CN115353211B - Application of bacillus megatherium LZP03 in treatment of pig raising wastewater - Google Patents

Abstract

The invention discloses application of bacillus megatherium LZP03 in treating pig raising wastewater. The bacillus megatherium LZP03 is preserved in China Center for Type Culture Collection (CCTCC) with a strain preservation number of CCTCC NO. M2018599. According to the invention, different kinds of beneficial microorganisms are inoculated into pig raising wastewater to screen and obtain bacillus megatherium LZP03 which grows in the pig raising wastewater and has a relatively high propagation speed, and the utilization condition of nutrient components in the pig raising wastewater and the degradation condition of pollutants in the pig raising wastewater are detected, so that LZP03 can grow in an original pig raising wastewater culture medium and has relatively high biomass, and the biomass is remarkably improved after the pig raising wastewater culture medium with optimized carbon nitrogen ratio is inoculated into LZP 03. The LZP strain is fermented in the pig raising wastewater culture medium with optimized carbon-nitrogen ratio, has good removal rate for COD, ammoniacal nitrogen and phosphorus, reduces the possibility of environmental pollution caused by the pig raising wastewater on one hand, and is more beneficial to the recycling of the pig raising wastewater on the other hand.

Description

Application of Bacillus megaterium LZP03 in treating pig wastewater

Technical field

The present invention relates to a microbial strain that can be used to treat pig wastewater, in particular to the application of Bacillus megaterium LZP03 in treating pig wastewater, and also relates to a method for treating pig wastewater. The invention belongs to the technical field of agricultural production.

Background technique

China is one of the countries with the largest large-scale pig breeding and consumption industry in the world. With the continuous development of the economy, the scale of the pig breeding industry chain continues to expand. According to the 2016 China Statistical Yearbook, my country's annual pork production in 2015 was 54.865 million tons. The scale of pig breeding is very huge (National Bureau of Statistics, 2016), and the poultry and livestock produced Feces has also become a major source of pollution, and the resulting environmental pollution problems have become increasingly prominent. The overall production of livestock manure in China has now reached 2.43x10 ⁸ tons, urine is 1.63x10 ⁸ tons, total nitrogen is 1.02x10 ⁶ tons, and total phosphorus is 1.60x10 ⁵ tons (Pan Qing, 2002), and COD emissions have reached 71.18 million tons, far exceeding the combined COD emissions of industrial wastewater and domestic wastewater. Since most pig farms use flushing to clean pig houses, the pig farm wastewater, pig urine and feces are mixed with each other, and the ammonia in the wastewater The nitrogen content, phosphorus content, suspended solids and organic matter concentration are high and the carbon-nitrogen ratio is seriously imbalanced. If a large amount of untreated emissions are discharged in lakes, rivers, farmland and other environments, it will lead to eutrophication of water bodies, changes in soil properties and a series of pollution problems. .

Today, pig wastewater treatment technologies at home and abroad mainly focus on three major categories: physical and chemical treatment technology, natural treatment technology and biological treatment technology. Among them, the most commonly used physical and chemical treatment methods are media adsorption method, flocculation sedimentation method, etc. For example, Qian Feng et al. used a zeolite-straw combination to filter pig urine wastewater. The removal rates of COD, ammonia nitrogen and phosphorus can reach 47.9% and 47.9% respectively. 72.9% and 50.1% (Qian Feng, 2008). Cui Lina and others were able to remove 61.02% of pig wastewater with a COD concentration of 3232 mg/L through magnetic flocculation (Cui Lina, 2010). Although the physicochemical method has a good pollutant removal rate for pig urine wastewater, it has disadvantages such as low broad-spectrum removal of pig urine wastewater pollution, high cost of pollutant removal, large investment in treatment equipment, and few engineering applications. . The natural treatment method generally uses the comprehensive action of natural soil, water and organisms to remove pollutants. For example, Zhu Xizhen and others use blast furnace slag and quartz sand to construct artificial wetlands to remove COD, BOD and phosphorus. The rates reached 71%-88%, 80%-89%, and 70%-85% respectively (Zhu Xizhen, 2003), and Lu Xiuguo and others used oxidation ponds to treat pig wastewater with COD ≤ 400 mg/L and ammonia nitrogen ≤ 70mg/L (Lu Xiuguo, 2009). The natural treatment method also has a relatively good decontamination ability for contaminated wastewater, but its stability is insufficient and the purification time is long. Biological treatment technology is a new method that uses the catalytic effect of microorganisms to treat high-concentration organic wastewater. For example, Liang Meidong and others use SRB reactors to aerate pig wastewater, which can increase the COD removal rate to more than 90% (Liang Meidong) , 2009), Li Fengmin et al. used aerobic-anaerobic combined treatment method to achieve ammonia nitrogen and total nitrogen removal rates of 99.7% and 50.7% (Li Fengmin, 2011). However, the process of treating wastewater through biological treatment will produce a large amount of activated sludge that cannot be treated, causing secondary pollution to the environment.

