DE102010001907A1 - Producing biogas using microalgae, comprises culturing the microalgae with a metal-containing mine water, and concentrating the algal biomass and displacing the mine water so that metals are sorbed from water into algal biomass - Google Patents

Abstract

The method for producing biogas using microalgae, comprises culturing the microalgae with a metal-containing mine water (1) as nutrient sources in a photo bioreactor, concentrating the algal biomass and displacing the metal-containing mine water so that the metals are sorbed from the water into the algal biomass, optionally separating mercury from the resulting metal-containing biomass, fermenting the metal-containing biomass into biogas in a fermenter (10), and obtaining the metals from the biomass. The microalgae with high binding affinity to heavy metals are cultured. The method for producing biogas using microalgae, comprises culturing the microalgae with a metal-containing mine water (1) as nutrient sources in a photo bioreactor, concentrating the algal biomass and displacing the metal-containing mine water so that the metals are sorbed from the water into the algal biomass, optionally separating mercury from the resulting metal-containing biomass, fermenting the metal-containing biomass into biogas in a fermenter (10), and obtaining the metals from the biomass. The microalgae with high binding affinity to heavy metals are cultured. The mine water is diluted by adding rain water, surface water (2) and/or process water. The culturing is carried out as parallel culturing of an algae type in a time-displaced light-dark-cycle, or two algae types possessing similar growth rate are cultured in the light-dark-cycle. A co-substrate is added before the metal-containing biomass is fermented to the biogas for lowering the metal concentration to a non-toxic level. The metal-containing biomass is utilized for direct or indirect desulfurization of the biogas, where suitable metal salts are added depending on the hydrogen sulfide-concentration of the biomass during the concentrating step of the biomass or during the fermentation step. A structured photobioreactor is used for culturing the algal biomass that comprises a system of meander-shaped structural pipes or structured planes inclined to a collecting basin (5), where the inclination angle lies between 3[deg] and 12[deg] . Independent claims are included for: (1) a structural pipe-photobioreactor; and (2) a system for producing biogas using microalgae.

Description

The invention relates to a method and a device for the production of biogas and simultaneous metal extraction from mining waters by means of microalgae. The algae are cultivated in a special photobioreactor and then fermented in a fermenter to biogas. The subject of the invention is also the special photobioreactor and a complete plant - preferably for use in adaptation to the geological environment - comprising photobioreactor, biogas fermenter and possibly BKHW.

The production of biogas is a sensitive process. Land and aquatic plants, vegetable and animal residues as well as organic waste can be used in many different ways as biomass. Biomass energy offers some advantages, such as: The conservation of scarce fossil resources or the greenhouse effect is not enhanced by a nearly closed CO ₂ cycle.

Algae are known to provide high quality biomass. In countries with sufficient sunlight, algae are cultivated by open systems. The simplest form is the Raceway-Pond. Technically more complex, but characterized by better light supply and gas exchange, are Inclined Surface Systems. They include one or more oblique planes with a 3-5 ° angle of inclination over which a thin liquid film with a thickness of approx. 3 cm is formed along the slope. After passing the surface, the liquid is collected and returned to the system by a pump from the highest point. At night, the algae are often stored in ventilated tanks or basins. Flow obstacles (static mixers such as baffles) installed on the levels provide additional turbulence to prevent algae from immobilizing and to provide optimal light. Also suitable for this are various structures of the reactor material and gassing devices with a corresponding gassing rate.

The coupling of devices for biomass production (eg photobioreactors for the cultivation of algae) with biogas plants is known per se. For example, in DE 10 2007 007 131 A1 describes a method according to which the resulting CO ₂ and the waste heat of a biogas plant for the production of biomass is used. This is then used again to produce biogas.

However, a combination of photobioreactor and biogas plant with the aim of bio-oil extraction also describes EP 1 995 304 A1 , The algae for bio-oil production grow in the reactor and are supplied by the biogas plant with CO ₂ and waste heat.

DE 10 2005 010 865 A1 describes a process for biological gas treatment, which first comprises the washing of the gas by means of a suspension of microorganisms. The CO ₂ contained in the gas partially dissolves and the mixture is transferred to a partially open photobioreactor. There, the CO _{2 is} partially photosynthetically fixed and released the resulting oxygen to the environment.

However, in the conventional smooth wall reactor systems, algal growth is hampered by biofilm formation. The causes are limited light conditions and contamination of biofilms by bacteria, fungi, yeasts, etc. Methods for suppressing biofilm formation, such as the use of spherical-like systems, are just as cost-intensive as methods for biofilm removal.

