Nutrient recovery from waste streams through struvite formation

Abstract: Popular Abstract in English These days we hear a lot about sustainability and most of us try to live in a more sustainable way. We use less water and energy, we sort our household waste and we prefer to consume products that are produced with less negative human impact. However, when it comes to our own excreta we definitely think of it as waste. And we are glad enough that wastewater treatment systems are there to take care of it! But the question is: how sustainable are our wastewater treatment systems? Today’s wastewater treatment systems are mainly built on the concept of removing substances that can be harmful to humans and the environment. The problem still remains; we are left with substances that we do not really know how to dispose of. However, considering the principles of sustainability recovering and reusing resources is a far superior approach than removing them. One good example of this is today’s unsustainable phosphorus flow; from its starting point in mining to its end point in discharging it to the environment. Phosphorus, which is mainly used as a fertilizer, is obtained by mining of phosphorus rock and deterioration of land is its obvious consequence. A lot of this phosphorus ends up on our plate and eventually in our excreta. But from this point on, this valuable element becomes waste. Phosphorus is a non-renewable resource and with its ever-increasing consumption, it is predicted to be depleted within 50 to 100 years. The goal of this thesis is to capture and reuse the phosphorus lost in our wastewater. For this purpose, magnesium is added to a process that, together with phosphorus and nitrogen, forms a crystal compound called struvite. Struvite can be separated from wastewater and can be used as a high-quality fertilizer. Currently, there are only a few full-scale struvite crystallization processes in use around the world. Several technical and economical limitations hinder wide application of this process. One of the main objectives of this study was to improve the process by either coagulation or aggregation of struvite crystals. It was also possible to efficiently capture both nitrogen and phosphorus from urine. This is an important finding for better use of potential future decentralized sanitation systems. The work throughout this thesis is a step towards a more sustainable waste management. It is an effort to further highlight the notion that “waste is a valuable resource”.