylamine is (coco alkyl)dimethylamine.

Examples of suitable fatty amine derivatives are the above-mentioned secondary or tertiary fatty amines or diamines of which at least one alkyl substituent has been replaced by a substituent selected from the group consisting of substituents comprising an aromatic group, such as a benzyl group; hydroxylated alkyl groups, such as a hydroxyethyl group; polyoxyethylene groups; aminoalkyl groups; and carboxylated alkyl groups such as a carboxym ethyl group. A preferred example of a tertiary fatty amine derivative is tallowbis(2-hydroxyethyl)amine.

As described before, the aluminium salt and the one or more fatty amines or fatty amine derivatives are preferably added to the return activated sludge before it is contacted with a new influent, to mixed liquor suspended solids in the aeration tank, to wastewater to be treated (so prior to the contacting step with micro-organisms), to a settling tank or any combination thereof. Addition to the return sludge is preferred, because then the aluminium salt and the one or more fatty amines or fatty amine derivatives are brought into contact with the activated sludge (suspended solids) in the highest concentration possible. The least preferred option is addition to the settling tank, since in that case a high percentage of the aluminium salt and fatty amine(s) or fatty amine derivative(s) will be lost.

The amount of aluminium which is used is typically calculated on the basis of the phosphate concentration to be chemically removed by precipitation. Preferably, the amount of aluminium salt used is such that the aluminium to phosphate molar ratio is between 0.1 to 20, more preferably 0.3 to 10, and most preferably 0.5 to 3. The total amount of fatty amine(s) and/or fatty amine derivative(s) is preferably such that the weight ratio of fatty amine(s) and/or fatty amine derivative(s) to the aluminium salt (i.e. the weight amount of fatty amine (derivative) divided by the weight amount of aluminium salt) is in the range of 1 to 200, more preferably in the range of 2 to 100.

The aluminium salt and the one or more fatty amines, fatty amine derivatives or a combination thereof according to the present invention may be dosed at one or more of the above-mentioned stages of the process in any conventional manner. The aluminium salt may be added pure (but only if it becomes bio- available by dissolving in the wastewater treatment plant) or in an aqueous solution. It may be added in a continuous manner or intermittently. The fatty amine(s) and/or fatty amine derivative(s) can be added in a pure form, as an emulsion, as a suspension or as solution in an organic solvent. Said organic solvent can obviously consist of a mixture of organic solvents. If the fatty amine(s) or fatty amine derivative(s) are water-soluble, they can also be added in an aqueous solution. It is also possible to add the fatty amine(s) or fatty amine derivative(s) in the form of an aqueous micellar system, by addition of non-ionic, cationic, amfoteric, or, although this is less preferred, anionic surfactants. The fatty amine(s) or fatty amine derivative(s) can be added in a continuous manner or intermittently, either together with the aluminium salt or separately. It is noted that it is possible to add the aluminium salt at a different stage of the process than the fatty amine(s) or fatty amine derivatives(s). However, it is preferred to add them at the same stage of the process, preferably even as closely together as possible, and most preferably the fatty amine(s) or fatty amine (derivatives) are dosed together with the aluminium salt. In a particularly preferred embodiment, the aluminium salt and the one or more fatty amines or fatty amine derivatives are pre-mixed to form a bulking sludge reducing composition before being dosed to the wastewater. Most preferably, the aluminium salt and the one or more fatty amines or fatty amine (derivatives) are added in the form of a macroscopically homogeneous mixture.

An additional object of the present invention is to provide a composition comprising an aluminium salt and one or more fatty amines or fatty amine derivatives which is readily usable in activated sludge wastewater treatment plants for reducing bulking sludge.

The objective has been met by providing compositions comprising an aluminium salt selected from the group consisting of aluminium chloride, aluminium sulphate, sodium aluminate, potassium aluminate, polyaluminium chloride, and mixtures thereof, and at least one fatty amine or fatty amine derivative. Preferably, the composition comprises

- between 3 and 9 wt% of aluminium, and more preferably between 4 and 8 wt% of aluminium, based on the total weight of the composition; - between 0.1 and 10 wt% of one or more fatty amines, one or more fatty amine derivatives, or a combination thereof, and more preferably between 0.5 and 5 wt% of one or more fatty amines, one or more fatty amine derivatives, or a combination thereof, based on the total weight of the composition;

- between 30 and 80 wt% of water, and more preferably between 35 and 75 wt% of water, based on the total weight of the composition;

- between 0.01 and 15 wt% of one or more organic solvents, and more preferably between 0.1 and 7 wt% of one or more organic solvents, based on the total weight of the composition; and

- between 0 and 10 wt% of one or more additives, and more preferably at most 5 wt% of one or more additives, based on the total weight of the composition. It is noted that with the wording "between 3 and 9 wt% of aluminium" is meant that the amount of aluminium salt used is such that this corresponds to the addition of between 3 and 9 wt% of aluminium. In case of AICI3, for example, this will mean that between 20 and 45 wt% of the AICI3 salt is used. From an economic point of view, preferably the lowest possible quantity of organic solvent and additives is used to meet the objective, i.e. to make a composition wherein the fatty amine(s) or fatty amine derivative(s) have been made compatible with the aluminium salt which is dissolved in water. Examples of suitable fatty amines or fatty amine derivatives are mentioned above. The use of a fatty amine according to the present invention is most preferred.

