EP3371120A1 - Granular pelletized glass material with trace elements, especially as growth support for selective nutrient supply of microorganisms - Google Patents

Abstract

A pelletized expanded glass material is provided, which is particularly suitable as a growth support for microorganisms, especially for use in a biogas plant or an anaerobic sewage treatment plant. The production process of the invention for the pelletized expanded glass material comprises the steps of: mixing ground glass, expanding agent and binder to give a starting mixture; pelletizing the starting mixture to give ground glass pellet green bodies; foaming the ground glass pellet green bodies to give expanded glass pellet particles at temperatures of 600 to 950°C. According to the invention, especially in the production of the starting mixture, minerals and or trace elements are added, which serve especially for the nutrient supply of microorganisms used in the biogas plant or the anaerobic sewage treatment plant.

Description

 description

 Expanded glass granules with trace elements, in particular as growth carrier for targeted nutrient supply of microorganisms

The invention relates to a process for producing expanded glass granules, in particular for use in a biogas plant or an anaerobic sewage treatment plant. The invention furthermore relates to expanded glass granules, in particular for use in a biogas plant or an anaerobic sewage treatment plant.

Today's power generation system is based on the use of fossil energy. The energy sources used are sometimes exposed to strong price increases resulting from a foreseeable shortage of resources. Moreover, as fossil fuels are the main cause of the anthropogenic greenhouse effect, more efforts have been made in recent years to reduce their share of final energy consumption.

At the European level, an agreement was reached on an "integral climate protection strategy" in December 2008. By 2020, a reduction in CO ₂ emissions of at least 20% based on the value of 1990 is to be achieved [KIENBERGER Th: 2010].

One of the most promising approaches is the use of biomass and the resulting potential production of biogas. Since their energy / thermal use generates just as much C0 ₂ as was previously recorded during growth, they are considered to be "CO ₂ -neutral", which means that climate-neutral use can ideally be achieved. In Germany at the beginning of 2012 there were approximately 6,900 plants in which biogas is produced by fermentation of biomass. The conversion of biomass into biogas achieves the highest energy yield per hectare cultivated area.

Compared to BtL second-generation fuels, which will only become commercially available in a few years, biogas or bio-methane produced from biomass can already be used today in all natural gas vehicles without any technical modifications. Biogas or biomethane can be emitted in corresponding engines with very high efficiencies. The range of a biogas-fueled passenger car is approximately 67,600 km per hectare of cultivated area.

In a biogas plant, there is basically the problem that those microorganisms that metabolize biomass to biogas typically have very low growth rates, which is associated with a low conversion rate of biomass to biogas. In order nevertheless to ensure an acceptable conversion rate in a biogas plant by means of a comparatively high concentration of microorganisms, biogas plants frequently employ growth carriers on which the microorganisms settle as biofilms and are thus immobilized. For the retention of the immobilized microorganisms in the reaction space of the biogas plant, for example, a magnetic expanded glass granules is used as a growth medium. Such a magnetic blown glass developed by the applicant is known from DE 10 2010 039 232 B4 of the Applicant.

The invention has for its object to provide a Blähglasgranulat, which is particularly suitable as a growth medium for microorganisms, in particular for use in a biogas plant or an anaerobic sewage treatment plant.

With regard to a method for producing the expanded glass granules, the object is achieved according to the invention by the features of claim 1. With respect to the expanded glass granules, the object is achieved according to the invention by the features of claim 8. Advantageous and partly inventive in itself. tions and further developments of the invention are set forth in the subclaims and the description below.

The process according to the invention for producing expanded glass granules, which is intended in particular for use in a biogas plant or an anaerobic sewage treatment plant, comprises the following process steps:

Mixing glass flour, blowing agent and binder to a starting mixture,

 Granulating the starting mixture into expanded glass granules green bodies, and

Foaming the expanded glass granulate green bodies into expanded glass granules

Particles at temperatures of 600 ° C to 950 ° C.

According to the invention, minerals and / or trace elements are added in the preparation of the expanded glass granules, and in particular in the preparation of the aforementioned starting mixture, which serve in particular for the nutrient supply of microorganisms used in the biogas plant or the anaerobic sewage treatment plant.

The expanded glass granulate according to the invention, which is used in particular for use in a biogas plant or an anaerobic sewage treatment plant, is correspondingly produced from glass flour, a blowing agent and a binder, wherein the expanded glass granules are characterized by an addition of minerals and / or trace elements. The glass powder used is preferably a soda lime silicate glass powder, and the binder used is preferably an alkali silicate water glass.

As minerals (also referred to as "macronutrients") are here and below referred to such substances that are taken by living things, specifically microorganisms, especially of the microorganisms used in the biogas plant and the anaerobic wastewater treatment plant, and metabolized for life and growth , Preferably, but not by way of limitation, carbon, nitrogen, phosphorus, sulfur, sodium, calcium, magnesium and / or iron are added as minerals in the manufacture of the expanded glass granules.

Trace elements (also referred to as "micronutrients") are those substances which are necessary for living beings, again in particular for the microorganisms used in the biogas plant or the anaerobic sewage treatment plant, and in mass fractions of less than 50 mg / kg in the organism Preferably, but again not limiting, trace elements based on cobalt, manganese, molybdenum, nickel, selenium, tungsten and / or zinc are added in the preparation of the expanded glass granules.

In experiments, in view of the nature and advantages of the expanded glass granules according to the invention (and in particular with regard to their use as growth carriers for microorganisms), the following findings have been obtained:

The expanded glass granules according to the invention are in principle suitable as carriers of biogas and methane-forming biofilms.

 • Fermentation processes with growth carriers according to the invention always proved to be superior in comparison with control processes without growth carrier with regard to the stability of the biogas process.

 Expediently, the growth carriers are broken before use in a fermenter / bioreactor and sieved to a defined grain size. The resulting irregular surface texture results in biofilm formation, i. the settlement of microorganisms, very contrary.

 • The development of adherent biofilm mass is largely determined by the nature of the growth carrier and the residence time in the fermenter.

 • The colonization of microorganisms on the surfaces of the

Growth carrier is very selective - the proportion of methanogenic organisms is significantly higher than in the surrounding fermentation fluid or inoculum. • The melting of trace elements and minerals in the expanded glass granulate or in the growth media increases the biogas yield compared to the yield obtained with the aid of conventional growth media.

 • Under the conditions in a biogas fermenter / bioreactor, the trace elements and mineral substances go into solution over a long period of time.

 • The growth carriers bring a significant buffer capacity into the system and thus counteract any process disturbances caused by overacidification.

 • At the surface of the growth media, an apparently optimal "micro-environment" is formed for the biofilms, which allows the archaea (i.e., the methane gas producing microorganisms) to survive even in an acidified environment.

In a preferred process variant, a ground soda lime silicate glass, in particular with a weight fraction of 60 to 70%, is used as glass flour.

The binder used is preferably an alkali-silicate-water glass, in particular with a weight fraction of 15 to 25% added. Advantageously, it is possible when using alkali silicate-water glass as a binder with appropriate temperature control and residence time during the sintering process to achieve a desired ratio between the necessary resistance and desired solubility targeted.

It has proved to be advantageous to additionally introduce minerals and / or trace elements into the starting mixture by the blowing agent, in particular by using one or more blowing agents of the following substances: dextrose, sodium nitrate, potassium nitrate, sodium carbonate, potassium carbonate, calcium carbonate and dolomite. For additional mineral supply of the microorganisms, in particular with calcium, magnesium and / or iron, a release agent in the form of calcium carbonate, dolomite and / or bentonite is added to the expanded glass granules green bodies before foaming in a preferred embodiment.

