RO133775A0 - Process for advanced purification of waste water resulting from husbandry farms-epuragrotech/echo - Google Patents

Abstract

The invention relates to a process for advanced purification of waste water by which the chemical and microbiological pollutants contained in the waters from animal husbandry farms are removed or reduced below certain limits by chemical methods, so that the resulting water can be reused for irrigation of crops. According to the invention the process has two stages: 1. the electrochemical treatment stage which facilitates the elimination of organic and inorganic impurities by electrocoagulation with aluminum electrodes followed by the flocculation and separation of the resulting sludge, and 2. the stage of advanced oxidation of the organic matter and ozone disinfection, followed by correcting the pH with phosphoric acid, the process ensuring a higher efficiency of removal of organic substances ranging between 60...90% COD-Cr, of biodegradable organic substances ranging between 60...80% BOD, of materials in suspension with an efficiency > 80%, of the saline residue ranging between 40...60% and inactivation of faecal coliform bacteria up to 100%.

Description

PROCESS FOR ADVANCED WASTEWATER FROM ZOOTECHNIC FARMS

DESCRIPTION OF THE INVENTION

The present invention addresses a problem in the field of water management, namely that of wastewater treatment, which must be viewed from the perspective of the existing concerns at the level of the authorities and specialists for identifying alternative water sources in the deficient areas and at the same time to prevent the pollution of the environment. .

Wastewater from livestock farms has a high content of nitrogen and phosphorus, representing a potential source of nutrients to stimulate plant growth. For the recovery of waste water from animal husbandry to irrigation of agricultural crops, it is necessary to purify them in order to reduce the pollutant load. Public health and potential agricultural and environmental adverse effects should be considered as priority elements in the successful development of irrigation water reuse projects.

National regulations as well as those existing at international level prohibit irrigation of agricultural crops with raw wastewater. They provide usage rules depending on the quality achieved by the purification process in correlation with soil types / crop plants [1,2], in general, the management of waste water within an economic society involves the collection and local treatment of waste water in depending on the disposal method and conditions in the environment. In the case of zootechnical farms, conventional wastewater treatment systems are encountered which include a primary step in which mechanical separation of coarse materials is carried out and a secondary step in which aerobic or anaerobic biological treatment of waste water is performed.

Specific pollutants of a chemical and microbiological nature that cannot be removed by conventional methods require processing in an advanced (tertiary) additional treatment phase, aiming to obtain a high quality effluent by eliminating the suspended and dissolved substances remaining in water after run-off. the classical stages. A wide variety of processes have been studied, developed and applied for the removal of contaminants of interest depending on the type of wastewater subject to treatment [3].

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Wastewater resulting from zootechnical activities is characterized by a complex and varied composition, having high content of organic substances, nitrogen, phosphorus and suspended solids, but also containing dangerous, persistent or difficult to degrade compounds, such as pesticides and antibiotics. Conventionally, the waters resulting from zootechnical activities are purified by natural or intensive mechanical and biological processes, by which solids and biodegradable organic compounds are removed. The specialized literature describes wastewater treatment processes resulting from zootechnical activities by conventional and advanced methods. Patent RO 110932 B1 presents a process for purifying biodegradable wastewater resulting from the specific processes of zootechnical complexes by using a combined system, mechanical and biological, consisting of the following stages: retaining solid suspensions on site, decanting water, activating water in magnetic field and purifying biological with aquatic plants.

The purification of waste water resulting from animal husbandry is performed according to patent KR 100414580 B1 through optional aerobic biological processes, pH correction, flocculation, flocculation removal by flotation, a first ozonation step, aeration for a long time, precipitation, flocculation, followed by a second stage of ozonation and filtration of effluent on activated carbon. A wastewater treatment system from zootechnics is presented in KR 20030033812 A and it contains aerobic basin, anaerobic basin, membrane bioreactor, catalytic ozonation / oxidation basin and zeolite treatment, in which part of the effluent from the aerobic basin. it is recycled into the anaerobic basin, and the active sludge from the bioreactor is introduced into the anaerobic basin. US Patent 7005068 B2 describes the treatment of wastewater from livestock breeding by decanting, followed by nitrification / denitrification, the resulting water being used for irrigation; the solid part is subjected to anaerobic treatment with biogas. According to US patent 6054044 A, the treatment of this type of wastewater is accomplished by a physical process of separation of suspended matter, anoxic biological processes, anaerobic biological processes, followed by aerobic processes, with the recirculation of the water resulting from the treatment by aerobic processes. in anoxic processes and leads to obtaining an adequate effluent for irrigation of agricultural crops. Other examples of wastewater treatment from animal husbandry by aerobic and anaerobic biological methods in open or closed systems, followed by the separation of solids are described in the patents CN 101343133 B, CN 101767879 B, CN 101774696 B, CN 20191773

