Nutrient recovery from waste streams through struvite formation

Abstract: Eutrophication or the nutrient enrichment of water bodies, typically by nitrogen and phosphorus has adversely affected the aquatic life and the quality of water. Governments have been forced to take actions in order to reduce the release of these nutrients into the environment. To date the main global effort has been to remove such nutrients at source. However, with an increase in awareness of the importance of phosphorus as a non-renewable resource, more studies are being carried out to find methods to prevent loss of phosphorus and to recover it instead. The struvite crystallization process has been shown to be a promising technology to efficiently recover phosphorus from point sources such as municipal, agricultural and industrial wastewater. The work throughout this thesis deals with the use of the struvite crystallization process as a mean to recover nitrogen and phosphorus from waste streams. To prevent the formation of struvite fine crystals, which are difficult to harvest; aggregation of struvite crystals was promoted using a fluidized bed reactor. Further analysis of the precipitates using X-ray diffraction proved that these precipitated aggregates were in fact struvite. In cases where crystal aggregation cannot be performed, it has been suggested that harvesting of struvite fine crystals can be improved by the addition of coagulants and coagulating aids such as chitosan and bentonite, which have been shown to be efficient in increasing the setting velocity of the crystals. Furthermore, struvite crystals were formulated into granules to create a product with a higher commercial value. The quality of this product as a fertilizer was investigated in terms of its physical and chemical properties. Finally, the use of struvite crystallization followed by a struvite recycling process to recover nutrients from urine was investigated. Using this process, it was possible to recover 90% of both nitrogen and phosphorus from urine.