Preferably, several of the following minerals and trace elements are used with appropriate proportions by weight:

Sodium selenite pentahydrate 0.02000-0.04000%

 Nickel (II) chloride hexahydrate 0.00010 - 0.00030%

 Disodium molybdate 0.00010 - 0.00030%

 Borax 0.00010 - 0.00030%

 Zinc Sulphate Heptahydrate 0,00010 - 0,00020%

 Cobalt (II) chloride hexahydrate 0.00100 - 0.00200%

 Copper (I) chloride 0.00010 - 0.00030%

 Potassium permanganate 0,00020 - 0,00040%

The expanded glass granulate according to the invention, or its granulate particles, in particular have particle sizes which are less than 2.5 mm, preferably between 0.25 and 1.5 mm.

The expanded glass granulate according to the invention is used in particular as a growth carrier for microorganisms in a bioreactor, in particular in a biogas plant or an anaerobic sewage treatment plant.

Embodiments of the invention will be explained in more detail with reference to a drawing. Show:

Fig. 1 is a diagram of the anaerobic degradation of organic substance, changed to Weiland / P. Weiland, 2001 /,

2 shows the cofactor F430 of methyl coenzyme M reductase,

3 schematically shows the supply and the availability of micronutrients in a biogas fermenter, Fig. 4 shows a PCR-SSCP analysis of samples from a mesophilic

 Biogas fermenter / LfL /,

 FIG. 5 is a diagram of feeding quantity and gas development in a screening experiment with different growth carriers, FIG.

6 shows a diagram of the basic composition and possible variations for adjusting the chemical resistance in an alkali-earth-alkali borosilicate glass,

 7 shows a (glass) syringe as a miniature experimental fermenter for carrying out colonization experiments on different growth carriers,

8 shows a bogie for supporting a plurality of syringes according to FIG.

 7,

 9 is a bar graph showing the time evolution of the concentration of the dry biofilm in colonization experiments with different growth carriers,

 10 is a bar chart showing the time evolution of

 Microorganism population in colonization experiments with different crops,

 Fig. 1 1 in a bar chart, the temporal evolution of

 Microorganism group (BAC and ARC), ARC and their percentage of the total population in colonization trials with different crops, and

 FIG. 12 again shows in a bar chart the concentration of the dry biofilm and the biogas yield in colonization experiments with different growth carriers.

Corresponding parts and steps are always provided in all figures with the same reference numerals.

1. Background information relevant to the invention

To explain the invention, some microbiological, biochemical and procedural aspects relating to the invention will first be listed below. 1.1 The biogas process

Basics of biogas formation

 The anaerobic conversion of biomass and thus the extraction of the renewable energy source methane is one of the currently most efficient processes for the production of regenerative energy sources from biomass / SRU, 2007 /.

Based on the energy generated by photosynthesis, macromolecules are synthesized by the plants as metabolic power. Stoichiometrically, these macromolecules can be converted into methane and carbon dioxide at very high efficiency in anaerobic digestion in biogas plants.

This transformation is shown schematically in FIG.

The decomposition of organic matter (ie biomass 1, for example, polysaccharides, proteins, lipids) under exclusion of air is always initiated by the so-called. Primary fermentation 2 (marked in Fig. 1 as gray box). The fermentation itself is a microbial conversion process for the purpose of energy production. However, neither oxygen nor any other external electron acceptor (eg N0 ₃ ^" ) is included in this energy metabolism.

The primary fermenters secrete exo-enzymes, which dissolve the complex macromolecules of the starting materials by breaking down the hydrogen bonds with the simultaneous incorporation of water. This step is called hydrolysis 3 and allows the microorganisms to take up and convert the formed monomers 4 and dimers, respectively.

The individual building blocks (monomers 4) taken up by the primary digesters are converted by the microorganisms into building blocks 5, namely organic acids, alcohols and carbon dioxide (FIG. 1, 2nd step), the acidogenesis 6.

In the third conversion step, acetogenesis 7, the secondary fermentation 8 converts the acids and alcohols formed to acetic acid (acetate 9), hydrogen and carbon dioxide. The fourth conversion step, methanogenesis 10, occurs only under severe exclusion of air (indicated as anaerobic respiration 1 in Figure 1). In this stage, the methanogenic microorganisms from acetic acid or from hydrogen and carbon dioxide form the methane and carbon dioxide contained in the biogas 12.

While the direct conversion of acetic acid into methane and carbon dioxide is a simple disproportionation, the formation of methane from carbon dioxide and hydrogen is biochemically an anaerobic respiration process. This refers to the oxidation of organic compounds in the absence of air, in which, in place of oxygen, oxidized organic or inorganic compounds act as electron acceptor / Klocke et al., 2009 /.

1.2. Bioreactor / fermenter

 Bioreactors, often referred to as fermenters, are containers in which certain microorganisms, cells or small plants are cultured (fermented) under optimal conditions.

Important factors controllable or controllable in most bioreactors are the composition of the nutrient medium (nutrient solution or substrate), the oxygen supply or tightness against the ingress of oxygen, temperature, pH, sterility and others. The purpose of cultivating in a bioreactor may be to recover the cells or constituents of the cells or recover metabolic products. The degradation of chemical compounds can take place in bioreactors, such. B. in wastewater treatment in sewage treatment plants.

In bioreactors a wide variety of organisms are cultivated for different purposes. Therefore, several reactor variants are available in different designs. Typical are stirred tank reactors made of metal, but also strong distinctive variants, such. As fixed bed reactors, photobioreactors, etc. are used.

Bioreactors are used in various areas of the process industry, such as:

Wastewater treatment plants, with biological process stages. In the activated sludge process, an aerobic step first takes place, in which dissolved compounds of microorganisms are bound in the form of the biomass formed.

Another process-biological step is anaerobic wastewater treatment, which at very high COD load serves to remove harmful or interfering organic carbon compounds through microbiological degradation processes that take place without the presence of oxygen (anaerobic). Here, bacteria gain the energy required for their metabolism from the conversion of organic carbon compounds to organic acids and subsequently mainly to methane, carbon dioxide, hydrocarbon.

In the anaerobic system, only about 0.1 kg of sludge dry matter is formed from 1 kg COD load, the remaining carbon is converted to about 90% in methane, C0 ₂ and H ₂ 0.

The Aerobsystem converts 1 kg COD load into approx. 0.5 kg sludge dry substance formed, approx. 50% is converted to C0 ₂ and H ₂ 0.

The biomass produced from the activated sludge process (aerobic system) can be passed through an anaerobic process step in an additional fermenter

(Digestion tower), are converted to methane-rich sewage gas.

biogas plants

The biomass 1 used is degraded in an anaerobic process with several steps (hydrolysis 3, Acidogenese 6, acetogenesis 7 and methanogenesis 10) to biogas 12 and digestate (see Fig. 1). The containers are hermetically sealed and usually have a stirrer. To operate biogas reactors It is important to know which biological and procedural conditions prevail in the fermenter and what their nutrient status is. However, at most plants only a few parameters are measurable, such as pH and gas quality. Frequently, information on methane or carbon dioxide levels in the gas is missing. Often the operators control their plants on the basis of experience.

Breweries and wineries

Also in the brewery or the winery bioreactors are needed, but here z. B. be referred to as Gärbottiche. The microorganisms used here are yeasts that convert the sugar from the mash or the grape juice into alcohol and carbon dioxide (CO ₂ ).

Pharmaceutical and cosmetics industry

 The most valuable products made in bioreactors are medical-pharmacological products such as the erythropoietin (EPO) known as doping agent or modern insulins.

 The biological activity of microorganisms in bioreactors is determined by their metabolism. The better the microorganisms convert organic substances, the higher the process-biological yields are. If the process parameters in the reactor are not optimal or lack nutrients, the biological activity of the microorganisms decreases.

