DE19717669A1 - Reducing heavy metal content of biogenic organic substrate without combustion - Google Patents

Abstract

Reducing heavy metal content of biogenic-organic substrates (I) comprises electrolysis using special sacrificial anodes. (I) are mixed with >= 0.7 part weight animal excrement with respect to dry organic matter. Process water is added, before or after mixing, so that the dry content is \} 13 wt.%. The mixture is subjected to anaerobic treatment and he fermented residue is electrolysed to deposit the harmful heavy metals at the cathode.

Description

The invention relates to a method for removing heavy metals from biogen organic substrates using methods of electrolysis and use of special sacrificial anodes, as is the case with the recycling of biogen organic raw materials, residues and waste materials is required.

The removal of raw, residual and waste materials from contaminants and contaminants in the course of the indispensable transition to a low-waste circular economy a key issue in waste management. There are several for that responsible objective constraints, one of which is the shortage of available Raw material and fossil fuel resources as well as the increasing cost of that Ecologically safe final storage of waste is of the utmost importance. There have already been many for contaminated inorganic residues and waste materials suitable technical solutions for pollutant removal and recycling developed. That is why they are remarkable, especially in urban areas Recycling rates while the corresponding decline Landfill utilization.

A completely different situation emerges when recycling contaminated materials organic residues and waste.

All thermal procedures in the treatment of contaminated inorganic substrates for the extraction of material in the Leading the economic cycle of traceable products prove to be for Treatment of organic substrates as unsuitable if next to one energetic use also the material recycling is intended. Organic substrates from the farm animal husbandry have, for example, generally striking levels of copper compounds due to the use of hoof care products and zinc compounds as a result the use of galvanized barn installations. For metal removal These substrates in the form of manure, liquid manure and liquid manure have so far been technical Solutions not available, which is why a metal enrichment on the usable areas supplied with these organic fertilizers are accepted got to.  

Another example is the recycling of municipal sewage sludge. The changing levels of heavy metal compounds, especially the Compounds of arsenic, lead, cadmium, chromium, mercury and zinc make it more difficult the material use of these substrates, which in addition to organic and humus-forming components also considerable levels of calcium, potassium, Magnesium, phosphorus and nitrogen compounds as important plant nutrients exhibit. In the absence of suitable technical solutions for the Heavy metal removal is currently being carried out in addition to a thermal treatment Use of the energy content and to reduce landfill use in primarily the final deposit in partially dewatered form. With thermal Treatment of organic substrates containing heavy metals released pollutants either separated from the flue gases or in the solid incineration residues.

So far, usable metal removal results have also been with technical Solutions achieved by planting contaminated organic substrates Enrichment of metal compounds in the plant roots and that Provide subsequent treatment of the root mass.

It is also known that the mobilization of predominantly the organic matrix bound metal compounds the use of highly oxidative mineral acids required to subsequently precipitate the mobilized metals by suitable ones To enable flocculants or precipitants. This kind of procedure is different but in connection with the material use of the organic matrix.

The well-known technical solutions for heavy metal removal from organic substrates have crucial shortcomings. Either they are known solutions simultaneously with the energetic utilization of the organic Substance and the shifting of the problem of removal into the field of accruing flue gases or in the area of solid incineration / charring residues connected or there are time and accepting vegetation processes that take up land. The use of mineral acids, flocculants and neutralizing additives is not only with a considerable cost but also for securing the required procedures, for example for loosening the metal compounds from the organic matrix, for the separation of organic matrix and liquid phase or for the separation of liquid phase and metal-containing precipitate or for the neutralization of the removed products.  

A technical solution for the rational removal of organic substrates from contained heavy metal compounds as a prerequisite for renewed material The use of these substrates in the economic cycle is not yet available.

The object of the invention is therefore to provide a technical solution, which no longer has the shortcomings of the known prior art.

A manageable technical solution for the removal of organic substrates of heavy metals is said to avoid unwanted biological processes if possible with the exclusion of atmospheric oxygen in a closed technical system can be realized. For monitoring and ecological reasons In addition, the insulated metal load should be as concentrated as possible for a subsequent treatment, recovery and / or disposal provided can be.

If possible, the technical solution to be created should include procedural steps be connected, which is also technical and economical for other reasons justify what the effort to apply to apply a solution for heavy metal removal be limited to an acceptable level can.

According to the invention, the task is essentially based on the grounds for protection Features of claim 1 solved.

