CN112321019A - Purification method for reducing phosphorus content in biogas slurry by using calcite - Google Patents

Purification method for reducing phosphorus content in biogas slurry by using calcite Download PDF

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CN112321019A
CN112321019A CN202011188319.3A CN202011188319A CN112321019A CN 112321019 A CN112321019 A CN 112321019A CN 202011188319 A CN202011188319 A CN 202011188319A CN 112321019 A CN112321019 A CN 112321019A
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biogas slurry
calcite
phosphorus
nitrogen
biogas
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黄利东
李仁英
李军贤
谢晓金
王虹艳
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Nanjing University of Information Science and Technology
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Nanjing University of Information Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/105—Phosphorus compounds

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Fertilizers (AREA)
  • Treatment Of Sludge (AREA)

Abstract

The invention discloses a purification method for reducing phosphorus content in biogas slurry by using calcite, which comprises the following steps of mixing 15-20Kg of calcite per m3Adding calcite into the biogas slurry according to the biogas slurry proportion, and carrying out intermittent stirring for 30-40 hours; standing for precipitation, and performing solid-liquid separation to obtain the purified biogas slurry with low phosphorus content. According to the invention, the phosphorus in the biogas slurry is recovered by using calcite powder, and the nitrogen-phosphorus ratio of the biogas slurry is optimized. Calcite powder is added into the biogas slurry according to a certain solid-liquid ratio, when the reaction time is 3 days, the phosphorus recovery rate of the biogas slurry can reach more than 70%, the conductivity of the biogas slurry slowly decreases within 3 days, and the pH value gradually stabilizes within the range of relevant industry standards. Calcite has no obvious influence on the nitrogen content of the biogas slurry, so that the nitrogen-phosphorus ratio of the biogas slurry after treatment is obviously optimized.