However, although pig wastewater will cause a series of pollution to the environment, it is undeniable that it contains a large amount of organic matter, nitrogen, phosphorus, potassium and other nutrients, and these elements are also necessary for the growth of microorganisms and are important for increasing the number of microorganisms. and quality are both positive. If pig wastewater is used as the basic culture medium for beneficial microbial fermentation production, the production cost of microbial fertilizer can be greatly reduced and pollution problems can be alleviated through biodegradation. In this way, wastewater can be turned into treasure, realize its residual value, and also It can save a large amount of resources used to control environmental pollution, and is of great significance in promoting the harmless resource utilization of environmental pollutants.

Therefore, the present invention uses pig-raising wastewater as a natural screening medium to screen different types of beneficial microbial strains to obtain strains that grow vigorously and reproduce quickly in pig-raising wastewater, and conduct nutritional analysis of the pig-raising wastewater culture medium. Optimize to increase the biomass of the bacteria, detect the utilization of nutrients in pig wastewater and the removal effect of pollutants by the bacteria after optimization, and explore the fermentation system and process of pig wastewater, so as to make pig wastewater harmless Provide technical support for resource utilization.

Contents of the invention

One of the objects of the present invention is to provide a microbial strain that can be used to treat pig wastewater;

The second object of the present invention is to provide a method for treating pig wastewater.

In order to achieve the above objects, the present invention adopts the following technical means:

The present invention inoculates different types of beneficial microorganisms into pig wastewater to screen to obtain Bacillus megaterium LZP03 (CCTCC NO: M2018599), a strain that grows and reproduces quickly in pig wastewater, and detects its effects on pig wastewater. The utilization of nutrients in pig wastewater and the degradation of pollutants in pig wastewater were found to be able to grow LZP03 in the original pig wastewater with higher biomass, while in pig wastewater with an optimized carbon-nitrogen ratio The increase in biomass was more significant, with the highest viable bacterial count of LZP03 being 4.26×10 ¹⁰ cfu/mL. Comparing the utilization of carbon, nitrogen and organic carbon by LZP03 strain in original and optimized pig wastewater proved that in the optimized culture medium The metabolism of each strain is more vigorous. The LZP03 strain has a good removal rate for COD, ammonia nitrogen and phosphorus content when fermented in a pig wastewater medium with an optimized carbon-nitrogen ratio. The COD removal rate reaches 92%, and the ammonia removal rate reaches 92%. The nitrogen removal rate is 90.35% and the phosphorus removal rate is 69.10%, and it can effectively adjust the pH value of the original pig wastewater, reducing the possibility of environmental pollution by fermentation waste liquid, and better improving the resource utilization of pig wastewater. use.

On the basis of the above research, the present invention first proposes the application of Bacillus megaterium LZP03 in treating pig wastewater. The Bacillus megaterium LZP03 is named Bacillus megaterium LZP03, and the classification name is Bacillus megaterium LZP03. Preserved In the China Type Culture Collection Center, the address is Wuhan University, Wuhan, China, the strain preservation number is CCTCC NO.M2018599, and the preservation date is September 6, 2018.

Among them, preferably, the seed liquid of Bacillus megaterium LZP03 is inoculated into the sterilized pig wastewater to be treated, and the treated pig wastewater can be obtained after fermentation. The treated pig wastewater is less polluted than before treatment. content has decreased.

Wherein, preferably, it also includes the step of adding brown sugar to the sterilized pig wastewater to be treated, so that the carbon-nitrogen ratio of the pig wastewater is 16-20:1.

