KR102577177B1 - Phosphorus removal agent from wastewater and its manufacturing method - Google Patents

Abstract

It relates to a phosphorus remover from wastewater and a method for manufacturing the same. More specifically, it relates to a phosphorus remover from wastewater produced by drying or pyrolyzing coagulated sludge generated at a water purification plant and a method for producing the same.

Description

Phosphorus removal agent from wastewater and its manufacturing method}

The present invention relates to a phosphorus remover from wastewater and a method for manufacturing the same, and more specifically, to a phosphorus remover from wastewater produced by drying or pyrolyzing coagulated sludge generated at a water purification plant and a method for producing the same.

Tap water production using surface water is expected to continue to increase in the future, and a huge amount of residual purified water sludge will be generated in water purification plants using surface water. Water purification sludge causes environmental problems due to the coagulants used, organic matter and high metal content (Fe, Al) and heavy metals. If not properly treated, sludge can have long-term detrimental effects on the soil and water bodies where it is discharged and disposed of, as well as on nearby organisms and human health. For example, sludge toxicity to Daphnia similis has been reported in water purification sludge containing Al and Fe. Although no acute toxicity was observed, long-term exposure to both types of sludge was reported to reduce reproduction and cause some deaths. Additionally, the presence of aluminum (Al) in soil or groundwater is known to hinder plant growth, and monomeric aluminum (Al) is correlated with reduced root growth in some plants.

Additionally, sludge treatment accounts for a significant portion of water purification plant operating costs. Therefore, in preparation for strict regulations on the discharge of water purification sludge, interest in technologies that can simultaneously meet effective treatment, reuse, and recycling is increasing. Water purification sludge contains contaminants such as organic matter, suspended solids, microorganisms, and metals, as well as chemical components such as metals such as Al, Fe, Ca, Cl, and S contained in water treatment agents. Until now, Al and Fe-based chemicals are widely used metal coagulants in water treatment, and aluminum (Al) salts in particular are widely used due to their high efficiency and low cost characteristics. Water purification sludge generated from aluminum (Al) coagulants contains a significant amount of aluminum (Al). Various approaches have been studied to utilize aluminum (Al) sludge (or alum sludge, AS) as a pollutant adsorbent for heavy metals, phosphorus (P), and fluoride, as a wastewater treatment flocculant, as a substrate for artificial wetlands, and as a soil amendment. , it has been studied as a replacement for brick manufacturing, but technology development is still required.

Korean registered patent 10-1295437 Korean registered patent 10-1788374

Therefore, the present invention is intended to solve various shortcomings and problems caused by prior technologies in consideration of the above-described circumstances, by removing impurities such as organic substances from coagulated sludge generated in water purification plants through various heat treatments and removing aluminum-rich particles. The purpose is to improve the removal rate of the phosphorus (P) component of wastewater through adsorption and coagulation.

In addition, the purpose is to reduce the risk of pollutants contained in the coagulated sludge being released into an aqueous solution during phosphorus (P) removal using coagulated sludge generated at a water purification plant.

In addition, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the description below.

In order to achieve the above object, according to an embodiment of the present invention, removal of phosphorus components of wastewater produced by drying or pyrolyzing coagulated sludge generated in a water purification plant is provided.

According to another embodiment, the thermal decomposition may be performed at 500 to 700°C.

According to another embodiment, the drying may be at least one of air drying or oven drying.

According to another embodiment, the oven drying may be performed at 50 to 150°C.

According to another embodiment, the coagulated sludge may be pretreated to a size of 0.7 to 1 mm before drying or pyrolysis.

According to another embodiment of the present invention, a method for producing a phosphorus component remover for wastewater comprising the steps of collecting coagulated sludge generated in a water purification plant and pre-treating it to a size of 0.7 to 1 mm, and drying or thermally decomposing the pre-treated coagulated sludge. This is provided.

According to another embodiment, the drying may be performed by leaving the pretreated flocculated sludge at 15 to 20°C for 36 to 60 hours so that the moisture content is 10 to 30%.

According to another embodiment, the drying may include drying the pretreated coagulated sludge in an oven heated to 100 to 110° C. for 12 to 36 hours.

According to another embodiment, the thermal decomposition may be performed at a heating rate of 10 to 30°C/min at 500 to 700°C.

According to another embodiment, nitrogen gas may be supplied at a flow rate of 100 to 300 mL/min during the thermal decomposition.

