How then is waste from human society to be processed? A model can be found in food -derived bones, they simply go into landfills along with calcium phosphate sludge from phosphate recovery at the wastewater works. All of this ends up in the landfills. Some bones from slaughter house waste are converted into bone meal, but the vast majority of phosphate is landfilled. An exception to the general wastage of phosphate is basic slag from steel smelting. The slag is often made into high strength concrete, (when mixed with portland cement). It is also used as fertilizer. However, even in poorer societies bones are not much used (except perhaps for carving). The problem is that managed competition keeps the price of superphosphate fertilizer very cheap. The North African phosphate deposits are almost depleted and other deposits (such as deep sea nodules) are limited in abundance and expensive to exploit. In industry & the home, bones are rarely collected and converted back into superphosphate by acid addition (H2SO4).
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