02/07/2019

CN 102807302 B, CN 103435224 A, KR 100403850 B1, KR 100419827 B1, KR 100951184 B1, KR 101393712 B1 if US 5795480 A.

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Removal of organic substances (expressed as CCO-Cr), total nitrogen and phosphorus and suspended matter from wastewater from livestock farms can be achieved according to CN patent 108975643 A through a series of steps comprising neutralization, precipitation, nitrification. , denitrification and ozonation, with removal efficiencies of 78% CCO-Cr, 66% ammonium, 54% total nitrogen, 72% total phosphorus and 78% suspended matter.

US 6261459B 1 discloses a method for removing the specific odor of wastewater from animal husbandry using clay and a quaternary ammonium salt after a chemical coagulation step has been previously performed, followed by a process of separating solids by filtration or flotation. with air. Another possibility of purification of these wastewater is by coagulation, flocculation, followed by the separation of the sludge and the resulting water through membranes, according to the patent AU 2017203147 B2.

Electrocoagulation is a wastewater treatment technique that allows the removal of organic and inorganic matter in suspension and dissolved, by generating aluminum or iron ions that destabilize the colloids and facilitate their coagulation. Aluminum or iron ions are generated by applying an electric current between at least two electrodes (an anode - called a sacrifice and a cathode) immersed in the waste water. Aluminum or iron ions generated by dissolving the anode undergo hydrolysis process with formation of species (mainly hydroxides) which act as coagulant. Electrocoagulation has the advantage that, unlike conventional coagulation in which aluminum or iron salts are added, it does not require the addition of chemical reagents and is an easier and safer process to exploit [4-6]. According to the literature data, electrocoagulation occurs at relatively low current densities, in the range 80-100 A / m ² if iron electrodes and approx. 150 A / m ² if using aluminum electrodes [7], CA 2755161 (A1) describes a wastewater treatment system by electrocoagulation with aluminum and iron electrodes, at current densities of 2,000-30,000 A / m ² , for 120 minutes, with the cathode repositioned so that the anode dissolution process can be controlled. US Patent 2009/0242424 A1 presents a method of preventing electrode passivation by reversing their polarity at regular time intervals.

Electrocoagulation is described in US patent 6325916 as a wastewater treatment method that can be used in conjunction with a gas oxidant combined with cavitation.

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02/07/2019 hydraulics for the removal of contaminants. The wastewater treatment process according to US patent 4149953 includes electrocoagulation with aluminum anode and iron cathode, followed by the separation of the sludge formed by conventional methods.

Ozonation is an advanced oxidation process that uses ozone to oxidize organic matter from wastewater. Ozone has the potential for high oxidation and reactivity, being efficient in removing highly degradable organic compounds through conventional processes, such as pharmaceuticals and pesticides [8-10]. According to WO 2011054155 A1, ozonation is applied for the treatment of wastewater after a step of electrocoagulation with iron electrodes. WO 2011025183 discloses a purification process comprising coarsening, electrocoagulation, filtration, ozonation and chlorination steps.

For wastewater resulting from animal husbandry, the literature describes various systems that incorporate the methods of treatment by electrocoagulation and / or ozonation. Patent KR 20080037761 A describes a wastewater treatment system by electrocoagulation and ozonation, followed by effluent filtration. The degree of removal of biodegradable organic substances (expressed as CBO5) from wastewater resulting from animal husbandry can reach up to 88% by electrocoagulation, according to patent KR 20040078173 (A). The purification of wastewater resulting from zootechnics through ozonation leads to the removal of the color according to the patent KR 100450588 B1, until they have completely bleached.

