In soil environment, heavy metal pollution is the most common, which directly affects the health and safety of soil, and can be harmful to human body when serious. To solve the soil problem of heavy metal pollution, our team constructed a combination of heavy metal plants to repair soil. The environment of the soil is complex and changeable, and the control is weak. The influence of the treatment of heavy metal in soil and the influence of the growth condition and the external environment. Therefore, we will analyze the factors influencing the phosphorous bacteria in soil, and use the response surface optimization method to explore the optimal combination, optimal conditions and optimal results.
Mainly through software Design-Expert to realize optimization. The Box-Behnken experiment not only has a better effect. And the number of trials required is limited. Therefore, we adopt Box-Behnken experiment to optimize the adsorption process of heavy metal lead soil for PSB. Select the adsorption efficiency as the response value. The temperature, water and pH were selected as the influencing factors. The influence factors of PSB adsorption process are further discussed and studied. Get the best solution.
RSM design of plant growth
In this paper, the factors that affect the lead pollution in soil are studied and discussed in order to obtain the best solution. The influence factors of single factor test design were determined and the adsorption efficiency of lead in soil was selected. The following is a comparison of the actual value and the predicted value. It can be seen from the figure. The result is a good prediction of the actual soil conditions.
In order to improve the fixed efficiency of lead pollution, the response surface design method was adopted to optimize the fixed efficiency of soil. Firstly, the influences of several major factors in the environment, namely temperature, moisture content and pH. The three factors influencing single factor test were determined, and the optimal value of the interval was determined. The temperature, water and pH were selected as the influencing factors. Then the test scheme of the design of the software was designed. The temperature, water and pH were selected as the influencing factors. We use A as Temperature: B as pH: and C as Wet. The multivariate quadratic regression equation is obtained by experimental results.
In the optimal conditions:
RSM 3D surface figure(The values of C is 3.07)
Analyze the results. The optimal soil conditions are: the water content is 3.07g/kg , the temperature is 23.88 degrees Celsius, and The pH is 6.98.The maximum Adsorption efficiency can be achieved.55.09 %
We hope that this model can guide the control of soil conditions in phosphate-solubilizing bacteria(psb). Let the phosphate-solubilizing bacteria(psb) grow better and promote Phytoremediation process. To achieve the best effect of soil heavy metal treatment.
The growth curve model of PSB
The pollution of heavy metals in soil is a major problem of environmental sanitation in the world. The governance process faces many difficulties. Phytoremediation is a promising technology because it does not cause secondary pollution and low cost. However, the growth process of these plants are typically inhibited by high concentrations of heavy metals, It causes slow growth of plants and decelerates the phytoextraction process. Therefore, our team engineer a class of phosphate-solubilizing bacteria (PSB) to reduce the concentration of heavy metal ions in the soil. It also accelerates the growth of plants and repairs soil. Faced with severe heavy metal pollution, the environment of soil is complex and diverse.
Be familiar with the growth condition of the PSB. It becomes very important. In order to better understand the growth condition of phosphate-solubilizing bacteria (PSB), we adopted the classic Gompertz model. The following is the fitting effect diagram of growth curve
The growth curve model of PSB
y: the absorance in the OD 600
A; B; k; : undetermined coefficient
A model of the growth curve of phosphorus was developed by using the classic Gompertz model. In the chart, it can be seen that there is a delay in 5 hours, and a logarithmic growth phase from 10 to 35 hours, This stage’s bacterial strains is used as the experimental materialsthen stable period occur from 30 to 85 hours, after 85 hours is a degenerating period. In this point, the spores are ripe .Begin the preservation of the fungus seeds.
Master the growth rule of PSB. It has important guiding significance to study PSB physiology and production practice. In order to facilitate the future cooperation with fertilizers and other ways to repair soil environment
Plant growth influenced by heavy metal
Phytoremediation is a promising technology.However, the growth process of these plants are typically inhibited by high concentrations of heavy metals, It causes slow growth of plants and decelerates the phytoextraction process. So build this model.Better to explore the growth of plants. Verify that PSB can reduce the inhibition of heavy metal to plant growth.It can promote the growth of plants
Let's say there's no upper limit for plant growth and The density of plant unit volume is consistent,
W: Quantity of plants. v:Plant volume growth. ρ：The density of plants
w0:the initial plant quality
In fact, plant growth is restrained
assume that k=(a-bw),next substitute
In the soil of heavy metal pollution, the effects of metal ions on plant growth cannot be ignored.So we're going to have a separate discussion, introducing an impact factor R.So there are
wmax: The maximum quality that a plant can achieve。wu) ：The quality of the plant under normal conditions。
The heavy metal ions in soil can affect the growth of plants, thus affecting the efficiency of phytoextraction process.The influence factor R is proportional to the concentration of metal ions in the soil.Namely, the greater the heavy metal concentration, the greater the influence effect and the obvious hindering of plant growth.The heavy metal ions in soil are a dynamic process in the process of repair and gradually decrease.The R value also changes.R=k(Si-q1(t)-q2(t)+q3(t))
Si：The amount of metal ions in the soil
q1): The amount of heavy metal ions absorbed by plants
q2: the amount of heavy metal ions absorbed sby PSB
q3 the amount of heavy metal ions released by PSB.
Specific adsorption and repair processes at certain times our cooperative partner BNU-China has established detailed models.So the concentration of heavy metal ions in the soil. The adsorption kinetics is considered.The second stage kinetic adsorption equation is suitable for the control of the adsorption efficiency hand chemical mechanism.This is roughly in line with our plant and PSB adsorption mechanisms
qt：The adsorption quantity at the equilibrium moment of adsorption equilibrium (t)
qe：The amount of metal ions （e）on the adsorbent at the equilibrium moment of adsorption equilibrium.
So we can see that we have put in the soil of the PSB that we converted.The inhibition of superrich plant growth was reduced.To allow it to grow normally.The ion of heavy metals decreases faster than the non-input, the R value is lower, and the R value decreases faster.The growth of plants and the efficiency of plant adsorption play a important role.
It can be explained that our project is feasible and effective in helping plants to repair and control heavy metal pollution.
PSB-assisted phytoremediation dynamic system
Based on the data and information we provided, BNU-China helped us to construct a PSB-assisted phytoremediation dynamic system mathematical model for the implementation. The whole system was separated by three main processes——the phytoremediation process, the organic ptoduction process and the bingding of heavy metal ion with MBP secreted by modified Bacillus megaterium. The effect factors of the system are complex under lab condition not mention to physical circumstances which refers to the soil properties, the concentration of heavy metal ions, the population and equilibrium of bacteria, the degradation rate of protein and a series of chemical reaction. Although in this case, BNU-China helped us predict the feasibility of our project in almost perfect way. And according to the positive feedback done by them, our projected is worthy of further analysis and efforts in experiment and implementation. Thank you very much.
As the increasing addition of our engineered PSB, the population in soil could be seen soaring at the very beginning of stage in few hours. When it reaches at the peak of growth curve, the vitality of our chassis are in a steady increasing status that could be showed in the first row and right pic that the secretion of organic acid. At the same time, the concentration of binding metal proteins rise significantly from 0 to 20h. All in all, the last pic shows stable decline of heavy metal ions in the soil, that means the heavy metal ion could be extracted by our hyperaccumulator.
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