The European Union (EU) has recently accepted new fertiliser regulations which encourage and facilitate the recycled use of secondary sources of phosphorus (P) and other nutrients while defined contaminant limits protecting agricultural soils in Europe from pollution (European Commission 2019). Currently, new inputs of fertiliser phosphate to agricultural soils, apart from the within-farm recycling of manures, have been from processed mined rock phosphate, which can contain contaminants such as cadmium (Cd), but which is a finite natural resource, with a declining quality of its reserves. Phosphorus is an essential non-substitutable element for all plants and animals, with that required by humans being provided by food. The need for phosphate inputs to agriculture will continue to grow as the global population and overall P-flux increase, resulting in greater quantities of P in wastewater and sewage sludge. The efficient recycling of this P is essential for global food security, indeed ultimately for human survival.
ICL Fertilizers Europe C.V. in Amsterdam opened their Phosphate Recycling Unit in March 2019 to process sewage sludge ash (SSA) and meat and bone meal ash (MBMA) into recycled fertiliser products. A small amount of struvite is also processed into fertiliser. Other materials have the potential to be recycled into concentrated fertilisers, although additional treatment will be necessary for those materials. Pig manure is typically contaminated with copper (Cu) and zinc (Zn) and cattle manure can be contaminated with manganese (Mn). To reduce metal contamination in from these manures and other secondary (recycled) P-sources, both acid leaching and thermochemical treatment can provide solutions. These are well-developed technologies but face financial challenges as thermochemical treatment is very energy intensive and acid leaching requires large volumes of liquids and additives. To overcome these challenges, creative solutions need to be found to reduce these operating costs. An example is by using waste products from other industries as additives. Calcium silicates are a waste product from both the cement and steel making industry and is useful in both thermochemical processes, as well as for simple P precipitation processes for P recovery from sludge liquors. Finally, ecological engineering has proved to be effective for P-recovery and is often a practical way to reduce the costs of other processes.
Sabrina Brandjes, ICL Fertilizers Europe C.V., Amsterdam, Netherlands.
24 pages, 4 figures, 3 tables, 46 references