WO2007023170A1

WO2007023170A1 - Device and method for treating waste waters

Info

Publication number: WO2007023170A1
Application number: PCT/EP2006/065608
Authority: WO
Inventors: Thomas Dockhorn
Original assignee: Thomas Dockhorn
Priority date: 2005-08-23
Filing date: 2006-08-23
Publication date: 2007-03-01
Also published as: DE102005040018B4; DE102005040018A1

Abstract

The invention relates to a device and method for treating waste waters, wherein said device and method are suitable for separating phosphorus and /or phosphate, which are contained in the waste waters, in the form of magnesium ammonium phosphate (MAP) and for subsequently using them. According to said invention, a thermophile digestion is used for removing centrifuge effluent waters from excess sludge and subsequently mixing them with seawater in such a way that the MAP is precipitated.

Description

Apparatus and process for wastewater treatment

The present invention relates to an apparatus and a method for the treatment of wastewater, each of which is suitable to separate in the wastewater contained phosphorus or phosphate in the form of magnesium ammonium phosphate (MAP, MgNH ₄ PO ₄ x 6H ₂ O) and provide for further use.

The recovery of phosphorus from wastewater is of great importance, since phosphate is an essential component of fertilizers as an irreplaceable nutrient for plants. A currently important source of phosphate are phosphate ores, from which phosphorus must be recovered by chemical or thermal processes and converted into a usable form for further production processes. The disadvantage of the use of phosphate ores is not only their content of heavy metals, in particular cadmium, but also the limited nature of natural deposits.

It is known that phosphates can also be precipitated from wastewater, for example during wastewater treatment in sewage treatment plants. Instead of recovering phosphates as

However, in the practice of wastewater treatment, secondary raw material is currently still the prevention of water reutilisation due to the elimination of phosphates from the wastewater, which is to be discharged into a receiving water.

A targeted recovery of phosphate, however, is hardly possible with the methods used in conventional sewage treatment plants for phosphate elimination.

State of the art

The precipitation of phosphate in the form of magnesium ammonium phosphate (MAP) from wastewater is known and is part of various processes. The MAP precipitation may be e.g. directly from process water streams in sewage treatment plants, where nitrogen compounds and phosphorus are precipitated from the process water stream after raising the pH and adding magnesium ions as MAP. In addition, some of the phosphate bound in the sewage sludge can be recovered in the form of MAP, but phosphate must first be dissolved back by an acid digestion before the actual precipitation. The known methods require the use of not insignificant amounts of resources in the form of magnesium ions, alkalis and / or acids.

By subsequently heating MAP, nitrogen can be separated in the form of NH ₃ -GaS, leaving behind magnesium hydrogenphosphate. This in turn can be used for MAP precipitation, if in the wastewater to be treated ammonium is in excess of stoichiometry relative to phosphate and the MAP precipitation in addition to the extraction of phosphate should primarily fulfill the purpose of nitrogen elimination.

In general, it is known to recover phosphate from various partial streams within a conventional sewage treatment plant, for example, following an anaerobic stage, discharged from the digested sludge and separated, for example, in a separator in Zentratwasser and dehydrated digested sludge. Phosphorus may be precipitated from the resulting centrate water, or redissolved from the thickened digested sludge by acid treatment and then precipitated separately, or precipitated separately after drying and incineration of the thickened sludge from the sludge ash after reconstitution. For the separation of precipitated MAP (also called struvite), a fluidized bed reactor can be used (Conference Summary, Second International Conference on Recovery of Phosphates from Sewage and Animal Wastes, Noordwijkerhout, 12-13 March 2001). This separation process is described using the example of centrate water after anaerobic digestion and is intended to produce MAP pellets.

Other precipitation processes for phosphates use iron or calcium salts to Eisenbzw. Precipitate calcium phosphate.

For precipitation of MAP during wastewater treatment, centrate water is added with magnesium ions, and it is also known to use seawater as a source of magnesium ions. For raising the pH of centrate water separated from digested sludge, aeration can be used which discharges carbon dioxide.

Regy et al. describe in the report "Phosphate recovery in Waste Water by Cristallization" (22.06.2002) various methods for the recovery of MAP: For example, with reference to Battistonis fluidized bed columns, methods are presented in which crystallization is induced by stripping carbon dioxide The supernatant (centrate water) of the anaerobic digestion was prepared on a belt press and to achieve a suitable for the MAP precipitation phosphate concentration of originally 24 mg / L by the addition of phosphate on 160 mg / L In cases where phosphate is added prior to MAP precipitation, the process is usually used to eliminate ammonia nitrogen in excess of the stoichiometric ratio.