The organic solvent is generally a solvent in which the aluminium salt and the fatty amine(s) and/or fatty amine derivative(s) will dissolve or in which these components are readily dispersible. Preferably, said organic solvent has a δ(ρ) of at least 8, a 6(d) of at most 19, and a 6(h) of between 6 and 26. δ(ρ), 6(d), and 6(h) are also known as Hansen solubility parameters. More information can be found in Allan Barton, CRC Handbook of Solubility Parameters and Other Cohesion Parameters, 2 ^nd Edition, A.F.M. Barton, 1991 , Chapters 5.9 - 5.1 1 . Preferably, the organic solvent of the invention is either a single organic compound or a mixture of organic compounds. The organic compound is a liquid which comprises at least one -XR group with X being 0 or S, at least one -NR ₂ group, or any combination thereof, with R being hydrogen or a substituent comprising from 1 to 20 carbon atoms. The R-group may contain one or more heteroatoms like 0, N, or S. More preferably, the organic compound is selected from the group consisting of alcohols, esters, ethers, carboxylic acids, thioethers, ketones, and aldehydes. For economic feasibility, most preferably the organic compound is mainly composed of an alcohol. Suitable examples of alcohols include methanol, ethanol, (iso-)propanol, (iso-)butanol, glycol, propylene glycol, butylene glycol, and glycerol.

Additives that can be used in the compositions according to the present invention are compounds having the following Hansen solubility parameters: a δ(ρ) of at least 8, a 6(d) of at most 19, and a 6(h) of between 6 and 26.

Preferably, for sake of costs, the additive is an alcohol.

It is noted that the composition according to the present invention preferably does not comprise intercalated polymers and/or polymeric coagulants. When the composition according to the present invention is concentrated, i.e. it is a composition comprising an aluminium salt selected from the group consisting of aluminium chloride, aluminium sulphate sodium aluminate, potassium aluminate, polyaluminium chloride, and mixtures thereof, and at least one fatty amine or fatty amine derivative, which is concentrated in fatty amine (derivative), the composition is denoted as a pre-mix. An advantage of such a pre-mix is that it gives flexibility. It can for example be diluted with the required amount of aluminium salt. It is also possible to add the additional aluminium salt separately either continuously or intermittently. The pre-mix can also be used as such in case of excessive bulking sludge.

It is noted that the pre-mix composition according to the present invention preferably does not comprise intercalated polymers and/or polymeric coagulants.

The bulking sludge reducing composition comprising the aluminium salt and one or more fatty amines or fatty amine derivatives which is readily usable in activated sludge wastewater treatment plants for reducing bulking sludge can be prepared by mixing the components in a conventional manner, optionally using ultrasonic equipment and/or heating. Preferably, however, a mixture of fatty amine(s) and/or fatty amine derivative(s) is prepared in an organic solvent, optionally with additives, after which an aqueous solution of the aluminium salt is added with stirring.

The process according to the present invention is further illustrated by the following non-limiting examples.

EXAMPLES

The activated sludge and wastewater used in the Examples were collected from the wastewater treatment plant (VWVTP) Nieuwgraaf in Duiven, The Netherlands. The VWVTP Nieuwgraaf is an activated sludge plant treating predominantly domestic wastewater. The primary settled wastewater was collected weekly and stored at -20°C until required.

The experiments were performed in lab-scale sequencing batch reactors (SBR) working volumes of 150 mL. These reactors were operated with a fill and react time of 8 hours, a react time of 14 to 15 hours, and a settle time of 1 to 2 hours, and a draw period (for the effluent) of a few minutes. More particularly, 150 mL of activated sludge containing approximately 3 g/L dry weight of suspended solids was used to inoculate the sequencing batch reactors. The activated sludge was allowed to settle during 1 to 2 hours. 100 mL of clarified effluent was drawn from the reactor. Subsequently, 100 mL of domestic wastewater still to be treated was added to the SBR, said domestic wastewater containing 1 g/L of milk powder (coffee creamer ex Landhof). This operation procedure stimulated excessive growth of filamentous bacteria. The growth of filamentous bacteria resulted in bulking sludge.

