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. 2023 Jun 21;8(26):23545–23553. doi: 10.1021/acsomega.3c01128

Research and Application of Shallow Geothermal Energy Development and Utilization in Shandong Province

Qi Shao †, Chengwei Zhang ‡,*, Mingyuan Sun †, Tao Chen ‡, Xueyou Yu †, Huiyong Yin ‡, Bingfeng Wang †
PMCID: PMC10324059  PMID: 37426208

Abstract

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Shallow geothermal energy reserves are abundant and widely distributed in Shandong Province. Vigorously developing and utilizing shallow geothermal energy will play a significant role in improving energy pressure in Shandong Province. The energy efficiency of ground source heat pumps is closely related to geological and other conditions. However, few studies on geothermal exploitation and utilization have been affected by economic policies. This article will investigate the operation of shallow geothermal engineering in Shandong Province, summarize the current number of operating projects, calculate the engineering annual comprehensive performance coefficient (ACOP), analyze the size characteristics of different cities, and analyze their correlation with economy and policy. Through research, it is found that the number of shallow geothermal energy development and utilization is significantly positively correlated with socioeconomic level and policy orientation, and has a relatively small relationship with ACOP. The research results provide a basis and suggestions for improving and optimizing the energy efficiency coefficient of geothermal heat pumps and promoting the development and utilization of shallow geothermal.

1. Introduction

Shallow geothermal energy, also known as shallow geothermal energy, refers to the geothermal energy stored in water, soil, and rock at a temperature below 25 °C from the surface to 200 m underground, which can be extracted using heat pump technology for heating or cooling of buildings.1 Shallow geothermal energy is a kind of renewable energy with suitable energy-saving and emission reduction benefits.2 Shandong province is a period of rapid economic development, energy conservation, and emission reduction, and energy structure adjustment pressure is enormous. Vigorously developing and utilizing shallow geothermal energy is significant for Shandong Province to build a resource-saving and environment-friendly society, ensure energy security, improve the existing energy structure, promote energy conservation and emission reduction strategies, and achieve Shandong’s green development goals.3

The development and utilization of shallow geothermal energy mainly adopt ground source heat pumps. The ground source heat pump system mainly includes groundwater source heat pump system, ground source heat pump system, surface water source heat pump system, and compound ground source heat pump system. The ground source heat pump (ground source heat pump system with buried pipes) is a system for heat exchange between vertical or horizontal ground heat exchangers and rock and soil by heat transfer medium. There are two kinds of buried pipe heat exchangers, horizontal and vertical. The vertical buried pipe method can obtain a larger heat transfer capacity in a small area; the temperature and thermal properties of horizontal buried tube heat exchangers suitable for shallow rock and soil are less affected by climate, rainwater, and burial depth.4 The underground water source heat pump system is a kind of system that uses groundwater as a low-grade heat source and uses heat pump technology, through a small amount of high power input, to realize the transfer of cold and heat from low energy to high energy, so as to achieve heating or cooling for the object. Groundwater source heat pump system is suitable for abundant groundwater resources, but the utilization process depends on the water quality treatment and recharge mode of groundwater.5 Surface water source heat pump systems use the low-temperature and low-heat-energy resources in the earth’s surface water sources such as rivers, lakes, or pools, and adopt the principle of heat pump to realize the transfer of low heat energy to high heat energy through a small amount of high power input.6 Typical compound ground source heat pump systems mainly include ground source heat pump and solar energy compound systems, ground source heat pump and ice storage compound systems, ground source heat pump and cooling tower compound systems, ground source heat pump hot water systems, etc.7

With the progress and development of science and technology, Society has paid more and more attention to the requirements of environmental protection and energy utilization, formulating a series of relevant laws and regulations, and the ground source heat pump technology has been greatly developed.8,9 Shandong Province is one of the earliest provinces in China to research and develop shallow geothermal energy. At present, ground source heat pump projects are being developed and utilized in all cities of the province, and a mature and perfect industrial chain of development and utilization has been formed. The scale of development is increasing. At present, cities are improving relevant management methods and actively introducing incentive policies. In the future, shallow geothermal energy will become an important energy-saving and environmental protection energy in Shandong Province. From 1999 to 2005, Shandong Province built a small-scale water source heat pump project, and the main building type is an office building. From 2006 to 2010, the development and utilization of shallow geothermal energy in Shandong Province entered a large-scale development stage,10 and the number of completed geothermal energy increased rapidly at a rate of 35–60% per year. From 2011 to 2019, the domestic real estate and construction development market entered a turbulent period (Figure 1). Therefore, the development and utilization of shallow geothermal energy in this stage present a steady development state.11

Figure 1.

