RO133775B1 - Process for advanced purification of waste water resulting from husbandry farms - Google Patents

Description

RO 133775 Β1

The present invention addresses an issue in the field of water management, namely that of wastewater treatment, which must be seen from the perspective of existing concerns of authorities and specialists to identify alternative water sources in deficient areas and at the same time to prevent environmental pollution. .

Wastewater from livestock farms has a high content of nitrogen and phosphorus, representing a potential source of nutrients to stimulate plant growth. In order to capitalize on wastewater from animal husbandry to irrigate agricultural crops, it is necessary to properly treat them in order to reduce the pollutant load. Public health and potential agricultural and environmental adverse effects must be considered as priorities in the successful development of irrigation water reuse projects.

National as well as international regulations prohibit the irrigation of agricultural crops with raw wastewater. They provide norms of use depending on the quality achieved by the treatment process in correlation with the types of soil / crop plants [STAS 9450: 1988, Water for irrigation of agricultural crops, Romanian Association for Standardization (ASRO), ISO 16075-2: 2015 , Guidelines for treated wastewater use for irrigation projects - Part 2: Development of the project, International Organization for Standardization (ISO)].

In general, wastewater management in an economic society involves the local collection and treatment of wastewater depending on how it is disposed of in the environment. in the case of livestock farms, there are conventional wastewater treatment systems that include a primary stage in which mechanical separation of coarse materials is performed and a secondary stage in which aerobic or anaerobic biological wastewater treatment is performed.

Specific chemical and microbiological pollutants that cannot be removed by conventional methods require processing in an additional - advanced (tertiary) treatment phase, with the aim of obtaining a high quality effluent by removing the suspended and dissolved substances left in the water after going through the classic 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 [Tchobanoglous G., Burton F.L., Stensel H.D., 2003, Wastewater Engineering. Treatment and Reuse, 4th edition, Mc. Graw Hill, New York],

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

Wastewater treatment resulting from animal husbandry is performed according to the patent KR 100414580 B1 by optional aerobic biological processes, pH correction, flocculation, removal of flakes by flotation, a first stage of ozonation, aeration for a long time, precipitation, flocculation, followed by a second stage of ozonation and filtration

RO 133775 Β1 activated carbon efficiency. A system of wastewater treatment in animal husbandry is 1 presented in the patent KR 20030033812 A and it contains aerobic basin, anaerobic basin, bioreactor with membranes, catalytic ozonation / oxidation basin and zeolite treatment, in which 3 part of the effluent from the aerobic basin is recirculated to the anaerobic basin, and the active sludge from the bioreactor is introduced into the anaerobic basin. U.S. Patent No. 7,750,508 B2 describes the treatment of waste water from animal husbandry by settling, followed by nitrification / denitrification, the resulting water can be used for irrigation; the solid part is subjected to an anaerobic treatment, with 7 obtaining biogas. According to US patent 6054044 A, the treatment of this type of wastewater is performed by a physical process of separation of suspended matter, anoxic biological processes, anaerobic biological processes, followed by aerobic processes, with the recirculation of water resulting from the treatment by processes aerobic in anoxic processes and leads to obtaining an 11 effluent suitable for irrigation of agricultural crops. Other examples of aerobic and anaerobic biological wastewater treatment in open or closed systems, followed by solids separation, are described in patents CN 101343133 B, CN 101767879 B, CN 101774696 B, CN 102807302 B, CN 103435224 A, KR 100403850 B1, KR 100419827 B1, 15

KR 100951184 B1, KR 101393712 B1 and US 5795480 A.

The removal of organic substances (expressed as CCO-Cr), total nitrogen and phosphorus 17 and suspended solids from wastewater from livestock farms can be achieved according to patent CN 108975643 A through a sequence of steps comprising 19 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. 21 U.S. Pat. No. 6,261,459 B1 discloses a method for removing the specific odor of livestock wastewater using clay and a quaternary ammonium salt after a chemical coagulation step has previously been performed, followed by a process of separating the solids by filtration. or air flotation. Another possibility for treating this wastewater 25 is by coagulation, flocculation, followed by the separation of sludge and the resulting water through membranes, according to AU patent 2017203147 B2. 27

