CN105819891A - Preparation method of sludge ceramsite used for medium and low concentration ammonia nitrogen wastewater treatment - Google Patents

Abstract

The invention provides a preparation method of sludge ceramsite used for the treatment of medium and low concentration ammonia nitrogen wastewater: soak fly ash with 3%~6% NaOH solution at 20~30°C for 3~4 days, then use deionized water After cleaning, dry at 100-110°C; dry the remaining sludge and clay at 100-110°C; dry the above three raw materials, crush them, and sieve them for later use; the mass ratio of the above-mentioned pretreated materials is 30%-60 % of fly ash, 30%~60% of excess sludge, and 10% of clay are thoroughly mixed to obtain a dry material; add an appropriate amount of deionized water to the above dry material and stir evenly to make a blank material of 1~3mm , and place it on a tray and dry it in an oven at 110°C until there is no moisture on the surface; put the dried billet into a muffle furnace and heat it to 350°C~500°C, preheat for 10~40 minutes, and then heat up to 800°C Burn at ℃~1100℃ for 10~25 minutes, and take it out when it is cooled to 180~200℃ in the furnace to obtain sludge ceramsite. The sludge ceramsite prepared by the method of the invention is cheap, economical, efficient and environmentally friendly, and is suitable for the treatment of medium and low concentration ammonia nitrogen wastewater.

Description

A preparation method of sludge ceramsite for medium and low concentration ammonia nitrogen wastewater treatment

technical field

The invention relates to a preparation method of sludge ceramsite which can be used for the treatment of medium and low concentration ammonia nitrogen wastewater, and belongs to the fields of waste resource utilization and sewage treatment.

Background technique

Ammonia nitrogen refers to nitrogen that exists in the form of free ammonia (or called non-ionic ammonia NH ₃ ,) or ionic ammonia (NH ₄ ⁺ ). Ammonia nitrogen mainly comes from human and animal excrement, rainwater runoff, loss of agricultural fertilizers, and industrial wastewater such as petrochemical, metallurgy, gas, and coking ^[1] . The harm caused by the massive discharge of ammonia nitrogen wastewater is firstly the excessive consumption of dissolved oxygen in water, which leads to the death of fish and other aquatic organisms due to hypoxia, and at the same time causes the phenomenon of eutrophication in water bodies; secondly, the ammonia nitrogen oxidation product nitrite nitrogen is toxic and easily causes The function of the liver, spleen and kidneys is incomplete, the oxygen supply capacity of the blood is gradually lost, and a variety of diseases are infected. In order to reduce water pollution and protect the ecological environment, the country requires that ammonia-nitrogen-containing wastewater must meet the "Comprehensive Discharge Standard for Sewage" (GB8978-2002) (the primary discharge standard for ammonia nitrogen is ≤15mg/L, and the secondary discharge standard is ≤25mg/L). Dischargeable.

At present, the treatment methods of ammonia nitrogen wastewater mainly include the following types: biological method, ion exchange adsorption method, chemical precipitation method, membrane separation method, wet oxidation method, break point chlorination method, stripping and stripping method, electrochemical method, etc. ^[2] . Each method has its advantages and disadvantages and applicable conditions. It is necessary to conduct a comprehensive analysis according to the specific situation of the wastewater to determine the appropriate treatment method or to adopt a combination of several methods. Generally speaking, for high-concentration ammonia nitrogen wastewater (ammonia nitrogen concentration greater than 500mg/L), the commonly used treatment methods are: air stripping method + biological method, air stripping method + break point chlorination, chemical precipitation method + biological method, etc. For medium and low concentration ammonia nitrogen wastewater (low concentration refers to ammonia nitrogen concentration less than 50mg/L, medium concentration refers to ammonia nitrogen concentration 50-500mg/L), commonly used methods are: ion exchange adsorption method, biological denitrification method, etc.

