Aggregated physical structure of phosphorus use
Phosphate rock is a non-renewable resource, disregarding the tens of millions of years needed for geological transformation from ocean sediments. Today, enormous quantities of phosphates are extracted annually from the Earth’s crust. Most are then applied to agricultural soils where phosphorus availability declines because of removal in harvested crops, and immobilization by biochemical bonding with clay.
China – being the second largest phosphorus reserve-rich country in the world – has become one of the most intensively engaged in phosphorus-processing in its region. As presented in Figure 1, the national direct material input (DMIP) – an indicator of total substance use – accounted for 5984 thousands metric tons of phosphorus [kmt (P)] in 2000. Domestic extraction played a dominant role in DMIP, for which it was responsible for 82%. Most of the extracted ores were consumed domestically and only 9%, accounting for 451 kmt (P), were exported.
The excessive use accelerates the depletion of a non-renewable mineral resource. Relying on statistics from United States Geological Survey, China’s phosphorus reserves constitute 26% of the world’s total, second only to Morocco and the Western Sahara (USGS 2006). However, with such high intensive extraction activity as well as the huge amount of losses incurred during mining, the basic reserve of national phosphorus resources, i.e. 4054 million tonnes with average P2O5 content of 17%–22%, could be used up in 64 – 83 years. As a result, the Ministry of Land and Resources (MLR) in China counts phosphorus as one of the unsustainable resources for China’s development in this century.
Movement of minerals involves the removal and processing of raw ores, during which a huge quantity of gangue is discarded. As this mass doesn’t enter the economy, and is therefore barely recorded, it is sometimes classified as a “hidden flow”. According to our estimations, 45% of raw ores were lost with the production of marketable ore yield through the beneficiation processes of washing and flotation. These mine wastes are usually discarded in heaps. Although their environmental impacts are not immediate, an increasing ecological risk has occurred.
Phosphorus commodity imports were 1099 kmt (P), while exports were 713 kmt (P) in 2000, accounting for 18% and 12% of DMIP, respectively. The net import of phosphorus, i.e. 386 kmt (P) in 2000, was processed, utilized and eventually accumulated in domestic environments via various paths. The huge gap in the phosphorus budget of international trading was mainly attributed to the huge import quantity of chemical fertilizers. Since domestic demand for high quality compound fertilizers has been increasing annually, the international trade deficit in terms of phosphorus fluxes is likely to stay relatively stable. This will consequently result in an increase in the total quantity of phosphorus accumulation in Chinese soils and waters.
It is apparent that the international trade in agricultural products has only a slight influence on the aggregate physical structure of China’s phosphorus flows, in light of the huge throughput of minerals and fertilizers. However, the figures can be quite different from a global point of view. Although grain self-sufficiency remains a priority in China, the gradual increase in demand for food and feed has led to a net import of crop products. Measured by phosphorus, the imports of cereal grains and soybeans contributed to 33% and 38% of the total import of agricultural commodities and were equivalent to 3% and 83% of domestic yields in 2000, respectively. In this sense, imports of crops partially abate farming-induced emissions and thus alleviate domestic environmental pressure. There is some controversy on the food security of China, as well as the world. For instance, imported cereal grains and soybeans accounted for 4% and 26%, respectively, of the global trade of these commodities in 2000. Not surprisingly, therefore, it is argued that China’s import of soybeans, in particular, has driven world production and the global market price.
