KR20050026294A - Method for treating and reusing high-strength organic wastewater - Google Patents

Abstract

To provide a method for treating highly concentrated organic wastewater, which is able to effectively and simply remove suspended solids such as volatile fatty acids from the wastewater within a short period of time. The method comprises the steps of: (a) injecting ferric sulfate into a reactor containing wastewater under the high-speed mixture condition until pH of the wastewater being adjusted to 3.0-5.5; (b) injecting an alkaline agent into the wastewater treated by the step (a) to adjust the pH of the treated water; (c) injecting a polymeric coagulant into the treated water with mixing under the low-speed mixture condition to form floc and then solid-liquid separating the formed floc; and (d) treating the solid-liquid separated treated water through a reverse osmosis process.

Description

Method for treating and reusing high-strength organic wastewater

The present invention relates to a method for the treatment and reuse of high concentration organic wastewater. More specifically, the present invention relates to a method for treating swine wastewater containing a high concentration of suspended solids. More specifically, the wastewater can be treated in a simpler and drastically faster time than the prior art, and the chemical coagulation process and the filter press which automate the reaction pH as an operating factor, in particular, using ferrous sulfate as the cheapest and most effective It consists of the solid-liquid separation and the reverse osmosis treatment process used, and relates to a treatment method that can ensure a constant outflow water quality regardless of the type of swine wastewater.

Swine wastewater is largely divided into high concentration wastewater from slurry type piglet and low concentration wastewater from scraper type piglet, and the concentration of contaminants in the wastewater varies greatly depending on the type of house and cleaning method. Biological treatment of wastewater can lead to frequent operational failures and poor water quality. In particular, high concentrations of suspended solids in swine wastewater are difficult to maintain if the bioreactor is introduced into the bioreactor without proper pretreatment.

In the case of livestock wastewater, the effluent standard of the livestock wastewater treatment plant and the water quality standard for the individual treatment facility (enforced on January 1, 2000) are different as shown in Table 1 below. Nitrogen and phosphorus removal method of livestock wastewater or manure advanced treatment in liquid erosion method (Special 10-0342667), "Circulation treatment method and system of livestock wastewater using soil microorganisms (Special 2001-0036777)", The treatment of manure and organic wastewater through the predominance of Bacillus bacteria (Tec. 0151928) also has the disadvantages of process complexity, severe changes in livestock wastewater properties, long hydraulic residence time (15-30 days) and high treatment costs. In addition, maintenance difficulties are serious due to frequent driving failures. In particular, the increase in the use of chemicals due to frequent farming due to infectious diseases is accompanied by severe inhibition of the biological treatment process consisting of nitrification / denitrification microorganisms, leading to sudden deterioration of treated water quality.

The "High Concentration Wastewater Treatment Method Using Membrane Separation", which combines anaerobic treatment, ultrafiltration and reverse osmosis, was also invented, but the long hydraulic residence time of the anaerobic treatment (10-30 days) and The ultrafiltration method for solid-liquid separation and subsequent reverse osmosis processes have not been applied to the field since the first half of 2003 due to the complexity of the process and the long hydraulic residence time.

Therefore, it is almost impossible to apply these techniques at farm scales in other regions and regulated regions of relatively small farms. Numerous technologies have been developed at home and abroad, but few technologies consistently meet the effluent water quality standards.

On the other hand, Watren Co., Ltd. "High concentration wastewater purification method by chemical adsorption reaction using hydrolysis and ionization tendency of metal salts" (Korean Patent Publication No. 10-0341467) is a livestock wastewater by solid-liquid separation by chemical flocculation and ammonia deaeration As a treatment technique, it was applicable to low concentrations of low molecular weight organic matter in high concentration wastewater, but it was difficult to remove organic matter effectively when low molecular weight organic matter such as volatile fatty acid was present at high concentration during solid-liquid separation by chemical coagulation. However, in the method according to the present invention, the solid-liquid separation technique by chemical flocculation was able to completely separate the suspended solids in the wastewater regardless of the type and concentration of the livestock wastewater.

Treatment Plant Mode Individual treatment plant Public treatment plant Farm scale Permitted Area Regulated Area area Specific area Other Area Specific area Other Area BOD ₅ (mg / L) 50 150 150 350 30 COD _Mn (mg / L) - - - - 50 SS (mg / L) 50 150 150 350 30 Coliform group (dog / 100mL) - - - - 3,000 TN (mg / L) 260 - - - 60 TP (mg / L) 50 - - - 8

The present invention aims to solve the above problems, and aims at treating a high concentration of organic wastewater in a simpler and significantly faster time than the prior art. In addition, when the low molecular weight organic materials such as volatile fatty acids are present in high concentration, it is an object to effectively remove the organic material. Thus, it is an object of the present invention to ensure a constant outflow water quality regardless of the type of swine wastewater.

