WO2002090270A1 - Bioreactor used for the oxidation of fe(ii) to fe(iii) - Google Patents

Abstract

The invention relates to a bioreactor which is used for the oxidation of Fe(II) to Fe(III) and which takes the form of a cylindrical container having a lower feed inlet and an upper effluent outlet. Said container houses an internal structure in which a series of cylindrical mesh tubes are connected by means of guide rods. Said cylindrical tubes contain independent polyurethane foam (or other elastomer polymer) units in which the micro-organisms are immobilised. Said internal structure, which is fixed to the container by means of a cover, can be removed from said container and, owing to its design, the cylindrical tubes can be handled independently for colonisation purposes, repair purposes, etc. Furthermore, the inventive reactor comprises aeration and thermostat control elements. Said reactor can be used in a procedure for eliminating hydrogen sulphide (H2S) present in biogas flows. In said procedure, the gas is washed with ferric sulphate, thereby oxidising the H2S to elemental sulphur and producing ferrous sulphate. In order to recover the ferric sulphate from the ferrous sulphate, the bioreactor containing immobilised iron-oxidising micro-organisms, such as Thiobacillus ferrooxidans, is used.

Description

Improvement of the patent P200101053, of a biological reactor for the oxidation of Fe (ll) to Fe (lll) by means of iron oxidizing bacteria immobilized on supports.

SECTOR OF THE TECHNIQUE Biological reactors.

STATE OF THE TECHNIQUE

The invention relates to a biological reactor for the oxidation of Fe (ll) to Fe (lll), for insertion into a process for removing hydrogen sulfide (H ₂ S) present in the gas streams, in particular of biogas In said process the gas is washed with an aqueous washing liquid (ferric sulfate) and the spent liquid (ferrous sulfate) is treated in the biological reactor to recover the washing liquid and can be reused.

Background of the invention

Decontamination and recycling of waste activities are acquiring a growing presence in our society. Law 10/1998, of April 21, on waste, promotes the recycling of organic matter, considering it as "the transformation of waste into a production process, for its initial purpose or for other purposes, including composting and biomethanization (anaerobic digestion). "

Among the main advantages of anaerobic digestion of biodegradable substances, is the generation of biogas, which can be energized by its methane content, which gives it a PCS in volume at 5,250 kcal / Nm ³

The use of internal combustion engines for the cogeneration of electric and thermal energy, which is widespread in the US, is taking a great boom in our country. Today there are large operating facilities in Asturias, Ávila, Barcelona, Burgos, Cádiz, Coruña, Granada and Pamplona that use biogas, which they themselves produce, as fuel in cogeneration systems. Thermal energy is obtained from engine cooling and heat recovery from combustion exhaust gases, and electrical energy from the motive energy that communicates the engine to an alternator.

Through the good use of biogas, producing companies can carry out an economic and environmentally beneficial activity, since it is included in the promotion of the use of so-called renewable energy, contributing, although in some cases be in a testimonial way, to the saving of primary energy and reinforcing the image of an entity that respects the environment and is committed to the society it serves. It does not seem appropriate to burn the biogas in a torch, without taking advantage of its energy content and contributing to the greenhouse effect, or even worse, in cases of torch failures, directly emitting methane which is one of the precursors of the destruction of the ozone layer

In the biogas that originates from the anaerobic waste treatment, a harmful compound such as hydrogen sulfide (H ₂ S) is frequently present, which is formed in the reduction of sulfates by anaerobic bacteria. The sulfates present in anaerobic digesters come, mainly, from those existing in the supply of drinking water, industrial discharges and the decomposition of organic compounds containing sulfur, such as proteins and urine [1] [3] [3. Andrades, JA, Campos, E., Macías, M., Cantero, D., (1999) Water Technology, 193, 71-86].

Within this context, the presence of hydrogen sulfide (H ₂ S) in the biogas at concentrations that can exceed 10,000 ppmv, the average values being normally around 2,500 ppmv, presents two serious drawbacks for its energy application . On the one hand it involves significant corrosion damage in the facilities, especially in which condensation water accumulates when forming H ₂ S0 ₄ . On the other, the production of sulfur oxides (S0 ₂ and S0 ₃ ) as a result of combustion that contribute to air pollution [1] [2] [2. Dezham, P., Rosenblum, E., Jenkins, D., (1988) Journal WPCF 60, 514-517].

To reduce the content of this compound, physical-chemical conditioning treatments or a system consisting of the addition of iron salts [1] [2] [4] [4. Kohl, A., Nielsen, R. (1997). Gas Purification 5th ed. Gulf Publishing Company, Texas]. These systems entail considerable installation and operation costs when consuming reagents, as in the case of iron salts, risks of endangering the anaerobic digestion process by lowering the pH [1] [2].

