Phosphorus recovery from co-digested pig slurry: development of the RePeat process

In the Netherlands, the agricultural sector produces more manure than can be applied on agricultural land within the P application standards. The excess amount of manure should be exportedto other regions with a demand for P fertilisers. An alternative for current manure export is manure processing in which manure is processed into valuable fertiliser products. This reports describes a process in which the solid fraction of co-digested manure is processed into a concentrated P fertiliser and a nutrient-poor organic soil improver. The recovered P fertiliser can be used as a secondary raw material for fertiliser production or for export whereas the soil improver can be used on arable soils in the nearby region of the manure treatment plant. The separation process, called RePeat, consists of a acidification and dilution step to extract P from the solid fraction followed by a base addition step to recovery P. The proof of principle was given in a previous report (Schoumans et al., 2017). This reports describes additional laboratory and pilot tests (Chapter 2-4). Attention was given to the reuse of water within the process, the dewatering of calcium phosphate versus struvite and the selection of separation equipment for a demonstration plant. Chapter 5 gives the process mass balances calculated using a mass balance model. Chapter 6 assesses the quality of the organic soil improver in terms of its carbon- and nitrogen mineralisation rate. An example of a business case for the process is included in Chapter 7. The results were used to design a demonstration plant for the RePeat process to be built at Groot Zevert Vergisting B.V. in Beltrum.