EP4291534A1

EP4291534A1 - Method for the combined recycling of phosphate and nitrogen from sewage sludge and optionally biological waste

Info

Publication number: EP4291534A1
Application number: EP22711461.8A
Authority: EP
Inventors: Martin Lebek
Original assignee: Remondis Aqua GmbH and Co KG
Current assignee: Remondis Aqua GmbH and Co KG
Priority date: 2021-02-15
Filing date: 2022-02-15
Publication date: 2023-12-20
Also published as: CA3207915A1; WO2022171252A1; DE112022001097A5; AU2022219144A1; JP2024509713A; US20240116792A1

Abstract

The invention relates to a method for the combined recycling of phosphate and nitrogen from sewage sludge. The core task of the invention consists in the recycling of phosphorus from sewage sludge ash and the reaction of phosphorus with nitrogen from the vapors of the sewage sludge drying and the manure to form the NP fertilizer diammonium phosphate.

Description

Process for the combined recovery of phosphate and nitrogen

Sewage sludge and qeqalso biological waste

subject of the invention

The invention relates to a method for the combined recovery of phosphate and nitrogen from sewage sludge and optionally biological waste such as liquid manure, which comprises an aqueous liquid phase. The core task of the invention is the recovery of phosphorus from sewage sludge ash and the conversion of phosphorus with nitrogen from the vapors of sewage sludge drying and from liquid manure to the NP fertilizer diammonium phosphate.

Background of the Invention

Phosphorus in all its compounds is essential for life. People, animals and plants depend on its availability. However, phosphate is mainly extracted from phosphate-bearing rocks in geogenic deposits (Morocco, China, USA). Germany is 100% dependent on imports. The problem that arises from this is that these deposits are finite and the heavy metal pollution from cadmium and uranium increases with increasing mining depth. For resource and environmental protection reasons, the recycling of phosphorus is an indispensable step.

Since sewage sludge as a resource offers the greatest phosphorus recycling potential, new political and legal framework conditions were created at federal level by amending the Waste Sewage Sludge Ordinance (AbfKlärV). In the future, the recovery of phosphorus in the course of sewage sludge disposal in Germany will be of central importance and will be required by law.

Processes for recovering phosphorus from sewage sludge ash are shown by the applicant's property rights DE 102013018650 B3, DE 102013018652 A1 and DE 102014006 278 B3. The amendment of the Sewage Sludge Ordinance (AbfKlärV) of October 3rd, 2017 aims in particular to return the valuable components of the sewage sludge (phosphorus) more comprehensively than before to the economic cycle and at the same time to significantly restrict the conventional soil-related sewage sludge utilization for the purpose of further reducing the pollutant input into the soil . According to the AbfKlärV, all sewage treatment plant operators are obliged to recycle phosphorus. Agricultural recycling will only be possible to a limited extent in the future.

It would therefore be desirable to dispose of sewage sludge or sewage sludge ash in an economical manner and at the same time to recover the combined valuable phosphate and nitrogen contained therein.

Object of the invention:

The object of the present invention was therefore to provide methods for the combined recovery of phosphate and nitrogen from sewage sludge or sewage sludge ash.

Overview of the invention:

As already stated above, the core task of the invention is the recovery of phosphorus from sewage sludge ash and the conversion of phosphorus with nitrogen from the vapors of sewage sludge drying and from liquid manure to the NP fertilizer diammonium phosphate. The invention offers the enormous advantage that methods are offered here for the first time in which phosphate and nitrogen are combined and recovered from sewage sludge or sewage sludge ash in an integrated process.

The recovery of phosphorus from sewage sludge is a central process component of the invention, as is the recovery of nitrogen from liquid manure, with NH3 being obtained by stripping. This is converted together with the NH3-containing vapors from the KS post-drying with the phosphoric acid obtained to form diammonium phosphate. The patent right DE DE102016 122869 B4 of the applicant shows a method for treating liquid manure. The generation of sewage sludge ash is an integral part of phosphorus recycling based on material and energetic intersections and synergies.

Phosphorus is then extracted from this ash in the form of phosphoric acid. It is the central basic chemical of the phosphorus industry. In addition to phosphoric acid, other secondary raw materials such as gypsum and metal salts (iron, aluminum) are recovered. The recyclables are used in the building materials industry (gypsum) and as precipitants in sewage treatment plants (metal salts). The liming residue left over at the end of the process is used as an aggregate in the building materials industry.

During the post-drying of the sewage sludge to approx. 40% dry matter required for incineration. (dry matter), NFl ₃ -rich vapors are formed, which are condensed and directly reacted with phosphoric acid in a phosphoric acid trickling system. The resulting diammonium phosphate is used locally as an aqueous, approx. 10% solution directly as a fertilizer or is crystallized out by evaporation and cooling and dried and granulated to form a common NP fertilizer.