Within physical-chemical treatments, redox processes are especially useful in the elimination of hydrogen sulfide [4] [5] [5. Hammond, SD, Haug, RT, Harrison, DS, Izatt, BT, (1996) Proceedings 10 TH Re-siduals & Biosolids Management Conference, WEF]. The use of ferric sulfate solutions as an oxidant has been well studied [6] [6. Asai, S., Konishi, Y., Yabu, T., (1990) AlChE Journal 36, 1331-1338]., Presenting the drawback of the cost of reagent consumption. The treatment of gaseous effluents through chemical-biological treatments has a much lower cost depending on the flows and concentrations to be treated, obtaining adequate yields [7] [8] [7. Jensen, AB, Webb, C, (1995) Enzyme Microbiol. Technol 17, 2-10], [8. Pagella, C, Perego P., Zilli, M. (1996) Chem. Eng. Technol.

19, 78-88].

EXPLANATION OF THE INVENTION

The process for eliminating H ₂ S, of which the biological reactor object of the patent is part, contacts in a absorber a solution of ferric sulfate with the biogas containing H ₂ S. The solution absorbs the H ₂ S oxidizing it to elemental sulfur, which is periodically removed from the medium through a separation operation. The process can be represented by the following chemical reaction:

H ₂ S (g) + Fe ₂ (S0 ₄ ) ₃ (aq) ^• »S (s) + 2FeS0 ₄ (aq) + H ₂ S0 ₄ (aq)

The resulting solution of ferrous sulfate is passed through a biological reactor, where ferric sulfate is regenerated according to the following equation:

2FeS0 ₄ (aq) + H ₂ S0 ₄ (aq) + A 0 ₂ - Fe ₂ (S0) ₃ (aq) + H ₂ 0

The biological stage minimizes the consumption of oxidizing reagent in the absorber. The design of the biological reactor is therefore basic in the economic viability of the process.

The reactors currently on the market are not designed for installation in plants where investments and, above all, operating costs must be minimal, such as the WWTP and EDAI, MSW biomethanization plants and landfills.

Description of the invention

The present invention object of a patent, biological reactor for the oxidation of Fe (ll) to Fe (lll), by means of iron oxidizing bacteria immobilized in solid support of the polyurethane foam type, consists in the design of a low maintenance and low reactor cost, which allows to place, in independent cells, a set of support units on which the microorganism is immobilized. The reactor consists of a cylindrical tank, with a lower inlet for the feed and an upper outlet for the effluent. Inside the tank, and supported by the bottom of the tank, are a set of elements that constitute the reactor core. In it, there are the air diffusers, the temperature control coil and the guide rods for the cylinders with the different support units. The whole assembly can be removed from the tank and is attached to it, by a closing piece. Said piece has the mission of maintaining the set of supports within the liquid under reaction.

The support units consist of small pieces of polyurethane foam with a volume between 4 and 8 cm ³ . These units are introduced in cylinders formed by a grid grid of 1 cm side, divided into compartments to avoid compression of the support units.

The biological reactor performs oxidation effectively, and has the following advantages:

1. Use of conventional materials and easily affordable equipment.

2. Flexibility in operability against very wide ranges of operation. 3. Few land needs for its implementation.

4. Infrequent and economical maintenance operations, which also should not be performed by highly qualified personnel.

5. Low labor requirements for the operation and control of the system.

6. Possibility of complete automation of the entire process. 7. High degree of reliability of the oxidation process.

8. The adopted design allows the colonization of the supports by the microorganism in the same reactor. In the same way it is possible to extract one or several of the cylinders with the support to replace the foam units when necessary, or serve as inoculum to other reactors.

The biological reactor according to the invention is therefore not limited to a biogas treatment process. It can also be used in procedures to treat combustion gases and ventilation air.

The biological reactor according to the invention is not limited to a biogas treatment process, but can be used in any process where the use of ferric sulfate is necessary. The biological reactor is physically described below:

Reaction tank

The reaction vessel is a cylindrical vessel that rests on a flat base. In the upper and lower part there are two conduits for the coupling of the supply and effluent pipes. On the upper edge of the tank are the fastener that fixes the tank cover. It is prepared to be equipped with instruments for temperature and level control, pH determination, etc.

Internal structure

In the internal structure of the reactor are the elements that contain the support units and those that allow the aeration and thermostatization of the assembly.

It consists of a central tube through which the air and water pipes for thermostatization run to the bottom. In solidarity with said tube, there is a structure in which the guide rods for the cylinders containing the supports of the microorganisms are welded. The coil of the thermostat system and the aeration system is located at the bottom of the tube and integral with it.

- Support units for the microorganism

Polyurethane sponges with a density of 20 Kg / m ³ , in cubic form, placed in cylindrical tubes, 1.5 meters high and 0.1 m in diameter. Each tube has six independent sections to prevent compression of the support units. The cylindrical tubes are constructed in mesh.