|Table 1. Physical profiles of phosphorus flows in China in 2000.|
|DMIP (kmt P)||5984|
|Notes: a DPOP-CS, DPOP-NS and DPOP-SW represent the quantities of phosphorus accumulated in cultivated soils, natural soils and surface water, respectively.|
While import and output of livestock products was generally equilibrated in 2000, the export of meat products accounted for 7% of domestic outputs and was responsible for 8% of animal wastes emission, as weighted by phosphorus content. It is evidenced that the capture and recycling of animal wastes from feedlots is generally ineffective, especially in Southeast China where population is dense, surface water is plentiful, and where over half of industrialized feedlots are located. Hence, export-oriented animal husbandry tends to become one of the substantial sources of phosphorus emissions in certain local areas. Further, the average cultivated area per individual farmer in China is only 0.1 hectare (ha), standing at 9% of the global average. This implies less capacity for manure application than might exist elsewhere. Moreover, it is argued that China has produced excessive meat produce – well over its domestic demands. The export of live pigs, for instance, reached a surprising 13% of total global exports in 2000. In contrast to its slight contribution to national exports (2% of the value of food and live animals used chiefly for food), the environmental consequences of intensified husbandry could be dominant, especially in some highly urbanized areas.
Domestic production output (DPO) indicates the quantity of material accumulated in domestic environments. It is indicative that an input of 100 units DMIP, through various paths of societal metabolism, led to an effluent output of 88 units DPOP among these environmental sinks. In 2000, DPOP amounted to 5271 kmt (P) of which phosphorus effluents to cultivated soils, natural soils and surface water were 40%, 40% and 20% of the total, respectively. Notably, taking into account DHFP, there were 4286 kmt (P), accounting for roughly half of TMRP, ultimately accumulated in domestic natural soils, the largest sink for phosphorus.
The phosphorus outflow to the domestic environments brings forth some implications. Firstly, the phosphorus deposited in the topsoil of cultivated land via fertilizer application can be regarded as a potential ecological-risky time bomb. Although phosphorus transfer occurs very slowly in soil layers, continuous accumulation can not only undermine farming productivity, but also inevitably threaten waterbodies via a slow but continuous leaching into groundwater, as well as surface runoff. Secondly, a huge amount of phosphorus, in the form of various inorganic or organic solid wastes, is transferred into natural soils through incineration, landfill or dumping. This strongly suggests the underlying inappropriateness of those technical approaches that focus on ‘end-of-pipe’ control but ignore resource reuse. Thirdly, only one fifth of DPOP was leaked into surface waters yet this has led to the extensive eutrophication in Chinese lakes and riverine estuaries. This implies that the waterbodies are very sensitive and reactive to phosphorus loads. Therefore a precautionary strategy to reduce phosphorus inflows to waterbodies – instead of later recovery and recycling of phosphorus from the waters or silt – should be applied.
The discussion of aggregate structure of China’s phosphorus flows generates an overall insight into national material uses. Some relevant indicators of the aggregate physical profiles of national phosphorus use are calculated as shown in Table 1.
Sectoral metabolic efficiency of phosphorus use
The sectoral phosphorus-based efficiencies of production, emission, accumulation and recycling are simply defined as a ratio of the outflow divided by the inflow. In addition, internal reuses of phosphorus are treated as a part of the input and discounted from the recycling efficiencies. Due to data insufficiency, not all but most of the values of these indicators are presented in Table 2. The mining industry, among others, is neglected in our subsequent discussion, because: 1) its dominant influences on the overall physical profiles of phosphorus throughput, with respect to the enormous domestic extractions and hidden flows, were already analyzed previously; and 2) unfortunately there is no data available for the emission and recycling flows of the mining sector.
|Table 2. Material use efficiencies of phosphorus flows in China in 2000.|
|Material use efficiencies||Mining||Industry||Farming||Intensified animal husbandry||Family-based breeding||Urban household||Rural household|
|Note: a) n.a. refers to no data available; b) n.s. refers to figures that are not significant; and c) here, the recycling indicators disregard the internal reuse of by-products.|
The manufacture of chemical fertilizers is responsible for 79% of domestically consumed ores, and produced 3509 kmt (P), which accounted for 20% of global total phosphate fertilizers yield in 2000. Other industrial products included 228 kmt (P) of feed additives, 171 kmt (P) of sodium tripolyphosphate (STPP, Na5P3O10) and 37 kmt (P) of various industrial additives or reagents. Comparing the outputs of various chemical products and the consumed phosphate ores, the gross production efficiency of the phosphate industry accounted for 88% of total production in China in 2000, as shown in Table 2. Phospho-gypsum constituted the largest quantity of solid wastes generated by the phosphate industries. Due to contamination (e.g. by thorium), the lack of feasible techniques and absence of practical economic applications, these bulk by-products have been barely reused in China, or elsewhere in the world. According to the PHOSFLOW model, phospho-gypsum was responsible for 84% of phosphorus-related industrial wastes in total. However, lack of data prevents us from assessing the emission and recycling efficiencies of the phosphate industries in greater detail.