Example 1 and Comparative Examples A-C A combination of aluminium chloride (30% aqueous solution of AICI3 ex AkzoNobel Industrial Chemicals) and cocoamine (Armeen® C ex AkzoNobel Surface Chemistry) was used to control bulking sludge (Example 1 ). The results were compared to the results of using only cocoamine as additive (Comparative Example A), using only AICI3 as additive (Comparative Example B), and a control test wherein no additive was used (Comparative Example C). The following procedure was followed.

A pre-mix, containing 51 .8 wt% of cocoamine and 25.9 wt% of ethanol (96%) and 22.3 wt% of acetic acid (70%), was prepared for use in Examples 1 and 2 and Comparative Example A. All other chemicals used were of reagent grade quality. The deionized water used contained no more than 0.01 mg Cu/L. This water was prepared in a water purification system.

The effect of daily dosages of the additive on filamentous bacteria was assessed by measuring the sludge volume index and through microscopic observations. The performance of the reactors was assessed by determining the removal of chemical oxygen demand from the wastewater.

The additive (being a combination of aluminium chloride and cocoamine (Example 1 ), cocoamine only (Comparative Example A), AICI3 only (Comparative Example B), and no additive (Comparative Example C)) was tested in 150 ml_ Sequencing Batch Reactors (SBR) at a temperature of 20 ± 2 °C. At the start, each SBR unit was filled with 150 ml_ of activated sludge (3 g/L dry weight) and the sludge was settled for 1 hour. Subsequently, the additive was added to the settled sludge (the sludge remaining in the respective reactors after withdrawal of the treated water). Subsequently, the addition of 100 ml domestic wastewater spiked with 1 g/L of milk powder was started. The SBRs were operated as described above. The sludge retention time in the SBR units was set at 30 days by removing 5 ml_ of suspended solids prior to settling. The hydraulic retention time was 36 hours. Supernatant drawn off was analysed for the chemical oxygen demand (COD).

In the SBR unit of Example 1 , cocoamine pre-mix (prepared as described above) and subsequently, an aqueous AICI3 solution, were added daily (i.e. one dose per 24 hours) at dosages of 0.9 mg/L and 2.6 mg/L, respectively, of cocoamine in the wastewater. One SBR unit was fed with only the aqueous AICI3 solution, one with only the cocoamine pre-mix (0.9 mg/L cocoamine in the wastewater) and one control SBR unit was not dosed with an additive. The AICI3 concentration in the wastewater was 32 mg/L, based on the chemical phosphate removal of 5 mg/L P0 ₄ -P from the influent.

The dry weight (DW) of the activated sludge inoculum was determined by filtering 50 mL of the activated sludge over a preweighed 12 μηι Schleicher and Schull filter. This filter was dried for 2 hours at 104°C and weighed after cooling. DW was calculated by subtracting the weight of the filter and by dividing the difference by the filtered volume. During the test activated sludge samples of 5 mL were taken to determine the dry weight. The sludge volume index (SVI) were measured by assessing the volume in mL occupied by one gram of activated sludge after settling for 30 minutes in a 1 L calibrated cylinder. Alternatively, the settability of the sludge was measured directly in the SBRs. In the SBR the settability was determined at various time intervals. The volume occupied by the sludge in the SBR was related to the SVI measured in 1 L calibrated cylinders. Volumes obtained in the SBR with activated sludge with various SVIs are given in Figures 1 and 2 (see Figure 1 : Sludge volumes in SBRs with a working volume of 150 mL after a sedimentation period of 45 minutes. The sludge concentrations in the SBR were 1 .0 (■), 2.0 (□), 3.0 (·), and 4.0 (o) g/L dry weight; and Figure 2: Volumes in SBRs with a working volume of 150 mL after a sedimentation period of 30 minutes. The sludge concentrations in the SBR were 2.0 (□), 3.0 (·), and 4.0 (■) g/L dry weight). When the sludge concentration is known, these Figures can be used to relate a volume determined during the settling period of the SBR to the SVI of the sludge. The pH of the supernatant liquors was determined with a Knick 765 calimatic pH meter (Elektronische Messgerate GmbH, Berlin, Germany).

Before analyzing the COD, the effluents of the SBR units were filtered using Schleicher and Schull (cellulose nitrate) filters with pores of 8.0 μηι to remove sludge particles. The chemical oxygen demand (COD) of the influent and effluent was determined by oxidation with an acid-dichromate mixture in which Cr ⁶⁺ was reduced to Cr ³⁺ using Hach Lange test kits (LCK 1 14 and 314). The reaction vials were sealed and placed in a heating block and the contents heated at a temperature of 148°C for two hours. The spectrophotometer (Xion 500) and heating block used were obtained from Hach Lange, Dusseldorf, Germany.