Among them, preferably, the fermentation refers to fermentation and culture at 30°C and 120 r/min for 24-96 hours.

Among them, preferably, the contents of total nitrogen, total carbon, total organic carbon, COD, ammonia nitrogen, and phosphorus in the treated pig wastewater are reduced compared with those before treatment.

Furthermore, the present invention also proposes a method for treating pig wastewater, which includes the following steps:

(1) Bacillus megaterium LZP03 was inoculated into beef extract peptone culture medium for activation, the activated strain was grafted into beef extract peptone culture medium and then the concentration of the strain was adjusted to OD ₆₀₀ = 1.0 using sterile water as the seed liquid; The Bacillus megaterium LZP03 is deposited in the China Type Culture Collection Center, and its strain preservation number is CCTCCNO.M 2018599;

(2) The seed liquid is inoculated into the sterilized pig wastewater to be treated, and the treated pig wastewater can be obtained after fermentation. The treated pig wastewater has a reduced content of pollutants compared to before treatment.

Preferably, step (2) also includes the step of adding brown sugar to the sterilized pig wastewater to be treated, so that the carbon-nitrogen ratio of the pig wastewater is 16-20:1.

Among them, preferably, in step (2), the seed liquid is inoculated into the sterilized pig wastewater to be treated at an inoculation amount of 1-2 vol%.

Among them, preferably, the fermentation described in step (2) refers to fermentation and culture at 30°C and 120 r/min for 24-96 hours.

Among them, preferably, the contents of total nitrogen, total carbon, total organic carbon, COD, ammonia nitrogen, and phosphorus in the treated pig wastewater are reduced compared with those before treatment.

Compared with the existing technology, the beneficial effects of the present invention are:

This invention uses beneficial microorganisms to realize the utilization of pig wastewater resources. This technology is also based on biological treatment methods. Its core is to use microbial aerobic-anaerobic combined treatment to remove pollutants from pig wastewater, and it is groundbreaking. The rich nutrients in pig wastewater are used to achieve large-scale reproduction of beneficial microorganisms to obtain beneficial microbial cells for the production of microbial inoculants, which remove pollutants and protect the environment while creating economic value. The present invention uses pig-raising wastewater as a natural medium to cultivate microorganisms. The pig-raising wastewater is selected because it contains a large amount of organic matter, carbon sources, nitrogen sources and other nutrients that can provide sufficient nutrients for the growth of microorganisms. Microorganisms are cultivated. It is a natural hotbed, and during the growth process of microorganisms, it can absorb, transform and fix environmentally harmful substances in pig wastewater for the proliferation of the bacteria themselves and the secretion of metabolites. This on the one hand reduces the environmental impact of pig wastewater. Safety poses a threat to pollution sources such as ammonia nitrogen, organic matter, phosphorus, etc. On the other hand, a large number of microbial cells cultured through pig wastewater can be collected to use microbial preparations for plant growth promotion, crop biocontrol, pollutant degradation, etc., killing two birds with one stone. , and the high cost of culture media during the cultivation process of microorganisms is one of the main reasons for the high price of microbial inoculants. The use of pig wastewater to cultivate beneficial microbial strains is close to the number of viable bacteria in traditional culture media. , but the cost has dropped significantly, which is of great significance to the promotion of microbial inoculants to reduce the use of pesticides and fertilizers and achieve green agriculture.

The present invention optimizes and adjusts the carbon-nitrogen ratio of pig wastewater and then inoculates it with beneficial microorganisms. Through screening, a beneficial microorganism LZP03 with a higher viable bacterial count is finally obtained. It has excellent effects in promoting crop growth, and the highest viable bacterial count of LZP03 can reach 4.26. ×10 ¹⁰ cfu/mL, and then centrifuged to collect the bacteria and then tested the fermentation waste liquid. It was found that it has a good removal rate for pig wastewater pollutants. The organic matter removal rate of LZP03 was 89.62%, and the COD removal rate reached 92 %, the ammonia nitrogen removal rate is 90.35%, the phosphorus content removal rate can reach 69.10%, and LZP03 can effectively reduce the pH of the original pig wastewater, reducing it from the original alkaline solution to a neutral or acidic pH solution. Prevent the filtered wastewater from causing soil salinization and damaging the soil structure.