For example, in the constructed wetland sewage treatment system, the main mechanism of nitrogen removal is microbial nitrification-denitrification, but due to the lack of DO in the constructed wetland, the nitrification cannot be fully carried out, resulting in the inability to convert ammonia nitrogen into nitrate nitrogen, resulting in a lower nitrogen removal efficiency. decline. At present, similar to constructed wetlands, there are anaerobic and anoxic biological filters, which cannot achieve good denitrification effects by biological methods due to the lack of oxygen or even anaerobic substrates. Therefore, the adsorption method for treating low-concentration ammonia-nitrogen wastewater has received more and more attention in recent years.

At present, the materials that can be used for ammonia nitrogen adsorption mainly include: zeolite, activated carbon, montmorillonite, cinder, alumina, silica gel, diatomaceous earth, kaolin, medical stone and ion exchange resin. Most studies have shown that the mechanism for the adsorption of ammonia nitrogen by these substances is ion exchange ^[3] . Some studies on zeolite adsorption of low-concentration ammonia-nitrogen wastewater ^[4-9] show that: no matter natural zeolite or modified zeolite, even if there are interfering cations such as calcium and magnesium in the water, zeolite still has good selective adsorption performance for low-concentration ammonia-nitrogen. The removal of ammonia nitrogen by adsorption has the advantages of simple process and convenient operation. The disadvantages are that the exchange capacity of the adsorption material is limited, the specific surface area is not large enough, the desorption process is frequent, and it will also consume the reserve resources of minerals such as zeolite in my country. Therefore, it is imminent to develop ammonia nitrogen adsorption materials with excellent adsorption effect, low price and easy recovery of ammonia nitrogen.

Based on this, the present invention attempts to use waste resources such as fly ash and urban sewage plant residual sludge as main raw materials to prepare sludge ceramsite with ammonia nitrogen adsorption capacity, which is used as an adsorbent for the treatment of medium and low concentration ammonia nitrogen wastewater.

Fly ash is a kind of industrial waste discharged from the flue of coal-fired thermal power plants. One of the "three wastes" of industry. If the fly ash is not disposed of properly, it will cause many hazards, such as air pollution or its late impact on the environment during its utilization. Therefore, how to use fly ash safely and effectively has become an urgent problem to be solved ^[10] .

The chemical composition of fly ash is similar to the mineral composition of zeolite, which has a large specific surface area and solid adsorbent properties ^[11,12] . Studies have shown that [13,14], using alkaline solution mixed at a certain temperature to modify fly ash, the modified fly ash can greatly improve the adsorption performance and the denitrification function of wastewater.

While paying attention to the comprehensive utilization of fly ash, the resource utilization of another kind of waste—surplus sludge has also begun to attract the attention of scientific and technological workers. With the rapid development of social economy and urbanization in our country, the scale and treatment degree of urban sewage treatment plants are increasing day by day. A large amount of excess sludge is produced while treating sewage, and the output of excess sludge is about 0.15% to 1% of the treated water volume ^[15] . Although it contains nutrients such as N and P, it usually also contains a large amount of toxic and harmful substances. If it is not handled properly and placed randomly, it will cause secondary pollution. The commonly used sludge treatment technologies in China include sludge concentration, sludge conditioning, anaerobic digestion, dehydration, composting, etc. ^[16] . It is of great significance to carry out harmless and resourceful treatment of sludge, turn waste into treasure, and treat waste with waste, which meets the requirements of sustainable social and economic development.

The invention describes a method for preparing sludge ceramsite by using waste resources such as fly ash and excess sludge from sewage plants as main raw materials. After special pretreatment, the sludge ceramsite has the function of ammonia nitrogen adsorption and can be used as an adsorbent in Treatment of low concentration ammonia nitrogen wastewater. The sludge ceramsite of the present invention has high efficiency of adsorbing ammonia nitrogen and low cost, and can also realize the goal of resource utilization of waste by treating waste and turning waste into treasure.

references:

[1] Wang Liping, Cao Guoping, Zhou Xiaohong. Research progress of ammonia nitrogen wastewater treatment technology [J]. Chemical propellants and polymer materials. 2009, 7(3): 26-32.

[2] Li Jianchang. Research on Zeolite Removal of Medium and Low Concentration Industrial Ammonia Nitrogen Wastewater [D] Dissertation. 2009,12.