Combining domestic production and imports, the gross consumed quantity of synthetical fertilizers totaled 4348 kmt (P) in China, accounting for 27% of global consumption in 2000 (CNCIC 2003). The nationwide intensity of fertilizer application reached 34 kg (P) per hectare of farmland in 2000 – over three times the world average. Together with the phosphorus-content of organic manure, this figure increased to 47 kg (P)/ha. The high intensity of inputs did not necessitate an efficient utilization of phosphorus from minerals into crops via cultivated soils. It is calculated that the gross harvest of crops provided 3691 kmt (P) in 2000. Thus, phosphorus uptake crops accounted for 61% of total nutrient inputs, relying on the steady-state assumption of a static SFA approach. However, because a part of harvested phosphorus – in forms of crops straws and residues – could return to the pool of cultivated soils as organic fertilizers, the net phosphorus output from cultivated lands was only 2995 kmt (P), which provided for ultimate consumption as food, feed, seed or primary materials for industrial manufacturing. This leads to estimates of production efficiency and accumulation efficiency for the farming sector at 50% and 43%, respectively. It is evident that phosphorus applied in both organic and inorganic fertilizers entails complex reactions that transform a large part of soluble phosphates into much less soluble compounds – subsequently leading to difficulties for crops in absorbing this part of immobilized nutrients again. Hence, “re-extraction” of the phosphorus mobilized in agricultural soils can provide a conceivable strategy for ecologically restructuring the whole phosphorus societal cycle. However, the gap of knowledge on the complicated biochemical dynamics of phosphorus transformation in soils significantly hampers desired re-extraction.
Industrialized husbandry and family-farm-based breeding consumed 1214 kmt (P) and 1067 kmt (P), in harvest grains, crop residues, feed additives, food industry by-products and kitchen organic wastes in 2000, respectively. The production efficiencies indicate conversion ratios of phosphorus from vegetable to animal nutrients accounted for only 5% and 7%, respectively – far less than that of the farming sector (61%). As a consequence, the provision of livestock products generated a huge amount of animal wastes, of which 717 kmt (P) was subject to dumping around the countryside, 1044 kmt (P) was recycled to farmlands and 387 kmt (P) was discharged into surrounding waterbodies. In comparison to dispersed family-based animal feeding activities, intensive feedlots contributed to 74% and 72% of the dumped and emitted phosphorus in animal wastes, but were responsible for only 33% of manure reuse. Measured by our material indicators of phosphorus uses, the emission, accumulation and recycling efficiencies of intensified animal husbandry were 24%, 43% and 28% in 2000, while the figures for family farms were calculated as 9%, 19% and 65%, respectively, as shown in Table 2. The results suggest that industrialized animal husbandry feedlots operate in a less environmentally sound way in comparison to dispersed and small-scale family farms.
