Natural cohesive soil has the ability to block and purify garbage pollutants. On the one hand, this barrier and purification ability is that cohesive soil has chemical functions such as mechanical filtration, ion exchange, physical adsorption, complexing, chelating and decomposition. On the other hand, there are a lot of microbial activities in the soil, which have biological and biochemical effects on garbage pollutants and can transform toxic and harmful substances into non-toxic and harmless substances. However, how big is the purification effect of microorganisms in this soil on garbage pollutants? Can the nutrients of soil microorganisms be added to the soil layer to promote the reproduction of dominant microbial strains and enhance their ability to purify pollutants? The answers to these questions are of great significance to the breakthrough of landfill technology and the development of microbial geochemistry theory and method. At present, the research of soil microbiology has entered a new field. People can use microorganisms to treat pollutants and sewage, degrade organic pollutants in soil and eliminate soil infectious diseases of crops, which is of great benefit to purifying the environment and soil health care. However, the research on the purification of pollutants in landfill leachate by microorganisms in soil has not been reported in domestic academic journals, and it is rare in foreign academic journals. This is a new research field and has become one of the focuses of environmental scientists. Therefore, this study has particularly important theoretical research value.
Improper disposal of municipal solid waste has caused human health and environmental problems all over the world, and effective control, treatment and disposal of it has become one of the common concerns of all countries. Among the disposal methods of solid waste, geological landfill is the most commonly used method in the world. The key technology of this treatment method is to lay impervious liner in the site. So far, the idea of preventing landfill leachate from polluting the environment at home and abroad is to prohibit leachate from leaking outside the site. Under the guidance of this idea, in order to protect the environment, landfill leachate treatment adopts the methods of laying liners and building sewage treatment plants. The geomembrane with low water permeability should be laid in the used impervious liner, which makes the cushion structure complicated, the material expensive, the laying difficult and the cost expensive. The cost of a medium-sized landfill liner is as high as hundreds of millions to tens of millions of yuan, while the establishment and operation of a landfill leachate treatment plant needs tens of millions of yuan. The need for such a high fee is a heavy burden for ordinary small and medium-sized cities. Many garbage dumps in our country pollute the environment, which is caused by not laying anti-seepage liner or the landfill leachate treatment plant is not in place. How to make the impervious layer have a good environmental protection effect without treating the landfill leachate, so that the cost can be greatly reduced even if the landfill has a good environmental protection effect, which is the goal pursued by the landfill disposal. It is of great practical significance to explore the purification effect of soil microorganisms on garbage pollutants and achieve this goal, which can not only produce huge environmental benefits, but also produce huge economic benefits.
Based on this, we conducted an experimental study on microbial purification of garbage pollutants in soil in the laboratory.
Second, experimental research methods
(A) experimental research ideas
Generally speaking, the microorganisms in leachate and impervious clay at the bottom of landfill are mainly anaerobic or facultative microorganisms, such as denitrifying bacteria, denitrifying bacteria, sulfate reducing bacteria (Pseudomonas), acetic acid reducing bacteria, methanogenic bacteria and so on. In the laboratory, we use soil column to simulate the environmental conditions of microbial growth at the bottom of garbage dump and in the soil layer under leachate, and cultivate anaerobic or facultative microbial liquid in the laboratory, and put it on the surface of the simulated soil column, so that bacterial liquid containing a large number of microorganisms can enter the soil with landfill leachate, thus participating in the whole process of soil layer purifying garbage pollutants. At the same time, water samples were taken at different depths of the soil column to analyze and test the pollution components of garbage. At the same time, the parallel soil column leaching purification experiment without artificial culture colonies was carried out, and the results were compared to study the purification effect of microorganisms on soil layer garbage pollutants.
(B) experimental research methods
1. Analog test device
The simulation experiment device is shown in Figure 5-2 and Figure 5-3.
Figure 5-2 Simulation Test Device for Purification of Waste Pollutants in Soil by Anaerobic Microorganisms
Figure 5-3 Simulation Test Device for Purification of Waste Pollutants by Cohesive Soil
2. Preparation of waste contaminated liquid
Landfill leachate is taken from the bottom of Beitiantang garbage dump in Fengtai District, Beijing.
3. Specific experiments
In the laboratory with adjustable temperature and humidity, the simulation experiment of combined purification of polluted wastewater by anaerobic microorganisms in soil and soil was carried out. First, 0.2? Compound phosphate fertilizer with G 12% phosphorus content 1600? ML landfill leachate was injected into the experimental soil column, and various anaerobic or facultative microorganisms such as thiobacillus denitrificans and denitrifying bacteria were inoculated with landfill leachate to optimize domestication. Bacteria), sulfate-reducing bacteria (Pseudomonas), fermentation acid-producing bacteria, specific acetic acid-reducing bacteria, methanogenic bacteria, denitrifying bacteria, etc. ML*** 200？ ML, respectively injected into the soil below the liquid level in the column under anaerobic conditions, and kept the room temperature at 30 ~ 35℃. In order to keep the experiment in the soil column in anaerobic state, a sealant plug with one-way air outlet was placed above the liquid level of the soil column to keep the microorganisms in anaerobic environment. Four sampling holes are arranged at equal intervals along the soil column from top to bottom, and the negative pressure unidirectional sampler is connected to the negative pressure sampling bottle through PVC pipe, and water samples are taken regularly for testing and analysis. The experimental test items mainly include. * * * The same test was conducted six times.
Third, the experimental research results
Through the above experiments, the results as shown in Figure 5-4 are obtained.
Figure 5-4 Effect Diagram of Microbial Purification of Garbage Pollutants in Soil
It can be seen from Figure 5-4 and Table 5-3 that the interception value of waste pollutants in the first cycle of the test is greater than that in the second, third, fourth and fifth cycles, regardless of the soil column with anaerobic microbial liquid or the natural soil column without microbial liquid, and the interception value in the last cycle is always greater than that in the next cycle. More importantly, compared with the natural soil column without anaerobic microbial liquid, the interception value of TDS and so on. The soil column with anaerobic microbial liquid is higher than the natural soil column without anaerobic microbial liquid. This shows that the purification effect of microorganisms on pollutants in clay soil has been improved after adding anaerobic microbial liquid. After adding anaerobic microbial liquid into cohesive soil, the interception effect is obviously improved, the interception capacity is increased by 3% ~ 90%, and the cumulative interception value is increased by 4% ~ 265,438+0% each time. With the increase of test times, the role of microorganisms tends to increase.
Table 5-3 Comparison Table on the Improvement of Natural Soil Pollutant Removal Rate under the Action of Enhanced Microbes
Four. conclusion
According to the above research results, we can draw the following conclusions:
(1) The study of soil microorganism purifying pollutants is one of the frontier fields of environmental science research in the world, which has important practical significance in both theory and application practice of environmental pollution control.
(2) Adding anaerobic microbial liquid into the clay liner of the garbage disposal site can strengthen the microbial function and obviously improve the degradation of garbage pollutants by microorganisms in the impermeable layer. This opens up an idea for developing cheap and high-quality landfill liners and provides an effective treatment method for landfills with pollution problems.
(3) Adding anaerobic microbial liquid into cohesive soil, through the joint action of soil layer and microorganisms, to improve the interception and purification method of garbage pollutants, only a preliminary attempt has been made at present. Due to the complexity of microbial growth and growth environment and the diversity of garbage pollutants, a lot of work needs to be done to form a set of mature methods or technologies.