JP 102 49 359 and Kumashiro et al. (2 ^nd International Conference on Recovery of Phosphate from Sewage and Animal Wasts, Holland, March 12 and 13, 2001) describe the use of seawater as a source of magnesium for the precipitation of phosphate as MAP from process streams that occur in wastewater treatment. Centrifugal water from a belt press or centrifuge is used as the process stream. The ratio of added seawater was between 2 and 15% by volume to the process stream. For precipitation, the crystal formation is used in a vertical liquid column, in which by feeding air at the lower end of a loop movement is generated around an axially disposed guide tube. The hydraulic residence times in the loop reactor were between 7 and 58 minutes. Special attention was paid to the formation of MAP crystals with a size of approx. 1 mm in order to better separate them. The process operated at a mean pH of 7.7, resulting in only about 75% of the phosphate contained in the centrate water being eliminated.

Shimamura et al. (Water Science and Technology, Volume 48, 1, pages 163-170) describe a further development of the crystallization of MAP in a vertical column of liquid, in which a downstream second liquid column serves to form nuclei of MAP, which in turn for inoculation of the upstream larger Can serve reactor. In this way, the crystal growth of MAP can be controlled to produce a uniform crystal size.

The additions of caustic used in the prior art for adjusting a basic pH in the centrate water give a clear indication that the digestion was carried out in the mesophilic range, since this only leads to neutral to slightly alkaline centrate water (pH about 6.8 - 7.4), which is below the optimum pH for MAP precipitation.

DE 10 2005 002 066 A1, which was published after the priority date of the present application, describes a method for MAP precipitation from stabilized sludge of a sewage treatment plant by introducing ammonia water and / or hot process water into dewatered stabilized sludge and precipitating phosphate salts from the extracted sludge water by adding metal ions. DE 10 2005 002 066 A1 neither recognizes that in the case of thermophilic digestion from the centrate water by the addition of seawater phosphate in the form of MAP can be effectively precipitated, nor the remobilization of phosphate from activated sludge.

DE 43 33 177 A1 describes the optimization of the biogas production in the digestion stage by intermediate treatment of a part of the anaerobic biomass of the digestion stage to the To stabilize process conditions. A precipitation of phosphate in the form of MAP is not described.

Object of the invention

Compared with the known methods of eliminating or recovering phosphorus in the form of MAP from wastewater, the object of the present invention is to provide an alternative, preferably more efficient apparatus and a more efficient method of recovering MAP from wastewater. Another object of the present invention is to minimize the use of resources.

General description of the invention

The invention achieves the abovementioned object by providing a device for clarifying wastewater, in particular municipal wastewater streams, process waters in sewage treatment plants, wastewater from livestock farming, and industrial wastewater by the fact that the device according to the invention, in a modification of known plants, has a device for anaerobic thermophilic digestion , is discharged from the digested sludge and in a solid-liquid separation, such as a decanter, centrate water is generated. This Zentratwasser contains phosphate in addition to ammonium ions. By admixing seawater, MAP is precipitated therefrom.

It is a particular advantage of the present invention that a suitable pH for the MAP precipitation (preferably in the range of 8-10, more preferably 8.5-9.5) already present in the centrate, since according to the invention, the digestion under thermophilic Conditions are fulfilled. The adjustment of the pH by addition of alkaline compounds is therefore not required, which brings advantages in the process and the costs.

Furthermore, centrate water, which is obtained from the thermophilic sludge digestion, a significantly higher phosphate content than Zentratwasser, which results from mesophilic digestion. For precipitation of the phosphate contained in the Zentratwasser seawater is added and mixed with the Zentratwasser in a mixing device. The crystallization of MAP begins already in the mixing device. The continuation of the crystal growth of MAP and its separation take place in a subsequently arranged apparatus for solid-liquid separation, for example a sedimentation tank or a decanter. In the preferred embodiment, the separation of MAP crystals occurs in a fluidized bed reactor where the MAP crystallization and filtration bed is formed without particulate solids additives such as sand.

In the event that no separate separation of MAP from the remaining components of the thermophilic sludge digestion products is required, MAP precipitation can also be achieved by adding seawater to the thermophilic sludge. The precipitated MAP can then no longer or only with increased effort separate from the solids of the digested sludge, but this may be of interest if only depletion of the subsequently produced centrate water of phosphate and / or ammonia is desired. Because the Zentratwasser is depleted in this embodiment by the precipitation of the MAP of phosphate and ammonia. Accordingly, the apparatus for solid-liquid separation of the digested sludge generated by the thermophilic digestion apparatus is not required in this embodiment and may be omitted. The addition of seawater for MAP precipitation can be carried out in the subsequently permeable mixing device for mixing thermophilic sludge and fed seawater. A subsequently throughflowable solid-liquid separation device is optionally usable if the centrate water discharged from MAP is to be separated from the mixture of MAP and solids of the digested sludge; when using the digested sludge with precipitated MAP without thickening this device can be omitted for solid-liquid separation.

