Dynamics Of Phosphorus In Waste And Its Recycling Potential In China

Phosphorus(P)is an essential nutrient for life on the earth.The phosphorus cycle is closely related to food security and environmental pollution,which are global key issues.Human activities have greatly changed the natural phosphorus cycle.As a non-renewable resource,phosphorus is facing a crisis of resource depletion.The break of the phosphorus cycle has led to excessive phosphorus input of water bodies,causing serious water eutrophication problems around the world.An effective measure to alleviate these resource and environmental problems is to improve the recycling efficiency of phosphorus-containing waste(P waste).China is a populous country and has become the largest producer and consumer of phosphate rock.The eutrophication in inland water bodies is still a prominent problem across the country,and the use efficiency of phosphorus resources continues to decline.Therefore,China urgently needs to achieve phosphorus sustainability.This research built the phosphorus waste analysis model(P-WAM)to make quantitative analysis of phosphorus waste in a human socio-economic system.The establishment of P-WAM model is based on the principle of Material Flow Analysis method.Compared with the traditional P flow analysis model,this model adopted a new flow division method where P flows are divided into product flow,waste flow and recycling flow.PWAM focuses on the fate of P waste and quantify the generation,recycling and discharge process of P waste.This facilitates to understand the driving factors of P loss.P-WAM was used to conduct a quantitative analysis of P waste in China from 1900 to 2015.Based on the historic trend of P waste in China and its driving mechanism,a phosphorus waste prediction model was constructed.A series of phosphorus management scenarios were set according to the driving factors of P waste generation and recycling patterns.The P waste patterns from 2020~2050 under different P management scenarios were simulated through the prediction model.This study also establish a technology assessment method for P waste recycling technologies,the available technologies were assessed from the perspective of economic benefits,environmental impact and resource consumption.Finally,we gave a catalog of technologies suitable for promotion,and proposed recommendations for the development of P waste recycling technology in the future.The major results and conclusions are as follows:Phosphorus-containing product has increased greatly in the past century.P fertilizer consumption increased thousands of times from 1950 to 2015 while phosphate rock increased tens of thousands of times.From 1900 to 2015,the phosphorus in crop has increased by 3 times,owing to the wide application of P fertilizer.From 1900 to 2015,P waste production in China has increased by 7 times,from 1.2 Mt P y-1 to 8.7 Mt P y-1.The amount grew slowly before 1950,and after 1950,especially after1978,it began grow rapidly.In the past century,animal husbandry has been the largest producer of P waste but the phosphorus waste generation intensity(PWI)showed a downward trend,due to the rapid decrease in the proportion of horse,donkey and mule.The phosphorus waste of phosphate mining and phosphorus chemical production grew the fastest.The most important phosphorus waste of the two systems are phosphate tailings and phosphogypsum.With the continuous improvement of the requirements of phosphorus chemical industry on ore quality,the PWIs of phosphate mining and phosphorus chemical production are continuously improved.The PWI of aquaculture is much higher than that of other systems,as well as the continuous expansion of aquaculture scale in recent years,resulting in the rapid growth of aquaculture P waste,and there is no slowing down trend until now.The evolution trend of P waste production in each system is mainly affected by economic growth,rapid urbanization,change in agricultural planting mode and residents' dietary choice.From 1900 to 2015,the recycled P waste increased from 0.9 Mt P y-1 to 4.6 Mt P y-1.The overall phosphorus waste recycling rate(PWR)has dropped from 75% to less than 53%.About 90% of the total recycled P waste are from animal husbandry,agricultural product processing and crop farming.The PWR of crop farming gradually decreased from 50% to20%,and animal husbandry declined rapidly after 1990.The PWR of the human consumption has dropped from 91% to 15%,due to the rapid urbanization and increasing sewage treatment rate.Both the PWRs of the phosphorus chemical production and waste treatment system showed a rising trend.In the early 20 th century,the most important P sink was the inland water bodies,followed by the atmosphere.About 70% of P loss entered inland waters and 30% was lost to the atmosphere.As the legacy P in cultivated increased rapidly since 1960,cultivated has become the largest P sink.P loss to non-arable land increased significantly from1990,causing non-arable land the second largest P sink.Before 1950,90% of P loss to non-arable land came from the human consumption.However,in the past few decades,phosphate mining,phosphorous chemical production,animal husbandry and waste treatment systems has gradually replaced human consumption.In the early 20 th century,crop farming contributed 80% of the P loss to inland water,but the percentage has dropped to 29%.Aquaculture has become the largest contributor.Crop farming is the largest source of P loss.Although its share in the total has decreased after 1980,it still contributed more than half of the total at present.Animal husbandry is the second largest source,accounting for 12% of the total.In the past 30 years,phosphate mining and P chemical production have increased the most rapidly,accounting for 9%and 7% of the total in 2015,respectively.Aquaculture also increased significantly,currently accounting for 9%.The percentage of human consumption has been declining over the century and dropped to 2%.The major P sink for crop farming has changed from inland waters to cultivated land,and animal husbandry has changed from inland waters to non-arable land.The P loss of aquaculture to the ocean is increasing rapidly.The simulation results of scenario analysis showed that the transation to a healthier diet would lead to a substantial increase in the production and discharge of P waste.Increasing the import rate of P products and control cropland P input can effectively reduce the amount of P waste generated.Control cropland P input and improving the waste recycling rate can largely mitigate P discharge.Waste recycling is thd best approach to extend the life span of phosphate reserve.In the integrated scenario,the consumption of phosphorus fertilizer declined to below 2 Mt P while phosphate consumption dropped to 3.3 Mt P.Increasing the waste recycled as fertilizer would cause higher phosphate consumption and P discharge,while The ‘recycled as feed' route obtained higher environmental and resource benefit.Hence,‘recycled as feed' route is the best recycling route as to improving phosphorus sutainability.Based on the framework of multi-criteria decision analysis,a technology assessment method was constructed.The evaluation system includes three goals of economic benefit,environmental benefit and resource benefit and 14 bottom indexes.According to the assessment results,technologies that performed well in economy,environment and resource benefit are listed as recommended technologies,including T03 phosphate tailings to produce calcium magnesium phosphate fertilizer,T25 component recovery for domestic garbage,T30 processing food waste with black soldier fly,and T35 anaerobic digestion of sludge + land application.The technologies that show varing performance in different aspects include T09 straw pyrolysis polygeneration system,T11 straw to ethanol,T12 straw direct combustion for power generation,T15 straw to make pellet fuel,T16 straw to make paper,T28 underground soil infiltration of waste water,T32 sludge to make cement.These technologies require a more in-depth assessment to determine their promotion priority.There are abundant types of recycling technologies for straw,wastewater and household garbage,but the performance varies greatly in three aspects.Therefore,more detailed technical parameters should be obtained for the indepth assessment of these technologies in the future.