In order to achieve the above object, the high concentration organic wastewater treatment and reuse method according to the present invention, in the high concentration organic wastewater treatment and reuse method, such as livestock wastewater, ferric sulphate salts of the wastewater under high-speed mixing conditions a first step of reacting by adding the wastewater into the reactor until the pH reaches 3.0 to 5.5; A second step of adjusting the pH of the treated water by adding an alkaline agent to the treated water treated in the first step; A third step of forming a floc by injecting a polymer flocculant into the treated water after the second step and solid-liquid separating the formed floc; And a fourth step of treating the treated liquid separated in the third step by a reverse osmosis process.

In the method for treating and reusing high concentration organic wastewater according to the present invention, the reverse osmosis process of the fourth step is characterized by using a reverse osmosis system in which the reverse osmosis membrane is connected in parallel between a plurality of reverse osmosis membranes connected in series. .

In the above-described method for treating and recycling organic wastewater in high concentration, the ferric sulfate salt is reacted in the first step until the pH of the wastewater reaches 3.5 to 5.0.

Hereinafter, the present invention will be described in more detail.

(1) First step: ferric sulfate treatment

The present inventors have found that ferric chloride (Ferric chloride, FeCl ₃ ), polyaluminium chloride, alum (Alum, Aluminum sulfate, Al ₂ ) for the separation of solids in the wastewater, which is recognized as the biggest problem in the treatment of swine wastewater. Although flocculation tests were carried out using various inorganic coagulants such as (SO ₄ ) ₃ ) and ferric sulfate (Fe ₂ (SO ₄ ) ₃ ), a batch experiment was performed to determine the optimum amount of inorganic coagulant injection. It is difficult not only to satisfy the optimal conditions for swine wastewater changing from time to time, but also to accommodate the change of wastewater phase according to the pig farm, and the treatment cost per ton due to the amount of chemicals added in large quantities. There was a difficulty to rise sharply. Therefore, in the present invention, ferric sulfate was selected as the cheapest inorganic coagulant with excellent flocculation separation ability, and the optimum chemical amount was 3.0-5.5 when the wastewater pH was rapidly mixed under high-speed mixing conditions using the reaction characteristics between the wastewater and the flocculant. Add an inorganic coagulant until the reaction is about 2 hours.

If ferric sulphate is added until the pH of the wastewater is lower than 3.0, there is no big difference in performance, but the economic efficiency is drastically reduced due to the increase of sludge generation and the increase of chemical cost due to the addition of excess ferric sulphate. When ferric sulphate is added so that the pH of the wastewater is higher than 5.5, the concentration of iron ions, which play the role of inorganic coagulant in the solution, is significantly lower than the concentration of oil and minerals in the wastewater. The dewatering capacity of the sludge was then lowered to increase the concentration of suspended solids in the treated water. The preferred pH range is therefore 3.0 to 5.5. Especially preferred is until the pH is between 3.5 and 5.0.

It is preferable that the rotation speed at the time of the said mixing is 1,000-3,000 rpm. If the rotational speed is less than 1,000rpm, the mixing effect of the livestock wastewater in which the solids and the solution are mixed in the slurry state is insignificant, and the flocculation reaction does not occur efficiently.If the rotational speed exceeds 3,000rpm, not only waste of energy but also mechanical resistance This increases, resulting in premature replacement of the blades of the rotating shaft during long term operation. Thus, the preferred range of revolutions during the flocculation reaction is from 1,000 to 3000 rpm.

(2) second step: pH adjustment

By adding ferric sulfate in the first step, an alkaline agent such as NaOH is introduced into the reactor into raw water having a pH of 3.0 to 5.5, thereby increasing the pH in the reactor to 7.0 to 8.0. If the pH was less than 7.0, the iron concentration remaining after the condensation reaction was increased, the iron concentration in the treated water was increased, and the strength of the floc was also weakened. When the pH exceeds 8.0, the amount of alkaline agents such as NaOH is rapidly increased to increase the cost. Thus, the preferred pH range after the condensation reaction is between 7 and 8.

(3) step 3: floc forming and solid-liquid separation

In the second step, the raw water of which pH is adjusted is condensed by adding an anionic polymer coagulant under low speed mixing conditions, and then solid-liquid separation is performed as a filter press.

