ES2577309B1 - WASTE TREATMENT SYSTEM CONTAINING COMPLEX ORGANIC MATERIALS, USE OF THE SAME AND WASTE TREATMENT PROCESS USED BY THIS SYSTEM - Google Patents

Abstract

Waste treatment system of complex organic materials comprising an electrochemical reactor (1) configured to perform electrooxidation and / or electrooxidation-hydrolysis of the complex organic material; an anaerobic digestion reactor (10) configured to perform anaerobic degradation of the organic material; an exit port (7) configured for the exit of gases and a process that uses said system that can be carried out in two stages or in a single stage, use of said system in processes of co-digestion of waste and process of treatment of waste used by said system.

Description

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WASTE TREATMENT SYSTEM CONTAINING COMPLEX ORGANIC MATERIALS, USE OF THE SAME AND WASTE TREATMENT PROCESS USED BY THIS SYSTEM

DESCRIPTION

Object and field of the invention

The invention relates to a system for the treatment of waste containing complex organic materials, a use of said system and a treatment process that employs said system, in order to accelerate the hydrolysis of the present organic matter, reduce the levels of Volatile fatty acids and, therefore, reduce processing time, increase the capacity of organic load treatment and produce more biogas.

The system and process developed here are included in the field of water treatment, treatment of various wastes with organic material, for example, sludge from wastewater treatment plants.

Background of the invention

Within the treatment of wastewater and the like, anaerobic digestion is a proven and consolidated technology for the recovery of energy from organic waste and complex organic matter. Likewise, the development of the biorefinerla concept in recent years has placed anaerobic digestion as a key technology for the treatment of the generated by-products and obtaining electricity and heat for the plant. Some of its most striking advantages are that it allows operating at high organic loads, presenting low nutrient requirements and low investment, control and maintenance costs. Methanogenic archaea are responsible for the final and most critical stage of digestion: methane production. Due to the use of microorganisms in this technology, their sensitivity to environmental factors, such as abrupt changes in pH, organic loading, or high concentrations of salts, can lead to inhibition of the process and the accumulation of volatile fatty acids, which represents one of the main disadvantages of this technology.

In addition to the problems of instability noted, another of the important limitations of the digestion process is the slow degradation rate of certain substrates, which even presenting a high content in organic matter are slowly degraded by microorganisms. In fact, one of the most common problems when treated

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Complex waste is the limitation associated with the hydrolysis stage and the degree of resistance to degradation of certain complex molecules, which can cause instability in the process or the need to apply prolonged hydraulic retention times (HRT). Electroqulmic techniques such as electrocoagulation and electrooxidation have demonstrated high efficiency in the elimination of organic matter soluble in water and in the treatment of industrial effluents with a high content of recalcitrant compounds.

At present, various systems have been developed that include sludge stabilization through the use of electrochemical techniques. The CN1332898 C (Sludge stabilizing electrochemical treating process) patent describes a process of complete stabilization of primary and secondary sludge by direct electrolysis thereof, considering a treatment between 5 and 50 min, and the use of electrolytes such as sodium chloride or hydrochloric acid to achieve stabilization of the sludge and elimination of pathogens. Similarly, the use of ClO2 gas for the electrochemical oxidation of the mud components has been proposed through the use of a dimensionally stable anode with stainless steel cathode (CN103553286 A, Sludge reduction method by coupling electrochemical / chlorine dioxide catalytic oxidation) . In this case, the sludge stabilization treatment is achieved completely by electrochemical means with a low energy consumption but with a high cost of ClO2 gas. Another way to achieve sludge treatment is the one proposed by patent application US20120073985 A1 (Method for treating sludge), in which electrodes are used for the generation of hydroxyl radicals and ace! achieve the treatment of biological sludge.

In the case of patent application CN102515399 A (Electrochemical treatment method of sewage) an electrochemical system of mud treatment is proposed, but in this case using iron electrodes for the generation of Fe + 3 and Fe + 2 and as! facilitate the sedimentation process of the sludge, with the help of an aeration system (15-25 minutes) and the use of a stream of recirculation of the sludge.

Patent US8460520 B2 (Electrochemical system and method for the treatment of water and wastewater) describes the elimination of contaminants present in raw water or discharge water from treatment plants, such as domestic and industrial wastewater plants, by applying direct current through a series of separate and alternately charged electrodes to eliminate or minimize the

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electrode obstruction by contaminants. In this case, the system intends the elimination of the contaminants exclusively by electrochemical route focusing on a design that allows the total treatment of the effluent and avoids the problems of deposition on the electrodes generating the plugging of the plates on which the water circulates to be treated.