The advanced purification process according to the invention relates to the introduction of a tertiary step in the flow of the wastewater treatment process, in order to finish the quality of the effluents resulting from the livestock breeding farms, in order to use them to irrigate agricultural crops, according to the needs of the end users. (processed food crops, industrial and seed crops, energy plants, animal feed plots, ornamental plant crops, etc.).

The process of the present invention consists, according to the annexed technological scheme of principle (Figure 1), in two stages of waste water treatment:

- an electrochemical treatment step in which aluminum ions are introduced into the wastewater (electrocoagulation operation) to destabilize the suspended matter and colloids, leading to the formation of flakes with a tendency to separate under the action of a flocculating agent (flocculation - decanting operations) . In this way, a clear water is obtained, which mainly contains only dissolved organic and inorganic materials. As a beneficial side effect, the electrochemical treatment stage of 2019 00399

02/07/2019 leads to the reduction of the microbial load, with the separation of the suspensions to which the microorganisms joined, but also as a result of the oxidizing and reducing gases formed at the electrodes simultaneously with the anodic dissolution of the aluminum (O ₂ , Cl _2, etc.). The chemical sludge together with the foam formed during the electrocoagulation process are processed in a module consisting of homogenization systems, thickened and dehydrated, so that finally the obtained waste can be properly recovered / stored. For a pollutant loading of waste water characterized by an organic substance (CCO-Cr) content up to 1500 mg O ₂ / L and biodegradable organic substances (CBO ₅ ) up to 250 mg / L, suspended matter up to 300 mg / L and fecal coliform bacteria with a numerical density up to 10 ⁸ nr / 1000 mL, the electrocoagulation process can be operated at a dose of 100-300 mg Al ³⁺ / L waste water, current density of 100-150 A / m ² (DC source). The potential difference applied between the electrodes is at most 10 V to limit the electrochemical processes concurrent with the dissolution of aluminum ions, such as the Joule effect of water heating and the effect of electrolyte gas discharge to the electrodes. Agglomeration of the formed aggregates is made with cationic polyelectrolyte 0.1% solution (10-25 mg / L waste water) under slow mixing at 40 rpm for 10 minutes, for the gravitational decanting of the formed chemical sludge requiring a time of 15 -30 minutes.

- an advanced oxidation and ozone disinfection step that involves contacting the water with the reactant gas in a system of 4 successive columns with counter-current operation of the LG phases. Wastewater from livestock farms contains variable amounts of surfactants, which is why ozonation columns are provided with foam separators. The flow of gas flowing through the water column causes the flotation separation of a residual fraction rich in organic matter and partial oxidation products, sent later to the sludge processing module. The air enriched in ozone needed for the advanced oxidation of the chemical pollutants present in the waste water (2-8 g O ₃ / g CCO removed) is provided by an ozone generator whose operating principle is to ionize the oxygen present in the air through electric discharge of type High voltage corona. Electric discharge between electrodes propels electrons, dissociates oxygen molecules, and recombines ozone molecules. After the ozonation, the concentration of hydrogen ions is checked and the water purified with phosphoric acid is neutralized to pH = 6.5-8.5. The exhaust air is sent in a gas purification module made up of an adsorption system

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02/07/2019 on granulated activated carbon of the traces of unreacted ozone and of the gaseous products resulting from the chemical reactions, a system of filtration of the solid microparticles and a system of visual indication of the removal efficiency of the remaining ozone from the gas phase based on the reaction of iodine formation (yellow-brown) by oxidation of a solution of potassium iodide (colorless).

The advanced purification process according to the invention results in higher efficiencies for removal of organic substances including persistent ones (60-90% CCO-Cr), biodegradable organic substances (60-80% CBO ₅ ), suspended matter (over 80%) , but also the reduction of the saline residue (40-60%), the inactivation of fecal coliform bacteria up to 100% and the removal of the color and odor specific to the animals, resulting in a properly purified water for re-use for the purpose of fertilizing plant crops.

