Recovery of ammonia in digestates of calf manure through a struvite precipitation process using unconventional reagents

Land spreading of digestates causes the discharge of large quantities of nutrients into the environment, which contributes toeutrophication and depletion of dissolved oxygen in water bodies. For the removal of ammonia nitrogen, there is increasinginterest in the chemical precipitation of struvite, which is a mineral that can be reused as a slow-release fertilizer. However,this process is an expensive treatment of digestate because large amounts of magnesium and phosphorus reagents are required.In this paper, a struvite precipitation-based process is proposed for an efficient recovery of digestate nutrients using low-costreagents. In particular, seawater bittern, a by-product of marine salt manufacturing and bone meal, a by-product of the thermaltreatment of meat waste, have been used as low-cost sources of magnesium and phosphorus, respectively. Once the operatingconditions are defined, the process enables the removal of more than 90% ammonia load, the almost complete recovery ofmagnesium and phosphorus and the production of a potentially valuable precipitate containing struvite crystals