Then, in a first process step, those of heavy metals depleted biogenic-organic substrates with at least 0.7 parts by weight animal excrement mixed, the mass ratio according to the contents determined on organic dry matter. In a second process step the mixture components before or after mixing process water in one such a ratio added that a dry substance content in the substrate mixture of a maximum of 12.9% by mass is not exceeded. In a third Process step is the feed mixture of biogenic-organic to be depleted Substrates and animal excrement and process water of an anaerobic Undergone treatment. Then the fermented fermentation residue obtained subjected to an electrolytic aftertreatment, in which disturbing heavy metals be deposited cathodically.  

The post-treatment of the digestate is preferably also carried out under anaerobic conditions, in a post-treatment reactor used for this at the same time a sulfur separation from the resulting methane / carbon dioxide mixture, cooling and post-degassing of the digestate are provided can be.

It is possible to anaerobically treat the feed mixture at temperatures between 35 and 55 ° C. In addition, tried and tested Fermentation process in both the mesophilic and thermophilic range apply.

Those fermentation processes in which a Anaerobic treatment of the feed mixture over a period of 200 hours as well for partial flows of the feed mixture is not undercut.

The anaerobic treatment of the feed mixture fulfills several functions. she not only serves to dissolve the rough structure of the anaerobically to be treated organic materials and their effective hygiene, but at the same time the Destruction of the odor-intensive organic substances and the transformation from organic parts of the feed mixture to gaseous methane for Coverage of the required process energy as well as the provision of excess energy is used for external purposes. A essential function of the anaerobic treatment of the feed mixture serves under Avoiding nitrogen losses by reducing dissolved ammonia in the Mixture of uses, in the course of anaerobic treatment a predominantly mineral binding of the nitrogen contained in the feed mixture takes place. It has proven almost impossible in the presence of dissolved ammonia using common electrolysis conditions a cathodic Separation of those deposited predominantly on the organic solid matrix To achieve metal connections.

When the nitrogen contained in the feed mixture is oxidized as completely as possible to NO _x , however, the interfering metal compounds are surprisingly quickly and effectively deposited on the cathode, for which the material iron can be used if necessary.

In a special embodiment, those for electrolytic treatment required anodes be made of magnesium. That way additional magnesium as a welcome plant nutrient in the substrate without to also be subjected to cathodic deposition.  

It is also possible to use iron anodes, the one caused thereby Entry of iron in the organic substrate advantageous for binding the im Mixture of sulfur can be used, what with a Reduction of anaerobic treatment Hydrogen sulfide formation is connected.

Electrolysis at media temperatures has proven to be advantageous between 5 and 65 ° C. It is preferred that for used aftertreatment reactor or an electrolytic treatment upstream cooling vessel sensible heat with the help of the anaerobic Treated feed mixture withdrawn.

It is also possible to add heat energy to the fermented feed mixture feed and thus support the electrolytic metal deposition. The Thermal energy can be applied to the substrate to be electrolytically treated before or during be supplied to the electrolysis.

In a particular embodiment, the thermal energy is supplied to the substrate in a vessel upstream of the electrolysis by means of microwaves with a frequency of approximately 2.45 GHz and with energy densities in the medium to be treated of up to 50 W / dm ³ . Electrochemical metal deposition is already effectively supported if this microwave treatment of the substrate is maintained over a period of 2 minutes. In addition to the highly effective energy input for the purpose of heating the substrate, a marked mobilization of the metal ions attached to the solid matrix is also brought about.

A satisfactory de-loading result is already achieved if the electrolytic treatment for at least 30 minutes is maintained. It becomes relatively solid and dense Deposition of the different metals on the cathodes was observed.

The addition process is in this period by gently stirring the Mixtures effectively supported.

A preferred embodiment variant of the technical solution according to the invention is by the electrolytic treatment of the previously anaerobically treated Use mixture characterized at pH values of more than 7.5.  

In general, a sufficiently large amount of recipe already causes Animal excrement contains the desired pH value in the fermented feed mixture. However, that is also possible Addition of basic additives, preferably those containing plant nutrients basic additives, such as potassium hydroxide solution, quicklime, sintered dolomite or Calcium hydroxide.

It has also proven to be advantageous to subject the fermented feed mixture to an ultrasound treatment known per se with a specific load of at least 5 W / dm ³ before and / or during the electrolysis. In a special way, this procedure leads to a remarkable increase in the amount of metals deposited on the cathode.

According to a preferred embodiment of the invention, an oxidizing agent, for example H ₂ O ₂ and / or ozone, is added to the fermented feed mixture before and / or during the electrolysis.

The addition of these known oxidizing agents effectively promotes the Oxidation of the after the anaerobic treatment in the fermented feed mixture remaining portions of ammoniacal nitrogen and thus relieved the electrolytic deposition of interfering metal connections on the cathode.

