- Email: [email protected]
Conjoint analysis of nitrogen, phosphorus and sulfur metabolism: A case study of Liaoning Province, China
Ecological Modelling 390 (2018) 70–78
Contents lists available at ScienceDirect
Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel
Conjoint analysis of nitrogen, phosphorus and sulfur metabolism: A case study of Liaoning Province, China
T
⁎
Chengkang Gaoa,b, Shuaibing Zhanga,b, , Kaihui Songc, Hongming Naa,b, Fan Tiana,b, Menghui Zhanga,b, Wengang Gaoa,b a
State Environmental Protection (SEP) Key Laboratory of Eco-Industry, Northeastern University, Shenyang 110819, China School of Metallurgy, Northeastern University, Shenyang, Liaoning 110819, China c Department of Geographical Science, University of Maryland, College Park 20742, MD, USA b
A R T I C LE I N FO
A B S T R A C T
Keywords: Material metabolism Nitrogen-phosphorus-sulfur Conjoint analysis Environmental pollution Liaoning Province
The three types of elements nitrogen (N), phosphorus (P) and Sulfur (S) are inextricably linked from the source to the destination throughout the system. To analyze the environmental load caused by the three elements, this study established a material metabolism model to quantify the relationships among metabolic processes on the provincial scale and examined their environmental implications based on Substance Flow Analysis (SFA). The results show that the metabolic fluxes of nitrogen, phosphorus and sulfur in the socioeconomic system of Liaoning Province in 2016 were 5.339 million tons, 0.582 million tons and 3.084 million tons, respectively. The agricultural sector caused the greatest environmental pressures on water bodies, in which nitrogen and phosphorus accounted for 61.8% and 80.2% of the total water body load. For atmospheric load, the nitrogen and sulfur elements in the industrial sector caused the largest atmospheric load, accounting for 37.8% and 91.4% of the total atmospheric load, respectively. The main source of phosphorus soil load in Liaoning Province is the agricultural production, accounting for 85.3% of the total soil load caused by phosphorus.
1. Introduction The demand for nitrogen (N), phosphorus (P), and sulfur (S) has increased dramatically driven by the socioeconomic development, while exerts significant environmental pressures (Berlin et al.,2014). The increasing (eutrophication, haze and fog) environment problems caused by the overcharge of the three elements has drawn increasing attention. In recent decades, eutrophication has become one of the core issues of water pollution in China. In April 2007, the blue-green algae blooms in Taihu Lake caused shutdowns of nearby water treatment plant; as a result, most areas of the city run into water shortages (Qin et al., 2007). In addition, the air pollution caused by nitrogen oxide (NOx) and sulfide led to a series of environmental problems such as atmospheric acid deposition, ozone, and haze (Yeo and Kim, 2016). It is conservatively projected that NOx emissions in China will reach nearly 29 million tons in 2020 (Shi et al., 2014). It is reported that, from January to March in 2013, approximately 600 million people, accounting for 45% of China's total population, were adversely affected by haze. The metabolism of the three elements (N, P, S) has aroused heated discussion on addressing the environmental issues tailed by the misuse ⁎
and overuse of materials containing either of the three elements (Geng et al., 2015). Many scholars have researched on the metabolism of the three kinds of elements. Researchers have analyzed nitrogen metabolism on the national (Breemen et al., 2002; Filoso et al., 2006) and regional scales. Regional nitrogen metabolism mostly focused on urban (Parfitt et al., 2006) and watershed (Boyer et al., 2006; Bashkin et al., 2002; Yoshikawa et al., 2008). Zhang et al. (2016) analyzed the intensity of nitrogen metabolism in Beijing by means of ecological network analysis, and concluded that atmosphere, household, and industry had the most interactions with other nodes in the network. Compared with nitrogen and sulfur, more research focused on metabolic analysis of phosphorus, varying from global level to (Villalba et al.,2008) national (Li et al., 2015), regional (Yuan et al.,2011; Zhang et al., 2017), as well as urban levels (Kalmykova et al.,2012). Globally, the natural circulation metabolic intensity of global phosphorus is only 1/3 that of artificial circulation, indicating human activities have significant influences on phosphorus cycles (Smil, 2000). From the perspective of different sectors, Qiao et al. (2011) explored the phosphorus flows through food consumption in Beijing and Tianjin, using a material flow analysis (MFA) approach. The results showed that approximately 55% of the phosphorus contained in food for urban residents’ consumption
Corresponding author. E-mail address: [email protected] (S. Zhang).
https://doi.org/10.1016/j.ecolmodel.2018.10.020 Received 26 July 2018; Received in revised form 22 October 2018; Accepted 22 October 2018 Available online 02 November 2018 0304-3800/ © 2018 Elsevier B.V. All rights reserved.
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
(waste recycling), inlet flow of the machine manufacturing industry (reuse and recycling), and inlet flow at the waste treatment stage (harmful or hazardous industrial waste). SFA allows us to quantify relationships between the economy and the environment of a geographically demarcated system.
resulted in municipal sewage and sludge. In the case of the Korean steel industry (Jeong et al., 2009), phosphorus lost in steel-making slag is estimated to be 10% of domestic phosphorus consumption. Compared with the metabolic analysis of nitrogen and phosphorus, fewer studies concentrated on the metabolism of sulfur. Tian et al. (2012) used the Substance Flow Analysis (SFA) method to analyze the flow characteristics of sulfur in the Industrial Park in Hangzhou Bay. Zhang et al. (2015) combined the structure and functional attributes of Lubei EcoIndustrial Park in Shandong, constructed a sulfur metabolism network model based on SFA, and identified key nodes of the processes in the industrial sulfur metabolism. From the perspective of metabolic spatial scales, most studies highlighted the global, national, urban, and industrial parks while few studies of metabolism were conducted on the provincial scale. For the structure of metabolic tissues, most studies focused on the analysis of a single industrial system in the socioeconomic system, while few comprehensive studies on the whole socioeconomic system. In terms of metabolic research subjects, most studies concentrated on the metabolic analysis of single element, while few conducted combined analysis of nitrogen, phosphorus, and sulfur. Given the inextricably linked relationship between the three elements, and their coexistence in many substances (such as food, coal, and oil) it is essential to conduct a comprehensive analysis of nitrogen, phosphorus, and sulfur metabolism. The socioeconomic system is a complex system that composting of several industrial systems, which are interconnected but each different from each other. The study presents a comprehensive analysis of elemental metabolism to better explain environmental problems brought by misuse and overuse of substances containing N, P, S elements. The Substance Flow Analysis method is applied to carry out a joint metabolic analysis of the social and economic system supported by the underlying flows of nitrogen, phosphorus, and sulfur on the province level.
2.2. Nitrogen, phosphorus and sulfur metabolism analysis model on a provincial level Combined with the material flow analysis method, this study established an analysis model of nitrogen, phosphorus and sulfur metabolism in the provincial socioeconomic system. 2.2.1. Metabolic system boundary In the purpose of establishing the analysis model of nitrogen, phosphorus and sulfur metabolism in the provincial socioeconomic system, the system boundary needs to be defined clearly according to the purpose of research. So the provincial geographic boundary is defined as the metabolic system boundary. 2.2.2. Metabolic system framework Within boundaries of the metabolic system in the study, each subsystem is constructed in support of determining pathways of nitrogen, phosphorus and sulfur metabolism systematically. Based on the SFA analysis framework, this study builds a material metabolism system framework on the provincial level, as shown in Fig. 2. The provincial socioeconomic system is divided into four subsystems based on the attributes: resource system, environmental system, provincial socio-economic system, and raw material product system. The four subsystems form the framework of metabolic systems of nitrogen, phosphorus, and sulfur on the province level, as shown in Fig. 2. 2.2.3. Metabolic pathways of nitrogen, phosphorus, and sulfur The relationships between each pair of metabolic subsystems in the framework are analyzed by depicting the flows of nitrogen, phosphorus, and sulfur, and their internal connections with other subsystems. This framework serves to describe and explore the reasons that affect the production and conversion of nitrogen, phosphorus, and sulfur. The flows of nitrogen, phosphorus, and sulfur can be described as elements in the form of minerals, energy, industrial products, agricultural products, and other products enter the socio-economic system through transfers and exchanges. Solid waste treatments related to metabolic pathway mainly include incineration and landfill. Some of the elements are discharged into the atmosphere in the form of incineration waste gas, and the remaining part is buried in the soil. The nitrogen, phosphorus, and sulfur metabolism pathways are shown in Fig. 3 Despite the interconnection among various subsystems, the metabolic pathways of nitrogen, phosphorus, and sulfur are characterized and distinguished from each other through analyses. Nitrogen is mainly sourced from the atmosphere and imported into the socio-economic system in the form of gas, minerals, industrial products, agricultural products, and energy. Phosphorus is naturally stemmed from the phosphate rock and imported into the socioeconomic system mainly in the form of phosphate rock, industrial products, and agricultural products. Sulfur is mainly imported into the socio-economic system in the form of sulfur ore, industrial products, agricultural products, and energy. The ultimate destinations of nitrogen and sulfur are the atmosphere, soil, and water. Compared with nitrogen and sulfur, the ultimate fates of phosphorus are water and soil.