Figure 1

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Historical curve of shallow geothermal energy development in Shandong Province.

Annual comprehensive performance coefficient (ACOP) is the most intuitive performance to judge the energy efficiency of the heat pump system. Its size is mainly affected by the type of ground source heat pump,12 hydrogeological conditions, climatic conditions, and building conditions.13 Bai et al. investigated low-temperature and coeffificient of performance (COP) changes of a ground source heat pump system in Changchun to analyze the energy-saving effect of the heat pump system. It is considered that the area compensation method can alleviate the cold accumulation problem in cold regions.14 Yao et al. pointed out that intermittent operation mode is beneficial to maintain the efficient operation of the system by studying the influence of the long-term operation of the ground source heat pump on the underground temperature field and COP.15 Zheng et al. researched the influence of ground seepage on the ground temperature field of the buried pipe group, and seepage will slow down the decline rate of COP and help to improve the operation effect of the unit.16 Tong et al. use 10 air heat pumps for greenhouse heating. In order to study the COP of the heat pump system, a model is established by analyzing the energy balance of Ghp and Goh. It is concluded that the use of a high-performance heat pump system can also achieve the effect of conventional fuel heaters.17 Lim et al. In order to improve the COP of the geothermal system, Lim et al. used an underground heat exchanger composed of two balance wells to drain water in a mixed manner, which has a good effect. The energy efficiency of shallow geothermal energy development and utilization projects in Shandong Province can be mastered by calculating ACOP value, and the development potential of shallow geothermal energy in various cities can be analyzed more intuitively.18

This research systematically shows the number of ground source heat pump operation projects in 17 cities in Shandong Province, operation status, data, statistical ACOP spatial distribution characteristics, and their correlation with urban economy and incentive policies. The research results provide a reference for optimizing the energy efficiency of geothermal energy, promoting the development and utilization of shallow geothermal energy, saving energy, and reducing emissions. The main purpose of this research is to analyze the factors affecting the development and utilization of shallow geothermal energy. By analyzing the project return survey data of various cities and basic geological data such as hydrogeology and geothermal geology, the three aspects of ACOP value, socioeconomic level, and policy orientation are analyzed. This study is of great significance for the development and utilization of shallow geothermal energy.

2. Methodology

First, data collection was carried out, including the type of heat pump, the operation of the project, and so on. On this basis, the calculation method of calculating ACOP of the ground source heat pump project is introduced.

2.1. Data Sources

The data collected in this study, such as the number of geothermal heat pump operation projects, operation status, and data of 17 cities in Shandong Province, are all from Shandong Geology and Mineral Engineering Group Co., Ltd.

2.2. Engineering Survey

By the end of 2019, according to incomplete statistics, there were 932 shallow geothermal energy development and utilization projects in 16 cities of Shandong Province, with a total utilization area of about 5.5062 million m2. Among them, Dongying, Yantai, Jinan, Zibo, and Qingdao have the largest number and larger engineering scale. The total heating/cooling area of the five cities exceeds 30 million m2, and Qingdao ranks first in the province with 9.059 million m2, accounting for 12.68% of the province. Heze, Liaocheng, Binzhou, and other cities have developed rapidly, while the development and utilization of Tai’an, Linyi, Rizhao, and Dezhou are still in their infancy.

The main types of heat pump systems in Shandong Province are groundwater source heat pump systems, buried pipe ground source heat pump systems, and multi-energy combined heat pump systems. The COP value (the ratio of output power to input power in winter and summer) during the operation of each project is calculated by using the detailed engineering operation parameters of survey data and survey records. The development and utilization of shallow geothermal energy in Shandong Province are studied by ACOP value (Figure 2).

Figure 2.

Figure 2

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Site drawing of heat pump project. (Provided by Shandong Geological and Mineral Engineering Group Co., Ltd.).