As a helpful measure, it has surprisingly been found that the effectiveness of the electrolytic treatment can be significantly improved if the cathode current strength is periodically increased briefly to up to 400 A / m ² . Times between 1 and 7 minutes have been found to be practical for the high-current load, which is to be used periodically at intervals of between 20 and 40 minutes. The resulting increased dissociation of water is accepted as a helpful measure. Since the post-treatment of the fermented feed mixture continues to be carried out under anaerobic conditions, the resulting oxygen is available as an additional oxidizing agent for nitrogen oxidation, while the resulting hydrogen contributes to raising the calorific value of the biogas obtained.

The advantages of the invention are summarized in the fact that now created technical solution for the heavy metal removal of bio gene-organic substrates is available, which in addition to a very rational energetic recycling also the material use of the valuable materials contained of contaminated biogenic-organic substrates.

According to the task, the newly developed solution can be comparatively inexpensive way to combine procedures that bio gen-organic substrates for the purposes of environmentally friendly treatment anyway are preferably subjected.

With comparatively low mechanical, operational and energetic expenditures are created, also with Heavy metal compounds contaminated biogenic organic substrates supply material and energy recovery. That way The recoverable energy potential is considerably higher than the one to be used Process energy.

This ratio improves even further when in an energetic Overall view of those for the magnitude of the accessible Raw material and manufacturing costs that are not required are included will.

The invention will be explained in more detail below with exemplary embodiments. Show in the attached drawing

Fig. 1 is a schematic representation of the most important steps of the process according to the invention;

Fig. 2 shows the process schematic for the embodiment "electrolysis of the cooled fermented substrate";

Fig. 3 shows the process scheme for the variant "electrolysis during the ultrasonic treatment of the heated substrate fermented"

. Figure 4 shows the process diagram for the embodiment "electrolysis during the ultrasonic treatment of the heated by means of microwave treatment fermented substrate";

Figure 5 shows the process diagram for the embodiment "electrolysis after previous addition of potassium hydroxide solution and during the ultrasonic treatment of the heated substrate fermented.";

Fig. 6 shows the process scheme for the variant "electrolysis after previous addition of hydrogen peroxide and during the ultrasonic treatment of the heated substrate fermented".

Embodiments example 1

According to FIG. 1, 5 room parts (RT) of a cattle manure with a dry matter content (TS) of 12% were mixed with 1 RT of a sewage sludge with 31% TS. By adding 1.7 RT of a process water with 1% TS, 7.7 RT of a feed mixture with 12% TS were obtained.

This insert mixture was after a hygienization by heating on a Temperature of 70 ° C and a 30 minute tempering at this level cooled to a temperature of 38 ° C. Then the hygienized Feed mixture subjected to an anaerobic treatment at 37 ° C, the Residence time of the feed mixture under anaerobic conditions on average 35 days scam.

The fermented substrate had 6.3% TS and was immediately subjected to an electrolytic treatment with an energy consumption of 250 Wh / m ³ and a cathode current density of 21.2 A / m ² , using anodes and cathodes made of iron.

After the 80 minute electrolytic treatment was completed, one effective metal removal measured. For example, it was 22% for copper of the initial value and for zinc 13% of the initial value.  

Example 2

Referring to FIG. 2, the fermented under the conditions of Example 1 substrate after cooling to 20 ° C over 120 minutes was subjected to an electrolytic treatment. Anodes and cathodes made of iron were used. With the specific energetic parameters of the electrolysis unchanged from Example 1, the metal removal was 30% for copper and 15% for zinc.

Example 3

Referring to FIG. 3, the fermented under the conditions of example 1 substrate was subjected after heating to 60 ° C over 120 minutes to an electrolytic treatment. During the electrolysis, the substrate was additionally treated with ultrasound at a frequency of 37 kHz, the energy density in the treated substrate being 6 W / dm ³ .

Anodes and cathodes made of iron were used.

With specific energetic parameters unchanged compared to example 1 Electrolysis was 45% for copper and 33% for zinc.

Example 4

According to FIG. 4, the substrate fermented under the conditions of Example 1 was subjected to an electrolytic treatment by means of a preceding brief microwave treatment of 2 minutes by means of microwaves of 2.45 GHz and an energy density of 40 W / dm ³ and heating to 59 ° C. for 120 minutes Undergone treatment. This measure obviously caused an additional increase in the mobility of the metal ions connected to the solid matrix.

Anodes and cathodes made of iron were used.

With specific energetic parameters unchanged compared to example 1 The electrolysis was 62% for copper and 35% for zinc.  

Example 5

According to FIG. 3, the substrate fermented under the conditions of example 1 was subjected to an electrolytic treatment after heating to 55 ° C. for 120 minutes. During the electrolysis, the substrate was additionally treated with ultrasound at a frequency of 37 kHz, the energy density in the treated substrate being 6 W / dm ³ .

