Method of Manufacturing Artificial Lightweight Aggregate by Recycling Total Phosphorus Treatment Sludge

Abstract

The present invention relates to a method for manufacturing artificial lightweight aggregate that recycles total phosphorus treatment sludge in large quantities. The method involves mixing dried total phosphorus treatment sludge, clay minerals, and water to control the moisture content to 50% by weight or less, molding, drying, and calcining the mixture. This process recycles total phosphorus treatment sludge containing a large amount of phosphorus, which has a low organic matter content that limits its recycling as fuel and can cause eutrophication of rivers, and sinters the lightweight aggregate using internal heat generation to increase thermal efficiency and lower the calcination temperature.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing artificial lightweight aggregate by recycling total phosphorus treatment sludge generated during a sewage treatment process, and more specifically, to a method for manufacturing artificial lightweight aggregate by mixing total phosphorus treatment sludge and clay minerals, and molding, drying, and firing the mixture. Background Technology

[0003] In Korea, a large amount of household waste is generated daily. As the sewage system coverage has increased due to population growth and industrial development, the volume of sewage treatment has also risen. Sewage treatment involves advanced processes such as physical, biological, and chemical treatments. If the high concentrations of total phosphorus and total nitrogen present in the sewage are not treated properly, it exacerbates eutrophication in rivers and oceans, such as algal blooms and red tides; therefore, the concentrations of total phosphorus and total nitrogen in discharged water must be managed very strictly.

[0004] The Ministry of Environment has consistently amended the Sewerage Act to improve water quality in public waters and prevent eutrophication, and starting from July 2024, total phosphorus (TP) is subject to a discharge regulation range of 0.2–4 mg / L, depending on the capacity of the treatment facility and the discharge site. Total nitrogen is regulated at 20–40 mg / L (National Water Resources Management Information System). For this reason, the importance of additional total phosphorus treatment has recently been emphasized, and as of 2021, approximately 400 facilities are performing additional total phosphorus treatment (Status of Public Wastewater Treatment Facilities in 2021, Korea Environment Corporation). Although the exact amount of total phosphorus treatment sludge generated is not tallied, Korean Patent Publication No. 10-2016-0131645 states that approximately 600,000 tons were generated annually as of 2012, and it is estimated that a larger amount is generated now that regulatory limits have been lowered and the number of treatment plants performing total phosphorus treatment has increased.

[0005] This additional total phosphorus treatment process is primarily performed by precipitation and removal using chemical coagulants such as aluminum sulfate or polyaluminum chloride (PAC). This additional total phosphorus treatment process generates sludge containing a large amount of coagulant (hereinafter referred to as “total phosphorus treatment sludge”).

[0006] Currently, total phosphorus-treated sludge is generally disposed of by either being fed into anaerobic digesters in sewage treatment facilities for integrated processing, or by installing a separate centrifugal dewatering machine to reduce its moisture content to 75% or less before direct landfilling. Unlike general sewage sludge, total phosphorus-treated sludge is inorganic, so feeding it into anaerobic digesters leads to a decrease in digestion efficiency. Furthermore, direct landfilling can cause landfill collapse due to its high moisture content, and rising landfill costs can increase treatment expenses; therefore, recycling is the most desirable option.

[0007] Korean Registered Patent No. 10-1303965 discloses a method for manufacturing a pellet-type powder adsorbent by dewatering and drying total phosphorus sludge. Additionally, Korean Registered Patent No. 10-1534830 presents a method for manufacturing a granular adsorbent by producing total phosphorus sludge into a granular form and carbonizing it. However, these methods cannot adequately address the large volumes of total phosphorus sludge generated, and recycling sources are inevitably extremely limited. Furthermore, since total phosphorus sludge is an inorganic sludge, recycling it as a cement raw material or admixture could be considered; however, due to the phosphorus components contained in the sludge, phosphates dissolve during the cement hydration and hardening reaction. These phosphates occupy the reaction sites of tricalcium silicate, inhibiting the initial hydration of cement clinker and delaying the setting time, making recycling as a cement raw material or admixture impossible. Regarding the recycling of total phosphorus sludge, technological development has not been active to the extent that it is extremely difficult to find methods other than those mentioned above. In addition, since the amount of sludge generated is expected to increase due to the recent strengthening of environmental standards, technology capable of consuming large quantities of total phosphorus treatment sludge is required for the practical recycling of total phosphorus treatment sludge.