According to another embodiment of the present invention, a phosphorus component remover for wastewater produced by any of the above-described methods is provided.

The phosphorus component remover for wastewater of the present invention is a high-temperature heat treatment (ignition or thermal decomposition) of coagulated sludge generated at a water purification plant, and the remaining ash contains high concentrations of Al, Fe, Ca, etc., and these residues are removed from the flocculation facility of the wastewater treatment plant. It is effective to remove the phosphorus component of wastewater by adsorption or precipitation by mixing it with returned sludge and injecting it into the bioreactor.

In addition, if the coagulated water purification sludge is dried and then pyrolyzed at a high temperature, the organic matter contained in the sludge can be removed, preventing the organic matter from the sludge from leaking out during the phosphorus removal process and contaminating the water, and the heat treatment residue of the water purification sludge can be removed. There is an advantage in that the content of Al, Fe, and Ca increases. At this time, when Al, Fe, and Ca are burned at high temperature, oxides are generated, which can weaken the phosphorus agglomeration removal performance, so thermal decomposition under oxygen-free conditions is more advantageous. .

On the other hand, even if sludge heat treatment residues are mixed and processed with materials used to make carriers or filter media, the contents of Al, Fe, and Ca can be maintained high, so the phosphorus removal capacity per unit volume or unit mass of the manufactured carrier or filter media is high. This has the effect of improving phosphorus removal performance.

Figure 1 is a graph showing the pH _PZC measurements of air-dried, oven-dried, 500°C, and 700°C pyrolyzed AS.
Figure 2 is a graph showing the effect of pH on phosphate adsorption capacity using oven-dried AS with the lowest pH _PZC among pretreated AS.
Figure 3 is a graph comparing phosphate adsorption in wastewater of pyrolyzed AS and dried AS.
Figure 4 is a graph showing the amount of phosphate adsorption per Al content of AS according to adsorption time.
Figure 5 is a graph examining the phosphate adsorption characteristics of pretreated AS through an adsorption isotherm experiment.
Figure 6 is a graph showing the phosphate adsorption aspect per mass of Al.
Figures 7 to 9 are graphs showing Al dissolution and COD release in AS during the phosphate adsorption process.

Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in this specification and patent claims should not be construed as limited to their usual or dictionary meanings, and the inventor must appropriately use the concept of the term to explain his or her invention in the best way. It must be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined clearly. Accordingly, the configuration described in the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent the entire technical idea of the present invention, so at the time of filing this application, various equivalents and It should be understood that variations may exist.

Throughout the specification of the present invention, flocculated sludge generated in a water purification plant may be used interchangeably with flocculated water purification sludge, alum sludge, alum sludge, or its abbreviation AS.

The phosphorus component remover for wastewater according to an embodiment of the present invention may be manufactured by drying or thermally decomposing coagulated sludge generated at a water purification plant.

At this time, according to an embodiment of the present invention, the pyrolysis may be performed at 500 to 700 ℃, preferably at 500 ℃ or 700 ℃, and when the sludge is pyrolyzed at this temperature, the phosphate removal rate is improved. do.

Meanwhile, according to an embodiment of the present invention, drying may be at least one of air drying or oven drying.

At this time, the oven drying may be performed at 50 to 150°C, preferably at 50 or 105°C, and it can be confirmed that the efficiency of removing phosphorus components from diesel wastewater that satisfies the above temperature range is improved.

In addition, according to one embodiment of the present invention, the coagulated sludge may be pretreated to a size of 0.7 to 1 mm before drying or pyrolysis, and the pretreatment may be pulverized and then sieved to uniformly size 0.7 to 1 mm.

The method for producing a phosphorus component remover from wastewater according to an embodiment of the present invention includes a pretreatment step (S10) and a drying or thermal decomposition step (S20).

The pretreatment step (S10) may be collecting coagulated sludge generated at a water purification plant and uniformly sized to 0.7 to 1 mm.

Meanwhile, the drying or pyrolyzing step (S20) is a step of drying or pyrolyzing the pretreated coagulated sludge.

At this time, the drying may be performed by leaving the pretreated flocculated sludge at 15 to 20°C for 36 to 60 hours so that the moisture content is 10 to 30%. Preferably, the pretreated flocculated sludge is left at 15 to 20°C. It may be left for 48 hours to bring the moisture content to 20%, and if the above range is satisfied, the efficiency of removing phosphorus from wastewater is improved.