As is known, the pollution of surface and ground water with heavy metals from wastewater, but also from leachate from mining dumps, is a general accompanying and consequential phenomenon of mining. The metals contained are present in such low concentrations that their extraction is currently not taking place, in particular in Asian, African and South American countries, but is desirable for reasons of environmental protection or also for further utilization.

In addition to the use of algae to produce high-quality biomass, various microalgae and macroalgae also have the ability to bind metals. KR 10073264 B1 describes z. B. the Cu and Ni removal from wastewater by Chl. vulgaris, chl. pyrenoidosa, and chi. ellipsiodea, where dead algal biomass is mixed with low concentrated wastewater. DE 69824830 T2 describes a granular carrier medium which is overgrown with a biofilm (eg algae, bacteria). The metals from waters are sorbed to the biomass, which can be partially removed and recycled.

Although the active or passive sorption of metals from aqueous media to algal biomass is state of the art, these methods can not yet be integrated into technical applications.

The object of the invention is, on the one hand, to inexpensively recover metals from mining waters and, on the other hand, to avoid environmental pollution. The invention therefore an object of the invention to provide methods and devices that ensure the cost-effective extraction of metals from mining waters to provide a high-quality biomass, the biomass can continue to be used for the production of biogas, and whereby by a nearly closed loop with respect to carbon dioxide and energy balance a reduction of environmental pollution is to be effected.

The object is achieved by a method and a device for the production of biogas using microalgae. Preferred microalgae are those which have a high binding affinity to heavy metals. The used microalgae are selected depending on the metals present. In the process according to the invention, the microalgae are cultured with undiluted or diluted metal-containing mining water in a special structured-tube photobioreactor and then concentrated. Subsequently, the concentrated algal biomass is mixed with the undiluted or diluted mining water, with the metals sorbing from the waters to the algae. The mining water acts as a nutrient source for the algae in the photobioreactor. Optionally, additional nutrient salts are added. In order to prevent the algae from dying out, the mining water is used, if necessary, in a very diluted form for algae cultivation. After concentration, the algae can be exposed to undiluted mining water.

The metal-containing biomass is then used for biogas production. Should mercury be present in the waters, it must be separated from the resulting metal-containing biomass before further conversion to biogas. After fermentation of the metal-containing algal biomass in a fermenter to biogas, the metals are extracted from the biomass. If necessary, all metals can be removed from the biomass before biogas production.

Mining water according to the invention are mining wastewater, but also leachate from mining dumps.

If necessary, the metal concentration of the mining water is checked regularly. In order to avoid a toxic reaction to the algae during cultivation, the waters z. B. be diluted by the addition of surface and / or rainwater or circulated process water. Compared to conventional photobiological methods, mineral conditions on site for the cultivation of the algal biomass can also be taken into account with the method according to the invention. So z. B. dammed rainwater with surface waters and the mining waters are mixed so that the existing minerals and trace elements used for cultivation - but toxic influences by dilution of the metal concentrations are excluded.

The separation of the grown biomass in the photobioreactor is advantageously carried out continuously or quasi-continuously. The algae biomass is produced by various methods, e.g. As sedimentation, centrifugation, drying or flocculation and as a concentrated suspension or as a solid (algae dry mass) further mixed with the undiluted or optionally diluted metal-containing mining waters. By active or passive sorption of the metals to the algae, these can be removed from the waters. However, algae species which are suitable for passive sorption are preferably used in the process according to the invention. Passive sorption is beneficial as it occurs within minutes, is reversible, and is independent of temperature and cell metabolism. This means that even dormant or dead cells ensure sorption. For this reason, the mining water can easily be added undiluted, even if it contains the metals in concentrations that may be toxic to the algae.

The metal-containing algal biomass is then placed in a fermentation tank in which it is fermented to biogas. The biogas produced can be stored locally in the mine area or fed to a cogeneration unit and converted mainly into electrical energy. The process can be circulated, so the energy gained can also be used for algae cultivation (eg for agitators, additional lighting, for operating pump systems). The released during the biogas combustion carbon dioxide is z. B. used as a carbon source for the algae and the resulting waste heat u. a. for temperature control.

A recovery of the metals before biogas production can be carried out by chemical or thermal means. The metal recovery is achieved in a biosorption classically by pH reduction or combustion of the sorption matrix.