The liquid manure is used in an integrated overall process. The liquid manure is treated with CO ₂ under pressure in a pressure tank, during which the phosphate contained changes from the solid particulate phase to the liquid phase. After expansion, the solids are separated by centrifugation. The phosphorus and nitrogen contained in the manure are now concentrated in the liquid phase. By alkalising with milk of lime (Ca(OFI) ₂ ) and possibly introducing steam, NFI ₃ is stripped out and phosphorus is precipitated as tricalcium phosphate (apatite). The NFI ₃ is also converted into diammonium phosphate in the (for example Riesler) plant together with the NFI ₃ -rich vapors from the subsequent drying of sewage sludge as described above. The precipitated tricalcium phosphate is thermally treated together with dried KS in the planned sewage sludge incineration plant and then fed into the phosphorus recovery process. At the end of the treatment process, the liquid manure remains, which only contains traces of phosphorus and nitrogen, but is rich in potassium and can be used for irrigation or treated using a purification process in such a way that it can be returned to the water cycle. The dewatered solid phase can be further used in a biogas plant or used directly for soil improvement. Detailed description of the invention:

According to the invention, this object is achieved by methods for the combined recovery of phosphate and nitrogen from (and with treatment of) sewage sludge and optionally biological waste such as liquid manure, which comprises an aqueous liquid phase. In process (1), the combined recovery of phosphate and nitrogen occurs only from sewage sludge. In the combination process (2), the combined recovery of phosphate and nitrogen from sewage sludge is combined with the processing of biological waste, which includes an aqueous liquid phase, these being in particular liquid manure, liquid manure and fermentation residues from biogas plants.

In one aspect (1) of the invention, the invention relates to a method (1) for the combined recovery of phosphate and nitrogen from sewage sludge, comprising the following process steps:

Stage (1 A1): Optional disintegration of sewage sludge; Stage (1A2): drying of the sewage sludge, resulting in vapors rich in NH3 and dried sewage sludge;

Stage (1B1): Optional condensation of the NH3-rich vapors from stage (1A2);

Stage (1 B2): Optional alkalizing of the condensed NH3-rich vapors from stage (1 B1) with release of ammonia [NH3], (preferably using CaO or Ca(OH)2 (milk of lime), optionally in a mixture with NaOH,) and Expulsion of the ammonia [NH3] with heating and/or by applying a reduced pressure and/or with the aid of an air or steam stream (ammonia stripping 1);

stage (1D2): incineration of the dried sewage sludge from stage (1A) to sewage sludge ash;

Stage (1D3): treating the sewage sludge ash from stage (1D2) with phosphoric acid; Step (1D4): separating the acid-insoluble part of the treated sewage sludge ash from step (1D3) so that an acid-insoluble part and a filtrate or supernatant in the form of a phosphoric acid-containing liquid are produced;

Stage (1D5): optionally recycling at least part of the phosphoric acid-containing liquid from stage (1D4) for use in stage (1D3);

Step (1D6): purifying the phosphoric acid-containing liquid from step (1D4) by adding sulfuric acid to the phosphoric acid-containing liquid from step (1D4) so that a calcium sulfate precipitate is recovered and separated, and/or by applying by ion exchange or liquid-liquid extraction, resulting in a purified phosphoric acid-containing liquid;

Step (1D7): optionally concentrating at least part of the purified phosphoric acid-containing liquid from step (1D6) so that phosphoric acid is recovered and separated; and

Stage (1 E): Reaction of the condensed NFh-rich vapors from stage (1 B1) and/or the ammonia [NFI3] obtained in stage (1 B2) with phosphoric acid [FI3PO4] in the form of the phosphoric acid-containing liquid from stage (1 D4), the purified liquid containing phosphoric acid from stage (1D6) and/or the phosphoric acid from stage (1D7) to obtain ammonium phosphate compound, preferably diammonium hydrogen phosphate [(NFU^HPO^ (fertilizer), and optional separation of the ammonium phosphate compound obtained.

Figure 1 (Fig. 1) outlines and illustrates important stages of the process (1), as described above, in an overview.

In another aspect (2) of the invention, the invention relates to a

Combination method (2) for the combined recovery of phosphate and Nitrogen from sewage sludge and biological waste, the biological waste comprising an aqueous liquid phase in which at least urea and ammonium compounds and inorganically and organically bound phosphates are dissolved and/or contained in particulate form, comprising the following process stages:

Stage (2A1): Optional disintegration of the sewage sludge.

Stage (2A2): drying of the sewage sludge, resulting in vapors rich in NH3 and dried sewage sludge;

Stage (2B1): Optional condensing of the NH3-rich vapors from Stage (2A2);

Stage (2B2): Optional alkalising of the condensed NH3-rich vapors from stage (2B1) with the release of ammonia [NH3], and driving out the ammonia [NH3] with heating and/or by applying a reduced pressure and/or with the aid of an air or steam flow (ammonia stripping 2);

Step (2C1): Separating the solids of the biological waste from the liquid phase;

Step (2C1): introducing carbon dioxide gas [CO2] under increased pressure or supercritical carbon dioxide into the liquid phase of the biological waste in order to dissolve particulate-bound phosphates;

Step (2C2): reducing the CC content in the liquid phase from step (2C1) by acidifying the liquid phase and driving off dissolved CO2 and/or CO2 bound as carbonate;

Step (2C4): Alkalizing the liquid phase from step (2C2) or (2C3) under

Release of ammonia [NH3] and expulsion of the ammonia [NH3] with heating and/or by applying a vacuum and/or with the aid of an air or steam stream (ammonia stripping 3); step (2C5): precipitation and separation of calcium phosphate from the liquid phase from step (2C4);

Stage (2D1): admixing the precipitated and separated calcium phosphate from stage (2C5) to the dried sewage sludge from stage (2A);

stage (2D2): incineration of the mixture of precipitated and separated calcium phosphate from stage (2C4) and dried sewage sludge from stage (2A2) to sewage sludge ash;

step (2D3): treating the sludge ash from step (2D2) with phosphoric acid; Step (2D4): separating the acid-insoluble portion of the treated sewage sludge ash from step (2D3) to produce an acid-insoluble portion and a filtrate or supernatant in the form of a phosphoric acid-containing liquid;

Step (2D5): optionally recycling at least part of the phosphoric acid-containing liquid from step (2D4) for use in step (2D3);