On the basis of the previous shallow geothermal energy survey, engineering investigation and research return visit data were carried out. In this study, 483 questionnaires of ground source heat pump engineering were collected, including 396 ground source heat pump systems engineering, 52 ground source heat pump systems engineering, and 35 multi-energy combined heat pump systems engineering. Among them, 194 representative heat pump systems were selected for research and analysis. Among them, the basic operation, initial investment and construction, operation, and energy-saving of the project were investigated (Table 1).

Table 1. Number of Municipal Projects and Types of Heat Pumps.

city amount of engineering type of heat pump
Weifang 25 underground pipe
underwater
Binzhou 22 underground pipe
underwater
Dongying 27 underground pipe
Jinan 23 underground pipe
underwater
compound
Weihai 6 underground pipe
compound
Zibo 15 underground pipe
underwater
Yantai 3 underground pipe
Jining 8 underground pipe
underwater
Heze 4 underground pipe
Taian 8 underground pipe
Rizhao 19 underground pipe
underwater
Dezhou 13 underground pipe
underwater
Liaocheng 7 underground pipe
Linyi 2 underground pipe
Qingdao 7 underground pipe
Zaozhuang 5 underground pipe
total 196  
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2.3. Energy Efficiency Calculation

The coefficient of performance is the conversion ratio between energy and heat. When heating in winter, the ratio of heating capacity (W) to input power (W) is the cycle performance coefficient COP of the heat pump. In summer cooling, the ratio of the cooling capacity (W) to input power is the energy efficiency ratio (EER) of the heat pump, and COP and EER are expressed by COP for better comparison.19

The COP value of the ground source heat pump system in winter and summer is calculated by the following formulas

2.3. 1
2.3. 2
2.3. 3

where C is the winter and summer COP mean; WX1 is the summer engineering output power; WX2 is the summer project input power; WD1 is the winter engineering output power; WD2 is the winter project input power; CX is the summer COP value; and CD is the winter COP value.

The annual comprehensive performance coefficient (ACOP) can be expressed as

2.3. 4

where ∫Q(τ) dτ is the total heating capacity (kJ) for the whole year operation of heat pump system and ∫w(τ) dτ is the total electricity consumption for the annual operation of heat pumps (kW).

3. Outcome and Discussion

First, the development and utilization of shallow geothermal energy will be analyzed from the aspects of ACOP, socioeconomic level, and policy orientation. Then, the analysis shows that ACOP has a small relationship with development and utilization, and ACOP reflects the energy efficiency of ground source heat pump projects in various cities. The level of social economy and policy orientation has a great relationship with development and utilization, and has a positive correlation. Finally, the relationship between geological conditions and climate and ACOP will be further studied to improve the ACOP value of the heat pump system.

3.1. Ground Source Heat Pump Project and Operation Energy Efficiency

From the perspective of the development and utilization of shallow geothermal energy, there are various types of development and utilization in Shandong Province. In general, there are buried pipe heat pump, water source heat pump project, and multi-energy composite system. From the scale point of view, buried pipe heat transfer accounted for the largest proportion, accounting for 83.72% of the total area; groundwater source heat pump accounted for 14.34% of the total area; and other types accounted for only 1.94% (Figure 3).

Figure 3.

Figure 3

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Percentage map of shallow geothermal energy development and utilization types.

There are many problems in the development and utilization of shallow geothermal energy. Most projects are too concentrated, the development level outside the urban area is low, and the regional distribution is unbalanced. The development and utilization of the groundwater source heat pump system is unreasonable. More than 90% of the projects do not take recharge measures and directly discharge groundwater to the surface, which not only causes the waste of groundwater sources but also leads to the pollution of the ecosystem.

By calculating the ACOP value, according to the distribution range of the ACOP value in the figure, it can be seen that the COP value is mainly distributed in the range of 3.93–5.24, of which the distribution is in the range of 4.0–5.5, accounting for about 94% of the survey projects. Only Heze area has a lower ACOP value (Figure 4).

Figure 4.

Figure 4

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ACOP value of Shandong Province.

According to the Chinese standard, the energy efficiency ratio of system refrigeration is greater than 3.0, and the coefficient of system heating performance is greater than 2.6. The energy efficiency of China’s overall ground source heat pump system is about 2.28–4.88, and the energy efficiency of the groundwater source heat pump system is in the range of 2.26–3.56.20 In comparison, the energy efficiency of the ground source heat pump system in Shandong Province is higher and more suitable for development.