[0009] Accordingly, the inventors of the present invention have made diligent efforts to solve the problems of the prior art described above. As a result, they confirmed that by mixing total phosphorus sludge and clay minerals to control the moisture content to 40% by weight or less, and then molding, drying, and firing the mixture, it is possible to recycle a large amount of total phosphorus sludge, which is entirely being landfilled, while simultaneously saving the high energy costs required for manufacturing artificial lightweight aggregate due to internal heat generation, increasing thermal efficiency, and manufacturing artificial lightweight aggregate that meets the KS F 2527 standard for lightweight aggregates, thereby completing the present invention. Prior art literature

[0011] Republic of Korea Registered Patent No. 10-1303965 Republic of Korea Registered Patent No. 10-1534830 The problem to be solved

[0012] The objective of the present invention is to recycle total phosphorus treatment sludge, which is increasing in volume, in large quantities without landfilling it, to provide a reasonable process for manufacturing artificial lightweight aggregate, and to provide a method for manufacturing artificial lightweight aggregate that conforms to the KS F 2527 standard for lightweight aggregate. means of solving the problem

[0014] To achieve the above objectives, the present invention provides a method for manufacturing artificial lightweight aggregate recycled from total phosphorus sludge, comprising the steps of: (a) grinding dried total phosphorus sludge; (b) obtaining a mixture of 10 to 60 wt% powdered total phosphorus sludge and 40 to 90 wt% clay minerals; (c) molding and drying the mixture to obtain a molded body; and (d) firing the molded body.

[0015] The present invention provides a composition for manufacturing artificial lightweight aggregate comprising 10 to 60 wt% of total phosphorus treated sludge and 40 to 90 wt% of clay minerals. Effects of the invention

[0017] The method for manufacturing artificial lightweight aggregate according to the present invention has the following effects.

[0018] (1) Unlike general sewage sludge, total phosphorus treatment sludge is an inorganic sludge with a low organic matter content and has different characteristics from sewage sludge, so it is not suitable for use as fuel and there is no suitable recycling method. However, when recycled as a raw material for artificial lightweight aggregate, it can be recycled in relatively large quantities due to its low organic matter content.

[0019] (2) By sintering lightweight aggregate with internal heat, the thermal efficiency can be increased, and the calcination temperature can be lowered by 50 to 100°C due to the organic matter contained in the total phosphorus treatment sludge, thereby reducing fuel costs used during aggregate calcination.

[0020] (3) Total phosphorus sludge contains a large amount of adsorbent components used in water treatment, exists as fine powder, and can impart plasticity during the molding process, making it advantageous for the production process of artificial lightweight aggregates.

[0021] (4) P2O5 contained in total phosphorus sludge can lower the liquid phase formation temperature of the substrate in the ceramic process and can strengthen the structure. Brief explanation of the drawing

[0023] FIG. 1 is a schematic diagram showing the manufacturing process of an artificial lightweight aggregate according to one embodiment of the present invention. FIG. 2 is a cross-section of aggregate according to the content of total phosphorus treated sludge and general sludge according to one embodiment of the present invention. Figure 3 is a photograph of aggregate with a diameter of 10 to 15 mm prepared from total phosphorus treated sludge according to one embodiment of the present invention. Specific details for implementing the invention

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled expert in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0026] In this invention, it was confirmed that by crushing dried total phosphorus treatment sludge, mixing it with red clay, and then molding, drying, and firing it, it is possible to recycle the total phosphorus treatment sludge, which is currently entirely landfilled, in large quantities, save the high energy costs required for the manufacture of artificial lightweight aggregate, and produce artificial lightweight aggregate that meets the KS F 2527 standard for lightweight aggregate.