Step (2D6): purifying the phosphoric acid-containing liquid from step (2D4) by adding sulfuric acid to the phosphoric acid-containing liquid from step (2D4) so that a calcium sulfate precipitate is recovered and separated, and/or by applying ion exchange or Liquid-liquid extraction, resulting in a purified liquid containing phosphoric acid;

Step (2D7): optionally concentrating at least part of the purified phosphoric acid-containing liquid from step (2D6) so that phosphoric acid is recovered and separated;

Stage (2E): Reacting the condensed NFh-rich vapors from stage (2B1) and/or the ammonia [NFI3] obtained in stage (2B2) and the in Step (2C4) recovered ammonia [NH3] with phosphoric acid [H3PO4] in the form of the phosphoric acid-containing liquid from step (2D4), the purified phosphoric acid-containing liquid from step (2D6) and / or the phosphoric acid from step (2D7) to obtain of ammonium phosphate compound, and optionally separating the recovered ammonium phosphate compound.

Preferred embodiments of aspect (1) and/or aspect (2) are detailed below, it being noted that these can be combined with one another and, for example, particularly preferred embodiments of a stage with at least one other preferred embodiment of a stage or multiple stages can be combined.

In preferred embodiments of aspect (1) of the invention, the method (1) for the combined recovery of phosphate and nitrogen from sewage sludge, the sewage sludge ash in step (1D2) is exclusively ash obtained by incineration of the originally used sewage sludge from steps (1A1) and (1A2) arise. These are phosphate-containing sewage sludges. In an embodiment of aspect (1) of the invention, the method (1) for the combined recovery of phosphate and nitrogen from sewage sludge, the sewage sludge ash in step (1 D2) may also have other phosphate-containing ash added, for example any ash produced by incineration of phosphate-containing Sewage sludge, biodegradable waste, biowaste and/or animal waste is obtained in a waste incinerator. The sewage sludge ash resulting from the incineration of the sewage sludge (used in stages (1A1) and (1A2)) in stage (1D2) has a phosphate content (measured in P2O5) of > 3% by weight, of > 5% by weight , of > 7% by weight, of > 10% by weight, of > 15% by weight or of > 20% by weight (whereby a phosphate content (measured in P2O5) of > 40% by weight or > 35% by weight is rare is), or a phosphorus content (P) of > 1% by weight, > 2% by weight, > 3% by weight, > 5% by weight, > 8% by weight or > 10% by weight. % (a phosphate content (measured in P) of > 15% or > 14% by weight being rare).

In preferred embodiments of aspect (2) of the invention, the combination process (2) for the combined recovery of phosphate and Nitrogen both from sewage sludge and from biological waste, the biological waste is preferably liquid manure, liquid manure and/or leftovers from biogas plants. In preferred embodiments of aspect (2) of the invention, the combination process (2) for the combined recovery of phosphate and nitrogen from both sewage sludge and biological waste, the sewage sludge ash in step (2D2) is exclusively ash produced by incineration of the sewage sludge originally used Stages (2A1) and (2A2) arise. These are phosphate-containing sewage sludges. In one embodiment, other phosphate-containing ash may also be added to the sludge ash in step (2D2), for example any ash obtained by incineration of phosphate-containing sewage sludge, biodegradable waste, biowaste and/or animal waste in a waste incinerator. In principle, the sewage sludge ash can then also contain other (phosphate-containing) ash, for example ash obtained by incinerating phosphate-containing sewage sludge, biodegradable waste, biowaste and/or animal waste in a waste incineration plant. The sewage sludge ash resulting from the incineration of the sewage sludge (used in stages (2A1) and (2A2)) in stage (2D2) has a phosphate content (measured in P2O5) of > 3% by weight, of > 5% by weight, > 7% by weight, > 10% by weight, > 15% by weight or > 20% by weight (whereby a phosphate content (measured in P2O5) of > 40% by weight or > 35% by weight is rare ), or a phosphorus content (P) of > 1% by weight, > 2% by weight, > 3% by weight, > 5% by weight, > 8% by weight or > 10% by weight (whereby a phosphate content (measured in P) of >15 wt% or >14 wt% is rare). In preferred embodiments of aspect (2) of the invention, the combination process (2), flan contained in the biological waste with an aqueous liquid phase is hydrolyzed in the liquid phase by adding the enzyme urease to obtain ammonia and/or ammonium.

In preferred embodiments, step (1A1) or (2A1), the disintegration of the sewage sludge is carried out before step (1A2) or (2A2), step (1A1) or (2A1) preferably being carried out by mechanical treatment (e.g. using a ball mill), by treatment using ultrasound and/or at elevated pressure and temperature becomes. This disintegration increases the ammonia yield in the vapors formed as a result of the drying in stage (1A2) or (2A2).

In preferred embodiments of stage (1A2) or (2A2), the sewage sludge is dried at elevated temperatures and/or the NH3-rich vapors produced by the drying are collected directly at the drying site. Usually (mechanically) dewatered sewage sludge has, in particular, about 25% DM (dry matter, wt. %). For incineration it is necessary to dry the sewage sludge to approx. 40% DM (dry mass, wt.%). This takes place in this stage, for example belt dryers or fluidized bed dryers can be used and temperatures of 40°C to 95°C or 50°C to 80°C, or 60°C to 70°C can be used, for example.

In preferred embodiments of stage (1B1) or (2B1), the condensation of the NH3-rich vapors from stage (1A2) or (2A2) is carried out, preferably directly at the drying site. The stage can be omitted if the vapors are already liquid.