According to the invention, it is preferred that the fluidized bed consist essentially exclusively of the formed MAP crystals and that the flow rate be chosen so low (low) over the prior art that no expanded bed settles, but achieves a compact bed with increased physical filtration efficiency becomes. For the purposes of this invention, seawater is understood as meaning an aqueous solution containing magnesium ions, in particular natural seawater, enriched natural seawater, as used, for example, in salt gardens or plants for the treatment of salt Seawater desalination is obtained, in particular enriched natural seawater or sea salt with a high content of magnesium ions, and aqueous solutions containing magnesium ions, for example, magnesium chloride and / or magnesium hydroxide and / or magnesium oxide.

The volumetric proportion of non-enriched seawater to the centrate water may be, for example, in the range of 2 to 15 vol.% 1, so that the salt load, in particular sodium chloride, introduced by the seawater will be substantially free from stress in the subsequent subsequent, e.g. represents biological purification of the treated wastewater. Enriched seawater or aqueous solutions with a lower content of magnesium ions are to be mixed according to their magnesium ion concentration in a lower or higher volumetric ratio.

In studies, it has been found that a substantially stoichiometric ratio of magnesium to phosphate is sufficient to form MAP using seawater as the source of magnesium, whereas in the literature a stoichiometric ratio of magnesium to phosphate is recommended to achieve quantitative precipitation of the phosphate , In addition, the investigations have shown that in this procedure, ammonium can precipitate more than stoichiometrically in relation to the phosphate, which in turn represents a clear procedural and economic advantage over the prior art. The stoichiometric ratio of the precipitation of ammonium ions with the seawater MAP precipitation device according to the invention may be about 2 to 4 or more in relation to magnesium or phosphate.

In a further embodiment of the invention, it is possible to implement the separated MAP by thermal treatment to magnesium hydrogen phosphate, wherein the ammonium nitrogen is released in the form of gaseous ammonia. According to the invention, magnesium hydrogen phosphate obtained in this way can be recirculated to a device for wastewater treatment, preferably to be fed to the centrate water, in order in this way to reduce the ammonium concentration by reuse in the MAP precipitation. Since the release of ammonia gas from MAP used at temperatures of 55 ⁰ C or higher, it is preferable in the invention to use a solar dryer for thermal treatment of MAP, can be collected, optionally, wherein the ammonia gas or chemically bonded.

In a further embodiment of the invention, the content of phosphate and / or ammonium ions can be increased within the device according to the invention by supplying phosphate and / or ammonium aqueous wastewater streams, such as yellow water (urine) to favor the precipitation of MAP.

For example, effluents from domestic dishwashers or phosphate-containing effluents from industrial operations are suitable as phosphate-containing wastewater streams, which can be collected separately from municipal wastewater. In this way, e.g. the concentrated in the wastewater of (household) dishwashers or (household) washing machines phosphate used regardless of an aerobic treatment in the aeration tank and the thermophilic digestion to recover the phosphate as MAP, so that the intermediate losses in the conventional wastewater treatment by a biological or chemical fixation can be avoided. If such wastewater streams contain phosphate in the form of polyphosphates, for example triphosphates, hydrolysis to phosphate is required before MAP precipitation. This hydrolysis may be autoclaved by aerobic or anaerobic incubation, alternatively by incubation in admixture with activated sludge with optional aeration.

Alternatively, the hydrolysis of such polyphosphates may take place during collection in a collection container and / or during delivery to a mixing device having a seawater supply means without additives. The collecting container and / or the supply line can each form separately for phosphate-containing or ammonium-containing wastewaters or for both wastewaters in mixture with one another part of this apparatus according to the invention, with which phosphate is precipitated by admixing seawater to waste water or concentrated wastewater partial flows as MAP. The supply of such phosphate- and / or ammonium-containing wastewater streams is preferably carried out in the mixing device in which Zentratwasser is mixed with seawater. In a further embodiment of the invention can Phospat and ammonium concentrated wastewater streams, for example, separately from the rest of wastewater, such as municipal wastewater or wastewater collected from animal husbandry sub-streams are used by admixing seawater for MAP precipitation. Wastewater from domestic dishwashers, effluents from the phosphate-processing industry and other phosphate-containing industrial wastewater are to be mentioned as concentrated phosphate-containing wastewater partial stream. In particular, yellow water (urine), in which the hydrolysis of urea produces ammonium, is to be mentioned as the phosphate- and ammonium-containing wastewater partial stream. In one embodiment, it is therefore proposed to accumulate in household phosphate-containing wastewater streams, in particular dishwasher wastewater, and yellow water separately from the other wastewater separately or mixed with each other in collection devices.

