Method for recovering phosphorus in sludge

Abstract

The invention provides a sludge phosphorus recovery method, which specifically comprises: 1, collecting domestic sewage, sludge and human and animal excreta, completely mixing, and sequentially carrying out enzymolysis, flocculation, disinfection and filtration to obtain sewage and sludge; step 2, after the sewage is concentrated, adding a magnesium source and an alkali source, separating precipitate and supernate, adding an adsorbent into the supernate, and filtering to obtain filtrate and filter residues; 3, sludge is dried and smashed and then mixed with the filtrate and an EM microbial agent for fermentation, and the sludge can be used as a fertilizer or a soil conditioner; the recovery method disclosed by the invention is simple in process, convenient to operate, high in recovery efficiency and stable, does not need expensive equipment, does not need later maintenance cost, does not need to add a large amount of medicaments, can save cost and improve efficiency to the greatest extent, and is suitable for rural areas with relatively weak economic basis.

Description

Technical Field

[0001] The invention relates to the technical field of sludge recovery, and in particular to a method for recovering sludge phosphorus. Background Art

[0002] Phosphorus is one of the elements required for the growth of humans, animals and plants. It is a non-renewable and irreplaceable resource. It is mainly obtained from phosphate rock. The huge demand for mining has caused a serious shortage of phosphorus resources around the world. However, excessive phosphorus content is the main factor causing eutrophication and even black and smelly water bodies, threatening the balance of the ecosystem.

[0003] Due to differences in regional economy, natural conditions, drainage systems, and lifestyles, rural sludge and sewage have the highest phosphorus content, followed by urban sludge and sewage, and industrial wastewater has the lowest phosphorus content. Because industrial wastewater contains a large amount of heavy metal ions and other pollutants, industrial wastewater has a separate treatment process and discharge channel. Therefore, focusing on recovering phosphorus from rural and urban sewage and sludge will achieve twice the result with half the effort.

[0004] Each city has a separate sewage treatment plant that can collect residents' domestic sewage and sludge for centralized treatment. With the continuous development of science and technology, the treatment process is relatively mature and the phosphorus recovery efficiency is relatively high. However, due to the dispersed discharge of rural sewage and sludge, large fluctuations in water quality and relatively simple pollutants, many rural areas do not have separate sewage treatment plants, especially rural areas with weak economic foundations and rural areas in arid areas. Not only is the phosphorus content in sewage sludge high, but there are no relatively environmentally friendly discharge channels and relatively mature phosphorus recovery processes, resulting in the random discharge of rural domestic sewage and the random stacking of sludge, which not only wastes a lot of phosphorus resources, but also seriously pollutes the surrounding environment. Therefore, it is crucial to recover phosphorus from rural sludge and sewage to solve the problem of phosphorus resource shortage.

[0005] There are three main methods for phosphorus recovery: the first is to extract phosphorus from sludge incineration ashes, but it has the disadvantages of high equipment cost, high maintenance cost, high energy consumption, low bioavailability, and a large amount of atmospheric pollutants generated during the incineration process, so it is not suitable for rural areas; the second is to recover phosphorus from the solid phase of sludge, but because most of the phosphorus in it exists in the form of insoluble or poorly soluble phosphorus-containing compounds, it is difficult to be directly absorbed and utilized by plants, so it is also not suitable for rural areas; the third is to recover phosphorus from the liquid phase after the sludge is dehydrated, convert the phosphorus in the solid phase of the sludge into phosphorus that can be used by plants, and migrate it to the liquid phase. This method is low-cost and efficient, and can be directly absorbed and utilized by plants after recovery, so it is suitable for rural areas, but this method has high requirements on the pH of water and magnesium and phosphorus ions, and the phosphorus recovery rate is not stable.