In preferred embodiments of optional stage (1 B2) or (2B2) this is

Alkalizing the condensed NH3-rich vapors from stage (1B1) or (2B1) is not optionally carried out, but follows stage (1B1) or (2B1). In preferred embodiments of stage (1B2) or (2B2), the condensed NH3-rich vapors from stage (1B1) or (2B1) are alkalized by adding NaOH, optionally with further addition of CaO or Ca(OH)2 ( Lime milk), in particular optionally with the further addition of Ca(OH) 2 (lime milk). In preferred embodiments of step (1B2) or (2B2), the removal of the ammonia [NH3] (ammonia stripping 1 or 2) is carried out with heating. In preferred embodiments of stage (1B2) or (2B2), the ammonia [NH3] is driven off (ammonia stripping 1 or 2) by applying a reduced pressure. In preferred embodiments of step (1B2) or (2B2) this will Expulsion of the ammonia [NH3] (ammonia stripping 1 or 2) carried out with the aid of an air or steam stream. In preferred embodiments of step (1B2) or (2B2), the stripping of the ammonia [NH3] (ammonia stripping 1 or 2) is carried out with heating and with the aid of an air or steam stream. The release and stripping of the ammonia in the liquid phase in stage (1B2) or (2B2) of the process according to the invention, the so-called ammonia stripping, is known in principle. It is carried out according to the invention by making the liquid phase alkaline, for example using CaO or Ca(OH) 2 (lime milk), optionally in a mixture with NaOH, and driving out the gaseous ammonia with heating and/or by applying a reduced pressure and/or with the aid of an air or steam flow. The liquid phase can be alkalized up to a pH of 9 to 14, preferably 10 to 13, particularly preferably 11 to 12. The gaseous ammonia driven off can be absorbed in mineral acid or water (ammonia water).

In preferred embodiments, in step (2C1) the separation of

Solids (if any; for example plant residues or straw etc.) of the biological waste are separated from the liquid phase by mechanical separation. This can be done, for example, by sieving, using a rake, by sedimentation, filtration, centrifugation or a combination of these methods. Alternatively or additionally, the starting material can also be made to flow by mechanically crushing the coarse solids, for example by chopping, grinding or a comparable suitable method. The separation is preferably carried out by centrifugation. In one embodiment step (1C1) or (2C1) separating the solids of the biological waste from the liquid phase is carried out after step (2C2).

In preferred embodiments of step (2C2), the initiation of

Carbon dioxide gas [CO ₂ ] under elevated pressure or from supercritical Carbon dioxide is carried into the liquid phase of the biological waste in a pressure vessel. The aim is to bring particle-bound phosphates into solution. A method for obtaining phosphates from sewage sludge products by introducing carbon dioxide gas (CO 2 ) under elevated pressure or supercritical carbon dioxide into the liquid phase is known from DE 102009020745, which is incorporated herein by reference. The process described therein can be used accordingly in step (2C2) of the process according to the invention in order to bring particulate-bound phosphates into solution according to the invention.

In preferred embodiments of stage (2C3), the CO2 content in the liquid phase from stage (2C2) is reduced by acidifying the liquid phase using inorganic acids. This enables dissolved CO2 and/or CO2 bound as carbonate to be expelled from the liquid phase. Increasing the pH value by making it alkaline with NH ₃ and/or CaO or Ca(OH) 2 in the step (2C4) for the ammonia stripping (3) was not only what was desired due to the high CO 2 content in the liquid phase Calcium phosphate, but also a high proportion of unwanted calcium carbonate and precipitate. Before the liquid phase is made alkaline for the ammonia stripping in the subsequent stage (2C4), the CO ₂ content in the liquid phase is reduced according to the invention by acidifying the liquid phase and driving out dissolved CO 2 and/or CO 2 bound as carbonate. Acidification is preferably carried out with phosphoric acid. The expulsion of the CO2 can advantageously be accelerated by increasing the temperature and/or by stirring or otherwise moving the reaction mixture.

In preferred embodiments of step (2C4), basifying the

Liquid phase from stage (2C3) carried out by adding NaOH, if appropriate with further addition of CaO or Ca(OH) 2 (milk of lime), in particular if necessary with further addition of Ca(OH) 2 (milk of lime). In preferred embodiments of stage (2C4), the ammonia [NH3] is driven off (ammonia stripping 3) with heating. In preferred embodiments of stage (2C4), the ammonia [NH3] is driven off (ammonia stripping 3) by applying a reduced pressure. In preferred embodiments of stage (2C4), the ammonia [NH3] is driven off (ammonia stripping 3) with the aid of a stream of air or steam. In preferred embodiments of stage (2C4), the ammonia [NH3] is driven off (ammonia stripping) with heating and with the aid of a stream of air or steam (ammonia stripping 3). The release and expulsion of the ammonia in the liquid phase in stage (2C4) of the process according to the invention, the so-called ammonia stripping, is known in principle. It is carried out according to the invention by making the liquid phase alkaline, for example using CaO or Ca(OH) 2 (lime milk), optionally in a mixture with NaOH, and driving out the gaseous ammonia with heating and/or by applying a reduced pressure and/or with the aid of a stream of air or steam . The liquid phase can be alkalized up to a pH of 9 to 14, preferably 10 to 13, particularly preferably 11 to 12. The gaseous ammonia driven off can be absorbed in mineral acid or water (ammonia water).