Description

Purification method for reducing phosphorus content in biogas slurry by using calcite
Technical Field
The invention relates to the technical field of biogas slurry treatment, in particular to a purification method for reducing phosphorus content in biogas slurry by using calcite.
Background
According to the estimation of Ministry of agriculture, the pig manure is produced by more than 10 hundred million tons every year in China, and the treatment in a traditional composting and recycling mode exceeds the upper limit of the requirement of soil nutrients in some areas. The treatment amount of the solid can be greatly reduced by recycling the biogas near the pig farm, and the method is an economic and nearby treatment mode. But still needs to treat a large amount of biogas slurry generated, and the biogas slurry is still the main utilization way of the biogas slurry as a liquid fertilizer. The nitrogen-phosphorus ratio of the fermented biogas slurry is reduced, the nitrogen-phosphorus ratio required by common crops is higher, so that contradiction is generated between supply and demand, common agriculture is fertilized or topdressed on the basis of nitrogen, and if the biogas slurry is fertilized according to the basic amount of nitrogen, phosphorus is beyond the demand of the crops, and the phosphorus is accumulated in soil. The risk of phosphorus loss is thus significantly increased. In this case, part of phosphorus in the recovered biogas slurry can optimize the nitrogen-phosphorus ratio, and the method is more suitable for agricultural application.
At present, the method for recovering phosphorus in biogas slurry wastewater mainly comprises a struvite Method (MAP), but the struvite requires that the pH of the whole liquid must reach 11 for effective recovery, the method greatly interferes with the chemical background condition of the biogas slurry, and although a large amount of phosphorus can be recovered, the subsequent utilization of the biogas slurry becomes a problem, and the suspicion that sesame and watermelon are lost exists.
Aiming at the problems, the invention utilizes calcite to recover part of phosphorus in the biogas slurry under natural conditions (without adding any chemical reagent), thereby optimizing the nitrogen-phosphorus ratio of the biogas slurry, and reducing the interference on the chemical background of the biogas slurry to ensure the subsequent smooth use of the biogas slurry on soil.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a purification method for reducing the phosphorus content in biogas slurry by using calcite.
The purpose of the invention is realized by the following technical scheme:
a purification method for reducing the phosphorus content in biogas slurry by using calcite comprises the following specific steps:
step 1, performing solid-liquid separation on a biogas pool or a septic tank of a farm to obtain liquid biogas slurry;
step 2, according to 15-20Kg of calcite/m3Adding calcite powder into biogas slurry according to the proportion of the biogas slurry, and carrying out intermittent stirring for 30-40 hours;
and 3, standing for precipitation, and performing solid-liquid separation to obtain the purified biogas slurry with low phosphorus content.
In a further embodiment of the invention, the calcite proportion added in step 2 is 17.5kg calcite/m3Biogas slurry.
In a further design scheme of the invention, in the step 2, the intermittent stirring mode is to stir for 30 minutes by a stirrer every 2 hours, and the stirring speed is not lower than 50 rpm.
In a further design scheme of the invention, the calcite is dehydrated and dried after the solid-liquid separation in the step 3.
The invention has the following outstanding advantages:
1) according to the invention, phosphorus in biogas slurry is recovered by using calcite, no additional chemical reagent is needed to be added, the recovery rate of phosphorus can reach 70% after treatment for half a day, and the calcite belongs to cheap minerals, so that the technology belongs to a low-cost and high-efficiency phosphorus recovery technology;
2) according to the invention, the phosphorus in the biogas slurry recovered by calcite has very little interference on the chemical properties of the biogas slurry, even the salinity of the biogas slurry can be reduced, and the pH of the biogas slurry can be stabilized. Some processes and inventions utilize calcium hydroxide and magnesium hydroxide or other strong bases to recover phosphorus, and while these techniques can achieve high phosphorus recovery efficiencies, they have a damaging effect on the solution, which cannot be reused, and even the cost of treating these solutions to environmental standards is very high. Therefore, the phosphorus in the calcite-recovered biogas slurry belongs to a green technology with low background interference
3) The technology related by the invention has very low influence on nitrogen in the biogas slurry, reduces phosphorus in the biogas slurry, improves the nitrogen-phosphorus ratio of the biogas slurry, enables the biogas slurry to better meet the requirement rule of crops, reduces the application amount of phosphorus in soil according to the nitrogen standard biogas slurry fertilization, reduces the loss risk of phosphorus, and is beneficial to protecting the fragile water environment.
4) The chemicals used in the invention are calcite, belong to nontoxic and harmless minerals, and are very commonly applied in life. Other inventions involve the addition of alkali or acid or other chemicals, which should be considered dangerous. At present, the national control on strong acid and strong base is very strict, the purchase and storage cost is high, and the strong acid and strong base are avoided as much as possible in the actual production. In contrast, phosphorus recovery from calcite is a safe, clean, and green process.
5) The invention has better operation. The invention has low requirement on the skill of personnel, and can be put on duty only by slightly training on the aspects of filtration, dosage, stirring and reaction time. Similar inventions, however, require strict control of the pH of the system or the dosage of auxiliary chemicals, which puts high demands on the skill and knowledge level of the personnel. Biogas slurry is generally generated in rural areas, and high-tech talents are in short supply. The complicated process means an increase in the cost of human resources. In comparison, the method has the advantages of simple process and no danger, and is suitable for large-scale popularization and use in rural areas.
Drawings
FIG. 1 is a schematic flow diagram of a purification method for reducing the phosphorus content in biogas slurry by using calcite in the example;
FIG. 2 shows the change of phosphorus concentration in the liquid (diluted by 100 times) with time after the biogas slurry is mixed with calcite in the example;
fig. 3 is the interference of calcite on the chemical background of biogas slurry in the examples;
FIG. 4 shows the change of conductivity of calcite-treated biogas slurry
FIG. 5 change of pH of calcite treatment biogas slurry
FIG. 6 variation of nitrogen content in biogas slurry treated with different reagents (results of 3-fold dilution)
In the figure, 1-a methane tank or a septic tank, 2-a pump, 3-a nylon screen, 4-a stirrer, 5-a reaction tank, 6-a methane liquid discharge port and 7-a calcite discharge port.
Detailed Description
The invention is further explained below with reference to the drawings and examples.
Example 1
A purification method for reducing phosphorus content in biogas slurry by using calcite comprises the following specific steps, referring to the attached figure 1:
step 1, carrying out solid-liquid separation on a biogas digester or a septic tank 1 of a farm, removing large-particle impurities in the fermented biogas slurry of pig manure through standing and precipitation, and fishing out light impurities floating on the surface of the biogas slurry. Then the biogas slurry is transferred into a reaction tank 5 through a pump 2, and in the process, the biogas slurry needs to pass through a nylon screen 3 with 100 meshes to further filter fine impurities, and in the process, the nylon screen 3 is frequently blocked, so that the impurities on the gauze are periodically scraped off, and the permeability of the gauze is kept by backwashing with water. Obtaining the liquid biogas slurry. The initial phosphorus content of the biogas slurry is about 42.6 mg/L.
Step 2, adding 17.5kg of calcite per m3The commercial calcite powder is added into the biogas slurry according to the proportion of the biogas slurry, and the mixed solution of the calcite and the biogas slurry in the reaction tank (which is also a sedimentation tank) is intermittently stirred by a stirrer 4 for 30 minutes every 2 hours. The shape of the calcite comprises granules, powder and the like, and the reaction mode comprises bulk addition, integral packaging addition, flow reaction and the like.
And 3, after about one and a half days (32 hours), separating the biogas slurry from calcite, and discharging the biogas slurry from a biogas slurry discharge port 6 and a calcite discharge port 7 respectively, wherein the density of the calcite is far greater than that of water, so that the biogas slurry with low phosphorus content after purification is obtained by adopting an unpowered precipitation separation method. The calcite after separation is dehydrated, subsequent resource utilization can be carried out, the adsorbed calcite can be used as a phosphate fertilizer, the properties of the treated biogas slurry are better optimized, and the biogas slurry is more suitable for agriculture.
The farm comprises a pig farm, a chicken farm, a cattle farm, a sheep farm or human excrement, the operation time for recycling phosphorus from calcite is suitable for spring and autumn, because the temperature in summer is high, flies and winged insects are more, and the flowing and storage of biogas slurry is easy to attract flies and produceThe other reason is that the biogas slurry is easy to grow microorganisms during the summer reaction, is easy to block a filter screen and generate odor, so the recycling ring is suitable (but can not be frozen) when the temperature is low. In order to achieve better recovery effect, biogas slurry needs to be pumped out of the biogas digester, filtered by a screen and cleaned regularly to keep the permeability of the screen. The calcite is added to the filtrate in a dose of 17.5kg calcite/m3The optimal reaction time of the biogas slurry is 3 days, and the calcite and the biogas slurry are fully mixed and contacted by stirring regularly in the reaction process. After the reaction is finished, recycling calcite through a sedimentation tank, and naturally drying; the treated biogas slurry can be directly used as fertilizer. A second batch of reaction may then be carried out, and so on.
The nitrogen-phosphorus ratio of the biogas slurry improved by the calcite can be adjusted according to any crop/vegetable/melon/tree, and the nitrogen-phosphorus ratio can be improved according to all plant requirements. And if the nitrogen-phosphorus ratio required by the grapes is 2: 1, the nitrogen-phosphorus ratio required by the tomatoes is 4: 1. the dosage and the reaction time of the calcite can be controlled and regulated to achieve the target nitrogen-phosphorus ratio. In general, the nitrogen-phosphorus ratio can be increased by increasing the dosage of calcite and increasing the reaction time, and vice versa.
The situation of recycling phosphorus in biogas slurry by calcite is shown in figures 2 and 3. The results shown in FIG. 2 show that (100 times dilution during analysis), the phosphorus concentration of the calcite-treated biogas slurry is reduced by 49% within 3 hours, and the residual amount is 21 mg.L-1. Then, over time, the fixed ratio of calcite to phosphorus reached 76% after 40 hours from the start of the test, and the residual amount of phosphorus in the biogas slurry was about 10 mg.L-1. Therefore, phosphorus in the biogas slurry can be effectively removed by calcite within 40 hours, so that the phosphorus is fixed on the surface of the calcite.
Conductivity and pH after calcite treatment of biogas slurry are shown in fig. 4 and fig. 5, and it can be seen from fig. 4 that as the reaction time increases, the initial conductivity of biogas slurry (9 us/cm) slowly begins to decrease, and the conductivity decreases to 7.7us/cm at the end of the treatment, which indicates that the total salt content in the biogas slurry begins to decrease. According to the technical specification for applying the biogas manure (NY/T2065-2011), the total salt content is less than or equal to 1000 mg/L, and the lower the salt content in the biogas slurry, the better the salt content. This shows that the phosphorus in the biogas slurry is recovered by using calcite, so that not only can the phosphorus be fixed, but also the salinity of the biogas slurry can be reduced.
After calcite is added into biogas slurry, the pH value of the system changes as shown in figure 5, the pH value of the solution is gradually increased from 8.05 to 8.1 at the initial moment, and then the pH value of the whole system is gradually stabilized to about 7.9 in a descending state, and the pH value of the biogas fertilizer is required to be between 6 and 8 according to technical Specification for biogas fertilizer application (NY/T2065-. Therefore, after calcite treatment, the pH of the biogas slurry is gradually stabilized within the range specified by the standard.
According to the method, calcite is added according to the proportion of 15kg calcite/m3Biogas slurry and 2015kg of calcite/m3The same results as above can be obtained by performing experiments on the biogas slurry ratio.
FIG. 6 is a graph showing the results of a study on the effect of calcite on nitrogen in biogas slurry after phosphorus recovery, wherein calcium hydroxide and calcite are used respectively (CaCO is shown in the graph)3) And magnesium hydroxide is used for treating the biogas slurry, and the nitrogen content before and after treatment is respectively detected, so that the result is shown in fig. 6, and the nitrogen content in the biogas slurry is hardly changed and the phosphorus content is reduced, which shows that the phosphorus in the calcite recovered biogas slurry can obviously improve the nitrogen-phosphorus ratio of the whole biogas slurry, optimize the nutritional structure in the biogas slurry and enable the nutrient ratio to be more in line with the crop demand ratio. Meanwhile, compared with other reagents, calcium hydroxide and magnesium hydroxide reduce the nitrogen content in the solution, and the nitrogen loss may be caused by phosphorus removal by using the calcium hydroxide and the magnesium hydroxide, or the nitrogen-phosphorus ratio is reduced (the nitrogen-phosphorus ratio is not optimized).
In conclusion, the biogas slurry is treated by calcite, so that phosphorus can be recovered, the salinity of the biogas slurry can be reduced, the pH of the biogas slurry is stabilized to within a standard, and the nitrogen-phosphorus ratio of the biogas slurry is optimized so that the biogas slurry can meet the crop requirements. The method for recycling phosphorus in the biogas slurry by calcite is a low background interference method, interference caused by continuous utilization of the biogas slurry is avoided, and the method is a clean recycling technology.
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.