2. Theories and methods 2.1. Substance flow analysis The core principle of Substance Flow Analysis is derived from the law of conservation of mass, whose outstanding advantages highlight the capability of addressing specific environmental problems. It enables people to explore the critical links and key flows that cause environmental pollution by tracking the input and output of substances in various aspects of the system and the environment, and to construct maps of material flow network and quantify the circulation of each link within the system. The framework of substance flow analysis is shown in Fig. 1. The SFA framework consists of four processes: production, fabrication and manufacture, consumption, and waste management. The waste generated in manufacturing and processing mainly comes from the following channels: material flow re-entering the production stage
2.2.4. Metabolism network of nitrogen, phosphorus, and sulfur The provincial network of nitrogen, phosphorus, and sulfur metabolism is based on the boundary of the metabolic system and metabolic pathways, including five types of nodes and five types of flows, as
Fig. 1. Substance flow analysis (SFA) framework. 71
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 2. Metabolism system framework on the provincial level.
final environmental attribution of materials. Five types of flows are described as follows. (1) The input flows, in the form of raw materials (or products), enter the provincial socioeconomic system; these processes are denoted by I. For example, I1 represents that the input flows into the provincial socio-economic system in the form of minerals. (2) The output flows of the provincial socio-economic system in the form of products are expressed by E. For example, E4 represents the output flow of the provincial socio-economic system in the form of agricultural products. (3) The element flows in the form of sewage and water reuse are expressed by W. For example, W1
shown in Fig. 4. The diagram contains five types of nodes and five types of flows. The nodes representing a material supply to the socio-economic system in the province are denoted by C. The nodes representing processes related to consumption and redistribution of materials within the socioeconomic system are denoted by P. The nodes that represent waste treatment are represented by T. The nodes that represent the ultimate disposition of the waste are denoted by D, which involves the processes of incineration, landfill, and other ways of waste treatment such as high temperature composting and recycling. Nodes denoted by S indicate the
Fig. 3. Metabolic pathways of nitrogen, phosphorus, and sulfur. 72
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 4. Elements metabolism diagram on the provincial level. *Retrieved from: http://italychinalink.com/vetrina/provincia-di-liaoning/.
represents the industrial wastewater flows, which are discharges into sewage treatment facilities of companies. (4) The element-contained flows in solid form, represented by X. For example, X3 represents the flow of household garbage. Besides, the flows of elements that are exchanged with the atmospheric contents are denoted by N. For example, N2 represents the flow of exhaust gases from industrial processes into the atmosphere. The element metabolism diagram at the provincial level constructed by SFA method describes in detail the processes of an element's input from the source, internal flow and transformation, and finally its return to the environment. It reflects the circulation of elements in the system. According to the functions and properties of each link within the system, the metabolic topological structure of elements at the provincial level includes the industrial system, agricultural system, and resident life system. The industrial system is a system to process and manufacture industrial products. Materials input to the industrial system are minerals, energy, industrial products, agricultural products, and other products. After raw materials being processed and manufactured in the industrial system, some of them are transformed into industrial products, while others are transformed into waste products. The agricultural system is a system of producing agricultural products, which consumes energy, industrial products, agricultural products, and other products. The agricultural production process mainly yields agricultural while still some waste products are disposed into the
environment. The residential life system is basically a consumption system, where energy, industrial products, agricultural products, and other products are consumed. They are disposed of in the form of household solid waste and liquid waste and discharges into environment. 2.2.5. Analytical model Based on the topological structure of element metabolism, quantification of the causal relationship of each link in the topological structure is of great importance in the purpose of element metabolism analysis. The elemental metabolic analysis model is based on the first law of thermodynamics – the principle of material conservation. This study is based on the assumption that the material metabolism in the socioeconomic system is stable, that is, input equals output. According to the topological structure of element metabolism, the model of element metabolism constructed in serving of provincial-level analysis is shown as follow: According to the properties of each fundamental flow, the analytical model is subdivided into a raw material (or product) flow model, a wastewater flow model, a solid waste flow model, an exhaust gas flow model, and a reuse flow model. The raw material (or product) flow model is used to account for the content of elements in various raw materials (or products). The raw material (or product) flow: 73
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 5. Geographical location of Liaoning Province in China.
E=
∑ Φi × ki
3. Results and discussions
Φi – The total amount of material (or product), t; ki – Elemental coefficient in the product; i – The type of products or material. Wastewater flow model is used to calculate the content of elements in industrial wastewater and domestic sewage. Wastewater flow:
Based on the elemental metabolic analysis model established above, this study analyzed the socioeconomic system of Liaoning Province. In order to obtain complete research data, this study selected 2016 as a time node. Further analysis is conducted on the influence of the industrial system, agricultural system, and resident living system on environment (water, air and soil) in Liaoning Province.
W= [ ∑ Φj × kj] × ka
Φj – Amount of wastewater, t; kj – Elemental coefficient in wastewater; kt – Element removal rate in sewage; j – Type of wastewater; a – Type of elements. Solid waste flow model is built to quantify the elemental content in industrial solid waste, agricultural solid waste, and domestic waste. Solid waste flow: X=
3.1. The overview of Liaoning Province Liaoning Province, located in northeast China, is one of the major traditional industrial bases in China. It is one of the provinces with the most complete industrial categories in China, with over 500 sub-industries. According to《China statistical yearbook 2016》and《Liaoning statistical yearbook 2016》: up until 2016, there had been 158 sewage treatment plants in Liaoning with a total sewage treatment capacity of 1.829 billion tons and an average sewage treatment capacity of 7.71 million tons per day; An estimated 268 million tons of general industrial solid waste was produced and the comprehensive utilization rate of solid waste was 43.8%; The domestic garbage clearance volume is 9.27 million tons with harmless disposal rate of 87.6%; In 2016, the total nitrogen oxide emissions of Liaoning Province ranked 8th among all the cities in China, with 27.2% of motor vehicles. From the above, Liaoning Province is a typical case. Liaoning province's geographical location in China is shown in Fig. 5.
∑ Φk × kk
Φk – The total amount of solid waste, t; kk – Elemental coefficient in solid waste; k – Type of solid waste. The exhaust gas flow model is used to calculate the content of elements in industrial waste gas, motor vehicle exhaust gas, and domestic exhaust gas. Exhaust gas flow:
N= [ ∑ Φl × kl] × kp
Φl – The total amount of fuel consumed, t; kl – Elemental coefficient in fuel; kp – Proportion of element emissions to the atmosphere during fuel consumption; l – Type of exhaust gas; p – Type of fuel. The recycled flow model is used to calculate the elemental content of the recycled wastewater and the recycled solid waste. Recycled flow:
3.2. Conjoint analysis 3.2.1. Metabolic structure and flux analysis In 2016, the input amounts of nitrogen, phosphorus, and sulfur in Liaoning socioeconomic system were respectively 5,339,000 tons, 5,820,000 tons and 3,084,000 tons, and the ratio of nitrogen, phosphorus, and sulfur was 9.2:1:5.3. It indicates that the demand for nitrogen and sulfur is higher than that for phosphorus in Liaoning Province. In the topological structure of element metabolism, there are some differences in the metabolic processes of the three elements. First, sulfur metabolism has no nodes and fluxes related to agricultural links. Second, phosphorus metabolic process has no relationship with
R= [ ∑ Φm × km] × kn
Φm – Total amount of original products, t; km – Elemental coefficients contained in recycled materials; kn – Recycling rate; m, n – Type of recycled materials. 74
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 6. The ratio of nitrogen, phosphorus and sulfur metabolic fluxes in Liaoning Province. (Notes: yellow represents the node of deficiency of sulfur metabolism; purple represents the node of deficiency of phosphorus metabolism; red represents the increased flow of nitrogen metabolism.). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
imported into the socioeconomic system in Liaoning Province in the form of industrial products (33.4%), because a large amount of nitrogen fertilizer and compound fertilizer were consumed in agricultural sector. Second, it is imported in the form of energy (32%), because industrial sector and residents' life are supported by consumption of coal and other energy sources with a large amount of nitrogen elements. Compared with the metabolic processes of phosphorus and sulfur elements, nitrogen metabolism is unique in its atmospheric inputs in the input source, which accounts for a high proportion, about 21.7%. The reason is that urea and synthetic ammonia are produced by artificial nitrogen fixation in the process of nitrogen fertilizer production. Phosphorus (P) was mainly introduced into the socioeconomic system in the form of industrial products (83.3%). It is because that the agricultural sector requires a large amount of phosphate fertilizer and compound fertilizer. Sulfur is mainly imported into the socioeconomic system in Liaoning Province in the form of energy (49%) and mineral products (38.2%). The energy source of sulfur is driven by a large number of consumption of coal and other fossil fuels in industrial sector and residential lives, while the mineral source is associated with the huge amount of iron sulfide ore mined in Liaoning Province, which was 2,142,300 tons in 2016. The input sources of Liaoning socioeconomic system are shown in Fig. 7. The dependence of nitrogen and sulfur elements on various input forms is relatively uniform, while phosphorus elements are overly dependent on the input of industrial products. About 83.3% of the phosphorus was imported into the socioeconomic system in Liaoning
Fig. 7. Input sources of socioeconomic system in Liaoning Province.