[0027] Accordingly, in one aspect, the present invention relates to a method for manufacturing artificial lightweight aggregate using total phosphorus treated sludge, comprising the steps of: (a) obtaining a mixture of 10 to 60 wt% total phosphorus treated sludge and 40 to 90 wt% clay minerals; (b) molding and drying the mixture to obtain a molded body; and (c) firing the molded body.

[0029] The present invention will be described in detail below.

[0030] The term “sewage sludge” used in the present invention refers to sludge collected during the sewage treatment process.

[0031] The term “total phosphorus treatment sludge” used in the present invention refers to inorganic sludge containing a high amount of phosphorus generated through a process of removing phosphorus from phosphorus-containing sewage and wastewater, wherein total phosphorus includes all phosphorus present in water.

[0032] The phosphorus content in typical total phosphorus treated sludge can be 3 wt% or more, preferably 5 to 30 wt%, and more preferably 5 to 15 wt%, and all total phosphorus treated sludge is included regardless of phosphorus content. In the example, 14.6 wt% was used, but it is not a significant issue as long as it falls within the above range.

[0033] General sewage sludge is known to have an organic matter content of 70 to 80 wt%. On the other hand, total phosphorus treated sludge was found to have an organic matter content of approximately 40 wt% based on measurement results. This implies that total phosphorus treated sludge has too low a calorific value for fuel production. However, Korean registered patent No. 10-2372282 describes an artificial lightweight aggregate recycled from anaerobic digestion sludge, stating that it is relatively free from limitations on the recycling rate due to its low organic matter content.

[0035] A method for manufacturing artificial lightweight aggregate using total phosphorus treated sludge according to the present invention may include: (a) a step of crushing dried total phosphorus sludge; (b) a step of obtaining a mixture mixed with 10 to 60 wt% of dried total phosphorus sludge and 40 to 90 wt% of clay minerals; (c) a step of molding and drying the mixture to obtain a molded body; and (d) a step of firing the molded body.

[0036] Specifically, the method for manufacturing lightweight aggregate using total phosphorus treated sludge and red clay according to the present invention may include a raw material mixing step of mixing, grinding, and mixing water with dried total phosphorus treated sludge and clay; a molding step of molding the prepared wet raw material into a cylinder shape through a clay mixer; a drying step of drying the molded body at 300 to 600°C; and a firing step of firing the dried body at 800 to 1200°C to reach a desired density.

[0037] In the present invention, the content in step (b) is limited to 10 to 60 wt%. If it is less than 10 wt%, the effect of recycling the total phosphorus treatment sludge is significantly reduced, and if it exceeds 60 wt%, the molding process becomes considerably difficult and the strength of the final aggregate is significantly lowered.

[0038] In the present invention, after step (b), a step of coating the molded body with sand having a diameter of 0.3 to 0.5 mm may be additionally included.

[0039] In the present invention, the clay mineral may be selected from one or more types from the group consisting of bentonite, zeolite, red clay, white clay, and acidic white clay.

[0040] In the present invention, the drying of step (b) can be performed at a temperature of 600°C or lower, preferably at a temperature of 300°C to 600°C. If drying is performed at a temperature below 300°C, there is a problem that the process time increases significantly because the drying speed is slow.

[0041] In the present invention, the calcination of step (c) can be performed at a temperature of 800 to 1200°C. If calcined at a temperature below 800°C, the reaction does not occur sufficiently, resulting in a problem where the strength of the aggregate is significantly lowered, and if calcined at a temperature above 1200°C, a fusion phenomenon occurs due to liquefaction of the surface.