Photographs of activated sludge were taken with a Zeiss Axioplan 2 microscope and a Jenoptik Jena Progres C10 ^plus camera (Carl Zeiss b.v. Sliedrecht, the Netherlands). The filament index (Fl) was determined by comparing the microscopic image of the sludge with a series of reference photographs given by E ike I boom in Process control of activated sludge plants by microscopic investigation (2000), pages 45-47.

The sludge used as inoculum obtained from the domestic WWTP Nieuwgraaf in Duiven settled well (SVI ~ 80; Fl = 2). The few filamentous microorganisms present in the sludge did not have a detectable negative effect on the settability.

After 14 days an increase of filamentous microorganisms was observed in the SBR unit of Comparative Example A, B and C. Daily dosing of cocoamine (2.6 mg/L wastewater) in combination with AICI3 solution prevented excessive growth of filamentous bacteria (Example 1 ). This demonstrates that the administration of cocoamine with an AICI3 solution is effective in reducing bulking sludge.

Different filamentous bacteria types were identified in the bulking sludge sample from the SBR unit dosed with 0.9 mg cocoamine/Liter wastewater in combination with AICI3 solution. For the identification and quantification of filamentous bacteria present in the activated sludge, VIT-kits based on gene probe technology were used, ex VERMICON AG, Munchen, Germany.The most dominant filamentous bacteria were of the Chloroflexi species, 60% represented by an unknown type and 40% by type 1851. Other dominant filamentous bacteria present were Haliscomenobacter hydrossis and Microthrix parvicella. The dry weight varied from 2 to 4 g/L and the pH of the effluent ranged from 7.0 - 7.5. These conditions allow a normal performance of the activated sludge process. The addition of cocoamine in combination with AICI3 did not have a negative effect on the performance of the wastewater treatment. This is shown by the unaffected COD removal of approximately 90%.

Table 1 Sludge Volume Index (SVI) and Filamentous Index (Fl) measured in SBRs after 14 days of operation

^* The Filamentous Index (Fl) is a measure of the number of filamentous microorganisms in activated sludge. A scale of 0 to 5 is used (from none to very many filaments). It is noted that bulking sludge problems arise when SVI is 200 or higher and the Fl index is 3 or higher. Examples 2 - 4 and Comparative Examples D-H

A combination of aluminium chloride (30 w/w% aqueous solution of AICI3 ex AkzoNobel Industrial Chemicals) and tallowamine (Armeen® T ex AkzoNobel Surface Chemistry) and oleyl-1 ,3-diaminopropane (Duomene® 0 ex AkzoNobel Surface Chemistry) was used to control bulking sludge (Examples 2 and 3, respectively). The results were compared to the results of using only tallowamine as additive (Comparative Example D), using only AICI3 as additive (Comparative Example G), and a control test wherein no additive was used (Comparative Example F). Furthermore, a combination of aluminiumhydroxy chloride (35 w/w% aqueous solution of polyaluminium(lll)hydroxide chloride, Quadroflo PUH ex AkzoNobel Industrial Chemicals) and tallowamine was used to control bulking sludge (Example 4). The result was compared to the results of using only tallowamine as additive (Comparative Example D), using only aluminiumhydroxy chloride (Comparative Example H), and the control test wherein no additive was used (Comparative Example G).

A procedure analogous to the one described for Example 1 and Comparative Examples A-C was followed, although the Sludge Volume Indexes and Filamentous Indexes were now determined after 19 or 27 days of operation (see Table 2). Table 2 summarizes the results.

Table 2 Sludge Volume Index (SVI) and Filamentous Index (Fl) measured in SBRs after 19 or 27 days of operation

* As mentioned for Table 1 , the Filamentous Index (Fl) is a measure of the number of filamentous micro-organisms in activated sludge. A scale of 0 to 5 is used (from none to very many filaments). It is noted that bulking sludge problems arise when SVI is 200 or higher and the Fl index is 3 or higher. In conclusion, bulking sludge can be reduced by the addition of cocoamine in combination with AICI3, or of tallowamine in combination with either AICI3 or aluminiumhydroxy chloride. It can also be reduced by the addition of oleyl-1 ,3- diaminopropane and AICI3. Neither the dosing of cocoamine, tallowamine or oleyl-1 ,3-diaminopropane without either of the two aluminium compounds nor the dosing of AICI3 or aluminiumhydroxy chloride alone retarded the growth of filamentous bacteria to the required extent.

It was found that the performance of the wastewater treatment was not negatively affected by the addition of cocamine and AICI3, tallowamine and AICI3, or tallowamine and aluminiumhydroxy chloride.

The control of filamentous bacteria by dosing AICI3 or aluminiumhydroxy chloride in combination with tallowamine is not specific; various types of filamentous bacteria are controlled. The same holds for use of the combination of AICI3 and oleyl-1 ,3-diaminopropane and cocoamine and AICI3.