KR100523518B1 - Zero discharge system of water treatment sludge through Alum recovery and reuse as a daily landfill cover soil - Google Patents

Abstract

According to the present invention, the sludge generated after the water treatment is separated into a filtrate containing aluminum and concentrated sludge through acid treatment, and then the aluminum of high purity is recovered from the filtrate and recycled back to a flocculant for water treatment, and the concentrated sludge is injected through slaked lime. The present invention relates to a zero discharge system that achieves neutralization treatment, improved dehydration and improved properties, and is used as a landfill replacement cover material, thereby completely recycling the purified sludge so that no waste comes out at all.

Description

 Zero discharge system of water treatment sludge through Alum recovery and reuse as a daily landfill cover soil}

According to the present invention, the sludge generated after the water treatment is separated into a filtrate containing aluminum and concentrated sludge through acid treatment, and then the aluminum of high purity is recovered from the filtrate and recycled back to a flocculant for water treatment, and the concentrated sludge is injected through slaked lime. The present invention relates to a zero discharge system that achieves neutralization treatment, improved dehydration, and improved properties, and is used as an alternative landfill cover material to completely recycle purified water sludge so that no waste sludge is generated.

Up to now, sludge generated in water purification, sewage or wastewater treatment processes has been treated by methods such as ocean dumping, landfilling, incineration, fertilization, solidification and melting. In the case of marine dumping sludge, sludge may be present in the form of agglomerate or suspended matter, causing marine pollution and blocking the oxygen supply to marine organisms, thereby causing environmental hazards. In addition, it is well known that in case of simple landfill sludge, leachate containing a large amount of pollutant is generated to cause landfill contamination, which may adversely affect the sanitary health of the surrounding environment. Incineration of sludge also causes many problems due to the generation of air pollutants and water pollutants generated during incineration. In addition, it will be readily understood by those skilled in the art that fertilizing sludge may cause soil contamination when the sludge is sprayed on the rust farmland without pretreatment due to contaminants such as heavy metals contained in the sludge. The solidification treatment generates odor during the treatment process and reduces the weight reduction effect as waste. To date, unless the sludge is recycled, it is well known that the least impact on environmental pollution on sludge treatment is melting, but this is economically inadequate.

At present, due to problems such as the absolute shortage of landfills, tightening related regulations, international restraint on ocean dumping, expensive disposal costs, etc. in this field, the amount of purified sludge generated is reduced and the recycling is promoted. Efforts have been studied in various ways.

Regarding the treatment for sludge produced after water treatment, some methods for recycling sludge in addition to the above treatment are known. In foreign countries, there was a study to selectively recover aluminum from sludge using a composite membrane in 1992. However, such a composition film is very expensive and this causes a problem in making the aluminum recovery process practical.

In Korea, Korean Patent No. 0148444 describes a method for recovering aluminum in sludge generated after wastewater treatment or water treatment. The patent describes a method of extracting aluminum and recovering it by acidifying the sludge in the aluminum recovery process, but this method may cause problems in the dehydration process because the concentrated sludge remaining after aluminum recovery has a low pH. This low pH acidic sludge may also cause problems in the treatment of dehydrated cakes such as landfills and incineration, and has not provided a solution to these problems.

In addition, Korean Patent No. 10-0341613 describes a method for recovering one or more metals, in particular iron and possibly aluminum, from a wastewater purification process in which wastewater is precipitated using chemicals containing iron and aluminum. However, the method of the patent also does not provide a method for recovering high purity aluminum by separating and recovering iron and aluminum together, and does not provide a solution for the treatment of acidified wastewater sludge after recovery.

In addition, the Republic of Korea Patent No. 10-279171 describes a method for producing a cover material that causes a small leachate by treating a solidifying agent containing an aluminum compound in the purified sludge, but the patent adds a compound containing aluminum as a solidifying agent In addition, it describes only the method of using purified sludge as a cover material, and did not suggest a method of recycling valuable metal aluminum contained in large quantities in purified sludge.

As described above, the related arts related to the recycling of valuable metals of purified sludge mainly aim to recover aluminum in sludge by acid treatment of purified sludge. However, there are two major problems when performing acid treatment.

First, the low pH of the sludge, as well as other heavy metals such as iron, manganese, and other sludges are recovered together, thereby lowering the purity of the recovered aluminum and possibly concentrating these heavy metals.

In addition, the remaining concentrated sludge after recovering aluminum by acid treatment is also a low pH state, may cause problems in the dehydration process in the dehydration process to reduce the volume / weight of the sludge, landfill, incineration, etc. after dehydration It can cause a lot of problems in the processing of.