[0006] Therefore, it is an urgent problem to provide a low-cost, high-efficiency, relatively stable method for sludge phosphorus recovery suitable for rural areas. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for recovering phosphorus from sludge, which specifically comprises the following steps: Step 1: collect grey water, black water, pond sludge, aquaculture tail water and livestock manure and mix them all to obtain a sewage sludge mixture, add complex enzymes to the sewage sludge mixture, perform enzymolysis at 45-55°C for 15-18 hours, then add flocculants and disinfectants and pass disinfectant gas, disinfect for 30-40 minutes and then filter to obtain sewage and sludge. The sewage at this time can be used directly for irrigation or be treated in step 2.

[0008] Step 2: Concentrate the sewage to 20-30% of its original volume at 80-90°C, add a magnesium source at a mass ratio of 10:1, then add an alkali source to adjust the pH to 10-11, stir at 120-150r / min for 20-30min, then centrifuge at 5000-6000r / min for 10-15min, separate the precipitate and the supernatant, collect the precipitate for later use, and the main component of the precipitate is struvite. The supernatant can be used directly for irrigation, or an adsorbent can be added to the supernatant at a mass ratio of 5:1, stirred at 30-40°C and 120-150r / min for 1-2h, filtered, and the filtrate and filter residue are collected separately for later use. The filtrate can be used directly for irrigation, or it can be mixed with the powder in step 3.

[0009] Step three, drying the sludge at 120-130°C to constant weight, crushing and sieving to obtain powder, adding filtrate to the powder until the moisture content of the powder is 70-80%, and adding EM bacterial agent, and fermenting at 30-50°C, aerobic and anaerobic alternation for 12-15 days. After the fermentation is completed, mix it with the precipitate and filter residue, and it can be used as a fertilizer or soil conditioner.

[0010] Preferably, the mass ratio of the sewage sludge mixture, disinfectant, flocculant and complex enzyme in step one is 1000:(10-20):(1-2):(10-20).

[0011] Preferably, the disinfectant in step one is a magnesium hypochlorite solution with a mass fraction of 0.1-0.3% or a sodium hypochlorite solution with a mass fraction of 0.1-0.3%, and the disinfecting gas is ozone or chlorine dioxide.

[0012] Preferably, the flocculant in step 1 is one or more of polyacrylamide, polyvinyl alcohol, chitosan, gelatin and alum.

[0013] Preferably, the complex enzyme in step one is cellulase, protease, lipase, amylase, lysozyme and catalase, and the mass ratio is 1:1:1:1:1:1:1.

[0014] Preferably, the alkali source in step 2 is one or more of wood ash, quicklime, potassium hydroxide and sodium hydroxide.

[0015] Preferably, the magnesium source in step 2 is one or more of fly ash, furnace ash, coal slag and wood ash.

[0016] Preferably, the adsorbent in step 2 is one or more of activated carbon, talcum powder and diatomaceous earth.

[0017] Preferably, the mass ratio of the powder and the EM bacterial agent in step three is 100:(1-2).

[0018] Preferably, the aerobic and anaerobic alternating fermentation in step three is aerobic fermentation for 2-4 hours followed by anaerobic fermentation for 1-2 hours.

[0019] Preferably, in step three, the sludge is not fermented after being crushed, but is directly mixed with the precipitate and the filter residue to prepare a fertilizer or a soil conditioner.

[0020] The present invention has the following advantages: (1) The present invention utilizes a composite enzyme to hydrolyze sludge, thereby fully releasing phosphorus in the solid phase of sludge that is difficult to be directly absorbed by plants into the liquid phase, thereby improving phosphorus recovery efficiency. At this time, the liquid phase contains a large amount of phosphorus, which can be subsequently crystallized and adsorbed, and then used to prepare fertilizers or soil conditioners, thereby improving resource utilization. It can also be directly used for irrigation and absorbed and utilized by crops, thereby reducing costs and improving resource utilization. Since most of the phosphorus in the solid phase after enzymatic hydrolysis is removed and does not contain other pollutants, it can be fermented to prepare organic fertilizers or soil conditioners.