atmosphere and its associated flows. Third, the metabolic process of nitrogen elements includes all nodes and flow stocks, and the nitrogen metabolism process also catalyzes the flow from the atmosphere to industry and the flow from logistics trade to the atmosphere within and outside the province. Fig. 6 shows the metabolic flux ratio of nitrogen, phosphorus, and sulfur in Liaoning Province. The three elements also differ significantly in the form of material input. Nitrogen (N) has two primary inputs. First, it was mainly
75
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Province in the form of industrial products. However, these industrial products are mainly concentrated phosphate fertilizers and compound fertilizers. This indicates that the critical nodes of phosphorus metabolism system in Liaoning Province is the phosphorus chemical industry. There are mainly two output sources. One is to export from the socioeconomic system in the form of products, and the other is to discharge waste (in forms of solid, liquid, and gas) into the environment. The output of nitrogen products, phosphorus products, and sulfurs products were 3,195,000 tons, 279,000 tons, and 1,924,000 tons, respectively. The product conversion rate of nitrogen, phosphorus and sulfur metabolic system can be defined based on the material input. The product conversion rate is expressed as the ratio of product output to material input, representing the level of system utilization of input materials. According to the input and output, the product conversion rate of nitrogen element is 59.8%, that of phosphorus element is 48.1%, and that of sulfur element is 62.4%. Moreover, the product conversion rate of nitrogen, phosphorus and sulfur in the socioeconomic system in Liaoning is not very high. Compared with nitrogen and sulfur, phosphorus has the lowest conversion rate, less than 50%. This indicates that the socioeconomic system of Liaoning Province has a low utilization level of phosphorus element, which causes an enormous waste of phosphorus element and further aggravates the pollution of phosphorus element to environment. In 2016, Liaoning's social and economic system exported 2,144,000 tons of nitrogen, 302,000 tons of phosphorus and 1,160,000 tons of sulfur to the environment. The discharges of nitrogen, phosphorus, and sulfur into the atmosphere, water and soil are shown in Fig. 8. It can be seen that a large amount of nitrogen, phosphorus, and sulfur was discharged to the soil, accounting for 45.5%, 89.4% and 48.6% of their total emissions respectively. There are two reasons that mainly account for the accumulation of nitrogen, phosphorus and sulfur elements in the soil. First, excessive inputs of nitrogen fertilizer, phosphate fertilizer and other fertilizers result in the accumulation of nutrients in the soil which cannot be absorbed by crops. Second, a large proportion of domestic garbage and solid waste are disposed by incineration and landfill, resulted large amount of elements remain in the soil. In addition to the accumulation in soil, there is also a large amount of nitrogen and sulfur elements emitting to the atmosphere, accounting for 40.6% and 49.4% of their total emissions respectively. The consumption of coal and other energy and the burning of solid waste are the main reasons for the large amount of nitrogen and sulfur elements being discharged into the atmosphere. Besides, the nitrogen released into the atmosphere were also due to the volatilization of nitrogen fertilizer and the emission of nitrogen oxides from vehicle exhaust. The number of nitrogen, phosphorus, and sulfur released to water is
Fig. 9. Proportion of water load for various pollution sources in Liaoning Province.
relatively less, accounting for 13.9%, 10.6% and 2% of the total emission respectively. However, it leads to severe water pollution, especially eutrophication, indicating that the water environment in Liaoning Province is very fragile. 3.2.2. Water load The main sources of water pollution in Liaoning Province are industry, agriculture, and resident life. In 2016, the socioeconomic system of Liaoning Province discharged 297,840 tons of nitrogen, 32,078 tons of phosphorus and 22,910 tons of sulfur into water, accounting for 5.6%, 5.5% and 0.74% of the total input respectively. The proportion of water load caused by various pollution sources in Liaoning Province is shown in Fig. 9. The water load composition of various pollution sources of nitrogen is roughly similar to that of phosphorus elements in Liaoning Province, as shown in Fig. 9. The agricultural links are major contributors to the accumulation of nitrogen and phosphorus in water bodies, resulting in N and P accounting for 61.8% and 80.2% of the total water load respectively. Residential life is a less important source of nitrogen and phosphorus, accounting for 33.1% and 18.4% of the total water load respectively. The process of sulfur metabolism lacks agricultural links. The largest component of the water load of the sulfur element is from the life of residents, accounting for 83.2% of the total water load of sulfur element. As a result, the contribution of three kinds of pollution to water load level can be identified as: agriculture sector (N: 61.8%, P: 61.8%) > residents live sector (N: 33.1%, P: 33.1%, S: 83.2%) > industry sector (N: 5.1%, P: 5.1%, S: 16.8%). Most of the water load caused by the agricultural link comes from the livestock and poultry breeding industry. The water load ratio of Liaoning agricultural sector is shown in Fig. 10. For both nitrogen and phosphorus, the water load caused by livestock and poultry breeding industry accounts for more than 90% of the total water load in the agricultural sector. It is mainly caused by the low
Fig. 8. Environmental loads in Liaoning Province.
Fig. 10. Proportion of water loads in agricultural links in Liaoning Province. 76
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
efficiency livestock and poultry sectors (Qian et al., 2017). Meanwhile, a large quantity of livestock and poultry excrement is treated simply, resulting in the low utilization rate of manure and in turn less circulation of the elements. The water load caused by the three types of elements in the domestic wastewater is significantly higher than that of the industry sector. The water load of nitrogen, phosphorus, and sulfur caused by domestic sewage is more than four times higher than that of industry sector. On the one hand, it indicates that Liaoning Province has made remarkable achievements in the treatment of industrial wastewater; on the other hand, it also indicates that Liaoning Province has great defects in the treatment of domestic sewage. No matter in quantity or pollution degree, the influence of nitrogen, phosphorus and sulfur elements in domestic sewage on water has far exceeded that of industrial wastewater. Therefore, in the efforts of prevention and control of water pollution caused by nitrogen, phosphorus and sulfur elements, attention should be paid not only to industrial links, but also to agricultural links and residential life links.
Fig. 12. Proportion of soil load for various pollution sources in Liaoning Province.
3.2.4. Soil environmental load This study presents impacts on soil environment in two parts: cultivated soil and non-cultivated soil. The cultivated land is mainly polluted by the unused chemical fertilizer in the process of crop production, while the non-cultivated land is mainly polluted by various solid wastes. In 2016, the amount of nitrogen, phosphorus, and sulfur released from the socioeconomic system in Liaoning to the soil was 974,344 tons, 270,181 tons and 564,079 tons, accounting for 18.2%, 46.4% and 18.3% of the total input respectively. The ratio of soil load of various pollution sources in Liaoning Province is shown in Fig. 12. It can be seen from Fig. 12 that the largest load of nitrogen and sulfur elements in soil is industry, accounting for 68.9% and 90% of the total load of soil. It is caused by the large amount of industrial solid wastes (fly ash, slag, etc.) produced in industrial sector, which contain nitrogen and sulfur. Moreover, the comprehensive utilization rate of industrial solid wastes in Liaoning Province is as low as only 43.8%. The remaining industrial solid waste discharged into the non-arable land soil through landfill, waste and other ways. The most significant component of soil load caused by phosphorus is agriculture, accounting for 85.3% of total soil load of phosphorus. The main reason for the above phenomena is that the excessive use of phosphate fertilizer in agricultural production leaves a large amount of phosphorus in the cultivated soil. In summary, the contribution of various pollution sources to soil load during nitrogen metabolism can be expressed as industrial sector (68.9%) > agricultural production (24.8%) > domestic pollution (6.3%). The contribution of various pollution sources to soil load during phosphorus metabolism can be described as agricultural production (85.3%) > industrial sector (9.4%) > domestic pollution (5.3%). The contribution of various pollution sources to soil load during sulfur metabolism can be described as industrial sector (90%) > domestic pollution (10%).
3.2.3. Atmospheric load For atmospheric load, the main sources of atmospheric load produced by three kinds of elements are very different. Phosphorus has few effects on the atmosphere. Nevertheless, the main sources of air pollution caused by sulfur are industrial emissions, domestic pollution, and waste incineration. Compared with the sulfur element, the nitrogen released into the atmosphere were due to agricultural sector and vehicle emissions. In 2016, the element emission ratio of various sources in the atmosphere in Liaoning Province is shown in Fig. 11. The contribution of various pollution sources to atmospheric load during nitrogen metabolism can be expressed as: the industrial sector (37.8%) > agricultural production (27.7%) > waste incineration (18.1%) > motor vehicle emissions (13.7%) > domestic pollution (2.7%). The contribution of various pollution sources to atmospheric load during sulfur metabolism can be described as: industrial sectors (91.4%) > domestic pollution (7.8%) > waste incineration (0.8%). No matter nitrogen element or sulfur element, industrial emissions are the main sources that cause the most atmospheric load, accounting for 37.8% and 91.4% of the total atmospheric load respectively, which is mainly associated with the industrial structure and energy utilization structure of Liaoning Province. Meanwhile, it should be noted that industrial emissions are major contributors to atmospheric load during sulfur metabolism. In nitrogen metabolism, agriculture, waste incineration, and motor vehicle emissions contribute to 27.7% of the total nitrogen atmosphere load. Accordingly, to control air pollution caused by nitrogen, policymakers should not only pay attention to the air pollution from industrial emissions, but pay attention to impacts of agriculture, waste incineration, motor vehicle emissions on the air.