This proves that the "beneficial microorganisms realize the resource utilization of pig wastewater" technology can decontaminate pig wastewater no less than the mainstream domestic and foreign physical and chemical treatment technology, natural treatment technology and traditional biological treatment technology. The effect is even better and is even better for pig wastewater treatment. The types of pollutants removed from pig wastewater are more comprehensive and broad-spectrum; pig wastewater treatment through microbial fermentation is cheaper in terms of decontamination costs, requires less equipment investment, does not require a large amount of space, and does not require a large decontamination cycle. Short, small fermentation equipment can be quickly built close to the source for pig wastewater treatment, and small enterprises can also afford the cost of system construction; using beneficial microorganisms for fermentation can not only treat pig wastewater, but also harvest beneficial microbial strains for use in microbial bacteria. The production and use of agents not only reduces the environmental damage caused by pollutants during the treatment of pig wastewater, but also returns economic benefits. It can also promote the promotion of microbial agents and accelerate the development of green agriculture, creating an ecological protection-agricultural development model. The virtuous cycle system is in line with the general direction of China's sustainable development strategy.

Description of the drawings

Figure 1 shows the changes in biomass of LZP03 strain over time in the original and optimized pig wastewater;

Figure 2 shows the comparison of the changes in total nitrogen content and the decrease rate (A) of the original (B) and optimized pig wastewater (C) after LZP03 treatment;

Figure 3 shows the comparison of the changes in total carbon content and the decrease rate (A) of the original (B) and optimized pig wastewater (C) after LZP03 treatment;

Figure 4 shows the comparison of the changes in total organic carbon content and the decrease rate (A) of the original (B) and optimized pig wastewater (C) after LZP03 treatment;

Figure 5 shows the comparison of the decline rates of total nitrogen, total carbon, and total organic carbon in the supernatant of LZP03 fermentation broth;

Figure 6 shows the pH change trend of LZP03 in the optimized medium with fermentation time;

Figure 7 shows the COD removal rate of LZP03 in the fermentation broth and its trend over time;

Figure 8 shows the removal rate of ammonia nitrogen and phosphorus content by LZP03.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments can be obtained by those of ordinary skill in the art without making creative efforts. , all belong to the protection scope of the present invention.

Example 1 Screening of bacterial strains and their application in pig wastewater treatment

1Materials and methods

1.1 Physical and chemical properties of original pig wastewater

The pig wastewater used in the experiment was taken from a pig farm in Fularji District, Qiqihar City. The collected pig wastewater was stored at 4°C for subsequent experiments. The basic characteristics of the pig wastewater are shown in Table 1.

Table 1 Physical and chemical properties of pig wastewater

1.2 Source of test strains

The strains used in the test are all different types of pure cultured beneficial microorganisms isolated and screened by the research team. The research found that each strain is an efficient strain with good industrial application potential in plant growth promotion, biological control, pollutant control, etc. Store in a -80°C refrigerator until use. All strains were identified by strain morphology and 16SrDNA classification. The identification list is shown in Table 2.

Table 2 Test strains

1.3 Culture medium

Beef extract peptone culture medium: 10.00g peptone, 3.00g beef extract, 5.00g NaCl, 20.00g agar, dilute to 1000.00mL with distilled water, no agar is added to the liquid culture medium.

Original pig wastewater medium: pig wastewater transported from pig farms.

Pig wastewater culture medium with optimized carbon-to-nitrogen ratio: 10g of brown sugar, and the volume of pig wastewater is adjusted to 1000.00mL, so that the carbon-to-nitrogen ratio of pig wastewater is 16-20:1.

1.4 Preliminary screening of strains that can efficiently degrade pig wastewater

1.4.1 Preparation of seed liquid

The test strains in Table 2 were inoculated into beef extract peptone medium and cultured at 30°C for 24 hours for activation. The activated strains were grafted into beef extract peptone medium and cultured with shaking at 30°C and 120r/min. Then each strain cultured to the same concentration (OD600=1.0) was used as seed liquid for pig wastewater treatment test. .