After biogas production with metal-containing algal biomass, the metal sulfides present in the fermentation residue are converted by atmospheric oxygen to soluble sulfate.

The method has the great advantage that the concentrated algal biomass is used on the one hand as a sorbent for the metal extraction and the other hand, the metal-loaded biomass then serves as a substrate for biogas production. The algal biomass has a comparatively high biogas potential, especially if the fat content of the algae is very high. As already stated, according to the type and amount of metals bound to the algal biomass, it has to be decided whether a separation of the metals before the biogas process is necessary. If mercury contamination is present, the sorbed metal must be separated from the biomass to be fermented before biogas utilization. If the presence of mercury can be ruled out and the metal concentration in the algal biomass to be fermented is not toxic to the anaerobic cultures, a metal separation is carried out after the biogas utilization. If the concentration of the metals is too high, it can be regulated to a non-toxic range by the addition of co-substrates (eg green cuttings, food waste, etc.).

The biogas produced must generally be desulphurised before being recycled. This can be done directly or indirectly. For desulfurization either metal salts (eg iron compounds) are dosed into the fermenter (indirect desulphurization) or the gas is already processed directly with the help of the metals sorbed to the algae. Alternatively, a biological desulfurization or a combination of the methods.

A further variant consists in selectively adding further metal salts depending on the H ₂ S content of the metal-containing algal biomass, preferably iron salts (for example iron (II) chloride).

According to the invention, the cultivation of the microalgae takes place in a special photobioreactor. In addition to sunlight and CO ₂ , the algae require only inorganic nutrients, which they receive mainly from the mining waters, which ensures the nutrient supply of algae.

Since only a thin liquid film is to be produced (this is also important for the optimal illumination of algae), microalgae are used. The used microalgae are selected depending on the metals present and used targeted. But also temperature maxima, growth rate and fat content flow more or less into the selection.

For example, the following microalgae can be used: alga heavy metal Chlorella vulgaris Cu, Zn, Mn, Cd, Ni Spirulina sp. Mn, Cd, Cr, Cu Scenedesmus sp. Cu, Cd, Ni Palmaria palmata Pb, Cd, Cu, Ni Lyngbya taylorii Pb, Cu, Ni, Zn, Cd Euglena gracilis Cd, Zn, Pb Oscillatoria sp. Zn, Cu, Pb, Mn Stichococcus sp. Cd, Pb Stigoclonium sp. Zn Cosmarium sp. pb Microspora sp. Pb, Ni

They are cultivated in a special structured tube photobioreactor. Tubular reactors are known in principle. They consist essentially of a pipe system that can be arranged vertically or horizontally. The often very long pipes are made of glass or clear plastic (eg PVC, PMMA). The reactor fluid with the algae contained therein is constantly pumped through the tube system.

According to the invention, a structured-tube photobioreactor with specially structured and arranged tubes is now used. Structural tubes ( ) are pipes with specially shaped walls. For the forming The standard tubes available on the market can be used. The surface shape of the tubes is adapted to the desired properties such as increasing the heat and mass transfer. The structuring influences the external and internal flow and serves to prevent biofilm formation. The structural tubes can be adapted to the requirements by combining the different properties. Structures in the context of the invention therefore take place, for. As follows: Repeated incursions and / or protuberances of the pipe wall, the structuring as in shown achieved.

The invention therefore also relates to a structured-tube photobioreactor (US Pat. ) for algae cultivation. The structured-tube bioreactor used according to the invention is characterized by a meander-shaped design of structural tubes inclined to the collecting basin. This inclined design for the cultivation of algae with a preferred angle of inclination of 3 to 12 °, more preferably from 5 to 9 °, allows optimal lighting conditions and optimum water supply. A turbulent flow of the algal suspension is made possible by the flow rate and additionally by structure of the surface, thickness of the suspension layer, the inclination of the surface and the CO ₂ entry. The suspension is collected at the lowest point and returned to the highest by a pump. Adapted to the local conditions, the reactor with a slight inclination angle meandering z. B. lead down a mountainside. Alternatively, the reactor can also be configured as a structured flat-bed reactor.

Preferably, the required biomass is grown on-site at the mining site in the closed but non-sterile structured-tube bioreactor ( ). The translucent walls of the reactor (the tubes) are preferably made of plastic. At the bottom - or mountain side facing the reactor should contain a heat exchanger. Depending on the location of the ground or a mountain facing side is therefore not made of a translucent material but z. B. of metal. In a preferred embodiment, the specific conditions of the mining region such. As light conditions, water supply and geological profile and taken into account for the development of the photoreactor system.