1.3. Growth rates of microorganisms

Microorganisms can multiply at different rates. Their specific metabolic activity and thus the turnover of the substrate depend strongly on favorable environmental conditions, the presence of competitors / predators and on the energy that the reaction provides them. The denser the population and the higher the substrate availability, the faster substrate conversion takes place - but only within certain limits, as other factors can have a limiting effect. The growth of the hydrolytic and acidogenic microorganisms, as far as has been tested so far, on average faster than that of syntrophic bacteria and methanogenic archaea. The syntenes and methanogens thus usually represent the bottleneck of biogas production. They are the "weakest" link in the biocenosis according to which the overall process must be directed.

When starting up a fermenter, it is therefore useful to increase the substrate addition slowly and to provide a relatively long residence time to allow all members of the biogas biocenosis sufficient time to build an efficient population density. If too much substrate is added at once, especially the hydrolytic / acidogenic microorganisms grow and the resulting acids can not be completely converted to biogas. This results in a drop in the pH in the fermenter result.

Since methanogenic archees are more sensitive to acids than hydrolytic / acidogenic bacteria, the proportion of organic acids in the fermenter increases more and more and can lead to a crash if the load on the room is not significantly reduced or the feeding is suspended. Suspension of feeding lowers acid formation and, if timely, results in recovery of the process. A supporting measure may be an increase in the pH by addition of basic substances (for example sodium bicarbonate, lime, quick lime / hydrated lime).

For the same reasons, sudden changes in operation particularly affect the syntrophes and methanogens. These take the longest to adapt to the new conditions. The consequence is usually an acidification as described above.

Accordingly, care should be taken, for example, when changing the substrate or changing the operating temperature. If the operation was stable before the change, the space load with the new substrate should initially be low and the residence time should be kept high. This gives the weak links enough time to build an effective, adapted to the new conditions population with sufficient density. Once this newly synthesized biocenosis has stabilized (typically after about 20 days), the space load can be slowly increased. If the space load increases too fast, the syntrophic / methanogenic association can not regrow fast enough. Another approach is to ensure that the concentration of syntrophic

Methanogenic organisms process technology is kept artificially high, for example via fermentation residue recycling or immobilization.

For example, for maize silage and optimal trace element supply, the limit is 6 - 10 kg oTS / (m ^{3 *} d).

1.4 Minerals and trace elements

Definition of terms and meaning

 Minerals are essential inorganic nutrients that the organism can not produce itself; they have to be fed to him with food. Since the minerals are usually in the form of inorganic compounds, they are unlike some vitamins, insensitive to most cooking methods. For example, they can not be destroyed by heat or air. For the human, animal and plant organisms, minerals are important inorganic compounds. They do not serve to provide energy, but act as building and active substance and thus take over important regulatory functions in the organism. "They are involved as catalysts in the metabolism, indispensable for the regulation the pH, [...], for the creation of buffer systems, [...] or the promotion of enzyme systems "Hernes et al., 20051.

Minerals are taken up by plants through the roots of the soil and incorporated into their biomass. They can not be burned and therefore remain as unburned residue in the ash. This property can be used for the determination of the mineral content in the plant material or in the

Fermenterschlamm be used. Of the total of 92 different natural elements, 40-50 can be detected in plants. However, only 16 are indispensable for the plant. These nutrients are therefore also referred to as essential nutrients.

The minerals in an organism are divided into two dimensions, concentration or function.

Concentration: Elements in relatively high concentrations in the organism - over 50 mg per kg of body weight - are referred to as quantity or macroelements (minerals). Elements with less than 50 mg per kg body weight are called trace elements or microelements / Entrup et al., 20081. For a number of trace elements, it is still unclear whether they are a random component of the organism or whether they actually have a physiological function.

Function: According to their function in the organism, a distinction is made between building materials (minerals) and regulators (trace elements).

A comparison made by the University of Hohenheim of numerous biogas plants with similar technology, almost identical substrates and the same operating mode showed that above all the maximum achievable volume-specific performance of the plants varied widely.

In individual biogas plants, process disturbances already occurred as soon as the (on organic dry substance related) Faulraumbelastung on over 2 kg per cubic meter and day (oTS = 2 kg / (m ^{3 *} d)) was increased. In other biogas plants, however, could easily be more than twice as high

Faulraumbelastungen of partly over 5 kg / (m ^{3 *} d) (oTS) realize.

In the biogas laboratory of the University of Hohenheim conducted studies on "less efficient" fermentation substrates from practice facilities showed that the limited capacity of the fermenter biology on their "malnutrition" By adding previously lacking trace elements, the productivity of the bacteria was significantly increased, so that significantly more biomass could be converted to methane with unchanged fermentation volume during the same period.

Macronutrients / Minerals

 The microorganisms involved in the biogas process require different minerals for their metabolism and for building up their cell substance. The required amounts are species-specific. "The dry matter of microorganisms consists of about 50% carbon, 1 1% nitrogen, 2% phosphorus and 1% sulfur".

From this it can be deduced that carbon is the most important nutrient, followed by nitrogen, phosphorus and various sulfur compounds

I bishop sberger et al., 20051.

Carbon is the main constituent of microorganisms after water. The carbon source used is essentially the supplied substrate.

Nitrogen is the most needed nutrient after carbon. It is needed in particular for protein biosynthesis, ie for the formation of enzymes that carry out the reactions in the metabolism. Excessively high nitrogen contents in the substrate can, however, lead to an inhibition of the microbial activity in the fermenter.

Phosphorus is involved in the formation of the energy carriers ATP (adenosine triphosphate) and NADP (nicotinamide adenine dinucleotide phosphate) in the metabolism of microorganisms. Lack of phosphate therefore leads to the reduction of the metabolism.

Sulfur is part of the amino acids cysteine and histidine and thus essential for the formation of important enzymes in the metabolism. Other sulfur compounds also play a crucial role in the metabolic cycle, eg FeS complexes as redox partners in electron transport.

Sodium is important for (some) archaea, since the energy carrier ATP is not only generated by the power of "proton pumps" but also by "Na ⁺ pumps" / Deppenmeier et al., 1999 /. In the case of undersupply of Na ⁺ , the energy metabolism of the methanogens and thus the

Break down methanogenesis in biogas production. This may already be the case when 50 mg Na ⁺ / g TS are fallen short of.

In the area of mineral substances, C, N, P, S and Na ⁺ as well as calcium, magnesium and iron fulfill important functions in the metabolism. Calcium and magnesium are important structural elements eg for enzymes.

Eisen takes over three important tasks in the biogas process. On the one hand, iron is a binding element in the sulfide precipitation. As iron binds to sulfur, iron sulfide can precipitate, reducing sulfide toxicity in the fermenter.

On the other hand, iron in the microbial metabolism serves as a reaction partner.

Methanogenic bacteria require a transport system to reduce CO ² to CH ⁴ . By reducing Fe ³⁺ to Fe ²⁺ , iron first acts as an electron acceptor. As a result, Fe ²⁺ can be used later as an electron donor and thus as an energy carrier. Finally, iron is also part of many enzymes.

Basically, not only the amount of a nutrient counts, but also the optimal ratio of all nutrients to each other in order to obtain optimal process conditions. For this purpose, a C / N / P ratio of approximately between 100: 5: 1 and 200: 5: 1 was recommended / Effenberger et al., 2007 /. Micronutrients / trace elements

 Micronutrients are also referred to as trace elements due to their low concentration in the biomass. Trace elements enter the soil through physical and chemical rock weathering. Consequently, the trace element content in the soil varies depending on the source rock, climate and the impact of planting or management.

Plants need trace elements to survive. They extract these substances from the soil, but these are only a few grams per hectare. The micronutrient content in plant biomass is correspondingly low.

A sufficient presence and availability of some trace elements is vital for microorganisms. Methanogenic archees require the elements cobalt (Co), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), tungsten (W) and zinc (Zn).

Cobalt serves primarily as a central atom in Korrinoiden and vitamin B12 enzymes. Cobalt can be incorporated in three different forms as a central ion: as Co ³⁺ , Co ²⁺ or Co ⁺ . Cobalt-containing enzymes are present in both the methanogenic and the acetogenic bacteria.