By applying the advanced purification process according to the invention the following advantages are obtained:

- increased efficiency of removing the existing pollutants in wastewater, for their reproduction in the circuit of the hydric component of the environment to the parameters approved by the norms in force regarding the irrigation of agricultural crops;

- the removal of impurities by coagulation with aluminum is performed electrochemistry and thus avoids the use of chemical compounds (in the case of the classical method aluminum sulphate is used) which would bring a contribution of salts to the treated water, which would cause a very limited volume of effluent that can be applied to the soil to prevent its salinization and crop damage;

- the reduction by electrocoagulation of the concentration of suspended and dissolved inorganic substances (saline residue) that the waste water from the zootechnical farms contain and which cannot be removed by conventional wastewater treatment technologies;

- efficient destruction of pathogenic microorganisms (bacteria, including sporulated bacteria and viruses) through advanced oxidation with ozone in a system of successive columns, which ensures a longer contact of the waste water with ozone facilitating the process of pollutant degradation and superior use of the chemical agent disinfectant;

- degradation of persistent organic pollutants (pesticides, antibiotics, etc.), which cannot be removed by conventional wastewater treatment methods currently applied at livestock farms;

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- correction of alkalinity of the waters treated with phosphoric acid, which represents an addition of nutrient (phosphorus) to stimulate the development of plants;

- the possibility of realizing mobile equipment with rapid start-up of the purification process, given that the adopted technology requires relatively small volumes and spaces for implementation;

- the possibility of making modular equipment so that the stages of the purification process function singly or together depending on the purification requirement, due to the flexibility of the adopted technology.

The following is an example of the application of the invention.

Example. This example relates to the possibility of applying the invention to advanced wastewater treatment from a medium-sized bull farm. The waste water resulting from the activity of the farm has been purified locally in a system that involves the separation of coarse materials and the biological treatment in natural regime (oxidation pond). In order to test the advanced purification process according to the invention, the wastewater was treated by electrocoagulation with aluminum electrodes at a current density of 120 A / m ² , providing a dose of approx. 200 mg Al ³⁺ / L waste water. For the agglomeration of the flakes formed, 15 mg / L of ACEFLOC type cationic polyelectrolyte wastewater was added at a concentration of 0.1% and a slow mixing regime was maintained at 40 rpm for 10 minutes. The separation of the formed chemical sludge was done by gravitational decanting for 30 minutes. In the next step, the wastewater was subjected to an advanced oxidation process using a flow rate of 5 g Oyh, for a reaction time of 20 minutes, after which the pH was corrected with phosphoric acid solution to a pH value = 8.

The results presented below highlight superior efficiencies for removing chemical pollutants for water quality indicators that condition the use of effluent when irrigating agricultural crops. An important aspect is the reduction of the saline content of the treated water, which in this case determines the classification in a quality class that allows the irrigation of the permeable soils and of the plants tolerant to salinity.

The antimicrobial efficacy of the ozonation process was very good, the monitored bacteriological indicators being inactivated in proportion of over 99.9% and even 100%.

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Wastewater treatment efficiencies

Quality indicator Influential effluent Efficiency (%) LMA [1,2] Organic substances (CCO-Cr), mg O ₂ / L 984 90 91 - Biodegradable organic substances (CBOs), mg O ₂ / L 79 27 66 35 Suspended materials, mg / L 142 3 98 50 Aluminum, mg O ₂ / L 0.17 0.85 - 5 Residue saline, mg O ₂ / L 2746 1476 46 1500 Total co-uniform bacteria, no / 1000 mL 348,000 340 99.9 100 -100,000 Fecal co-uniform bacteria, no / 1000 mL 160,000 absent 100 10,000 Fecal streptococci, no / 1000 mL 8,900 absent 100 10,000 Color colored clear, without coloration - - Smell specific faint odor noticeable - appearance III ^v 'raw waste water treated waste water chemically ozonated waste water 5-10 minutes

LMA - the maximum allowable limit for non-food crops and permeable soils

The advanced purification process according to the invention offers the possibility of reusing wastewater from livestock farms to irrigate agricultural crops contributing to the conservation of water resources, in full accordance with the objectives of the circular economy.

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BIBLIOGRAPHY [1] STAS 9450: 1988, Water for irrigation of agricultural crops, Romanian Association for Standardization (ASRO).

[2] ISO 16075-2: 2015, Guidelines for treated wastewater use for irrigation projects Part 2: Project development, International Organization for Standardization (ISO).

[3] Tchobanoglous G., Burton F.L., Stensel H.D., 2003, Wastewater Engineering. Treatment and Reuse, 4th edition, Mc. Graw Hill, New York.