The algae can be optimally supplied with light by the surfaces structured in the reactor system according to the invention, biofilm formation is prevented and no damage can occur due to excessive shearing forces.

In a coordinated alternating cultivation in the light-dark cycle, the algae are cultivated in such a way that the entire reactor geometry is optimally utilized. The natural light supply is supplemented as required by artificial lighting so that the growth of algae is not limited by a light deficiency.

Another procedure for optimal reactor utilization is the parallel cultivation of a species of algae in a staggered light-dark cycle (optimal: 12 h-12 h) or the cultivation of at least two different species of algae in this rhythm. It is ensured that both have a similar growth rate, since the cultivation does not take place under sterile conditions. Additional lighting can also be used at night for cultivation.

The "dormant" Algenart is z. B. stirred in a ventilated tank and fed to a sedimentation tank for concentration at high cell density or returned at lower cell density back into the photobioreactor.

The invention further relates to a plant for producing biogas using microalgae (US Pat. ).

It is characterized by a tank for mining wastewater 1 , a tank for rain or surface water 2 , a toxicity sensor 3 , a structured-tube photobioreactor 4 with catch basin 5 for the cultivation of microalgae, two rest tanks 6 , a sedimentation tank 7 , a sorption stage 8th , a tank for metal recovery 9 , a biogas fermenter 10 and a CHP 11 as well as various inlets and outlets.

The process according to the invention has the great advantage that a high-quality algal biomass can be used simultaneously as sorbent and for biogas production. Another great advantage is that due to the metal content of the biomass, a direct or indirect desulfurization of the biogas can take place at the same time. Additional treatments can be avoided. The metal pollution of mining waters is reduced and the metals can be recovered. The possibility of multiple cultivation (day-night cycle) ensures optimal reactor utilization. Biogas, waste heat and electric energy are used almost 100%. A gas-tight design allows the supply of algae with CO ₂ from the exhaust gas of the CHP plant and / or the desulfurized biogas, which thereby also undergoes a separation of the disturbing and quality-reducing gases. In addition, the geological conditions of the mining region can be used.

embodiment

example 1

Representation of a plant with CHP

structural tubes

Structure tube photobioreactor with catch basin

Plant for biogas production

LIST OF REFERENCE NUMBERS

The plant for biogas production using microalgae is characterized by having a tank of mining water 1 which has a supply line with a catch basin 5 a structured-tube photobioreactor 4 with integrated pump for the cultivation of microalgae. A tank for rain and / or surface water 2 is also with the catch basin 5 of the structural tube photobioreactor 4 connected. This is a toxicity sensor 3 interposed. A supply line from the catch basin 5 leads to a sedimentation tank 7 , another supply leads from the catch basin 5 to two rest tanks 6 , then continue with the sedimentation tank 7 are connected. To the sedimentation tank 7 joins a sorption step 8th to which also a supply from the tank with mining water 1 leads, another supply leads via a tank for metal recovery 9 to a biogas fermenter 10 ,

The tank for metal recovery 9 can be arranged so that the supply line from the sorbent tank 8th directly to the fermenter 10 leads and the tank for metal extraction 9 first to the fermenter 10 followed. Another supply from the biogas fermenter 10 leads to the CHP 11 ,

The microalgae become in the structured tube photobioreactor 4 with catch basin 5 with the addition of mining water from the tank 1 cultured. About the toxicity sensor 3 the metal concentration is determined. If this is too toxic for the microalgae, rainwater and / or surface water will leak from the tank 2 of the structured-tube photobioreactor 4 fed. The cultivated algal biomass in the bioreactor 4 gets out of the catch basin 5 in the tank 7 transferred to the enrichment. When applying the parallel cultivation can create a culture in the rest tanks 6 be stored. Concentrated biomass is transformed into a sorption stage 8th transferred, the further, usually undiluted, metal-containing mining wastewater from the tank 1 is added. From the sorption stage 8th After the metals are sorbed to the biomass, the metal-containing biomass is introduced into the fermenter 10 transferred. The metal is in the container 9 separated by pH change and the fermented biogas G can, for. B. stored using the geological conditions and / or needs in a CHP 11 be recycled. The generated current E can also be used, for example, for the artificial lighting and drives of the delivery units. The resulting waste heat D is used for the temperature control of the photobioreactors 4 and the biogas plant 9 . 10 , as well as for the concentration of algal biomass in the tank 7 used. Required cooling energy is generated from the groundwater or an absorption cold, which is combined with the CHP. Resulting CO ₂ F can be fed to algae cultivation.