Other proposed systems for the treatment of drinking water, domestic and / or industrial wastewater are described in the following patent documents: EP2834197 A1 (Process and device for electrochemical treatment of industrial wastewater and drinking water), US6916427 B2 (Electrochemical method for treating wastewater) and EP2718235 A1 (Efficient treatment of wastewater using electrochemical cell).

The combination of electrochemical and biological processes has been proposed for the water treatment of the textile industry characterized by the presence of dyes. Patent CN102249486 B (Electrochemical-biological method combination device for treating printing and dyeing wastewater and wastewater treating method) involves the initial electrochemical treatment of textile wastewater followed by an anaerobic biological treatment in which the final elimination of organic compounds is adsorbed by the use of active carbon.

Considering the state of the art, the treatment system proposed here comprises combining, in a single system and treatment process, an electrochemical reactor, aimed at the hydrolysis and / or destruction of complex organic matter and / or accelerating the elimination of acidic intermediaries, and a digester, aimed at the digestion of organic material. The simplicity of the system allows its rapid application in conventional treatment systems and processes, allowing the reduction of installation costs compared to other processes for the same purpose, to improve anaerobic digestion and increase gas production.

The electrochemical treatment is responsible for reducing the levels of these acids and therefore preventing the states of inhibition of the digestion process. Also, it can act as a digestion post-treatment system for the elimination of recalcitrant organic matter characterized by containing aromatic compounds in its structure.

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Description of the invention

According to a first aspect, the present invention relates to a waste treatment system containing complex organic materials that allows to increase the yields of biogas production, accelerate the hydrolysis of the organic material, favor the elimination of intermediates and complex organic matter of aromatic structure To achieve these purposes, the system for the treatment of waste with complex organic materials comprises: an electrochemical reactor configured for an electro-oxidation and / or electrolysis of the complex organic material, an anaerobic digestion reactor configured to carry out anaerobic degradation of the organic material, an outlet port for the exit of gases and a set of pumping and transport elements configured to transport feed streams and products to and from said reactors, and between them.

From here on, the anaerobic digestion reactor will be called a digester.

According to an optional realization, the system is configured to place, as the first element acting on the organic material, that is, on the waste feed stream, the electrochemical reactor, in order to subject it to an electrochemical and hydrolysis treatment. Then, the current ace! treated is transported to the digester by a pumping system.

According to another option, the first element of the system that acts on the feed stream is the digester. Subsequently, the digestion product is transported by a pumping system to the electrochemical reactor, in order to remove the resistant or remaining organic material.

According to an additional realization option, both the electrochemical reactor and the digester are placed in the same equipment to treat the feed current.

The electrochemical reactor has a flat geometry and consists of at least two dimensionally stable electrodes as anodes and cathodes, which are parallel flat faces and equidistant from the surface. The electrodes shall be placed on a frame based on a material that does not deteriorate in the operating conditions to provide an anode-cathode separation of at least 4 mm. The electrodes will be submerged in the liquid waste to be treated.

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The set of elements for the recirculation of the current to the digester or from it is based on some ports for the entrance and exit of the liquid current, some ports for the connection to a pumping recirculation system and at least one port for the gas exhauster. The residence time inside the electrochemical reactor will depend on the characteristics of the supply current, that is, on the waste to be treated.

The electrodes of the reactor, anodes and cathodes, consist of materials based on a combination of metal-metal or diamond-metal, arranged in meshes of rectangular shape and of similar dimensions between them. The anode may be coated with metal oxides and doped with metalloids to improve performance. Oxide coatings may be stannous (Sn), plutonium (Pt), rubidium (Ru), titanium (Ti), molybdenum (Mo) or vanadium (V). The metalloids used to improve the process will be mainly antimony (Sb) and boron (B).

The potential or current density can be freely varied in order to exclusively produce electrooxidation or hydrolysis, as the case may be, of the organic material, or the joint electrooxidation-hydrolysis reaction of organic materials. The electrical connection with the outside is made by means of conductive wires, using direct current.

According to one option, the system is used in waste co-digestion processes that tend to acidification to accelerate the degradation of volatile fatty acids and stabilize the anaerobic digestion process.