[3] Zhang Qingdong, Zhao Dongfeng, Zhao Chaocheng. Present situation of denitrification by adsorption method and introduction of commonly used adsorbents [J]. Xinjiang Environmental Protection. 2002, 24(2): 43-46.

[4] Tang Dengyong, Zheng Zheng. Study on the adsorption of low concentration ammonia nitrogen wastewater by natural zeolite [J]. Environmental Science and Technology. 2010,33(12):206-209.

[5] Wen Donghui, Tang Xiaoyan. Natural clinoptilolite in solution The physical and chemical mechanism of [J]. Chinese Environmental Science, 2003, 23(5): 509-514.

[6] KomarowskiS, YuQ.AmmoniumIonRemovalfromWastewaterUsingAustralianNaturalZeolite: BatchEquilibriumandKneticStudies[J].EnvirTech,1997,18(11):1085-1097.

[7] NguyenML, TannerCC.AmmoniumRemovalfromWastewaterUsingNaturalNewZealandZeolites[J].NewZealandJoumalofAgriculturalResearch,1998,41(3):427-446.

[8]BookerNA,CooneyEl,PriestleyAJ.AmmoniaRemovalfromSewageUsingNaturalAustralianZeolite[J].WatSciTech,1996,34(9):17-24.

[9] Burgess RM, Perron MM, Cantwell MG, et al. Use of Zeolite for Removing Ammonia and Ammonia-caused Toxicity in Marine Toxicity Identification Evaluations [J]. Archives of Environmental Contamination and Toxicology, 2004, 10 (4): 440-447.

[10] Jiang Liping, Huang Lei. Comprehensive utilization and development trend of fly ash (J). Coal Chemical Industry. 2015,43(2):84-89.

[11] Zheng Yue, Liu Fang, Wu Yonggui. Study on the Adsorption Performance of Fly Ash on Ammonia Nitrogen in Industrial Wastewater [J]. Environmental Science and Technology, 2011, 34(1):50-53.

[12] Zhao Tonggang, Wu Deyi, Chen Jiangang, Kong Hainan, Zhang Baohua, Wang Zaosheng. Synchronous deamination and dephosphorization characteristics of zeolite synthesized from fly ash [J]. Environmental Science. 2006, 27(4): 696-700.

[13] Wang Hua, Song Cunyi, Zhang Qiang. Fly Ash Modified Adsorption Material and Its Adsorption Mechanism [J]. Fly Ash Comprehensive Utilization. 2007, 7(26):37-41.

[14] Wang Chunrong, Niu Haishan. Experimental research on the adsorption of ammonia nitrogen in wastewater by modified fly ash [J]. Comprehensive benefits of fly ash.

[15] Wang Zhiping. Discussion on sludge disposal and resource utilization technology of urban sewage plants [J]. Resource Conservation and Environmental Protection, 2014(11):77-85.

[16] Bao Lixin, Li Ji, Jiang Lanlan, et al. Discussion on Treatment and Disposal Technology of Surplus Sludge in Urban Sewage Treatment Plants [J]. China Water Supply and Drainage, 2012(13):152-156.

Contents of the invention

The invention provides a method for preparing sludge ceramsite which has adsorption effect on medium and low concentration ammonia nitrogen by using fly ash and excess sludge as main raw materials, reduces the environmental pollution caused by the two types of wastes, and meets the requirements of two-type society construction.

One of purpose of the present invention is to provide a kind of preparation method of the sludge ceramsite that is used for medium and low concentration ammonia nitrogen wastewater treatment, concrete steps are as follows:

1) Pretreatment of raw materials: Soak the fly ash at 20-30°C for 3-4 days with NaOH solution with a mass percentage of 3%-6%, wash it with deionized water, and place it in an electric heating constant temperature drying box at 100-110°C ℃ drying; drying the remaining sludge taken from the dehydration workshop of the urban sewage plant at 100-110 ℃; drying the clay at 100-110 ℃; the above three raw materials are dried and pulverized by a pulverizer, and passed through a 100-mesh sieve spare;

2) Mixing of raw materials: take the fly ash, 30% to 60% of excess sludge, and 10% of clay that have undergone the above pretreatment in a mass ratio of 30% to 60%, and fully mix them to obtain a dry material;

3) Granulation: add an appropriate amount of deionized water to the above dry material and stir evenly to make a 1-3mm billet, and place it on a tray and dry it in an oven at 110°C until the surface is free of moisture;

4) Firing: Put the dried billet into a muffle furnace and heat it to 350°C-500°C, preheat it for 10-40 minutes, then heat it up to 800°C-1100°C for 10-25 minutes, and put it in the furnace Take it out when it is cooled to 180-200°C to obtain sludge ceramsite.