[0021] (2) The present invention collects high-phosphorus wastes such as pond sludge, aquaculture tail water and livestock manure to increase the phosphorus content in the liquid phase, thereby improving resource utilization and effectively reducing the cost of adding phosphorus sources.

[0022] (3) The present invention uses waste materials such as wood ash, furnace ash, coal slag and fly ash commonly found in rural areas as alkali sources and magnesium sources, thereby improving resource utilization and effectively reducing the cost of adding magnesium sources and alkali sources.

[0023] (4) The raw materials used in the present invention are basically derived from common wastes in rural areas. By rationally utilizing these wastes, not only can a large amount of phosphorus in sludge and sewage be recovered, but also wastes such as wood ash, furnace ash, coal slag and fly ash can be reused, thereby maximizing the resource utilization rate.

[0024] (5) The recovery method of the present invention has a simple process, is easy to operate, does not require expensive equipment, has no subsequent maintenance costs, does not require the addition of a large amount of reagents, has high and stable recovery efficiency, can save costs and increase efficiency to the greatest extent, and is suitable for rural areas with a relatively weak economic foundation. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the invention, not all of the embodiments. Based on the embodiments of the invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the invention.

[0026] The cellulase, protease, lipase, amylase, lysozyme and catalase in the following examples and comparative examples were purchased from Xi'an Musen Bioengineering Co., Ltd.

[0027] The EM bacterial agents in the following examples and comparative examples were purchased from Jinan Yeqing Biotechnology Co., Ltd.

[0028] Grey water, black water, pond sludge, aquaculture tail water and livestock manure were collected and mixed to obtain a sewage sludge mixture, and the following examples and comparative examples were respectively implemented.

[0029] Example 1 Step 1, add compound enzyme to the sewage sludge mixture, enzymolysis at 50℃ for 16h, then add flocculant and disinfectant and pass disinfection gas, disinfect for 35min and filter to obtain sewage and sludge. The mass ratio of the sewage sludge mixture, disinfectant, flocculant and compound enzyme is 1000:15:2:20. The disinfectant is a magnesium hypochlorite solution with a mass fraction of 0.2%, and the disinfection gas is chlorine dioxide. The flocculant is polyacrylamide, chitosan and alum, with a mass ratio of 1:1:1. The compound enzyme is cellulase, protease, lipase, amylase, lysozyme and catalase, with a mass ratio of 1:1:1:1:1:1.

[0030] Step 2: Concentrate the sewage to 25% of its original volume at 85°C, add a magnesium source at a mass ratio of 10:1, then add an alkali source to adjust the pH to 10, stir at 130r / min for 25min, then centrifuge at 5500r / min for 15min, separate the precipitate and the supernatant, collect the precipitate for later use, add an adsorbent to the supernatant at a mass ratio of 5:1, stir at 35°C and 130r / min for 1.5h, filter, obtain the filtrate and the filter residue, and collect them separately for later use. The alkali source is plant ash, quicklime and sodium hydroxide at a mass ratio of 3:1:1. The magnesium source is fly ash, furnace ash, coal slag and plant ash at a mass ratio of 1:5:2:1. The adsorbent is activated carbon, talcum powder and diatomaceous earth at a mass ratio of 1:1:1.

[0031] Step 3: Dry the sludge at 120°C to constant weight, crush it through a 60-mesh sieve to obtain powder, add filtrate to the powder until the moisture content of the powder is 75%, and add EM bacterial agent, at a temperature of 40°C, and ferment it aerobically and anaerobically for 14 days. After the fermentation is completed, mix it with the precipitate and the filter residue, and use it as a fertilizer or soil conditioner. The mass ratio of the powder to the EM bacterial agent is 100:1. The aerobic and anaerobic alternating fermentation is aerobic fermentation for 2 hours and anaerobic fermentation for 1 hour.

[0032] Comparative Example 1 The difference from Example 1 is that this comparative example does not undergo enzymatic hydrolysis.