Example 2

Biogas production using iron-laden spirulina biomass

1 g TS Spirulina, which can absorb 0.3 mmol Fe (this is equivalent to 16.755 g Fe / kg DM)) is added in slight excess to the fermenter (requires about 16.755 g Fe for the desulfurization of 10.5 g H ₂ S).

From 1 kg TS of Spirulina about 0.4 m ^{3 of} biogas can be obtained. The produced biogas contains approx. 1 g H ₂ S / m ³ biogas.

For the production of 1 m ^{3 of} desulphurised biogas, 2.6 kg of TS spirulina are used, whereby at least 0.1 kg of TS spirulina with 16.5 g of bound iron must be present.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007007131 A1 [0004]
• EP 1995304 A1 [0005]
• DE 102005010865 A1 [0006]
• KR 10073264 B1 [0009]
• DE 69824830 T2 [0009]

Claims (11)

Process for the production of biogas using microalgae, characterized in that a) microalgae are cultivated with metal-containing mining water as a nutrient source in a photobioreactor, b) the algal biomass is concentrated and mixed with the metal-containing mining water, the metals sorbing from the water to the algal biomass, c) optionally present mercury is separated from the resulting metal-containing biomass, d) the metal-containing biomass is fermented in a fermenter to biogas and e) the metals are obtained from the biomass. A method according to claim 1, characterized in that microalgae are cultured with high binding affinity to heavy metals. Method according to one of claims 1 or 2, characterized in that for the cultivation of microalgae, the mining waters are diluted by the addition of rain, surface and / or process water. Method according to one of claims 1 to 3, characterized in that the cultivation is carried out as parallel cultivation of a species of algae in a staggered light-dark cycle, or at least two algae species which have a similar growth rate, are cultivated in this light-dark rhythm , Method according to one of claims 1 to 4, characterized in that the metal-containing biomass prior to fermentation to biogas in step d) to reduce the metal concentration in a non-toxic area co-substrates are added. Method according to one of claims 1 to 5, characterized in that the metal-containing biomass is used for direct or indirect desulfurization of the biogas, wherein, depending on the H ₂ S concentration of the biomass during the biomass concentration in step b) or during the fermentation in step d) suitable metal salts are added. Method according to one of claims 1 to 6, characterized in that for culturing the algal biomass, a structured photobioreactor is used, which has a system of inclined to the catch basin meandering arranged structural tubes or structured planes, the inclination angle is preferably between 3 and 12 °. Structure tube photobioreactor ( 4 ) with catch basin ( 5 ) for the cultivation of microalgae biomass comprising a translucent, meandering arranged, to catch basin ( 5 ) inclined structural tube system. Structure tube photobioreactor ( 4 ) according to claim 8, characterized in that the angle of inclination of the meandering structure tubes arranged between 3 and 12 °. Biogas production plant using microalgae, characterized in that it comprises a tank of mining water ( 1 ), which via a supply line with a catch basin ( 5 ) a structured-tube photobioreactor ( 4 ) with integrated pump for the cultivation of microalgae, a tank for rain and / or surface water ( 2 ) also with the catch basin ( 5 ) of the structured-tube photobioreactor ( 4 ), whereby a toxicity sensor ( 3 ), a supply line from the catch basin ( 5 ) to a sedimentation tank ( 7 ), another supply line from the catch basin ( 5 ) to two rest tanks ( 6 ), which is then more valuable with the sedimentation tank ( 7 ) is connected to the sedimentation tank ( 7 ) a sorption stage ( 8th ), to which a supply line from the tank of mining water ( 1 ), another supply via a tank for metal recovery ( 9 ) to a biogas fermenter ( 10 ), the metal recovery tank ( 9 ) can be arranged so that the supply line from the sorption ( 8th ) directly to the fermenter ( 10 ) and the tank for metal extraction ( 9 ) first to the fermenter ( 10 ), another supply line from the biogas fermenter ( 10 ) to the CHP ( 11 ) leads. Installation according to claim 10, characterized in that further lines are present, which lead the recovered electricity (E) to the lighting and to the drives of the delivery units, the accumulating Waste heat (D) to the bioreactor ( 4 ), the biogas plant ( 9 . 10 ) as well as to the sedimentation tank ( 7 ) and the resulting CO ₂ (F) to the reactor ( 4 ) to lead.

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