Keywords: Phosphorus, recycling, sanitation, solid waste, agriculture, fertiliser.
Commercially viable reserves of rock phosphate are limited and only a few countries are significant producers. China and the US will play a much smaller role within 50 years time and the bulk of the world’s mined phosphorus will come from Morocco. A conservative estimate of longevity of the resource shows that at a 1% exponential increase for the next 50 years followed by zero increase, the global reserves would last 235 years. If one uses the UN global population growth rate to determine future demand, with a stabilisation by 2100, the current global reserves would last 172 years. This estimate can be further reduced to 126 years if Africa develops its agriculture and to just 48 years if in addition bio-energy crops are given higher priority.
The phosphorus losses are significant in the mining/beneficiation/ /fertiliser production steps (35% of what is mined is not converted into usable product) and in agriculture (30% of what is added as fertiliser is not contained in agricultural output, with most being retained in the soil) but they are even higher within the areas of food processing, distribution and consumption (60% of the P in food is lost).
To reduce phosphorus losses the questions of erosion from farm fields and more effective handling of manure from high density livestock feedlots need to be addressed. When it comes to food processing, improvements in crop storage, processing facilities and trade methods are needed. At present most of the excreted phosphorus from humans ends up lost in the environment. Phosphorus extraction from wastewater, sludge, manures and other organic sources is only starting and needs worldwide promotion.
About one billion people are under-nourished and many are smallholder farmers that cannot afford chemical fertilisers. Food production in developing countries will probably have to double by 2050. More conservative policies and measures are required in the management of fertilisers to feed a world with 9 billion people. Countries need to further develop productive sanitation systems in order to safely reuse human and animal excreta. Guidelines now exist for the use of human urine as a substitute for chemical fertiliser in agriculture. There is a higher chance that food security can be achieved by maintaining soil fertility if all available sources of fertiliser resources are better managed — animal manure, crop and food residues, chemical fertilisers and human excreta.
For these reasons a much more conservative approach is needed in the exploitation of fossil phosphate-rock and that reuse and more efficient systems should be promoted and developed.
Arno Rosemarin, Linus Dagerskog, Stockholm Environment Institute, Sweden.
Jaap Schröder, Bert Smit, Wageningen University, Netherlands.
Dana Cordell, University of Technology, Sydney, Australia.
27 pages, 9 figures, 3 tables, 48 references.