According to another optional embodiment, the system is used in waste treatment processes that contain organic material of complex structure.

According to a second aspect of the invention, a waste treatment process with complex organic materials is provided that employs a system based on an electrochemical reactor and a digester, according to what has been described above, to treat an aqueous suspension of organic waste, that is, to treat a stream of waste with high organic content. The treatment process comprises an electrochemical treatment, which is performed in the electrochemical reactor, and an anaerobic digestion or digestion process, which is carried out in the digester.

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According to an optional realization of the process, the aqueous suspension is first subjected to an electrochemical treatment stage and, subsequently, is pumped to the digester to undergo anaerobic degradation. In the electrochemical treatment hydrogen (H2) is produced, whose generation will depend on the current density applied to the electrodes, which is evacuated through a gas outlet port and pumped to the digester. The objective of this is that that H2 generated in the reactor can be consumed by the hydrogenotrophic organisms and, thus, achieve the conversion of H2 and CO2 into methane. Therefore, an increase in the richness of the biogas generated in the digester used by the process is achieved.

According to this option, in which the first stage is electrochemical treatment, the aqueous suspension of the waste to be treated must have a total solids content between 2 and 6%. In this case, the aqueous suspension should be transported in ascending order to avoid the deposition of solids in the anode. By means of a recirculation pump, the aqueous suspension is transported to the point of entry of the anode to adjust its residence time inside the electrochemical reactor, according to the characteristics of the aqueous suspension to be treated.

The H2 produced in the electrochemical treatment of the aqueous suspension is transported to the anaerobic digestion stage, which is carried out in mesofflic or thermofflic conditions.

In anaerobic digestion strict and / or optional anaerobic microorganisms are used. Strict anaerobes possess enzymatic systems that only work in the absence of oxygen (O2), and facultative anaerobes can develop both a respiratory metabolism, using oxygen; as fermentative, in the absence of this. The microorganisms used in the process can be obtained from mesofflic digestion systems.

By "mesophilic conditions" is understood in the present invention those temperature conditions between 15 and 45 ° C. Preferably, the process temperature is between 30 and 40 ° C. By "thermophilic conditions" is understood in the present invention those temperature conditions between 45 and 65 ° C. Preferably, the process temperature is between 50 and 55 ° C.

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During anaerobic digestion there is, on the one hand, a gas stream that essentially contains methane and carbon dioxide, and, on the other, a liquid product or effluent that essentially contains anaerobically degraded water and organic matter.

According to another optional realization, under the same two-stage configuration, the process operates so that the first stage is anaerobic digestion or degradation in order to eliminate the biodegradable organic material. In this option, the aqueous suspension to be anaerobically degraded may contain between 2 and 25% of total solids content. In this first stage of biological degradation, a liquor is produced and then transferred to a separation unit of suspended solids. After the digestion stage, the supernatant liquid is transported to the electrochemical reactor to carry out the electrochemical treatment, in order to remove the recalcitrant or remaining organic matter. For this, the supernatant liquid is introduced into the anode of the electrochemical reactor and is maintained inside it by continuous recirculation of the fluid, until reaching the necessary residence time, depending on the desired elimination rate for the recalcitrant compound.

According to an additional option, the process is carried out through a single stage. In this case, the process is carried out in a system comprising an electrochemical reactor and a digester that are coupled and included within the same equipment. Here, the objective of the electrochemical reactor, which is coupled to the digester, is the elimination of acidic intermediates. Thus, the biological degradation of the feed stream is first performed, that is, the hydrolysis and acidification of the organic material contained in the aqueous suspension of the waste to be treated, which is highly biodegradable. For this option, the aqueous suspension may have a total solid content of up to 25%. Volatile organic acids will be generated as a result of biological hydrolysis.

The acids that accumulate in the liquor are degraded by the characteristic biological activity of the digester and electrochemical reactor, which relieves or reduces the inhibition exerted by this type of acids, so that the digestion metanogenesis phase can be carried cape. The power supply to the reactor will be provided exclusively when the reactor is acidified.