3.2.5. Countermeasures of environmental load The analysis of environmental load in Liaoning Province indicates that the socioeconomic system of Liaoning Province is an open system. The metabolic processes of nitrogen, phosphorus and sulfur in the system are linear, which will inevitably lead to unstable material metabolism structure, low material production efficiency, and imperfect system function. The metabolic patterns of nitrogen, phosphorus and sulfur in Liaoning Province can be highly summarized as linear opentype high-intensity material metabolism patterns, which inevitably causes severe resource depletion and huge environmental load. Therefore, in order to fundamentally solve the huge environmental load caused by nitrogen, phosphorus and sulfur, it is necessary to systematically regulate the existing elemental metabolic system structure. The system integrates and configures the flow path and circulation intensity of nitrogen, phosphorus and sulfur. This study proposed to build a closed loop from resources, products, waste, and renewable resources
Fig. 11. Proportion of element loads from various pollution sources in the atmosphere in Liaoning Province. 77
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
to achieve the twin goal of optimal resource utilization and minimum waste discharge. It would facilitate to achieving resource utilization optimization.
of Korea and the Yellow Sea region. Biogeochemistry 57–58 (1), 387–403. https:// doi.org/10.1023/A:1015767506197. Berlin, M., Kumar, G.S., Nambi, I.M., 2014. Numerical modeling on transport of nitrogen from wastewater and fertilizer applied on paddy fields. Ecol. Modell. 278, 85–99. Boyer, E., Howarth, R., Galloway, J., Dentener, F., Green, P., Vörösmarty, C., 2006. Riverine nitrogen export from the continents to the coasts. Global Biogeochem. Cycles 20 (1), 1–91. https://doi.org/10.1029/2005GB002537. Breemen, Nvan, Boyer, E.W., Goodale, C.L., Jaworski, N.A., Paustian, K., Seitzinger, S.P., Lajtha, K., Mayer, B., Dam, Dvan., Howarth, R.W., Nadelhoffer, K.J., Eve, M., Billen, G., 2002. Where did all the nitrogen? Fate of nitrogen inputs to large watersheds in the northeastern U.S.A. Biogeochemistry 57-58 (1), 267–293. https://doi.org/10. 1007/978-94-017-3405-9_8. Filoso, S., Martinelli, L., Howarth, R., Boyer, E.W., Dentener, F., 2006. Human activities changing the nitrogen cycle in Brazil. Biogeochemistry 79 (1), 61–89. https://doi. org/10.1007/s10533-006-9003-0. Geng, J.B., Ma, Q., Zhang, M., Li, C.L., Liu, Z.G., Lyu, X.X., Zheng, W.Q., 2015. Synchronized relationships between nitrogen release of controlled release nitrogen fertilizers and nitrogen requirements of cotton. Field Crops Res. 184, 9–16. https:// doi.org/10.1016/j.fcr.2015.09.001. Jeong, Y.S., Matsubae-Yokoyama, Kazuyo, Kubo, H., 2009. Substance flow analysis of phosphorus and manganese correlated with South Korean steel industry. Resour. Conserv. Recycl. 53 (9), 479–489. https://doi.org/10.1016/j.resconrec.2009.04.002. Kalmykova, Y., Harder, R., Borgestedt, H., Svanäng, I., 2012. Pathways and management of phosphorus in urban areas. J. Ind. Ecol. 16 (6), 928–939. https://doi.org/10.1111/ j.1530-9290.2012.00541.x. Li, B., Boiarkina, I., Young, B., Wei, Y., 2015. Substance flow analysis of phosphorus within New Zealand and comparison with other countries. Sci. Total Environ. 527–528, 483–492. https://doi.org/10.1016/j.scitotenv.2015.04.060. Parfitt, R.L., Schipper, L.A., Baisden, W.T., Elliott, A., 2006. Nitrogen inputs and outputs for New Zealand in 2001 at national and regional scales. Biogeochemistry 80 (1), 71–88. https://doi.org/10.1007/s10533-006-0002-y. Qian, Y., Song, K., Hu, T., Ying, T., 2017. Environmental status of livestock and poultry sectors in China under current transformation stage. Sci. Total Environ. 622, 702–709. https://doi.org/10.1016/j.scitotenv.2017.12.045. Qiao, M., Zheng, Y.M., Zhu, Y.G., 2011. Material flow analysis of phosphorus through food consumption in two megacities in northern China. Chemosphere 84 (6), 773–778. https://doi.org/10.1016/j.chemosphere.2011.01.050. Qin, B.Q., Wang, X.D., Tang, X.M., 2007. Drinking water crisis caused by eutrophication and Cyanobacteria bloom in Lake Taihu: cause and measurement. Adv. Earth Sci. 22 (9), 896–906. https://doi.org/10.11867/j.issn.1001-8166.2007.09.0896. Shi, Y., Xia, Y.F., Bi-Hong, L.U., 2014. Emission inventory and trends of NOx for China, 2000-2020. J. Zhejiang Univ. Sci. 15 (6), 454–464. Smil, V., 2000. Phosphorus in the environment: natural flows and human interferences. Environ. Resour. 25 (25), 53–88. https://doi.org/10.1146/annurev.energy.25.1.53. Tian, J.P., Shi, H., Chen, Y., Chen, L.J., 2012. Assessment of industrial metabolisms of sulfur in a Chinese fine chemical industrial park. J. Clean. Prod. 32 (3), 262–272. https://doi.org/10.1016/j.jclepro.2012.04.001. Villalba, G., Liu, Y., Schroder, H., 2008. Global phosphorus flows in the industrial economy from a production perspective. J. Ind. Ecol. 12 (4), 557–569. https://doi. org/10.1111/j.1530-9290.2008.00050.x. Yuan, Z., Liu, X., Wu, H., et al., 2011. Anthropogenic phosphorus flow analysis of Lujiang County, Anhui Province, Central China. Ecol. Modell. 222 (8), 1534–1543. Yoshikawa, N., Shiozawa, S., Ardiansyah, 2008. Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed. Biogeochemistry 87 (1), 1–15. https://doi. org/10.1007/s10533-007-9164-5. Yeo, M.J., Kim, Y.P., 2016. Sensitivity of the environmental costs of air pollution caused by SOx, NOx, and PM from power plants applied to the power mix configuration in South Korea. Air Quality Atmos. Health 9 (4), 1–8. Zhang, W.Q., Jin, X., Liu, D., Lang, C., Shan, B.Q., 2017. Temporal and spatial variation of nitrogen and phosphorus and eutrophication assessment for a typical arid river — Fuyang River in northern China. J. Environ. Sci. 55, 41–48. https://doi.org/10.1016/ j.jes.2016.07.004. Zhang, Y., Zheng, H.G., Yang, Z.F., Liu, G.Y., 2015. Analysis of the industrial metabolic processes for sulfur in the Lubei (Shandong Province, China) eco-industrial park. J. Clean. Prod. 96, 126–138. https://doi.org/10.1016/j.jclepro.2014.01.096. Zhang, Y., Lu, H., Fath, B.D., et al., 2016. Modelling urban nitrogen metabolic processes based on ecological network analysis: a case of study in Beijing, China. Ecol. Modell. 337, 29–38.
4. Conclusions The purpose of this study was to develop models and comprehensively analyze nitrogen, phosphorus and sulfur metabolism on the provincial scale, and take a typical Chinese industrial province Liaoning as a case. The developed model captures the interconnection within the industrial system and interconnection between subsystems of industrial systems, agricultural systems, and residential life systems, and further characterizes effects of element cycle on the environment including water, soil, and air. It not only describes the input and output of elements in every aspect of the system, but also reflects the relations between various flows in the system. The conjoint analysis model may assist the policymakers to investigate environmental problems caused by nitrogen, phosphorus and sulfur metabolism and develop appropriate measures to address environmental issues. In 2016, the total input of nitrogen, phosphorus and sulfur element in Liaoning social and economic system was 5,339,000 tons, 5,820,000 tons and 3,084,000 tons, respectively. The total amount of nitrogen, phosphorus and sulfur released to the environment was 2,140,000 tons, 3,020,000 tons and 1,160,000 tons respectively. The industrial sector is the key point that causes the atmospheric and soil pollution of nitrogen and sulfur in Liaoning Province. Pollution caused by agricultural production is the key to water pollution of nitrogen (61.8%) and phosphorus (80.2%) in Liaoning Province, respectively, accounted for 61.8% and 80% of the total emissions of the two types of elements. The nitrogen, phosphorus and sulfur elements emitted by domestic sewage into the water body are 98,469 tons, 5915 tons and 19,056 tons, respectively, which are 6.5 times, 13.2 times and 4.9 times of those discharged from industrial wastewater. The removal rate of three kinds of elements (22%, 37%, 32%) is much lower than that of industrial wastewater (72.1%, 54.3%, 54.5%). Therefore, sewage flow is a key stream for pollution prevention and control in Liaoning Province. The metabolic problems of high energy consumption, low output, and high pollution coexist in the current metabolic structure in Liaoning Province. We propose to take measures to control the total amount of input materials, build a substance recycling loop and improve the production efficiency of materials, to achieve the purpose of reducing the environmental load Acknowledgements This work was supported by the Based Research Projects of National Natural Science Foundation of China (41871212),the Based Research Projects of Northeastern University (N172504031). References Bashkin, V.N., Park, S.U., Choi, M.S., LEE, C.B., 2002. Nitrogen budgets for the Republic
78
Contents lists available at ScienceDirect
Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel
Conjoint analysis of nitrogen, phosphorus and sulfur metabolism: A case study of Liaoning Province, China
T
⁎
Chengkang Gaoa,b, Shuaibing Zhanga,b, , Kaihui Songc, Hongming Naa,b, Fan Tiana,b, Menghui Zhanga,b, Wengang Gaoa,b a
State Environmental Protection (SEP) Key Laboratory of Eco-Industry, Northeastern University, Shenyang 110819, China School of Metallurgy, Northeastern University, Shenyang, Liaoning 110819, China c Department of Geographical Science, University of Maryland, College Park 20742, MD, USA b
A R T I C LE I N FO
A B S T R A C T
Keywords: Material metabolism Nitrogen-phosphorus-sulfur Conjoint analysis Environmental pollution Liaoning Province
The three types of elements nitrogen (N), phosphorus (P) and Sulfur (S) are inextricably linked from the source to the destination throughout the system. To analyze the environmental load caused by the three elements, this study established a material metabolism model to quantify the relationships among metabolic processes on the provincial scale and examined their environmental implications based on Substance Flow Analysis (SFA). The results show that the metabolic fluxes of nitrogen, phosphorus and sulfur in the socioeconomic system of Liaoning Province in 2016 were 5.339 million tons, 0.582 million tons and 3.084 million tons, respectively. The agricultural sector caused the greatest environmental pressures on water bodies, in which nitrogen and phosphorus accounted for 61.8% and 80.2% of the total water body load. For atmospheric load, the nitrogen and sulfur elements in the industrial sector caused the largest atmospheric load, accounting for 37.8% and 91.4% of the total atmospheric load, respectively. The main source of phosphorus soil load in Liaoning Province is the agricultural production, accounting for 85.3% of the total soil load caused by phosphorus.