Manganese (Mn) has similar properties or functions to anaerobic organisms as iron. By reducing Mn ⁴⁺ to Mn ²⁺ and Fe ³⁺ to Fe ^2+, they use these micronutrients as oxidizing agents. Later oxidation reactions can in turn provide electrons for further reactions.

Nickel is a kind of universal element in the biogas process because it is involved in the construction of many different enzymes. For example, a nickel-centered atom occurs in urease, hydrogenase, the cofactor F430 and many other enzymes. Urease causes the hydrolysis of urea. The released ammonia serves many microorganisms as nitrogen source.

Hydrogenase catalyzes the oxidation-reduction reaction of hydrogen and plays an essential role.

The cofactor F430 (see Figure 2) is indispensable for the final step of methane formation. This cofactor has a nickel central atom.

Molybdenum (Mo) and tungsten (W) have similar chemical properties and perform similar tasks during anaerobic conversion. Thus, they usually catalyze the oxidation and reduction reactions of C0 ₂ . Research has also shown that molybdenum can in some cases be replaced by tungsten. Molybdenum is thus the only known example in which a central atom of one enzyme can be replaced by another, without losing the enzyme-specific effect / Bertram et al, 19941.

Selenium is especially useful for building proteins such as Selenocysteine or selenomethionine of importance. Some methanogenic archaea require the selenium-containing proteins to oxidize hydrogen. Inadequate selenium concentration can therefore also be a growth-limiting factor for these archaee / Chasteen, Bentley, 20031.

The importance of other elements (e.g., copper, aluminum, vanadium and boron) for biogas production is still unclear. However, the heavy metals copper, silver, lead, mercury, cadmium, gold and arsenic are typically toxic.

In all trace elements, the concentration in which the elements are present and their availability to the microorganisms is crucial / Ch. Bauer, M. Lebuhn, A. Gronauer; 2009 /. For each component, there is both a kind of minimum and a maximum concentration, with their respective Under- or exceeding the microbial metabolic process is restricted or inhibited / Bischofsberger et al., 20051.

If the trace elements are present in too low concentrations, among other things, the enzymes and coenzymes required for the metabolism can no longer be sufficiently formed. As a result, the performance of the methanogenic microorganisms decreases. The primary fermentation, d. H. the formation of the longer-chain carboxylic acids and alcohols is not affected. As a result, the metabolic products formed in these upstream process steps accumulate - above all the propionic acid.

Studies show that the nutrient contents in biogas plants vary widely. The fermentation substrate analyzes of over 700 different biogas plants show that the contents of individual elements can vary between the lowest and the highest values by a factor of 200 (Table

1 )-

Table 1: Mineral content in the fermentation substrate of biogas plants, data from 700 analyzes / Lindorfer, 2009 /

If a trace element deficiency is detected in the fermentation substrate of a fermenter and this is compensated individually by the addition of technical mineral mixtures, usually within a few days a clear process stabilization with concomitant acid degradation takes place and the digester space load can be increased again or further. Minerals and trace elements in the biogas fermenter

 Building on the findings from the ongoing experiments, the supply of the methane-forming biocenosis with nutrients and trace elements is increasingly becoming the focus of attention. Until about 5 years ago, there was a general lack of knowledge about the exact requirements in practice. Effenberger M., Lebuhn M., Gronauer A; 2007 /. Since then, much has been researched, published and patented by IHaun, 2008, Hölker, 2010, Agraferm, 2009 /. The necessary quantum of individual elements is e.g. for enzyme metabolism only one of the many factors of biogas yield

A variety of different suppliers for so-called "standard trace element mixtures" is already on the market.The diverse range and its correct dosage are difficult for the plant operator manageable.However, it is important for operators of biogas plants, however, that "much more "does not bring much more. On the contrary, an overdose can have an inhibitory or toxic effect on the biocenosis. Quite apart from the effects on the digestate quality and the bioavailability in the soil, which leads to conflicts e.g. with the Fertilizer Ordinance. This should be taken into account increasingly in the future.

Trace elements and other heavy metals enter the biogas fermenter through the added substrate, via equipment erosion and through process aids in bound, biologically often unavailable form (FIG. 3). By physical (e.g., temperature, friction, comminution), chemical (e.g., pH), and biological (e.g., microbial degradation) processes, these are dissolved and thereby become microbially available.

(Fig. 3 (1)). As acidic conditions promote their solubility, they are increasingly converted to sparingly soluble compounds at higher pH in the presence of free phosphate, sulfide, sulfate, and / or carbonate. They are thus initially deprived of direct access by microorganisms (2). However, some microorganisms can "capture" unavailable trace elements via chelating agents and make them usable (3). After this The death of microorganisms releases trace elements in bound and dissolved form (4) and can be reused in the internal circulation of nutrients. The discharge of trace elements takes place with the fermenter content and the biomass into the fermentation residue storage (5). In the case of a recirculation of the fermentation residue, the entrained trace elements and heavy metals are again available for the microorganisms in the fermenter (6).

In biogas plants, there is the danger of trace element shortage situations, especially in mono-renewable operation, but there are also such reports in systems with slurry additive. A typical consequence of trace element deficiency is the inhibition of methanogenesis and associated acidification.

In suitably simulated experiments with maize mono operation only hydrogenotrophic but no acetociastic methanogens could be detected in the acidified fermenters / Lebuhn et ai, 2008b /. The space load before the acidification was relatively low, which is why the presence of acetociastic methanogens was expected but not found. Apparently, hydrogenotrophic methanogens are less sensitive to a trace element deficiency with acidification than acetoclastic methanogens.

According to investigations / Lebuhn and Gronauer, 2009 /, a content of about 50 g Co / L (about 750 g Co / kg DM) seems to be a reasonable size for stable operation of a NawaRo plant. For selenium, the corresponding concentrations are about 5 times lower (about 10 g Se / L, or about 150 g Se / kg TS), for Mo but about a factor of 10 and for Ni about 40 times higher.

FIG. 4 shows the activating effect of the trace element additive for the methanogenic archae. It shows a PCR-SSCP analysis of various samples from a mesophilic maize silage fed only

Experimental fermenter of the Institute of Agricultural Engineering and Animal Husbandry of the LfL. A part of the DNA of the key enzyme of methanogenesis (mcrA / mrtÄ) was multiplied and separated. The resulting bands are therefore exclusive attributable to methanogenic archaea. Significant changes in banding patterns were found, depending on the mode of operation and the state of the methanogenic population. For example, the diversity and number of methanogens decreased during acidification of the fermentor. On the other hand, during the recovery caused by the addition of trace elements, new bands emerged, representing the growth of certain methanogenic archaea.

2. expanded glass granules as growth carrier for microorganisms

2.1 Preliminary tests with modified and new material types

Carrying out the preliminary tests

 In order to create a uniform environment, a screening test was carried out in the PORAVER Technikum / Klimaraum. For this purpose, 10 experimental fermenters, which were essentially formed by closed plastic containers, were constructed with the appropriate environment and charged with the material types listed below.

Type 1 round spray grain

 Type 2 broken grain

 Type 3 broken grain with xanthan coating

 Type 4 broken grain with xanthan gum / nutrient solution coating

 Type 5 broken grain with 3rd coating (version Südchemie)

 Type 6 broken grain with zeolite coating

 Type 7 reducing melted grain

 Type 8 dolomite as blowing agent

 Type 9 iron oxide granules (pure / unbeaten)

 Type 10 magnetic PORAVER (magnetic separator before loading)

 Table 2: Material types for further experiments at DP

Up to the number 6 are modifications to the test grain used already at the ATB. With the same recipe, only the manufacturing switched to the mixed granulation and broken the grain. The respective coatings were applied subsequently.