In preferred embodiments of stage (2C5), the precipitation and separation of calcium phosphate from the liquid phase from stage (2C4), the calcium phosphate is preferably in the form of tricalcium phosphate [Ca3(PÜ4)2] or hydroxyapatite [Cas(P0 ₄ ) ₃ (0H)]. Here, however, calcium phosphate includes Ca ₃ (P0 ₄ ) 2 ), CaHPO 4 , Ca ₅ (P0 ₄ ) 3 (0H) and Ca(H ₂ P0 ₄ ) 2 . In preferred embodiments of step (2C5), the removal of calcium phosphate from the liquid phase is carried out by means of filtration, centrifugation, sedimentation or a combination of the aforementioned methods. In preferred embodiments of stage (2D1), the precipitated and separated calcium phosphate from stage (2C5) is admixed to the dried sewage sludge from stage (2A), it being possible to use various mixing methods. The aim of this admixture is to eliminate the organic residues usually accompanying the calcium phosphate from step (2C5) by the subsequent combustion in step (2D2).

In preferred embodiments of stage (2D2), the mixture of precipitated and separated calcium phosphate from stage (2C4) and dried sewage sludge from stage (2A2) is incinerated to form sewage sludge ash, with the organic residues attached to the calcium phosphate from stage (2C4) also being removed be burned. In preferred embodiments of stage (2D2), the mixture of precipitated and separated calcium phosphate from stage (2C4) and dried sewage sludge from stage (2A2) is incinerated to sewage sludge ash in a waste incinerator at 600° to 1,200° C., preferably at 800° to 900°C.

In preferred embodiments of stage (1D2), the dried sewage sludge from stage (1A2) is incinerated to form sewage sludge ash, the organic residues in particular being incinerated. In preferred embodiments of stage (1D2), the incineration of sewage sludge from stage (1A2) to sewage sludge ash takes place in a waste incineration plant at 600° to 1,200°C, preferably at 800° to 900°C.

In preferred embodiments of stage (1 D3) or (2D3) is the

Sewage sludge ash from step (1D2) or (2D2) treated with phosphoric acid. Preferably, this treatment is carried out for a period of less than 5 minutes, or less than 2 minutes, or between 5 minutes and 45 minutes, or from 2 to 300 minutes, preferably from 10 to 60 minutes, or from 2 to 20 minutes and preferably this treatment is carried out at temperature of above 40°C or above 50°C or from 20°C to 90°C, preferably from 60 to 80°C or from 20 to 80°C or from 25 to 50°C. The acid is preferably present in a concentration of 5% to 50% by weight, preferably 10% to 30% by weight (in aqueous dilution) and/or the sewage sludge ash is treated with the acid in a reactor and/or the proportion of sewage sludge ash is 5% by weight to 50% by weight, preferably 20% by weight to 30% by weight or 25% by weight to 35% by weight, based on the acid. The treatment of the sewage sludge ash from stage (1D2) or (2D2) with phosphoric acid is particularly preferably carried out for a period of less than 2 minutes or from 2 to 20 minutes, at a temperature of from 20 to 80° C. or from 25 to 50° C. the acid is present in a concentration of 10% to 30% by weight (in aqueous dilution) and the proportion of sewage sludge ash is 20% to 30% by weight or 25% to 35% by weight on the acid. Particularly preferably, the treatment of the sewage sludge ash from stage (1D2) or (2D2) with phosphoric acid takes place for a period of 2 to 20 minutes at a temperature of 25 to 50° C., the acid is in a concentration of 10% by weight to 30% by weight (in aqueous dilution) and the proportion of sewage sludge ash is 25% by weight to 35% by weight, based on the acid.

In preferred embodiments of stage (2D4), the acid-insoluble part of the treated sewage sludge ash from stage (1D3) or (2D3) is separated, resulting in an acid-insoluble part and a filtrate or supernatant in the form of a liquid containing phosphoric acid. In preferred embodiments of the invention, the acid-insoluble portion of the treated sewage sludge ash from step (1D3) or (2D3) is separated by mechanical filtration and/or dewatering processes. In preferred embodiments of the invention, the acid-insoluble part of the treated sewage sludge ash from stage (1D3) or (2D3) is separated off with dewatering units (e.g. vacuum belt filter, chamber filter press, membrane filter press, belt filter press, centrifuge). In preferred embodiments of the invention, the acid-insoluble part of the treated sewage sludge ash from stage (1D3) or (2D3) is separated off with a vacuum belt filter. In preferred embodiments of the invention, after separation of the acid-insoluble part of the treated sewage sludge ash from stage (1D3) or (2D3), the residue is washed with water in the filter units and the washing water is returned to stage (1D3) or (2D3).

In preferred embodiments of stage (1D5) or (2D5), at least part of the phosphoric acid-containing liquid from stage (1D4) or (2D4) is recycled for use in stage (1D3) or (2D3). Preferably at least 10% of the phosphoric acid-containing liquid from step (1D4) or (2D4) is recycled for use in step (1D3) or (2D3), more preferably at least 20%, even more preferably 20% to 80%, and most preferably 40% to 60% based on the total amount of phosphoric acid-containing liquid obtained from step (1D4) or (2D4). In preferred embodiments of stage (1D5) or (2D5), this stage is carried out after stage (1D6) or after stage (2D6) and before stage (1D7) or (2D7).

In preferred embodiments of stage (1D6) or (2D6), the phosphoric acid-containing liquid from stage (1D4) or (2D4) is purified by adding sulfuric acid to the phosphoric acid-containing liquid from stage (1D4) or (2D4), see above that a calcium sulfate precipitate is recovered and separated. This can be followed - but only in a preferred embodiment - by applying ion exchange or liquid-liquid extraction, with the ion exchange (in particular using ion exchange resins and regeneration with mineral acids - is preferred. In any case, a purified liquid containing phosphoric acid is produced.