Electrocoagulation is a wastewater treatment technique that allows the removal of organic and inorganic matter in suspension and dissolved, by generating aluminum ions 29 or iron that destabilize colloids and facilitate their coagulation. Aluminum or iron ions are generated by applying an electric current between at least two electrodes (an anode 31 - called sacrificial and a cathode) immersed in wastewater. Aluminum or iron ions generated by dissolving the anode undergo a hydrolysis process with the formation of species (mainly hydroxides) 33 which act as coagulants. Electrocoagulation has the advantage that, unlike conventional coagulation in which aluminum or iron salts are added, it does not require the addition of 35 chemical reagents and is an easier and safer process to exploit [Yetilmezsoy K., Ilhan F., Sapci-Zengin Z., Sakar S., Gonullu MT, 2009, Decolorization and COD reduction 37 of UASB pretreated poultry manure wastewater by electrococagulation process: A post-treatment study, Journal of Hazardous Materials, 162 (1), pp. 120-132, TakB .Y., Tak 39 BS, Kim YJ, Park YJ, Yoon YH, Min GH, 2015, Optimization of color and COD removal from livestock wastewater by electrocoagulation process: Application of 41 Box-Behnken design (BBD), Journal of Industrial and Engineering Chemistry, 28, pp. 307-315, Pinedo-Hemandez J., Paternina-UrieR., Marrugo-Negrete J., 2016 Alternative 43 electrocoagulation for livestock wastewater treatment, Portugaliae Electrochimica Acta, 34 (4), pp. 277- 285], According to literature data, electrocoagulation occurs at densities 4 5 relatively small current, in the range of 80-100 A / m ² if iron electrodes are used and about 150 A / m ² if aluminum electrodes are used [Kobya M., Can OT, 47

RO 133775 Β1

Bayramoglu Μ., 2003, Treatment of textile wastewaters by electrocoagulation using iron and aluminum electrodes, Journal of Hazardous Matter, 100 (1-3), pp. 163-178]. CA 2755161 (A 1) describes a wastewater treatment system by electrocoagulation with aluminum and iron electrodes, at current densities of 2000-30000 A / m ² , for 120 min, with the repositioning of the cathode so that it can control the dissolution process of the anode. U.S. Patent No. 2009/0242424 A1 discloses a method of preventing the passivation of electrodes by reversing their polarity at regular intervals.

Electrocoagulation is described in US Pat. No. 6,325,916 as a method of wastewater treatment that can be used in conjunction with a gaseous oxidant combined with hydraulic cavitation to remove contaminants. The wastewater treatment process according to US patent 4149953 includes electrocoagulation with aluminum anode and iron cathode, followed by the separation of sludge formed by conventional methods.

Ozonation is an advanced oxidation process that uses ozone to oxidize organic matter in wastewater. Ozone has high oxidation and reactivity potential, being effective in removing hardly degradable organic compounds by conventional processes, such as pharmaceuticals and pesticides [Macauley JJ, Z. Qiang Z., Adams CD., Surampali R., Mormile MR, 2006, Disinfection of swine wastewater using chiorine, ultraviolet light and ozone, Water Research, 40 (10), pp. 2017-2026, Zheng C, Zhao L, Zhou X., Fu Z., Li A., 2013, Water Treatment, Ed. IntechOpen, available at: https://www.intechopen.com/books/water-treatment/treatment-technologies-fororganic-wastewater, Krzeminska D., Neczaj E., Borowski G., 2015, Advanced oxidation processes for food industrial wastewater decontamination, Journal of Ecologica! Engineering, 16 (2), pp. 61-71], According to WO 2011054155 A1, ozonation is applied for wastewater treatment after a step of electrocoagulation with iron electrodes. WO 2011025183 describes a purification process comprising steps for retaining coarse matter, electrocoagulation, filtration, ozonation and chlorination.

For wastewater resulting from animal husbandry, the literature describes various systems that incorporate electrocoagulation and / or ozonation treatment methods. Patent KR 20080037761 A describes a wastewater treatment system by electrocoagulation and ozonation, followed by effluent filtration. The degree of removal of biodegradable organic matter (expressed as CBO ₅ ) from wastewater resulting from animal husbandry can reach up to 88% by electrocoagulation, according to KR 20040078173 (A). The treatment of wastewater resulting from animal husbandry by ozonation leads to the removal of the color according to patent KR 100450588 B1, reaching their complete discoloration.