Structure for support of the cylinders and guide rods The cylinders with the support are introduced into the reactor following guides. These are rods attached to a circular structure of profiles in its lower part.

Central tube of the internal structure of the reactor The internal structure of the reactor is supported by a central tube on which the structure of the guides of the support cylinders, the aeration system and the thermostat system are coupled. Inside the central tube are the air and water pipes for aeration and thermostatting respectively. Aeration system The aeration system consists of an air duct in the central tube and EPDM polyurethane and elastic rubber base diffusers, placed at the base of the internal structure, which provide a suitable bubble size for the aeration needs of the reactor.

Thermostatization of the assembly Between the structure of the guides and the aerators there is a spiral coil for the thermostatization of the biological reactor.

Element for fixing the body to the tank.

The internal structure of the reactor is fixed to the tank by means of a cover that has profiles for fastening at the edge of the tank. The lid has a series of holes for the air outlet

Method of realization of the invention. Biological reactor example

An operational example for the biological oxidation of washing liquid with a total iron concentration of 20 g Fe (T) / L is shown in Table A

Table A

Description of the figures

Figure 1. An overview of the tank and the internal structure of the reactor suspended thereon is offered. You can see all the cylinders containing the support units and the air diffusers at the bottom.

Figure 2. A top view of the reactor appears once the internal structure has been introduced therein and closed with the lid. The purpose of the reactor cover is to prevent the movement of the cylinders with the support and avoid that, due to the buoyancy of the foam, in the initial phases of start-up, it leaves the reactor. The lifting hook of the internal structure and the entry of air and water in the central tube are also appreciated.

Figure 3. A detail of the lower part of the internal structure of the reactor can be seen. The guide rods of the cylinders are distinguished, as well as any of these. Air diffusers are also appreciated.

Figure 4. Elevation of the internal structure of the reactor.

Figure 5. Plant aeration system.

Figure 6. Plan of the support grid of the cylinder guides.

Claims

1. Biological reactor for the oxidation of Fe (ll) to Fe (lll) consisting of: a) reaction tank b) support for the immobilization of the microorganism responsible for the oxidative process. c) elements that allow aeration of the whole. d) elements that allow the thermostatization of the whole. characterized in that the support where the microorganism is immobilized is constituted by independent units of polyurethane foam or another elastomeric polymer, placed in cylindrical tubes that are arranged, together with the elements for aeration and thermostatting, on an internal structure fixed to the tank by a lid 2. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, characterized in that the reaction tank is a cylindrical vessel that rests on a flat base and which has two upper and lower parts conduits for the coupling of the effluent and feed pipes respectively. 3. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, characterized in that the internal structure on which the cylindrical tubes containing the support units with the immobilized microorganism are arranged consists of: a) a circular structure, coupled on a central tube, of guide rods for the placement of the cylindrical tubes containing the support units. b) a central tube not in solidarity with the tank. c) aeration system. d) thermostat system. 4. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1 and 3, characterized in that the support units for the microorganism are placed in cylindrical tubes constructed in mesh, which have independent sections to avoid the compression of the support units. 5. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1 and 3, characterized in that the cylinder tubes are introduced into the reactor following guide rods attached to a circular structure of profiles, which allow them to be manipulated independently, so that there is the possibility of expediting the colonization stage, and of renewing the support units without emptying the reactor or making stops longer than two hours. 6. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claims 1, 3 and 5, characterized in that the circular structure is composed of profiles arranged concentrically to reduce the total volume of the internal structure of the reactor. 7. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, 3, 5 and 6, characterized in that the guide rods and the circular structure are attached to a central tube that allows the lifting and extraction of the internal structure of the reactor to facilitate maintenance operations. 8. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, 3, 5, 6 and 7, characterized in that the aeration system and the thermostatting system are integral with the central tube. 9. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, 3, 5, 6, 7 and 8, characterized in that the air and water lines for the respective systems of water flow through the central tube aeration and thermostatization. 10. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, 3, 5, 6, 7, 8 and 9, characterized in that the aeration system consists of an air duct in the central tube and of diffusers whose placement, at the base of the internal structure, provides adequate aeration and agitation of the fermentation medium. 11. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, 3, 5, 6, 7, 8 and 9, characterized in that a coil is located between the guide structures and the air diffusers. spiral that allows to reach and maintain in an appropriate way the optimum growth temperature of the microorganisms. 12. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claims 1, 2 and 10, characterized in that the internal structure is maintained inside the tank by means of a cover that allows the exit of liquids and gases. 13. Biological reactor for the oxidation of Fe (ll) to Fe (lll), according to claim 1, 2, 10 and 12, characterized in that the lid is fixed to the tank by means of a quick closing mechanism, without threads, consisting of a set of plates that rotate an angle parallel to the ground line. 4. Biological reactor for the oxidation of Fe (II) to Fe (III) according to claim 1, characterized to be equipped with instruments for controlling temperature, level, pH determination, etc.