1. Introduction The demand for nitrogen (N), phosphorus (P), and sulfur (S) has increased dramatically driven by the socioeconomic development, while exerts significant environmental pressures (Berlin et al.,2014). The increasing (eutrophication, haze and fog) environment problems caused by the overcharge of the three elements has drawn increasing attention. In recent decades, eutrophication has become one of the core issues of water pollution in China. In April 2007, the blue-green algae blooms in Taihu Lake caused shutdowns of nearby water treatment plant; as a result, most areas of the city run into water shortages (Qin et al., 2007). In addition, the air pollution caused by nitrogen oxide (NOx) and sulfide led to a series of environmental problems such as atmospheric acid deposition, ozone, and haze (Yeo and Kim, 2016). It is conservatively projected that NOx emissions in China will reach nearly 29 million tons in 2020 (Shi et al., 2014). It is reported that, from January to March in 2013, approximately 600 million people, accounting for 45% of China's total population, were adversely affected by haze. The metabolism of the three elements (N, P, S) has aroused heated discussion on addressing the environmental issues tailed by the misuse ⁎
and overuse of materials containing either of the three elements (Geng et al., 2015). Many scholars have researched on the metabolism of the three kinds of elements. Researchers have analyzed nitrogen metabolism on the national (Breemen et al., 2002; Filoso et al., 2006) and regional scales. Regional nitrogen metabolism mostly focused on urban (Parfitt et al., 2006) and watershed (Boyer et al., 2006; Bashkin et al., 2002; Yoshikawa et al., 2008). Zhang et al. (2016) analyzed the intensity of nitrogen metabolism in Beijing by means of ecological network analysis, and concluded that atmosphere, household, and industry had the most interactions with other nodes in the network. Compared with nitrogen and sulfur, more research focused on metabolic analysis of phosphorus, varying from global level to (Villalba et al.,2008) national (Li et al., 2015), regional (Yuan et al.,2011; Zhang et al., 2017), as well as urban levels (Kalmykova et al.,2012). Globally, the natural circulation metabolic intensity of global phosphorus is only 1/3 that of artificial circulation, indicating human activities have significant influences on phosphorus cycles (Smil, 2000). From the perspective of different sectors, Qiao et al. (2011) explored the phosphorus flows through food consumption in Beijing and Tianjin, using a material flow analysis (MFA) approach. The results showed that approximately 55% of the phosphorus contained in food for urban residents’ consumption
Corresponding author. E-mail address: [email protected] (S. Zhang).
https://doi.org/10.1016/j.ecolmodel.2018.10.020 Received 26 July 2018; Received in revised form 22 October 2018; Accepted 22 October 2018 Available online 02 November 2018 0304-3800/ © 2018 Elsevier B.V. All rights reserved.
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
(waste recycling), inlet flow of the machine manufacturing industry (reuse and recycling), and inlet flow at the waste treatment stage (harmful or hazardous industrial waste). SFA allows us to quantify relationships between the economy and the environment of a geographically demarcated system.
resulted in municipal sewage and sludge. In the case of the Korean steel industry (Jeong et al., 2009), phosphorus lost in steel-making slag is estimated to be 10% of domestic phosphorus consumption. Compared with the metabolic analysis of nitrogen and phosphorus, fewer studies concentrated on the metabolism of sulfur. Tian et al. (2012) used the Substance Flow Analysis (SFA) method to analyze the flow characteristics of sulfur in the Industrial Park in Hangzhou Bay. Zhang et al. (2015) combined the structure and functional attributes of Lubei EcoIndustrial Park in Shandong, constructed a sulfur metabolism network model based on SFA, and identified key nodes of the processes in the industrial sulfur metabolism. From the perspective of metabolic spatial scales, most studies highlighted the global, national, urban, and industrial parks while few studies of metabolism were conducted on the provincial scale. For the structure of metabolic tissues, most studies focused on the analysis of a single industrial system in the socioeconomic system, while few comprehensive studies on the whole socioeconomic system. In terms of metabolic research subjects, most studies concentrated on the metabolic analysis of single element, while few conducted combined analysis of nitrogen, phosphorus, and sulfur. Given the inextricably linked relationship between the three elements, and their coexistence in many substances (such as food, coal, and oil) it is essential to conduct a comprehensive analysis of nitrogen, phosphorus, and sulfur metabolism. The socioeconomic system is a complex system that composting of several industrial systems, which are interconnected but each different from each other. The study presents a comprehensive analysis of elemental metabolism to better explain environmental problems brought by misuse and overuse of substances containing N, P, S elements. The Substance Flow Analysis method is applied to carry out a joint metabolic analysis of the social and economic system supported by the underlying flows of nitrogen, phosphorus, and sulfur on the province level.
2.2. Nitrogen, phosphorus and sulfur metabolism analysis model on a provincial level Combined with the material flow analysis method, this study established an analysis model of nitrogen, phosphorus and sulfur metabolism in the provincial socioeconomic system. 2.2.1. Metabolic system boundary In the purpose of establishing the analysis model of nitrogen, phosphorus and sulfur metabolism in the provincial socioeconomic system, the system boundary needs to be defined clearly according to the purpose of research. So the provincial geographic boundary is defined as the metabolic system boundary. 2.2.2. Metabolic system framework Within boundaries of the metabolic system in the study, each subsystem is constructed in support of determining pathways of nitrogen, phosphorus and sulfur metabolism systematically. Based on the SFA analysis framework, this study builds a material metabolism system framework on the provincial level, as shown in Fig. 2. The provincial socioeconomic system is divided into four subsystems based on the attributes: resource system, environmental system, provincial socio-economic system, and raw material product system. The four subsystems form the framework of metabolic systems of nitrogen, phosphorus, and sulfur on the province level, as shown in Fig. 2. 2.2.3. Metabolic pathways of nitrogen, phosphorus, and sulfur The relationships between each pair of metabolic subsystems in the framework are analyzed by depicting the flows of nitrogen, phosphorus, and sulfur, and their internal connections with other subsystems. This framework serves to describe and explore the reasons that affect the production and conversion of nitrogen, phosphorus, and sulfur. The flows of nitrogen, phosphorus, and sulfur can be described as elements in the form of minerals, energy, industrial products, agricultural products, and other products enter the socio-economic system through transfers and exchanges. Solid waste treatments related to metabolic pathway mainly include incineration and landfill. Some of the elements are discharged into the atmosphere in the form of incineration waste gas, and the remaining part is buried in the soil. The nitrogen, phosphorus, and sulfur metabolism pathways are shown in Fig. 3 Despite the interconnection among various subsystems, the metabolic pathways of nitrogen, phosphorus, and sulfur are characterized and distinguished from each other through analyses. Nitrogen is mainly sourced from the atmosphere and imported into the socio-economic system in the form of gas, minerals, industrial products, agricultural products, and energy. Phosphorus is naturally stemmed from the phosphate rock and imported into the socioeconomic system mainly in the form of phosphate rock, industrial products, and agricultural products. Sulfur is mainly imported into the socio-economic system in the form of sulfur ore, industrial products, agricultural products, and energy. The ultimate destinations of nitrogen and sulfur are the atmosphere, soil, and water. Compared with nitrogen and sulfur, the ultimate fates of phosphorus are water and soil.