With regard to purification by adding sulfuric acid to the phosphoric acid-containing liquid from stage (1D4) or (2D4), the sulfuric acid is preferably added in a stirred reactor. It is also preferred that the sulfuric acid is added in a dilution of 10 to 98% by weight, preferably 40 to 80% by weight, preferably in a stirred reactor, with the sulfuric acid preferably being added in a molar ratio that of the dissolved calcium - Concentration of 0.5 Ca to 1.5 SO4, preferably 1.0 Ca to 1.0 SO4. The residence time in the stirred reactor after addition of the sulfuric acid is 5 to 60 minutes, preferably 10 to 30 minutes, and/or the reaction temperature (precipitation of calcium sulfate after addition of sulfuric acid) in the stirred reactor is 20° to 90° C., preferably 60° to 90° C It is further preferred that the calcium sulphate precipitate is recovered and separated using a mechanical filtration and/or dewatering process. The calcium sulphate precipitate is preferably separated using dewatering units (e.g. vacuum belt filter, chamber filter press, membrane filter press, belt filter press, centrifuge). The calcium sulphate precipitate is particularly preferably separated off using a vacuum belt filter. Preferably, after the calcium sulphate precipitate has been separated off, the residue in the filter units is washed with water and the washing water is recycled for use in stage (1D3) or (2D3).

In preferred embodiments of stage (1D7) or (2D7), at least part of the purified phosphoric acid-containing liquid from stage (1D6) or (2D6) is concentrated so that phosphoric acid is recovered and separated, this preferably being done by evaporation.

In preferred embodiments of stage (2E), the ammonia [NH3] obtained in stage (2B2) and/or the ammonia [NH3] obtained in stage (2C4) are combined with phosphoric acid [FI3PO4] in the form of the phosphoric acid containing liquid from step (2D4), the purified phosphoric acid-containing liquid from step (2D6) and / or the phosphoric acid from step (2D7) reacted, wherein ammonium phosphate compound is obtained. Preferably, the ammonium phosphate compound is di-ammonium hydrogen phosphate [(NFI 4 ) 2 FIPO 4 ] (fertilizer). The resulting diammonium phosphate can be used locally as an aqueous, approx. 10% solution directly as a fertilizer or crystallized out by evaporation and cooling and dried and granulated to form a common NP fertilizer, with the optional separation of the ammonium phosphate compound obtained. The phosphoric acid is preferably added in the form of the phosphoric acid-containing liquid from stage (1D4) or the purified phosphoric acid-containing liquid from stage (1D6). The phosphoric acid is preferably added in the form of the phosphoric acid-containing liquid from step (1D4). The phosphoric acid is preferably added in the form of the purified phosphoric acid-containing liquid from step (1D6), in particular after the precipitation of calcium sulphate precipitate CaSO 4 . Preferably, the phosphoric acid is used at a concentration of 10-15%. The phosphoric acid [FI3PO4] can also be used in a concentration of 40-89% by weight, or in a concentration of 50-75% by weight. The ammonia is preferably used in the form of ammonia water. Preferably, the ammonia is used at a concentration of about 25%. The ammonia is preferably used in the form of ammonia water with a concentration of about 25%. The ammonia is preferably reacted with the phosphoric acid in a trickle (phosphoric acid trickle). In a preferred embodiment, in stage (2E) the ammonia obtained in stage (2B2) and in stage (2C4) is reacted with phosphoric acid.

The phosphoric acid is preferably used in the form of the purified phosphoric acid-containing liquid from step (2D6) and/or the phosphoric acid from step (2D7). In preferred embodiments of stage (1 E), the ammonia [NH3] obtained in stage (1 B2) is combined with phosphoric acid [H3P04] in the form of the liquid containing phosphoric acid from stage (1 D4), the purified liquid containing phosphoric acid from stage (1 D6 ) and/or the phosphoric acid from step (1 D7) to give an ammonium phosphate compound. Preferably, the ammonium phosphate compound is di-ammonium hydrogen phosphate [(NFI 4 ) 2 FIPO 4 ] (fertilizer). The resulting diammonium phosphate can be used locally as an aqueous, approx. 10% solution directly as a fertilizer or crystallized out by evaporation and cooling and dried and granulated to form a common NP fertilizer, with the optional separation of the ammonium phosphate compound obtained. The phosphoric acid is preferably added in the form of the phosphoric acid-containing liquid from stage (1D4) or the purified phosphoric acid-containing liquid from stage (1D6). The phosphoric acid is preferably added in the form of the phosphoric acid-containing liquid from step (1D4). The phosphoric acid is preferably added in the form of the purified phosphoric acid-containing liquid from step (1D6), in particular after the precipitation of calcium sulphate precipitate CaSO 4 . Preferably, the phosphoric acid is used at a concentration of 10-15%. The phosphoric acid [FI3PO4] can also be used in a concentration of 40-89% by weight, or in a concentration of 50-75% by weight. The ammonia is preferably used in the form of ammonia water. Preferably, the ammonia is used at a concentration of about 25%. The ammonia is preferably used in the form of ammonia water with a concentration of about 25%. The ammonia is preferably reacted with the phosphoric acid in a trickle (phosphoric acid trickle). In a preferred embodiment, the ammonia obtained in stage (1B2) is reacted with phosphoric acid in stage (1E). The phosphoric acid is preferably used in the form of the purified phosphoric acid-containing liquid from stage (1D6) and/or the phosphoric acid from stage (1D7). Definitions:

The term “calcium phosphate” within the meaning of the invention includes Ca ₃ (PC> ₄ ) ₂ ), CaHPO 4 , Ca ₅ (P0 ₄ ) 3 (OH) and Ca(H ₂ P0 ₄ ) 2 .