This separate from the rest of wastewater collection of phosphate or ammonium-containing wastewater streams can be realized as a special piping system or through collection containers that are periodically empty. In one embodiment, yellow water and dishwashing effluent are separated in separate collection containers, preferably in a common collection container substantially separate from the remaining domestic effluent, i. essentially free or separated from solids and preferably passed without additional (rinse) water. The supply line to the mixing container, which also has a feed device for seawater, may be transported by batch transport, e.g. by means of tank trucks, or by pipelines that run separately from the rest of the municipal sewage. Instead of using a common collection container or the separate collection container, a common or separate lines can be used to phosphates or ammonium-containing wastewater, preferably yellow water and dishwasher wastewater, to the mixing device to be mixed in the seawater for MAP precipitation.

By means of a feed device for seawater to yellow water and phosphate-containing wastewater substreams in a mixing device, MAP can be precipitated directly and separated by a subsequently through-flowable device for solid-liquid separation. The MAP precipitation can be carried out in mixing devices, for example simple containers or stirred kettles, the separation of MAP according to the others Embodiments of the invention, preferably in the fluidized bed, which forms a compact bed due to low flow rate.

An advantage of this embodiment is the high recovery rate of phosphate from phosphate- and ammonium-containing effluent streams, as these have higher concentrations of the components essential for MAP precipitation, phosphate and ammonium. Moreover, this embodiment requires no or only simple devices for separating solids from wastewater prior to MAP separation.

A further advantage of this embodiment is that both yellow waters with a pH> 9 and dishwasher effluents with a pH> 10 are sufficiently alkaline for a substantially quantitative MAP precipitation. Therefore, in this embodiment of the invention, no increase in pH by adding resources is required.

Wastewater from the industrial production of phosphate from phosphate ores can be used as further phosphate-containing wastewater from the phosphate processing industry. Here, MAP can be generated, for example, by adding yellow water to the phosphate-containing wastewater, and then or at the same time using seawater. MAP can then be separated in a known manner.

In a further, alternative or additional embodiment of the invention, the elimination of phosphate from wastewater is carried out independently of a treatment in the activated sludge tank or a thermophilic digestion, namely already from the aqueous phase of raw sewage. Here, the raw sewage untreated, that are used without deposition of solid ingredients, or be used free of solid ingredients, for example, after passing through a device for solid-liquid separation, a settling tank and / or a decanter. For the precipitation of phosphate in the form of MAP, it is only necessary to add to the untreated raw sewage or the aqueous phase of raw sewage a magnesium source, according to the invention seawater, since the raw sewage already contains phosphate and, more than stoichiometrically, ammonium ions. The pH of raw sewage is also suitable for precipitating at least a substantial portion of the phosphate contained therein in the form of MAP. If the pH of the raw sewage is too low for substantially complete MAP precipitation Bases are added to raise the pH to a preferred range of 8.5 to 9.5.

The mixing of the aqueous phase of the raw sewage with seawater can be carried out according to the other embodiments in a mixing device. The separation of the crystallizing MAP can be carried out according to the aforementioned embodiments of the invention via a device for solid-liquid separation. If solid ingredients have been removed from the raw sewage prior to the addition of seawater, the MAP separation preferably takes place in a fluidized bed consisting essentially of particulate MAP only. In the event that solid ingredients are not or not completely separated from the raw sewage prior to addition of seawater, precipitated MAP can be separated along with the solids from the aqueous phase of the raw sewage.

These embodiments of the invention for the treatment of raw sewage by MAP precipitation with or without prior separation of solid ingredients is then practical, if the load of the receiving water with organic pollutants plays a minor role, but the introduction of phosphate is subject to limits, as for example some Scandinavian countries is the case. In other cases, following the MAP precipitation from raw sewage, a conventional or inventive wastewater treatment apparatus may be connected.

In a further embodiment of the invention, it is preferable to recover phosphate by precipitation as MAP additionally already before the thermophilic digestion. For the recovery of phosphate before the thermophilic digestion, biologically and / or chemically fixed phosphate is redissolved from activated sludge, for example excess sludge, so that it is available for the subsequent precipitation as MAP. The term "activated sludge" here sludge understood that originally originates from the aeration tank and as so-called excess sludge from the way the device for wastewater treatment, which finally ends in the digester, is removed and present in concentrated form as thickened excess sludge.

It has been shown that the proportion of phosphate precipitable as MAP, which is in solution after thermophilic digestion in the centrate water and precipitates as MAP, only about 20% of the total phosphate contained in the sludge is, while in the embodiment according to the invention with redissolution from the activated sludge in the Mobilisierungsbehälter about 50 - 60% of the total phosphate contained in the sludge can be redissolved and precipitated from the aqueous phase of the mobilized sludge as MAP.

For the reconstitution of the biologically and / or chemically fixed phosphate in the mobilization tank from activated sludge, e.g. Excess sludge, which has preferably passed through a pre-thickening dewatering apparatus, requires an easily metabolizable substrate. As an easily metabolizable substrate, the excess sludge can serve itself, or it can be supplied at low cost substrates, for example, sucrose-containing substrates or production residues, but preferably primary sludge, which is anyway available from the primary treatment of the wastewater in a wastewater treatment plant.