Materials 7 and 8 are newly developed materials with altered chemical properties.

Types 9 and 10 served to secure the evidence of the effectiveness of the inventive growth medium.

To prepare the culture broth, inoculum from the experimental set-up at the ATB, rumen contents from the slaughterhouse Nuremberg and glass breakage from the glass pile of the PORAVER production were used. The glass breakage was added because it has long been known that a storage of the recycled recycled glass for several months causes composting and thereby organic impurities and buildup are broken down. Since anaerobic conditions certainly prevail inside the glass pile, it was assumed that a biocenosis develops in this environment, which should be well adapted to a glass substrate.

By continuous monitoring and measurement of the pH values, the FOS / TAC values and the gas formation rate of the individual fermenters, differences in the behavior of individual fermenters could be detected very quickly (FIG. 5).

Evaluation of the results of the preliminary tests

 Phase contrast microscopy studies to determine colonization density gave very encouraging results in some types of experiments. Due to poor representability, the results are not shown here.

Although the type 1 (but with prewashed surface) already in use at the ATB Potsdam was already in use at a much faster rate than in the preliminary project, it did significantly worse in terms of population and gas formation than any other variant in the test. This result It can be concluded that a smooth surface for physical reasons precludes a good colonization, although chemically the same environmental conditions exist as with the other material types.

In the iron-oxide granulate type 9 fermenter, hyperacidity occurred even at low volume and in the shortest possible time, leading to premature excretion of this type from the test series.

Magnetic PORAVER, type 10 is due to the very slow and inadequate colonization due to its smooth surface texture only conditionally as a growth medium.

The beneficial influence of a coating with xanthan (material types 3 and 4) on the colonization of the growth carrier was to be expected. This approach is well known in biotechnology and can be considered as prior art.

Of particular interest, however, were the results for type 4. In this variant, a very rapid and intensive colonization with above-average biogas formation was observed. This evidently proves the beneficial effect of nutrients on the vitality of the fermenter biocenosis.

As the trial progressed, however, the difference with the other types of broken grains became smaller and smaller and after a few weeks was no longer detectable. It can be deduced from this that the doping of the surface coating with nutrients during colonization has a positive effect. The supply of trace elements caused the microorganisms quite obviously prefer to settle in this environment and to react with increased metabolic activity. However, as an organic compound, xanthan gum is dissolved or degraded during the metabolic processes in the fermenter in a very short time.

If there is no coating left, then, as with the other ma- only the glass surface and its interaction with the colonizing microorganisms are crucial for further use.

The Bruchkorn type 2 as well as the material from the reducing smelted series, type 7, in which instead of the γ-Fe ₂ 0 ₃ the cheaper and better to be processed magnetite had been used, showed after slower start a very intensive bacterial colonization. In particular, methanogenic archae of the species Methanosarcina were detectable.

With dolomite as the blowing agent, type 8, a very strong and dense colonization with microorganisms developed after a delay at the beginning of the test period.

The initial difficulties in colonization are due to the fact that in the calcined dolomite (reactions see Section 2.2.3.) On the surface of the granules first the high pH value of 12.6 had to be reduced. This high alkalinity is due to the reaction of calcined dolomite when introduced into aqueous solution. After the high pH was buffered by the organic acids from the substrate, the organisms found appropriate environmental conditions, which caused them to colonize.

From the comparison with the other types of material in terms of population density and gas formation rate can be derived that in the presence of calcium and magnesium in slightly soluble form apparently the colonization of the growth medium is promoted.

The influence of unreacted calcium / magnesium carbonate as a buffer for pH stabilization in the substrate remains to be investigated.

In summary, it can be stated:

1 . Lime-soda-silicate glasses are well suited as a growth substrate for the immobilization of the fermenter biocenosis. 2. Broken grain is preferably colonized, since shearing and stripping of the biofilms by movement (agitators) is prevented due to the structurally rich surface.

 3. Chemical and physical properties of the glass seem to affect the vitality of the biocenoses.

 4. The application of minerals and / or trace elements during the swelling process and / or their admixture in the formulation show positive effects. The minerals or trace elements may be present in the form of oxides, carbonates and hydrates.

 5. Coatings with organic substrates have a positive influence, but are only necessary if a very fast colonization is desired.

2.2 Further developed expanded glass granules as growth carrier

2.2.1 Glass as the basis of the substrate material

 Alkali-alkaline earth silicate glasses are the oldest man-made glass type. These include the flat glass (window glass) melted in large quantities and packaging glass.

Borosilicate glasses are very chemical and temperature resistant glasses, which are mainly used for glassware in the laboratory, chemical engineering and in the household. The good chemical resistance to water, many chemicals and pharmaceutical products (hydrolytic class 1) is explained by the boron content of these glasses.

If glasses are exposed to an aqueous medium, the near-surface alkalis and alkaline earths first dissolve. Through this process, the structure is weakened and the network-forming SiO ₂ is also dissolved. The soluble oxides or their reaction products are, with the exception of SiO ₂ , in the list of minerals and trace elements (Section 1 .4) again. However, the typical utility glasses are classified as very stable in their chemical resistance (hydrolytic class 1 or 2). The expected dissolved amount of Na, K, Ca and Mg ions is so low that under normal conditions a sufficient and targeted nutrient supply of the microorganisms can not be assumed.

As shown by way of example in FIG. 6, it is fundamentally possible to melt a glass with a higher solubility (hydrolytic class 3) by changing the glass batch / mixture. The strongest influence on the chemical resistance is achieved by an increase of the alkali parts (Na ₂ 0, K ₂ 0). But also by the increase of the alkaline earth metal parts (CaO, MgO), however only in the glass technological given limits, a clear effect can be achieved.

However, this approach would presuppose that a separate glass would have to be melted for the start-ups. For the intended application, this prohibits for economic reasons. However, if an application in the area of food technology is envisaged in the course of further development, it will not be possible, for reasons of product safety and traceability, to use a specially produced glass.

2.2.2 Water glass to control the solubility

The green body used to produce the expanded glass granules is composed essentially of glass powder, iron oxide and water glass. The addition of different amounts of water glass provides a very good opportunity to set the chemical resistance of the entire system in aqueous media targeted and greatly reduced compared to the base glass. If an alkali silicate glass (water glass) is added to the ground basic glass (soda-lime glass), this, in addition to lowering the sintering temperature, depending on the amount added, also leads to a reduction in the chemical resistance. Due to its composition of only two components - the network former Si0 ₂ and a network converter (flux), in this case Na ₂ O, water glass is chemically unstable, especially at high alkali parts. With appropriate temperature control and residence time during the sintering process prevents the homogenization (oxide balance) between the base glass (glass flour) and the water glass. Thus, it is possible to achieve a desired relationship between necessary resistance (mechanical and chemical) and aimed solubility.

2.2.3 Release agents as additional minerals suppliers

 The use of a release agent is necessary in order to prevent the sticking together of the granules under the effect of heat during the swelling process. It is an inert material, which should be selected so that no or only very little interaction with the glass granules occur at the respective process conditions. Most are substances of mineral origin such. Sand, alumina, different carbonates but also high firing clays in the form of powders and flours.

In order to dope the growth carrier with the minerals calcium, magnesium and iron, limestone, dolomite and bentonite are in particular focus.

Dolomite is a carbonic calcium-magnesium mineral, CaMg (CO ₃ ) 2, it is rock forming in the rock of the same name, in dolomitic limestone and in various sedimentary rocks. Dolomite occurs alongside anchorite, CaFe (CO ₃ ) ₂ , often as a hydrothermal gangue. Its color can range from white, gray, yellowish to reddish brown. Under the action of heat, dolomite begins to decompose at about 830 ° C after the following reaction.