The term "ash" for the purpose of the invention refers to any solid residue from the combustion of organic material. In the context of this invention, it is in particular the solid residue from the incineration of sewage sludge. In principle, however, it can also be the solid residue from the incineration of biodegradable waste, biowaste and/or animal waste, slaughterhouse waste, eg animal meal. Ash mainly consists of oxides and (bi)carbonates of various metals, e.g. B. Al2O3, CaO, Fe ₂ 03, MgO, MnO, P ₂ Os, P ₄ Oio, K ₂ 0, Si0 ₂ , Na ₂ CO3, NaHCO3, etc.

The term "phosphate-containing ash" as used herein refers to ash as defined herein containing at least one phosphate as defined herein.

The term “phosphate” within the meaning of the invention refers on the one hand to P ₂ Os and P ₄ Oio. Furthermore, the term “phosphates” relates to the salts and esters of orthophosphoric acid (H ₃ PO ₄ ), and expressly also includes the condensates (polymers) of orthophosphoric acid and their esters. In particular, the term "phosphates" refers to metallic salts of phosphoric acid having the general formula X(Y)m(P0 ₄ )n, where X, and optionally Y, is a metal selected from the group consisting of aluminum, beryllium, bismuth, lead, Cadmium, Chromium, Iron, Gallium, Indium, Potassium, Cobalt, Copper, Magnesium, Manganese, Molybdenum, Sodium, Nickel, Osmium, Palladium, Rhodium, Ruthenium, Strontium, Titanium, Vanadium, Tungsten, Zinc, Tin.

The term "precipitate" in the context of the invention refers to the separation of a dissolved substance as a solid from a solution, usually triggered by the addition of suitable substances (precipitating agents). In particular, the term includes any fully or partially insoluble precipitate in the form of flakes, droplets or crystalline material, in any microcrystalline, crystalline or amorphous form. Of the The term “precipitate” expressly includes any further processing, modification, refining, etc., of the precipitates obtained in the process according to the invention to form powders, powders, dust, bulk material, granular materials, semolina, etc.

The term "waste incinerators" within the meaning of the invention refers to all systems, facilities and the like that are suitable for incinerating the atmospherically combustible fractions of any type of waste.

The term "sewage sludge" within the meaning of the invention refers to any suspension of finely divided particles of a solid substance in a liquid. The sewage sludge can be in the form of primary sludge, raw sludge, excess sludge, treated and/or stabilized sewage sludge (aerobic/anaerobic). In particular/preferably it is (mechanically) dewatered sewage sludge and/or in particular/preferably sewage sludge with 15% to 30% dry matter, in particular approx. 25% (DM, dry matter).

In a preferred embodiment, the liquid in which the particles are suspended is a waste water as defined herein.

The term "waste water" within the meaning of the invention refers to all liquids of an aqueous nature and/or organic nature, or mixtures thereof, which are not of drinking water quality within the meaning of the Drinking Water Ordinance (TrinkwV) and/or national and/or international drinking water standards (e.g. the DIN 2000 in Germany). The term waste water also includes all waste water according to § 54 paragraph 1 of the Water Resources Act (WHIG).

In a preferred embodiment, the wastewater within the meaning of the invention is water that has been contaminated through use or whose properties or composition have changed. Furthermore, the term "wastewater" within the meaning of the invention includes the water whose properties have changed as a result of domestic, commercial, agricultural or other use and the water that runs off together with it in dry weather (dirty water) as well as that collected from precipitation from the area of built-up or paved areas run-off water (rainwater). Liquids discharged and collected from waste treatment, storage and disposal facilities are also considered to be foul water. Wastewater is domestic waste water from toilets (faecal or black water), sanitary facilities, kitchens and washing machines (washing or gray water) as well as waste water from companies that discharge into the public sewage system (commercial or industrial waste water). Heated water from cooling systems also counts as waste water. Waste water that occurs in the most varied of cleaning and treatment techniques of water treatment plants belongs to the waste water within the meaning of the invention.

Claims

patent claims

1. Process (1) for the combined recovery of phosphate and nitrogen from sewage sludge, comprising the following process steps:

Stage (1A1): Optional disintegration of sewage sludge;

Stage (1A2): drying of the sewage sludge, resulting in vapors rich in NH3 and dried sewage sludge;

Stage (1B1): Optional condensation of the NH3-rich vapors from stage (1A2);

Stage (1 B2): Optional alkalizing of the condensed NH3-rich vapors from stage (1 B1) with release of ammonia [NH3], and expulsion of the ammonia [NH3] with heating and/or by applying a reduced pressure and/or with the aid of a air or steam flow (ammonia stripping 1);

stage (1D2): incineration of the dried sewage sludge from stage (1A2) to sewage sludge ash;

Stage (1D3): treating the sewage sludge ash from stage (1D2) with phosphoric acid;

Step (1D4): separating the acid-insoluble part of the treated sewage sludge ash from step (1D3) so that an acid-insoluble part and a filtrate or supernatant in the form of a phosphoric acid-containing liquid are produced;

Step (1D6): purifying the phosphoric acid-containing liquid from step (1D4) by adding sulfuric acid to the phosphoric acid-containing liquid step (1 D4) such that a calcium sulphate precipitate is recovered and separated and/or by applying ion exchange or liquid-liquid extraction, resulting in a purified phosphoric acid-containing liquid;

Stage (1 E): Reaction of the condensed NFh-rich vapors from stage (1 B1) and/or the ammonia [NFI3] obtained in stage (1 B2) with phosphoric acid [FI3PO4] in the form of the phosphoric acid-containing liquid from stage (1 D4), the purified liquid containing phosphoric acid from stage (1D6) and/or the phosphoric acid from stage (1D7) to obtain ammonium phosphate compound and optionally separating off the ammonium phosphate compound obtained.