To mobilize the biologically and / or chemically fixed in the activated sludge phosphate at least a portion of the activated sludge with the easily metabolizable substrate, such as primary sludge, combined in a Mobilisierungsbehälter and mixed and at mesophilic temperatures (about 33 - 38 ⁰ C) for a period under anaerobic Incubated conditions, for example, for 6 to 48 hours, preferably 12 to 24 hours hydraulic residence time. At lower temperatures, for example ambient temperatures up to 5 ^° C. or 10 ^° C., the residence time in the mobilization container is to be set longer, eg 1 to 8 days. Alternatively, the mobilization container may drain even at the temperatures of the thermophilic digestion, which accelerates the mobilization. At the same temperature ranges in the mobilization container and thermophilic digestion tower, the same heating device can be used for heating. Furthermore, apart from the compensation of heat losses, no additional heat input is required when heated in the mobilization tank and digester to the same Temperaturgbereich and the mobilized sludge is passed without cooling in the digester. In addition to the return of biologically fixed in activated sludge phosphate is precipitated in this approach also precipitated as iron phosphate phosphate. At present, it is believed that Fe ³⁺ is reduced to Fe ²⁺ by the iron reducer during the redissolution in the mobilization tank so that the phosphate bound as iron (III) phosphate can go into solution. For an effective mobilization of phosphate from activated sludge, it is preferred that no aluminum salts are used in the apparatus or the process carried out therein.

The precipitation of the phosphate in the mobilization container as MAP is preferably carried out after a solid-liquid separation, wherein the resulting liquid phase is mixed with seawater to provide the required concentration of magnesium ions. Since only little fixed ammonium in the mobilization tank into the aqueous phase, a further addition of ammonium ions is usually required. Ammonium ions can be supplied by admixing Zentratwasser from the thermophilic digestion or yellow water.

The precipitation and subsequent separation of MAP can be carried out according to the aforementioned embodiments in a mixing vessel with subsequent or simultaneously effective solid-liquid separation device.

The aqueous phase obtainable after the MAP precipitation can in turn be returned to the activated sludge tank; the solid phase is preferably to be supplied to the thermophilic digestion device.

In addition to the increased recovery of phosphate from wastewater, this embodiment of the invention enables a reduction in the use of iron salts as phosphate precipitation resources, since the iron reduced and dissolved following treatment in the mobilization vessel can be recycled to the aerobic stage of wastewater treatment after MAP precipitation and there, again after oxidation to Fe ³⁺ , for the precipitation of phosphate as iron (III) phosphate is available.

In this embodiment of the invention, in which the mobilized slurry obtained from the mobilization tank is immediately subjected to solid-liquid separation and phosphate is precipitated by adding seawater as MAP, a disadvantage may be that the pH of the liquid Phase is not alkaline enough to ensure optimal MAP precipitation. Therefore, in order to increase the MAP yield, it is possible here to increase the pH to the alkaline range, preferably 8-10, more preferably 8.5-9.5, by adding bases. As an alternative to increasing the pH of the aqueous phase of the mobilized sludge obtainable by solid-liquid separation following the treatment in the mobilization tank by adding alkalizing agents, this aqueous phase can be aerated so that organic acids can be degraded first and, if necessary Carbon dioxide is stripped off. In this embodiment, oxidation of Fe ²⁺ to Fe ³⁺ by iron oxidizers takes place in parallel. As a result, iron (III) will precipitate phosphate, which is available as a secondary raw material after separation in a device for solid-liquid separation.

As a first alternative of this activated sludge phosphate recovery tank mobilization apparatus, the aqueous phase of the mobilized sludge obtained following treatment in the mobilization tank by solid-liquid separation may be fed to the mixing apparatus instead of a direct separate MAP precipitation apparatus the centrate water from the thermophilic digestion is mixed with seawater. In this case, the aqueous phase of the mobilized sludge in combination with centrate water from the thermophilic digestion by the addition of seawater phosphate in the form of MAP is withdrawn. As a further option, in this alternative, at an undesirably low pH of the aqueous phase of the mobilized slurry for MAP precipitation, a base for alkalization to a pH of 8.5-9.5 may be added.

As a second and preferred alternative, the mobilized slurry available from the mobilization vessel may be fed directly to the thermophilic digestion device without separate solid-liquid separation and MAP precipitation being performed therefor. Because it has been shown that from the activated sludge, for example, excess sludge, in the mobilization tank re-dissolved phosphate and Fe ²⁺ remains substantially dissolved in a subsequent thermophilic digestion, that is essentially no longer fixed biologically by the subsequent thermophilic digestion. In this embodiment of the invention, phosphate fixed in the activated sludge is therefore redissolved and separated from the centrate water by precipitation as MAP after the thermophilic digestion. In turn, the advantage of the thermophilic digestion is used that the pH of the Zentratwassers is in the suitable for MAP precipitation alkaline range, so that can be dispensed with the addition of alkalizing. Following MAP precipitation, the phosphate depleted centrate water can be sent to the aeration tank. As a result, a significant proportion of the dissolved iron is returned to the phosphate precipitation by Fe ⁺ dissolved in the centrate water.