Additionally, the drying may include drying the pretreated coagulated sludge in an oven heated to 100 to 110°C for 12 to 36 hours, and preferably in an oven at 105°C for 24 hours.

Meanwhile, the thermal decomposition may be performed at a heating rate of 10 to 30°C/min at 500 to 700°C, and is preferably performed in a muffle furnace at 500 or 700°C for 1 hour at a heating rate of 20°C/min. It may be.

Meanwhile, during the thermal decomposition, nitrogen gas can be supplied to the muffle furnace at a flow rate of 100 to 300 mL/min, and preferably at a flow rate of 200 mL/min.

Hereinafter, the present invention will be described in further detail through examples, but it is obvious that the present invention is not limited by the following examples.

Alum sludge (AS) heat treatment

AS collected from the sludge filter press of the water purification plant (WTP) was stored in an airtight container at 5°C and immediately transported to the laboratory for use in experiments. To investigate and compare the phosphate removal efficiency from wastewater, three different heat treatments (oven drying at 105°C, pyrolysis at 500 and 700°C) and air drying were applied to AS and compared. Before heat treatment, the AS cake was crushed and sieved to achieve a uniform size of 0.7 to 1 mm. For air-dried AS, the ground and sieved AS was left in the laboratory for 48 hours (temperature: 15-20°C). The moisture content of air-dried AS was less than 20%. For oven drying, the pulverized sludge was dried in an oven at 105°C for 24 hours. For pyrolysis, the oven-dried sludge was pyrolyzed in a muffle furnace at 500 and 700°C for 1 hour at a heating rate of 20°C/min. To prevent oxidation during thermal decomposition, N ₂ gas was supplied to the muffle furnace at a flow rate of 200 mL/min. All pretreated AS were gently ground to a particle size of 0.7 to 1 mm using a standard sieve and stored in a desiccator before use.

Chemical analysis methods

The pH of AS was measured with a pH meter, and the ratio of fixed and volatile solids in the AS cake was measured according to Standard Methods. Total phosphorus (TP) and phosphate phosphorus (PO ₄ ^3- ) were measured using the sulfate and ascorbic acid methods, respectively.

The solid addition method was adopted to determine the zero charge point (pH _PZC ) of AS. Specifically, 0.1 g of AS was mixed with 25 mL of 0.1 M NaCl solution in a 100 mL flask adjusted to a pH ranging from 2 to 12 by adding 0.1 M HCl and NaOH, and then these flasks were incubated at 25 °C for 48 h. It was stirred in a shaking incubator. Finally, to find the pH _PZC at ΔpH = 0, the final pH value (pH _f ) and the subtraction (ΔpH) of the initial pH value (pH _i ) were measured and plotted against pH i . The elemental composition of AS was confirmed using X-ray fluorescence spectroscopy (XRF). To quantify the major metal content of AS, 1 g of each pretreated AS was autoclaved at 121°C for 30 minutes, decomposed in 20 mL of 7N nitric acid, filtered through a 0.45μm PTFE membrane filter, and inductively coupled plasma optical emission spectrum. Elements were analyzed by (ICP-OES).

The chemical oxygen demand (COD) of AS was measured using the US-EPA reactor digestion method. Basically, all types of AS were finely ground before homogenization, and 0.5 g of each AS was stirred and mixed with 50 mL distilled water for 24 h at room temperature. Afterwards, 2.0 mL of each mixture was added to the COD digestion vial and heated at 150 °C for 2 h in a reactor (HS-R200, Humas, Korea), then cooled to room temperature and measured in a spectrophotometer (HS-3300, Humas, Korea). It was measured.

Phosphate adsorption by pretreated water sludge (AS)

The effect of pH on phosphate adsorption of AS was studied by oven-dried AS with the lowest pH _PZC in 50 mL phosphate (KH ₂ PO ₄ ) solutions with concentration ranges from 30 to 500 mg/L at various pHs of 4, 6, 7, and 10. 0.1 g was added and tested at 250 rpm and 25°C for 48 hours. The pH ranges 4 and 6 of AS adsorption are lower than the pH _PZC of AS, and the adsorption pH ranges 7 and 10 are higher than the pH _PZC . In the phosphate adsorption kinetics experiment, 0.2 g of pretreated AS was mixed with 100 mL of phosphate solution (31 mg P/L) at pH 6.