[4] Yetilmezsoy K., Ilhan F., Sapci-Zengin Z., Sakar S., Gonullu MT, 2009, Decolorization and COD reduction of UASB pretreated poultry mango re wastewater by electrococagulation process: A post-treatment study, Journal of Hazardous Materials, 162 (1), pp. 120-132.

[5] Tak BY, Tak BS, Kim YJ, Park YJ, Yoon YH, Min GH, 2015, Color optimization and COD removal from livestock wastewater by electrocoagulation process: Application of Box-Behnken design (BBD), Journal of Industrial and Engineering Chemistry, 28, pp. 307-315.

[6] Pinedo-Hernandez J., Paternina-Urie R., Marrugo-Negrete J., 2016 Alternative electrocoagulation for livestock wastewater treatment, Portugal Electrochemical Acta, 34 (4), pp. 277-285.

[7] Kobya M., Can O.T., Bayramoglu M., 2003, Treatment of textile wastewaters by electrocoagulation using iron and aluminum electrodes, Journal of Hazardous Matter, 100 (1-3), pp. 163-178.

[8] Macauley J.J., Z. Qiang Z., Adams C.D., Surampali R., Mormile M.R., 2006, Disinfection of swine wastewater using chlorine, ultraviolet light and ozone, Water Research, 40 (10), pp. 2017-2026.

[9] Zheng C., Zhao L, Zhou X., Fu Z., Li A., 2013, Water Treatment, Ed. IntechOpen, available at: https://www.intechopen.com/books/water-treatment/ treatmenttechnoloqies-for-orcianic-wastewater.

[10] Krzeminska D., Neczaj E., Borowski G., 2015, Advanced oxidation processes for industrial food wastewater decontamination, Journal of Ecological Engineering, 16 (2), pp. 61-71.

Claims (3)

METHOD FOR ADVANCED WASTEWATER PROCESSING FROM ZOOTECHNICAL FARM CLAIMS 1. Advanced (tertiary) wastewater treatment process from zootechnical farms, characterized by the fact that it involves the use of a flexible technology and allows the rapid start-up of the process, which comprises two stages of treatment of wastewater containing organic substances expressed as CCO-Cr up to 1500 mg O2 / L and biodegradable organic substances expressed as CBO ₅ up to 250 mg / L, suspended matter up to 300 mg / L and fecal coliform bacteria with numerical density up to 10 ⁸ no / 1000 mL, in the first stage by electrocoagulation with aluminum electrodes, flocculation with cationic polyelectrolyte and the separation of the formed chemical sludge, followed by a second stage of advanced oxidation and disinfection with ozone of the clarified water in the previous stage and the correction of pH, with achieving higher efficiencies for removal of organic substances including persistent pesticides and antibiotics (60-90% C CO-Cr), biodegradable organic substances (60-80% CBO ₅ ), suspended matter (over 80%), but also the reduction of the saline residue (40-60%), inactivation of fecal coliform bacteria up to 100% and color removal and the odor specific to animals, resulting in a purified water suitable for reuse for the purpose of fertilizing plant crops. 02/07/2019 pH with phosphoric acid solution up to a value in the pH range = 6.5-8.5. 2. Process according to claim (1), characterized in that it involves the passage of wastewater through a step comprising electrocoagulation with aluminum electrodes, provided with the possibility of separate foam collection, operated at a dose of 100-300 mg Al ^3+. / L waste water, current density of 100-150 A / m ² and a current voltage of maximum 10 V, followed by flocculation operation with cationic polyelectrolyte 0.1% solution (10-25 mg / L waste water) below slow mixing at 40 rpm for 10 minutes and then decanting the chemical sludge formed for 15-30 minutes, after which the clarified water goes through an advanced oxidation and disinfection step with 2-8 g OVg CCO removed, in a system of 4 successive columns with counter-current operation of the LG phases and a hydraulic retention time of up to 40 minutes, provided with the possibility of separate foam collection, followed by the correction of 2019 00399 3. Process according to claim (1), characterized in that it ensures a longer contact of the waste water with ozone, through the 4-column system with counter-current operation of the LG phases, provided with foam separators, facilitating the degradation of pollutants and valorizing superior oxidizing chemical agent.