In a further alternative embodiment, but less preferred, seawater or a similarly concentrated saline solution (about 2-4% by weight) is added directly to the activated sludge in the mobilization tank instead of an additional easily metabolizable substrate. For it has been shown that only the addition of seawater or a saline solution, optionally with subsequent anaerobic incubation in Mobilisierungsbehälter, also leads to a return of bound phosphate, with a redissolution of up to 45% of the total phosphate contained in the activated sludge was measured.

Detailed description of the invention

The invention will now be described in more detail with reference to the figures in which

FIG. 1 shows a schematic overview of a device according to the invention for sewage and sludge treatment,

FIG. 2 shows a schematic overview of a device according to the invention for wastewater and sludge treatment in a preferred embodiment with redissolution of bound phosphate from activated sludge, and

Figure 3 shows schematically a device for solid-liquid separation for MAP precipitation according to the preferred embodiment of the invention.

FIG. 1 shows schematically a device according to the invention for precipitating MAP from waste water, in which raw sewage can first be mechanically cleaned in a primary clarifier, wherein the waste water is separated into primary sludge and a substantially aqueous phase. This aqueous phase of the raw sewage water is fed to an activated sludge tank in which a substantially aerobic treatment takes place. From the aeration tank so-called activated sludge is led into the secondary clarifier.

The course of the secondary settling tank consists of an activated sludge fraction, which is recycled as so-called return sludge into the activated sludge tank and an aqueous sludge tank Phase (treated wastewater), which can be discharged into the receiving water. Excess activated sludge is thickened as excess sludge, for example, in a device for solid-liquid separation to thickened excess sludge and passed into the apparatus for thermophilic digestion (digestion tower). The thermophilic digestion produces digested sludge which is discharged from the thermophilic digestion apparatus and separated in a solid-liquid separation apparatus, eg a decanter, in centrate water and dehydrated digested sludge. Also supplied to the digester is primary sludge, which is obtained from the primary treatment.

An exemplary process of the invention thermophilic digestion in the digester runs at a temperature of 40 to 70 ⁰ C, preferably at 50 to 60 or 58 ⁰ C, more preferably at 55 ± 3 ⁰ C from. The Zentratwasser available from the thermophilic sludge by solid-liquid separation has a content of phosphate in the range of 100 to 150 mg / L, wherein in experiments with devices of the invention phosphate concentrations of about 130 mg / L were determined when the raw sewage phosphate concentrations in the range of 10 mg / L. The nitrogen content of the centrate water was about 1400 mg / L in the form of ammonium in experiments with the device according to the invention, the COD was about 2500 mg / L.

The apparatus for solid-liquid separation of the excess sludge in Zentratwasser and thickened excess sludge can be formed by a settling tank, alternatively or additionally a decanter and / or a sludge press, for example a filter press.

According to the invention, the mixing device I, II for mixing centrate water and seawater, optionally an ammonium-containing aqueous solution, as a static mixer, as a container without driven stirring elements or as a stirred tank reactor can be performed.

After passing through the mixing device I, II, the aqueous composition is subjected to a solid-liquid separation in which phosphate-depleted wastewater can be separated from the precipitated MAP.

Also in this embodiment, the obtained MAP can be converted by thermal treatment to magnesium hydrogen phosphate and optionally in the inventive Return device can be recycled, for example, to centrate water to allow increased elimination of ammonium nitrogen.

Figure 2 illustrates the preferred embodiment of the invention and shows as an additional element the delivery of activated sludge into a mobilization vessel which, as an example of an easily metabolizable substrate, is fed sucrose, but preferably primary sludge or, less preferably, seawater or saline solution.

The redissolution of biologically bound phosphate in activated sludge and / or primary sludge, as well as chemically bound phosphate, e.g. in the form of iron (III) phosphate, takes place in the mobilization container, preferably under anaerobic conditions at ambient temperature, preferably in the mesophilic or thermophilic temperature range over a period of 12 to 24 hours.

For the further treatment of the discharged from the Mobilisierungsbehälter mixture, hereinafter also referred to as mobilized sludge, its direct discharge from the outlet of Mobilisierungsbehälters by means for feeding into the digester for thermophilic digestion according to the invention under A is shown.

