Prospects for the recovery of phosphorus from animal manures: A review

This paper reviews the potential for phosphorus (P) recovery from animal manures as a method of increasing the sustainability of the global P cycle. The P content of animal manures produced annually in the UK is currently estimated at over 120,000 t. This represents approximately twice the annual non-agricultural P requirement in the UK and has an approximate value of pound 76 M. Similar quantities of P are produced in manures in the Netherlands and an estimated 600 500 t are produced annually in the US. Up to 65% of manure P may be associated with an organic moiety. However, current methods to identify these including HPLC and P-31 NMR are under-developed while P fractionation procedures give only operational definitions. Combinations of current technologies developed for the treatment of sewage are likely to prove effective in the recovery of P from manures. Enhanced Biological Phosphorus Removal (EBPR) could he adapted to produce a concentrated P effluent. Recovery of P from which could be achieved by either of two crystallisation pathways to produce magnesium ammonium phosphate (struvite) or calcium phosphate (apatite). Recycling of manure P to land within the agricultural sector remains the best option in many cases. However, manure production in many areas such as Chesapeake Bay and the Everglades in North America, the Po Delta in Italy and the sand regions of the Netherlands is too intensive for locally available land to accommodate without the risk of transfer to surface waters. Legislation restricting recycling of P to land already exists in the Netherlands and is likely to become widely adopted. Under these circumstances recovery of P may alleviate manure management problems.