2. Combination process (2) for the combined recovery of phosphate and nitrogen from sewage sludge and biological waste, the biological waste comprising an aqueous liquid phase in which at least flan and ammonium compounds as well as inorganically and organically bound phosphates are dissolved and/or contained in particulate form, comprising the following process steps:

Stage (2A1): Optional disintegration of sewage sludge;

Stage (2A2): drying of the sewage sludge, resulting in NFI3-rich vapors and dried sewage sludge;

Stage (2B1): Optionally condensing the NFh-rich vapors from Stage (2A2);

Stage (2B2): Optional alkalizing of the condensed NFI3-rich vapors from stage (2B1) with release of ammonia [NFI3], and driving out the Ammonia [NH3] with heating and/or by applying a vacuum and/or with the aid of an air or steam stream (ammonia stripping 2);

Step (2C1): optionally separating the solids of the biological waste from the liquid phase;

Step (2C2): introducing carbon dioxide gas [CO2] under increased pressure or supercritical carbon dioxide into the liquid phase of the biological waste in order to dissolve particulate-bound phosphates;

Step (2C3): reducing the CC content in the liquid phase from step (2C2) by acidifying the liquid phase and driving off dissolved CO2 and/or CO2 bound as carbonate;

Step (2C4): Alkalizing the liquid phase from step (2C3) with the release of

Ammonia [NH3] and expulsion of the ammonia [NH3] with heating and/or by applying a vacuum and/or with the aid of an air or steam stream (ammonia stripping 3);

step (2C5): precipitation and separation of calcium phosphate from the liquid phase from step (2C4);

Stage (2D2): Combustion of the mixture of precipitated and separated calcium

phosphate from step (2C4) and dried sludge from step (2A) to sludge ash;

Stage (2E): Reacting the condensed NH3-rich vapors from stage (2B1) and/or the ammonia [NH3] obtained in stage (2B2) and the ammonia [NH3] obtained in stage (2C4) with phosphoric acid [H3PO ₄ ] in the form of the phosphoric acid-containing liquid from stage (2D4), the purified phosphoric acid-containing liquid from stage (2D6) and/or the phosphoric acid from stage (2D7) to obtain ammonium phosphate compound, and optionally separating off the ammonium phosphate compound.

3. Process (1) according to claim 1 or combination process (2) according to claim 2, wherein step (1D5) or (2D5), the recycling of the phosphoric acid-containing liquid from step (1D4) or (2D4) for use in stage (1D3) or (2D3), preferably wherein at least 10% of the phosphoric acid-containing liquid from stage (1D4) or (2D4) is recycled for use in stage (1D3) or (2D3), especially preferably at least 20%, more preferably 20% to 80%, and most preferably 40% to 60%, based on the total amount of the phosphoric acid-containing liquid obtained from step (1D4) or (2D4).

4. Process (1) according to claim 1 or 3 or combination process (2) according to claim 2 or 3, wherein step (1A1) or (2A1), the disintegration of the sewage sludge is carried out before step (1A2) or (2A2). , preferably by mechanical treatment, for example using a ball mill, by treatment using ultrasound and / or at elevated pressure and temperature.

5. Process (1) according to any one of claims 1, 3 or 4 or combination process (2) according to any one of claims 2 to 4, wherein stage (1B2) or (2B2), the alkalizing of the condensed NH3-rich vapors from stage (1B1) or (2B1) is carried out, preferably by means of addition of NaOH, optionally with further addition of CaO or Ca(OH)2 (lime milk), and/or with the aid of an air or steam stream.

6. Process (1) according to any one of claims 1 and 3 to 5 or combination process (2) according to any one of claims 2 to 5, wherein step (1D7) or (2D7), the concentration of at least part of the purified phosphoric acid-containing liquid from step (2D6) so that phosphoric acid is recovered and separated, preferably by evaporation.

7. Process (1) according to any one of claims 1 and 3 to 6 or combination process (2) according to any one of claims 2 to 6, wherein step (1D6) or (2D6), the purification of the phosphoric acid-containing liquid from step ( 1D4) or (2D4) by adding sulfuric acid so that a calcium sulfate precipitate is recovered and separated and a purified liquid containing phosphoric acid is produced.

8. Process (1) or combination process (2) according to claim 7, wherein in stage (1D6) or (2D6), the purification of the phosphoric acid-containing liquid from stage (1D4) or (2D4) by adding sulfuric acid, followed by further purification by using ion exchange or liquid-liquid extraction, particularly preferably by ion exchange.

9. Process (1) according to any one of claims 1 and 3 to 8 or combination process (2) according to any one of claims 2 to 8, wherein in stage (1E) the ammonia obtained in stage (1B2) is reacted with phosphoric acid or in Stage (2E) the ammonia obtained in stage (2B2) and in stage (2C4) is reacted with phosphoric acid, the phosphoric acid preferably being in the form of the purified liquid containing phosphoric acid from stage (1D6) or (2D6) and/or the phosphoric acid from step (1D7) or (2D7) is used.

10. Combination method (2) according to any one of claims 2 to 9, wherein step (2C1), the separation of the solids of the biological waste from the liquid phase, is carried out before step (2C2), preferably by centrifugation.