As an alternative to this immediate further treatment of the mobilized sludge by thermophilic digestion, B shows the solid-liquid separation into an aqueous phase and thickened mobilized sludge. The thickened mobilized sludge may in turn be fed to the thermophilic digestion while the aqueous phase is separated from a separate mixing device (II) for mixing with seawater, optionally with supply of an ammonium-containing substream to precipitate MAP and a subsequent solid-liquid separation device from MAP can be supplied by the phosphate depleted wastewater.

Schematically illustrated in Figure 2 is also the alternative or additional supply of the aqueous phase, which is generated from the mobilized sludge by solid-liquid separation, to the mixing device (I), which is also supplied Zentratwasser from the digester to mixed with seawater to become. In this way, only a minimum mixing device I for aqueous phases (aqueous phase from the Mobilisierungsbehälter and Zentratwasser from the thermophilic digestion) for mixing with seawater and only one then durchströmbare device for solid-liquid separation for the separation of precipitated MAP from phosphate-depleted wastewater required.

Figure 3 shows schematically a preferred apparatus for solid-liquid separation of MAP following the mixing of the centrate water, preferably additionally with the aqueous phase of the mobilized slurry, with seawater in the mixing apparatus. In a particularly preferred embodiment, a crystallization and filtration bed is generated in this device for solid-liquid separation for the separation of MAP, which is flowed from below and is formed essentially from MAP crystals.

It has been found that, in particular, at flow velocities in the range of at most 0.1 to 100 m / h, preferably 0.1 to 80 m / h, more preferably 0.1 to 10 m / h and most preferably 0.1 to <5 m / h very good separation of finely divided MAP particles in settling tanks is possible, but particularly preferably in a flowing from below fluidized bed.

In order to improve the precipitation of precipitated MAP particles in the settler, which may be a fluidized bed reactor, a settling tank, or a downflow column having an outlet opening above the inlet, a layer of individual floating plastic spheres (diameter of 1 to 15 mm, preferably 2 to 7 mm) or other floating plastic particles of similar maximum dimensions. In order to retain the floating plastic balls, provision must be made for a retaining device, for example a retaining plate provided with passage openings, which may also be referred to as a perforated plate or nozzle base. Such a retaining plate is to be arranged in the settling tank so that the plastic balls are retained in front of the outlet opening, for example, the retaining plate can be arranged horizontally below the outlet opening, wherein the floating plastic balls are arranged under the retaining plate. The plastic balls float due to a lower density in relation to the treated wastewater, for example Zentratwasser; the layer preferably has a thickness of 0.5 to 3 m. The increased separation of MAP particles by the layer of mutually movable, floating plastic balls within the Mixture of sewage and seawater is attributed to a physical room filtration effect of the layer of plastic balls.

Example 1 Precipitation of MAP from Centrifugal Water from Thermophilic Digestion Centrate water recovered from a thermophilic digester had a pH of 9.5. MAP was precipitated by addition of an aqueous solution having an Mg.sup.2 ⁺ concentration of 248 mg / l as seawater for the purposes of the invention.

After precipitation, the concentrations of ammonium and phosphate were measured in the remaining, phosphate-depleted aqueous phase and the following values for the precipitation were determined:

Table 1: Concentrations of phosphate and ammonium precipitated from centrate water after addition of seawater

The results shown in Table 1 make it clear that by adding seawater, an appropriate concentration of Mg ²⁺ can be adjusted, and also that a superstoichiometric elimination of ammonium ions by MAP precipitation is possible.

Example 2: Stoichiometric precipitation of ammonium ions by addition of

seawater

The example of yellow water as wastewater, which in addition to phosphate and ammonia ions from the hydrolysis of urea, it is clear that seawater, preferably natural seawater, in the MAP precipitation for superstoichiometric precipitation of

Ammonium ions leads. Accordingly, with the device according to the invention, ammonium can also precipitate superstoichiometrically from centrate water and / or the aqueous phase of mobilized sludge. The precipitate can be separated with solid-liquid separation devices according to the invention from the phosphate phase and ammonium-deposited liquid phase.

The wastewater used was yellow water, which was allowed to stand for 3 days at room temperature to hydrolyze urea. To this yellow water (500 mL, pH = 9.22, 4.42 mmol phosphate, ammonium 167.73 mmol) was added each in 1L beakers in Reihenrührer sea water (pH = 8.14, 248 mg Mg ²⁺ / L) in Increasing volume fractions added.

Table 2: Concentrations of phosphate and ammonium precipitated from the aqueous phase after addition of seawater

Example 3: Remobilization of phosphate as a function of the temperature, with or without readily available substrate

For the remobilization of phosphate from activated sludge for subsequent precipitation as MAP, activated sludge was incubated at different temperatures in batches with or without readily available substrate. As readily available substrate, 2 g sucrose per 750 mL activated sludge batch was added. After an incubation period of 2.5 days, the dissolved phosphate concentrations in the individual batches were determined, which represent the measure for the re-dissolution of phosphate. The results are shown in Table 3 below:

Table 3: Concentrations of phosphate remobilized from activated sludge at different incubation temperatures:

The redissolution was determined as part of the total phosphate concentration in the activated sludge after acid digestion.