Characteristics and chemical composition of water purification plant alum sludge (AS)

Table 1 shows the physicochemical properties of AS obtained from the water purification plant. The moisture content of dehydrated AS is approximately 80%, the fixed solids content of AS (53.3%) is slightly higher than the volatile solids (46.7%), and the total phosphorus (T-P) content is less than 0.1 g/kg. am. According to XRF analysis, Al is the most abundant element, followed by small amounts of C, Si, Fe, S, and Mn, and most heavy metals (Ni, Cu, Zn, As) are very low, below 0.1 mg/kg.

parameter value unit pH 6.69 ±0.02 - Total solids 187.79 ±0.95 g/kg AS Volatile solids 46.7 ±0.05 % Fixed solids 53.3 ±0.05 % T-P 0.08 ±0.002 g/kg AS As 0.09 ±0.001 mg/kg AS Cr 0.01 ±0.00 mg/kg AS Cu 0.07 ±0.001 mg/kg AS Ni 0.01 ±0.00 mg/kg AS Pb 0.11 ±0.002 mg/kg AS Zn 0.04 ±0.001 mg/kg AS Al ₂ O ₃ 47.20 % SiO ₂ 19.10 % _{Fe2O3 _} 2.10 % MnO 0.46 % _CO2 24.60 % SO ₃ 3.91 % Cl 0.80 % P ₂ O ₅ 0.37 % _K2O 0.46 % CaO 0.42 % MgO 0.18 % Na ₂ O 0.14 %

Effect of pH on Phosphate Adsorption

Most of the phosphorus present in wastewater exists in the form of phosphate, and phosphate is adsorbed on the surface of positively charged substances (aluminum hydrate, etc.) or is absorbed into substances such as Al ³⁺ , Fe ³⁺ (or Fe ²⁺ ), Ca ²⁺ , etc. It is removed by combining with positive (+) ions to form a precipitate. In the present invention, the particles obtained after heat treatment of AS are pulverized to the desired size (about 0.7 to 1 mm in diameter) and injected into a coagulation/mixing tank or sludge aeration tank of a wastewater treatment facility to remove phosphorus by adsorption/binding and precipitation.

The pH at which the net surface charge is zero (zero charge point, pH _PZC ) is an essential property for adsorption/flocculation of contaminants from aqueous solutions. If the pH of the solution is lower than the pH of the corresponding adsorbent surface, _PZC , it has a positive charge, and if it is higher, it has a negative charge. The pH _PZC of air-dried, oven-dried, 500°C, and 700°C pyrolyzed AS were 6.50, 6.28, 6.68, and 7.71, respectively (Figure 1). Except for AS pyrolyzed at 700°C, dried AS and AS pyrolyzed at 500°C had similar pH _PZC . Therefore, in order to improve phosphate adsorption in AS, the pH must be kept lower than the pH _PZC of AS. From that perspective, the phosphate adsorption capacity of AS pyrolyzed at 700°C has a higher pH _PZC than other AS, so more phosphate can be absorbed at the same pH. is absorbed.

The effect of pH on phosphate adsorption capacity was investigated using oven-dried AS, which had the lowest pH _PZC among the pretreated ASs. As a result, the adsorption capacity was significantly higher at pH 4 to 6 than at pH 7 to 10 (Figure 2). The pKa of phosphate can well explain these results. Phosphate mostly exists as H ₂ PO ₄ ^- in the pH range of 4 - 6, and when pH is higher than 6, it is more easily adsorbed than HPO ₄ ^2- or PO ₄ ^3- . As pH increased from 6 to 7, the phosphate adsorption capacity decreased rapidly. Therefore, it can be seen that pH has a more direct effect on phosphate adsorption than other factors.

Phosphate adsorption kinetics of AS

In phosphate adsorption from wastewater, pyrolyzed AS showed higher adsorption than dried AS (Figure 3). In addition, even in pyrolyzed AS, treatment at 700°C showed better adsorption performance than 500°C. Air-dried AS adsorbed more phosphate than oven-dried AS. Phosphate adsorption on pyrolyzed (500 °C) and oven-dried AS was saturated at 9.50 and 3.70 mg P/g AS, respectively, after 12 h. For air-dried AS, phosphate adsorption further increased after 12 hours, and the adsorption capacity doubled to 5.52 mg P/g AS at 48 hours. During the first 4 hours, pyrolyzed AS showed a faster adsorption rate than air-dried AS and oven-dried AS.