It is preferable that the rotation speed at the time of the said mixing is 100-500 rpm. If it is less than 100rpm, the condensation efficiency falls, and if it exceeds 500rpm, the condensed floc is broken and the dewatering efficiency decreases. Thus, the preferred slow stirring speed is between 100 and 300 rpm.

(4) Stage 4: Reverse Osmosis Process

After solid-liquid separation of swine wastewater by inorganic coagulant, reverse osmosis process was used to efficiently remove various contaminants such as organic matter, nitrogen, phosphorus, etc. remaining in the wastewater within a short time, and can be treated within 12 hours of hydraulic residence time. It was.

The reverse osmosis process in the method according to the invention utilizes a reverse osmosis system in which the reverse osmosis membrane is connected in series and in parallel in order to reprocess the concentrated water to maximize treated water and minimize the concentrated water. It is necessary to minimize the amount of concentrated water to meet the emission standards. As shown in FIG. 2, the reverse osmosis system includes a first reverse osmosis membrane 101, a second reverse osmosis membrane 102, and a third reverse osmosis membrane 103, and the first reverse osmosis membrane 101 and the third reverse osmosis membrane 103. The serial reverse osmosis membrane 101 and the second reverse osmosis membrane 102 are connected in parallel. Through such a series-parallel structure, the treated water after the inflow of the first reverse osmosis membrane 101 is transferred to the third reverse osmosis membrane 103, and the concentrated water is transferred to the second reverse osmosis membrane 102 (106). . The treated water separated through the reverse osmosis process from the second reverse osmosis membrane 102 is transferred to the third reverse osmosis membrane 103 for reprocessing, and the concentrated water separated from the second reverse osmosis membrane is discharged as the final concentrated water 105. Meanwhile, the treated water treated through the first reverse osmosis membrane 101 and transferred to the third reverse osmosis membrane 103 is further treated through the third reverse osmosis membrane together with the treated water transferred from the second reverse osmosis membrane to the final treatment. The concentrated water discharged into the water 104 and separated into the concentrated water through the third reverse osmosis membrane is returned to the first reverse osmosis membrane 101 and reprocessed together with the first influent.

(5) Post treatment: treatment of generated concentrated water

The concentrations of minerals were determined according to the chemical usage during chemical treatment, and the concentrations of these inorganic substances affected the recovery rate of reverse osmosis process, and the recovery rate of about 75% was obtained when the concentration of minerals was 1.5-2.0%. . The concentrated water produced by the reverse osmosis process contains high concentrations of organic matter and nitrogen, so that appropriate treatment such as use as liquid ratio, ocean dumping or consignment treatment is performed.

Hereinafter, the Example of this invention is described. However, the following examples are only preferred examples of the present invention to aid in understanding the present invention, and the present invention is not limited by these examples.

<Example>

In order to evaluate the wastewater treatment method according to the present invention, sludge type swine wastewater containing a high concentration of solids was first applied.

The following analysis method was used for the following examples.

. pH: pH meter (glass electrode method, Corning 120, TOA HM71)

.SS (floating solids): Total amount of suspended solids dried for 2 hours in a drying oven at 103-105 ° C. using a GF / C filter.

.TDS (Total Dissolved Solids): Total amount of dissolved solids where the GF / C filter filtrate was dried at 180 ° C. until water completely evaporated.

.FDS (Inorganic Dissolved Solids): The amount of dissolved solids remaining after burning the total amount of dissolved solids for 15-20 minutes in an electric furnace at 550 ± 50 ° C.

BOD ₅ : Determination of BOD after 5 days

CODcr: Titration K ₂ Cr ₂ O ₇ Closed reflux

NH ₄ ⁺ -N: Distillation and titration (Nonorganic Kjeldahl Method)

.PO ₄ ^3- -P (Total Phosphorus Content): Stannous Chloride Method (λ = 690 nm)

<Example 1>

Slurry pig wastewater with a chemical oxygen demand of 42,000 mg / L, a biological oxygen demand of 30,600 mg / L, a suspended solids content of 23,000 mg / L, total nitrogen of 2,200 mg / L and a total phosphorus of about 1,000 mg / L was prepared by the method described above. In a 50 L chemical reactor made of stainless steel, 11% ferric sulfate was added and rapidly mixed at 1,500 rpm for 2 hours, followed by 35% NaOH to adjust the pH of the reaction to 7.0-7.5, followed by stirring at 300 rpm. While reducing the speed, Leeyang Chemical's A601P was added as an anionic polymer flocculant. The floc formed reactants were subjected to solid-liquid separation using a solid-liquid separator such as a filter press. The results are shown in Table 2 below.