In this option of a single stage, the current density applied to the electrodes can also be variable, in order to generate hydroxyl radicals responsible for oxidizing

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Electroqulmically the acid intermediates of the digestion process. The current density can be increased to generate the release of H2 inside the reactor and favor the enrichment of biogas in methane, or to generate the release of oxygen and, thus, apply a micro-aeration process in the reactor , in order to accelerate the biological degradation and increase the stability of anaerobic digested by aerobic degradation of organic complex compounds. The micro-aeration also pursues the double objective of reducing hydrogen sulfide levels in biogas, thus achieving a biogas with low levels of hydrogen sulfide, and a greater conversion of organic matter, thanks to the realization of a mixed anaerobic-aerobic process.

Because the biological hydrolysis is carried out at a faster rate than methanogenesis, as a result of the high biodegradability of the raw material, an accumulation of organic acids occurs inside the system or equipment. The conversion of complex organic compounds to acids of even number of carbons (C2, C4 and C6) and odd number of carbons (C3 and C5) will cause a reduction in the process between volatile fatty acids and total alkalinity. When this ratio reaches a value of less than 0.4-0.3, the electrodes will be activated to initiate oxidation by hydroxyl radicals of acidic intermediates.

The electrodes will be responsible for reducing the levels of organic acids in the reactor. They also have the ability to generate H2, which can be used by hydrogenotrophic microorganisms or can generate oxygen to provide a micro-aeration to the system and accelerate as well! the consumption of acid intermediaries by the optional and / or aerobic microorganisms present with the autochthonous mud microflora. The elevation of the current applied to the electrodes favors the stabilization of the sludge and the reduction of the levels of H2S (hydrogen sulfide) in the generated biogas.

Brief description of the drawings

Next, drawings that help to better understand the invention and that expressly relate to optional embodiments, which are presented as non-limiting examples of the invention, are described very briefly.

Figure 1: Represents a configuration of the process operating in two stages using a system consisting of an electrochemical reactor and a digester.

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Figure 2: Represents a configuration of the process, which uses the system of the invention, operating as a single stage.

For clarity, the following list of references used in the drawings is presented

1. Electrochemical reactor

2. Electrode

3. anode

4. Catodo

5. Port of entry

6. Port for effluent

7. Gas outlet

8. Electrical connections

9. Gas inlet

10. Anaerobic digester or reactor

Detailed description of the invention

The system comprises, on the one hand, an electrochemical reactor (1) configured to effect the electro-oxidation or electrolysis of an aqueous suspension of residues with high content of organic material and, on the other, a digester (10) for digestion or degradation anaerobic aqueous suspension.

In this case, the system is configured to act firstly the electrochemical reactor (1), which receives the aqueous suspension and treats it, and so that, after this, the digester (10) acts. See Figure 1.

The electrochemical reactor (1) is of flat geometry and consists of at least one pair of electrodes (2) composed of anode (3) and cathode (4), with parallel flat faces and equidistant from the surface. The electrodes are placed on a frame based on a material that does not deteriorate in the operating conditions and maintaining an anode-cathode separation of at least 4 mm. The electrodes will be submerged in the liquid waste to be treated. The electrodes of the reactor, anode (3) and cathode (4), consist of materials based on a combination of metal-metal or diamond-metal. The anode in the electrodes may be coated with metal oxides and doped with metalloids to improve performance. For example, oxide coatings of tin (Sn), plutonium (Pt), rubidium (Ru), titanium (Ti), molybdenum (Mo) or vanadium (V), and antimony (Sb) and boron (B).

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The system of the invention also comprises a set of fluid pumping and transport elements based on inlet (5) and outlet (6) ports, located respectively in the lower and upper base of the digester (10), for the recirculation of the aqueous suspension to be treated in the digester, and at least one port (7) for the exit of gases, for example hydrogen (H2).

The reactor (1) has an electrical connection with the outside (8), by means of conductive wires, to use direct current. This allows the potential or current density to be freely varied in order to exclusively produce the electro-oxidation or hydrolysis, as the case may be, of the organic material, or the joint electro-oxidation-hydrolysis reaction of the compounds. organic.

The system, according to another option (Figure 2), can first dispose of the digester to receive the aqueous suspension and then the electrochemical reactor operates.

The treatment process that uses the system detailed above can be carried out in two stages: first, the electrochemical treatment and then the anaerobic digestion stage (Figure 1). The effluent or liquid product that comes from the first stage carried out in the electrochemical reactor is pumped to the digester (10) and introduced into it through an inlet port (5) to continue anaerobic degradation. Through an outlet port (7) at the top of the reactor (1), a stream containing hydrogen (H2) is introduced in the second stage through the inlet port (9) into the digester (10), for its degradation. H2 is consumed by hydrogenotrophic organisms and, in this way, the conversion of H2 and CO2 into methane is achieved and an increase in the richness of the biogas generated in the digester is achieved.