As a preference, in the step 2), 30% fly ash, 60% excess sludge and 10% clay are taken in a mass ratio and fully mixed to obtain a dry material.

As a preference, in the step 4), put the dried billet into a muffle furnace and heat it to 350°C, preheat it for 30 minutes, then raise the temperature to 800°C and burn it for 10 minutes, and cool it in the furnace to 180-200°C. Take it out at 200°C to get sludge ceramsite.

Another object of the present invention is to provide a kind of regeneration method of the sludge ceramsite prepared according to the above-mentioned method: adopt the plexiglass cylindrical rinsing device, fill the sludge ceramsite that absorbs ammonia nitrogen to reach saturation in the device, no Use any alkali or salt as the eluent, the eluent is tap water, the water flows in and out at a flow rate of 0.531mL/s for leaching, and the leachate is collected at the outlet at the lower end at regular intervals, and Nessler's reagent is used to Colorimetric method (HJ535-2009. Environmental Protection Standard of the People's Republic of China. Determination of Ammonia Nitrogen in Water Quality. Nessler's Reagent Spectrophotometry [S]. Beijing: China Environmental Science Press, 2009.) Determination of ammonia nitrogen content in water samples. The elution test proves that the ammonia nitrogen after adsorption saturation can be eluted quickly, thereby restoring the adsorption performance of sludge ceramsite. The eluted ammonia nitrogen can be used as available nitrogen in forest land and landscaping.

The raw materials used to prepare sludge ceramsite in the method of the present invention are all taken from the remaining sludge of urban sewage treatment plants and the fly ash of coal-fired power plants, both of which are wastes, and random discharge will pollute the environment and endanger human health; After treatment, the function of adsorbing ammonia nitrogen is enhanced, and finally sludge ceramsite can be used as a medium and low concentration ammonia nitrogen adsorbent. After the sludge ceramsite absorbs ammonia nitrogen to saturation, it can be regenerated quickly with only tap water, and the eluted ammonia nitrogen can be used as available nitrogen in forest land and landscape greening. This invention not only solves the problem of ammonia nitrogen treatment in sewage, but also solves the problem of waste treatment and disposal such as excess sludge and fly ash. .

Compared with the prior art, the inventive method has the following advantages:

(1) Sludge ceramsite uses solid waste as raw material, the mass percentage of fly ash in the formula reaches 30%, and the mass percentage of residual sludge reaches 60%, which provides a more effective way for sludge disposal and truly achieves low cost ,Turning waste into treasure.

(2) In the sludge ceramsite formula of the present invention, utilize the contained chemical composition of each component of raw material, carry out reasonable collocation, the fly ash after the pretreatment has strengthened the intensity of ceramsite while enhancing the ammonia nitrogen adsorption function, The remaining sludge and clay contain a large amount of organic matter and humus. During the roasting process, the organic matter volatilizes. Therefore, a large number of pores are formed in the case of low-temperature sintering, which increases the specific surface area of the sludge ceramsite, which is beneficial to the ammonia nitrogen. adsorption. The larger the ceramsite of the specific surface area, the more sites for adsorbing ammonia nitrogen can be provided on it, and the treatment concentration of ammonia nitrogen is correspondingly improved; the specific surface area of the sludge ceramsite prepared by the present invention is 2.40m ² /g, and the initial concentration of ammonia nitrogen ( That is, the concentration of ammonia nitrogen in the solution at the beginning of adsorption) can reach 120mg/L, and the adsorption capacity (that is, the mass mg/g of ammonia nitrogen adsorbed in unit mass of sludge ceramsite when the adsorption reaches saturation) can reach 1.0mg/g.