2. Theories and methods 2.1. Substance flow analysis The core principle of Substance Flow Analysis is derived from the law of conservation of mass, whose outstanding advantages highlight the capability of addressing specific environmental problems. It enables people to explore the critical links and key flows that cause environmental pollution by tracking the input and output of substances in various aspects of the system and the environment, and to construct maps of material flow network and quantify the circulation of each link within the system. The framework of substance flow analysis is shown in Fig. 1. The SFA framework consists of four processes: production, fabrication and manufacture, consumption, and waste management. The waste generated in manufacturing and processing mainly comes from the following channels: material flow re-entering the production stage
2.2.4. Metabolism network of nitrogen, phosphorus, and sulfur The provincial network of nitrogen, phosphorus, and sulfur metabolism is based on the boundary of the metabolic system and metabolic pathways, including five types of nodes and five types of flows, as
Fig. 1. Substance flow analysis (SFA) framework. 71
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 2. Metabolism system framework on the provincial level.
final environmental attribution of materials. Five types of flows are described as follows. (1) The input flows, in the form of raw materials (or products), enter the provincial socioeconomic system; these processes are denoted by I. For example, I1 represents that the input flows into the provincial socio-economic system in the form of minerals. (2) The output flows of the provincial socio-economic system in the form of products are expressed by E. For example, E4 represents the output flow of the provincial socio-economic system in the form of agricultural products. (3) The element flows in the form of sewage and water reuse are expressed by W. For example, W1
shown in Fig. 4. The diagram contains five types of nodes and five types of flows. The nodes representing a material supply to the socio-economic system in the province are denoted by C. The nodes representing processes related to consumption and redistribution of materials within the socioeconomic system are denoted by P. The nodes that represent waste treatment are represented by T. The nodes that represent the ultimate disposition of the waste are denoted by D, which involves the processes of incineration, landfill, and other ways of waste treatment such as high temperature composting and recycling. Nodes denoted by S indicate the
Fig. 3. Metabolic pathways of nitrogen, phosphorus, and sulfur. 72
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 4. Elements metabolism diagram on the provincial level. *Retrieved from: http://italychinalink.com/vetrina/provincia-di-liaoning/.
represents the industrial wastewater flows, which are discharges into sewage treatment facilities of companies. (4) The element-contained flows in solid form, represented by X. For example, X3 represents the flow of household garbage. Besides, the flows of elements that are exchanged with the atmospheric contents are denoted by N. For example, N2 represents the flow of exhaust gases from industrial processes into the atmosphere. The element metabolism diagram at the provincial level constructed by SFA method describes in detail the processes of an element's input from the source, internal flow and transformation, and finally its return to the environment. It reflects the circulation of elements in the system. According to the functions and properties of each link within the system, the metabolic topological structure of elements at the provincial level includes the industrial system, agricultural system, and resident life system. The industrial system is a system to process and manufacture industrial products. Materials input to the industrial system are minerals, energy, industrial products, agricultural products, and other products. After raw materials being processed and manufactured in the industrial system, some of them are transformed into industrial products, while others are transformed into waste products. The agricultural system is a system of producing agricultural products, which consumes energy, industrial products, agricultural products, and other products. The agricultural production process mainly yields agricultural while still some waste products are disposed into the
environment. The residential life system is basically a consumption system, where energy, industrial products, agricultural products, and other products are consumed. They are disposed of in the form of household solid waste and liquid waste and discharges into environment. 2.2.5. Analytical model Based on the topological structure of element metabolism, quantification of the causal relationship of each link in the topological structure is of great importance in the purpose of element metabolism analysis. The elemental metabolic analysis model is based on the first law of thermodynamics – the principle of material conservation. This study is based on the assumption that the material metabolism in the socioeconomic system is stable, that is, input equals output. According to the topological structure of element metabolism, the model of element metabolism constructed in serving of provincial-level analysis is shown as follow: According to the properties of each fundamental flow, the analytical model is subdivided into a raw material (or product) flow model, a wastewater flow model, a solid waste flow model, an exhaust gas flow model, and a reuse flow model. The raw material (or product) flow model is used to account for the content of elements in various raw materials (or products). The raw material (or product) flow: 73
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 5. Geographical location of Liaoning Province in China.
E=
∑ Φi × ki
3. Results and discussions
Φi – The total amount of material (or product), t; ki – Elemental coefficient in the product; i – The type of products or material. Wastewater flow model is used to calculate the content of elements in industrial wastewater and domestic sewage. Wastewater flow:
Based on the elemental metabolic analysis model established above, this study analyzed the socioeconomic system of Liaoning Province. In order to obtain complete research data, this study selected 2016 as a time node. Further analysis is conducted on the influence of the industrial system, agricultural system, and resident living system on environment (water, air and soil) in Liaoning Province.
W= [ ∑ Φj × kj] × ka
Φj – Amount of wastewater, t; kj – Elemental coefficient in wastewater; kt – Element removal rate in sewage; j – Type of wastewater; a – Type of elements. Solid waste flow model is built to quantify the elemental content in industrial solid waste, agricultural solid waste, and domestic waste. Solid waste flow: X=
3.1. The overview of Liaoning Province Liaoning Province, located in northeast China, is one of the major traditional industrial bases in China. It is one of the provinces with the most complete industrial categories in China, with over 500 sub-industries. According to《China statistical yearbook 2016》and《Liaoning statistical yearbook 2016》: up until 2016, there had been 158 sewage treatment plants in Liaoning with a total sewage treatment capacity of 1.829 billion tons and an average sewage treatment capacity of 7.71 million tons per day; An estimated 268 million tons of general industrial solid waste was produced and the comprehensive utilization rate of solid waste was 43.8%; The domestic garbage clearance volume is 9.27 million tons with harmless disposal rate of 87.6%; In 2016, the total nitrogen oxide emissions of Liaoning Province ranked 8th among all the cities in China, with 27.2% of motor vehicles. From the above, Liaoning Province is a typical case. Liaoning province's geographical location in China is shown in Fig. 5.
∑ Φk × kk
Φk – The total amount of solid waste, t; kk – Elemental coefficient in solid waste; k – Type of solid waste. The exhaust gas flow model is used to calculate the content of elements in industrial waste gas, motor vehicle exhaust gas, and domestic exhaust gas. Exhaust gas flow:
N= [ ∑ Φl × kl] × kp
Φl – The total amount of fuel consumed, t; kl – Elemental coefficient in fuel; kp – Proportion of element emissions to the atmosphere during fuel consumption; l – Type of exhaust gas; p – Type of fuel. The recycled flow model is used to calculate the elemental content of the recycled wastewater and the recycled solid waste. Recycled flow:
3.2. Conjoint analysis 3.2.1. Metabolic structure and flux analysis In 2016, the input amounts of nitrogen, phosphorus, and sulfur in Liaoning socioeconomic system were respectively 5,339,000 tons, 5,820,000 tons and 3,084,000 tons, and the ratio of nitrogen, phosphorus, and sulfur was 9.2:1:5.3. It indicates that the demand for nitrogen and sulfur is higher than that for phosphorus in Liaoning Province. In the topological structure of element metabolism, there are some differences in the metabolic processes of the three elements. First, sulfur metabolism has no nodes and fluxes related to agricultural links. Second, phosphorus metabolic process has no relationship with
R= [ ∑ Φm × km] × kn
Φm – Total amount of original products, t; km – Elemental coefficients contained in recycled materials; kn – Recycling rate; m, n – Type of recycled materials. 74
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Fig. 6. The ratio of nitrogen, phosphorus and sulfur metabolic fluxes in Liaoning Province. (Notes: yellow represents the node of deficiency of sulfur metabolism; purple represents the node of deficiency of phosphorus metabolism; red represents the increased flow of nitrogen metabolism.). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
imported into the socioeconomic system in Liaoning Province in the form of industrial products (33.4%), because a large amount of nitrogen fertilizer and compound fertilizer were consumed in agricultural sector. Second, it is imported in the form of energy (32%), because industrial sector and residents' life are supported by consumption of coal and other energy sources with a large amount of nitrogen elements. Compared with the metabolic processes of phosphorus and sulfur elements, nitrogen metabolism is unique in its atmospheric inputs in the input source, which accounts for a high proportion, about 21.7%. The reason is that urea and synthetic ammonia are produced by artificial nitrogen fixation in the process of nitrogen fertilizer production. Phosphorus (P) was mainly introduced into the socioeconomic system in the form of industrial products (83.3%). It is because that the agricultural sector requires a large amount of phosphate fertilizer and compound fertilizer. Sulfur is mainly imported into the socioeconomic system in Liaoning Province in the form of energy (49%) and mineral products (38.2%). The energy source of sulfur is driven by a large number of consumption of coal and other fossil fuels in industrial sector and residential lives, while the mineral source is associated with the huge amount of iron sulfide ore mined in Liaoning Province, which was 2,142,300 tons in 2016. The input sources of Liaoning socioeconomic system are shown in Fig. 7. The dependence of nitrogen and sulfur elements on various input forms is relatively uniform, while phosphorus elements are overly dependent on the input of industrial products. About 83.3% of the phosphorus was imported into the socioeconomic system in Liaoning
Fig. 7. Input sources of socioeconomic system in Liaoning Province.