In the year 2000, the Chinese population consumed 1502 kmt (P), consisting of 1401 kmt (P) in food and 101 kmt (P) in detergents, accounting for 25% of the national DMIP. That is to say three-fourths of the phosphorus originally input into the economy was lost or dissipated before it reached residential households. As phosphorus has been mainly mobilized as an indispensable nutrient, as opposed to its various, but marginal, industrial uses, the percentage of phosphorus in food to DMIP – an approximate of the accumulated metabolic efficiency of the whole society through the productions of fertilizers, crops and livestock products – implied that China’s economy was basically operating at a low nutrient conversion rate. Due to considerable differences in treatment and disposal of human wastes among urban and rural areas, the material use efficiencies were correspondingly different. As shown in Table 1, the recycling of urban household wastes in terms of application of human manure and composted organic garbage accounted for 8% of total consumed phosphorus. The rest was dissipated into the environmental sinks of natural soil and surface waters, resulting in high accumulation and emission efficiency, i.e. 59% and 33%, respectively. Regarding water pollution, intensive emissions were due to the underdevelopment of urban sewage systems. In contrast to the huge nutrient rift between urban areas and farmlands, 74% of consumed phosphorus by rural residents was subject to efficient recycling as organic manure (58%) or animal feeds (42%). Consequently, the accumulation and emission efficiency of the rural household sector in our model amounted to only 9% and 16%, respectively. As most human excreta and kitchen garbage in rural areas were recycled, the consumption of detergents in rural households was responsible for 44% of the sector’s emissions – almost three times that of urban areas.
All material use efficiencies discussed above are illustrated in Figure 2. The graph reveals cross-sectoral physical profiles for phosphorus flows. It is evidenced that production efficiencies in general declined in this sequence: mining, industry, farming, intensified husbandry and family-based animal breeding. Accordingly, the material use efficiencies of emission, accumulation and recycling were correspondingly higher.
Discussions and conclusions
The mass balance calculations present to what extent phosphorus was efficiently mobilized and processed within the societal metabolism. The results illustrate that phosphorus cycles in China, in general, operate in a high-intensive but “open-loop” way. This implies that, to a large extent, the Chinese economy has been increasingly “materialized” with phosphorus. This could eventually result in ecological deterioration as the consumed phosphorus cannot physically disappear.
Physical flow configurations offer an adequate starting point for future policy analysis and decision making. However, as phosphorus uses are connected to many – if not all – production and consumption activities within our economies, it is nearly impossible to individually examine all potential indications of relevant policies to their related physical flows. It is equally important to keep in mind that the physical profiles of phosphorus use in different regions vary considerably. There is a need to identify the most critical – and therefore most worthwhile to address – social sector or flow. The discussion of aggregate and sectoral efficiencies of phosphorus use can help to distinguish those environmentally dominant pivots on which desired policies should preferentially focus. This systematic approach challenges a conventional policy analysis that basically focuses on the cost-effectiveness of end-of-pipe measures.
Compared to overall phosphorus consumption, only a small fraction ends up in water. However, waterborne phosphates are primarily responsible for undesired eutrophication. As phosphorus leakages take place in all societal sectors, it could be extremely difficult – as well as expensive – to intercept all phosphorus effluents that potentially harm the surface water by conventional end-of-pipe approaches. Instead of continuously trying to limit the growth of phosphorus inflows into waters, therefore, there is a great need to ecologically restructure the current one-through mode of societal phosphorus metabolism, leading to a structural shift in the societal production and consumption of phosphorus flows. From an industrial ecology perspective, the desired switch should contribute to a substantial decrease in phosphorus outflows by minimizing the inputs and maximizing the recycling of phosphorus. This could be a more promising approach to curbing water eutrophication.
Crop farming, animal husbandry, food consumption and detergents use are together responsible for 88% of national and 94% of the regional phosphorus emissions to water. These flows – responsible for water eutrophication – are crucial and should be of central concern in material-based policy design. Theoretically, a number of agronomic factors, involving farmland uses, planting styles and traditions, landscape, crops varieties, cultivated soils, fertilization application, etc., could affect agricultural runoff. While improvements in each can lead to a corresponding reduction in phosphorus loss; the results strongly suggest that a desired environmental policy should also consider factors of affluence plant uptake and the re-mobilization of phosphorus in soils, aiming to reduce the agricultural use, and thus the runoff, of phosphorus.