[0042] In the present invention, a grinding process of the raw material may be additionally included prior to step (a). The material may be ground to a particle size of 200 Mesh or less (75 μm or less).

[0043] In the present invention, the molding in step (b) can be formed into a spherical shape using a pelletizer, and can also be formed into a cylindrical shape using a clay mixer.

[0044] According to a preferred embodiment of the present invention, a method for manufacturing artificial lightweight aggregate containing a large amount of total phosphorus treated sludge is provided, comprising: a first step of preparing a mixture by mixing 10 to 60 wt% of total phosphorus treated sludge dry powder with 70 to 90 wt% of clay minerals (bentonite zeolite, red clay, white clay, acidic white clay, etc.); a second step of feeding the mixture into a clay mixer and molding it into a cylinder shape; a third step of coating the molded body with sand of 0.3 to 0.5 mm to prevent fusion during firing and to sphericalize the molded body; a fourth step of drying the molded body at a high temperature before firing; and a fifth step of firing to improve the strength and lighten the aggregate.

[0045] In the first step above, the total phosphorus treatment sludge includes secondary and tertiary sludge generated during the sewage treatment process, and clay acts as a binder, including, for example, red clay, bentonite, zeolite, etc.

[0046] In the second step above, the moisture content of the wet mixture is designed to be 50 wt% or less. In addition, the diameter of the aggregate that can be molded in the second step is in the range of 5 to 15 mm.

[0047] In the third step above, the particle size of the sand for coating is 0.3 to 0.5 mm, and the sand for coating may include silica, limestone, dolomite, etc.

[0048] In the above fourth step, the drying temperature is 300℃ or lower, and the moisture is dried to 15% by weight or less for 60 to 120 minutes.

[0049] The above 5th step is characterized by including a process of firing at a firing temperature of 800 to 1200℃.

[0050] The artificial lightweight aggregate obtained through the above manufacturing method satisfies KS F 2527, and the manufactured aggregate has a mass per unit volume of 0.88 kg / L or less.

[0051] In another aspect, the present invention relates to a composition for manufacturing artificial lightweight aggregate comprising 10 to 60 wt% of total phosphorus treated sludge and 40 to 90 wt% of clay minerals.

[0052] In the composition for manufacturing artificial lightweight aggregate according to the present invention, the clay mineral may be selected from one or more types from the group consisting of red clay, bentonite, zeolite, dredged soil, white clay, and acidic white clay.

[0053] The present invention provides a method for recycling total phosphorus treatment sludge generated during the total phosphorus treatment process in sewage treatment, while simultaneously producing artificial lightweight aggregate, a high-value-added construction material.

[0054] In addition, the method presented in this invention maximizes the recycling rate by drying and using the total phosphorus treatment sludge, and the 30-40 wt% of organic matter contained in the total phosphorus treatment sludge is utilized as a heat source in the lightweight aggregate calcination process, thereby lowering the calcination temperature of the existing aggregate by about 100°C and reducing input energy. Furthermore, the manufactured lightweight aggregate can be used in various ways for landscaping, lightweight concrete, and lightweight panels, and it is environmentally desirable as it can replace crushed stone aggregate, which is used at a rate of about 200 million tons per year as of 2019.

[0056] The present invention will be described in more detail below through examples. These examples are solely for illustrating the present invention, and it will be obvious to those skilled in the art that the scope of the present invention is not to be interpreted as being limited by these examples.

[0058] [Example]

[0059] Example 1

[0060] The total phosphorus treatment sludge used in the example was generated at the Bucheon Wastewater Treatment Plant, and the chemical composition (unit: weight%) of the total phosphorus treatment sludge and red clay was analyzed by XRF (ZSX-100e, Rigaku, Japan) and is shown in Table 1.