(3) The sludge ceramsite prepared by the present invention meets the requirements of "Artificial ceramsite filter material for water treatment" (CJ/T299-2008), and it is also feasible to be used as a water treatment filter material.

(4) The sludge ceramsite prepared by the present invention has high strength, large specific surface area, rough surface, and large porosity is conducive to adsorption and film formation; heavy metal leaching toxicity meets "Leaking Toxicity Identification of Hazardous Waste Identification Standards" (GB5085.3-2007 ), which can be used in water treatment engineering.

(5) The regeneration mode of the sludge ceramsite prepared by the present invention for the treatment of medium and low concentration ammonia nitrogen wastewater is simple and low in cost. The eluent is only tap water instead of conventional alkali or salt such as NaOH or NaCl. The leaching test proves that the ammonia nitrogen after adsorption saturation can be quickly eluted, and can be collected as available nitrogen for forest land and landscaping. This method not only saves the cost of chemical agents required for the regeneration of ceramsite, but also finds a way out for the collection of ammonia nitrogen. It is a better choice for the resource utilization of saturated sludge ceramsite.

(6) The sludge ceramsite used for the treatment of medium and low concentration ammonia nitrogen wastewater prepared by the present invention overcomes the shortcomings of biological denitrification, zeolite adsorption and chemical precipitation, etc. in cost and denitrification efficiency, and its price is low, It is economical, efficient and environmentally friendly, and is suitable for the treatment of medium and low concentration ammonia nitrogen wastewater.

Description of drawings

Figure 1: Scanning electron microscope image of sludge ceramsite;

Figure 2: Physical map of sludge ceramsite;

Figure 3: Effect of the amount of sludge ceramsite on the equilibrium concentration of ammonia nitrogen;

Figure 4: Effect of the initial concentration of ammonia nitrogen on the adsorption capacity of sludge ceramsite;

Figure 5: The effect of solution pH on the adsorption capacity of sludge ceramsite;

Figure 6: The effect of adsorption time on the adsorption capacity of sludge ceramsite;

Figure 7: The effect of adsorption temperature on the adsorption capacity of sludge ceramsite;

Figure 8: Schematic diagram of the structure of the washing test device;

Figure 9: Changes of ammonia nitrogen over time in the leaching test.

detailed description

List 4 examples below, the present invention is described further, but the present invention is not limited to these examples.

Example 1

1) Pretreatment of raw materials: Soak the fly ash at 25°C for 3 days with 5% NaOH solution by mass percentage, wash it with deionized water, and dry it at 105°C in an electric constant temperature drying oven; The remaining sludge in the dehydration workshop of the factory is dried at 105°C; the clay is dried at 105°C; the above three raw materials are dried and pulverized by a pulverizer, and passed through a 100-mesh sieve for later use;

2) Mixing of raw materials: take pretreated fly ash, 60% residual sludge, and 10% clay in a mass ratio of 30% and fully mix to obtain a dry material;

3) Granulation: add an appropriate amount of deionized water to the above dry material and stir evenly to make a 1-3mm billet, and place it on a tray and dry it in an oven at 110°C until the surface is free of moisture;

4) Firing: Put the dried billet into the muffle furnace and heat it to 350°C, preheat for 30 minutes, then heat up to 800°C and fire for 10 minutes, and take it out when it is cooled to 180-200°C in the furnace. That is, sludge ceramsite is obtained.

Fig. 1 is a scanning electron microscope image of the sludge ceramsite prepared in this example, and Fig. 2 is a physical picture of the sludge ceramsite prepared in this example. The specific surface area of the sludge ceramsite prepared in this example is 2.40m ² /g, the sum of the breakage rate and wear rate is 0.82%, the apparent density is 1020.4kg/cm ³ , and the bulk density is 581.9kg/cm ³ . It meets the requirements of "Artificial Ceramsite Filter Media for Water Treatment" (CJ/T299-2008). According to "Solid Waste Leaching Toxicity Leaching Method—Horizontal Oscillating Method" (GB50862.2-1997), the sludge ceramsite leaching solution was prepared, and the leaching concentration of several heavy metals was detected. The results are as follows: Cu0.002mg/L, Zn0. 0013mg/L, Cd0.0014mg/L, Cr0.002mg/L, As0.117mg/L, Hg0.0002mg/L. The concentrations of various heavy metal elements in the sludge ceramsite leachate are far lower than the regulations in the "Identification Standards for Hazardous Wastes - Identification of Leaching Toxicity" (GB5085.3-2007). Therefore, it is safe to use the above sludge ceramsite for water treatment.