      Item (mg / L) Sample Type SS BOD ₅ COD _Cr T-N T-P Wastewater 23,000 30,563 44,200 2,220 1,017 Reaction pH 2.5 63 10,632 18,421 1,693 0.2 Reaction pH 3.0 64 10,545 18,770 1,670 0.2 Reaction pH 3.5 3 10,345 15,363 1,541 0.2 Reaction pH 4.5 2 10,815 15,560 1,590 0.2 Reaction pH 5.0 20 11,012 17,945 1,617 0.1 Reaction pH 5.5 25 11,475 18,530 1,680 0.1 Reaction pH 6.0 1,200 17,200 24,380 1,720 52.6

As shown in the experimental results, when ferric sulfate was added until the pH in the reactor reached 5.5, the removal rate of the suspended solids was more than 99.7%, but when sludge was injected only until the pH in the reactor reached 6.0, The water content rapidly deteriorated, and the concentration of suspended solids in the treated water also increased. The removal rate of chemical oxygen demand in the chemical coagulation process was dependent on the content of suspended solids and macromolecular organic matter in the livestock wastewater, and the remaining organic matter was mostly volatile fatty acids. On the other hand, when ferric sulfate was added until the pH in the reactor was 2.5, there was no significant difference in performance compared to the case where the ferric sulfate was injected until the pH was 3.5, and the treatment efficiency was lowered.

<Example 2>

50L of slurry-type pig wastewater with chemical oxygen demand 42,000 mg / L, biological oxygen demand 30,600 mg / L, suspended solids content 23,000 mg / L, total nitrogen 2,200 mg / L and total phosphorus approximately 1,000 mg / L In the chemical reaction tank, 11% ferric sulfate was added until the reaction pH was 4.5 and rapidly mixed at 1,500 rpm for 2 hours, and then 35% NaOH was added to adjust the pH of the reaction to 7.0-7.5 and 300 rpm. A601P of Leeyang Chemical was added as anionic polymer flocculant while reducing the stirring speed. The floc formed reactants were subjected to solid-liquid separation using a solid-liquid separator such as a filter press.

As a result of several tests on pig wastewater under the above conditions, the concentration of suspended solids in pig wastewater after chemical flocculation was maintained below 50 mg / L in all experiments as shown in Table 3 below. The concentration of could also be treated to less than 0.5 mg / L.

The concentration of organic matter remaining after chemical treatment was dependent on the concentration of volatile fatty acids, which are low molecular organic substances in pig wastewater. When the concentration of volatile fatty acids in raw wastewater is high, the COD removal rate is greatly reduced, whereas the concentration of volatile fatty acids in wastewater Low wastewater showed good COD removal rate. On the other hand, in the case of ammonia nitrogen, ammonia nitrogen present in the solid was easily removed by solid-liquid separation, but dissolved ammonia nitrogen was hardly removed.

Therefore, in consideration of the excellent solid-liquid separation characteristics of the DPC (Disposal by physical and chemical methods) process (steps 1 to 3), the treatment time can be greatly reduced, and the reverse osmosis process can reuse the treated water. The treatability was investigated. As a result of the experiment using the reverse osmosis system shown in Figure 2, the treated water was able to treat all the COD _Mn , BOD ₅ , SS, TN, TP and the like below the regulatory standard of the public livestock wastewater treatment plant, as shown in Table 3, Chromaticity was also completely removed. The recovery rate of the R / O (reverse osmosis) system operated at an operating pressure of 50-60 kg / cm ² was about 75-80%. In the pilot-scale R / O system used in this study, three membranes were arranged in series as shown in FIG. 2 to reduce the amount of concentrated water generated. In the case of the target farm pig wastewater, about 20% (F _S ) of solids was generated after chemical precipitation, and the treated water was found to be recoverable as reused water over 75% (F _T ). The amount of concentrated water generated after the final treatment due to the combination of the reverse osmosis process was about 20% of the raw water by Equation 1 below.