Thermal decomposition AS showed phosphate adsorption amounts two and three times higher than oven and air-dried AS, respectively. The high adsorption kinetics and adsorption capacity of pyrolyzed AS appear to be mostly due to the high Al content of pyrolyzed AS. Thermal decomposition converts the volatile organic matter of AS into inorganic carbon or vaporizes or liquefies it, while metals such as Al remain as is, so the Al content of AS is higher than that of dry AS. There is a strong electrostatic attraction between the positively charged aluminum (oxide) surface and the negative (-) ion phosphate.

Figure 4 shows the amount of phosphate adsorption per Al content of AS according to adsorption time. Except for oven-dried AS, pyrolyzed and air-dried AS showed similar phosphate adsorption properties. The experimental results show that the Al content of AS is one of the most important parameters determining phosphate adsorption, and the structure and form of Al distribution in AS can also affect phosphate adsorption. Air-dried AS had an adsorption capacity of 55.21 mg P/g Al, whereas oven-dried AS had 22.35 mg P/g Al, less than half that of air-dried AS.

The ICP-OES analysis results before and after phosphate adsorption showed that the Al contents of the four pretreated ASs were 126.1, 164.6, 249.2, and 280.9 mg Al/g AS, respectively, in that order: air-dried AS, oven-dried AS, and AS pyrolyzed at 500 and 700 °C. It shows that it has increased. Air-dried AS obtained the highest phosphate adsorption capacity of 55.21 mg P/g Al (Figure 4). Meanwhile, the phosphate adsorption capacity of oven-dried AS and AS pyrolyzed at 500°C and 700°C was directly proportional to the Al content at 22.35, 37.42, and 43.77 mg P/g Al, respectively, after 48 hours. It is believed that phosphate adsorption on air-dried AS is due to other processes such as pore and surface diffusion mentioned above rather than direct Al binding or reaction mechanism.

Phosphate adsorption isotherm of AS

Phosphate adsorption characteristics of pretreated AS were investigated through adsorption isotherm experiments. While the maximum isothermal adsorption of oven-dried AS was 15.06 mg P/g AS, the maximum phosphate adsorption of pyrolyzed AS and air-dried AS showed similar values at 30.83 to 34.53 mg P/g AS (Figure 5). Oven-dried AS showed much lower phosphate adsorption than other pretreated AS. In terms of phosphate adsorption per mass of Al, air-dried AS showed the highest P adsorption amount (Fig. 6). In terms of kL value, the adsorption affinity of phosphate was highest for AS pyrolyzed at 700°C, followed by AS at 500°C, air-dried AS, and oven-dried AS. The adsorption kinetics and isotherm results showed that AS pyrolyzed at 700°C showed the best performance in phosphate removal.

Al dissolution and COD release in AS during phosphate adsorption process

To evaluate the release of contaminants (especially Al and COD) contained in AS when using AS as an adsorbent in wastewater treatment, the release of Al and COD under phosphate solution (1 mM) adsorption conditions was investigated. All four pretreated ASs showed Al dissolution rates of less than 0.2% (2 mg Al/g Al) (Figure 7). In phosphate solution, oven-dried and air-dried AS showed Al dissolution rates of 0.04 and 0.05%, respectively, which were much lower than pyrolyzed AS. The high organic content of air-dried and oven-dried AS appears to form a strong attractive force on aluminum, inhibiting Al dissolution. Additionally, Al dissolution in air-dried AS is low in phosphate solutions (pH 4 - 7) and is more soluble in acidic or alkaline conditions. In general, Al is known to be strongly soluble in acidic or alkaline conditions due to the amphoteric nature of aluminum. Considering the effect of the thermal decomposition temperature of AS, 700°C has less dissolution than 500°C. In summary, Al dissolution in AS was very low in dried AS.