1.4.2 Preliminary screening of strains

In order to screen strains that can grow in large quantities in pig wastewater, the seed liquids of different strains were inoculated into triangular flasks containing 100mL of sterilized pig wastewater at an inoculation volume of 1vol%, and the flasks were shaken at 30°C and 120r/min. Culture, sample the fermentation broth every 24 hours, and detect the number of viable bacteria in each time period to determine the maximum number of viable bacteria of the strain. The number of viable bacteria is determined by the dilution coating method. Take 10 mL of the fermented culture medium and put it into a 90 mL Erlenmeyer flask filled with glass beads and sterile water. Shake it in a shaker at 200 r/min for 30 minutes and then carry out gradient dilution. Select Take 0.1 mL of the appropriate dilution concentration and spread it on the beef extract peptone medium solid plate, culture it at 30°C for 24 hours, calculate the number of viable bacteria (cfu/mL), and set up three parallel groups. Then select strains with higher fermentation biomass for subsequent experiments.

1.5 Research on the effect of screening bacterial strains on the utilization of pig wastewater resources

1.5.1 Changes in the growth and treatment effects of each screened strain over time in the original wastewater and wastewater with optimized carbon-nitrogen ratio

Since the small carbon-to-nitrogen ratio in the raw solution of pig wastewater may inhibit the growth and reproduction of bacteria and reduce the treatment effect of pig wastewater, the appropriate carbon-nitrogen ratio of the pig wastewater culture medium should be optimized to test whether the bacterial content can be increased and strengthen the Treatment capacity of pig wastewater. The dominant bacterial strains obtained after screening were inoculated into beef extract peptone culture medium to prepare seed liquid, and inoculated into 300 mL of original pig wastewater culture medium and optimized culture medium with 1wt% brown sugar added at an inoculation volume of 2vol%, at 30 ℃, 120r/min shake flask culture, samples were taken every 24 hours to measure various indicators.

1.5.2 Treatment effect of centrifuged pig wastewater with optimized carbon-nitrogen ratio treated by selected strains

In order to simulate whether the pig waste liquid treated with various bacterial strains after obtaining the bacteria in the industrial production process can further reduce the potential of environmental threats, this experiment carried out indicator detection by centrifuging the sample liquid at different fermentation times. The seed liquid of the selected strains was inoculated into the optimized culture medium, and cultured in a shake flask at 30°C and 120 r/min. Samples were sampled every 24 hours and centrifuged at 12,000 rpm for 5 min, and then the indicators were measured.

1.6 Test measurement indicators

1.6.1 Water quality indicators

The COD, pH, total nitrogen, total carbon, total organic carbon, ammonia nitrogen, and phosphorus content of the samples were measured.

1.6.2 Microbial indicators

Put 10 mL of fermentation broth into 90 mL of sterile water and shake it in a shaker at 200 r/min for 30 minutes, then perform gradient dilution to obtain dilutions with concentrations of 10 ^-7 , 10 ^-8 , and 10 ^-9 , and then take 0.1 mL for dilution The solution was spread on the beef extract peptone medium plate, cultured at 30°C for 24 hours, and the number of viable bacteria (cfu/mL) was calculated. Three parallel groups were set up.

2. Results and discussion

2.1 Screening of pig wastewater treatment strains

By detecting the maximum viable bacterial count of each strain in pig wastewater, the purpose of screening different strains was achieved. By using pig wastewater to culture various beneficial strains, it was found that LZP03 can grow in pig wastewater and has a high The maximum number of viable bacteria in pig wastewater is LZP03=1.76×10 ¹⁰ cfu/mL. Compared with other strains, the number of viable bacteria is higher and used for subsequent tests.

2.2 Comparison of bacterial growth over time of LZP03 in the original and optimized pig wastewater culture media

In order to determine the biomass size of LZP03 strain in different culture media, the number of viable bacteria was determined by inoculation into the original and optimized culture media using the gradient dilution plate method. It can be seen from Figure 1 that when LZP03 was grown in the original pig wastewater culture medium, the number of viable bacteria reached the maximum number of 1.76×10 ¹⁰ cfu/mL after 72 hours of culture, and the maximum number of viable bacteria was reached at 96 hours in the optimized pig wastewater culture medium. is 4.26×10 ¹⁰ cfu/mL, which increases the biomass by 56.86%. Therefore, adding brown sugar to optimize the carbon-nitrogen ratio can significantly increase the biomass of each strain in pig wastewater and improve the ability of the bacteria to treat pig wastewater. And it can better improve the acquisition of beneficial microorganisms.