The raw material, that is, the aqueous suspension of the waste to be treated must have a total solids content between 2 and 6%. Through the pumping and fluid transport elements, the suspension is transported in an ascending manner to avoid the deposition of solids on the anode (3). The recirculation pump pumps the fluid back to the point of entry of the anode (3) to adjust the residence time of the fluid inside the electrochemical reactor (1) according to the characteristics of the aqueous suspension to be treated.

The invention will be illustrated below by means of two tests that show the

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effectiveness of the system and method of the invention for the hydrolysis of sludge from sewage stations and its effectiveness in the use of electrodes under the configuration of a single stage as a system of relief of inhibitions by organic overload.

Essay 1

The hydrolysis of the secondary sludge obtained from a wastewater treatment plant has been evaluated. Different types of dimensionally stable electrodes with an area of 50 mm2 have been used for the electrochemical hydrolysis process. The hydrolysis of the sludge was evaluated for a time of 1 h. An evolution of hydrogen (H2) of 160 ml was obtained during the period of treatment of the residue. Subsequently, the hydrolyzed residue was subjected to anaerobic digestion, obtaining an increase in the production of sludge gas of 35% under mesophilic conditions using discontinuous systems as a comparison.

Essay 2

The joint process of anaerobic digestion and electrochemical oxidation of acid intermediates has been evaluated using glucose as a substrate in the co-digestion process in order to accelerate the generation of acid intermediates. The process of co-digestion of sewage sludge was carried out in batch. The addition of glucose to the process mimics the addition of a highly biodegradable co-substrate to a conventional co-digestion system. A punctual overload was applied to the digestion process of 15 g / l of glucose, which resulted in the accelerated production of C2-C6 organic fatty acids with even and odd numbers of carbons. The total fatty acid content rose to 9 g / l, with acetic and butyl acid being the main acids. The operation of dimensionally stable electrodes allowed to maintain levels of organic acids below 4.0 g / l avoiding the absolute inhibition of the digestion process.

Claims (12)

5 10 fifteen twenty 25 30 35 1. Waste treatment system containing complex organic materials, characterized in that it comprises: an electrochemical reactor (1) configured to perform an electrooxidation and / or electrooxidation-hydrolysis of the complex organic material; an anaerobic digestion reactor (10) configured to perform anaerobic degradation of organic material; an outlet port (7) configured for the output of gases and a set of elements (5, 6) configured for the transport and pumping of currents to and from said reactors, and between these. 2. System according to claim 1, characterized in that it locates, as the first element acting on the organic material, the electrochemical reactor (1). 3. System according to claim 1, characterized in that the anaerobic digestion reactor (10) is situated as the first element acting on the organic material. 4. System according to claim 1, characterized in that the electrochemical reactor (1) and the anaerobic digestion reactor (10) are located in the same equipment. 5. System according to claims 1 to 4, characterized in that the electrochemical reactor is formed by at least two dimensionally stable electrodes, one as an anode (3) and the other as a cathode (4), with parallel flat faces and equidistant, which consist of materials based on combinations of metal-metal and diamond-metal. 6. System according to claim 5, characterized in that the anode-like electrodes (3) are coated with metal oxides selected from the following: SnO2, PtO2, Ru2O, TiO2, MoO3, V2O5, Sb2O3 and B2O3. 7. Use of the system as defined in claim 1 in waste co-digestion processes that tend to acidification to accelerate the degradation of volatile fatty acids and stabilize the digestion. 8. Use of the system as defined in claim 1 in waste treatment processes containing organic material of complex structure. 9. Waste treatment process with complex organic material, by means of a system comprising an electrochemical reactor (1), an anaerobic digestion reactor (10), an outlet port (7) for the exit of gases, characterized in that, from the introduction of the residue, it comprises performing an electrochemical treatment of the material 5 in the electrochemical reactor (1) and anaerobic digestion in the anaerobic digestion reactor (10). 10. Process according to claim 9, characterized by first performing the electro-chemical treatment of the organic material. 10 11. Process according to claim 9, characterized by first performing anaerobic digestion. 12. Process according to claim 9, characterized in that the electrochemical treatment and anaerobic digestion are carried out in a single stage.