Prospects and Issues of Phosphorus Recovery as Struvite from Waste Streams

Abstract

Finite resources of non-substitutable plant nutrient like phosphorus (P) make recovery of it an attractive option of renewed interest from alternative waste sources. In this context, feasibility of struvite recovery (MgNH4PO4. 6H2O), an alternative P fertilizer, is already established from different waste streams with reasonably high ortho-P recovery efficiency ({\textasciitilde}90%). Feasibility of struvite recovery has been established at laboratory scale for a range of sources of farm, municipal, and industrial origin. Municipal wastewater is the most common struvite recovery source, whereas farm wastes represent easily accessible stock with reliable availability. Depending on the source characteristics, the recovery of struvite may require some process modifications such as addition of P and NH4+ salt and incorporation of pretreatments. However, except for municipal sludge and urine, development of cost-effective, targeted, and environmentally friendly full-scale recovery of struvite is limited due to inherently heterogeneous nature of the sources and unfavorable economics. In recent years, an increasing research concern can be seen toward the techno-economical aspects of the process for development of competent and energy-efficient process from alternative potential struvite sources with incorporation of more efficient method, Mg source, and seed material. Studies on struvite's application aspect identify its favorable impact on crop though with variation attributed to soil type, plant type, and climate; however, its field-scale long-term impact, its applicability within regulatory limits of fertilizer, and users' perception remain other concerns. Nevertheless, considering the related benefits of recovery process, struvite recovery appears to be an attractive and feasible pathway provided uncertain aspects are addressed through appropriate research and development.