The advanced treatment process according to the invention relates to the introduction of a tertiary step in the flow of wastewater treatment process, to finish the quality of effluents from livestock farms, in order to use them for irrigation of crops, depending on the needs of their users. final (processed food crops, industrial and seed crops, energy plants, animal feed plots, ornamental plant crops, etc.).

The process which is the subject of the present invention consists, according to the attached technological scheme in principle (fig. 1), in two stages of wastewater treatment:

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

RO 133775 Β1 stage of electrochemical treatment also leads to the reduction of the microbial load with 1 separation of the suspensions to which the microorganisms adhered, but also as a result of oxidizing and reducing gases formed at electrodes simultaneously with the anodic dissolution of aluminum (O ₂ , 3

Cl ₂ etc). The chemical sludge together with the foam formed during the electrocoagulation process are processed in a module composed of homogenization, thickening and dehydration systems, so that in the end the obtained waste is recovered / stored properly. For a pollutant loading of waste water characterized by a content of organic substances 7 (CCO-Cr) of up to 1500 mg O ₂ / L and of biodegradable organic substances (CBO ₅ ) of up to 250 mg / L, materials in suspension of up to 300 mg / L and fecal coliform bacteria with 9 numerical density up to 10 ⁸ nr / 1000 mL, the electrocoagulation process can be operated at a dose of 100-300 mg AI ³ 7L wastewater, current density of 100-150 A / m ² (11 direct current source). The potential difference applied between the electrodes is a maximum of 10 V to limit the electrochemical processes competing with the dissolution of aluminum ions, such as the 13 Joule effect of water heating and the effect of discharging electrolytic gases to the electrodes. The agglomeration of the formed aggregates is done with cationic polyelectrolyte 0.1% solution (10-25 mg / L 15 wastewater) under slow mixing at 40 rpm, for 10 min, for the gravitational decantation of the formed chemical sludge being necessary a time of 15-30 min. 17 .0 stage of advanced oxidation and ozone disinfection involving the contact of water with the reactant gas in a system of 4 successive columns with countercurrent operation of 19 LG phases. Wastewater from livestock farms contains varying amounts of surfactants, which is why the ozonation columns are provided with foam separators 21. The gas flow through the water column causes the separation by flotation of a residual fraction rich in organic matter and partial oxidation products, which is then sent 23 to the sludge processing module. The ozone-enriched air necessary for the advanced oxidation of chemical pollutants present in wastewater (2-8 g O ₃ / g CCO removed) is supplied by an ozone generator whose operating principle consists in the ionization of oxygen present in the air by electric discharges of high voltage Corona type. The electric discharge produced 27 between the electrodes propels the electrons, dissociates the oxygen molecules and forms by recombination ozone molecules. After ozonation, the concentration of hydrogen ions 29 is checked and the water treated with phosphoric acid is neutralized to pH = 6.5-8.5. The exhaust air flow is sent to a gas purification module consisting of a system of 31 adsorption on granular activated carbon of unreacted ozone traces and gaseous products resulting from chemical reactions, a system for filtering solid microparticles and a system 33 for visual indication of the efficiency of removal of residual ozone from the gas phase based on the iodine formation reaction (yellow-brown) by oxidation of a solution of potassium iodide 35 (colorless).

The advanced treatment process according to the invention leads to higher efficiencies for the removal of organic substances including persistent ones (60-90% CCOCr), biodegradable organic substances (60-80% CBO ₅ ), suspended solids (over 39 80%) , but also the reduction of saline residue (40-60%), inactivation of fecal coliform bacteria up to 100% and removal of color and odor specific to animals, resulting in a water 41 properly treated for reuse in order to fertilize plant crops.

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

- increased efficiency of removal of existing pollutants in wastewater, for their return in the circuit of the water component of the environment to the parameters approved by the rules in force regarding the irrigation of agricultural crops; 47

RO 133775 Β1

- the removal of impurities by coagulation with aluminum is done electrochemically and thus avoids the use of chemical compounds (in the case of the classical method uses aluminum sulfate) which would bring a supply of salts in the treated water, which would greatly limit the volume of effluent that can be applied to the soil to prevent its salinization and damage to crops;

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

- the efficient destruction of pathogenic microorganisms (bacteria, including sporulated bacteria and viruses) by advanced oxidation with ozone in a system of successive columns, which ensures a longer contact of wastewater with ozone facilitating the degradation of pollutants and superior recovery of the chemical disinfectant;

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

- correcting the alkalinity of treated water with phosphoric acid, which is an addition of nutrients (phosphorus) to stimulate plant development;

- the possibility of making mobile equipment with fast priming of the treatment process, given the fact that the adopted technology requires relatively small volumes and implementation spaces;

- the possibility of making modular equipment so that the stages of the treatment process work individually or together depending on the treatment needs, due to the flexibility of the technology adopted.