By analyzing the correlation between the number of heat pump system construction projects in various cities and ACOP, it is found that the correlation is relatively small (Figure 5). Among them, the number of projects in Rizhao area is 19, but the ACOP value is lower than that in Tai’an and other places. The ACOP value of geothermal heat pump system is mainly affected by the geological, hydrogeological, and geothermal conditions of the site and the type of heat pump system. These factors can all affect the operational energy efficiency of the heat pump system to varying degrees. According to previous research, changing the spacing of heat exchange holes, backfill materials, drilling depth, and other influencing factors can improve the COP value of the heat pump system.

Figure 5.

Figure 5

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Correlation diagram between engineering quantity and ACOP indicators.

3.2. Socioeconomic Level

The social and economic level of a city can be measured by the average annual GDP, per capita GDP, and energy consumption of the city (when calculated, the data before 2018, Laiwu into Jinan). Through the analysis of these indicators in various cities, it is concluded that in 2015–2019, Qingdao, Jinan, Yantai, and Weifang had stable annual GDP and annual GDP rankings. According to the top four of the province, Heze, Liaocheng, Rizhao, Zaozhuang, and other places have relatively backward annual GDP rankings, and their rankings will change each year appropriately. In 2017–2019, the per capita GDP of Dongying was the highest, followed by Qingdao, Weihai, Yantai, Zibo, Jinan (ranked sixth), and Heze (lowest) (Table 2).

Table 2. Energy Consumption Level of Cities in 2014–2019a.

city 2019 2018 2017 2016 2015 annual GDP per capita GDP mean energy consumption
Qingdao 11 741 12 001 11 037 10 100 9300 10 835.8 64 425 461 502.45
Jinan 9443 8862 7202 6800 6100 7681.4 53497 373 370.87
Yantai 7653 7833 7339 7003 6446 7254.8 55436 343 786.33
Weifang 5688 6157 5859 5746 5100 5710 34 036 272 341.57
Jining 4370 4931 4650 4620 4013 4516.8 29 647 267 996.40
Zibo 3642 5068 4781 4400 4130 4404.2 54 904 251 256.03
Linyi 4600 4718 4345 4305 3763 4346.2 22 712 207 278.97
Dongying 2916 4152 3802 4013 3450 3666.6 96 540 176 088.23
Taian 2663 3652 3585 3630 3240 3354 33 584 176 038.50
Weihai 2964 3641 3480 3257 3002 3268.8 64 371 171 638.15
Dezhou 3022 3380 3140 2990 2750 3056.4 29 062 165 461.35
Heze 3409 3079 2820 2550 2401 2851.8 17 646 145 912.62
Liaocheng 2260 3152 3064 2905 2664 2809 27 641 145 543.17
Binzhou 2457 2641 2613 2587 2355 2530.6 33 819 143 192.55
Zaozhuang 1694 2402 2316 2357 2031 2160 32 152 142 316.95
Rizhao 1949 2202 2003 2587 1671 2082.4 37 451 106 576.14
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a

Unit: ton.

Energy consumption refers to the energy consumption of people’s production and life around the city. Energy consumption per capita is an important indicator of a country’s economic development and people’s living standards. The more energy consumption per capita, the greater the GDP, and the richer the society.21 The general change of the energy consumption intensity is closely related to the industrialization process. With economic growth, energy consumption in the early and middle stages of industrialization generally shows a slow upward trend. When economic development enters the post-industrialization stage, the mode of economic growth changes significantly, and the energy consumption intensity begins to decline. From 2014 to 2019, the average energy consumption of each city was the highest, and Jinan, Zibo, and Qingdao ranked top three in Shandong Province, with Weihai, Rizhao, and Heze the lowest.

From the trend chart of the relationship between the three indicators mentioned above and the current shallow geothermal energy development and utilization quantity that is not fully counted in various cities (Figure 6), it can be seen that there is a significant positive correlation between the quantity of shallow geothermal energy development and utilization and per capita GDP, and the strongest correlation is found in cities with extremely high and low levels of economic and social development, such as Qingdao, Jinan, Rizhao, Dezhou, Liaocheng, etc. Cities with a middle level of economic and social development, such as Tai’an, Zaozhuang, and Jining, have relatively weak positive correlations. It has little correlation with the average GDP and urban energy consumption in the past 5 years and has the most minor correlation with urban energy consumption. It is speculated that because some cities in Shandong Province are heavy industrial cities, they rely heavily on traditional energy such as coal and oil, and the proportion of energy cannot be changed significantly in the short term. Hence, the development of new energy utilization in these cities is slow.