Magnesium anodes and iron cathodes were used.

With specific energetic parameters unchanged compared to example 1 Electrolysis was 60% for copper and 39% for zinc.

Example 6

Referring to FIG. 5, the fermented under the conditions of example 1 substrate was subjected after heating to 55 ° C over 120 minutes to an electrolytic treatment.

Before the electrolytic treatment, a 40% potassium hydroxide solution in the ratio of 100 RT substrate to 1 RT potassium hydroxide solution was added to the fermented substrate. During the electrolysis, the substrate was additionally treated with ultrasound at a frequency of 37 kHz, the energy density in the treated substrate being 6 W / dm ³ .

Anodes and cathodes made of iron were used.

With specific energetic parameters unchanged compared to example 1 Electrolysis was 57% for copper and 32% for zinc.

Example 7

Referring to FIG. 6, the fermented under the conditions of example 1 substrate was subjected after heating to 60 ° C over 120 minutes to an electrolytic treatment. Before the electrolytic treatment, hydrogen peroxide was added to the fermented substrate in the ratio of 100 RT substrate to 1 RT hydrogen peroxide. During the electrolysis, the substrate was additionally treated with ultrasound at a frequency of 37 kHz, the energy density in the treated substrate being 6 W / dm ³ .

Anodes and cathodes made of iron were used.  

With specific energetic parameters unchanged compared to example 1 Electrolysis was 53% for copper and 35% for zinc.

Example 8

A biogen-organic feed mixture according to Example 1 is subjected to an electrolytic treatment at a cathode current density of approx. 20 W / m ² for a period of on average 28 days after the anaerobic treatment in a post-treatment reactor with exclusion of air for a period of 120 minutes . The gas space above the biogen-organic substrate is connected to the biogas storage. At intervals of 30 minutes, the cathode current density is pulsed to a value of 400 W / m ² for 2 minutes each. The gas formation at the electrodes causes strong turbulence in the aftertreatment reactor. The molecular oxygen formed obviously leads to the oxidation of the ammoniacally bound nitrogen remaining in the substrate despite the previous anaerobic treatment. This means that deposition rates of more than 65% are achieved for zinc and copper.

Claims (15)

1. A method for heavy metal removal from biogen-organic substrates using methods of electrolysis and the use of special sacrificial anodes, characterized in that
that the biogen-organic substrates to be depleted of heavy metals are mixed with at least 0.7 parts by weight of animal excrement, the mass ratio being determined by the contents of organic dry matter,
that process water is added to the mixture components before or after the mixing in such a ratio that a dry substance content of a maximum of 13% by mass is not exceeded in the substrate mixture,
that the feed mixture of biogenic-organic substrates to be depleted and animal excrement and process water is subjected to an anaerobic treatment,
that the fermented fermentation residue obtained is subjected to an electrolytic aftertreatment in which disruptive heavy metals are deposited cathodically. 2. The method according to claim 1, characterized in that that the anaerobic treatment of the feed mixture at temperatures between 35 and 55 ° C is carried out. 3. The method according to claims 1 and 2, characterized in that the anaerobic treatment of the feed mixture over a period of is maintained for at least 200 hours.   4. The method according to claims 1 to 3, characterized in that iron cathodes are used. 5. The method according to claims 1 to 4, characterized in that magnesium anodes are used. 6. The method according to claims 1 to 4, characterized in that iron anodes are used. 7. The method according to claims 1 to 6, characterized in that electrolysis at media temperatures between 5 and 65 ° C is carried out. 8. The method according to claims 1 to 7, characterized in that the heating of the fermented feed mixture prior to electrolysis is carried out using microwaves mobilizing the metal ions at a frequency of approximately 2.45 GHz and an energy density of up to 50 W / dm ³ becomes. 9. The method according to claims 1 to 8, characterized in that the electrolytic treatment over a period of at least Maintained for 30 minutes. 10. The method according to claims 1 to 9, characterized in that the electrolytic treatment at pH values of more than 7.5 is carried out.   11. The method according to claim 10, characterized in that the fermented fermentation residue to raise the pH of potassium hydroxide is added. 12. The method according to claims 1 to 11, characterized in that the fermented feed mixture is subjected to a known ultrasonic treatment with a specific load of at least 5 W / dm ³ before and / or during the electrolysis. 13. The method according to claims 1 to 12, characterized in that the fermented feed mixture before and / or during the An oxidizing agent is added to electrolysis. 14. The method according to claim 13, characterized in that H ₂ O ₂ and / or ozone are used as the oxidizing agent. 15. The method according to claims 1 to 14, characterized in that the electrolysis is carried out at least temporarily at up to 400 A / m ² increased cathode current density.