In this example, the ammonia nitrogen adsorption performance of sludge ceramsite was measured to investigate the effect of the amount of sludge ceramsite on the equilibrium concentration of ammonia nitrogen, and the effect of the initial concentration of ammonia nitrogen, solution pH, adsorption time, and adsorption temperature on the adsorption of sludge ceramsite. capacity impact.

The test method of the adsorption performance measurement of the present embodiment is as follows:

Ammonia nitrogen solution and sludge ceramsite were respectively added into a series of Erlenmeyer flasks, and placed in a constant temperature shaker for oscillation. After the shaking is over, let the sedimentation stand to take the supernatant to measure the equilibrium concentration of ammonia nitrogen (referring to the concentration of ammonia nitrogen in the solution when the adsorption reaches equilibrium), and use the ammonia nitrogen adsorption capacity to evaluate the adsorption performance of the sludge ceramsite on ammonia nitrogen. Ammonia nitrogen was tested using Nessler's reagent colorimetric method.

Figure 3-7 is drawn out according to the data measured by the above-mentioned test, and the optimum conditions for sludge ceramsite adsorption of ammonia nitrogen in the present invention are: the amount of sludge ceramsite is 10g, the initial concentration of ammonia nitrogen is 120mg/L, the pH value is 9, and the adsorption time for 18h, and the adsorption temperature was 30°C. The adsorption of sludge ceramsite in the present invention to ammonia nitrogen in the solution meets the Langmuir monomolecular layer adsorption model, and the adsorption isotherm formula is:

$\frac{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; e</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 5.6472</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 117.54</span>}<span\; class="notranslate">\; ;</span>$

The adsorption kinetic model for ammonia nitrogen conforms to the Elovich adsorption kinetic model, and the formula is: q _t =-25.991×lnt+81.047.

Example 2

1) Pretreatment of raw materials: Soak the fly ash at 25°C for 3 days with 5% NaOH solution by mass percentage, wash it with deionized water, and dry it at 105°C in an electric constant temperature drying oven; The remaining sludge in the dehydration workshop of the factory is dried at 105°C; the clay is dried at 105°C; the above three raw materials are dried and pulverized by a pulverizer, and passed through a 100-mesh sieve for later use;

2) Mixing of raw materials: taking pretreated fly ash, 40% of excess sludge and 10% of clay in a mass ratio of 50% and fully mixing to obtain a dry material;

3) Granulation: add an appropriate amount of deionized water to the above dry material and stir evenly to make a 1-3mm billet, and place it on a tray and dry it in an oven at 110°C until there is no moisture on the surface;

4) Firing: Put the dried billet into a muffle furnace and heat it to 450°C, preheat for 40 minutes, then heat up to 800°C and fire for 15 minutes, and take it out when it is cooled to 180-200°C in the furnace. That is, sludge ceramsite is obtained.

The sludge ceramsite prepared in this example has a specific surface area of 1.90 m ² /g, a sum of breakage and wear rates of 3%, and an apparent density of 961 kg/cm ³ . The bulk density is 631.9kg/cm ³ . It meets the requirements of "Artificial Ceramsite Filter Media for Water Treatment" (CJ/T299-2008). According to the "Solid Waste Leaching Toxicity Leaching Method - Horizontal Oscillation Method" (GB50862.2-1997), the sludge ceramsite leaching solution was prepared, and the leaching concentration of several heavy metals was detected. The results are as follows: Cu0.0018mg/L, Zn0. 0013mg/L, Cd0.0010mg/L, Cr0.002mg/L, As0.116mg/L, Hg0.0002mg/L. The concentrations of various heavy metal elements in the sludge ceramsite leachate are far lower than the regulations in the "Identification Standards for Hazardous Wastes - Identification of Leaching Toxicity" (GB5085.3-2007). Therefore, it is safe to use the sludge ceramsite in this embodiment as water treatment.