atmosphere and its associated flows. Third, the metabolic process of nitrogen elements includes all nodes and flow stocks, and the nitrogen metabolism process also catalyzes the flow from the atmosphere to industry and the flow from logistics trade to the atmosphere within and outside the province. Fig. 6 shows the metabolic flux ratio of nitrogen, phosphorus, and sulfur in Liaoning Province. The three elements also differ significantly in the form of material input. Nitrogen (N) has two primary inputs. First, it was mainly
75
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
Province in the form of industrial products. However, these industrial products are mainly concentrated phosphate fertilizers and compound fertilizers. This indicates that the critical nodes of phosphorus metabolism system in Liaoning Province is the phosphorus chemical industry. There are mainly two output sources. One is to export from the socioeconomic system in the form of products, and the other is to discharge waste (in forms of solid, liquid, and gas) into the environment. The output of nitrogen products, phosphorus products, and sulfurs products were 3,195,000 tons, 279,000 tons, and 1,924,000 tons, respectively. The product conversion rate of nitrogen, phosphorus and sulfur metabolic system can be defined based on the material input. The product conversion rate is expressed as the ratio of product output to material input, representing the level of system utilization of input materials. According to the input and output, the product conversion rate of nitrogen element is 59.8%, that of phosphorus element is 48.1%, and that of sulfur element is 62.4%. Moreover, the product conversion rate of nitrogen, phosphorus and sulfur in the socioeconomic system in Liaoning is not very high. Compared with nitrogen and sulfur, phosphorus has the lowest conversion rate, less than 50%. This indicates that the socioeconomic system of Liaoning Province has a low utilization level of phosphorus element, which causes an enormous waste of phosphorus element and further aggravates the pollution of phosphorus element to environment. In 2016, Liaoning's social and economic system exported 2,144,000 tons of nitrogen, 302,000 tons of phosphorus and 1,160,000 tons of sulfur to the environment. The discharges of nitrogen, phosphorus, and sulfur into the atmosphere, water and soil are shown in Fig. 8. It can be seen that a large amount of nitrogen, phosphorus, and sulfur was discharged to the soil, accounting for 45.5%, 89.4% and 48.6% of their total emissions respectively. There are two reasons that mainly account for the accumulation of nitrogen, phosphorus and sulfur elements in the soil. First, excessive inputs of nitrogen fertilizer, phosphate fertilizer and other fertilizers result in the accumulation of nutrients in the soil which cannot be absorbed by crops. Second, a large proportion of domestic garbage and solid waste are disposed by incineration and landfill, resulted large amount of elements remain in the soil. In addition to the accumulation in soil, there is also a large amount of nitrogen and sulfur elements emitting to the atmosphere, accounting for 40.6% and 49.4% of their total emissions respectively. The consumption of coal and other energy and the burning of solid waste are the main reasons for the large amount of nitrogen and sulfur elements being discharged into the atmosphere. Besides, the nitrogen released into the atmosphere were also due to the volatilization of nitrogen fertilizer and the emission of nitrogen oxides from vehicle exhaust. The number of nitrogen, phosphorus, and sulfur released to water is
Fig. 9. Proportion of water load for various pollution sources in Liaoning Province.
relatively less, accounting for 13.9%, 10.6% and 2% of the total emission respectively. However, it leads to severe water pollution, especially eutrophication, indicating that the water environment in Liaoning Province is very fragile. 3.2.2. Water load The main sources of water pollution in Liaoning Province are industry, agriculture, and resident life. In 2016, the socioeconomic system of Liaoning Province discharged 297,840 tons of nitrogen, 32,078 tons of phosphorus and 22,910 tons of sulfur into water, accounting for 5.6%, 5.5% and 0.74% of the total input respectively. The proportion of water load caused by various pollution sources in Liaoning Province is shown in Fig. 9. The water load composition of various pollution sources of nitrogen is roughly similar to that of phosphorus elements in Liaoning Province, as shown in Fig. 9. The agricultural links are major contributors to the accumulation of nitrogen and phosphorus in water bodies, resulting in N and P accounting for 61.8% and 80.2% of the total water load respectively. Residential life is a less important source of nitrogen and phosphorus, accounting for 33.1% and 18.4% of the total water load respectively. The process of sulfur metabolism lacks agricultural links. The largest component of the water load of the sulfur element is from the life of residents, accounting for 83.2% of the total water load of sulfur element. As a result, the contribution of three kinds of pollution to water load level can be identified as: agriculture sector (N: 61.8%, P: 61.8%) > residents live sector (N: 33.1%, P: 33.1%, S: 83.2%) > industry sector (N: 5.1%, P: 5.1%, S: 16.8%). Most of the water load caused by the agricultural link comes from the livestock and poultry breeding industry. The water load ratio of Liaoning agricultural sector is shown in Fig. 10. For both nitrogen and phosphorus, the water load caused by livestock and poultry breeding industry accounts for more than 90% of the total water load in the agricultural sector. It is mainly caused by the low
Fig. 8. Environmental loads in Liaoning Province.
Fig. 10. Proportion of water loads in agricultural links in Liaoning Province. 76
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
efficiency livestock and poultry sectors (Qian et al., 2017). Meanwhile, a large quantity of livestock and poultry excrement is treated simply, resulting in the low utilization rate of manure and in turn less circulation of the elements. The water load caused by the three types of elements in the domestic wastewater is significantly higher than that of the industry sector. The water load of nitrogen, phosphorus, and sulfur caused by domestic sewage is more than four times higher than that of industry sector. On the one hand, it indicates that Liaoning Province has made remarkable achievements in the treatment of industrial wastewater; on the other hand, it also indicates that Liaoning Province has great defects in the treatment of domestic sewage. No matter in quantity or pollution degree, the influence of nitrogen, phosphorus and sulfur elements in domestic sewage on water has far exceeded that of industrial wastewater. Therefore, in the efforts of prevention and control of water pollution caused by nitrogen, phosphorus and sulfur elements, attention should be paid not only to industrial links, but also to agricultural links and residential life links.
Fig. 12. Proportion of soil load for various pollution sources in Liaoning Province.
3.2.4. Soil environmental load This study presents impacts on soil environment in two parts: cultivated soil and non-cultivated soil. The cultivated land is mainly polluted by the unused chemical fertilizer in the process of crop production, while the non-cultivated land is mainly polluted by various solid wastes. In 2016, the amount of nitrogen, phosphorus, and sulfur released from the socioeconomic system in Liaoning to the soil was 974,344 tons, 270,181 tons and 564,079 tons, accounting for 18.2%, 46.4% and 18.3% of the total input respectively. The ratio of soil load of various pollution sources in Liaoning Province is shown in Fig. 12. It can be seen from Fig. 12 that the largest load of nitrogen and sulfur elements in soil is industry, accounting for 68.9% and 90% of the total load of soil. It is caused by the large amount of industrial solid wastes (fly ash, slag, etc.) produced in industrial sector, which contain nitrogen and sulfur. Moreover, the comprehensive utilization rate of industrial solid wastes in Liaoning Province is as low as only 43.8%. The remaining industrial solid waste discharged into the non-arable land soil through landfill, waste and other ways. The most significant component of soil load caused by phosphorus is agriculture, accounting for 85.3% of total soil load of phosphorus. The main reason for the above phenomena is that the excessive use of phosphate fertilizer in agricultural production leaves a large amount of phosphorus in the cultivated soil. In summary, the contribution of various pollution sources to soil load during nitrogen metabolism can be expressed as industrial sector (68.9%) > agricultural production (24.8%) > domestic pollution (6.3%). The contribution of various pollution sources to soil load during phosphorus metabolism can be described as agricultural production (85.3%) > industrial sector (9.4%) > domestic pollution (5.3%). The contribution of various pollution sources to soil load during sulfur metabolism can be described as industrial sector (90%) > domestic pollution (10%).
3.2.3. Atmospheric load For atmospheric load, the main sources of atmospheric load produced by three kinds of elements are very different. Phosphorus has few effects on the atmosphere. Nevertheless, the main sources of air pollution caused by sulfur are industrial emissions, domestic pollution, and waste incineration. Compared with the sulfur element, the nitrogen released into the atmosphere were due to agricultural sector and vehicle emissions. In 2016, the element emission ratio of various sources in the atmosphere in Liaoning Province is shown in Fig. 11. The contribution of various pollution sources to atmospheric load during nitrogen metabolism can be expressed as: the industrial sector (37.8%) > agricultural production (27.7%) > waste incineration (18.1%) > motor vehicle emissions (13.7%) > domestic pollution (2.7%). The contribution of various pollution sources to atmospheric load during sulfur metabolism can be described as: industrial sectors (91.4%) > domestic pollution (7.8%) > waste incineration (0.8%). No matter nitrogen element or sulfur element, industrial emissions are the main sources that cause the most atmospheric load, accounting for 37.8% and 91.4% of the total atmospheric load respectively, which is mainly associated with the industrial structure and energy utilization structure of Liaoning Province. Meanwhile, it should be noted that industrial emissions are major contributors to atmospheric load during sulfur metabolism. In nitrogen metabolism, agriculture, waste incineration, and motor vehicle emissions contribute to 27.7% of the total nitrogen atmosphere load. Accordingly, to control air pollution caused by nitrogen, policymakers should not only pay attention to the air pollution from industrial emissions, but pay attention to impacts of agriculture, waste incineration, motor vehicle emissions on the air.