On the one hand, the test data determined in Table 3 show a significant temperature dependence of the remobilization in that, in the case of activated sludge without sucrose, an increase in the remobilization of phosphate is observed with increasing temperature, with maximum redissolution in the thermophilic range being observed. The slurries of activated sludge with sucrose generally show a higher remobilization of phosphate and have an optimum in the mesophilic to thermophilic range, ie at temperatures of about 30 to 52 ⁰ C.

Furthermore, the results show that the remobilization of phosphate from activated sludge even without readily available substrate alone by incubation, preferably thermophilic, of Activated sludge takes place. By adding an easily metabolizable substrate, shown here by the example of sucrose, the remobilization of phosphate from activated sludge is significantly higher. Moreover, the experimental approaches showed a pronounced pH dependency in that the remobilization of phosphate was increased at pH's of 5.5 or lower, so that for the remobilization of phosphate from activated sludge, a pH of 5.5 or lower is preferred.

Claims

claims

An apparatus for precipitating magnesium ammonium phosphate (MAP) from waste water, comprising a seawater supply means, a waste water supply means and a sludge dewatering apparatus, characterized by

a device for thermophilic digestion, a device for solid-liquid separation of digested sludge, which from the

Apparatus for thermophilic digestion is available in thickened

Excess sludge and Zentratwasser, then a flow-through mixing device (I) for mixing

Zentratwasser and supplied seawater, and then a through-flowable device for solid-liquid separation of

Separation of particulate MAP from the mixture of Zentratwasser and

Seawater.

2. Apparatus according to claim 1, characterized by an activated sludge tank for the aerobic treatment of wastewater or wastewater fractions and a mobilization tank for supplying activated sludge, which has a supply device for easily metabolizable substrate and / or aqueous solutions.

3. A device according to claim 2, characterized in that the means for supplying easily metabolizable substrate primary sludge from the primary treatment of wastewater or raw sewage feeds into the mobilization container.

4. Device according to one of the preceding claims, characterized by means for supplying the mobilized sludge from the outlet of Mobilisierungsbehälters to the device for thermophilic digestion.

5. Device according to one of the preceding claims, characterized by a device for solid-liquid separation of the mobilized sludge from the outlet of Mobilisierungsbehälters and means for supplying the aqueous phase to the mixing device (I) for mixing Zentratwasser with feeding device for seawater with subsequently flowed through device for separating precipitated MAPs.

6. Device according to one of the preceding claims, characterized in that it comprises one of the mixing device (I) for mixing Zentratwasser with seawater separate mixing device (II) with feeding the aqueous phase of mobilized sludge and feeding device for seawater.

7. Device according to one of the preceding claims, characterized by an additional feeding device for an ammonium-containing wastewater partial stream to the mixing device.

8. The device according to claim 7, characterized in that the ammonium-containing wastewater partial stream is yellow water.

9. Device according to one of the preceding claims, characterized by an additional feeding device for a phosphate-containing wastewater partial stream to a mixing device.

10. The device according to claim 9, characterized in that the phosphate-containing wastewater partial stream is selected from the group comprising waste water from dishwashers and / or washing machines, phosphate-containing industrial wastewater, wastewater from the phosphate processing industry and substantially solids-freed raw sewage.

11. Device according to one of the preceding claims, characterized in that the mixing device is a static mixer and / or a stirred tank reactor.

12. Device according to one of the preceding claims, characterized in that the device for solid-liquid separation of digested sludge in thickened digested sludge and Zentratwasser is a settling tank, a decanter, a filter press or a combination of these.

13. Device according to one of the preceding claims, characterized in that the device for solid-liquid separation of MAP and phosphate-depleted waste water following the mixing device for mixing Zentratwasser and seawater has a fluidized bed reactor whose fluidized bed substantially only of MAP particles is formed.

14. A process for the treatment of wastewater, characterized by the use of a device according to any one of the preceding claims.

15. An apparatus for precipitating magnesium ammonium phosphate (MAP) from wastewater, comprising a feed for seawater and a feed for waste water, characterized in that it comprises a mixing tank for mixing phosphate and ammonium-containing wastewater streams, which are substantially free of solids.

16. The apparatus according to claim 15, characterized in that it comprises a collecting container and / or separate manifolds for supplying the phosphate and ammonium-containing substreams, from which the phosphate and ammonium-containing wastewater streams are fed to the mixing container.

17. The device according to any one of claims 15 or 16, characterized in that the phosphate and ammonium-containing substreams are selected from yellow water, waste water from dishwashers and / or washing machines, phosphate-containing industrial wastewater and wastewater of the phosphate processing industry.

18. A process for the treatment of wastewater, characterized by the use of a device according to one of claims 1 to 17.