CaMg (C0 ₃ ) ₂ + Temp. CaO + MgO + 2 C0 ₂

The reaction products CaO, MgO, but also unreacted CaMg (CO ₃ ) 2 accumulate on the surface of the foamed granules by adhesion or Van der Waals forces. If these are introduced into an aqueous solution, then CaO / MgO act as an acid buffer and as hydroxides are very quickly available to the microorganisms for metabolism.

CaO + MgO + 2H ₂ O Ca (OH) ₂ + Mg (OH) ₂

In the case of a saturated solution (1, 7 g / L or 0.009 g / L), the pH is around 12.

Bentonite is a mixture of different clay minerals, which contains montmorillonite (60-80%) as its main constituent, which explains its strong water absorption and swelling capacity. Further accompanying minerals are quartz, mica, feldspar, pyrite or calcite. It was formed mainly by weathering from volcanic ash.

2.2.4 Growth carrier with trace elements and minerals

Added trace elements

 Based on the results of previous experiments, current results from biogas research on the nutrient supply of microorganisms, a new growth carrier has been developed.

The basic composition corresponds to the two types of material 7 or 8 of the preliminary tests. Type and amount of the added trace elements were based on a dissertation on substrate conversion of Methanosarcina mazei / Krätzer 201 11 and work on the same topic at the LfL in Freising / Bauer, Lebuhn, Gronauer; 20091 compiled.

In a first variant for producing expanded glass granules with trace elements, a starting mixture of premix one and premix two was mixed according to the following composition.

Premix one

• iron oxide 316 14.3764% • Glass flour series 64.3987%

Premix two

 Dextrose C-DEX 02001 2,1663%

 Water glass 19.0242%

 Hot water

 Sodium selenite pentahydrate 0.03151% CAS number: 26970-82-1 nickel (II) chloride hexahydrate 0.00020% 7791 -20-0 disodium molybdate 0.00020% 7631 -95-0 borax 0.00020% 1330- 43-4

Zinc sulfate heptahydrate 0.00012% 13986-24-8 cobalt (II) chloride hexahydrate 0.00158% 7791 -13-1 copper (I) chloride 0.00016% 7758-89-6 potassium permanganate 0.00028% 7722-64 -7

In a second production variant dolomite was used as the blowing agent upon heating cleaved C0 ₂ should not change the redox potential of magnetite but contribute calcium and magnesium in the form of easily soluble in the growth substrate.

Premix one

 • Iron Oxide 316 14.4544%

 • Glass flour Series 64,7481%

Premix two

 • Dolomite 1, 6355%

 • water glass 19,1274%

 • Hot water

 • Sodium selenite pentahydrate 0.03168% CAS number: 26970-82-1

• Nickel (II) chloride hexahydrate 0.00020% 7791-20-0

• disodium molybdate 0.00020% 7631 -95-0

Borax 0.00020% 1330-43-4

• Zinc sulfate heptahydrate 0.00012% 13986-24-8

• Cobalt (II) chloride hexahydrate 0.00158% 7791 -13-1 • Copper (I) chloride 0.00016% 7758-89-6

• Potassium permanganate 0.00028% 7722-64-7

In both embodiments, the green grain produced from the starting mixture in a granulation process was dried at a temperature of 120 ° C in a rotary kiln and then the classification was carried out with a sieve limit of 0.25 mm.

The green bodies obtained were mixed with 10 to 15% by weight of release agent and foamed in the directly heated rotary kiln at temperatures between 780 ° C and 815 ° C with a flow time of 10 to 15 minutes.

Apart from kaolin, bentonite was used as the release agent. After this

Foaming and cooling, the granules were broken and sieved to a particle size of 0.25-1.5 mm.

3. Experimental investigations on the evaluation of expanded glass granules as a growth carrier in biogas production

3.1. Solubility of minerals and trace elements

 In order for the trace elements and minerals melted down in the growth medium to become bioavailable for the microorganisms in the fermenter, it is necessary for them to be specifically dissolved in water or aqueous media under the conditions of this process.

In order to obtain the solution behavior over time, the test material was subjected to elution.

In the DEV S4 elution test, the samples, solid, pasty and muddy materials, are slowly turned overhead or shaken in distilled water for 24 hours. The liquid / solid ratio should be adjusted to a ratio of 10/1. The sample should remain constantly in motion, further comminution e.g. However, be avoided by abrasion.

In principle, this procedure assumes that the voting substances are soluble in water. To answer specific questions, it may be appropriate to use other elution liquids as distilled water, so that solutions with a defined pH can be used as eluent.

In a first test run, the pH was adjusted to 8 daily. The background for this experimental setup was that the pH levels in a optimally running fermenter are in the range of 7-8.

Table 3: Dissolved fractions after 1 and 4 days in the elution test with pH adjustment by 8.

It was found that in a slightly alkaline environment, the leaching of the trace elements started much faster, but the alkalis and alkaline earths were slightly delayed in their solubility. This result largely confirms the theoretical foundations of glass corrosion. In the second eluate approach, the test batch was adjusted once with acetic acid to a pH of 5 and determined over a period of 45 days in addition to the solutes and the adjusting pH. In addition to the solubility, the buffer capacity of the growth media in the fermenter should be determined with this experimental setup.

If a fermenter begins to acidify due to process disturbances (see 1 .1 Fundamentals of biogas and 1 .3. Growth rates of the microorganisms), the alkalis and alkaline earths in solution from the inventive growth medium counteract the acidification.

Table 4: Dissolved fractions after 1 and 3 days in the elution test with a single pH adjustment to 5. In experimental fermenters it could be demonstrated that the methanogenic archae in biofilms which had formed on the growth media survived even in a fermenter broth with a pH between 5 and 6. After taking appropriate measures to raise the pH to 8, biogas production started very quickly again, starting from the growth sources.

3.2 Settlement attempts of different growth carriers

Hohenheim biogas test

 The University of Hohenheim has developed the so-called HBT Test, which is used to evaluate different substrates and starting materials as well as to present different process engineering conditions in fermenters of biogas plants and sewage treatment plants. Since up to 200 samples are used in the sample carrier, sufficient statistical protection can be achieved via this test.

The core pieces of the experimental set-up are reaction vessels in the form of syringes 20 made of glass (FIG. 7) and a device for storing these syringes 20, the bogie 25 (FIG. 8). The syringes 20 have a filling volume of 100 ml and are equipped with a three-way stopcock 26. In the bogie 25, the syringes can be stored horizontally. It is equipped with a controllable drive which allows rotation of the bogie 25 about the longitudinal axis of the syringes stored therein. The rotation can take place at speeds in the range of 5 to 50 min ^-1 . The bogie 25 and a fermenter with a

Inoculate culture are housed in a heated climate chamber.

In the syringes 20 experimental approaches were filled, which consist of the inoculum (monosubstrate from sugar beet silage from the preliminary experiments) and each one variety of different growth medium. In addition, control approaches without growth carriers were also tested. The volume of the batches in the syringes and the mass concentration of the growth carriers in the batch were kept constant within a series of experiments. The volume of the lugs must be well below the maximum filling volume of the syringe 20, since residual volume is still required for the biogas formed by the batch. In order to In order to allow ambient air to escape, the three-way cock 26 is opened and the piston 27 of the syringe 20 is pushed in to the volume occupied by the projection. The syringes 20 filled with the batches were stored in the bogie 25 over the entire duration of a test series. To maintain the process temperature, the climate chamber was heated to 37 ° C.

In the following, the test results of the colonization experiments for growth carriers with fused trace elements are presented in comparison to selected growth carriers of the preliminary experiments. The following sample names are used throughout:

• B1: granules with magnetite, without calcium, corresponds to type 7 of the preliminary tests

• B2: like B1 with dolomite as the blowing agent, type 8 corresponds to the preliminary tests

 • B3: as B1 with trace element addition (according to first production variant)

• B4: like B1 with trace element addition with dolomite as blowing agent (according to the second production variant).