Figure 6.

Figure 6

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Relationship between economic and social indicators and the number of heat pump projects.

However, overall, there is a certain degree of correlation between the quantity of shallow geothermal energy development and utilization and the socioeconomic level (Figure 7). The scale, mode, and quantity of shallow geothermal energy development and utilization in a place are directly affected by the economic and social level, especially the per capita GDP, energy consumption level, etc. The higher the economic and social level, the more advanced and innovative the shallow geothermal energy development and utilization mode. The more cutting-edge the method, the more energy-efficient and optimized new technologies can be integrated into the heat pump system.

Figure 7.

Figure 7

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(a–c) Correlation between the number of projects and socioeconomic indicators. (a) Correlation between the number of projects and the average GDP over the past 5 years. (b) Correlation between the number of projects and per capita GDP. (c) Correlation map between engineering quantity and energy consumption.

3.3. Policy Orientation

The rapid development of shallow geothermal energy development and utilization is closely related to the gradual increase of government policy support. China in its “2005 energy conservation medium and long-term special plan” clearly pointed out to speed up the use of geothermal and other renewable resources in buildings.22 The Renewable Energy Law of the People’s Republic of China implemented in 2006 explicitly included the development and utilization of geothermal energy in the development scope encouraged by new energy. The Thirteenth Five-Year Plan for the Development and Utilization of Geothermal Energy implemented in 2017 promoted the vigorous development of shallow geothermal energy in China.23 Winter Clean Heating Plan of Shandong Province (2018–2022), issued by Shandong Provincial People’s Government in 2018, pointed out that shallow geothermal energy heating should be vigorously developed. According to the principle of ″adjusting measures to local conditions, intensive development, strengthening supervision and focusing on environmental protection″, heat pump technology should be adopted as the main method to develop and utilize shallow geothermal energy heating (refrigeration) instead of loose coal heating economically and efficiently. The anticipated target of shallow geothermal heating in the next few years has been clearly defined. In 2019, Shandong Provincial People’s Government issued the Measures for Promoting Green Buildings in Shandong Province, which stipulates that shallow geothermal energy should be used preferentially for heating and cooling of public building projects invested by the government.

In order to study the degree of policy orientation on the development and utilization of shallow geothermal energy in different cities, after analyzing the policies, laws, and regulations related to the development, utilization, and promotion of shallow geothermal energy introduced by different cities, according to the number, intensity, reward or subsidy policies, and the degree of policy implementation of policies introduced by different cities in this field, they are comprehensively divided into four levels of strong policy orientation, secondary strong policy orientation, medium policy orientation, and poor policy orientation according to the expert evaluation method, so as to more intuitively reflect the work done by different cities in the field of clean energy of shallow geothermal energy and the degree of attention paid to the development and utilization of clean geothermal energy (Table 3).

Table 3. Classification Scheme of Policy Orientation Degree.

planning score remark
the relevant norms, policies, plans, programs, and notices of shallow geothermal energy have been issued 3 the introduction of 1 point, more than 3 points; undesigned geothermal and other related clean energy is not scored
encouragement programmes and subsidy policies for the development and utilization of shallow geothermal energy have been clearly defined but not implemented 3 one subsidy policy scored 1 and more than three scored 3
the encouragement scheme and subsidy policy for shallow geothermal energy are clarified in the implementation process 6 according to the amount of subsidies or subsidies size from 2 to 6 points; nonscores not implemented
the subsidy scheme has been implemented, and the subsidy period is more than 2 years 5 the subsidy scheme does not score below 2 years
local shallow geothermal energy development and utilization of related enterprises, and the development of enterprises issued preferential policies, documents, notices, to geothermal energy cleaner production enterprises to give incentives, recognition, or policy support 3  
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The overall score of more than 15 points was defined as a strong degree of orientation, 10–15 points within the scope of the definition of a strong degree of orientation, 5–10 points within the scope of the definition of a moderate degree of orientation, less than 5 points poor degree of orientation.

The above partition results are not static (Table 4). With the improvement of local governments’ awareness of the development and utilization of shallow geothermal energy and the increase of attention, various policy support and subsidy schemes will be introduced in succession, and their policy orientation levels will also change. Therefore, the partition of policy orientation degree is only suitable for studying its influence on the development and utilization of shallow geothermal energy, and it does not have long-term reference value.

