Microalgae grow on source separated human urine in Nordic climate: Outdoor pilot-scale cultivation.

Human urine contributes approximately 80% of nitrogen and 50% of phosphorous in urban wastewaters while having a volume of only 1-1.5 L/d per capita compared to 150-200 L/d per capita of wastewater generated. There is interest to study source separation of urine and search methods to recover the nutrients form the urine. In this study, the objective was to use the nutrients in source separated urine for outdoor cultivation of microalgae in Nordic climate. A freshwater green microalga Scenedesmus acuminatus was grown in different dilutions (1:20 and 1:15) of source separated human urine, in a semi-continuously operated outdoor raceway pond with a liquid volume of 2000 L, at hydraulic retention time of 15 d. The microalgae could remove 52% nitrogen and 38% phosphorus even at culture temperatures as low as 5 °C, while obtaining a biomass density of 0.34 g VSS/L. Harvested microalgal biomass could be used to produce methane with a yield of 285 L CH4/kg volatile solids.

Particles as carriers of matter in the aquatic environment: Challenges and ways ahead for transdisciplinary research.

A diverse array of natural and anthropogenic particles found in the aquatic environment, can act as carriers of co-transported matter (CTM), such as nutrients, genetic material and contaminants. Thus, understanding carrier particle transport will increase our understanding of local and global fluxes of exogenous CTM (affiliated with the particle) and endogenous CTM (an inherent part of the particle). In the present contribution, researchers from multiple disciplines collaborated to provide perspectives on the interactions between carrier particles and CTM, and the fundamentals of transport of particles found in the aquatic environment and the generic spherical smooth particles, often used to make predictions about particle behavior in suspension. Evidently, the particles in the aquatic environment show a great variety of characteristics and vary greatly from each other as well as from the generic particle. However, in spite of these differences, many fundamental concepts apply to particles in general. We emphasize the importance of understanding the basic concepts of transport of particle-associated CTM, and the main assumptions in the generic-founded models, which are challenged by the diverging characteristics of particles found in the aquatic environment, as paramount moving forward. Additionally, we identified the need for a conceptual and semantic link between different scientific fields of particle research and initiated the formation of a consistent terminology. Disciplinary and organizational (academic and funding) barriers need to be overcome to enable individual researchers to move beyond their knowledge sphere, to stimulate future interdisciplinary collaborations and to avoid research silos. Hereby, we can foster faster and better progress of evolving research fields on new and emerging anthropogenic carrier particles, and stimulate the development of solutions to the technological and environmental challenges.