An object of the present invention is to apply acid treatment and liquid film method to purified water sludge to recover a large amount of aluminum contained in purified water sludge and recycle it as a coagulant (recover valuable metals), and inject the lime into the concentrated sludge remaining after recovery of aluminum. By providing neutralization treatment, improvement of dehydration, improvement of its own properties, and using it as a landfill replacement cover material, it provides a novel process of a non-discharge system that does not zero discharge the purified sludge to be disposed of as a waste and a method of using the same. It is.

The terms used in the present invention are defined as follows.

In general, the term "purified sludge" refers to a mud-like substance produced by the precipitation of contaminating substances in water containing a large amount of aluminum generated in the treatment of a constant using an aluminum compound.

The term "acid treatment" is the step of acidifying the sludge to dissolve the metal from the purified sludge. Acidification methods include lowering the pH of the sludge to 1-3 with sulfuric acid or hydrochloric acid.

The term “extraction process” is the step of filtering off aluminum from concentrated sludge by acidification of purified sludge and extracting aluminum from the separated filtrate. Extractants can use any extractant known in the art, examples of which are illustrated below.

The term "liquid membrane method" is a method generally used together with a solvent extraction method and an ion exchange resin method for recovering and removing heavy metal ions present in an aqueous solution. U. S. Patent No. 3,410, 794 describes a method for ion separation by such a liquid membrane method.

The term "regeneration process" is the step of recovering aluminum ions extracted with extractant to pure aluminum. The regenerant used is sulfuric acid, and after completion of the extraction step, the mixture is allowed to stand and mixed with sulfuric acid to recover aluminum in the form of liquid aluminum sulfate, and the extractant can be recycled.

The term "aluminum flocculant" is an aluminum compound used in a method of coprecipitation of a substance to be removed by injection in a wastewater treatment method with aluminum hydroxide to remove its precipitate.

The term "dewatered cake" means dehydrated sludge produced by concentrated drying of sludge in the treatment of water, sewage and wastewater.

The term "landfill material" refers to a substance used to cover landfills in landfill disposal of waste, and soil (dirt), which is mainly used as landfill material, is used for accessing insects that carry rodents, wildlife, and pathogens, and outflow of waste from the workplace. It is used to cover the middle and middle of landfills in order to prevent sedimentation, to strengthen the soil early and to minimize contamination by leachate. By using the dewatering cake of purified water sludge as a landfill replacement cover material, there is an advantage that can reduce the amount of soil used in the cover, and recycle the purified sludge.

As used herein, the term "drainage free system" refers to all water sludge discharged from a water purification plant by separating and recovering valuable metal aluminum from purified water sludge according to the present invention, making the remaining sludge into a dewatered cake and using it as a substitute cover material. Means a process system that completely recycles the waste so that no sludge is disposed of at all.

The present invention relates to a non-discharge system for completely recovering purified water sludge by recovering valuable metal aluminum in sludge generated after water treatment and recycling the remaining dewatered cake of concentrated sludge into landfill replacement cover material.

In the present invention, the purified sludge formed in the water treatment process is acid treated to separate the concentrated sludge and the filtrate, and the filtrate is recovered from the filtrate through an extraction process and a regeneration process, and recycled as an aluminum flocculant for water treatment. It also provides a way to neutralize the concentrated sludge into a dehydrated cake and recycle it as a landfill replacement cover material.

Hereinafter, with reference to the accompanying drawings, a non-discharge system according to the present invention will be described in detail.

The no-discharge system of the present invention can be largely divided into an aluminum recovery process and a treatment process of concentrated sludge. Hereinafter, the aluminum recovery process will be described in detail.

The acid treatment step indicated by ① in FIG. 1 is a step of acidifying the sludge in order to dissolve the metal. Acid materials used in the acidification step are sulfuric acid or hydrochloric acid, preferably sulfuric acid is used, the optimum pH used is 3. In the acid treatment step of purified water sludge, sulfuric acid is added to the sludge to lower the pH to 3, thereby improving the concentration of sludge and eluting the aluminum component in the sludge into the filtrate. In the acid treatment step, the insoluble materials are filtered and treated in the concentrated sludge treatment process, and the filtrate is subjected to the extraction process, which is the next step in the aluminum recovery process. Since the filtrate may contain not only the aluminum component but also other heavy metals, insoluble solid fine particles, colloidal components, humic acids and the like, an additional extraction process is required for the recovery of aluminum.