Example 3

1) Pretreatment of raw materials: Soak the fly ash at 25°C for 3 days with 5% NaOH solution by mass percentage, wash it with deionized water, and dry it at 105°C in an electric constant temperature drying oven; The remaining sludge in the dehydration workshop of the factory is dried at 105°C; the clay is dried at 105°C; the above three raw materials are dried and pulverized by a pulverizer, and passed through a 100-mesh sieve for later use;

2) Mixing of raw materials: take pretreated fly ash, 30% residual sludge, and 10% clay in a mass ratio of 60% and fully mix to obtain a dry material;

3) Granulation: add an appropriate amount of deionized water to the above dry material and stir evenly to make a 1-3mm billet, and place it on a tray and dry it in an oven at 110°C until there is no moisture on the surface;

4) Firing: Put the dried billet into a muffle furnace and heat it to 500°C, preheat it for 10 minutes, then raise the temperature to 1100°C and fire it for 25 minutes, and take it out when it is cooled to 180-200°C in the furnace. That is, sludge ceramsite is obtained.

The specific surface area of the sludge ceramsite prepared in this example is 1.69m ² /g, the sum of the breakage rate and wear rate is 0.28%, and the apparent density is 1428kg/cm ³ , which conforms to "Artificial ceramsite filter material for water treatment" (CJ /T299-2008) requirements. According to the "Solid Waste Leaching Toxicity Leaching Method-Horizontal Oscillating Method" (GB50862.2-1997), the sludge ceramsite leaching solution was prepared, and the leaching concentration of several heavy metals was detected. The results are as follows: Cu0.001mg/L, Zn0. 0010mg/L, Cd0.0013mg/L, Cr0.002mg/L, As0.115mg/L, Hg0.0002mg/L. The concentrations of various heavy metal elements in the sludge ceramsite leachate are far lower than the regulations in the "Identification Standards for Hazardous Wastes - Identification of Leaching Toxicity" (GB5085.3-2007). Therefore, it is safe to use sludge ceramsite in this example for water treatment.

It should be noted that the step 1) described in the above embodiments 1 to 3 is only used as a preferred raw material pretreatment method. In the preparation process of the sludge ceramsite of the present invention, for the pretreatment of raw materials, the soaking solution of fly ash can be selected as 3%～6% NaOH solution by mass percentage, and the soaking temperature of fly ash can be set as 20 ~30°C, the immersion time of fly ash can be set at 3~4 days, and the drying temperature of fly ash and other raw materials can be set at 100~110°C.

Example 4

In order to study the regeneration of the sludge ceramsite with saturated adsorption of ammonia nitrogen, a self-designed downward flow cylindrical plexiglass device was used to conduct a leaching test on the sludge ceramsite with saturated adsorption of ammonia nitrogen, and the change of ammonia nitrogen content in the water was detected. , to investigate the release law of ammonia nitrogen with the change of leaching time.

1. Test device and method

The leaching test device as shown in Figure 8 is adopted, which is cylindrical, with a diameter of 8 cm and a height of 50 cm, of which the bottom 5 cm is a crushed stone support layer, which plays the role of supporting sludge ceramsite and preventing ceramsite loss; The support layer is filled with sludge ceramsite which absorbs ammonia nitrogen to reach saturation, the height is 40cm, and above the sludge ceramsite is a 5cm gravel layer, the purpose is to make the inflow evenly distributed and prevent short flow inside the ceramsite. A water outlet is set at the lower part of the device 5cm from the ground. The water flows in from 2cm away from the upper crushed stone layer, from top to bottom, and maintains a flow rate of 0.531mL/s to rinse the sludge ceramsite that has reached saturation, and collects the leachate at the lower outlet at regular intervals , with Nessler's reagent colorimetric method (HJ535-2009. Environmental Protection Standard of the People's Republic of China. Determination of Ammonia Nitrogen in Water Quality. Nessler's Reagent Spectrophotometry [S]. Beijing: China Environmental Science Press, 2009.) Determination of in water samples ammonia nitrogen content. It should be noted that different sizes of rinsing devices have different optimal rinsing speeds, and the optimal rinsing speed of the rinsing device designed in this experiment is 0.531mL/s.