Table 4. Score Interval of Policy Orientation Degree.

score range of policy orientation [0,5] (5,10] (10,15) [15,20]
city Zaozhuang Dezhou Jinan Qingdao, Yantai, Weihai, Rizhao, Weifang, Liaocheng, Heze
Jining Zibo Binzhou
Taian Linyi Dongying
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By analyzing the relationship between the number of projects, the number of projects completed in the past 3 years after policy formulation, and the score of policy orientation, it can be demonstrated that the subsidy policies issued by cities for shallow geothermal clean energy will stimulate or promote the promotion and utilization of shallow geothermal energy to a certain extent (Figure 8). However, it is not absolute. The implementation of support and reward policies in most cities has a significant promoting effect on the development and utilization of shallow geothermal energy. Furthermore, in some cities, such as Zaozhuang, Jining, and Heze, the promotion of policies on shallow geothermal energy development is not obvious (Figure 9). In short, the development of shallow geothermal energy cannot be separated from the introduction of relevant incentive and subsidy policies by local governments. Therefore, the introduction and implementation of government programs, plans, notifications, and policies are necessary conditions to promote the development and utilization of shallow geothermal energy.24

Figure 8.

Figure 8

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Comparison of government guidance policy direction and number of heat pump projects.

Figure 9.

Figure 9

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Correlation between the degree of policy orientation and the number of projects completed in the past 3 years after policy formulation.

However, through investigation and research, it has been found that during the operation of shallow geothermal energy projects in Shandong Province, due to the electricity policy issues in Shandong Province, the operating costs are relatively high, which has caused certain restrictions and impacts on the project before construction. Therefore, in the future development and utilization process, it is urgent to introduce related incentive policies, preferably reducing electricity costs to increase society’s acceptance of shallow geothermal energy development and utilization projects; strengthen social propaganda work; increase public awareness; and increase the popularization of shallow geothermal heat pumps. Shallow ground temperature has the advantages of clean and environmental protection and will be widely used in urban construction.

In cities with high policy orientation, the development and utilization of shallow geothermal energy are relatively good. Therefore, if cities want to accelerate the development and utilization of shallow geothermal energy, they can promote the acceptance of shallow geothermal heat pump systems in urban construction by increasing subsidy policies and reducing electricity costs.

4. Conclusions

  • 1.

    The ACOP value is not only influenced by the type of heat pump system but also by the geological conditions and climate of the building’s geographical location. Although the ACOP value in various cities meets the basic requirements of Chinese standards, the energy efficiency is relatively low.

  • 2.

    There is a certain degree of correlation between the quantity of shallow geothermal energy development and utilization and the socioeconomic level. The scale, mode, and quantity of shallow geothermal energy development and utilization in a place are directly affected by the economic and social level, especially the per capita GDP. The higher the general economic and social level, the more advanced the shallow geothermal energy development and utilization mode, the more innovative and cutting-edge the method, and the more energy-efficient the heat pump system can be integrated to optimized new technologies.

  • 3.

    Policy orientation has a significant promoting effect on the development and utilization of shallow geothermal energy. The government’s plans and policy guidelines have authority and persuasiveness, and can play an excellent promotional role. Moreover, it has a good reference value for developing shallow geothermal energy in other regions. The popularization of heat pump systems can be promoted by introducing relevant regulations and preferential policies.

  • 4.

    Through research, it has been found that the ACOP of heat pump systems is better in areas with better geological, hydrogeological, and geothermal geological conditions. However, due to low policies and socioeconomic levels, the development and utilization of shallow geothermal energy are also not high. Therefore, in areas where this situation exists, increasing preferential subsidies and other policies can promote the development and utilization of shallow geothermal energy from multiple aspects.

Author Contributions

Resources: Q.S. and M.S.; investigation: X.Y.; writing—original draft: C.Z. and T.C.; supervision: B.W. and H.Y.; funding acquisition: M.S.; methodology: C.Z. and T.C.; format analysis: C.Z. and H.Y.

This research was funded by [The National Natural Science Foundation of Shandong Province] grant number [ZR2021QD130].

The authors declare no competing financial interest.

Notes

All authors have read and agreed to the published version of the manuscript.

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