In FIG. 1, the extraction step indicated by ② is a step of extracting aluminum from the filtrate. Solvent extraction of metals from strongly acidic solutions is known from the treatment of acid waste solutions. U. S. Patent 5,051, 186 describes a process for separating iron and zinc by solvent extraction using diethyl hexyl phosphate (DEHPA) as the extractant. See also Cornwell et al., J. Water Opllu Control Fed, Vol 49, p. 600-612 suggested aluminum recovery by solvent extraction using a mixture of monoethyl hexyl phosphate (MEHPA) and diethyl hexyl phosphate (DEHPA).

Extraction solutions that can be used in the extraction process of the present invention contain organic phosphates, organic solvents and long chain alcohols. Organic phosphates include monoalkyl phosphates (eg mono- (2-ethyl hexyl) phosphate (MEHPA)), dialkyl phosphates (eg di- (2-ethyl hexyl) phosphate (DEHPA)) and trialkyl phosphates Alkyl phosphates such as tributyl phosphate, or mixtures of MEHPA and DEHPA (MDEHPA). The extraction solution may also contain another organic reagent, such as a hydroxyquinoline derivative including 8-hydroxyquinoline. The organic solvent is preferably a long-chain hydrocarbon solvent such as kerosene, and 2-octanol is preferable as the long-chain alcohol.

The extraction process of aluminum of the present invention is a process of increasing the recyclability of aluminum by selectively recovering and concentrating aluminum in the filtrate using mono- and di-ethyl hexyl phosphate (MDEHPA), which is a mixture of MEHPA and DEHPA as extractant. High concentrations of aluminum could be recovered, excluding other heavy metals that emerged as problems during acid treatment.

The regeneration process is performed after the extraction process. The regeneration process is a step of recovering aluminum ions extracted with the extractant to pure aluminum. The regenerant used is sulfuric acid, and after completion of the extraction step, it is mixed with sulfuric acid and left to stand to recover aluminum in the form of liquid aluminum sulfate, and the extractant is recycled.

The aluminum ③ recovered as described above is recovered in the form of Alum flocculant currently used in the water purification plant, and thus can be reused again in the water purification plant.

The process for treating acidified concentrated sludge for the production of dehydrated cakes which can then be used as alternative cover material is described.

The process for manufacturing an alternative cover material is a manufacturing process for producing a cover material for a waste landfill that can be recycled by neutralizing the concentrated sludge acidified by acid treatment for the aluminum recovery process. The method of increasing the value of soil cover material by adding slaked lime to the purified sludge cake produced in the water treatment process is improved as soil cover material [Korean Journal of Water and Sewerage Systems Vol. 14, No. 3, p. 231-239 (2000). The injection of slaked lime in the present invention primarily aims to neutralize the acidified concentrated sludge, and further aims to improve dehydration using exothermicity of slaked lime. In addition, the physical properties as a cover material can be improved even more ideally by using a mixture of soil sand and slaked lime.

The neutralization step indicated by ④ in FIG. 1 uses hydrated lime, in particular waste hydrated lime, and through the neutralization treatment based on such lime, it is possible to carry out the neutralization and dehydration process of pH, thereby making the mechanical for using sludge as cover material Properties, physical properties, prevention of harmful heavy metal elution and neutral pH can be achieved.

Example 1

Aluminum Extraction and Recovery

Experiments were conducted after stabilizing the concentrated sludge in the secondary sedimentation tank at Gwanggyo Water Purification Plant at 4 ° C for 24 hours. The pH of the concentrated sludge was 7.1, the solids content (TS) was 4.9%, the volatile solids (VS) was 19.2%, the aluminum concentration in the sludge was 3742 mg / L, and the concentration of Al in the filtrate was 0 mg / L. Sulfuric acid was added to 500 mL of sludge to adjust the pH to 2, 3, 4, 5, 6, and then 10 minutes with rapid stirring (150 rpm) using a Jar Tester and 15 with slow stirring (50 rpm). Stirring was performed for a minute. After stirring, the sludge was concentrated for 24 hours, and then, the supernatant was collected and the concentration of aluminum was measured (the concentration of aluminum was measured with an atomic absorption spectrophotometer (Hitachi, Model Z-6100, Japan), followed by N ₂ OC ₂ H ₂ gas. And a high temperature head burner) were used for the next step, the extraction step. MDEHPA (mono- and di- (2-ethylhexyl) phosphate) was used as extractant to extract aluminum. The extractant was diluted in kerosene, a type of diluent, at a concentration of 5 to 20% (oil phase), and the ratio of the supernatant (water phase) eluted at pH 3 to the extractant was 1: 1, 2 The concentration of aluminum remaining in the supernatant was measured for each reaction time from 0 to 60 minutes. And in order to regenerate the aluminum extracted in the oil merchant extractant, the extracted extractant is extracted with 2, 4, 6, 8, 10 N (normal) H ₂ SO ₄ and 1: 1, 2: 1, 4: 1, The reaction was carried out as 9: 1 to recover aluminum sulfate. As a result, 91% of the aluminum in the supernatant was extracted under the condition of 15% extractant, supernatant: extractant = 2: 1, and reaction time 30 minutes, and the ratio of the extractant to the H ₂ SO ₄ solution was used to recover the extracted aluminum. From 1: 1 to 4: 1, the optimum recovery was shown at 6N of H ₂ SO ₄ solution, recovery was continued up to 10N at 9: 1 ratio, and 26,000 mg / L of the highest concentration of aluminum sulfate was recovered. Could.