F _C = [1-F _S ] X [1-F _T ]

Where F _C = fraction of concentrated water after reverse osmosis

F _S = fraction of solids after chemical solids separation

F _T = fraction of treated water after reverse osmosis

      Item (mg / L) Sample Type SS BOD ₅ COD _Cr COD _Mn T-N T-P Wastewater 23,000 30,563 44,200 11,058 2,220 1,017 DPC Treatment 6 15,930 20,480 997 1,682 0.1 R / O treatment water ND ^* 28 37 14 6 ND ^* R / O concentrated water 45 48,300 63,770 3,490 5,342 0.4

* ND: Not Detected

Chemical treatment and reverse osmosis process The concentrated water of the treated water contains high concentrations of organic matter and nitrogen, so it needs to be used as liquid ratio, ocean dumping or consignment treatment or appropriate treatment. The analysis results of the concentrated water generated during the R / O treatment for the DPC treated water are shown in Table 4 below. It can be used to process the flower solution ratio to a level that is relatively suitable to the flower solution ratio standard of the fertilizer process standards.

Item Total nitrogen,% receptivity Phosphoric Acid, mg / kg receptivity Girly,% receptivity Goto,% receptivity calcium, % receptivity Manganese, mg / kg receptivity Boron, mg / kg R / O concentration 0.63 15.35 0.07 0.10 0.21 119.30 14.71 Item receptivity Iron, mg / kg receptivity Zinc, mg / kg Cyan Oxide,% Arsenic,% Nitrous acid,% Burette nitrogen, % Sulfamine Acid,% R / O concentration 1.27 13.61 ND ND ND ND ND Type of fertilizer Minimum amount of active ingredient to be contained (%) Maximum Amount of Hazardous Ingredients It Can Contain (%) Remarks For flowers (new'96.1.10) The total amount of two or more of nitrogen, water-soluble phosphate, or water-soluble fluorine should be 0.2% or less, and the content of guaranteed components for each component should be 0.1% or less (Rev. '01 .1.4) 2. Water content of two or more of the following components must be guaranteed: Water Solubility Goto: 0.01 Soluble Manganese: 0.001 Soluble Boron: 0.001 Soluble Iron: 0.01 Soluble Zinc: 0.001 Soluble Copper: 0.001 Nitrogen, phosphoric acid, and girly content Total content of 1% Sulfur oxide: 0.005 Arsenic: 0.002 Nitrous acid: 0.02 Burette nitrogen: 0.01 Sulfamic acid: 0.005 Liquid fertilizers only

 * ND: Not Detected

By using the high concentration organic wastewater treatment and reuse method according to the present invention, it is possible to treat the high concentration organic wastewater in a simpler and significantly faster time than the prior art. In addition, when a low molecular weight organic material such as volatile fatty acid is present in high concentration, it is possible to effectively remove the organic material. As a result, there is an excellent effect of ensuring a constant outflow water quality regardless of the type of swine wastewater. In addition, there is an effect that the livestock wastewater of various characteristics can be treated within one day of the total hydraulic residence time.

1 is a view schematically showing the configuration of a system for performing a method for treating and recycling high concentration organic wastewater according to the present invention.

2 is a view showing a module of the reverse osmosis system for increasing the recovery rate of the treatment and reuse method of the high concentration organic wastewater according to the invention.

<Explanation of symbols for the main parts of the drawings>

 1: raw wastewater 10: chemical reactor

11: stirrer 12: pH meter

13: ferric sulfate 14: sodium hydroxide

15: anionic polymer coagulant 16: filter press

17: Storage tank 18: Sludge generated during chemical treatment

20: reverse osmosis system 100: chemical solid-liquid separation treatment

101: first reverse osmosis membrane 102: second reverse osmosis membrane

103: third reverse osmosis membrane 104: final treated water

105: final concentrated water 106: primary concentrated water

107: secondary concentrated water 200: path of the filtrate

300: route of the concentrate

Claims (3)

In the method of treatment and reuse of high concentration organic wastewater, such as livestock wastewater, A first step of reacting the wastewater with ferric sulfate in a reactor containing the wastewater until the pH of the wastewater reaches 3.0 to 5.5 under high speed mixing conditions; A second step of adjusting the pH of the treated water by adding an alkaline agent to the treated water treated in the first step; A third step of forming a floc by injecting a polymer flocculant into the treated water after the second step and solid-liquid separating the formed floc; And And a fourth step of treating the treated water separated in the third step by a reverse osmosis process. The method of claim 1, wherein the reverse osmosis process of the fourth step uses a reverse osmosis system in which the reverse osmosis membrane is connected again in parallel between a plurality of reverse osmosis membranes connected in series. The method of claim 1 or 2, wherein the ferric sulfate is reacted in the first step until the pH of the wastewater reaches 3.5 to 5.0.