Claims (4)

1. A purification method for reducing phosphorus content in biogas slurry by using calcite is characterized by comprising the following specific steps:
step 1, performing solid-liquid separation on a biogas pool or a septic tank of a farm to obtain liquid biogas slurry;
step 2, according to 15-20Kg of calcite/m3Adding calcite powder into biogas slurry according to the proportion of the biogas slurry, and carrying out intermittent stirring for 30-40 hours;
and 3, standing for precipitation, and performing solid-liquid separation to obtain the purified biogas slurry with low phosphorus content.
2. The purification method for reducing the phosphorus content in biogas slurry by using calcite as claimed in claim 1, wherein the calcite is added in the ratio of 17.5kg calcite/m in step 23Biogas slurry.
3. The purification method for reducing the phosphorus content in the biogas slurry by using calcite as claimed in claim 1, wherein the intermittent stirring manner in the step 2 is that the stirring is performed for 30 minutes every 2 hours by using a stirrer, and the stirring speed is not lower than 50 rpm.
4. The purification method for reducing the phosphorus content in biogas slurry by using calcite according to claim 1, wherein the calcite is subjected to dehydration and airing treatment after solid-liquid separation in step 3.
CN202011188319.3A 2020-10-30 2020-10-30 Purification method for reducing phosphorus content in biogas slurry by using calcite Pending CN112321019A (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102092898A (en) * 2010-12-24 2011-06-15 东南大学 Efficient denitrification, dephosphorization, denitrification and phosphorus resource recycling process for urban sewage
CN102173495A (en) * 2011-03-11 2011-09-07 中国科学院南京土壤研究所 Method and device for accelerating removal of high-concentration phosphorus in waste water by using calcite
CN102241445A (en) * 2011-05-17 2011-11-16 桂林理工大学 Method for removing and recycling phosphorus from phosphorus-rich water bodies or sewage by using natural mineral mixture
CN102898213A (en) * 2012-10-12 2013-01-30 常州大学 Method for recovering nitrogen and phosphorus from biogas slurry from pig farms
CN111470555A (en) * 2020-04-23 2020-07-31 立达超微工业（苏州）有限公司 Device for promoting removal of high-concentration phosphorus in wastewater by calcite

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102092898A (en) * 2010-12-24 2011-06-15 东南大学 Efficient denitrification, dephosphorization, denitrification and phosphorus resource recycling process for urban sewage
CN102173495A (en) * 2011-03-11 2011-09-07 中国科学院南京土壤研究所 Method and device for accelerating removal of high-concentration phosphorus in waste water by using calcite
CN102241445A (en) * 2011-05-17 2011-11-16 桂林理工大学 Method for removing and recycling phosphorus from phosphorus-rich water bodies or sewage by using natural mineral mixture
CN102898213A (en) * 2012-10-12 2013-01-30 常州大学 Method for recovering nitrogen and phosphorus from biogas slurry from pig farms
CN111470555A (en) * 2020-04-23 2020-07-31 立达超微工业（苏州）有限公司 Device for promoting removal of high-concentration phosphorus in wastewater by calcite

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Application publication date: 20210205