Secondly, the features of the P-waste flows from animal feedlots differ from those of family-based animal breeding activities. These fundamental differences suggest a need to narrow the focus of policy makers to those places where livestock and poultry are bred in centralized and industrialized feedlots. In particular, as huge amounts of non-reused animal wastes from feedlots threaten surrounding waterbodies, manure application should be one of the central concerns.
Human excreta and detergents are the largest contributors to phosphorus in domestic wastewater. As the treatment of urban excreta has distinct traits and is more likely to cause environmental damage, the urban infrastructure – combining urban sewages and a number of centralized treatment facilities and related existing regulations – should become the third focused pivot. However, this may be insufficient for detergents control. Besides the end-of-pipe technical solution, a number of economic and social instruments regarding bans or limitation of phosphorus-contained detergents have been introduced in some regions of China and other places in western countries – aimed at an effective abatement at source. These measures are regarded as – if not the first – the most independent phosphorus-based regulations. Both effectiveness and efficiency of these regulations have in practice been criticized. This perhaps implies that a comprehensive material-based policy should also take economic costs and social values into consideration.
Last, but not least, the desired policies should also take into account technological options for restructuring the physical pattern of phosphorus flows. Technically feasible solutions for recovery of phosphorus from animal wastes, wastewaters and secondary sludge have increasingly emerged; some have even been put into practice in a few European countries and North America. Perhaps more exciting, there has also been some new progress in monitoring and analytical techniques of biochemistry and soil sciences, providing a promising basis for re-extraction of phosphorus mobilized in agricultural soils – soon to be the largest sink of phosphorus in the terrestrial system.
- ADB. 2004. Comprehensive Report on Key Problems and Underlying Causes of Rural NSP in China (Study on Control and Management of Rural Non-Point Source Pollution, TA No.3891-PRC). Mandaluyong, Philippines: Asian Development Bank.
- Brett, S., J. Guy, G. K. Morse, et al. 1997. Phosphorus Removal and Recovery Technologies. Brussels, Belguim: CEEP (Centre Europeen d'Etudes des Polyphosphates E.V.).
- Brown, L. R., and B. Halweil. 1998. China's water shortage could shake world food security. World Watch, 11(4):10-21.
- CEEP. 1998. Phosphate recovery from animal manure. Brussels, Belgium: Van Ruiten Adviesbureau, Centre Europeen d'Etudes des Polyphosphates (the West European Phosphate Industry's Joint Research Association).
- Cestti, R., J. Srivastava, and S. Jung. 2003. Agriculture Non-Point Source Pollution Control: Good Management Practices. Washington, D.C.: Environmentally and Socially Development Unit, Europe and Central Asia, the World Bank. ISBN: 0821355236
- CNCIC, ed. 2003. China Chemical Industry Yearbook 2002-2003. Beijing: China National Chemical Information Center.
- Driver, J. 1998. Phosphates recovery for recycling from sewage and animal wastes. Phosphorus and Potassium, 216 (Jul/Aug):17-21.
- EEA. 2005. Source apportionment of nitrogen and phosphorus inputs into the aquatic environment. No.7/2005. Copenhagen: European Environment Agency. ISBN: 9291677779
- Emsley, J. 1980. The phosphorus cycle. In The Handbook of Environmental Chemistry: The Natural Environment and the Biogeochemical Cycles, edited by O. Hutzinger, p:147-167. New York: Springer-Verlag Berlin Heidelberg. ISBN: 0387096884
- FAO. 2003. Food Balance Sheet for China. Food and Agriculture Organization of the United Nations, 2003 [cited Dec. 12 2003].
- FAO. FAOSTAT Statistics Division, Food and Agriculture Organization of the United Nations (FAO), 2006.
- Follmi, K. B. 1996. The phosphorus cycle, phosphogenesis and marine phosphate-rich deposits. Earth-Science Reviews, 40(1-2):55-124.