The following is an example of application of the invention.

Example

This example relates to the possibility of applying the invention to the advanced treatment of wastewater from a medium-sized cattle farm. The wastewater resulting from the activity of the farm was treated locally in a system that involves the separation of coarse materials and biological treatment in natural regime (oxidation pond). In order to test the advanced treatment 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 approximately 200 mg AI ³ 7L wastewater. To agglomerate the flakes formed, 15 mg / L cationic polyelectrolyte wastewater type ACEFLOC was added at a concentration of 0.1% and a slow mixing regime was maintained at 40 rpm for 10 min. The separation of the formed chemical sludge was done by gravity settling for 30 min. In the next step, the wastewater was subjected to an advanced oxidation process using a flow rate of 5 g O ₃ / h, for a reaction time of 20 min, after which the pH was corrected with phosphoric acid solution up to a pH value = 8.

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

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

RO 133775 Β1

Wastewater treatment efficiencies

Quality indicator Influential FACILITIES Efficiency (%) LMA [1,2] Organic substances (CCO-Cr), mg O ₂ / L 984 90 91 - Biodegradable organic substances (CBO ₅ ), mg O ₂ / L 79 27 66 35 Suspended matter, mg / L 142 3 98 50 Aluminum, mg O ₂ / L 0.17 0.85 - 5 Saline residue, mg O ₂ / L 2746 1476 46 1500 Total coliform bacteria, no / 1000 mL 348,000 340 99.9 100-100,000 Fecal coliform bacteria, no / 1000 mL 160,000 absent 100 10,000 Fecal streptococci, no / 1000 mL 8,900 absent 100 10,000 Color colored clear, no coloring - - Smell specific faintly perceptible odor - - appearance S ir wastewater treated with treated water CiiirWip ί> Ί0 tnwuî®

LMA- maximum permissible limit for non-food crops and permeable soils

The advanced treatment 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 compliance with the objectives of the circular economy.

Claims (3)

RO 133775 Β1 Claims 1. Process for the advanced treatment of waste water from livestock farms by electrocoagulation and advanced oxidation, characterized in that it comprises two stages of treatment of waste water containing organic substances expressed as CCO-Cr up to 1500 mg O ₂ / L and biodegradable organic substances expressed as CBO ₅ up to 250 mg / L, suspended solids up to 300 mg / L and fecal coliform bacteria with a numerical density of up to 10 ⁸ nr / 1000 mL, in a first stage by electrocoagulation with aluminum electrodes, flocculation with cationic polyelectrolyte and separation of the formed chemical sludge, followed by a second stage of advanced oxidation and ozone disinfection of clarified waters from the previous stage and pH correction, with efficient removal of substances organic substances including persistent ones such as pesticides and antibiotics of 60 .. .90% CCO-Cr, biodegradable organic substances of 60 ... 80% CBO ₅ , suspended solids over 80%, yes r and reduction of the saline residue by 40 .. .60%, inactivation of fecal coliform bacteria up to 100% and removal of the color and odor specific to animals, resulting in a water purified properly for reuse in order to fertilize plant crops. Process according to Claim 1, characterized in that the electrocoagulation step with aluminum electrodes is provided with the possibility of collecting the foam separately, operated at a dose of 100-300 mg AI ³ 7L wastewater, current density of 100 ... 150 A / m ² and a current voltage of maximum 10 V and is followed by the flocculation operation with cationic polyelectrolyte 0.1% solution in an amount of 10 .. .25 mg / L wastewater, under slow mixing at 40 rpm for 10 min and then settling the chemical sludge formed for 15 ... 30 min. Process according to Claim 1, characterized in that the step of advanced oxidation and disinfection with 2 ... 8 g O ₃ / g of removed CCO takes place in a system of 4 successive columns with countercurrent operation of the LG phases and a hydraulic retention time of up to 40 min, is provided with the possibility of separate collection of foam, followed by pH correction with phosphoric acid solution up to a value in the pH range = 6.5 ... 8.5 .