2.3 Changes in total nitrogen, total carbon and total organic carbon of the fermentation broth during the growth of LZP03 in the original and optimized pig wastewater culture media

2.3.1 Changes in total nitrogen of LZP03 in the original and optimized pig wastewater culture media

LZP03 was inoculated into the original pig wastewater culture medium and the optimized pig wastewater culture medium, and the total nitrogen of the fermentation broth was measured every 24 hours. It can be seen from Figure 2 that after the original pig wastewater was inoculated with the LZP03 strain, the total nitrogen content of the fermentation broth generally showed a declining trend with the increase of the strain fermentation time. At 96 hours of cultivation, the total nitrogen content of the LZP03 fermentation broth dropped to the lowest value. 178.4mg/L, the total nitrogen content decreased by 55.75% compared with the control group. The total nitrogen content of LZP03 fermentation broth using the optimized pig wastewater culture medium also showed an overall downward trend with the extension of fermentation time, and the total nitrogen content dropped rapidly in the fermentation interval of 0-24h, and then leveled off, LZP03 When cultured for 96 hours, the total nitrogen content reached the minimum value of 104.8 mg/L, which was a 68.62% decrease in total nitrogen compared with the control group LZP03. Through comparison, it can be found that the decrease rate and speed of the total nitrogen in the fermentation liquid of LZP03 grown in the original pig wastewater are less than that of the pig wastewater fermentation liquid after inoculation with optimized carbon-nitrogen ratio. This may be due to denitrification in the culture medium. Nitrogen overflow, so optimizing the carbon-nitrogen ratio can better improve the bacterial strain's utilization of nitrogen.

2.3.2 Comparison of total carbon treatment in original and optimized pig wastewater culture media

The selected strains were inoculated into the original pig wastewater culture medium and the optimized pig wastewater culture medium, and the total carbon of the fermentation broth was measured every 24 hours. As shown in Figure 3, after the LZP03 strain was inoculated into the original pig wastewater culture medium, the total carbon content in the fermentation broth showed a slow decline and then stabilized with the increase of culture time. The total carbon content of the LZP03 fermentation broth dropped to The lowest value was 740.0mg/L. Compared with the control group, the total carbon reduction rate of the fermentation broth of the screened strain LZP03 was 24.61%. After the selected strains were inoculated into the optimized pig wastewater culture medium, the total carbon content in the fermentation broth continued to decrease with the increase of culture time, and the speed eventually tended to decrease slowly. After 96 hours of cultivation, the total carbon content of the fermentation broth of each strain The content reached the minimum value LZP03 = 1722mg/L, and the total carbon reduction rate was 66.60% lower than that of the control group. When LZP03 was cultured in the optimized culture medium, the reduction rate of the total carbon content in the fermentation broth was significantly higher than that in the original pig wastewater. The reduction in the total carbon content may be due to the growth process of microorganisms. The continuous aerobic respiration to discharge carbon dioxide leads to a decrease in the total carbon content, indicating that the growth and metabolism of microorganisms are more active in the optimized culture medium. Therefore, the optimized pig wastewater culture medium can effectively promote the growth of strains and improve their metabolism. ability.

2.3.3 Comparison of total organic carbon treatment in original and optimized pig wastewater fermentation broth

As can be seen from Figure 4, after inoculation with the LZP03 strain, the total organic carbon content in the original pig wastewater fermentation broth showed a trend of first increasing and then decreasing as the bacterial culture time increased. Compared with the control group, the total organic carbon content after LZP03 fermentation The minimum organic carbon content was 294.8 mg/L, and the total organic carbon reduction rate was 18.54%. When LZP03 was inoculated into the optimized pig wastewater culture medium, the total organic carbon content of the fermentation broth continued to decrease with the extension of the culture time at 96 hours. When reaching the minimum value, the decrease rate of LZP03 in the control group reached 70.56%. Compared with the original pig wastewater medium, the optimized pig wastewater medium consumed total organic carbon more rapidly and at a faster rate. The increase and then decrease in total organic carbon in the fermentation broth of the original pig wastewater culture strain may be due to the microorganisms degrading some insoluble solid pig manure and impurities in the pig wastewater. In the early stage, the degradation rate of the bacteria was greater than that of the bacteria. The total organic carbon consumed by its own synthesis or metabolism, so there is a continuous accumulation of total organic carbon. Then as the number of strains continues to increase, the total organic carbon consumption continues to increase. In addition, the amount of substrate is continuously consumed, which leads to the accumulation of total organic carbon in the fermentation broth. The rate is less than the consumption rate, and the total organic carbon content continues to decrease. The continuous reduction of total organic carbon consumption in the optimized culture medium may be due to the fact that after carbon source supplementation, the bacterial cells quickly entered the logarithmic phase of growth in the early stage and the number increased rapidly. The total organic carbon content consumed for their own synthesis and metabolism was far greater than the accumulated amount, so the total organic carbon content was much greater than the accumulated amount. Organic carbon content continues to decrease.