[0033] Test Example 1 During the implementation of Example 1, the mass concentrations of orthophosphate and ammonia nitrogen in the liquid phase were detected before enzymatic hydrolysis, after enzymatic hydrolysis, after precipitation and after adsorption, and the average value was taken after three repetitions. The results are shown in Table 1. During the implementation of Comparative Example 1, the mass concentrations of orthophosphate and ammonia nitrogen in the liquid phase were detected before and after precipitation, and the average value was taken after three repetitions. The results are shown in Table 2.

[0034] Table 1 Table 2

[0035] As shown in Table 1-2, enzymatic hydrolysis of sludge before precipitation can significantly release phosphorus in sludge that is difficult for plants to use into the liquid phase, thereby realizing the recovery of phosphorus in sludge. The method provided by the present invention can effectively recover phosphorus in sludge, with high and stable recovery efficiency, and can also recover wastewater with high phosphorus content, and the crystallized struvite and the adsorbent after adsorption can be used to prepare fertilizers or soil conditioners, and the enzymatically hydrolyzed sludge can be fermented to prepare organic fertilizers or soil conditioners, or can be prepared into fertilizers or soil conditioners without fermentation, and has strong applicability.

[0036] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recovering phosphorus from sludge, characterized in that: The following steps are involved: Step 1: collect grey water, black water, pond sludge, aquaculture tail water and livestock manure and mix them all to obtain a sewage sludge mixture, add complex enzyme to the sewage sludge mixture, perform enzymolysis at 45-55° C. for 15-18 hours, then add flocculant and disinfectant and pass disinfectant gas, disinfect for 30-40 minutes and then filter to obtain sewage and sludge; Step 2: Concentrate the sewage to 20-30% of the original volume at 80-90°C, first add a magnesium source at a mass ratio of 10:1, then add an alkali source to adjust the pH to 10-11, stir at 120-150r / min for 20-30min, then centrifuge at 5000-6000r / min for 10-15min, separate the precipitate and the supernatant, collect the precipitate for later use, add an adsorbent to the supernatant at a mass ratio of 5:1, stir at 30-40°C and 120-150r / min for 1-2h, filter, obtain the filtrate and the filter residue, and collect them separately for later use; Step three, drying the sludge at 120-130°C to constant weight, crushing and sieving to obtain powder, adding filtrate to the powder until the moisture content of the powder is 70-80%, and adding EM bacterial agent, and fermenting at 30-50°C, aerobic and anaerobic alternation for 12-15 days. After the fermentation is completed, mix it with the precipitate and filter residue, and it can be used as a fertilizer or soil conditioner.

2. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The mass ratio of the sewage sludge mixture, disinfectant, flocculant and complex enzyme in step 1 is 1000:(10-20):(1-2):(10-20).

3. The method for recovering phosphorus from sludge according to claim 1, characterized in that: In step 1, the disinfectant is a magnesium hypochlorite solution with a mass fraction of 0.1-0.3% or a sodium hypochlorite solution with a mass fraction of 0.1-0.3%, and the disinfecting gas is ozone or chlorine dioxide.

4. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The flocculant in step 1 is one or more of polyacrylamide, polyvinyl alcohol, chitosan, gelatin and alum.

5. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The complex enzyme in step one is cellulase, protease, lipase, amylase, lysozyme and catalase, and the mass ratio is 1:1:1:1:1:1:

1.

6. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The alkali source in step 2 is one or more of wood ash, quicklime, potassium hydroxide and sodium hydroxide.

7. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The magnesium source in step 2 is one or more of fly ash, furnace ash, coal slag and plant ash.

8. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The adsorbent in step 2 is one or more of activated carbon, talcum powder and diatomaceous earth.

9. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The mass ratio of the powder and the EM bacterial agent in step 3 is 100:(1-2).

10. The method for recovering phosphorus from sludge according to claim 1, characterized in that: The aerobic and anaerobic alternating fermentation in step 3 is aerobic fermentation for 2-4 hours followed by anaerobic fermentation for 1-2 hours.

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