- Grove, T. L. 1992. Phosphorus, biogeochemistry. In Encyclopedia of Earth System Science, edited by W. A. Nierenberg, pp. 579-587. London: Academic Press. ISBN: 0122267192
- Hart, M. R., B. F. Quin, and M. L. Nguyen. 2004. Phosphorus runoff from agricultural land and direct fertilizer effects: a review. Journal of Environmental Quality, 33(6):1954-1972.
- Heilig, G. K. 1999. ChinaFood: Can China Feed Itself? Laxenburg: IIASA. CD-ROM Vers. 1.1.
- Lee, G. F., and A. Jones-Lee. 2001. Issues in managing the water quality impacts of phosphorus in runoff from agricultural lands. In Environmental Impact of Fertilizer Products in Soil, Air and Water, edited by William L. Hall and Wayne P. Robarge. Chicago: American Chemical Society. ISBN: 0841238111
- Liu, Y. 2005. Phosphorus Flows in China: Physical Profiles and Environmental Regulation. PhD Thesis, Environmental Policy Group, Department of Social Sciences, Wageningen University, Wageningen, the Netherlands.
- Liu, Y., J. Chen, A. P. J. Mol, et al., in press. Comparative analysis of phosphorus use within national and local economies in China. Resources, Conservation and Recycling, in press, Corrected Proof.
- Liu, Y., A. P. J. Mol and J. N. Chen. 2004. Material Flow and Ecological Restructuring in China: the Case of Phosphorus. Journal of Industrial Ecology, 8(3):103-120.
- Moss, B. 2000. Phosphorus, detergents and eutrophication control - A summary of experience in Europe and North America. Detergent and Cosmetics, 23(2, Supplement, July):117-129.
- Rosegrant, M. W., M. S. Paisner, S. Meijer, et al. 2001. 2020 Global Food Outlook: Trends, Alternatives, and Choices. Washington, D.C.: International Food Policy Research Institute.
- SCOPE. 2001. Phosphate recovery: where do we stand today? Brussels, Belgium: SCOPE (Scientific Committee on Phosphates in Europe).
- SEPA. 2002. Investigation on the Pollution of National Livestock and Poultry Breeding in Scale and Its Control Strategy. Beijing: China Environmental Science Press. In Chinese.
- Smil, V. 2000a. Feeding the World: A Challenge for the Twenty-First Century. Cambridge, Massachusetts: The MIT Press. ISBN: 0262692716
- Smil, V. 2000b. Phosphorus in the environment: natural flows and human interferences. Annual Review of Energy and Environment, 25:53-88.
- Tiessen, H., and J. W. B. Stewart. 1985. The biogeochemistry of soil phosphorus. In Planetary Ecology, edited by D. E. Caldwell, J. A. Brierley and C. L. Brierley, pp. 463-472. New York: van Nostrand Reinhold. ISBN: 0442240074
- Turner, B. L., E. Frossard, and D. S. Baldwin, eds. 2005. Organic Phosphorus in the Environment. Wallingford, UK: CABI Publishing. ISBN: 0851998224
- USDA. 2002. China's Food and Agriculture: Issues for the 21st Century. Agriculture Information Bulletin No. 775. Washington, DC: Market and Trade Economics Division, Economic Research Service, U.S. Department of Agriculture.
- USGS. 2006. Mineral Commodity Summaries 2006. Washington, D.C.: U.S. Geological Survey, U.S. Department of the Interior. ISBN: 0160754283
- Valsami-Jones, E., ed. 2004. Phosphorus in Environmental Technology: Principles and Applications. Edited by P. Lens, Integrated Environmental Technology Series. Cornwall, UK: IWA Publishing. ISBN: 1843390019
- Wang, L. M., and J. Davis. 2000. China's Grain Economy: The challenge of feeding more than a billion. Aldershot, England: Ashgate. ISBN: 1855219573