The COD contents of air-dried and oven-dried AS were 143 and 204 mg/g AS, while the COD content of pyrolyzed AS was less than 15 mg/g (Figure 8). However, unlike the COD content, the COD release rate (%) of AS showed the lowest COD release rate (%) for AS that was air-dried, followed by AS pyrolyzed at 700°C, AS dried in an oven, and AS pyrolyzed at 500°C. The release rate increased in the AS order (Figure 7). However, the amount of COD released (mg/g AS) was lowest for AS pyrolyzed at 700 °C, followed by 500 °C, air-dried, and oven-dried AS (Figure 9). After P adsorption, significantly more COD was released from oven-dried AS than from air-dried AS. The pyrolyzed AS had a low COD content, so its COD release was low, below 1 mg COD/g AS. In the case of Al (aluminum), the maximum amount released per g of AS was less than 0.5 mg, so it was not a major problem.

The reduction of COD during the AS pyrolysis process significantly helped reduce the risk of pollutant emissions, and the pyrolyzed AS was found to be more suitable for use as a phosphate adsorbent compared to air-dried and oven-dried AS.

Meanwhile, in order to use it for water phosphate removal, AS is pretreated by methods such as air drying and oven drying at 50 and 105°C, and then the AS is pulverized into particle sizes of 0.063 mm or less, 0.1 to 0.3 mm, 0.15 to 0.6 mm, and 1.25 mm. As a result of a phosphorus removal experiment at ~1.65 mm, etc., the smaller the particle size of AS, the higher the P adsorption amount and adsorption rate. The particle size of AS is directly related to the diffusion and adsorption of P into the particle. However, considering the sedimentation speed of Al particles adsorbing P, the larger the particle size, the greater the sedimentation speed, so it is judged that the optimal AS size for P removal is approximately 0.7 to 1 mm.

Phosphate removal efficiency depends on the pretreatment method of AS. In order to minimize the change in AS structure from amorphous to crystalline and secure the maximum adsorbable hydroxide surface area (hydroxide active sites), it is advantageous to dry AS in an oven at 105°C immediately after sample collection. However, another study showed that air-dried AS (25 and 31.9 mg P/g AS) at the same pH 4 had significantly higher P adsorption compared to oven-dried AS (1.11 and 4.86 mg P/g AS) at 105 and 103 °C. It looks like Additionally, the risk assessment of the release of organic pollutants and metals, such as COD, including Al, from AS during the P removal process is still unknown.

Recently, calcinated AS was applied to remove water pollutants such as methylene blue and arsenic (V). As a result, AS calcined at 700°C showed a maximum methylene blue adsorption of 68.97 mg/g AS, and AS calcined at 300°C showed a maximum adsorption of methylene blue of 68.97 mg/g AS. showed arsenic (V) adsorption of 53.15 mg/g AS. In addition to drying and calcination of AS, pyrolysis removes most organic contaminants and volatile impurities, enriching AS in Al. Pretreatment of AS by pyrolysis concentrates Al, removes organic matter, provides more positively charged adsorption sites on Al for P adsorption from solution, and weakly negatively charged sites by organic matter, thereby providing P It is advantageous for removal.

In addition, alum sludge generated from a water purification plant was dried and pyrolyzed and used to remove phosphate from wastewater, and its removal characteristics were investigated. The pH _PZC results of AS showed that pyrolyzed AS was more effective in adsorption of phosphate than dried AS. In the kinetic analysis of phosphate adsorption, the phosphate removal rate was fastest in the order of pyrolyzed AS at 700°C and 500°C, followed by air-dried and oven-dried AS. Phosphate adsorption is directly related to the Al content of AS. The results of kinetic adsorption modeling of phosphate showed that chemical adsorption was the main mechanism for phosphate removal, as the pseudo second order model was the most appropriate model. The adsorption isotherm of phosphate showed that pyrolyzed AS and air-dried AS had adsorption capacities of 30.83 to 34.53 mg P/g AS. Al dissolution in AS was minimal, less than 2 mg/g Al in all samples, but COD release was up to 8.0 mg COD/g AS in dried AS and less than 1 mg COD/g AS in pyrolyzed AS. Overall, AS pyrolyzed at 700°C was the most effective in removing phosphate from wastewater.

Claims (11)

delete delete delete delete delete Collecting coagulated sludge generated from a water purification plant and pretreating it to a size of 0.7 to 1 mm;
Drying the pretreated flocculated sludge in an oven heated to 100 to 110°C; and
A method for producing a phosphorus component remover for wastewater comprising the step of thermally decomposing the dried sludge at 700°C. delete delete delete According to clause 6,
A method for producing a phosphorus component remover for wastewater, wherein nitrogen gas is supplied at a flow rate of 100 to 300 mL/min during the thermal decomposition. delete