2. Test results and analysis

The change of ammonia nitrogen in the leached liquid during the leaching process is shown in Figure 9.

The release law of ammonia nitrogen: the release rate is very fast in the first 7 hours of leaching. By the 7th hour, the ammonia nitrogen in the effluent has dropped from 23.785mg/L at the beginning of leaching to 1.215mg/L. After the 7th hour, the dissolution was very slow, basically maintained between 0.2 and 1.2 mg/L. This is because at the beginning of leaching, the surface of the sludge ceramsite with saturated ammonia nitrogen adsorption is rich in a large amount of ammonia nitrogen, and the ammonia nitrogen is released rapidly. As the leaching progresses, the ammonia nitrogen adsorbed inside the sludge ceramsite is gradually precipitated. After leaching for 41 hours, the ammonia nitrogen in the effluent was 0.21 mg/L, and until 48 hours, the value hardly changed. At this time, the ammonia nitrogen adsorbed on the inside and surface of the sludge ceramsite had been completely released, and the leaching was over. The eluent of the leaching test did not use any conventional alkali or salt such as NaOH or NaCl, but only leached with tap water. The purpose was to quickly elute the ammonia nitrogen in the saturated sludge ceramsite, as a forestry product. The use of quick-acting nitrogen fertilizers for greening land not only saves the cost of chemicals needed for ceramsite regeneration, but also finds a way out for the collection of ammonia nitrogen. It is a better choice for resource utilization of saturated sludge ceramsite.

Claims (4)

1. a preparation method for the sludge ceramsite of medium and low concentration ammonia nitrogen wastewater treatment, it is characterized in that comprising the following steps: 1) Pretreatment of raw materials: Soak the fly ash at 20-30°C for 3-4 days with NaOH solution with a mass percentage of 3%-6%, wash it with deionized water, and place it in an electric heating constant temperature drying box at 100-110°C ℃ drying; drying the remaining sludge taken from the dehydration workshop of the urban sewage plant at 100-110 ℃, and drying the clay at 100-110 ℃; after the above three raw materials are dried, they are pulverized by a pulverizer and passed through a 100-mesh sieve spare; 2) Mixing of raw materials: fully mix pretreated fly ash with a mass ratio of 30% to 60%, excess sludge of 30% to 60%, and clay of 10% to obtain a dry material; 3) Granulation: add an appropriate amount of deionized water to the above dry material and stir evenly to make a 1-3mm billet, and place it on a tray and dry it in an oven at 110°C until the surface is free of moisture; 4) Firing: Put the dried billet into a muffle furnace and heat it to 350°C-500°C, preheat it for 10-40 minutes, then heat it up to 800°C-1100°C for 10-25 minutes, and put it in the furnace Take it out when it is cooled to 180-200°C to obtain sludge ceramsite. 2. the preparation method of sludge ceramsite according to claim 1 is characterized in that: in described step 2), getting mass ratio is 30% fly ash, 60% surplus sludge, 10% clay Mix thoroughly to obtain dry material. 3. The preparation method of sludge ceramsite according to claim 1 or 2, characterized in that: in the step 4), the dried blank is put into a muffle furnace and heated to 350° C., preheated After 30 minutes, heat up to 800°C and burn for 10 minutes, and take it out when it is cooled to 180-200°C in the furnace to obtain sludge ceramsite. 4. a method for regeneration of sludge ceramsite prepared according to the method of claim 1, characterized in that: a plexiglass cylindrical rinsing device is used, and the sludge ceramsite filled with adsorption of ammonia nitrogen in the device reaches saturation, and the leaching process The eluent used in the test is tap water, and the water flows in and out at a flow rate of 0.531mL/s for rinsing. The eluate is collected at the water outlet at the lower end at regular intervals, and the Nessler reagent colorimetric method is used to determine the concentration of water in the water sample. ammonia nitrogen content.