2.4 Changes in various indicators of fermentation waste liquid after removing bacteria from pig wastewater treated with LZP03

By comparing the changes in biomass, total nitrogen, total carbon, and total organic carbon of LZP03 during the growth process of the original and optimized pig wastewater culture media, it was found that the strain can grow better in the optimized pig wastewater culture medium. The growth and reproduction biomass has increased significantly and its own ability to metabolize and utilize nutrients in pig wastewater is stronger. Therefore, the optimized pig wastewater culture medium was selected as the basic culture medium for industrial fermentation of beneficial microorganisms. At the same time, in order to simulate industrial production During the process, whether LZP03 can better reduce the potential threat to the environment from the filtered fermentation waste liquid after fermenting pig wastewater and harvesting the cells. Therefore, this experiment uses high-speed centrifugation to remove the cells in the strain fermentation liquid. And the changes in total nitrogen, total carbon, total organic carbon, COD, ammonia nitrogen, and phosphorus in the supernatant liquid were measured.

2.4.1 Changes in total nitrogen, total carbon and total organic carbon content of LZP03 in the optimized pig wastewater culture medium

LZP03 was inoculated into the optimized pig wastewater culture medium, and the supernatant after centrifugation was measured for total nitrogen, total carbon and total organic carbon every 24 hours. As can be seen from Figure 5, compared with the control group, the total nitrogen content in the supernatant of the centrifuged LZP03 fermentation broth decreased by 94.58%, the total carbon content decreased by 85.96%, and the total organic carbon content decreased by 89.62%. This shows that the LZP03 strains can better utilize the nutrients in pig wastewater for their own growth, reproduction and metabolic activities, and prevent the filtered fermentation waste liquid from being eutrophic and causing environmental pollution.

2.4.2 pH changes of LZP03 in the optimized pig wastewater culture medium

The pH of the fermentation broth of each strain was measured every 24 hours. It can be seen from Figure 6 that after 96 hours of fermentation by the LZP03 strain, the pH of the pig wastewater dropped from the original alkaline solution of pH=8.85 to the neutral fermentation broth of pH=7.34. This may be due to During the fermentation process, the strain will secrete a certain amount of organic acid when it grows in the alkaline pig wastewater by utilizing the nutrients of the pig wastewater, thereby lowering the pH value of the highly alkaline pig wastewater, which is beneficial to preventing filtration. Wastewater discharge causes soil salinization and damages soil structure, which is of great significance.

2.4.3 Changes in COD content and removal rate of LZP03 in the optimized pig wastewater culture medium

In order to determine the effect of the selected strain on COD removal from pig wastewater, COD detection was performed on the supernatant of the LZP03 fermentation broth. It can be seen from Figure 7 that as the fermentation time of the strain continues to increase, its COD content continues to decrease rapidly from the original COD=16000mg/L. The maximum dropped to COD = 1280mg/L, and the COD removal rate reached LZP03 = 92%, indicating that LZP03 has a good removal rate for COD and reduces the threat of filtrated waste liquid to the environment. In the trend chart of COD changes in LZP03 fermentation broth over time It was found that the COD content of the strain increased slightly during the time interval of 72h-96h of culture. This may be because the number of newly added bacterial cells at the end of the stationary phase of the strain is less than the number of dead cells, and the ability to remove COD is reduced and due to the destruction of intracellular materials by dead bacteria. The outflow causes a certain rebound in COD concentration.