[0061] General sewage sludge is known to have an organic matter content of 70 to 80 wt%. On the other hand, total phosphorus treated sludge was found to have an organic matter content of approximately 40 wt% based on measurement results. This implies that total phosphorus treated sludge has too low a calorific value for fuel conversion. However, Korean registered patent No. 10-2372282 describes an artificial lightweight aggregate recycled from anaerobic digestion sludge, stating that it is relatively free from limitations on the recycling rate due to its low organic matter content.

[0062] Chemical composition (wt%) of total phosphorus treatment sludge SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO Na 2 O K 2 O TiO 2 P 2 O 5 Cr 2 O 3 MnO LOI total Total phosphorus treatment sludge 1.71 36.58 0.44 1.33 0.19 0.65 0.39 0 14.6 0 0.09 44.02 100 red clay 62.39 18.35 5.38 0.66 1.05 0.41 1.74 0.98 0 0 0 9.04 100

[0064] A mixture was prepared by mixing 30 kg of dried powder of total phosphorus treatment sludge with 70 kg of red clay and kneading it to a moisture content of 40 wt%, molding it into a diameter of 10 mm, and rapidly sintering it at 1050°C to produce an aggregate with a weight of 0.72 kg / L per unit volume, and the aggregate satisfies KS F 2527.

[0066] Example 2: Comparison of aggregate properties according to sludge content

[0067] Table 2 compares the weight per unit volume of aggregates according to content of sewage sludge and artificial lightweight aggregates containing total phosphorus treatment sludge dry powder.

[0068] Artificial lightweight aggregate containing sewage sludge dry powder and total phosphorus-treated sludge dry powder exhibited similar weight per unit volume at the same addition amount. As the content increased, the weight per unit volume decreased. All lightweight aggregates manufactured within the content range of 10–60 wt% satisfied KS F 2527 (Fig. 2).

[0069] Change in weight per unit volume of aggregate according to the content of sewage sludge and total phosphorus treatment sludge Sludge content 10 30 60 sewage sludge 0.82㎏ / L 0.72㎏ / L 0.65㎏ / L Total phosphorus sludge 0.84㎏ / L 0.75㎏ / L 0.69㎏ / L

[0071] Example 3

[0072] Aggregates with a diameter of 5 to 15 mm were manufactured using the above total phosphorus treated sludge. The mixing ratio consisted of 20 kg of dried total phosphorus treated sludge powder and 80 kg of red clay, which were then molded into a pelletizing machine and fired in a rotary kiln at a temperature of 1000 to 1030°C. The manufactured aggregate satisfied KS F 2527 with a mass per unit volume of 0.78 kg / L, and the manufactured aggregate is shown in Fig. 3.

[0074] Foregoing, specific parts of the present invention have been described in detail. It will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the invention. Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.

Claims

Claim 1 A method for manufacturing artificial lightweight aggregate comprising the following steps: (a) obtaining a mixture of 10 to 60 wt% total phosphorus treated sludge and 40 to 90 wt% clay minerals; (b) adjusting the moisture content of the mixture to 40 wt% or less, then molding and drying to obtain a molded body; (c) coating the molded body with sand having a diameter of 0.3 to 0.5 mm; and (d) firing the sand-coated molded body, wherein the clay minerals are selected from one or more of the group consisting of red clay, bentonite, zeolite, dredged soil, white clay, and acidic white clay, and the phosphorus content of the total phosphorus treated sludge is 3 wt% or more. Claim 2 A method for manufacturing artificial lightweight aggregate according to claim 1, characterized in that the drying in step (b) is performed at a temperature of 100 to 600℃. Claim 3 A method for manufacturing artificial lightweight aggregate according to claim 1, characterized in that the calcination of step (d) is performed at a temperature of 800 to 1200℃. Claim 4 A method for manufacturing artificial lightweight aggregate according to claim 1, further comprising a crushing process after step (a). Claim 5 A method for manufacturing artificial lightweight aggregate according to claim 1, wherein the molding in step (b) is formed into a spherical shape using a pelletizer or formed into a cylindrical shape using a clay mixer.

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