Microbiological investigations - molecular genetic analysis

 In FIGS. 9 to 11, the temporal evolution of the biofilm is shown in FIGS

Within a trial period of 54 weeks, with syringes 20 after 5.7 weeks ("5.7 weeks"), 12.7 weeks ("12.7 weeks"), 20.7 weeks ("20.7 weeks"). ) and 5 weeks ("54 weeks").

Are plotted in Fig. 9, the values of concentration of the dry biofilm on the nursery carriers in (mg ₀ Ts / g growth substrate) in Fig. 10, the microbial total ^¬ population (BAC and ARC) in (10 ⁹ 16S rRNA gene copies (GFM) ¹ ) and in FIG. 11 the occurrence of archae (ARC) in (10 ⁹ 16S rRNA gene copies (gFM) ^"1 ) (left scale) and their proportion of the total population in% (right scale). The values of the inoculum (IN) are also shown in Figs. 10 and 11. When looking at the diagrams, it is noticeable that the biofilm mass was determined almost exclusively by the two factors "material type of the growth medium" and "time".

It was noticeable that the overall population in samples B1 and B2 increased until around the 20th week and then declined. Patterns B3 and B4 showed a constant increase to significantly higher values over the entire observation period. The 12 week value for B4 had to be discarded due to a sampling error. The proportion of methanogenic organisms follows essentially the same pattern. However, as of the 20th week, the percentage of archae in the total population decreased significantly in all the samples studied.

This discovery can not be conclusively explained at the present time. On the one hand, it suggests that the use of growth carriers with trace elements favors the colonization and propagation of microorganisms, on the other hand, the low reproducibility of the methanogens (see 1, 3 growth rates of microorganisms) also seems to play a role. The diversity of the various growth carrier species with respect to methanogenic organisms was homogeneous.

3.3 Biogas production

In order to be able to make a statement on the biogas formation of the individual types of material, the concentration of the dry biofilm on the growth media was determined after a growth time of 33 days (mg ₀ Ts / gAutwuchsträger) - Fig. 12, left scale, white bars - and each achieved Biogas yield (Ißiogas / kg ₀ s) - Fig. 12, right scale, gray bars - opposite.

From Fig. 12, a relationship between the biogas yield and the concentration of the dry biofilm can be derived on the different growth carriers. As has already been stated above, the growth carriers B3 and B4, in which trace elements are melted down, appear to promote biofilm formation and thereby achieve a higher biogas yield. The lower biofilm mass in sample B4 with simultaneously high biogas yield indicates after this first evaluation that the microorganisms present in the sample had a higher metabolic activity at the time of the measurement. This behavior in biofilms is known. If enough food and optimal living conditions are available to a population that has united into a colony in a biofilm, the microorganisms react with an increased metabolic activity or partially re-dissolve the biofilms and migrate into the fermentation fluid.

3.4 confirmation attempts

 In order to be able to evaluate the influence and the interactions between growth carrier and the suspended microbial biomass, another attempt was made in which, in addition to the different growth carriers, the fermentation fluid was evaluated after two and twelve weeks. (Results not shown)

The number of gene copies was in almost all growth carriers in the same magnitude of the previous experiment. From a molecular genetic point of view, they can therefore be regarded as approximately the same. The proportion of archaea in the total population increased significantly among all young adults. In the growth carrier pattern B3, the greatest increase occurred with the incubation period - especially in the population of the archae.

In B1, a large decrease in the microorganism population was noted. This could be due to a detachment of the biofilm from the surface of the

Growth carriers indicate that saturation had already occurred and that the maximum ratio of growth carrier and biofilm is between 40 and 50 mg oTS per g of growth carrier. In the fermentation liquid, similar total populations of microorganisms could be detected as on the growth media. In approaches B2 to B4, the population of the archaea and their proportion of the total population increased with the incubation period - the values of the growth carriers were not reached. A strong promotion of methanogenic organisms in the fermentation liquid by the use of the growth carrier could not be detected.

3.5. Microscopic examinations

 The microscopic examinations (not shown) provided important conclusions which can be used to assess the suitability of the different growth carriers. The degree and shape of the colonization of the growth media could be well assessed by the DNA staining (fluorescence microscopy) of the microorganisms present. The presence of methanogenic organisms was assessed by their autofluorescence. Autofluorescence also occurred in all microbial colonies detected by DNA staining in each of the investigated growth media. Accordingly, methanogenic organisms were represented in all microorganisms colonies of biofilms.

Experiments were carried out with growth carriers type 1 (the preliminary tests) and B3 (with melted trace elements) after several months of use in

Versuchsfermentern, which were fed with beet silage compared. While in type 1, a large number of growth carriers are only very poorly populated or not populated at all, pattern B3 shows a nearly flat colonization. It can be clearly seen that methanogenic microorganisms also preferentially settle on the growth carriers with trace elements. The strong luminosity in UV autofluorescence is an indication of a high metabolic activity of this population.

4. Conclusion

In summary, it can be stated for the growth carriers according to the invention: Growth carriers are basically suitable as carriers of biogas and methane-forming biofilms.

 The particle-free control fermenters were the most unstable variant in the entire course of the experiment. Thus, the positive effect of

To regard the growth of the biogas process as secure.

 The growth media must be crushed before use in a fermenter / bioreactor and sifted to a defined particle size. The resulting irregular surface structure is very conducive to biofilm formation.

 The development of the adherent biofilm mass is largely determined by the nature of the growth medium and the residence time in the fermenter.

 The mass of the biofilm adhering to a growth carrier alone does not allow any statements about the quality of the biofilm. The molecular genetic analysis allows a deeper insight.

The colonization of microorganisms on the surfaces of

Growth carrier is very selective - the proportion of methanogenic organisms is significantly higher than in the surrounding fermentation fluid or inoculum.

 The melting of trace elements and minerals in the

Growth carrier, depending on the substrate, has a positive effect on sufficient incubation time.

 Under the conditions in a biogas fermenter / bioreactor, the trace elements and minerals go into solution over a long period of time. When considering the amount of about 2% growth carrier on the total filling weight of a fermenter / bioreactor, an overload or even process inhibition by "critical" trace elements seems excluded.

The growth carriers bring a significant buffer capacity into the system and thus counteract any process disturbances caused by overacidification. On the surface of the growth medium, an obviously optimal "micro-environment" is formed for the biofilms, which allows the archae to survive even in an acidified environment.

The invention will be particularly evident in the embodiments described above, but is not limited to these. Rather, further embodiments of the invention can be derived from the claims and the vorste-ing description. List of abbreviations / glossary

 Acetogenesis: Formation of acetic acid

 Acidogenesis: Formation of (organic) acids

 Acidophil: acid-loving

 Acetoclastic: decomposing acetic acid

 Anion: negatively charged atom or molecule

 ATP: adenosine triphosphate (universal biochemical

 Fuels)

 Biocenosis: (alt. Βίος bios. Life 'and κοινός koinos. Together') is a community of organisms of various species in a definable

 Habitat, here in the fermenter, bioreactor.