Example 2

Preparation and Characterization of Alternative Cover Material

After acid treatment, Ca (OH) ₂ was added to the concentrated sludge from which the filtrate was removed to neutralize the sludge, and then the dissolution test, the uniaxial compressive strength, and the coefficient of permeability were measured.

In the dissolution test, a suitable amount of the sample was weighed according to the waste process test method, and then mixed with a solvent adjusted to pH 5.8 to 6.3 by adding hydrochloric acid to distilled water at a ratio of 1:10 (W: V). The mixed solution was shaken continuously for 6 hours in a shaker having an amplitude of 4 to 5 cm and a shaking speed of about 200 times per minute, and then filtered to measure the heavy metal concentration of the filtrate. Uniaxial compressive strength is widely used to determine soil strength by uniaxial compressive strength according to KSF2314. Compression test specimens were formed in a cylindrical shape and manufactured with a diameter of 5.5 cm and a height of 11 cm. The pressure at the instant of breakage was gradually measured as a compression device, and the sample was tested with a water content of 50%. Permeability coefficient represents the moving speed of water in the soil, in this embodiment was measured permeability coefficient using a variable head permeability test apparatus (Variable head permeability test apparatus).

As a result, in the dissolution test, most items were below the regulated value even if they were not detected or detected. Unconfined compressive strength of 1.22 to 1.46 kg / to cm ² was high, as compared to the other common sludge 0.3 to 0.5 kg / cm ^2, the permeability was 2.42 × 10 ⁷ cm / sec to 10 ⁷ Permeability of the landfill liner level As the result was close to cm / sec, it could be used as a cover layer of landfill.

Heavy Metal Concentration Results Item Standard ^* (ppm) Experimental value (ppm) PbCuAsHgCdCr ⁶⁺ CNOrg-PTCEPCE 331.50.0050.31.5110.30.1 N.D.0.020.02N.D.N.D.N.D.N.D .--- ^* Waste Management Act Enforcement Rule Article 2 Annex 1

According to the present invention, aluminum obtained through the acid treatment and aluminum extraction process of purified water sludge according to the present invention is recovered in the form of Alum flocculant which is currently used in water treatment process in a water treatment plant. It offers the advantage of recycling, and neutralizes and dehydrates the remaining acidified concentrated sludge, which can all be recycled as alternative cover material. Thus, all of the purified sludge discharged from the purification plant can be recycled to provide a zero discharge system.

1 is a block diagram of a process for recovering aluminum from the water purification sludge according to the present invention as a flocculant for a water treatment process and a recovery process for using the concentrated sludge as a cover material.

Claims (5)

1) acid treating the purified sludge to dissolve aluminum and other metals present in the purified sludge; 2) separating the purified sludge into a filtrate comprising dissolved aluminum and an acidified concentrated sludge; 3) extracting aluminum in an aluminum ion state using an extractant from a filtrate comprising dissolved aluminum; 4) regenerating aluminum as aluminum sulfate using sulfuric acid to recycle the recovered aluminum as Alum flocculant in a water treatment process; 5) treating the acidified concentrated sludge separated from step 2) with hydrated lime to neutralize and dehydrate the concentrated sludge to prepare a dehydrated cake; 6) recycling the obtained dewatered cake as a substitute cover material. The purified sludge treatment system of claim 1, wherein the acid used in the acid treatment step 1) is sulfuric acid. 2. The purified sludge treatment system of claim 1, wherein the extractant used in extraction step 3) is mono- and di-ethylhexyl phosphate (MDEHPA). The purified sludge treatment system of claim 1, wherein the slaked lime used in step 5) is waste slaked lime. A method for recovering aluminum of high purity by using purified water sludge treatment system according to any one of claims 1 to 4, and using dewatered cake as an alternative cover material.