2.4.4 Removal rate of ammonia nitrogen and phosphorus by LZP03 in optimized pig wastewater

The ammonia nitrogen content of the fermentation broth supernatant of LZP03 at different fermentation times was measured. From Figure 8, it can be seen that the LZP03 strain can significantly reduce the ammonia nitrogen content in the fermentation waste liquid, and the ammonia nitrogen removal rate reaches 90.35%. It has a better effect on removing ammonia nitrogen. Similarly, after the strain fermentation, the phosphorus content of the fermentation liquid supernatant was measured to see whether the strain could better reduce the phosphorus content in the fermentation waste liquid. It can be seen from the figure that compared with the control group, the phosphorus removal rate of LZP03 can reach 69.10%, indicating that it has a certain ability to remove phosphorus.

3Conclusion

(1) LZP03 can grow in the original pig wastewater and has a high biomass. However, the biomass increase is more significant in the pig wastewater with an optimized carbon and nitrogen ratio. The highest viable bacterial count of LZP03 is 4.26×10 ¹⁰ cfu/ mL, and by comparing the utilization of carbon, nitrogen, and organic carbon by the LZP03 strain in the original and optimized pig wastewater, it was proved that the metabolism of each strain in the optimized medium was more vigorous, so the pig wastewater after the carbon-nitrogen ratio was optimized is more suitable for the strain Growth, reproduction and resource utilization.

(2) The fermentation of LZP03 strain in the pig wastewater medium with optimized carbon-nitrogen ratio has a good removal rate for COD, ammonia nitrogen and phosphorus content. The COD removal rate reaches 92%, and the ammonia nitrogen removal rate reaches 92%. The removal rate of phosphorus is 90.35% and 69.10%, and it can effectively adjust the pH value of the original pig wastewater, reducing the possibility of environmental pollution by fermentation waste liquid, and better improving the resource utilization of pig wastewater.

Claims (10)

1. Application of Bacillus megaterium LZP03 in treating pig wastewater. The Bacillus megaterium LZP03 is deposited in the China Type Culture Collection Center, and its strain preservation number is CCTCC NO.M 2018599. 2. Application as claimed in claim 1, characterized in that, the seed liquid of Bacillus megaterium LZP03 is inoculated into the sterilized pig wastewater to be treated, and the treated pig wastewater can be obtained through fermentation. The pollutant content of the pig wastewater has decreased compared with that before treatment. 3. The application according to claim 1, further comprising the step of adding brown sugar to the sterilized pig wastewater to be treated, so that the carbon-nitrogen ratio of the pig wastewater is 16-20:1. 4. The application according to claim 2, characterized in that the fermentation refers to fermentation and culture at 30°C and 120 r/min for 24-96 hours. 5. The application according to claim 3, characterized in that the treated pig wastewater has a reduced content of total nitrogen, total carbon, total organic carbon, COD, ammonia nitrogen and phosphorus compared to before treatment. . 6. A method for treating pig wastewater, characterized by comprising the following steps: (1) Bacillus megaterium LZP03 was inoculated into beef extract peptone culture medium for activation, the activated strain was grafted into beef extract peptone culture medium and then the concentration of the strain was adjusted to OD ₆₀₀ = 1.0 using sterile water as the seed liquid; The Bacillus megaterium LZP03 is deposited in the China Type Culture Collection Center, and its strain preservation number is CCTCC NO.M2018599; (2) The seed liquid is inoculated into the sterilized pig wastewater to be treated, and the treated pig wastewater can be obtained after fermentation. The treated pig wastewater has a reduced content of pollutants compared to before treatment. 7. The method of claim 6, wherein step (2) further includes the step of adding brown sugar to the sterilized pig wastewater to be treated, so that the carbon-nitrogen ratio of the pig wastewater is 16-20 :1. 8. The method of claim 6, wherein in step (2), the seed liquid is inoculated into the sterilized pig wastewater to be treated at an inoculation amount of 1-2 vol%. 9. The method of claim 6, wherein the fermentation in step (2) refers to fermentation and culture at 30°C and 120 r/min for 24-96 hours. 10. The method of claim 6, wherein the treated pig wastewater has a reduced content of total nitrogen, total carbon, total organic carbon, COD, ammonia nitrogen and phosphorus compared to before treatment. .