BtL Biomass to Liquid

 Cellulolytic: dissolving / degrading cellulose fibers

COD: Chemical oxygen demand, measure of the sum of all (in water), under certain conditions oxidizable substances

 DGGE: denaturing gradient gel electrophoresis, method for the specific detection of certain DNA sections with the help of the running behavior in a gel with a gradient of denaturing substances

Disproportionation: is especially common in redox reactions. Then it is a reaction in which one and the same compound is oxidized and reduced at the same time and the oxidation numbers of several atoms of the same kind change in different directions. Disproportionation of chlorine (Oxidation number of chlorine atoms in Cl ₂ = zero) in

 Sodium hydroxide to chloride (-1) and hypochlorite (+1)

Diversity: Number of different taxa (mostly species) in a population

 DNA: deoxyribonucleic acid, carrier of the genetic material e-: electron (s)

 EDTA: ethylenediaminetetraacetic acid

 Electron acceptor: element by changing its valency

 Absorbs electrons

 Electron donor: element that changes its value

 Emit electrons

 Electron carrier: molecule that transfers electrons to the reduction of another molecule

 Ergodicity: refers to the mean behavior of a system. Such a system is described by a pattern function that determines the evolution of the system over its current state

 FOS / TAC: ratio of volatile organic acids to inorganic carbonate, = parameter for assessing the stability of the biocenosis; from about 0.6 an acidification is indicated

 Glucose: glucose

Green body designation in the ceramic for an unfired / unsintered blank,

 Halophil: loving saline conditions

HBT Hohenheim biogas test

 Hydrogenotrophic: Utilizing hydrogen for growth

Hydrolysis: Cleavage of molecules under reaction with water

 Hydrolytic resistance Resistance of the glass surface to aqueous

attack Immobilization: the spatial fixation of bacteria, cells or

 Enzymes in gel particles, capsules or in confined reaction spaces. The immobilization leads to a shift in the catalytic activity of submicroscopic and microscopic units in macroscopic particles to achieve retention

 Inoculum: In biotechnology one understands under this

 Term the amount of cells with which a fermenter is inoculated

 Kosubstrat: waste and food leftovers, but also special energy crops for biogas production

Cation: positively charged atom or molecule

 Lignocellulose: compound of cellulose with lignin (- inclusions)

LGR: Bayerische Landesanstalt für Landwirtschaft mcrA / mrtA gene of subunit A of the key enzyme of the

 methanogenic

 Mesophile: loving a medium temperature level (about 30 - 40 ° C)

 Methanogenesis: Formation of methane

methanogenic archae: methane gas producing microorganisms

Module: the ratio of silica and alkali oxide at

 water glass

 NawaRo: Renewable resources

Network creators: also called glass formers, form the molecular

 Basic structure of glass. For the glass formation no further substances are necessary. For example,

Quartz glass as the only constituent Si0 ₂

 Network Converters: Connections that form a glass together with one or more network creators.

Network converters change the structure and properties of the glass OLR: organic loading rate, organic room load oTS: organic dry matter

 Oxidation: state change of a molecule under electron donation

PCR: Polymerase chain reaction, polymerase chain reaction, molecular biology method for the amplification of specific sections of DNA in order to specifically detect them

 Polar molecule: Molecule with positively and negatively charged end Proteases: Protein-splitting enzymes

 Room load: is the amount of organic dry matter

(oTS) in kilograms per m ^{3 of} fermenter volume and day

 Reduction: state change of a molecule under electron uptake

 Sequence: sequence of bases (adenine, cytosine, guanine,

 Thymine) in the DNA

 Sequencing: determination of the base sequence of the investigated

 THEN (using different methods)

Species: Species, taxonomic term, close relatives:>

 97.5%

 SpE: trace element cocktail with defined composition

 SSCP: Single Strand conformation polymorphism, method for the specific detection of certain DNA segments with the help of the folding of single-stranded DNA

 Stabilizers: can be both network converters and network formers in the glass. However, they are not able to form a single component as a glass

Substrate: material that is fermented in a biogas plant Supplementation: Add, Add

Syntrophic: Growing together, relying on one another in nutrient utilization

 Taxon: {that, plural: taxa; to Greek τάξις täxis. (arrangement, rank) designates in biology a group recognized as a systematic unit of

Creature

 Thermophilic: a high temperature level loving (about 45 - 65 ° C)

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Weiland, P: Biogas a pioneering energy source. Renewable Energy in the Land (economy) 2001. Zeven: Publishing House for Agricultural Publications, M.C. Medenbach, 2001

Dr. rer. nat. Merrettig-Bruns Ute, Fraunhofer Institute for Environmental, Safety and Energy Technology: Test for measuring the metabolic activity of bacteria in the fermentation tank

LIST OF REFERENCE NUMBERS

1 biomass

 2 primary fermentation 3 hydrolysis

 4 monomer

 5 module

 6 Acidogenesis

7 acetogenesis 8 secondary fermentation

9 acetate

 10 Methanogenesis

1 1 anaerobic respiration

12 biogas

20 syringe

 25 bogie

26 three-way stopcock

27 pistons

Claims

claims

1 . Process for producing expanded glass granules, in particular for use in a biogas plant or an anaerobic sewage treatment plant, comprising the following process steps:

 Mixing glass flour, blowing agent and binder to a starting mixture,

 Granulating the starting mixture into expanded glass granules green bodies, and

 Foaming the expanded glass granulate green bodies into expanded glass granulate particles at temperatures of 600 ° C. to 950 ° C.,

 characterized in that

 In the production of, in particular, the starting mixture, minerals and / or trace elements are added in particular for the nutrient supply of microorganisms used in the biogas plant or the anaerobic sewage treatment plant.

2. The method according to claim 1, characterized in that as minerals carbon, nitrogen, phosphorus, sulfur, sodium, calcium, magnesium and / or iron are added.

3. The method according to claim 1 or 2, characterized in that trace elements based on cobalt, manganese, molybdenum, nickel, selenium, tungsten and / or zinc are added.

4. The method according to any one of the preceding claims, characterized in that a ground soda-lime silicate glass, in particular with a weight fraction of 60 to 70%, is used as glass flour.

5. The method according to any one of the preceding claims, characterized in that an alkali-silicate-water glass, in particular with a weight proportion of 15 to 25%, is added as the binder. Method according to one of the preceding claims, characterized in that the Blähglasgranulat green bodies for additional mineral supply especially with calcium, magnesium and / or iron before foaming a release agent in the form of calcium carbonate, dolomite and / or bentonite is added.

Method according to one of the preceding claims, characterized in that one or more of the following minerals and trace elements are used with corresponding proportions by weight:

 Sodium selenite pentahydrate 0.02000-0.04000%

 Nickel (II) chloride hexahydrate 0.00010 - 0.00030%

 Disodium molybdate 0.00010 - 0.00030%

 Borax 0.00010 - 0.00030%

 Zinc Sulphate Heptahydrate 0,00010 - 0,00020%

 Cobalt (II) chloride hexahydrate 0.00100 - 0.00200%

 Copper (I) chloride 0.00010 - 0.00030%

 Potassium permanganate 0,00020 - 0,00040%

8. expanded glass granules, in particular for use in a biogas plant or an anaerobic sewage treatment plant, made of glass flour, preferably soda-lime silicate glass flour, a blowing agent and a binder, preferably alkali silicate water glass, characterized by an addition of minerals and / or trace elements.

9. expanded glass granules according to claim 8, characterized in that as minerals carbon, nitrogen, phosphorus, sulfur, sodium, calcium, magnesium and / or iron are included.

10. expanded glass granules according to claim 8 or 9, characterized in that

Trace elements based on cobalt, manganese, molybdenum, nickel, selenium, tungsten and / or zinc are included.

1 1. Expanded glass granules according to one of claims 8 to 10, characterized in that a release agent in the form of calcium carbonate, dolomite and / or bentonite is added.

Expanded glass granules according to any one of claims 8 to 1 1, characterized in that one or more of the following minerals and trace elements are contained with corresponding proportions by weight:

 Sodium selenite pentahydrate 0.02000-0.04000%

Nickel (II) chloride hexahydrate 0.00010 - 0.00030%

Disodium molybdate 0.00010 - 0.00030%

Borax 0.00010 - 0.00030%

Zinc Sulphate Heptahydrate 0,00010 - 0,00020%

Cobalt (II) chloride hexahydrate 0.00100 - 0.00200%

Copper (I) chloride 0.00010 - 0.00030%

Potassium permanganate 0,00020 - 0,00040%

13. Use of the expanded glass granules according to one of claims 8 to 12 as a growth carrier for microorganisms in a bioreactor, in particular in a biogas plant or an anaerobic sewage treatment plant.