3.2.5. Countermeasures of environmental load The analysis of environmental load in Liaoning Province indicates that the socioeconomic system of Liaoning Province is an open system. The metabolic processes of nitrogen, phosphorus and sulfur in the system are linear, which will inevitably lead to unstable material metabolism structure, low material production efficiency, and imperfect system function. The metabolic patterns of nitrogen, phosphorus and sulfur in Liaoning Province can be highly summarized as linear opentype high-intensity material metabolism patterns, which inevitably causes severe resource depletion and huge environmental load. Therefore, in order to fundamentally solve the huge environmental load caused by nitrogen, phosphorus and sulfur, it is necessary to systematically regulate the existing elemental metabolic system structure. The system integrates and configures the flow path and circulation intensity of nitrogen, phosphorus and sulfur. This study proposed to build a closed loop from resources, products, waste, and renewable resources
Fig. 11. Proportion of element loads from various pollution sources in the atmosphere in Liaoning Province. 77
Ecological Modelling 390 (2018) 70–78
C. Gao et al.
to achieve the twin goal of optimal resource utilization and minimum waste discharge. It would facilitate to achieving resource utilization optimization.
of Korea and the Yellow Sea region. Biogeochemistry 57–58 (1), 387–403. https:// doi.org/10.1023/A:1015767506197. Berlin, M., Kumar, G.S., Nambi, I.M., 2014. Numerical modeling on transport of nitrogen from wastewater and fertilizer applied on paddy fields. Ecol. Modell. 278, 85–99. Boyer, E., Howarth, R., Galloway, J., Dentener, F., Green, P., Vörösmarty, C., 2006. Riverine nitrogen export from the continents to the coasts. Global Biogeochem. Cycles 20 (1), 1–91. https://doi.org/10.1029/2005GB002537. Breemen, Nvan, Boyer, E.W., Goodale, C.L., Jaworski, N.A., Paustian, K., Seitzinger, S.P., Lajtha, K., Mayer, B., Dam, Dvan., Howarth, R.W., Nadelhoffer, K.J., Eve, M., Billen, G., 2002. Where did all the nitrogen? Fate of nitrogen inputs to large watersheds in the northeastern U.S.A. Biogeochemistry 57-58 (1), 267–293. https://doi.org/10. 1007/978-94-017-3405-9_8. Filoso, S., Martinelli, L., Howarth, R., Boyer, E.W., Dentener, F., 2006. Human activities changing the nitrogen cycle in Brazil. Biogeochemistry 79 (1), 61–89. https://doi. org/10.1007/s10533-006-9003-0. Geng, J.B., Ma, Q., Zhang, M., Li, C.L., Liu, Z.G., Lyu, X.X., Zheng, W.Q., 2015. Synchronized relationships between nitrogen release of controlled release nitrogen fertilizers and nitrogen requirements of cotton. Field Crops Res. 184, 9–16. https:// doi.org/10.1016/j.fcr.2015.09.001. Jeong, Y.S., Matsubae-Yokoyama, Kazuyo, Kubo, H., 2009. Substance flow analysis of phosphorus and manganese correlated with South Korean steel industry. Resour. Conserv. Recycl. 53 (9), 479–489. https://doi.org/10.1016/j.resconrec.2009.04.002. Kalmykova, Y., Harder, R., Borgestedt, H., Svanäng, I., 2012. Pathways and management of phosphorus in urban areas. J. Ind. Ecol. 16 (6), 928–939. https://doi.org/10.1111/ j.1530-9290.2012.00541.x. Li, B., Boiarkina, I., Young, B., Wei, Y., 2015. Substance flow analysis of phosphorus within New Zealand and comparison with other countries. Sci. Total Environ. 527–528, 483–492. https://doi.org/10.1016/j.scitotenv.2015.04.060. Parfitt, R.L., Schipper, L.A., Baisden, W.T., Elliott, A., 2006. Nitrogen inputs and outputs for New Zealand in 2001 at national and regional scales. Biogeochemistry 80 (1), 71–88. https://doi.org/10.1007/s10533-006-0002-y. Qian, Y., Song, K., Hu, T., Ying, T., 2017. Environmental status of livestock and poultry sectors in China under current transformation stage. Sci. Total Environ. 622, 702–709. https://doi.org/10.1016/j.scitotenv.2017.12.045. Qiao, M., Zheng, Y.M., Zhu, Y.G., 2011. Material flow analysis of phosphorus through food consumption in two megacities in northern China. Chemosphere 84 (6), 773–778. https://doi.org/10.1016/j.chemosphere.2011.01.050. Qin, B.Q., Wang, X.D., Tang, X.M., 2007. Drinking water crisis caused by eutrophication and Cyanobacteria bloom in Lake Taihu: cause and measurement. Adv. Earth Sci. 22 (9), 896–906. https://doi.org/10.11867/j.issn.1001-8166.2007.09.0896. Shi, Y., Xia, Y.F., Bi-Hong, L.U., 2014. Emission inventory and trends of NOx for China, 2000-2020. J. Zhejiang Univ. Sci. 15 (6), 454–464. Smil, V., 2000. Phosphorus in the environment: natural flows and human interferences. Environ. Resour. 25 (25), 53–88. https://doi.org/10.1146/annurev.energy.25.1.53. Tian, J.P., Shi, H., Chen, Y., Chen, L.J., 2012. Assessment of industrial metabolisms of sulfur in a Chinese fine chemical industrial park. J. Clean. Prod. 32 (3), 262–272. https://doi.org/10.1016/j.jclepro.2012.04.001. Villalba, G., Liu, Y., Schroder, H., 2008. Global phosphorus flows in the industrial economy from a production perspective. J. Ind. Ecol. 12 (4), 557–569. https://doi. org/10.1111/j.1530-9290.2008.00050.x. Yuan, Z., Liu, X., Wu, H., et al., 2011. Anthropogenic phosphorus flow analysis of Lujiang County, Anhui Province, Central China. Ecol. Modell. 222 (8), 1534–1543. Yoshikawa, N., Shiozawa, S., Ardiansyah, 2008. Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed. Biogeochemistry 87 (1), 1–15. https://doi. org/10.1007/s10533-007-9164-5. Yeo, M.J., Kim, Y.P., 2016. Sensitivity of the environmental costs of air pollution caused by SOx, NOx, and PM from power plants applied to the power mix configuration in South Korea. Air Quality Atmos. Health 9 (4), 1–8. Zhang, W.Q., Jin, X., Liu, D., Lang, C., Shan, B.Q., 2017. Temporal and spatial variation of nitrogen and phosphorus and eutrophication assessment for a typical arid river — Fuyang River in northern China. J. Environ. Sci. 55, 41–48. https://doi.org/10.1016/ j.jes.2016.07.004. Zhang, Y., Zheng, H.G., Yang, Z.F., Liu, G.Y., 2015. Analysis of the industrial metabolic processes for sulfur in the Lubei (Shandong Province, China) eco-industrial park. J. Clean. Prod. 96, 126–138. https://doi.org/10.1016/j.jclepro.2014.01.096. Zhang, Y., Lu, H., Fath, B.D., et al., 2016. Modelling urban nitrogen metabolic processes based on ecological network analysis: a case of study in Beijing, China. Ecol. Modell. 337, 29–38.
4. Conclusions The purpose of this study was to develop models and comprehensively analyze nitrogen, phosphorus and sulfur metabolism on the provincial scale, and take a typical Chinese industrial province Liaoning as a case. The developed model captures the interconnection within the industrial system and interconnection between subsystems of industrial systems, agricultural systems, and residential life systems, and further characterizes effects of element cycle on the environment including water, soil, and air. It not only describes the input and output of elements in every aspect of the system, but also reflects the relations between various flows in the system. The conjoint analysis model may assist the policymakers to investigate environmental problems caused by nitrogen, phosphorus and sulfur metabolism and develop appropriate measures to address environmental issues. In 2016, the total input of nitrogen, phosphorus and sulfur element in Liaoning social and economic system was 5,339,000 tons, 5,820,000 tons and 3,084,000 tons, respectively. The total amount of nitrogen, phosphorus and sulfur released to the environment was 2,140,000 tons, 3,020,000 tons and 1,160,000 tons respectively. The industrial sector is the key point that causes the atmospheric and soil pollution of nitrogen and sulfur in Liaoning Province. Pollution caused by agricultural production is the key to water pollution of nitrogen (61.8%) and phosphorus (80.2%) in Liaoning Province, respectively, accounted for 61.8% and 80% of the total emissions of the two types of elements. The nitrogen, phosphorus and sulfur elements emitted by domestic sewage into the water body are 98,469 tons, 5915 tons and 19,056 tons, respectively, which are 6.5 times, 13.2 times and 4.9 times of those discharged from industrial wastewater. The removal rate of three kinds of elements (22%, 37%, 32%) is much lower than that of industrial wastewater (72.1%, 54.3%, 54.5%). Therefore, sewage flow is a key stream for pollution prevention and control in Liaoning Province. The metabolic problems of high energy consumption, low output, and high pollution coexist in the current metabolic structure in Liaoning Province. We propose to take measures to control the total amount of input materials, build a substance recycling loop and improve the production efficiency of materials, to achieve the purpose of reducing the environmental load Acknowledgements This work was supported by the Based Research Projects of National Natural Science Foundation of China (41871212),the Based Research Projects of Northeastern University (N172504031). References Bashkin, V.N., Park, S.U., Choi, M.S., LEE, C.B., 2002. Nitrogen budgets for the Republic
78